Atomic spectrometry update. X-ray fluorescence spectrometry

Margaret West,*aAndrew T. Ellis,

bPeter Kregsamer,

cPhilip J. Potts,

d

Christina Streli,cChristine Vanhoof

eand Peter Wobrauschek

c

Received 6th August 2007

First published as an Advance Article on the web 3rd September 2007

DOI: 10.1039/b712079f

1 Introduction and reviews

2 Instrumentation

2.1 General instrumentation and excitation sources

2.2 Detectors

3 Spectrum analysis, matrix correction and calibration

procedures

3.1 Spectrum analysis

3.2 Matrix correction and calibration procedures

4 X-ray optics and microfluorescence

5 Synchrotron radiation

5.1 Instrumentation

5.2 Applications

6 TXRF

6.1 Instrumentation

6.2 Synchrotron radiation induced TXRF

6.3 Applications

7 Portable and mobile XRF

8 On-line XRF

9 Applications

9.1 Sampling, sample preparation and pre-concentration

techniques

9.2 Geological and industrial minerals

9.3 Environmental

9.3.1 Atmospheric particulate matter

9.3.2 Other environmental studies

9.4 Archaeological, cultural heritage and forensic

9.5 Industrial

9.6 Clinical and biological

9.7 Thin films and coatings

9.8 Chemical state, speciation and crystal characterisation

10 Abbreviations

11 References

This annual review of X-ray fluorescence covers developments

over the period 2006–2007 in instrumentation and detectors,

matrix correction and spectrum analysis procedures, X-ray

optics and micro-fluorescence, synchrotron XRF, TXRF, porta-

ble XRF and on-line applications as assessed from the published

literature. The review also covers a survey of applications,

including sample preparation, geological, environmental, ar-

chaeological, forensic, biological, clinical, thin films, chemical

state and speciation studies. Interest continues in micro-analy-

tical instrumentation with synchrotron-based systems benefiting

from the availability of more intense beams and efficient focusing

optics. Many authors have strengthened the influence of their

work with data presented as elemental maps and, where appro-

priate, factor analysis continues to feature. In common with

other analytical techniques, this review demonstrates the emer-

ging field of metallomics to assist in the understanding of how

metals and metalloids interact within cells and tissues. Progress

continues to support legislation with further analytical methods

and reference materials available for environmental and indus-

trial applications. Improvements in detector resolution and

excitation optics have helped to strengthen interest in EDXRF

systems to meet the demands from society for a reduction in

pollutants in ambient air. The writing team would welcome

feedback from readers of this review and invite you to com-

plete the Atomic Spectroscopy Updates questionnaire on

www.asureviews.org.

1 Introduction and reviews

This review continues the series of annual Atomic Spectro-

scopy Updates in X-ray Fluorescence Spectrometry1 and

should be read in conjunction with other related reviews in

the series.2–4 In preparing this review, the writing team con-

sidered the wealth of XRF papers published during the period

2006–7. As the XRF technique matures, it is inevitable that

many papers concentrate on applications, with fewer publica-

tions related to instrumentation, spectrum analysis, matrix

correction and calibration procedures. In an attempt to im-

prove the reader’s experience, this review has concentrated on

papers that demonstrated progress in XRF techniques in the

hope of encouraging further developments to assist analytical

endeavours.

The XRF community is now supported by a number of

conferences that offer delegates both oral and poster presenta-

tions along with the opportunity to meet suppliers in an

exhibition forum. The 12th European X-ray Spectrometry

Conference5 was held in June 2006 in Paris, with invited

speakers from ten countries. In August 2006, the 55th Annual

Denver X-ray Conference returned to its Colorado home with

its familiar mix of sessions and workshops for users of both

XRF and XRD. This year the British Crystallography Asso-

ciation celebrated their 25th Annual Spring Meeting6 in

Canterbury with a series of XRF sessions organised by their

Industrial Group.

aWest X-ray Solutions Ltd, 405 Whirlowdale Road, Sheffield, UKS11 9NF

bOxford Instruments Analytical Oy, Nihtisillankuja 5, FI-02630Espoo, Finland

c TU Wien, Atominstitut der Osterreichischen Universitaten,Stadionallee 2, A-1020 Vienna, Austria

d Faculty of Science, The Open University, Walton Hall, MiltonKeynes, UK MK7 6AA

eVITO, Environmental Measurements, Boeretang 200, B-2400 Mol,Belgium

1304 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

ASU REVIEW www.rsc.org/jaas | Journal of Analytical Atomic Spectrometry

A practical handbook7 with contributions from many

authors from academia and industry provided self-contained

modules featuring XRF instrumentation, quantification meth-

ods and most of the current XRF applications. This book was

designed as a resource for graduate students, research scientist

and industrial readers. Thomsen8 published a timeline of

atomic spectroscopy that provided a short history of the

experimental and theoretical developments for elemental spec-

trochemical analysis. The instrumental techniques included

optical emission (flame, arc/spark, ICP, glow-discharge and

laser ablation), atomic absorption and XRF.

Analytical chemists striving to report reliable results on

elemental mass fractions will be familiar with quality manage-

ment systems and efforts to demonstrate traceability. Padilla

Alvarez led an international group9 on work to demonstrate

traceability and the evaluation of the performance of EDXRF

systems. The authors considered linearity, working range,

precision, trueness and detection limits, with recommenda-

tions for the quantification of uncertainty and the organisation

of internal quality control practices.

2 Instrumentation

2.1 General instrumentation and excitation sources

The range of commercial spectrometers continues to increase

with configurations available to satisfy the demand from both

industry and academia for cost-effective, rapid, non-destruc-

tive quantitative analysis. Energy dispersive X-ray spectro-

meters have gained in popularity in recent years, being

available for laboratory based and in situ applications. How-

ever, it is recognised that the main disadvantages of EDXRF

compared with WDXRF systems are the lower energy resolu-

tion and the count-rate limitation, which lead to reduced

accuracy and precision. Padilla Alvarez and colleagues10 pre-

sented research that combined a compact design for secondary

target excitation in a polarised energy dispersive configuration

with a digital signal processing-based spectrometer. The ar-

rangement was designed to increase the effective solid angles

and to reduce the distances between secondary target, sample

and detector in order to achieve larger X-ray fluxes for both

excitation and detection. The improvement achieved in instru-

mental sensitivity gave better counting statistics and reduced

measuring times to satisfy the authors’ aim of achieving more

accurate and less time-consuming analyses of metal pollutants

in environmental samples and improvements for the determi-

nation of trace elements in archaeological ceramics. The

authors quoted an increase in instrumental sensitivity by a

factor of45 without increasing the dead time above 20%. The

purchase of EDXRF instrumentation requires critical evalua-

tion of a wide range of instrumental features in relation to the

intended application and these were comprehensively covered

in a recent report by the Instrumental Criteria Sub-committee

of the Analytical Methods Committee of the Royal Society of

Chemistry.11 This report may also be useful as a teaching aid.

Wavelength dispersive spectrometry for ‘‘soft’’ X-rays re-

quires monochromators that are efficient in terms of both

luminosity and resolution. Andre et al.12 offered a solution

for wavelengths larger than 3 nm through the use of multi-

layer interference mirrors (MIMs) consisting of a periodic

stack of bilayers with alternating light and heavy materials

on the nano-scale. In 1992, it was proposed that decreasing the

bandwidth of MIMs by etching mirrors with a large number of

bilayers, according to the profile of a lamellar grating, an

improvement in resolution could be obtained. To date, much

progress has been made in the design and fabrication of such

monochromators, enabling the authors to demonstrate an

improvement in resolving power when compared with inter-

ference mirrors. This publication also reported developments

in tunable radiation sources based on the interaction of

medium-energy electron beams with periodic multi-layer

structures.

Dukhanin and Pavlinsky13 compared X-ray tubes with

different anodes and varying beryllium window thicknesses

for the selective excitation of fluorine, oxygen, nitrogen and

carbon. The authors recognised that for these low atomic

number analytes, ionisation of the atoms may occur due to

L-radiation of the matrix arising as a result of intra-atomic

cascade transitions as well as the familiar effects due to

K-radiation or L-radiation of the matrix. Cascade transitions

change primary photons into low-energy photons of the

matrix, which are effective in exciting X-ray fluorescence of

elements with low Z values. Selective excitation effect values

were calculated with consideration of atom excitation by

photo and Auger electrons that originated in the irradiated

sample material.

Moving up the periodic table, Etschmann et al.14 developed

a selective X-ray Bragg spectrometer for an XRF microprobe

for the detection of precious metals in geological and biologi-

cal samples. Their aim was to improve detection limits and

reduce interference from major elements in the sample matrix

and the scattered beam. The configuration used Bragg diffrac-

tion from a surface shaped to a log-spiral to focus X-rays of a

particular energy onto a solid-state detector. The authors

reported enhancement of the precious metal lines within the

relatively narrow bandpass of the Bragg crystal surface and

suppression of sample matrix interference and detector arte-

facts such as tailing and escape peaks. Their efforts were

rewarded with an improvement in the detection limit for Au

in geological samples by an order of magnitude.

2.2 Detectors

In what was generally a sparse year, the number of publica-

tions on pixellated semiconductor detectors stands out and

provides most of the interest from the review year. That said,

most of the work on pixellated detectors is obviously targeted

at imaging applications such as X-ray astronomy or high

energy physics experiments. A silicon CCD employing a

p-channel design on an n-type silicon wafer was described by

Matsuura and co-workers.15 The advantage of the n-type

structure was the high resistivity of the base material and the

depletion depth thickness of 300 mm that could be achieved

compared with the more typical o50 mm active thickness of

conventional CCDs. A 512 by 512 array of 24 by 24 mm2 pixels

was fabricated and when cooled to �110 1C an energy resolu-

tion of 202 eV was obtained at 5.9 keV at a readout frequency

of 67 kHz. The poor effective stopping power for higher

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energy photons (up to 100 keV) of silicon CCDs was addressed

by Miyata et al.,16,17 who directly coupled a scintillating

material to the rear surface of a back-illuminated CCD. Low

energy (o10 keV) X-rays were detected conventionally in the

silicon CCD and high energy ones in the scintillation layer

behind. The scintillation material was needle-like CsI(Tl) and

the high efficiency for visible light of the CCD was valuable

but the energy resolution of the resulting detector was a dismal

6.3 keV at 22.1 keV and 15 keV at 59.5 keV. The detector was

suitable for wide-band X-ray photon counting/imaging in its

intended use in a hard X-ray space telescope, but little else.

Much better stopping power can be obtained using pixels of

materials other than silicon and an array of 1 mm thick CdTe

pixels bump bonded to Medipix readout chips on a 55 mmpitch was studied by Maiorino et al.18 The pixel material and

thickness yielded high detection efficiency for the 122 keV line

from a 57Co radioisotope source. These authors reported in

detail their studies on the critically important charge sharing

effects in such pixellated detectors, which is an issue often

skimmed over but of particular importance for detectors with

larger volume pixels and for high energy photons. The charge

collection characteristics of pnCCDs developed by a team at

MPI Munich were modelled and reported by Kimmel et al.19

Their purely analytical model was able to reconstruct charge

collection parameters for single photon interactions and the

precision of the model data was determined by means of

Monte Carlo simulations and the analysis of experimental

data. An interesting hetero-structure pixellated detector with

high X-ray stopping power was described by Kostamo and co-

workers.20 The novel device comprised a high purity germa-

nium active volume onto which a gallium arsenide layer was

deposited by means of a vertical furnace vapour-phase epitaxy

system. The gallium arsenide layer replaced the typical lithium

diffused n+ contact and the authors concluded that the n+

contact was formed by diffusion of arsenic into the germanium

layer during deposition. The authors claimed that the proces-

sing of detectors of this type was straightforward and that the

detectors exhibited low leakage current at 77 K, although full

X-ray detection characteristics remain to be published. The

signal processing electronics for pixel array detectors are

particularly challenging but Porro et al.21 successfully applied

their DePMOS readout technology, also used for SDD read-

out, to provide time-variant filtering and what was claimed to

be zero added reset noise for pixel array detectors. A compact,

low-power CMOS device was reported by Bastia et al.22 for

providing reset and pileup rejection circuitry for pixel array

detectors. Fanti and co-workers23 described a portable read-

out and acquisition system comprising a USB data interface

and suitable for use with a 256 by 256 Medipix2 pixel readout

chips. Finally, Ercan and co-workers24 reviewed the pixel

array detector systems that have been developed at Cornell

University in the USA.

Not to be outdone by truly pixellated detectors, a strong

team with members in Milan, Munich and Berlin reported25 a

four-element silicon semiconductor detector comprising four

15 mm2 SDDs on a single substrate arranged around a central,

laser-cut hole. The four SDD channels offered excellent energy

resolution of o140 eV at 5.9 keV and the ability to process

very high data rates. An extremely efficient geometry was

obtained with this annular SDD array, which, when combined

with excitation using an X-ray tube and a polycapillary X-ray

optic or SR delivering high intensity excitation through the

central hole, provided a very effective, if rather costly, X-ray

element mapping spectrometry system. The system was used to

good effect in applications such as archaeometry, fine art and

biological studies. A more conventional, but more complex

and costly, approach was described26 in which 13 Si(Li)

detectors, conventionally-cooled by liquid nitrogen, were built

into a single cryostat and set up to detect X-rays from the same

geometric point. A complete pulse processor chain was used

for each detector and, perhaps unsurprisingly, the detector was

installed at a beam line at ESRF, Grenoble, and used for hard

X-ray microanalysis. Once optimised, the system was reported

to offer a 10-fold reduction in acquisition time compared with

the use of a single Si(Li) detector. In the area of less exotic

Si(Li)detectors, Sokolov and colleagues27 described the state

of their art in the development of electrically-cooled Si(Li)

detectors. In their latest system a low power (60 W) Klimenko

cycle cooler was used and an energy resolution of 135 eV at

5.6 keV was obtained for a 20 mm2 device and 1 kcps output

rate, compared with 164 eV for an equivalent setup that used

Peltier cooling. Other than improved stopping power from the

4–5 mm thick Si(Li) devices, it is difficult to see how such an

approach offers significant advantage over modern SDDs that

require lower power yet provide improved energy resolution

and much higher count rates. A novel double layer silicon PIN

detector was described28 in which two, 6 mm2 and 500 mmthick silicon PIN diode detectors were mounted one in front of

the other. Each detector had its own read-out and pulse

processing channel and the reported energy resolution was

220 eV at 5.9 keV when operated at �35 1C. Although offering

significantly better stopping power for the 15–30 keV range, a

single 1 mm thick device would offer less complexity for

straightforward EDXRF applications where increased stop-

ping power is particularly important. The structure of the

assembly also introduced some inevitable contamination

peaks, although those were acceptable for the X-ray astron-

omy application for which the device was designed.

A commercially available avalanche photodiode detector

(APD) was studied by Yatsu et al.,29 who reported that the

detector had the best energy resolution seen to date for an

APD. The measured energy resolution was a rather unexciting

377 eV at 5.9 keV when the 3 mm diameter device was

operated at �20 1C but a very impressive maximum count

rate of 108 cps was obtained and the device was shown to be

extremely radiation-hard. The device also had an encouraging

depletion depth of 130 mm. A study by Ogasawara et al.,30 also

on a commercially available APD, reported an energy resolu-

tion of around 1 keV over the 2–20 keV energy range.

However, the authors’ application was for the detection of

low energy electrons so a depletion depth of only 30 mm was

suitable for their work providing the dead layer was thin,

which it was found to be for this device. Such a device is

unattractive for EDXRF applications and APDs seem likely

to remain of limited interest for X-ray spectrometry generally.

An interesting paper by Cola et al.31 described the novel

electro-optical Pockels effect and how it could be used to

determine the electric field distribution and charge transport

1306 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

properties in CdTe detector structures. The results provided a

unique insight into the effect of detector bias, diode structures

and contact types, and the method could be used to improve

performance in CdTe detectors, which already offer some

useful attributes in a number of EDXRF applications.

The area of cryogenic X-ray detectors based upon super-

conducting tunnel junctions (STJ) or microcalorimeters/

bolometers continues to migrate during the review period to

the margins of XRF analysis. The attractiveness of ultra-high

energy resolution a decade ago seemed to outweigh the

practical challenges of actually deploying the technologies

and led to a high degree of interest, particularly in the

microanalysis community. That interest is now greatly dimin-

ished and interest in cryogenic detectors is now left to those

engaged in SR X-ray and X-ray astronomy experiments where

the technology challenges are better aligned with their needs,

capabilities and funding. It is, however, perhaps worth draw-

ing attention to the use of STJ array detectors for: metal

speciation;32,33 materials and device fabrication;34–37 charac-

terisation and modelling;38,39 and the design of a novel TES

layout that could lead to very large arrays of detectors for use

in X-ray astronomy.40

Finally, Smith41 joined ancient and modern in a review of

the use of gas proportional detectors in SR X-ray experiments.

