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From Lab to Field:Why Teaching XRF Matters
Welcome
2
Alexander SeyfarthProduct Manager , XRFBruker AXS [email protected]+1.608.276.3040
Dr. Peter PalmerProfessor, Analytical-Environmental ChemistrySan Francisco State [email protected]+1.415.338.7717
John Patterson, Ph.D.Director of Marketing and Product ManagementBruker [email protected]+1.609.847.9468
Today’s Agenda
• Introduction
• Dr. Peter Palmer will describe his approach to teaching XRF and give you examples of applications he has used in his curriculum
• Alexander Seyfarth will describe several different types of XRF equipment and the appropriate application of each
• Summary
• Question and answer session
3
Please use your mouse to answer the question to the right of your screen:
What elemental analysis techniques do your students gain experience with as part of your undergraduate laboratory curriculum? (Check all that apply.)
Gravimetric methods (ex. Cl via precipitation with AgNO3)
Titrimetric methods (ex. Ca via EDTA titration)
UV-Visible Spectrophotometry (ex. Pb via chelation with dithizone andUV/Vis)
Atomic Spectrophotometry (ex. Pb via Flame Atomic Absorption Spectrophotometry)
X-ray Fluorescence Spectrometry
Other
Audience Poll
4
From Lab to Field:Why Teaching XRF Matters
Introduction:• XRF theory is well understood and easy to teach
• Technique provides qualitative, semi-quantitative and quantitative analysis
• Provides opportunity to teach not just the technique but also scientific thought
• The equipment is relatively inexpensive
• Handheld equipment is portable enough to take it almost anywhere from the Laboratory to the Field
Poll Results
5
Teaching XRF
Dr. Peter Palmer
6
http://www.xkcd.com/7
FIT OF XRF IN THE SCIENCES
• Although XRF is a physical phenomena involving the interaction of X-rays with matter, the applications of XRF are in areas predominantly outside of physics (geology, anthropology, environmental sciences, etc.)
• Although XRF, like any other spectroscopic technique, requires specialized knowledge in chemistry (spectral interpretation, calibration, sample prep, etc.), it is not even mentioned in 99% of undergraduate chemistry programsin the U.S.
• With continuing advances in technology and ever growing number of XRF applications, it is critically important to bring more attention to XRF and related techniques within the U.S. academic system
SF State University is one of only a very few universities to integrate XRF into its undergraduate chemistry curriculum
• Quantitative Chemical Analysis (lecture and lab)• Instrumental Analysis (lecture and lab)• Independent research projects
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ELECTROMAGNETIC SPECTRUM
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ATOMIC SPECTROMETRY FUNDAMENTALS
Atomic Absorption
Mass Spectrometry
Atomic Emission
Selectivity based on use of element-specificlight source (Hollow Cathode Lamp)
Light absorption is proportional toconcentration: A = -log(P/P0) = εbC
Light of specific wavelengthfrom Hollow Cathode Lamppromotes electron to higherenergy level (excitation)
Heat energy from high intensity source (flame or plasma) promotes electron to higherenergy level (excitation)
Heat energy from high intensity source (plasma) separates electron from atom (ionization)
Selectivity based on emission of light at characteristic λ for element
Light emission is proportional toelemental concentration: I = kC
-
-
-
- -
-
-
Selectivity based on use of measurement of characteristic mass of elemental ion
Ion intensity is proportional to elemental concentration: I = kC
GroundState
ExcitedState
Δ
-
- -
Δ
-
- -
Δ
Δ
X-Ray FluorescenceEnergy from X-Rays (high energy) separates electron from atom (ionization), then inner shell electron fills vacant hole by emitting light -
-
Selectivity based on use of emission of light at characteristic λ for element (X-Ray)
Light intensity is proportional to elemental concentration: I = kC
-
-
