TRACE ELEMENT ANALYSIS USING EDXRF WITH ... elements are clearly detected. Table 1 and Table 2 list the analyzed results of hazardous FP method Non-measuring balance components are

TRACE ELEMENT ANALYSIS USING EDXRF WITH POLARIZED OPTICS

Takao Moriyama1, Satoshi Ikeda1, Makoto Doi1 and Scott Fess2 1Rigaku Corporation, Takatsuki, Osaka 569-1146, Japan 2Applied Rigaku Technologies, Inc., Austin, TX 78717

ABSTRACT

We have developed an EDXRF spectrometer with polarized optics and new quantification

software which estimates non-measuring sample matrices using scattering intensities and full

profile fitting method combined with FP method. Accurate analysis down to ppm level can be

achieved even in complex sample composition with the quantification software. The

scattering FP method corrects for non-measuring components in samples such as coal fly ash,

soils and biological samples by using Compton and Thomson scattering intensities from a Mo

secondary target. Additionally, it is possible to analyze thickness and composition of

multi-layer thin films considering interlayer secondary excitation.

INTRODUCTION

Energy dispersive types of x-ray spectrometers are useful analytical tools for screening

analysis, such as for environmental applications, due to compact and easy sample handling.

However, the preparation of standard samples that match analyzing samples in applications

such as for industrial waste and recycling raw materials often requires special attention to

match sample types and preparation. This is because their sample matrices are complicated

and improved sensitivities for trace elements are demanded for these environmental

applications.

We have developed an EDXRF spectrometer with polarized optics and software using a

fundamental parameter method for accurate quantification combined with full profile fitting

method, including estimating non-measuring sample matrices using scattering intensities.

INSTRUMENT

The specifications of the new Rigaku EDXRF spectrometer NEX CG used in this study are as

follows:

X-ray tube : Pd target, air cooled

Tube power : 50W(50kV-2mA)

Secondary targets : 5 targets (max)

Detector : High performance SDD

(Silicon Drift Detector)

288Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 289Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002Advances in X-ray Analysis, Volume 54

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Atmosphere : Vacuum, Air, He

Measuring area : 20mm diameter

METHODS

(1) Secondary targets with polarized optics optimized for low ppm applications

Secondary targets and polarized optics provide high P/B ratio spectra compared to direct

excitation optics in a wide energy range.

Blue and red lines in Fig. 1 show measurements of a multi-element oil sample by the

polarized optics and direct excitation optics, respectively. The polarized optics gives greatly

improved performance compared to the direct excitation optics for trace element analysis

(2) RPF-SQX (Rigaku Profile Fitting - Spectra Quant X) analysis

RPF-SQX is a standardless analysis

(Kataoka, 1989) software with a

fundamental parameters method for

accurate quantification combined with full

profile fitting method. This method is useful

for samples with complex matrices. Fig.2

shows an example of a fitted and measured

profile using the standard soil sample

JSAC0466. The fitted spectrum consists of

the sum of individually generated profiles

using the response function (Campbell and

Wang, 1992) for each element obtained by the FP method. Quantification results are obtained

by iteratively adjusting the fitted spectrum until it matches the measured spectrum. As shown

in Fig. 2, the calculated spectrum is in good agreement with the measured spectrum.

1.E+02

1.E+03

1.E+04

1.E+05

4 6 8 10 12 14 16 18

keV

Intensity (A

rb.U

nit)

EDXL300

Direct

Direct excitation optics

Polarized optics

X-ray tube

Secondary Targets

Sample

Detector

Pb-

L

Pb-

L

10 11 12 130

2000

4000

6000

8000

10000

Measure

Total profile

As profile

Se profile

Pb profile

Hg profile

X-r

ay in

tens

ity (

a.u.

)

Energy ( keV)10 11 12 13 keV

X-r

ay in

tens

ity (

a.u.

)

As -

K

Se-K

As -

K

Fig. 2. Measured and fitted spectra of the soil

standard JSAC0466S

Fig. 1. Polarized optics and measurement comparison to direct excitation optics

of an oil sample


(3) Scattering FP method for estimating non-measuring components

In the conventional FP method,

the information of all components

in a sample is required for

accurate analysis. The contents of

non-measuring elements can be

obtained when the elements and

the composition are known. For

example, �CH2� is set in

polyethylene as the balance.