3 Spectrum analysis, matrix correction and

calibration procedures

3.1 Spectrum analysis

All EDXRF detection and signal processing systems suffer to a

greater or lesser degree from pulse pileup which increases

continuum background and causes specific sum peaks in the

measured spectrum. Most electronic pulse processing systems

provide a degree of electronic pileup protection but none can

completely eliminate pileup effects, particularly at higher

count rates and the typical dead times of 430% used in many

real-life measurements. Barradas and Reis42 briefly reviewed

the existing numerical methods for correcting pulse pileup and

proposed an extension to a previously published analytical

algorithm that was based on first-principles statistical analysis

and required knowledge of very few system parameters. De-

tails were given of the first and second order pileup corrections

and of the simple iterative scheme used in their approach.

Some impressive results were shown for continuum and sum

peak correction in PIXE spectra from a selenium target but the

n3 channel scaling of the statistical approach meant that

calculation times for a 1 k spectrum were in the range of ‘‘a

few seconds to less than a minute’’, which limits the applica-

tion of this approach and makes it unsuitable in practice for

X-ray mapping and fast, high count rate applications such as

alloy sorting.

The estimation and correction of spectrum background is

critical for accurate XRF analysis and Verkhovodov43

reported an interesting study on three sources of spectrum

background in a WDXRF spectrometer. The author studied

background for: characteristic lines of the material of the

blades of the secondary collimator; secondary radiation from

the sample scattered by the same blades; and scattered radia-

tion from the dispersing crystal of the spectrometer, which was

in the Cauchois geometry. Measurements were made using a

scintillation detector at the spectrometer exit slit with and

without the dispersing crystal being in place. These measure-

ments on a series of 22 samples containing elements in the Z

range 4–83 enabled the identification of the background

components from the collimator blade but showed no signifi-

cant effect from radiation scattered from the dispersing crystal,

in contradiction to a previous study. The corrected back-

ground was to provide a reliable method for estimating sample

mass absorption coefficient based upon the ratio of corrected

background at 0.30 and 0.75 A and the new method was used

to good effect in the analysis of Ag, Pd, Rh and Ru in

metalliferous powders. Monakhov and co-workers44 reported

a so-called ‘envelope method’ for the estimation and removal

of background in WDXRF spectra. The details of this algo-

rithm were given, which was a straightforward search algo-

rithm to find spectrum background points and then connect

them with a straight line, or better a parabolic spline. The

method was shown to be effective for the estimation and

removal of background in model spectra of Conostan oil

reference samples but no experimental data were considered

and special care or pre-processing was required when noise

was small or generated downward spikes in the spectrum. The

specific background shoulder on XRF peaks excited by the

59.5 keV radiation from an 241Am radioisotope source was

shown by Uroic et al.45,46 to be due to Compton scattering of

the source line by the material of the source itself. The authors

showed how careful source system design could help minimize

this effect and their calculations of the source-induced

shoulder were shown to be in good agreement with experi-

mental spectra.

The subject of peak shape in EDXRF spectra was poorly

represented in the review year with only a single paper,47

which considered the theoretical peak shape for Pb K spectra.

Of particular concern to these authors were satellite lines due

to multiple ionizations in Pb and, more particularly, the

generation of those effects by light and heavy projectiles at

various energies. Details were given of the theoretical calcula-

tion based upon multi-configuration Dirac–Fock methodol-

ogy and the authors investigated 12 different satellite lines and

showed the detailed K spectra that contained them. The

complexity of the K spectra simulated by the authors should

act as a salutary reminder to all XRF spectroscopists using

simple models for the estimation of the K series XRF lines of

high Z elements that their bliss in achieving excellent practical

data may be tempered by selective ignorance of the underlying

complexity.

3.2 Matrix correction and calibration procedures

The use of empirical or theoretical coefficients for the correc-

tion of matrix effects remains widespread and Rousseau,48

who has for many years developed and taught the topic,

provided an excellent tutorial on correction methods using

such coefficients. The mathematical models of Lachance–

Traill, Claisse–Quintin and Rousseau were all covered in detail

and all of the variables in these models were described and

presented such that numerical values could be substituted to

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study practical application of these important models. The use

of theoretical influence coefficients for matrix correction in

samples of intermediate thickness was described in very read-

able detail by Sitko.49 The correction algorithm was derived

from the Sherman equation and built upon earlier work where

significant simplifications were made such that fixed coeffi-

cients could be used. Such an approach was applicable only to

limited mass thickness and composition ranges and the new

algorithm was developed to remove these limitations by means

of theoretically calculated variable coefficients. The depen-

dence of the calculated coefficients upon mass thickness and

composition was explained and shown in detail and impressive

results were obtained for a number of samples such as Black

Shale and other geological RMs, few-element spinels and

ferroelectric ceramics in the range from 1 to 5 mg cm�2. The

proposed calculation method was straightforward and the

factors affecting accuracy were also presented for the guidance

of those considering the use of this attractive approach.

An interesting experimental setup was described by Bielews-

ki and co-workers50 for the correction of absorption effects in

the mEDXRF analysis of glass microspheres. Excitation was by

means of a high power molybdenum target X-ray tube oper-

ated at 45 kV and 40 mA coupled with a monocapillary X-ray

optic that provided a 15 mm diameter beam. An SDD, capable

of measuring at high rates (250 ns shaping time) was posi-

tioned behind the samples to measure the direct beam and

calculate the absorption factors and the particle diameters and

an 80 mm2 Si(Li) detector was used to collect the XRF

spectrum that was used to determine analyte peak intensities.

Combination of the two data sets with the proposed correction

algorithm allowed the authors to improve the accuracy of

analysis by up to 28%, for groups of 12 or 16 NIST glass

microspheres of 25 or 40 mm diameter, compared with other

methods of extracting sample particle diameter based upon

optical microscopy or X-ray backscatter. Approximations

were made in this approach for the excitation in that an

‘‘effective wavelength’’ for each analyte line was established

by means of the direct, transmitted spectrum and the author

also identified a rather stringent limitation that the particle

diameter could only be established reliably by this direct,

primary beam method if the particles/grains were all of

identical or very similar chemical composition.

The use of fundamental parameter (FP) calculations for

matrix corrections is widespread but the algorithms can also

be used to calculate from first principles the complete X-ray

spectrum. Just such an approach was reported by Elam and

colleagues51 who were able to model spectra for several

compounds covering a wide range of compositions and also

included scattering of the tube anode characteristic peak,

continuum and the Compton scatter peak. An FP method

was used by Pavlinsky et al.52 for the challenging situation of

C in a high Z matrix but good agreement was reported

between the theoretical and experimental C K intensities from

various carbon-containing compounds. In work also on heavy

element matrices, in which excitation was achieved using the

59.5 keV line from an 241Am radioisotope source, Icelli53

reported good agreement between theoretical and experimen-

tal Compton and Rayleigh peak intensities for BaO, CeO2,

La2O3, Nd2O3 and Sb2O3 samples. The author used the

Rayleigh to Compton ratio in a practical method to determine

the effective atomic number of these high Z oxides, which

could then be used in a number of matrix correction proce-

dures. It is also worth mentioning the report by Shanker54 on

the calculation of Bremsstrahlung produced by the impact of

2–30 keV electrons on thick solid targets, which may be useful

for comparing with other models used for the tube spectrum in

FP correction calculations.

In what was a very sparse year for the application of

chemometrics to XRF spectrometry, the only paper reviewed

was a comprehensive review by Luo.55 The techniques of curve

fitting, multivariate calibration and pattern recognition were

discussed in detail and applications for fields other than X-ray

or gamma spectrometry were also included. The author

focused on the use for XRF spectrometry of genetic algo-

rithms, neural networks, the more-recent support vector ma-

chine and pattern recognition and made clear some of the real

pitfalls as well as attraction of the methods. In concluding, a

hybrid combination of genetic algorithms and neural networks

was proposed as the most likely route to the wider application

of chemometric methods in XRF, although there was no

compelling reason to abandon yet our armoury of fast,

accurate and trusted methods based upon well known FP

and empirical calibration and correction models.

4 X-ray optics and microfluorescence

Capillary and polycapillary optics continue to attract interest in

the development of XRF microanalysis as shown by Sun and

Ding,56 who undertook further work to characterise the

properties of a polycapillary X-ray lens. In particular, they

measured the energy dependence of the focal spot size, trans-

mission efficiency and output focal distance, all of which are

influenced by the dependence on X-ray energy of the critical

angle for total internal reflection. They used a low powered

X-ray tube and a high count rate detection system to overcome

the technical limitations of previous work. Bjeoumikhov

et al.57 discussed the principles and characteristics of X-ray

capillary optics, with particular emphasis on intensity gain,

focal spot size and beam divergence. Their specific interest was

in XRD applications. Lin et al.58 described a new method of

measuring the divergence of X-ray beams from various types

of capillary based on Bragg’s Law. The use of ‘needle type’

collimators was investigated by Tsuji et al.59 and Matsuda and

Tsuji60 in an application designed to excite and analyse small

volumes (estimated to be 0.24 mm3) inside soft tissue samples

(oyster was used as an example). The instrumental configura-

tion used such a collimator to define both the primary and

fluorescence X-ray beams and delineate the detected volume.

Performance data for an agar sample were reported to be 85,

154 and 8 mg kg�1 for the detection limit of Ca, K and Zn,

respectively. A report that significantly extended the concept

of capillary optics was presented by Beuthan et al.61 Their

interest was in the use of capillary fibre optics to realise the

concept of an endoscope for XRF analysis and they prepared

an artificial scattering material containing zinc oxide nano-

particles and clusters to simulate cell layers. Encouraging

results were observed with contrast in the XRF image being

1308 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

an order of magnitude greater than that of a conventional

optical image.

Other forms of waveguide can also be used to define X-ray

beams and Hertlein and colleagues62 presented a detailed

description of the production of multi-layer X-ray optics using

sputter deposition methods and the characteristics of their

application for making X-ray analytical measurements. Lee

et al.58 made an important contribution in understanding the

role of resonance modes in X-ray waveguides based on thin

films by showing that X-ray reflectivity was extremely sensitive

to the electron density distribution in the thin film. This

realisation resulted from experiments on thin films into which

had been embedded gold nanoparticles, which altered the

waveguide properties.

In the field of X-ray imaging, a scanning X-ray analytical

microscope was developed by Katsuta and colleagues63 speci-

fically to measure sedimentary layers associated with lacus-

trine sediments from Lake Suigetsu, Japan, which were

associated with volcanic eruption events. Interpretation of

results provided millennial-scale variations in the Holocene

that could be correlated with ice-rafting events in the North

Atlantic. Patterson et al.64 used micro-XRF combined with

FTIR imaging to investigate the ageing of polydimethylsil-

oxane foam. Species of particular interest in understanding

this process were residual tin, organotin functional group

moieties and the presence of nitroplasticisers from an exogen-

ous source. This work built on a previous study that had

shown tin to migrate to the foam upper surface and the

authors noted the role of stannous 2-ethylhexanoate as the

polymerisation catalyst. Benedetti et al.65 described the ana-

lysis and evaluation of the phase composition of samples a few

mm in size in cultural heritage studies. Awareness of the

capabilities of confocal XRF microscopy in the elemental

imaging of three-dimensional objects in a variety of applica-

tions was raised by Patterson and Havrilla.66

Of course, synchrotron beams have substantial advantages in

any micro-XRF configuration, being high brilliance focused

beams, although there continue to be technical challenges in

maximising resolution. However, Gelfi et al.67 reported that

although in the field of metallurgy SR experiments have been

undertaken with beams smaller than 1 mm, developments in

high resolution and large area detectors (such as the image

plate detector) have allowed conventional laboratory X-ray

sources to be used to achieve spatial resolutions of a few tens

of mm. The authors described the use of this laboratory-based

micro-fluorescence technology complemented by micro-XRD

to characterise deposits from superheater tubes of solid waste

incinerators with a view to understanding corrosion mechan-

isms. In contrast, Nogita et al.68 used the micro-XRF beam-

line at SPring-8 to characterise the segregation of strontium in

a modified hypo-eutectic aluminium–silicon alloy. Experi-

ments showed that Sr exclusively segregated into the eutectic

silicon phase with important implications for the modification

of this eutectic alloy. A combination of SR techniques (micro-

XRF, micro-XRD and micro-XANES) were used by Martinez

et al.69 to measure the solid-phase speciation of Zn in metalli-

ferous organic-rich surface soils and found that highly cova-

lent Zn–organic bonds were present, explaining in part why

metal partition coefficients are generally higher in organic soils

and why toxic thresholds for total metal concentrations are

higher in organic as opposed to mineral soils.

Finally for this section, Minogue et al.70 described an ultra-

high throughput, micro-XRF technique for the double combi-

natorial screening of peptide–metal binding. The method is tag-

free and sensitive in providing a rapid and quantitative means

of identifying metal–ligand interactions.

5 Synchrotron radiation

Mineral elements, often at the trace level, play a considerable

role in the physiology and pathology of biological systems.

Metallogenomics, metalloproteomics, and metallomics are

among the emerging disciplines that are critically dependent

on spatially resolved concentration maps of trace elements in a

cell or tissue, on information from chemical speciation and on

metal-binding coordination sites. Lobinski et al.71 presented a

review paper on recent progress in element profiling at the

genome scale, biological trace element imaging, identification

and the quantification of chemical species in biological envir-

onments. Imaging techniques covered by this publication

included PIXE, m-SRXRF, SIMS and laser ablation ICP-

MS. Information on oxidation states was obtained from

nano-flow chromatography and capillary electrophoresis

coupled with element specific ICP-MS and molecular-specific

electrospray MS/MS. Synchrotron radiation based techniques

in the form of EXAFS and XANES provided crucial specia-

tion of elements in the micro-samples. The authors recognised

that the increasing sensitivity of EXAFS and XANES now

benefit from the availability of more intense synchrotron

beams and efficient focusing optics and presented information

on oxidation state, fingerprint speciation of metal sites and

metal-site structures.

5.1 Instrumentation

Several instrumental novelties were published during this re-

view period. The SPring-8 facility is well known for its intense

high energy flux, particularly suited for the excitation of

K-shell radiation of elements with high atomic number.

Nishiwaki et al.72 exploited this feature in a forensic non-

destructive examination of small glass fragments (o1 mg) to

analyse 34 elements, in particular Ba and rare-earth elements,

with mono-chromatic excitation energy of 116 keV. The Ce to

Ba ratio was used as an effective parameter for identification,

coupled with information on trace levels of Bi, Cs, Mo, Pd and

Sb, and enabled the authors to develop a useful index for the

discrimination of the glass samples. There has been a long

lasting dispute as to whether the REE L-lines, overlapped by

the K-lines of major elements in a sample, can be de-con-

voluted and quantified in an adequate manner for such

forensic applications. However, in utilising high energy SR-

XRF, this powerful excitation source enabled the authors to

overcome all such critical concerns. Eba and Sakurai73 devel-

oped an image plate detection system for 2D-imaging (8 �8 mm2) in combination with XAFS analysis for combinatorial

substrates of manganese–cobalt spinel and lithium ferrite.

Because no x–y scans of the sample were needed, the method

drastically reduced the total analysis time, with an exposure

time of 1–3 s per pixel reported to be sufficient. Hence,

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combinatorial libraries could be screened very rapidly and

efficiently, using this X-ray imaging system. Woll et al.74

developed a confocal XRF microscope for depth profiling of

historic paintings; in particular, the excitation radiation passed

through a borosilicate monocapillary, whereas a borosilicate

polycapillary was used in front of the detector for the fluor-

escence radiation of interest. In a test painting, four distinct

layers ranging from 10–80 mm were claimed to be differen-

tiated. The next step was reported to be a large area scanner

for 3D imaging that is currently under construction.

There is an emerging trend to combine several synchrotron

radiation-based micro-analytical techniques at certain storage

ring beam lines. The amalgamation of m-SRXRF, m-EXAFS

in fluorescence mode, m-XANES and m-XRD provides com-

prehensive data for the characterisation of samples. Both the

speciation and local distribution of phosphorus in fertilized

soil was investigated by Lombi et al.75 down to nano-levels.

Phosphorus availability is often a limiting factor in crop

production around the world. However, for wheat grown in

calcareous soils, fluid fertilisers were shown to be more

efficient than granular products. Using nano-XRF, the

authors showed that P was invariably associated with Ca

rather than Fe; moreover, nano-XANES indicated that the P

precipitation was in the form of octa-calcium phosphate which

is known to hinder the P exchangeability. This process was less

prominent when fluid fertilisers were applied to the soil. It is

hoped that this kind of research will assist in efforts to help

relieve hunger in developing countries. A plant-based diet is

known to contribute to iron deficiency, resulting in a major

human nutritional problem. Kim et al.76 used XRF m-tomo-

graphy to visualise Fe in Arabidopsis seeds, a model organism

for studying plant sciences, including genetics and plant

development. This work enabled the authors to demonstrate

that iron was localised primarily in the provascular strands of

the embryo in the Arabidopsis seeds. Such localisation was

found to be completely abolished when the vacuolar iron

uptake transporter was disrupted. Bulska et al.77 studied the

distribution and local speciation of selenium in roots and

leaves of onions in vivo by m-XANES and confocal m-XRF,

without the need for any form of pre-treatment or subsequent

sample preparation. The plants were grown in a standard

medium containing inorganic selenium compounds. Using

both analytical techniques, the authors reported that the ratio

of inorganic to amino acid selenium compounds differed in

various sub-parts of the plant. Kashiwabara et al.78,79 deter-

mined the distribution of As and K plus the oxidation state of

arsenic in the roots of a fern, Pteris vittata L. by K edge

XANES. They prepared their specimens by freeze-drying. The

concentration of As was found to increase from the base to the

tip of the roots whereas the K content remained almost

constant. The oxidation state of arsenic at the tip of the roots

was predominantly AsIII, whilst that at the base was AsV.