1. When an X-ray photon of sufficient energy strikes an atom, it dislodges an electron from one of its inner orbitals (recall that X-rays are ionizing radiation)
2. To regain stability, the atom fills the vacancy with an electron from an outer orbital
3. As electron drops to lower energy state, excess energy is released as an X-ray
Step 1:Step 2:
Step 3:
XRF – PHYSICAL PROCESS
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• Quantum states for each element are different, and hence the characteristic energy of X-ray fluorescence can be correlated to a specific element(s)
• The XRF spectrum of an element is independent of its chemical form (recall that we’re removing inner shell electrons, not bonding electrons)
XRF – PHYSICAL PROCESS
K
L
M
∞
1s2
2s2p6
3s2p3d10Lβ 12.55 keV
N 4s2p3d10f14
Lα 10.61 keV
Pb
>16 keV
Pb
SIMPLE XRF SPECTRUM~10% Pb in imported tableware
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30 35 40
Energy (keV)
Inte
nsity
(cps
)
Pb Lα line10.55 keV
Pb Lβ line 12.61 keV
• Presence of Pb confirmed through observation of two peaks centered at energies close to their tabulated (reference) line energies
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0
5
10
15
5 6 7 8 9 10 11 12 13 14 15
Energy (keV)
Inte
nsity
(cps
)
ZnGaGeAsSe
XRF SPECTRAConsecutive elements in periodic table
• Energy (keV) proportional to atomic number Z2 (Moseley’s law)14
BOX DIAGRAM OF XRF INSTRUMENT
• X-ray sourceX-ray tube (range of energies)
• Detector and digital pulse processorEnergy-dispersive (no monochromator required)Peltier-cooled solid state detector (Li-doped Si or newer Si drift detector)This is a multi-channel analyzer that measures the
energy of photon in keV - related to type of elementemission rate in counts-per-second (cps) – related to concentration of element
• Analyzer software converts spectral data to direct readout of resultsConcentration of an element determined from factory calibration data, sample
thickness as estimated from source backscatter, and other parameters While this software is powerful, it can still yield false positives, false negatives,
and erroneous concentration data
X-raySource Detector
Sample
Digital PulseProcessor
XRFSpectrum
(cps vs keV)
Results(elements
and conc’s)software
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BRUKER TRACER III-SD XRF SYSTEM
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SAFETY CONSIDERATIONSScenario/situation exposure units
Exposures from background radiation sourcesChest X-ray 100 mREM/X-rayGrand Central Station 120 mREM/yearAirline worker 1000 mREM/year
Exposure limits set by regulatory agenciesMax Permissible Limit during pregnancy 500 mREM/9 monthsMax Permissible Limit for entire body 5000 mREM/yearMax Permissible Limit for an extremity (i.e., finger) 50,000 mREM
Exposures from normal operation of XRF analyzer in sampling standLeft/right/behind analyzer << 0.1 mREM/hour
Exposures from unacceptable use of XRF analyzer outside sampling stand4 feet directly in front of analyzer window 14 mREM/hour1 foot in front of analyzer window 186 mREM/hourDirectly in front of analyzer window 20,000 mREM/hour
• Any device which generates X-rays must be operated in a manner which ensures that human exposure to these X-rays is “as low as reasonably achievable” (ALARA)
• When the XRF analyzer is used properly (using sampling stand), radiation exposure will be non-detectable
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QUALITATIVE ANALYSISIssues to consider
WHAT ELEMENTS do we want to look for (toxic elements such as As, Cd, Hg, Pb, and Se, nutrient elements such as Fe, etc.)?
Define the problem – what are element(s) of interest
Are there any SPECTRAL OVERLAPS with other elements in sample?Determine potential overlapping species (i.e., Pb and As)
If we detect a toxic element, do we know for certain that it is in the product and NOT in the background materials used to hold the sample or the product packaging?
Measure what you want to measure
How do we know that the analyzer is not generating an ERRONEOUS identification (false positives or false negatives)?