However, when non-measuring

elements are not known, accurate calculation cannot be done using conventional fundamental

parameters (FP). The scattering FP method (Kataoka, et al., 2005) estimates the

non-measuring components from the scattering x-ray intensities of Compton and Thomson of

Mo-K line from the Mo secondary target as shown in Fig. 3. This method gives accurate

results for the applications having complex non-measuring components such a soil, scale and

so on.

RESULTS

Four typical application results are described below. The measurement conditions are

summarized in Table 6.

(A) Coal fly ash and soil

The hazardous element

analyses of fly ash and soil are

current topics in XRF analysis.

The CRMs of coal fly ash and

soil analyzed were measured by

loose powder method. Two

grams of the sample was set in

polyethylene sample cups of

32mm diameter opening with 4

um Prolene film support. Fig. 4

shows the spectra of the

samples of fly ash and soil

samples of NIST CRMs. It

shows the energy range for As,

Se and Pb and the peaks of the

trace elements are clearly detected. Table 1 and Table 2 list the analyzed results of hazardous

FP method

Non-measuring balance components are not known.

Metal

Polymer

Liquid

Scattering FP method

Soil, Scale, Waste oil

Non-measuring balance components are known.

Oxide

X-r

ay I

nten

sity

7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0keV

Fig. 4. Measured spectra of coal fly ash(NIST1633a:

blue line) and San Joaquin soil (NIST2709: red line)

in the range of 7 to 14 keV using Mo secondary

target

Fig. 3. Applicable samples of scattering FP method


elements and major elements, respectively. The RPF-SQX with the scattering FP method was

applied to the analysis of both samples. The analyzed results matched well with the certified

values even though the fly ash sample contains unburned carbon and the soil sample contains

organic matter.

(B) Thickness measurements of multilayer films on Si wafers

Multilayer thin film analysis is important in semi-conductor applications, as well as other

application such as photovoltaics. The multilayer thin film of Ti/Ni/Ag on Si wafers

illustrated in Fig. 5 were analyzed using the multilayer thin film FP software (Laguitton and

Mantler, 1977; Kataoka and Arai, 1990) and sensitivities of individual elements obtained by

measuring bulk pure metals are stored in the sensitivity library of the software for

standardless analysis. Table 3 lists the analyzed results of the two samples including repeat

measurement result to check the repeatability. The FP software in the NEX CG includes the

computation of the interlayer secondary excitation for accurate theoretical intensity

calculation. In this sample, secondary excitation calculation from Ni layer (Ni-K) to Ti

layer (Ti-K) is included. As shown in Table 3, good agreement between analyzed and

standard values was obtained without using standards with the same film structure.

(C) Biological samples

Analysis of mineral elements such as Mg, Ca and K and hazardous heavy elements are

important in biological samples. The CRMs of biological samples analyzed were prepared by

weighing 2 grams of the sample and making a hydraulically pressed pellet in 32mm of

diameter using 10 tons of pressure for 30 seconds. Fig. 6 shows the spectra of hazardous

heavy elements obtained by measuring various kinds of biological samples. The peaks of

several ppm of hazardous elements can be clearly seen. Fig. 7 shows the spectra of mineral

elements in plant and food samples. High P/B ratio could be obtained for the peaks of Na and

Table 1 Analyzed results of trace hazardous elements

Samples As

Cd Cr

Hg

Pb Se

San Joaquin Soil

Analyzed

17.9

n.d.

120.6

3.9

21.2

2.3

NIST2709

Std. Val. 17.7

0.4

130.0

1.4

18.9

1.6

Coal Fly Ash

Analyzed 149

n.d.

189

n.d.

75.8

12.6

NIST1633a

Std. Val.

145

1.0

196

0.16

72.4

10.3

Unit : ppm

Na

Mg

Al

Si

P S K Ca

Ti

Fe

San Joaquin Soil

Analyzed

1.35

1.84

7.93

29.26

0.063

0.090

1.95

2.02

0.34

3.51

NIST2709

Std. Val.