Chlorine speciation in environmental samples was reported by

Leri et al.80 with reliable XANES measurements in plant, soil

and natural water down to the 5–10 mg g�1 range. They were

able to distinguish between inorganic and organic chlorine as

well as aliphatic and aromatic organic chlorine. Brugger

et al.81 used the combination of m-XRF and m-XANES on

the Eu L3 edge to determine the distribution and valence state

of Eu in scheelite (CaWO4) collected from hydrothermal gold

deposits in Western Australia. The XANES spectroscopy

revealed the coexistence of Eu2+ and Eu3+ in both scheelite

samples. Farges et al.82 studied the speciation and weathering

of copper in ‘‘copper red ruby’’ medieval flashed glasses from

Tours cathedral. Using m-XRF and m-XANES/EXAFS at the

Cu K edge, the authors found two main types of red glasses

with distinct Cu speciation. In the first type, Cu was present in

sub-micron metallic nucleates co-existing with monovalent Cu

(30:70 at%), whereas the second type (feuillete glass) showed

mostly monovalent Cu. The feuillete glasses were also weath-

ered at their surface with a formation of amorphous CuII

species related to a copper sulfate.

Cement-based materials play an important role in multi-

barrier concepts developed worldwide for the safe disposal of

industrial and both low- and intermediate-level radioactive

waste. A group from the Paul Scherrer Institute, Switzer-

land,83–86 studied the Co and Ni uptake in cement by

m-XANES and m-XRF methods with the aim of improving

the understanding of immobilization processes at the molecu-

lar level. XRF mapping revealed a highly heterogeneous

elemental distribution. The X-ray absorption studies showed

that NiII formed layered double hydroxide phases, whereas Co

was found to be present in the oxidation states CoII and CoIII.

Van Oort et al.87 studied the micro-scale distribution patterns

of Pb and Zn in sub-surface soils using synchrotron based

m-XRF. At a depth of 70 cm, the Zn accumulation was found

to be predominantly associated with clay-iron coating whereas

there was no significant correlation between Pb and Zn.

However, at a depth of 100 cm, a clear Pb accumulation was

observed in distinct iron coatings whereas a correlation be-

tween Fe and Zn was absent. Kirpichtchikova et al.88 used

synchrotron based m-XRF in combination with m-EXAFS,

chemical extraction and thermo-dynamic modelling to study

the speciation and solubility of heavy metals in contaminated

soil. The most abundant contaminant was reported to be Zn

(1103 mg kg�1) followed by Pb (535 mg kg�1) and Cu (290 mg

kg�1). The authors studied the extractability of these three

elements and found that the lower extraction level measured

for Zn was due to a zinc phyllosilicate component that was less

soluble than zinc phosphate and zinc ferrihydrite.

5.2 Applications

In this section of the review, consideration is given to those

papers that demonstrate the development of SRXRF in rela-

tion to medical and biological applications. One of the main

threats to human health from heavy metals is associated with

exposure to Pb leading to chronic diseases of the nervous,

hematopoietic, skeletal, renal and endocrine systems. Lead

exposure in industrialised countries stems from the workplace,

leaded pipes and, up to the 1980s, from leaded gasoline;

therefore, most adults have already accumulated a substantial

body burden of Pb. Diseases or conditions with increased bone

turnover, such as osteoporosis, pregnancy, hyperthyroidism

and hyperparathyroidism are associated with increased mobi-

lisation of Pb from the skeleton. Ageing-associated release of

bone-lead into circulation is a potentially important source of

soft-tissue lead exposure and toxicity. Surprisingly little is

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known about how lead is distributed in bone and cartilage

at the microscopic level. Zoeger et al.89 presented a study in

which four macroscopically normal femoral heads and

three patellas were taken from randomly selected forensic

autopsies. All subjects had died from acute illnesses, had no

history of work-related exposure to Pb and had no metabolic

bone diseases. The elemental distribution of Ca, Pb, Sr and Zn

in the chondral and subchondral region was detected using

high resolution SR induced m-XRF analysis in confocal

geometry with a lens also in front of the detector for depth

defined area scans and for 3D-reconstruction. The authors

undertook SR measurements at HASYLAB, beam line L, with

typical area scans of 41 � 41 pixels (400 � 400 mm2), a

measuring time of 5 s per pixel and an inspected volume of

22 � 14 � 20 mm3. A highly specific accumulation of Pb was

found in the tidemark of articular cartilage (the transition zone

between calcified and non-calcified articular cartilage) and

interestingly a correlation between Pb and Zn was reported.

Finally, a complete 3D-reconstruction of the elemental

distribution was presented. Hu et al.90 studied the effect of

Zhugu capsule on osteoporotic rat bone by means of SR and

NAA and found an increased content of Ca, Sr and Zn.

Farquharson et al.91 correlated the distribution of Cu and

other trace elements with the concentration of cancer cells in

human breast tumour specimens by a combination of elemen-

tal mapping and high resolution light transmission imaging.

Perez et al.92 examined lyophilised kidney sections from

normal and arsenic-treated rats to show their 2D elemental

distribution using a collimated white synchrotron spectrum. A

correlation between the distribution of As and Zn was

observed.

Other applications related to art, geology and environmental

studies have also benefited from studies using SR-XRF. The

traditional and acknowledged approach to examining spatially

resolved, rare pieces of art by m-PIXE with an external proton

beam was challenged during this review period by m-SRXRF

(BAMline at BESSY II, Berlin). Reiche et al.93 performed

measurements on a series of silverpoint drawings from the

17th century by Rembrandt Harmensz van Rijn, kept nowa-

days at the Kupferstichkabinett of the State Museums of

Berlin. The data increased the existing database on metal

point drawings, thereby reinforcing art historical assumptions

on the dating of drawings. Cauzid et al.94 studied several single

or two phase fluid inclusions in samples from the Brusson gold

deposit (Italy). The authors claimed to have developed a

standardless quantification procedure and compared it with

previously published, internal and external standardisation

procedures. Their standardless method yielded more accurate

results than the existing standard procedures, but they ad-

mitted that there were uncertainties in results for low atomic

number elements depending upon the inclusion depths. Naga-

seki et al.95 preferred a ‘‘relative intensity’’ approach for the

quantitative analysis of fluid inclusions in synthetic quartz. Ma

et al.96 studied the elemental distribution and morphological

information in individual rain droplets by m-SRXRF to specify

their chemical properties. The authors employed their so-

called collodion replication technique for the indirect determi-

nation of the droplet diameter after the evaporation of the

original water matrix with the elements of interest remaining

as residue. This interesting technique provided a means for the

quantification of masses at the femtogram level.

6 TXRF

A number of review papers on developments in TXRF have

been published in the current period. Streli97 covered the

principles of TXRF as well as a wide range of applications.

Challenges of TXRF for surface and thin layer analysis were

summarised by Klockenkamper.98 Markowicz et al.99

described the activities in the IAEA XRF Laboratory in

Seibersdorf, the philosophy of training in methodology and

applications of XRF techniques in IAEA developing member

states with an emphasis on both quality assurance and control.

An example of a member state contribution on QC was the

publication by Owoade et al.100 dealing with the estimation of

uncertainties in TXRF calibration. A comprehensive overview

of recent developments in TXRF may also be found in the

proceedings101 of the 11th Conference on TXRF and related

techniques.

6.1 Instrumentation

Improvements in detection limits can be achieved either by

integration of X-ray optics (to increase the intensity of the

exciting radation) or by using new higher efficiency detector

types. Korotkikh102 proposed a way of reducing the diver-

gence obtained from X-ray optics using one curved mirror by

adding a second mirror. The benefit of this change was to

increase the intensity of the exciting beam by a factor of 4. An

impressive detection limit of 1 pg for nickel was reported by

Waldschlaeger.103 He used a combination of a microfocus low

power X-ray tube with a larger area silicon drift detector

(SDD) in an optimised geometry. Pahlke et al.104 adapted a

commercial TXRF analyser for wafer surface analysis by

replacing the originally large area SiLi detector with a

10 mm2 silicon drift device. Although the area of the SDD

was smaller by a factor of 8, detection limits were only a factor

of 2 worse, due to the improved detection geometry.

There have been some fascinating developments in micro-

analysis combined with TXRF. Micro-TXRF was first

reported by Tsuji et al.105 The authors performed elemental

mapping from residue samples by reducing the area seen by

the detector down to that of the sample spot. This was

achieved by using pinholes, with diameters ranging from 1

to 0.1 mm, mounted in front of the detector. The same

innovative group also developed a TXRF instrument using a

polycapillary lens106 followed by a horizontal slit to reduce the

divergence in the beam, so that the expected angular behaviour

of the fluorescence signal in TXRF was observed. This in-

strumentation was evaluated by analysing single particles on

silicon substrates. Sparks et al.107 successfully investigated the

applicability of an automated nanolitre deposition system for

semiconductor samples following the work of other groups as

a non-instrumental way of achieving m-TXRF.

A number of other interesting developments have been

published during the current review period. Resonant X-ray

Raman scattering was studied by Szlachetko et al.,108 who

made an important contribution by reporting cross sections,

which were very helpful for background correction when

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silicon wafers were measured with an excitation energy just

below the silicon K edge. Okhrimovskyy and Tsuji109 pub-

lished a numerical approach for depth profiling based on

three-parametric Gaussian profiles. Using grazing exit XRF,

the algorithm enabled the authors to construct depth profiles

of atoms implanted in a substrate. Novikova et al.110 applied

the standing wave technique (grazing incidence XRF) in an

investigation of molecular organisation in Langmuir–Blodgett

films of a liquid crystalline lanthanide complex deposited on

silicon substrates.

6.2 Synchrotron radiation induced TXRF

There has been a considerable increase in the number of SR-

TXRF publications in the current review period describing

particular innovation in complementing elemental mapping by

m-SRXRF with speciation data obtained by XANES, which is

referred to as SR-TXRF-XANES.

Streli et al.111 used this combination of techniques for

arsenic speciation (AsIII and AsV) in xylem sap of cucumber

plants and achieved very good detection limits of As of

170 ng l�1. The authors also reported further results for

aerosols and trace elements in aluminium oxide. These mea-

surements were performed at Beamline L at HASYLAB,

Hamburg, Germany. Osan et al.112 used the PTB laboratory

at BESSY, Berlin, Germany, to apply the SR-TXRF-XANES

technique to low Z elements. They reported the ammonium to

nitrate ratio in Antarctic fine aerosols collected from less than

2 m3 of air. For Antarctic fine aerosols in the size range of

0.25–0.5 mm, nitrogen was observed to be present almost

entirely as the ammonium species. When the size of aerosol

particles increased in the range of 0.25–2 mm, the content of

ammonium decreased and that of nitrate increased. Both

groups drew attention to the considerable advantage of SR-

TXRF for aerosol analysis in that a short collection time was

sufficient to gather enough sample mass for analysis to provide

a means of monitoring rapid changes in aerosol composition.

The increasing interest in linking TXRF measurements with

speciation data (SR-TXRF-XANES) was also supported by

an increase in the use of a chemical pre-treatment approach

instead of XANES. Samek et al.113 used a sequential leaching

technique to investigate the speciation of selected metals (Ca,

Fe, K, Pb and Zn) in aerosol samples. The aim of this work

was to investigate the mobility of these elements in order to

ascertain which components were harmful to works of art.

Fittschen et al.114 published a new technique for the deposi-

tion of standard solutions by inkjet printers and its applicability

for aerosol analysis. Droplet sizes of 50–200 mm were achieved

(which are smaller than the available synchrotron beam) and

the authors reported an absolute calibration of the number of

droplets versusmeasured Co intensity. These results lead to the

conclusion that this technique is very promising for the

quantification of aerosol samples collected by those impactors

that produce a pattern and not a single spot.

SR-TXRF applied to environmental monitoring was

published by groups working at LNLS, Campinas, Brazil.

De Vives et al.115 analysed tree rings from samples of wood

collected from a specific species, Caesalinia peotophoroides,

which is common in Brazil in both urban and country areas.

The samples were digested prior to measurement by

TXRF and the authors found a decrease in the K/Ca, K/P

and Pb/Ca ratios towards the bark. The same group re-

ported116 the use of fish samples as environmental monitors

and discussed the risks to human health by the ingestion of fish

contaminated by metals and other toxic elements. The ability

of Tillandsia (an epiphyte widely used as an atmospheric

monitor) to accumulate heavy metals was successfully tested

by Wannaz et al.117 to provenance atmospheric emission

sources in Argentina.

In the field of clinical applications, Canellas et al.118 deter-

mined trace and major elements in the serum of patients with

chronic myelogenous leukaemia (CML). They found that the

concentrations of Ca, Cr, Cu, Fe, Mn, P, Rb and S differed

significantly between groups of healthy and CML patients.

Serpa et al.119 studied cognitive impairment related to changes

in elemental concentrations in the brain of old rats. Higher Br

and Cu values were found in certain brain regions of the

cognitively impaired group in comparison with the control

group.

6.3 Applications

The determination of Hg was investigated by 2 groups. The

Crete research group led by Kallithrakos-Kontos120 immobi-

lised various complexing reagents on the surface of quartz

reflectors. These authors applied this technique to the analysis

of Hg in sea-water121 and achieved good detection limits of

0.4 mg l�1. A similar approach for Hg determination was

reported by Custo et al.122

Various medical/clinical applications of TXRF have been

reported showing the applicability of TXRF in that field.

Varga123 assessed the possible contamination problem from

steel needles in liver biopsies, but concluded that no measur-

able Fe contamination was detected. Ostachowicz et al.124

analysed cerebrospinal fluid and serum of patients suffering

from amyotrophic lateral sclerosis (ALS) and included low-Z

elements down to Na. Lower values of Mg, Na and Zn and

higher values of Ca were found in the ALS group. Platina in

the plasma of chemotherapy patients was investigated by

Greaves et al.125 after pipetting ml amounts of blood plasma

on to a reflector without using any sample preparation. The

blood of seals from the North Sea was analysed by Griesel

et al.126 who proposed a method suitable for additional

biomonitoring for the health assessment of seals in terms of

electrolyte balance and hydration status. Magalhaes et al.127

investigated trace elements in human cancerous and healthy

tissue from the same individual and compared TXRF with

EDXRF. Increased or constant values of Ca, Cu, Fe, K, P and

S and decreased values of Br and Zn were found in carcinoma

tissue. The influence of certain elements in the dynamics of the

carcinogenic process was investigated by Gierat-Kucharzews-

ka et al.128 The authors judged from their results that low

concentrations of Cu, Fe, Ni, Se, Sr and Zn, together with

higher concentrations of Cd, Co, Cr and Pb, in the carietic

teeth could be one of the caries risk factors. Varga129 analysed

iodine in dietary supplement products and used precipitation

of silver iodide to prevent loss of volatile iodine during solvent

evaporation. The author compared the results with data

1312 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

obtained by ICP-AES and reported serious spectral line over-

lap between the iodine and phosphorus lines.

In comparison with former review periods, few applications

in surface analysis have been found. Hellin et al.130 reviewed

trends in TXRF for metallic contamination control in semi-

conductor nanotechnology. Tsuji et al.131 investigated the

suitability of TXRF for investigating processes on a chemical

microchip. They made measurements of a drying process in a

reaction channel on a flat region of the surface. A linear

calibration curve for Zn from standard solutions was

obtained, leading to the conclusion that TXRF was feasible

for this application.

Hoefler et al.132 determined low Z elements in environmental

samples, especially biofilms used as biomonitors. The element

of interest was carbon as it is correlated to the growth rate of

the biofilm. These biofilms were directly grown on the reflector

without any sample preparation and the linearity of the

carbon calibration curve and its dependence on sample mass

was investigated. This work was undertaken using a specially

designed TXRF spectrometer with a Cr anode X-ray tube as

excitation source, a vacuum chamber and a detector with an

ultra-thin window, all optimised for the detection of low Z

elements. Mages et al133 also analysed biofilms as a biomo-

nitor in mine surface drainage water to determine the influence

of copper mining on the environment. The trace element

content of individual micro-crustaceans (copepod specimens)

and a Brazilian waterweed (Egeria densa) from a metal-con-

taminated Chilean wetland were measured by Woelfl et al.134

The same author135 also used macro-zoobenthos from the

Tisza and Szamos rivers to test whether the zoobenthic fauna

showed an enhanced metal content three years after an

industrial accident in the Romanian mining industry. Fe was

much lower and Mn and Zn much higher in concentration in

benthos from the more contaminated river. The authors

concluded that the benthos was suitable as a bio-indicator

for metal contamination, but the sediment bioaccumulation

factor turned out to be low, offering low bioavailability of the

contamination element for benthic organisms. Gruber et al.136

analysed Austrian wine without any sample preparation and

was able to use elemental fingerprinting to identify the wine

brand, vineyard and the year of vintage of the 11 different

wines tested.