Users must evaluate the spectrum to verify the reported results –positive identification of an element requires observation of two peaks at energies close to their tabulated values
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0
1
2
3
4
5
8 9 10 11 12 13
Basket Sample 16.4723
100 ppm Hg and As standard
As Kα
Hg Lα
Pb Lα Pb Lβ
Overlapping linesAs Kβ and Hg Lβ
Br Kα
Br Kβ
Zn Kα
Zn Kβ
Inte
nsity
(cps
)
Energy (keV)
SPECTRAL OVERLAPS
• Neither Hg nor As is present in this basket sample 19
Are the element concentrations within detection range of XRF (% to ppm)?Define the problem – research sample composition or take a measurement
Can the samples be analyzed as is or is some sample prep required?Define the problem – is sample homogeneous, can sample be ground up, what sort of accuracy and precision are required
What is the most appropriate calibration model to use?Fundamental Parameters (used for metallic samples)Compton Normalization (used for soil samples)Thin Film mode (used for filter samples)Empirical Calibration (are appropriate standards available?)Standard Additions (used to correct for matrix effects)
QUANTITATIVE ANALYSISIssues to consider
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CALIBRATION CURVESAs, Hg, and Pb in cellulose
Asy = 0.7477x - 0.2422
R2 = 0.9995
Pby = 0.4355x + 0.4354
R2 = 0.9994
Hgy = 0.345x - 0.3067
R2 = 0.9991
0
10
20
30
40
0 10 20 30 40 50 60
Concentration (ppm)
Inte
nsity
(cps
)
As
Hg
Pb
• Linear cal curves indicate acceptable method for preparation of authentic standards (dispersing metal salt into cellulose using powder or cryogenic mill)
• LODs in single ppm range (surprisingly just as sensitive as lab-grade XRF instrument)
21
Please use your mouse to answer the question to the right of your screen:
What are the barriers to teaching XRF in your curriculum? (Check all that apply.)
Expertise or knowledge of technique
Availability of teaching materials (lecture notes, lab experiments)
Access to an XRF instrument (lack of funding, cost of equipment)
Effort involved in changing the curriculum
Safety concerns
Other
Audience Poll
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STUDENTS IMPACTEDUndergraduate and Graduate Classes22 students from Quantitative Analysis in Spring 200960 students from Quantitative Analysis in Fall 200968 students from Quantitative Analysis in Spring 201012 students in Instrumental Analysis in Spring 201010 students in grad level X-Ray Techniques class in Spring 201090 attendees for Dr. Bruce Kaiser’s XRF Workshop
Independent ResearchMatt Sanchez Fe in beerPatience Adagba Cl in PVCCharlie Bupp identifying fake drugsHeather Gregory identifying fake drugsPete Baker ppb levels of As in drinking waterRene Johnson ppb levels of As in drinking waterDavid Luong Pb in tableware leachateAnthony Trinh Pb in tablewareKara Cross As and Hg in basket collectionsBrian Rebold toxic elements in soilChris Alleyne-Chin paint analysisKensuke Yamamoto toxic elements in supplementsSiri Webber toxic elements in supplementsYeon Kyoung Hwang toxic elements in foodKelly Ferguson toxic elements in food
Poll Results23
XRF LAB MODULE20 students in each Quantitative Chemical Analysis lab section4 groups comprised of 5 students, each working on different XRF application 1 or 2 XRF analzyers (Niton XLt, Innov-X α, Bruker Tracer III-V)
DAY 1:• Lecture (theory, qual and quant analysis)• Demo (instrument operation, acquiring spectra, analyzing data)• Define application (target element, lines of interest, expected conc’s)
DAY 2:• Prep standards and samples (homogenization) • Develop method (excitation conditions, measurement time)• Acquire data and download spectra to Excel (for subsequent plotting of
spectra and generation of cal curves)
DAY 3:• Evaluate results, compute figures of merit (linearity, accuracy, precision),
and give brief presentation to entire lab• Group discussion on XRF versus other analytical methods
24
XRF EXPERIMENTS IN QUANT
Hazmat analysis• Students analyzed several samples and
identified U, lead arsenate, Th, and V• Software enables verification of presence of
an element from its reference line energies• Results clearly showed utility of XRF as
powerful screening tool
25
XRF EXPERIMENTS IN QUANT (Cont.)