1.16

1.51

7.50

29.66

0.062

0.089

2.03

1.89

0.34

3.50

Coal Fly Ash

Analyzed

0.31

0.405

14.4

23.3

0.23

0.19

1.91

1.06

0.31

9.0

NIST1633a

Std. Val.

0.17

0.455

14.3

22.8

- - 1.88

1.11

- 9.4

Unit : mass% Table 2 Analyzed results of major elements

Samples


Mg by using a special secondary target for light element analysis equipped in the NEX CG

without interference of higher energy peaks as shown in Fig. 7 (c).

Table 4 shows the analyzed results of the aforementioned biological samples using the

RPF-SQX software with the scattering FP method. The influence of non-measuring elements

highly contained in these biological samples such as N, O, C and H, were effectively

corrected.

Si Wafer

Ag (1200A)

Ni (4000,2000A)

Ti (1000A)

Ti Ni Ag

n=1 976 3917 1166

2 978 3923 1177

3 983 3921 1167

4 970 3923 1185

5 976 3921 1196

6 968 3923 1169

7 970 3921 1212

8 990 3917 11699 973 3925 1201

10 968 3921 1172

Average 975 3921 1181

Std. dev. 7.1 2.6 16.4

RSD% 0.7 0.1 1.4

Ti Ni Ag

n=1 1066 2016 11772 1052 2013 1187

3 1056 2008 1170

4 1066 2013 1162

5 1066 2013 1201

6 1065 2020 1178

7 1065 2015 11928 1078 2012 1145

9 1064 2013 1171

10 1056 2015 1180

Average 1063 2014 1176

Std. dev. 7.3 3.1 15.8

RSD% 0.7 0.2 1.3

Unit:AngstromTi/Ni/Ag/Si Wafer

Unit:Angstrom

Fig. 5. Structure of

multilayer film

Table 3 Analyzed results of Ti/Ni/Ag film on Si Wafer Sample A

Sample B


(a)

Hg-

L

Se

As-

K

6.06 ppm 5.63 ppm

1.40 ppm

21.6 ppm

18.0 ppm

16.6 ppm

6.0

8.0 10.0 12.0 14.0keV

4.64 ppm

2.14 ppm

0.27 ppm

(b)

Hg -

L

X-r

ay I

nten

sity

keV9.6 10.0 10.4 10.8

Cd-

K

26.8 ppm

20.8 ppm

0.043 ppm

(c)

Ag-

K

keV

X-r

ay I

nten

sity

20.0 21.0 22.0 23.0 24.0

Heavy elements

5.0 5.4 5.8 6.2

X-r

ay I

nten

sity

keV

(d)

34.7 ppm

0.77 ppm

Cr -

K

X-r

ay I

nten

sity

Fig. 7. Spectra of Peach Leaves (NIST1547)

and Non-fat Milk Powder (NIST1549)

NIST1547:(a) RX9 secondary target, (b) Cu

secondary target

NIST1549:(c) Comparison of spectra

compared between RX9 secondary target and

special secondary target for light elements

Fig. 6. Spectra of marine organism standard samples of National Research Council Canada

Red lines : Lobster Hepatopancreas (TORT-2), Blue lines : Dogfish Muscle (DORM-2), Green

lines :Dogfish Liver (DOLT-2) (a) Mo secondary target, (b) magnified spectrum of (a) in

region of Hg, (c) Al secondary target, (d) Cu secondary target

(a)

X-r

ay I

nten

sity

keV1.4 1.8 2.2 2.6

1370 ppm

2000 ppm

360 ppm

(b)

X-r

ay I

nten

sity

2.8 3.2 3.6 4.0 4.4keV

2.43 mass%

1.56 mass%

Light elements

4970 ppm 1200 ppm

0.7 0.8 0.9 1.0 1.1 1.2 1.3

X-r

ay I

nten

sity

keV

Na-K á

Cl-

K e

scap

e-pe

ak

Na-

Ká

RX9 secondary target Secondary target for light elements(c)

Si-K

P-K

S-K

Cl-

K

Al-

K

Ca-

K

K-K

Na-

K

Mg-

K


(D) Copper Alloy

Copper alloy samples were analyzed as examples of trace element analysis in metal samples.