Applications from various other fields were published: Nishi-

waki et al.137 analysed small glass fragments and was able to

distinguish glass fragments by their elemental ratios. This

discrimination could not be achieved by measuring the refrac-

tive index. Metal ion diffusion through polymeric matrices was

investigated by Boeykens et al.138 This work has potential

importance in drug control release, microbiological corrosion

protection and enhanced oil recovery. Uranium was deter-

mined in sea-water by Misra et al.139 whilst Nigerian fossil

fuels were measured by Mokobia et al.140

7 Portable and mobile XRF

Some of the more exciting developments in portable XRF

instrumentation continue to be in the area of planetary

exploration. Much recent interest has centred on the explora-

tion of Mars and, in particular, the discovery of evidence of

water on Mars. The contribution of Mallett et al.141 is, there-

fore, timely in modifying and extending an existing Monte

Carlo code with a view to developing a method for detecting

OH and H2O in Martian rocks and soil. This development was

based on comparing the predicted and measured ratio of

elastically and inelastically scattered plutonium La X-rays

from rock or soil samples measured by the Mars Exploration

Rover’s alpha particle X-ray spectrometer. As this ratio is

sensitive to the mean atomic number of the sample, so the

difference between the predicted ratio, based on an anhydrous

sample, and the measured ratio gives information about the

‘invisible’ (as far as XRF is concerned) elements in the sample.

One of the problems encountered in the design of the Beagle 2

instrumentation package was the conflict between incorporat-

ing both a Mossbauer and XRF spectrometer, both instru-

ments with radioactive sources, in relatively close proximity,

with the potential loss in scientific performance due to

enhanced background radiation levels. Butcher et al.142 con-

sidered these and other issues surrounding the management of

radiation hazards and background effects posed by radioactive

sources for planetary missions. Okada et al.143 continued the

design study and specification for the Japanese SELENE-B

mission to the Moon, which will comprise a static lander and

rover that will incorporate a sample analysis package with an

XRF/XRD. The highest priority for this mission will be to

provide evidence for the origin and evolution of the Moon by

the analysis of sub-crustal material that is exposed at a crater’s

central peak.

Lead (Pb) in soil is one of the more common terrestrial

applications of portable XRF and Clark et al.144 undertook an

important study of the sources, sinks and exposure pathways

of Pb in urban soil in 103 gardens in Roxbury and Dorchester,

Massachusetts, USA, and remarkably found that 88% con-

tained Pb at concentrations above the US-EPA reportable

limit of 400 mg kg�1. Supplementary laboratory (including

isotopic) analyses indicated that the major sources of Pb were

automobile gasolene and Pb-based paint with the latter source

contributing 40–80% of the mass balance. Results from test

crops grown in soil from this locality indicated that consump-

tion of these crops would be equivalent to 10–25% of a child’s

daily exposure from tap water—food for thought! Minimising

the risk of contamination from Pb in soil was the basis of a

study by Dixon et al.,145 who were concerned about the

effectiveness of low-cost soil treatments designed to reduce

exposure to contaminated soil in the ‘yards’ adjacent to

buildings in Boston, MA, USA. The yards recruited for this

study had been treated with ground coverings and ground

barriers in 2000–2001 and were found by PXRF to have fallen

from an average of 2021 mg kg�1 Pb to 206 mg kg�1 a year

after treatment. As a result, the amount of Pb contamination

at the building entry was found to have been reduced by about

20%. Kilbride et al.146 analysed a cocktail of elements of

environmental interest in soil using two types of field portable

XRF and found the results to be broadly comparable with

those from ICP-AES after an aqua regia extraction.

The capability of PXRF for in situ measurements is a major

advantage of the technique, but also gives rise to the problem

that sample surfaces are unlikely to be flat and positioned

exactly in the analytical plane of the instrument, requiring a

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supplementary correction for these surface irregularity effects.

A number of approaches have already been found in the

literature to correct the consequent discrepancies and mini-

mise bias, a topic to which Bonizzoni et al.147 returned in the

analysis of metal objects of irregular shape. Their approach

was to calculate corrective irregular shape factors based on

modifications to the conventional fundamental parameter

approach, which assumes the excitation and detection geome-

try angles are equal and of constant value for all samples.

Applications of PXRF, including the development of innova-

tive instrumental configurations continue to expand in popu-

larity and reflect increasing recognition of the versatility of the

technique. Thus, Emery and Morgenstein148 used a portable

XRF to analyse mud brick used at an ancient town site of El

Hibeh (Egypt) with the aim of establishing the source of this

material from surface sediments in the local Nile floodplain.

Gianoncelli et al.’s interest149 was in the glazes on two

sculptures located in the cathedral of Seville (Spain) in relation

to Florentine production methods during the Renaissance

period. Michelangelo’s statue of David was the object of

investigation for Castellano et al.,150 whose interest lay in

mapping the presence of sulfur to help restorers choose the

most suitable method of treatment for cleaning the statue.

Papadopoulou et al.151 described a portable micro-XRF in-

strument fitted with a monocapillary lens designed for the

analysis of cultural objects and gave some examples of the

quantitative analysis of ancient Greek ceramic samples. The

instrumentation described by Desnica and Schreiner152 for use

in analysing art objects at the Academy of Fine Arts, Vienna,

incorporated a miniature X-ray tube and silicon drift detector

and two laser locating devices. Suzuki and McDermot153 used

in situ XRF in combination with FTIR for the analysis of

titanates, with the specific aim of identifying and evaluating

the frequency of occurrence of the use of nickel titanate

(a yellow pigment) and chrome titanate (a yellow–orange

pigment) in US automobile finishes between 1974 and 1989.

Both these pigments were used as replacements for lead

chromate pigments that were finally withdrawn in the early

1990s. Andrikopoulos et al.154 described a mobile instrument

that incorporated two complementary techniques of consider-

able potential interest, Raman spectroscopy and XRF. The

influence stemmed from the ability to acquire details of the

structural properties of pigments by Raman and their elemen-

tal composition by XRF (including the composition of invi-

sible under-layers). Use of this instrument was validated on an

experimental icon painted using traditional Byzantine techni-

ques and it was found that almost all pigments could be

identified, including those hidden by over-painting. An addi-

tional contribution worthy of mention is the mobile laboratory

XRF application that Shalev et al.155 used to analyse artefacts

and sediments during the field study of a small archaeological

copper smelting site in the Negev, about 30 km west of a

complex of ancient copper mines, in Jordan. Results were

interpreted to estimate the scale of copper production during

the first period of operation at the end of the Early Bronze

Age. Stosnach156 tested a portable TXRF spectrometer for its

suitability for on-site analysis of heavy metal contaminated

areas and compared the results with TXRF measurements

after complete microwave assisted acid digestion. Finally,

Herman et al.157 undertook an interesting study of the health

hazards associated with the use of lead (Pb) in the workplace,

where workers face risk of exposure through inhalation,

ingestion and sometimes through dermal exposure. Risks also

extend to outside the workplace from the inhalation of lead-

contaminated air, the ingestion of lead-contaminated dust and

soil, lead polluted water, lead adulterated food and lead

supplemented medicine. The study involved an evaluation of

lead in blood levels (using an analyser based on the principle of

ASV) and field portable XRF to measure environmental lead

in paint, soil and dust. The results of this study was to reveal a

high incidence of lead toxicity in workers in the lead industry

at four facilities in India and high levels of lead in associated

environmental samples. These results indicate that developing

countries, such as India, have not benefited from the stringent

national and international policies that are now enforced in

many developed countries.

8 On-line XRF

We believe that on line XRF continues to have a key role to

play in a number of industrial processes, but that innovations

remain under-represented in the literature. It is a pleasure,

therefore, to report the work of de Mussy et al.,158 who

described an on- line micro-XRF instrument for assessing

the thickness of copper on patterned wafers during an electro-

plating and chemical mechanical polishing process.

9 Applications

9.1 Sampling, sample preparation and pre-concentration

techniques

Ameasurement process comprises both sampling and chemical

analysis, with sampling being of crucial importance as the

reported result may only be derived from the test portion

presented to the spectrometer. In many applications it is the

sampling phase that generates the highest component of

uncertainty. When sampling brownfield sites, where the in-

herent heterogeneity of contaminants within the site is a major

factor, the literature offers a variety of sampling designs and a

choice of depth and mass recovery with in situ measurement

strategies increasingly being used as a powerful technique to

reduce the overall time taken to complete a survey. Taylor and

Ramsey159 offered a new approach for those concerned with

strategies for sampling contaminated land. Various methods

are currently used to estimate uncertainty, balancing factors

such as cost and fitness-for-purpose, to ensure that subsequent

decisions based on the chemical analyses are acceptable. Their

approach offered the ‘‘optimised contaminated land investiga-

tion’’ method that considered site-specific variables, such as

measurement costs, against the level of uncertainty and sub-

sequent costs that may arise from missclassification of the land

in question. This new method provided an objective and

traceable judgement as to whether the reported chemical

analyses were fit-for-purpose. A similar exercise was reported

by Gustavsson et al.160 who were concerned with a site that

had contaminated ‘‘hot spots’’ where the components contri-

buting to the total sampling error were reduced and the

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analytical error increased. They concluded that the low con-

centration of contaminant, small extracted sample size and

large particles in the collected samples contributed to the level

of uncertainty. These studies are a timely reminder that

analysts should define their adopted sampling strategy to

ensure that the commissioner of a survey of contaminated

land is able to judge whether the reported results are asso-

ciated with an acceptable level of uncertainty to support a

subsequent decision as to the classification of land under

investigation.

This review has followed the development of a technique for

the analysis of small volumes of liquid, typically microlitres to

millilitres, onto thin film substrates and allowing the liquid to

dry into a concentrated residue or ‘‘dried spot’’. The main

advantage over conventional direct liquid analysis is that

liquid matrix effects, such as scattering, are minimised and

the sample analytes are concentrated, thereby enhancing both

the quality and sensitivity of analysis. Miller et al. built on

their earlier work of using nanolitre dried spots that decreased

reagent consumption and produced specimens of uniform

shape to enable the detection of elements with picogram

sensitivity by micro X-ray fluorescence and TXRF. Their

current publication161 overcame the major drawback in the

preparation of nanolitre dried spots due to operator variables

as the droplets were deposited manually through a contact

injection method onto different analysis substrates. This tech-

nique, however, introduced sample preparation errors due to

variations in the contact geometry of the injector tip with the

substrate surface between droplet injections plus a human

factor arising from differences in user technique. Practitioners

will also recognise that the consequence of such a contact

deposition method could be contamination as the tip interacts

with different substrates. The authors explored the use of non-

contact automated printing technology as an alternative

method for the preparation of nanolitre dried spots by dis-

pensing 20 and 50 nl volumes of multi-element standard

solutions onto AP1 and Kapton film substrates. Multiple dried

spots were found to be reproducibly deposited in the same

precise location on the film substrate surface, allowing in-

creased sample loadings for higher element sensitivity. How-

ever, the characteristics of the substrate did affect the quality

of dried spot formation as irregularly shaped spots developed

on the thicker, more hydrophobic Kapton film when higher

droplet mass loadings were attempted. This problem was

overcome by increasing in the area analysed to ensure that

the entire dried spot residue was measured. This method for

sample preparation may also be of interest to readers using

other analytical techniques involving small quantities of

liquid, such as IR, Raman or UV/fluorescence spectroscopy.

An alternative to evaporation for the immobilisation of

trace analytes in aqueous samples has resulted in a plethora

of published work on preconcentration techniques as workers

continue to refine methods and take advantage of new materi-

als. Many methods are application-specific but readers famil-

iar with the damage caused to delicate specimens by the

intense X-radiation from modern 4 kW wavelength dispersive

spectrometers may benefit from the work of Abe et al.,162 who

protected both faces of their specimens with a commercially

available laminate film. Trace amounts of Cd, Co, Cu, Fe, Hg,

Mn, Ni, Pb and Zn in environmental water were pre-concen-

trated with an iminodiacetate extraction disc (IED) which

comprised beads of polystyrene–divinylbenzene copolymer

containing iminodiacetate knitted among its polytetrafluor-

oethylene (PTFE) fibres. The high extraction rate and volume

offered by these discs was preferred when compared with

column and static ion-exchange methods. Subsequent lamina-

tion of the IED was reported to prolong measurement times

from 7 to about 200 min when irradiated at 4 kW whilst

negligibly decreasing the detected signal from the analytes of

interest. It was, of course, necessary to reduce the power of the

X-ray tube to 1.5 kW to compensate for Hg evaporation. The

authors reported linear calibration curves over the range

500 mg to 5 mg with detection limits corresponding to three

times the standard deviation of the blank intensity of 0.1–

0.4 mg for Co, Mn and Ni, 0.5–0.8 mg for Cu, Fe, Pb and Zn

and 7 mg for Cd. A spike test for 10 mg of eight analytes,

excluding Mn, showed good recoveries (90–100%) for muni-

cipal tap water and rainwater. Fontas et al.163 compared two

different types of membrane used for the concentration and

determination of CrVI in electroplating water from galvanic

baths. The anion-exchanger extractant, Aliquat 336, was

selected for the enrichment of Cr using (a) an impregnated

membrane, where the organic solution of the extractant filled

the pores of a polymeric membrane, and (b) a polymer

inclusion membrane, prepared by physical inclusion of Ali-

quat 336 in the matrix formed by either cellulose triacetate or

poly(vinyl chloride) and the plasticizer 2-nitrophenyl octyl

ether. Both types of membrane were reported to be stable

and efficient, with the polymeric membranes made of PVC

showing a higher degree of homogeneity in terms of metal

distribution. The EDXRF data from the preferred PVC-based

membranes gave a linear calibration curve over the concentra-

tion range 0.3–8.8 mg L�1 with a detection limit of 0.3 mg L�1.

Orescanin et al.164 offered a procedure for the determination

of lanthanides in environmental samples after separation from

the major matrix elements on Dowex 50W-X80 resin followed

by pre-concentration with the chelating agent ammonium

pyrrolidine dithiocarbamate (APDC). The influence of pH of

the solution and presence of organic matter on the complexa-

tion was investigated using certified reference materials and

environmental samples of red mud. Whilst maximum recovery

was reported at pH = 8, the presence of organic matter

slightly modified the complexation giving higher recovery at

pH = 7. However, it was interesting to note that recovery

varied from 91.4% for Pr to only 24.9% for Dy. The EDXRF

spectrometer used a 109Cd source for excitation of the La lines

of the lanthanides.

Other preparation techniques included an investigation by

Manara et al.165 of the behaviour of sulfur in silicate glasses

and melts used for the incorporation of radioactive waste.

Sulfates are known to have low solubility in the vitreous phase

and the authors investigated the relationship between the

ratio, R, of Na2O to B2O3, from variations in the type of

sulfate added and the effect of V2O5 on the incorporation of

sulfates in borosilicate glasses. The oxides were melted in Pt/

Au crucibles in air. The work confirmed that the incorporation

process is favoured by the network depolymerisation that

evolves with the ratio R. It was found that V2O5 accelerated

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the kinetics of sulfur incorporation in the glass by modifying

the borate network and fostering the formation of voids

compatible with the sulfur co-ordinate polyhedron in the

glassy network. The study also found that the kinetics of

X2SO4 incorporation was slower when X = Cs. Celik and

Oner166 compared the characterisation of narrowly sized

fractions of clinker ground by a ball mill and high-pressure

grinding rollers. A higher degree of liberation of mineral

phases resulting from inter-granular breakage along grain

boundaries was attributed to the high-pressure grinding roll-

ers, thereby improving the properties of the final cement

product.

9.2 Geological and industrial minerals

Because of its capability of measuring a range of important

major and trace elements, XRF continues to be widely used in

supporting geochemical research, in part because of the way

analytical results can contribute to an understanding of geo-

chemical processes. In many of these studies, XRF is one of a

number of techniques that is used to contribute data. Thus,

Cutten et al.167 used XRF to ‘fingerprint’ the composition of

sandstone and schist conglomerate clasts from the Maruia

Basin, adjacent to the New Zealand Alpine Fault, to identify

source terrains and hence understand fault movement over the

last 11.5 Ma. Ostrooumov and Banerjee168 used XRF as one

of the techniques to characterise amazonite, a potassium

feldspar, in the Keivy granitic pegmatite from the Kola

Penninsula, Russia. Their particular interest was in the differ-

ent colours (blue through green) found in various generations

of this mineral, with the possibility that the chemical and

spectrometric parameters of this mineral might be an impor-

tant exploration indicator for REE mineralisation. Adams

et al.169 used XRF and EPMA to analyse glass shards from

the San Miguel de Allende graben, Guanajuanto, Mexico,

which, with other stratographic data, was designed to provide

an understanding of the timing of the volcanism, date and age

of extension, and a better understanding of the tectonic and

volcanic evolution of Central Mexico. XRF, XRD and optical

microscopy were used by Sanchez-Munoz et al.170 to study 86

microclines from 7 granitic pegmatites with the aim of under-

standing better the evolution of these species in relation to the

rate of cooling and interaction with aqueous fluids. Moller

et al.’s171 interests lay in climatic changes in the Holocene

period in southwest Greenland as indicated by sedimentolo-

gical and geochemical (XRF) data derived from a 3.5 m

gravity core from Ameralik Fjord. Bahr et al.172 also studied

gravity cores with XRF playing a supporting role to high

resolution stable oxygen isotope data on ostracod shells to

evaluate the late glacial to Holocene palaeoenvironment of the

Black Sea. Their interpretation was that a climate mode like

the North Atlantic Oscillation was governing the inter-annual

variability in the flow of water from the River Danube. Events

contributing to boundary layers are of considerable interest to

geologists and Zhang et al.173 used XRF as one of the

techniques to analyse claystones and mudstones at the Chahe

section (Guizhou, South China) of the terrestrial Permian–

Triassic boundary. The claystones in this section were of

volcanic origin and the absence of spherules provided no

evidence of an extraterrestial impact event. Schroder et al.174

adopted a multi-technique approach to analyse two drill cores

from Agouron, Transvaal, South Africa, to elucidate the

deposition sequence and regional geology. Another interesting

geochemical investigation was a detailed micro-XRF/XRD/

EXAFS study of the mineralogy of natural ferromanganese

coatings on quartz by Manceau et al.175 The coatings com-

prised alternating Fe-rich (ferrihydrite) and Mn-rich (verna-

dite) layers that were irregularly distributed and not always

continuous. The trace elements Ba, Ni and Zn were associated

with vernadite and As with ferrihydrite and the authors gave

full details of the inter-layer structures of these coatings as well

as the substitution mechanisms for the trace elements.

In addition to the mainly ‘hard rock’ studies summarised

above, XRF has contributed to a number of studies on soils

and sediments. The Indian monsoon was a topic of interest to

Von Rad and colleagues176 and in particular its link to climate

change over the Late Holocene period, based on a high

resolution record of laminated sediments deposited off the

coast of Pakistan. The three proxys for climate change were

varve thickness, stable oxygen isotopic ratios and inorganic

geochemical compositional data, all used to infer the monsoon

driven ‘moisture history’ of the northeastern Arabian Sea. The

Cenomanian–Turonian Boundary Event (Cretaceous) was

investigated by Turgeon and Brumsack177 using sediments

from the Umbria–Marche Basin of central Italy in a project

designed to elucidate one of the most spectacular ‘oceanic

anoxic events’. McCarty et al.178 undertook a meticulous

investigation of the relationship between composition and

lattice parameters of some sedimentary dolomites of various

composition, location and age. The main outcome was to

determine the relationships between the lattice parameters and

the Ca-content in non-stoichiometric dolomite. A study of the

geochemistry of soils on a catena on basalt at Khon Buri,

northeast Thailand, was carried out by Thanachit et al.179 who

described the geochemical characteristics of soils developed on

the crest, backslope, footslope and valley floor on an undulat-

ing basaltic lava corrosion plain. It was found that element

behaviour in these soils could be categorised as the Al, Ca, Fe

and Mn groups.

Geologists often avoid weathered surfaces, preferring

freshly broken surfaces to overcome the difficulty weathering

causes in rock recognition and geochemistry. However, weath-

ering is rather an important process, not the least in the

evolution of soils. Taboada et al.180 used XRF to measure

the Th and U concentration and SEM to study the corre-

sponding mineralogy of the rock and soils developed on

granitic rocks in northwest Spain, with determinations made

on rock, bulk soil, and then in the sand (50–200 mm), silt (2–

50 mm) and clay (o2 mm) fractions. Although the bulk soil had

similar concentrations to the rock, the U and Th concentration

in the sand fraction was always lowest and that in the clay

fraction highest (always higher than that of the rock). Leach-

ing of U and Th from the top to the bottom soil horizons

appeared to be the major influence on the environmental

impact of these elements, noting the risk of redistribution in

the potentially airborne fraction. The same authors181 under-

took an analogous study of the behaviour of Ti and Zr and

found that Zr was enriched in the silt fraction (at a

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concentration of up to 5 times that of the parent rock), whilst

Ti was enriched in both the silt (up to 5 times) and clay (up to

12 times rock) fractions. Weathering was also of interest to

Jones et al.,182 but more in the manner of how to compensate

for it. The aim was to use portable XRF to assess geochemical

variations within and between rock outcrops of spotted doler-

ite on the Preseli mountains in SouthWales, a project linked to

the origin of some of the blue stones at Stonehenge. The

sampling strategy involved making two neighbouring but

independent measurements on the weathered rock surface at

a number of locations across the outcrop with the intention of

measuring the within-outcrop and between-outcrop variabil-

ity. Several outcrops were heterogeneous at the 5% signifi-

cance level for one or more elements and geochemical

differences were demonstrated between some of the outcrops

using discriminant analysis.

Rocks are not often directly associated with a radiation

hazard, although all contain naturally occurring isotopes of K,

Th and U, often at enhanced concentrations in granites. Brai

et al.183 correlated radioactivity measurements and air kerma

rates (i.e., a measure of the radiation dose in air) with

geological features of Sicily. Samples of rocks and soils which

contributed to this study were analysed by XRF. Geochem-

ical, mineralogical and petrographic features were in good

agreement with radiometric data, allowing an evaluation to be

made of the public health implications of natural radioactivity.

Because of the concentrations of K, Th and U, granite used as

a building stone or for ornamental purposes also carries a

small risk of exposure to ionising radiations, as highlighted by

Salas et al.,184 who collected 100 samples of granite from

traders in Balo Hoizonte, Brazil. These samples were analysed

by a range of techniques, including XRF, which showed that

some samples contained up to 30 mg kg�1 U and 130 mg kg�1

Th. The radiation hazard was calculated by assuming a

standard room tiled with granite containing more than

60 mg kg�1 U and Th. The estimated radiation dose was

between 0.11 and 0.34 mSv year�1, which is significantly lower

than the international exposure limit of 1.0 mSv year�1.

Another radiation-related geochemical contribution concern-

ing the geochemical environment surrounding a shallow geo-

logical repository for radioactive waste was presented by

Akagawa et al.185 This work addressed the issue of redox

fronts formed in fractured crystalline rock caused by the

infiltration of oxidised pore water and was based on measure-

ments of a redox front in Cretaceous granitic rocks in central

Japan. XRF, ICP-MS and EPMA showed that REE, Cs and

U had migrated to the front with U enriched at the front edge,

probably retained by Fe-oxyhydroxides. The authors sug-

gested that matrix diffusion in the oxidising zone could be

an effective way of retarding the release of contaminants.

A few technical advances in XRF methodology have been

published in the current review period. Although glass disks

are almost universally used for the XRF determination of the

major elements, chromite ores present a number of challenges

because of their highly refractory nature. However, Sanchez

Ramos et al.186 undertook an in-depth study to optimise the

preparation of chromite ore glass disks and recommended the

following experimental conditions: lithium tetraborate as flux

at a sample to flux ratio of 1 to 40 with the addition of one or

two drops of lithium bromide solution; fuse for 30 min at

1200 1C. The authors prepared calibrator disks using similar

reference material and different high purity ignited oxides to

obtain calibration curves for Al, Ca, Cr, Fe, K, Mg, Mn, Na,

Si and Ti (as oxides) and gave satisfactory accuracy. Nakaya-

ma et al.187 described a comprehensive scheme for the XRF

analysis of felsic rocks for 42 oxides and elements based on 1:1,

1:2, and 1:10 sample:flux glass disks. ‘Low dilution’ glass disks

of satisfactory homogeneity with a 1:1 flux to sample ratio

were prepared using a double fusion method in which the melt

was allowed to cool to room temperature before the second

heating stage. The scheme involved the determination on 1:10

glass disks of the major elements and Rb, Sr, Y and Zr: on 1:2

glass disks—As, Ba, Co, Cr, Cu, Ga, Nb, Ni, Pb, Th, U, V, W,

Zn and on 1:1 glass disks—Cs, Hf, Sc, Sn, Ta and REE. Safi et

al.188 investigated the chemical analysis of phosphate rock

using different methods, but highlighting modern XRF in-

strumentation. Evaluations are not often published concern-

ing the effectiveness of the calibration function in XRF

analysis, however Guevara et al.189 undertook a comparison

of linear regression models for quantitative geochemical ana-

lysis, using XRF as an exemplar, including ordinary least

squares fitting, weighted least squares and maximum like-

lihood fitting, and concluded that the latter two approaches

were statistically more consistent.

XRF has been applied to a number of aspects of the

processing of industrial minerals, including a study by Banza

et al.190 that was designed to reduce the processing time to

reduce the Fe content of glass grade sand for special glass

applications. XRF was used to monitor the Fe content (pre-

sent in the raw sand as pyrite) and in place of a ‘dump leach’

process that took several weeks, an acid leach (with an

investigation into the effect of the continuous addition of

H2O2) resulted in a five-fold reduction in the Fe content over

a period of 2 d. Olubambi et al.191 also used XRF as part of a

study to optimise the recovery of base metals from a complex

sulfide ore from Ishiagu (Eboyin State, Nigeria). The extrac-

tion of ferronickel, as part of the mining process, left a residual

solid (scum) of a vitreous material that created an environ-

mental problem. Hernandez et al.192 investigated this material

using XRF, XRD and EPR. This ‘scum’ was found to

comprise oxides rich in Fe2O3 and NiO as well as enstatite

and a-alumina and Fe3+ glassy phases and the study repre-

sented the first exploratory stage to identify a potential

application that would reduce this environmental problem.

Bernaus et al.193 undertook a multi-technique study of Hg in

the mining district of Almaden in Spain, using SR-based

techniques and micro-EXAFS. Part of the study was to assess

the potential availability and part to understand its mineral-

ogy and elemental associations. Cinnabar was one of the main

species in the Hg-rich particles studied, together with more

soluble mercury compounds such as schuetteite and mercur-

y(II) oxide.

9.3 Environmental

9.3.1 Atmospheric particulate matter. As industrial socie-

ties have become more aware of the extent of particulate

matter that we inhale, legislation has been put in place to

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reduce such pollution, resulting in the need to measure and

monitor concentrations in ambient air. This, in turn, has

resulted in an improvement in air quality and a reduction in

the concentration of heavy metals analysed. It is expected that

the regulatory limits will continue to be reduced, thereby

challenging analysts to develop methods with sufficient sensi-

tivity to meet any new need. In recent years, this review has

commented on the increasing ability of EDXRF systems to

satisfy analytical needs that had previously been the domain of

wavelength dispersive configurations. Literature under review

during this current period and discussions at XRF confer-

ences5,6,194 have demonstrated the ability of polarised EDXRF

spectrometers to achieve the expected lower limits of detec-

tion. Therefore, as the expected concentration of atmospheric

particulates collected by samplers falls, attention turns to the

homogeneity of the filters presented for analysis. Owoade

et al.195 utilised the enhanced sensitivity of polarised EDXRF

in their study of the uniformity of particulates collected by a

PM10 sampler when the size of the incident X-ray beam was

less than the diameter of the filter. Each filter sample was

divided into four quadrants with each quadrant analysed using

the same conditions. All sixteen analytes were detected in

every sample with less than 10% deviation in concentrations

between quadrants for most analytes except Ba and Cs, where

the deviation was of the order of 20%. The authors concluded

that the PM10 sampler was reliable in terms of homogeneity of

the deposition and where analytes were found at low concen-

trations, it was important to ensure that sampling time be

increased to enable a higher mass deposition on the filter.

Attitudes towards the disposal of waste have changed as

people recognise the need for waste separation and recycling of

products and materials to create a sustainable society. In

Sweden, the deposition of combustible waste to landfill was

prohibited in 2002 and the city of Boras responded by

introducing new incinerators at their district heating plant.

Ahoh et al.196 used EDXRF to characterise the elemental

contents in PM2.5 aerosols collected in the city dominated by

this modern waste incineration plant. Ambient air is a complex

mixture of gasses and particles, and this study recorded data

on particle mass and black carbon together with SO2 and NO2.

Using principal component analysis (PCA), five major sources

of the collected PM2.5 were identified: the waste incineration

plant itself together with other local sources; oil incineration,

biomass burning, long-distance transport and traffic emis-

sions. The authors were aware that the quantitative contribu-

tion from these different sources must be considered only as

informative, since the number of observations was small

compared to the number of identified variables and further

work is expected. Moving indoors, Wang et al.197 determined

the chemical composition of the PM2.5 fraction from incense-

burning in a large environmental chamber. Chemical analyses

by XRF for elemental species, ion chromatography for water

soluble organics (ammonium, chloride, nitrate, potassium,

sodium and sulfate) and thermal/optical reflectance analysis

for carbon were performed for the combustion of three incense

categories (traditional, aromatic and church incense). The

average organic carbon and elemental carbon concentrations

in the PM2.5 were church incense 4 traditional incense 4aromatic incense. The inorganic ion concentration sequence

was traditional incense 4 church incense 4 aromatic incense

and the elemental profiles were found to be dominated by Cl,

K and Na. Readers with an interest in the analysis of fine

aerosols down to 0.25 mmwill find comment on the application

of SR-TXRF in section 6.2 of this review where the advantage

of this technique is described for the analysis of low mass

samples.

Harper and Pacolay198 continued their extensive series of

studies of workplace air quality that compared various types of

sampler used for the collection of lead in different environ-

ments for subsequent presentation to a portable XRF analy-

ser. In this investigation personal samples were taken at a

manufacturer of solder alloys consisting mainly of lead and

tin. The same five samplers were assessed, namely: the close-

faced 37 mm cassette (CFC), the 37 mm GSP or ‘‘cone’’

sampler, the 25 turn Institute of Occupational Medicine

(IOM) ‘‘inhalable’’ sampler, the 25 mm button sampler and

the open-face 25 mm cassette. Mixed cellulose ester filters were

used in all the samplers. Following XRF analysis, the sample

filters were digested in acid and analysed by ICP. The internal

surfaces of the CFC samplers and 25 mm open-face cassettes

were also wiped, and the wipes analysed for lead to assess wall-

losses in these two samplers. In addition to Pb, other metals

(Ag, Cd, Cu, Fe and Sb) were detected in some or all of the

samples by ICP analysis, but only Cu and Fe could be

determined by the PXRF under test. All five samplers gave

good correlations (r2 4 0.9) between the two methods over the

entire range of found Pb mass, which encompassed both the

action level and the permissible exposure limit enforced in the

USA. The average of three readings across filters from the

GSP sampler gave the best result: however, analysis of the

wipes from the interior of the cassettes showed a substantial

loss of sample to the walls. Even larger wall losses were

recorded in the 25 mm open-faced cassette. Neither this

sampler nor the IOM or button samplers met the 95%

criterion.

9.3.2 Other environmental studies. XRF analysis is now

widely accepted as the technique of choice for the analysis of

not only atmospheric particulates collected on filters but also

precipitates of river and lake sediments, suspensions, rocks

and minerals, etc. An empirical method for correction of matrix

effects in samples collected on membrane filters was proposed

by Sitko.199 Better sensitivities and detection limits, especially

for low Z elements, are generally obtained for thin samples in

comparison with thicker ones due to the small or negligible

absorption effects and associated low background. However,

many samples collected on filters are, in fact, of intermediate

thickness and manifest absorption and enhancement effects.

Therefore, an improvement in the quality of data from these

intermediate samples can be achieved if experimental or

mathematical correction methods are employed. Sitko’s ap-

proach for the analysis of elements from Z = 19 (K) to Z =

92 (U) used the familiar ratio of coherent (Rayleigh) to

incoherent (Compton) X-ray intensities but also recognised

the fact that, in the case of samples collected on filters, the

coherent and incoherent scattering observed was the sum of

the contributions from both the filter and the material

collected. Measurements were made using a WDXRF

1318 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

spectrometer, fitted with a Mo target X-ray tube, of Ka lines

for elements from K to Sr: La1 lines for Ba, Ce, Cs, La, Nd, Th

and U and Lb1 for Pb. Net intensities were collected for each

sample by measuring the analyte peak and the continuum

close to the peak. Samples of geological reference materials

(silicates and aluminosilicates) and fly ash were collected on

two types of membrane filter: Sartorius (acetate, 0.2 mm pore

size and 47 mm diameter) andMillipore (type RA, 1.2 mm pore

size and 47 mm diameter). The Sartorius filter was found to

scatter X-rays to a greater extent and thought to be due to the

difference in mass per unit area between the two filters (4.81

and 4.46 mg cm�2 for Sartorius and Millipore, respectively).

The validity of the algorithm was reported to be satisfactory

for samples of mass per unit area between 1 and 3 mg cm�2

and indicated its usefulness for the filters and samples tested.

The search for safer materials to prevent the release of heavy

metals into the environment continues. All ships have their

underwater hulls treated with antifouling (AF) paint in order

to minimise operating expenses. The treatment increases the

speed of a vessel through the water, reduces noise and

decreases fuel costs but has a negative influence on the

environment. Whilst the use of tributyltin is subject to world-

wide restriction and will be completely prohibited in 2008,

alternative AF paints continue to use copper and organic

biocides. Valkovic et al.200 used EDXRF to determine the

concentration of the biocidal elements As, Cu, Pb and Zn plus

Br, Ca, Cr, Fe, K, Mn, Ni, Rb, Sr, Ti and Y in surface

sediments from Kvarner Bay on the Adriatic coast, where the

high density of boats and restricted tidal movements was a

concern. The same laboratory201 also studied surface and core

coastal sediments in Punat Bay and Soline Bay, Croatia, to

demonstrate the negative environmental influence of marinas,

shipyards and ports caused by restricted water exchange in

these bays with the open sea. In common with many other

environmental investigations, the authors used their data to

produce contour maps and perform factor analysis to

strengthen the influence of their work. Concentrations in mg

kg�1 were 1.1–524.4 for As, 5–12 640 for Cu, 3–1430 for Pb

and 12–11 860 for Zn and the authors hoped to use these

results to contribute to a proposal for remediation measures

on the Adriatic coast. Lebow et al.202 reported a statistical

analysis of their data on the influence of soil and wood

properties on the leaching of As and Cu from yellow pine

sapwood treated with chromated copper arsenate. Specimens

were leached by an accelerated laboratory method for 12

weeks in different soils or in water. XRF was used to measure

the loss of As and Cu and correlated with various physical and

chemical soil properties. The average loss of copper was

reported to be approximately equal to or greater than the

arsenic loss for specimens exposed to soil whereas, for those

leached in water, the arsenic loss was twice that of copper loss.