The copper alloy samples were polished using a lathe to make flat surface. Fig. 8 shows the

spectra obtained by measuring a naval brass standard. A Pb peak of 0.069mass% can be seen

with high P/B ratio due to the high speed detector with pile-up rejection and Mo secondary

target. Fig. 9 shows the spectra in the light element range obtained by measuring three copper

alloys containing phosphorous. Monochromatic Pd-L line effectively excites the P-K line

so that the peak of 90 ppm phosphorous could be seen in the spectrum. The detection of

P-K is difficult in WDXRF due to the interference by the 4-th order of Cu-K line. Table 5

exhibits the analyzed results of various kinds of copper alloys and the results match well with

the standard values from low level to high contents.

Fig. 8. Spectra of naval brass standard (NIST C1108) (a) Mo secondary target, (b) Al

secondary target

6.0 8.0 10.0 12.0 14.0 keV

10.0 11.0 12.0 13.0

Pb-

L

Pb-

L (a)

Alターゲット

20.0 24.0 28.0 32.0 36.0 keV

(b)

X-r

ay I

nten

sity

X-r

ay I

nten

sity

165.0 - NRCC DOLT-2 Analyzed

n.d. 27.7 90.8 14.2 5.7 23.7 2.0 2.7 21.1 n.d. 1.6

Dogfish Liver Std. Val. - 25.8 85.8 16.6 6.1 - - - 20.8 -

Samples

NIST1570aSpinach Leaves

NIES CRM No.1Pepperbush

Analyzed Std. Val.

Analyzed

Std. Val.

Samples

Ni Cu Zn As Se Br Rb Sr Cd Ba Hg ppmppmppmppmppmppmppmppmppmppmppm

2.1 2.2

12.2

14.0

82.0

80.0

- n.d.

-

n.d.

-

34.5

13.0 13.0

55.6

52.7

-

n.d. -

n.d.

- n.d

8.7 10.3

12.0

12.9

340.0

347.5

- n.d.

-

n.d.

-

0.8 75.0 75.5

36.0

35.0

6.7 5.7 165.5 n.d.

Table 4 Analyzed results of various biological samples

Na Mg Si P S Cl K Ca Mn Fe Co

mass% mass% mass% mass% mass% mass% mass% mass% ppm ppm ppm

NIST1570a Analyzed 1.83 0.85 0.11 0.59 0.50 0.65 2.79 1.47 66.5 271 n.d. Spinach Leaves Std. Val. 1.82 0.89 - 0.52 0.46 - 2.90 1.53 - - - NIES CRM No.1 Analyzed

n.d. 0.38 0.27 0.14 0.26 0.39 1.58 1.45 2021 215 15.6

Pepperbush Std. Val. - 0.41 - 0.11 - - 1.51 1.38 2030 205 23.0

NRCC DOLT-2 Analyzed

0.83 0.12 n.d. 1.08 1.29 0.83 0.87 0.06 5.7 1124 n.d. Dogfish Liver Std. Val. - - - - - - - - 6.9 1103 -


Table 6 Measurement conditions

(A) Coal fly ash and soil Atmosphere: helium

Secondary target Light element

target RX9 Cu Mo Al

kV-mA 25-auto *) 25-auto 50-auto 50-auto 50-auto

Energy ranges(KeV) 1.0-1.3 1.3-2.8 2.8-8.0 8.0-15.0 15.0-40.0

Counting time (s) 200 100 100 100 200

*) auto: current is adjusted such that dead time is at a predetermined level.

(B) Multilayer film Atmosphere: vacuum

Secondary target Cu Mo Al

kV-mA 50-auto 50-auto 50-auto

Energy ranges(KeV) 2.8-8.0 8.0-15.0 15.0-40.0

Counting time (s) 100 100 100

Table 5 Analysis results of copper alloy samples

Samples

Cu Zn Pb Fe Sn Ni Al Sb As Mn P mass% mass% mass% mass% mass% mass% mass% mass% mass% mass% mass%

NISTC1103

Free-CuttingBrass

Analyzed 59.1 35.6 3.88 0.25 0.869 0.17 n.d. n.d. n.d. n.d. 0.0045

Std. 59.19 35.7 3.81 0.26 0.88 0.16 - - - - 0.003 NISTC1108

Naval Brass Analyzed 65.0 34.4 0.069 0.048 0.397 0.031 n.d. n.d. n.d. 0.029 0.003 Std. 64.95 34.42 0.063 0.05 0.39 0.033 - - - 0.025 -

NISTC1115

CommercialBronze

Analyzed

88.1 11.6 0.011 0.127 0.102 0.070 n.d. n.d. n.d. 0.004 0.003

Std. 87.96 11.73 0.013 0.13 0.1 0.074 - - - - 0.005 NISTC1118

AluminumBrass

Analyzed

75.3 21.8 0.022 0.060 0.0047 n.d. 2.88 n.d. 0.009 0.002 0.133

Std. 75.1 21.9 0.025 0.065 - - 2.8 - 0.007 - 0.13 NISTC1119

AluminumBrass

Analyzed

77.2 20.2 0.053 0.028 n.d. n.d. 2.09 0.049 0.043 0.005 0.062

Std. 77.1 20.4 0.05 0.03 - - 2.14 0.05 0.04 - 0.07

Fig. 9. Spectra of light element range including phosphorus of copper alloys

Blue: NIST C1118, red:NIST C1119, green:NIST C1114

0.13mass%

0.07mass%

0.009mass%

0.8 1.0 1.2 1.4 1.6 1.8 2.0

2.2 2.4

keV

X-r

ay I

nten

sity


(C) Biological samples Atmosphere: vacuum

Secondary target Light element

target RX9 Cu Mo Al

kV-mA 25-auto 25-auto 50-auto 50-auto 50-auto

Energy ranges(KeV) 1-1.3 1.3-2.8 2.8-8.0 8.0-15.0 15.0-40.0

Counting time (s) 600 300 300 300 600

(D) Copper alloy Atmosphere: vacuum

Secondary target RX9 Cu Mo Al

kV-mA 25-auto 50-auto 50-auto 50-auto

Energy ranges(KeV) 1.0-2.8 2.8-8.0 8.0-15.0 15.0-40.0

Counting time (s) 100 50 50 50

CONCLUSION

The spectrometer with secondary targets, polarized optics, and high speed detector with

pile-up rejection demonstrated extremely high P/B ratios from light to heavy elements

resulting in low LLD results. Accurate analyses down to ppm level could be achieved even in

complex sample composition for the quantification software which combined fundamental

parameter method and full profile fitting. The scattering FP method corrected for

non-measuring components in samples such as soils, biological samples by using Compton

and Thomson scattering intensities from Mo secondary target.

Additionally, good results of multilayer thin films could be obtained by the thin film FP

software considering interlayer secondary excitation.

REFERENCES

Campbell, J. L. and Wang, J.-X. (1992), �Lorentzian contributions to x-ray lineshapes in

Si(Li) spectroscopy�, X-ray Spectrometry, 21, 223-227.

Kataoka, Y. (1989), �Standardless x-ray fluorescence spectrometry (Fundamental parameter

method using sensitivity library), The Rigaku Journal, 6, 33-39.

Kataoka, Y. and Arai, T. (1990), �Basic studies of multi-layer thin film analysis using

fundamental parameter method�, Advances in X-ray Analysis, 33, 213-223.

Kataoka, Y., Kawahara, N., Hara, S., Yamada, Y., Matsuo, T. and Mantler, M. (2005),

�Fundamental parameter method using scattering x-rays in x-ray fluorescence analysis�,

Advances in X-ray Analysis, 40, 255-260.

Laguitton, D. and Mantler, M. (1977), �LAMA I-A general fortran program for quantitative


x-ray fluorescence analysis�, Advances in X-ray Analysis, 20, 515-528 .


Documents

TRACE ELEMENT ANALYSIS USING EDXRF WITH ... elements are clearly detected. Table 1 and Table 2 list the analyzed results of hazardous FP method Non-measuring balance components are