This study suggested that ground-contact leaching should be

employed for realistic depletion measurements of copper-rich

preservatives and that the data would be helpful in the

development of a standard laboratory method for the timber

industry.

The systematic classification of plants began in 1735 and was

formally postulated by Carl von Linne with additional genetic

aspects introduced by Charles Darwin in 1859. The Linnaean

system has followed basically the same fundamentals until

today, and has caused great discord amongst taxonomists

since it is still based on visual inspection. As analysts, benefit-

ing from the wealth of data produced by XRF and other

instrumental techniques plus the awareness of accuracy, we

can appreciate the confusion due to such a subjective classifi-

cation. Chemical methods based on the determination of

proteins in a species were proposed and used to clarify some

impasses and to assist in the classification of family species or

of a specific variety. These chemical methods were destructive

and also time and reagent consuming, therefore new methods

were urgently needed to end the controversy caused by the

classification system. Alexandre and Bueno203 have developed

a reliable, non-destructive method for the classification of

seeds of species and varieties of carnations and species of

banana using conventional EDXRF combined with chemo-

metrics and both PCA and hierarchical cluster analysis

(HCA). Their method was based on multivariate analysis of

spectra, including Raman scattering profiles that occurred

around the Compton and Rayleigh peaks from organic sam-

ples. It will be interesting to see if taxonomists accept X-ray

scattering spectrometry. Margui et al.204 used selective excita-

tion, from different secondary target materials, in a polarised

EDXRF configuration to solve the familiar mutual interfer-

ence of As and Pb when analysing trace levels in different

vegetation species collected at two mining areas in Spain.

Cadmium was also measured using the Ka line. A standardless

fundamental approach (IAEA QXAS) was adopted to deter-

mine other metals in the absence of suitable certified reference

materials and to compensate accurately for self-attenuation

effects in the samples. Arsenic speciation was described by

Mihucz et al.,205 who combined off-line layer chromatography

with TXRF and applied the technique to As speciation in root

extracts of cucumber plants. Xu et al.206 studied the cellular

distribution of Mn in the toxic, accumulator plant Phytolacca

acinosa. The intention was to obtain essential information on

metal toxicity and the bioaccumulation mechanism. As a

result, Mn was identified as a key player in the detoxification

mechanism of Phytolacca acinosa. This plant, also known for

its high biomass and fast growth, was found as a good

candidate for phytoremediation of manganese-polluted soil.

The analysis of other environmental samples in the future

will benefit from the workers at NIST207 who have recently

extended their collection of environmental SRMs that began

in the late 1960s with the introduction of fuel and biologically-

related materials. Those who have joined programmes to

generate CRMs will be familiar with the difficulties experi-

enced when recruiting contributing analysts. Advances in

analytical methodology, including multi-element isotope dilu-

tion mass spectrometry (IDMS) and expanded instrumental

neutron activation analysis (INAA), have enabled value-as-

signment based on fewer but better characterised independent

analytical techniques. The advantages of IDMS for the deter-

mination of Hg and S and multi-element small sample air

particulate matter (SRM 2783) serve as examples of the new

approach by NIST. Developments in the production of SRMs

included the issue of fresh-frozen biological materials and of

jet-milled natural matrix materials with improved homogene-

ity, such as a highly homogeneous air particulate matter and

This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1319

sediment SRMs for small sample analytical techniques. Terai

et al.208 reported the synthesis of CrVI in portlandite,

Ca(OH)2, suspensions for the immobilisation of hazardous

hexavalent Cr. Solutions of 0.1 mol L�1 of NaAlO2 and CrO3

were prepared in deionised water which were then mixed with

portlandite suspensions and stirred for 3 h in a CO2 free

synthetic air. Ca:Al atomic ratios were varied from 1.0 to

5.0 against Cr:Al atomic ratios of 1.0, 1.5 and 2.0. By using a

combination of XRF, XRD and ESEM the authors found that

CrVI–ettringite formed at pH 10.9 and associates with calcite.

No CrVI–ettringite was found below pH 10.9. A comprehen-

sive review of all analytical techniques for environmental

analysis may also be found in our companion Atomic Spectro-

scopy Update.209

9.4 Archaeological, cultural heritage and forensic

Some of the more interesting contributions in these categories

this year involve the analysis of inks, papers and parchment,

and indeed can truly be regarded as extending from the ancient

to the modern. The ancient often features, so commencing

with the opposite end of the time scale, Trzcinska210 was

interested in developing a method for classifying black powder

toners used in laser printers and copiers for obvious forensic

reasons. Discrimination was based on the use of Fourier

transform infrared spectrometry to distinguish the polymer

used in the toner and EDXRF to distinguish the inorganic

elemental content. Some 95.8% of pairs of samples could be

distinguished on the basis of FTIR and EDXRF spectra, with

the long term aim of creating an appropriate database. This

work appears to be a development of a related publication by

the same author.211 FTIR, Raman spectroscopy and XRF

were the combination of techniques used by Zieba-Palus and

Kunicki212 to characterise blue and black ballpoint pen and

gel ink and found that 90% of the samples could be distin-

guished using these methods. Gall inks used in works of art

were the topic of analysis by Hahn et al.,213 who included

measurements of pencils and coloured crayons by micro-XRF

in their studies to fingerprint compositions that characterise

gall inks used by an individual artist and to establish a

chronology of use. EDXRF was the technique of choice of

Manso and Carvalho214 to identify different types of paper

used in the production of an Italian book published in 1941.

The elements Ba, Ca, Cu, Sr, Ti, Zn could be used in a

principal component analysis approach to show that the book

was manufactured using three different types of paper—an

interesting development that could have forensic applications.

Although many applications of XRF are published each

year, few if any cover the authentication of postal pieces.

However, Sanchez and Valentinuzzi215 used XRF as one of

a number of complementary techniques to analyse different

inks used on stamps, postmarks and postage stamps. Spatial

resolution was achieved by use of micro-collimators and

mono-capillaries and the results could be used to authenticate

postal pieces through the elemental composition of the inks.

A number of studies directly related to forensic applications

have been published in the current review period. One of the

more interesting was the work of Worley et al.216 in the

detection of visible and latent fingerprints by micro-XRF,

based on the inorganic elements present in the print. The

major advantage of this approach was that the prints are left

unaltered by this process. Key elements for imaging were Cl

and K, although Al, Ca, Mg, P, S and Si could also be

detected, and it was reported that the success of this approach

could be person- or diet-dependent as the prints from one

subject could not be detected by this process. The character-

isation of small glass fragments217,218 is a relatively common

forensic application, and the role XRF might play in con-

tributing Sr data to the multi-technique characterisation of

elephant ivory to control the illegal trade219 is also expected,

but the investigation of gun shot residues is a little more

unusual. This study, by Berendes et al.220 was designed to

develop a method to visualise gun shot residue patterns caused

by the use of heavy metal-free ammunition to determine

shooting distances as well as the general composition of

particles. A millimetre-resolution XRF spectrometer was

found to offer a significant reduction in analysis time com-

pared with m-XRF and distribution patterns of Ga, K and Ti

provided the appropriate visualisation. A further study with

direct human interest was undertaken by Rebocho et al.221 to

measure the lead uptake of human bones from the Middle

Ages using portable XRF instrumentation. Significant con-

tamination by Pb of spongy bones that had been kept in a lead

coffin was reported (250–350 mg Pb g�1 bone mineral) com-

pared with 4–7 mg Pb g�1 bone mineral, for bone buried in soil.

The analysis of paints and pigments is one of the more

visually attractive applications of XRF with examples this

year that span the investigation of materials and techniques,

through to conservation. In the area of conservation, Cotte

et al.222 investigated the blackening of the Pompeian paintings,

which have a deep red colouring associated with the use of

cinnabar (HgS) as a pigment. SR-based micro-XRF revealed

‘peculiar’ distributions of Cl and S, which were confirmed as

degradation products by X-ray absorption spectrometry as

Hg–Cl compounds and gypsum, formed by calcite sulfanation.

Angelini et al.223 used the chemical characterisation of the red

decorative pigment and of the stone surface of the Capestrano

Warrior (Archaeological Museum of Chieti, Italy) by portable

XRF as an example of a non-destructive testing method that is

very important to conservators and art historians. Aceto

et al.224 used portable XRF and Raman to investigate the

degradation of an alloy pigment on an ancient Italian manu-

script (Homilies on the Gospels of Gregory the Great), datable

to the IX century. Probably because of conditions of storage,

part of the decoration (described as being ‘of golden fashion’),

which was found to be an alloy of Cu, Pb and Zn, had

degraded to inorganic Cu salts, which gave it a green colora-

tion. The non-invasive properties of EDXRF (together with

reflectance spectroscopy) were used by Bonizzoni et al.225 to

reconstruct layers on Renaissance paintings executed on wood

or canvas. Civici226 used TXRF to characterise the palette in

five Albanian icons painted by Onufri Qiprioti (16th to 17th

century). The palette included white lead, calcium white, gold,

orpiment, yellow and red ochre, vermilion, red lead, a copper-

based green pigment and smalt. This study was extended by

Pavlidou et al.227 to include data by m-FTIR, optical micro-

scopy and SEM, which showed the presence of calcium

carbonate as the main component in all pigments, pointing

1320 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

towards a fresco technique. In the study of ancient Egyptian

boat models, TXRF was claimed by Huhnerfuss et al.228 to

have the potential to dissipate some uncertainties when apply-

ing classical archaeological dating methods based on the

analysis of pigments.

Because of its capability for fingerprinting samples for

provenancing studies, XRF remains a popular choice of

technique in the analysis of pottery and ceramics. One

approach is to employ multivariate statistical analysis to

categorise samples, as exemplified by the work of Papachris-

todoulou et al.229 in demonstrating different local production

practices from EDXRF data on 64 potsherds from Orraon,

northwestern Greece. Bakraji230 and Bakraji et al.231 used a

radioisotope XRF instrument to separate archaeological pot-

tery samples from Katana and from the Tel Kouzama site near

Damascus, Syria, into four distinct groups. The second com-

mon approach is to use EDXRF as one of a suite of techniques

selected to characterise artefacts. XRD and optical and scan-

ning electron microscopy were used by Giannotta et al.232 to

demonstrate cultural exchanges between Apulia and the Mid-

dle East during the Middle Ages from the results of an

investigation of siliceous paste fragments from an archaeolo-

gical site at Siponto (Foggia, Italy). A similar array of

techniques was used to support XRF in the analysis of Mayan

ceramic figurines from Calakmull (Campeche, Mexico) by

Garcia-Heras et al.233 Results were interpreted as showing

that the manufacture of ceramic figurines could be associated

with workshops linked to a monopoly on ceramic production

performed by centralised influence of the town of Calakmul.

Peng et al.234 used a microprobe EDXRF instrument to

analyse glaze layers on ancient celadon material (1127–1279

AD) from Zhejiang, China and associated their provenance to

Chinese imperial and Chinese popular kilns, whereas Civici235

used XRF to determine the type of raw material used for the

manufacture and provenance of terracotta figurines (3rd cen-

tury BC) found in the Seferan Lake, Central Albania. The

author demonstrated that the figurines were made of local

clays, although it was not certain whether the black external

coating, made of an iron-rich material, originated from weath-

ering under water or had been applied during manufacture.

Moroni and Conti236 were interested in the technology of

pottery production and used a basket of techniques, including

XRF, to analyse the products of firing experiments on two

clays selected to best represent XVIth century ceramic tiles and

wares and proposed that a low rate of heating and the amount

of calcite present in the clay were important parameters when

matching the test pieces with archaeological artefacts. Barilaro

et al.237 were interested in trading patterns of amphorae in the

5th to the 3rd century BC after excavation of amphorae

fragments from southern Italy and used both XRF and FTIR

analysis. Adan-Bayewitz et al.238 found unusually high and

variable adundances of Ag in pottery samples from 38 Ro-

man-period sites in Jerusalem and attributed the presence of

Ag to human origin.

The analysis of glazes can also yield useful evidence of the

provenance of ceramics, as exemplified by the work of Roldan

et al.,239 who used EDXRF to show that elements such as As,

Co, Cu, Fe, Mn, Ni and Zn were characteristic of ‘cobalt’ blue

pigments in glazes on Valencian ceramics manufactured from

the 14th to the 20th century. Colour variations in Hispanic

lustre decoration on late 13th century Hispano-Moresque

potsherd were examined using EXAFS by Smith et al.240 with

a particular interest in the influence of the Cu/Ag ratio. Gold

lustre on Italian Renaissance pottery was of interest to Bon-

tempi et al.241 who extended earlier studies that involved XRF,

which had demonstrated that the lustre comprises a hetero-

geneous metal–glass composite film, formed by Ag and Cu

nanoparticles dispersed in the outer layer of a tin-opacified

lead glaze. Their present study used grazing incidence XRD to

characterise the structure and depth distribution of the Ag

nanoparticles.

Conservation of archaeological artefacts is sometimes a

challenging area of endeavour in which there is considerable

benefit in understanding the mechanism of deterioration.

Carmona et al.242 studied the biodegradation of five stained

glass windows at the Cartuja de Miraflores Monastery (Bour-

gos, Brazil) using UV-Vis spectrophotometry, XRF, optical

and electron microscopy and X-ray microanalysis. Heteroge-

neous dark brown interconnected crusts were found covering

most of the external surface of the glass, together with craters

and pits filled with whitish deposits. Microbial colonisation of

the glass was also observed and both bacteria and fungi were

characterised. Protective glazing can be used to reduce the rate

of deterioration of historic stained glass windows from atmo-

spheric pollutants and particulates and Godoi et al.243 mon-

itored for one year the Sainte Chapelle (Paris), using passive

diffusion tubes, to monitor SO2, NO2 and O3 with EDXRF to

measure the accumulation and re-suspension of particulate

materials. Results indicated the beneficial outcome from the

use of protective glazing. The same pollutant species were

monitored by Worobiec et al.,244 who studied the indoor/

outdoor air exchange and its influence on air quality and the

preservation of works of art in St. Michael Archangel’s

Church, Szalowa, Poland. Suspended particulate material in

this wooden church was generally considered to have an

outdoor source. Laser cleaning has begun to be widely used

in art restoration but requires careful optimisation to ensure

that only contaminants and encrustations are removed and the

original material is not damaged. Hence the need for the study

by Benedetti et al.245 who used m-XRF and m-XRD to evaluate

laser cleaning of a 4th century BC chamber gravesite in

Torricelle, near Nori (Naples). Their preliminary results sug-

gested a possible influence of the laser on the calcite–aragonite

transformation. In a contrasting approach to conservation,

Maravelaki-Kalaitzaki et al.246 treated deteriorated porous

bioclastic limestones from the archaeological area of Aptera,

Crete, with various silicon-based strengthening products and

used EDXRF and FTIR to measure the depth of penetration,

which was up to 30 mm. Improved reinforcement results were

obtained by applying an elastified silicic acid ethyl ester.

Angelini et al.247 were interested in an integrated approach

to the characterisation and conservation of artefacts from the

Brazilian colonial period using XRF and other techniques,

and described the long-term protection of copper-based alloys

by coating them with SiO2-like films using a home-made

reactor fed with a tetraethoxysilane–oxygen–argon mixture.

As with other inorganic archaeological artefacts, XRF

continues to be widely used for the characterisation of metallic

This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1321

objects. Cartechini et al.248 used a range of techniques to

characterise the compositional and textural properties of

Etruscan bronzes, in part to correctly assign several fragments

to recompose the original pieces. Although providing indica-

tive data, XRF and SEM/EPMA were strongly affected by

surface alteration and contamination, with neutron diffraction

favoured in providing sensitive information on composition

and phase quantification in a non-destructive manner. Pisto-

fidis et al.249 reported that 3 silver coins from the IIIrd century

found in the ancient Greek cities of Dyrrachion and Korkyra

had different chemical compositions and microstructures, with

XRF being used to provide the compositional results. Inter-

pretation of the multi-technique results gave an insight into

differences in the minting processes. A multi-technique

approach (incuding XRF) was also used by Schwab et al.250

to provenance iron artefacts found at Manching, southern

Bavaria, to a specific source of iron ore near the Danube.

Provenancing of lithic artefacts is one of the simpler applica-

tions of XRF, exemplified this year by the work of Triscari

et al.251 who were interested in the source of volcanic rocks

used in medieval buildings in north-eastern Sicily and southern

Calabria and showed an origin to the Etnean and Aeolian

volcanic areas. In contrast, Negash et al.252 used EDXRF to

provenance 10 Early Stone Age obsidian artefacts from the

Milka Konture site, Ethiopia, to a source located a short

distance away.

9.5 Industrial

Since the implementation of the new EU Directives on Re-

striction on Hazardous Substances (RoHS) and Waste Elec-

trical and Electronic Equipment (WEEE) in July 2006, the

development of analytical methods, including new reference

materials, to control the level of these hazardous substances is

making significant progress. Matsuda et al.253 set up a method

for the determination of Cd, Cr and Pb in shaped brass

samples using EDXRF with polarisation optics. For each

element a calibration curve was set up using bulk CRMs

comprising flat brass standard samples and measurements

were performed with dedicated secondary targets. To take

into account small and shaped samples, corrections were made

using Rayleigh scatter peak intensities. Lower limits of detec-

tion were achieved of 3.3 mg g�1 for Cd, 6.6 mg g�1 for Cr and

29 mg g�1 for Pb, with 300 s measurement time, which were all

significantly lower than the legal limit value of 0.01% m/m for

Cd and 0.1% m/m for Pb and CrVI. Comparison with mea-

surements by ICP-AES proved the validity of this method for

the analysis of small and shaped brass samples. Commercial

requirements have led to the production of new polymer

reference materials. The Japanese Society of Analytical Chem-

istry developed two new types of plastic disc RMs for use in

XRF screening, both described by Nakano et al.254,255 The

former, Japanese language, paper described the certification of

a polyester reference material for the elements Cd, Cr and Pb,

whilst the latter (in English) presented the certification for the

element Hg, also in polyester. Both types of CRMs were

prepared by casting the polyester mixed with a toluene solu-

tion of the relevant organometallic compound. For each

element, five concentration levels were prepared, ranging from

0 to 50 mg kg�1 for Cd, 0 to 200 mg kg�1 for Cr and Pb, and 0

to 250 mg kg�1 for Hg. The certified value, together with the

measurement uncertainty at a confidence level of 95%, was

determined on the basis of the results of an inter-laboratory

study with 21 participants for the determination of Cd, Cr and

Pb, whilst 15 laboratories participated in the Hg certification

process. Song et al.,256 on the other hand, presented a paper in

Chinese concerning the use of in-house reference materials

containing the elements Br, Cd, Cr, Hg and Pb at concentra-

tion levels ranging from 100 to 1500 mg kg�1. Linear XRF

calibration curves were set up and the matrix effect was

corrected by empirical coefficients, using scattered radiation

as an internal standard. The accuracy of the method was

proved by analysis of the certified BCR 681 polymer and a

precision of less than 5.0% was achieved. For the calibration

of XRF spectrometers, Swagten et al.257 described the devel-

opment and the characterisation of homogeneous polyethy-

lene reference materials, using a preparation procedure that

can also be implemented in future projects for other type of

elements. In this contribution the reference materials were

prepared by incorporating additives to ‘‘virgin’’ polyethylene.

The calibration of the reference material was performed using

ICP-AES for the elements Al, Ca, Mg, Na, P, Ti and Zn,

whereas k(0)-NAA was used for the same elements together

with F. Over the complete concentration range, starting from

5 mg kg�1 for Ti up to 600 mg kg�1 for Mg, a good agreement

of the results between both techniques was obtained.

In the framework for reducing the waste burden to the

environment, more and more emphasis is being put on the

recycling and re-use of waste produced in several branches of

industry. Limbachiya et al.258 reported the use of recycled

concrete aggregate (RCA) in concrete production using XRF

for the determination of the elemental composition. XRF

analyses of commercially produced coarse RCA and natural

aggregates showed a comparable chemical composition be-

tween recycled and natural aggregates, and the original source

of RCA had a negligible effect on the major elements. Test

results indicated that up to 30% coarse RCA, as a substitute

for natural gravel, had no effect on the main three oxides

(Al2O3, CaO and SiO2) in concrete, but thereafter slight

changes in composition were observed. Rossini and Ber-

nardes259 reported a laboratory scale study, based on sulfate

roasting for the selective recovery of valuable metals from

galvanic sludge. Of particular interest in this treatment was the

use of two hazardous wastes as raw materials, both generated

in large quantities at coal extraction sites (coal waste/pyritic

waste) and at plating shops (galvanic sludge). The XRF

characterisation showed a high Cu content in the sludge of

more than 14% on a dry base. In the roasting process, the

conditions that best reflected a compromise between the

recovery of the valuable metals and the economic viability of

the process were achieved using a 1:0.4 galvanic sludge/pyrite

ratio, with 90 min of roasting time at 550 1C, which resulted in

a recovery of 50% Cu, 43% Ni and 60% Zn. Additionally, Xu

et al.260 used dried sewage sludge as raw material for the

production of ceramsite, used for the treatment of municipal

waste water. Under the most appropriate conditions, a mix-

ture of dried sewage sludge, water glass and clay was sintered

at 1000 1C, and subsequently characterised by XRF combined

1322 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

with other analytical techniques. The ceramsite produced was

appropriate for the removal of several contaminants from

municipal waste water.

As can be deduced from the large number of papers

published in this review period, the X-ray fluorescence tech-

nique in combination with other analytical techniques has

proved to be a matured and routinely applied analytical

technique for the characterisation of newly developed cera-

mics, cement samples and catalysts, including the monitoring

of catalytic processes. Readers interested in the performance

of these new materials should also consult the companion

ASU review on Industrial Analysis: Metals, Chemicals and

Advanced Materials.4 Some typical examples are presented in

this review section. Ramos and co-workers261 used both

FAAS and XRF for the quantitative analysis of Pb, S and

Zn in zinc oxide samples, commonly used to make industrial

ceramic enamels. Owing to the high loss on ignition values, the

working conditions for XRF analysis were optimised by

analysing the samples as pellets. For PbO, an accuracy of

1.06% and a precision of �0.06% were obtained, for SO3

4.76% and �0.25%, respectively, and for ZnO 0.46% and

�0.2%, respectively. These values were satisfactory, given that

Pb and S were only present in small amounts. Barba et al.262

adapted a WDXRF methodology previously established by

the authors for the characterisation of chromium-containing

ceramic pigments, in order to analyse cobalt-containing pig-

ments. The chemical and mineralogical evaluation of slag

products derived from the pyrolysis/melting treatment of

municipal solid waste was performed by Saffarzadeh et al.263

This study revealed that the major constituents were glass

(over 95%), oxide and silicate minerals, as well as individual

metallic inclusions. Elevated concentrations of Ba, Cr, Cu, Pb

and Zn were measured in the bulk composition, of which Ba,

Cu and Pb in the glassy phase behaved as incompatible

elements, whereas Cr and Zn were strongly incorporated into

the silicate structure.

Another interesting application was presented by Cernohors-

ky et al.,264 describing the use of a combined fundamental

parameter method for the EDXRF analysis of precious metal

alloys. This method combined the standardless FP method

with an empirical calibration using reference materials con-

sisting of Pt–Ir, Pt–Rh, Pt–Ir–Rh and Pt–Rh–Pd. Results

obtained by this approach agreed well with the corresponding

certified values or ICP-AES results, respectively. Miskolczi

et al.265 determined the sulfur content of diesel fuels and diesel-

fuel-like fractions of waste polymer cracking material, using

both ICP-AES and EDXRF. In the case of XRF analysis, the

effect of various types of thin foils on the accuracy was

evaluated, showing considerable differences and deterioration

of the accuracy as a function of type of foil. An appropriate

correlation was obtained between the results for ICP-AES and

EDXRF analyses, although some differences could be ob-

served, which could be explained by different proportions of

C/H in the samples. Finally, Y. Mino266 presented alarming

WDXRF results of dissolved Sn still present in canned foods,

as had been previously highlighted by other workers. As

sample pre-treatment, a pellet was made from freeze-dried

sample syrup or a homogenate solution of fruit or meat after

dilution with the same weight of cellulose powder. The ana-

lyses of several kinds of canned foods from the Japanese

market, indicated that exceptional concentrations of up to

100 300 mg kg�1 of Sn were present, and a relationship was

observed between the concentration level and the time after

production. Moreover, once a can was opened the amount of

dissolved Sn increased rapidly if the product remained in the

can.

9.6 Clinical and biological

X-ray fluorescence spectrometry takes a prominent place as an

analytical technique for a wide variety of clinical and biologi-

cal applications, as emphasised in several reviews. Garcia

et al.267 described the recent trend in metal-binding and

metalloprotein analysis using a broad range of analytical

techniques, including capillary electrophoresis-SRXRF. The

latest challenges in metallomics were also discussed. Paunesku

et al.,268 on the other hand, reported on the evolution of the X-

ray fluorescence microscopy technique to establish elemental

analysis in cell and tissue samples. Recent examples showed

the maturity of this technique in bio-medical applications,

especially thanks to the development of third-generation

synchrotrons. Chettle269 presented a review dealing with in

vivo trace element analysis of living humans in order to gain

insights into the relationship between chronic exposure to

toxic elements and health effects. The most fully developed

analytical techniques were for Cd and Pb, with the 109Cd shell

X-ray fluorescence being the most widely used.

As an alternative excitation to 109Cd excited K-XRF for the

in vivo measurement of Pb in bone, Cernohlawek et al.270

evaluated the use of X-ray tubes with various anode materials,

filters, as well as different secondary targets and low-Z polari-

sers. Using a portable XRF spectrometer equipped with a

50 W Pd X-ray tube, a Mo secondary target and a Peltier-

cooled Si-drift detector, a promising lower limit of detection of

0.6 mg g�1 for Pb in bone was obtained, determined on a

plaster of Paris phantom doped with a known Pb concentra-

tion and without overlying tissues. Nevertheless, whilst the

research continues for alternative sources, the 109Cd K-XRF

technique remains a well established method, as reflected by

the high number of contributions presenting extended experi-

mental studies on the influence of cumulative Pb exposure on

different health issues. Potula et al.271–273 performed several

studies among female former smelter workers, indicating each

time the negative effect of extended Pb exposure on their

health. The results showed that blood Pb might adversely

affect bone mineral density, that Pb exposure resulted in

higher blood Pb levels, especially during menopause, and that

changes in blood and bone Pb levels over time were associated

with increased bone resorption. Other work on this topic may

be found in Section 5 of this review, dedicated to work using

synchrotron radiation. Both Weisskopf et al.274 and Shih

et al.275 proved that long-term Pb exposure might have

persistent effects on cognitive functions among elderly men.

Martin et al.276 demonstrated that a cumulative Pb dose had

an acute effect on blood pressure and a chronic effect on the

risk of hypertension, whereas other workers277 found evidence

that the intake of low dietary Ca might be helpful in the

prevention of hypertension induced by an elevated Pb burden.

This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1323

Besides a broad range of routine measurements, research into

the improvement of detection limits for in vivo measurements

is still in progress as well as for Pb measurements in bone using109Cd278 and Sr measurements in bone using 125I279 as the

excitation source. One particular challenge presented was to

increase the sensitivity for Hg determinations in kidney using109Cd K-XRF for which preliminary results were presented by

Grinyer et al.280

Elemental composition analysis of biological tissues was

studied by Serpa et al.,281 who compared the elemental con-

centration in different brain structures, namely the temporal

cortex, entorhinal cortex, visual cortex and hippocampus,

from female rats of different ages. SR-TXRF measurements

of Al, Br, Ca, Cl, Cu Fe, K, Ni, P, Rb, S and Zn in these

tissues were performed at the Synchrotron Light Brazilian

Laboratory, indicating distributions depending on structure

and ageing. Of particular interest, the authors reported a

correlation between the increase in Fe with ageing in the

hippocampus, since it is involved in oxidative stress which is

recognized as one of the main causes for neuronal death in

Parkinson’s disease. Kwiatek et al.282 evaluated the elemental

distributions of Cu, Fe, Mn and Zn using SRXRF to distin-

guish prostate cancer from hyperplasia. These measurements,

performed on the L-beam line at the HASYLAB, Desy,

Germany, showed elevated concentrations for these elements

in cancerous tissues, as compared with normal and hyperplas-

tic ones.

The use of X-ray fluorescence spectrometry in dentistry

remains a recurring issue. Hurrell-Gillingham et al.283 evalu-

ated the in vitro biocompatibility of a novel Fe2O3-based glass

ionomer cement. Conventional ionomer glasses used in den-

tistry, but also in nose and throat surgery, contain Al3+, a

component linked to poor bone mineralisation and neurotoxi-

city. The substitution of Al2O3 with Fe2O3 was investigated

using both XRF and XRD. The results indicated that the

prepared Fe2O3-based glasses had Al2O3 contamination from

the crucibles and also had undergone substantial F� losses.

Nevertheless, cements could be prepared from these Fe2O3-

based ionomer glasses, and the cement setting times appeared

to be related to the P2O5 content. Moreover, these Fe2O3-

based cements showed good in vitro biocompatibility. A more

lugubrious but interesting study was presented by Bush

et al.,284 who demonstrated the use of portable XRF in

detection and analysis of restorative materials present in

non-cremated, cremated and processed-cremated individuals.

For this extended study 70 unique combinations of resins were

made in six human cadavers and simulated ante-mortem dental

records were created. Firstly, it was demonstrated that the

portable XRF system could be used to localise these restora-

tions in non-cremated individuals and to identify more than

75% of the resin brands, which was sufficient to enable

positive victim identification. A more challenging task was

the identification of individuals after cremation and, more-

over, after processed cremains, as the dentition alters by

shrinkage and fragmentation. Nevertheless, the authors were

able to distinguish each individual in the study group posi-

tively under both circumstances (the cadavers were cremated,

and subsequently after XRF analysis, the cremains were

processed and re-measured). Once more, this study empha-

sised not only the wide applicability of (portable) XRF, now in

the domain of forensic odontology, but also the significant

value of restorative resins in victim identification, even after

cremation.

In contrast to these dedicated and bizarre applications,

X-ray spectrometry remains widely used in the more tradi-

tional application area of quality control of food and drugs.

Brazilian workers285 evaluated the elemental content of exotic

Brazilian tropical fruits by EDXRF. Consumer awareness

regarding balanced diets, encouraged the authors to determine

the nutritional composition (vitamins and minerals) in tropical

fruits. Using EDXRF, macro (Ca and K) and trace elements

(Br, Cu, Fe, Mn and Zn) were measured in 8 Brazilian tropical

fruits. The highest value of K amounted to 1.725 mg per 100 g,

whilst for Ca a value of 680 mg per 100 g was detected. The

trace elements ranged from 0.3 to 1.3 mg per 100 g for Br, 0.5

to 1.0 mg per 100 g for Cu, 3.9 to 11.4 mg per 100 g for Fe, 0.9

to 2.0 mg per 100 g for Mn and 0.6 to 1.5 mg per 100 g for Zn.

Comparative analysis with other tropical fruits indicated that

some of the Brazilian examples could be classified as rich

sources for these macro and trace elements. Mahawatte

et al.286 verified the quality of some Ayurvedic drugs by

measuring nineteen elements using EDXRF with a Mo target.

In all of the nineteen analysed samples Ca, Fe and K were

present, with a concentration ranging from 0.346 to 8.65%,

0.007 to 36.7% and 0.35 to 2.88%, respectively. The authors

were pleased to report that EDXRF provided a simple, non-

destructive and multi-element method to perform quality

control of drugs.

The distribution of Cd in plant material using a SEM-EDX

and the more sensitive m-SRXRF technique was studied by

Isaure et al.287 In addition, the chemical form was investigated

using Cd L-III-edge m-XANES. The results suggested that in

the roots, Cd was localised in vascular bundles and coordi-

nated to S ligands, whereas in the leaves, the Cd accumulation

was mainly focused in the trichomes (epidermal hair) and

mainly bound to O/N ligands, with only a minor fraction

bound to S-containing ligands. The fact that Cd mainly

accumulated in certain parts of trichomes was confirmed in

a comparable study of Hokura et al.288 An interesting con-

tribution was presented by Poussart et al.,289 showing the first

results for Ca from a ringless tree using the X-ray microprobe

synchrotron technique in order to estimate the tree’s age and

growth history. The Ca age model agreed within less than 2

years of radiocarbon age estimates and confirmed that the

cycles were seasonal. Moreover, the amplitude of the Ca

annual cycle significantly correlated with growth and the

annual Ca maxima correlated with the amount of dry season

rainfall. As these synchrotron measurements were fast, a

feasible analytical tool now seemed to be available for produ-

cing sufficient numbers of replicated multi-century tropical

dendrochemistry climate records. Serbian workers290 pre-

sented a rapid, simple and sensitive EDXRF procedure for

measuring W in tobacco plants after antiviral treatment with

12-tungstophosphoric acid and its compounds. Only 0.1 g of

dried plant material (tablets) was analysed instead of the usual

1 g. Using a 109Cd excitation source and 2000 s measurement

time, a detection limit for W of 15 mg kg�1 on a dry base could

be estimated. Quantitative analysis of different parts of the

1324 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

treated plant together with the washings gave 94.5% recovery

of the applied W in different compound forms. Moreover, the

EDXRF results indicated that W was distributed both verti-

cally and horizontally throughout the tobacco plant.

Finally, readers still seeking additional clinical and biologi-

cal applications should refer to our companion Atomic Spec-

trometry Updates on Clinical and Biological Materials, Foods

and Beverages.3

9.7 Thin films and coatings

In recent years, considerable advances have been made in the

preparation of thin films, with industrial applications such as

protection, decoration and the fabrication of photoelectric

devices featuring extensively in the literature, where XRF

techniques have assisted in the understanding of the pro-

cesses involved. Transparent conducting oxides (TCOs) have

found extensive application in devices such as liquid crystal

displays, transducers and solar cells. ZnO is now regarded as

a promising material for TCOs due to its high transmission

over a wide spectral range and characteristics such as low

toxicity, relatively low cost and stability in reduced chemical

environments. Bacaksiz et al.291 studied spray pyrolysis

Cd1�xZnxO thin films prepared in an air atmosphere on glass

substrates at 250 1C and Zn-doped CdO films with high

optical transmittance for possible use as the window layer

of CdO/CdTe and Cd/CuInSe2 solar cells. The Kb/Ka X-ray

intensity ratio for elements on these types of film has been

reported in the past where it has featured in publications on

recent advances in solid state X-ray detectors, such as Si(Li)

and Ge detectors because it is considered a characteristic

quantity for each element in the film. In this paper, the

authors found that the Kb/Ka intensity ratio was changed

by the alloying effects in Cd1�xZnxO semiconductor thin

films as x varied from 0 to 0.60. The results were compared

with theoretical values anticipated. Dakhel292 continued his

investigations of manganese(III) thin films with a paper this

year on frequency-dependent conductivity in tri(acetylaceto-

nato) MnIII films of amorphous structure prepared by va-

cuum deposition on glass and Si(100) substrates. These films

were investigated for use as insulators for Al/insulator/Si(P)

metal-insulator-semiconductor (MIS) structures which were

characterised by the measurement of their capacitance and

ac-conductance as a function of gate voltage. The instru-

mental techniques used were XRF, XRD and optical absorp-

tion spectroscopy with the films analysed as-deposited and

annealed-in-vacuum. The work showed that tri(acetylaceto-

nato) MnIII films grown on Si(100) were a promising candi-

date for high-epsilon dielectric applications displaying

sufficiently high-8 value in the range 30–40. Yamaguchi et

al.293 characterised Cu(In, Ga)(S, Se)2 thin films prepared by

sequential evaporation from the ternary compounds Cu-

GaSe2, CuInSe2 and In2S3 for possible use as photovoltaic

devices. The XRF analysis showed Cu: (In + Ga): (S + Se)

atomic ratio in all the thin films was approximately 1:1:2. As

the In2S3/(CuGaSe2 + CuInSe2) mole ratio in the evaporat-

ing materials increased, the S/(S + Se) atomic ratio increased

from 0 to 0.6. XRD confirmed the prepared films had a

chalcopyrite structure and that the preferred orientation was

to the 112 plane. Putkonen and Niinisto294 investigated

atomic layer deposition of boron oxide thin films at room

temperature using BBr3 and H2O as precursors. Stoichiome-

try and possible impurities were determined by XRF with

other characteristics measured by XRD and time-of-flight

elastic recoil detection analysis. The as-deposited films were

amorphous and found to react readily with the atmosphere if

not protected by an alumina over-layer.

The electronic structure of Co-doped anatase (TiO2)

epitaxial thin films grown at different partial oxygen pressures

was investigated by Chang et al.295 using soft X-ray emission

spectroscopy. The resonantly excited Co L-2, L-3 emission

spectra of ferromagnetic Ti0.96Co0.04O2 samples for the

oxygen-deficient regime showed that the ratio of integral

intensities for Co L-2 and L-3 emission lines significantly

decreased with respect to non-magnetic samples in the oxygen

rich regime. This was due to L2L3M4,5 Coster–Kronig

transitions and suggested that the ferromagnetic samples had

n-type charge carriers and Co–Co bonds were dominant in

non-magnetic samples in the oxygen-rich regime. Electronic

structure calculations of the films also showed that the pre-

sence of free charge carriers and Co segregation play a crucial

role in strong ferromagnetism at room temperature. Jonnard

et al.296 showed that X-ray emission spectroscopy (XES)

induced by electrons and analysed with high spectral resolu-

tion by a wavelength dispersive Johann-type spectrometer was

a powerful technique for the study of Mo/Si multi-layers. The

optical properties of such Mo/Si periodic multi-layers depend

on the quality of the interfaces within the stacks. If the

inter-layers are formed as a result of a diffusion process at

the Mo-on-Si and Si-on-Mo interfaces, the optical

performance may be optimised. Several methods, such as

X-ray photo-electronic spectroscopy, Auger emission and

X-ray absorption are available to characterise these inter-

layers but are sensitive to the superficial 10 nm zone of the

sample because they use electrons as the detected particle.

However, XES induced by electrons is a more convenient

method, as the detected particles are photons that have a

much longer path in matter than electrons of the same energy.

Hence, information concerning electronic structure comes

from a thickness determined by the energy of the incident

electrons. In this way, it was possible to vary the electron

energy to probe all or only the first bi-layers in a stack.

Furthermore, information on the chemical state of the ele-

ments present at an interface of a periodic stack may be

obtained from analysis of the X-ray emission bonds. These

emissions involve valence electrons that are less tightly bound

and depend on the nature of the chemical bond formed in the

solid. By using a high resolution X-ray spectrometer, the

authors were able to observe the variation of the emission

band shape. They then evolved the shape of the Si Kbemission band (3p–1s transition) as a function of the chemical

environment of the Si atoms. A series of Mo/Si multi-layers

were studied where the thickness of the Si layers were 2 nm

and that of the Mo layers was 1, 2, 3 or 4 nm. The data

showed that the emission band from the Si atoms was

different from that of amorphous Si (a-Si) that should have

been observed if no diffusion process had taken place at the

interfaces. It was therefore possible to deduce the composition

This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1325

of the inter-layers and estimate their thickness as 0.4 � 0.1 nm

or 0.8 � 0.2 nm depending on the samples concerned.

In previous reviews, EDXRF has been reported as a means

of measuring the thickness of the cellulose nitrate layer of the

commonly used LR115 solid-state nuclear track detector

(SSNTD). Ng and Yu297 investigated whether the X-radiation

involved in the analytical process would induce degradation of

the cellulose nitrate. The nitrate functions were examined by

FTIR spectroscopy (at wavenumber 1598 cm�1) and the

glycosidic bonds (at 1146 cm�1) for the typical irradiation

time involved in the EDXRF analysis. It was pleasing to note

that no significant changes were reported for exposures up to

3000 s, which equated to the time required for 10 scans, far

longer than the time actually needed for a determination of the

cellulose nitrate-layer thickness. Therefore EDXRF remains

the technique of choice for the measurement of active layer

thickness of SSNTDs.

The literature during this review period continues to reflect

interest in nano-materials where it is inevitable that special

techniques are needed to handle and analyse these delicate

fabrications. Sachdeva et al.298 used an energy dispersive

spectrometer attached to an environmental scanning electron

microscope to investigate silver nano-particles formed by

chemical reduction of Ag+ in polyperfluorosulfonic acid

membranes with NaBH4. X-ray elemental mapping across

the thickness of the membrane indicated that Na+ and Ag+

were uniformly distributed in the membrane before reduction,

with the Ag concentration considerably increased after reduc-

tion. Furthermore, the nano-particles were formed only on the

membrane surface that was exposed to NaBH4 solution. The

average size of the nano-particles was found to be 15 � 3 nm.

Self diffusion of water, Na+ and Cs+ ions in the loaded

membrane was found not to affect the diffusion properties of

the membrane. The ion-exchange capacity and water uptake

were similarly unaffected. Azurdia et al.299 reported the use of

liquid feed flame pyrolysis to produce a series of nano-powders

along the CoOx–Al2O3 tie line. This general aerosol combus-

tion synthesis technique produced a wide range of lightly

agglomerated oxide nano-powders from aerosols of ethanol

solutions of alumatrane, Al(OCH2CH2)3N, and a cobalt pre-

cursor made by reacting Co(NO3)2 � 6H2O crystals with pro-

pionic acid. Nine samples were prepared and studied by XRF,

BET, SEM, high resolution TEM, XRD, TGA and FTIR.

From the wealth of data produced, the powders were reported

to consist of single crystal particles o40 nm in diameter and

with a specific surface area of 20–60 m2 g�1. A gradual change

in the XRD powder patterns from delta Al2O3 to Co3O4 was

seen with a cobalt aluminate spinel phase that had not

previously been published in phase diagrams. High cobalt

content samples exhibited a sharp mass-loss that was attrib-

uted to the decomposition of Co3O4 to CoO. Magnesia is an

accepted additive to BaTiO3 powder for use in the manufac-

ture of multi-layer ceramic capacitors (MLCC). Kim et al.300

investigated a nano-coating process for the production of a

MgO shell layer onto BaTiO3 core powder. Several deposition

reaction routes were examined with a magnesium nitrate–urea

system reported to be satisfactory. The core shell morphology

was characterised by SEM and TEM, whereas the composi-

tion of the shell layer was determined by ICP-AES and XRF.

Those embarking on investigations of coating samples may

be interested in a paper by Han et al.,301 who calculated the

fluorescence intensity enhanced by scattering effects for coat-

ing samples based on the familiar fundamental parameter

models. They calculated the contribution of secondary en-

hancement due to scattered radiation from the same layer or

between layer and substrate and the primary fluorescence that

was scattered into the direction of a detector by atoms in a

layer or substrate. Using a hypothetical Zn coating on an

infinite Fe substrate the contributions from these different

scattering effects were shown to relate to coating thickness

and were up to several percent of the primary fluorescent

intensity.

9.8 Chemical state, speciation and crystal characterisation

In this section of the review we consider studies on informa-

tion gained from X-ray absorption spectroscopy (XAS) based

on the excitation of electrons from the deep core levels of an

atom by the absorption of an X-ray photon. The XAS

spectrum is divided into two parts: X-ray absorption near

edge structure (XANES) and extended X-ray absorption fine

structure (EXAFS). XANES extends from a few eV below the

absorption edge of an element to about 40–50 eV above the

edge, whereas EXAFS provides information from 50–1000 eV

above the edge. Goraieb et al.302 used both conventional XRF

and XAS for the characterisation of titania grafted onto the

surface of silica used as a support medium in HPLC. The TiO2

layer is known to have the same chemical properties as the

bulk crystalline phase when trapped on a mechanically resis-

tant silica matrix and these workers analysed the treated

support medium before and after extensive use in reversed-

phase HPLC. The XRF data indicated the formation of a

complete 2:1 monolayer whereas XAS suggested the presence

of more than one structure of titanium oxide after use.

Pinakidou et al.303 studied EXAFS spectra of Fe in a series

of vitrified Fe and Pb rich industrial waste samples that

contained toxic ash. XRF mapping in combination with

m-XAS of samples containing 50% and 60% ash demonstrated

that annealing at temperatures above 600 1C induced loss of

homogeneity and the formation of Fe rich micro-crystalline

‘‘islands’’. It is pleasing to note that information available

from the study of absorption spectra is now appreciated in the

wider X-ray community and finding application outside

academe.

An alternative approach to EXAFS and XANES is to study

the radiative Auger spectra generated by photon excitation.

Raju et al.304 gathered K X-ray emission spectra to study the

Ka hyper-satellite, KbL1 and Kb5 satellites, as well as KMM

radiative Auger emissions of elements from K to Mn in the

periodic table. Ka hyper-satellite lines are the weak lines that

appear on the high energy side of the diagram lines when an

atom is doubly ionised in the K shell and if these holes are

filled by transitions from the outer shells. Such transitions

originate from L, M, N. . .shells and are known as Ka, Kb,Kg. . .hyper-satellites, respectively. If ionisation occurs in just

the K shell and all the other shells are filled, the resulting

hyper-satellites are denoted as KahL0, but if there is simulta-

neous ionisation in the L shell, this de-excitation of the atom

1326 | J. Anal. At. Spectrom., 2007, 22, 1304–1332 This journal is �c The Royal Society of Chemistry 2007

gives rise to satellites of hyper-satellites denoted as KahLn or

Ka2Ln, where n is the number of holes in the l shell. Using a

conventional WDXRF with LiF200 and LiF220 crystals, the

authors investigated the Z-dependence of the energy shift and

relative intensity of these weak lines (humps and bumps) with

respect to their conventional characteristic lines. Only energy

shifts were examined in the KMM radiative Auger spectra. All

the data were compared with the available predictions. To

assist in the understanding and identification of these weak

KMM spectra, the authors assigned the transitions as

K–M1M2 (3p), K–M1M2 (1p) and K–M1M2 (1s). It is thought

that studies such as these may take time to find practical

application.

Whilst polarised EDXRF spectrometers are appreciated for

their enhanced sensitivity when compared with WDXRF

configurations, the resolution offered by the latter may be

used to good effect by those interested in studies of peak shape

and profiles. Deluigi and colleagues305 proposed an index for

chemical state analysis based on information from such spec-

tra following their studies on the Kb emissions of Cr in

different compounds. Higher resolution measurements from

the Kb1,3 line were also obtained using a spectrometer based

on a back diffracting crystal analyser with spherical focusing

and excitation from monochromatic synchrotron radiation.

Kb1,3 line shifts were seen from metallic Cr to higher energies

for CrIII and to lower energies for CrVI. The authors also

reported that the natural width of the Kb1,3 line, the ionisationenergy of the 3p orbital of Cr and the relative intensities of Kband Kb2,5 lines increased as the oxidation state increased. Two

authors from the same team in Argentina306 also studied the

Kb profiles from six different oxidation states of sulfur. The

structural changes were observed using WDXRF and showed

good agreement with theoretical data calculated using mole-

cular orbital theory available in the literature. Han et al.307

studied different valency states of Mn and Fe in a Chinese

language paper. They used a spectral processing software

programme, ‘‘Peakfit’’ and found that the Kb lines were

appropriate for Mn whereas the L lines were better than the

K lines for studies of the chemical state of Fe. They also used a

conventional wavelength dispersive spectrometer.

10 Abbreviations

AD Anno Domini

AF Antifouling

ALS Amyotrophic lateral sclerosis

APD Avalanche photodiode detector

APDC Ammonium pyrrolidine dithiocarbamate

ASV Anodic stripping voltammetry

BET Brunauer, Emmett and Teller surface

area analysis

BC Before Christ

CCD Charge coupled detector

CFC Close faced cassette

CML Chronic myelogenous leukaemia

CMOS Complementary metal oxide semiconductor

CRM Certified reference material

D Dimensional

(continued )

DePMOS Drain extended p-channel

metal oxide semiconductor

EDXRF Energy dispersive X-ray fluorescence

EPMA Electron probe microanalysis

EPR Electron Paramagnetic Resonance

EPA Environmental Protection Agency

ESEM Environmental scanning electron

microscope

ESRF European synchrotron radiation facility

EXAFS Extended X-ray absorption fine structure

FAAS Flame atomic absorption spectrometry

FTIR Fourier transform infrared spectroscopy

FP Fundamental parameters

HCA Hierarchical cluster analysis

HPLC High-performance liquid chromatography

IAEA International Atomic Energy Agency

ICP-AES Inductively coupled plasma-atomic

emission spectrometry

ICP-MS Inductively coupled plasma-mass

spectrometry

ICP-OES Inductively coupled plasma-optical

emission spectroscopy

IDMS Isotope dilution mass spectrometry

IED Iminodiacetate extraction disc

INAA Instrumental neutron activation analysis

IOM Institute of Occupational Medicine

LNLS Laboratorio National de Luz Synchrotron

MIMs Multilayer interference mirrors

MLCC Multilayer ceramic capacitors

MPI Max Planck Institute

MS Mass spectrometry

NAA Neutron activation analysis

NIST National Institute of Standards and

Technology

PCA Principle component analysis

PIXE Particle induced X-ray emission

PM Particulate matter

PTB Physikalisch-Technische Bundesanstalt

PTFE Polytetrafluoroethylene

PVC Poly(vinyl chloride)

PXRF Portable X-ray fluorescence

RCA Recycled concrete aggregates

REE Rare earth element(s)

RM Reference material

RoHS Restriction on Hazardous Substances

QC Quality control

QXAS Quantitative X-ray analysis system

SDD Silicon drift detector

SEM Scanning electron microscopy

SIMS Secondary ion mass spectrometry

SR Synchrotron radiation

SRM Standard reference material

SRXRF Synchrotron radiation X-ray

fluorescence

SR-TXRF Synchrotron radiation-total

reflection X-ray fluorescence

SSNTD Solid-state nuclear track detector

This journal is �c The Royal Society of Chemistry 2007 J. Anal. At. Spectrom., 2007, 22, 1304–1332 | 1327

(continued )

STJ Superconducting tunnel junctions

TCO Transparent conducting oxides

TEM Transmission electron microscope

TES Transition-edge-sensor

TGA Thermo-gravimetric analysis

TXRF Total reflection X-ray fluorescence

USA United States of America

UV-VIS Ultraviolet–visible spectroscopy

WDXRF Wavelength dispersive X-ray

fluorescence

WEEE Waste Electrical and Electronic

Equipment

XAFS X-Ray absorption fine structure

spectroscopy

XANES X-ray absorption near edge structure

XAS X-ray absorption spectroscopy

XES X-ray emission spectroscopy

XRD X-ray diffraction

XRF X-ray fluorescence

Z Atomic number

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