Hazmat analysis• Students analyzed several samples and
identified U, lead arsenate, Th, and V• Software enables verification of presence of
an element from its reference line energies• Results clearly showed utility of XRF as
powerful screening tool
26
XRF EXPERIMENTS IN QUANTDetermination of Ca in powdered milk
• Sample contained 1% Ca
• Students often failed to correctly prepare several standards of CaCO3 in cellulose or use actual concentrations in their cal curves (teaching moment)
• Use of external standards (CaCO3 in cellulose) gave erroneously low results due to attenuation of Ca fluorescence by K in milk
• Use of standard additions (CaCO3 in powdered milk) corrected for this matrix effect (<1% error)
• Compared to classical EDTA titration method, XRF simpler, faster, gives [Ca]
Ca in Milk via Standard Additions
y = 6262.2x + 6314.2R2 = 0.9982
0
10000
20000
30000
40000
-2 -1 0 1 2 3 4 5 6
% Ca
Peak
Are
a
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Determination of Pb in SRM
• SRM contained 2480 ppm Pb
• Students prepared standards of Pb salt in Cab-O-Sil matrix in attempt to emulate composition of SRM (mostly Si)
• Linear cal curve showed evidence of self-absorption (fall off in intensity at higher concentrations)
• Nonlinear cal curve gave better fit of standards and blank and more accurate quantitation of Pb in SRM (< 3% error)
• XRF results obtained much faster than FAAS method
XRF EXPERIMENTS IN QUANT
LINEAR FIT for Pb in Cab-O-Sil via XRF
y = 2.4033x + 45429R2 = 0.9967
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
0 10000 20000 30000 40000 50000
ppm Pb
Inte
nsity
(cps
)
2nd ORDER FIT for Pb in Cab-O-Sil via XRF
y = -5.79E-05x2 + 5.77E+00x + 1.10E+04R2 = 9.94E-01
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
0 10000 20000 30000 40000 50000
ppm Pb
Inte
nsity
(cps
)
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Determination of Pb in tableware
• Students prepared aqueous standards of Pb and leachate extracts from 13 different pieces of imported Mexican tableware
• XRF results showed Pb ranging from ND to over 4000 ppm, with most samples giving levels well above the FDA limit of 1 ppm
• Comparison of XRF vs FAAS results showed results were not statistically different at 95% confidence level
• Compared to FAAS method, XRF results obtained much faster, gave cal curve linear from 1-5000 ppm, and readily identified presence of Cu in new glaze
XRF EXPERIMENTS IN QUANT
y = 0.0012x + 0.0030R2 = 1.0000
0.01
0.10
1.00
10.00
1 10 100 1000 10000
ppm Pb
Pb R
espo
nse
/ Com
pton
Res
pons
e
29
Criteria FAAS GFAAS ICP-AES ICP-MS XRF
Sample Prep [significant - homogenization, digestion, filtration] minimal
Detection Limits ppm-ppb ppb-ppt ppb ppt ppm
Dynamic Range 1-2 2-3 4-6 9 3
Interferences Moderate Moderate Significant Few Moderate
Speed Moderate Slow Moderate Moderate Fast
Elemental Coverage Moderate Moderate Moderate Excellent Moderate
Multi-element No No Yes Yes Yes
Sample Size mL μL mL mL mL/g
Capital Cost $ $$ $$ $$$ $
Operating Cost $ $$ $$ $$$ $
COMPARISON OF ELEMENTAL ANALYSIS METHODS
30
TRENDS IN ELEMENTAL ANALYSIS METHODS* Denotes multi-element analysis technique
REQ
UIR
ED D
ETEC
TIO
N L
IMIT
S
NUMBER OF SAMPLES
low
high
highlow
GFAAS
FAAS ICP-AES*
ICP-MS*
XRF*
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FINAL THOUGHTS ON ACADEMIC USE OF HANDHELD XRF ANALYZERSWhat can we do to further this discipline?
• Promote inclusion of XRF into analytical chemistry textbooks
• Promote integration of XRF into undergraduate lecture and lab classes (quant analysis, instrumental analysis, environmental chem, material science, special topics course on X-ray techniques)
– FAST measurement times suitable for large lab sections– INEXPENSIVE handheld instrument, can be rented or purchased– COMPLEMENT/REPLACE classical gravimetric and titrimetric experiments– ENGAGE students with state of the art instrument and relevant applications
Provides many opportunities to TEACH relevant analytical chemistry topics (sample homogeneity, preparing standards, calibration models, instrument optimization, data analysis)
– Focus students on interpreting and understanding SPECTRA (not list of elements and concentrations)
– Get students to THINK about the measurement process
• Develop more active XRF research programs – Case studies and field work
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XRFInstrumentation
Alexander Seyfarth
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How characteristic X-rays are generated in an atom
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XRF: X-ray Fluorescence Analysis
Energy of X-ray photons• Which element • Qualitative analysis
Number of X-ray photons at a given energy • Concentration • Quantitative analysis
Sample
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X-ray Fluorescence Analysis: Energy-Dispersive XRF (EDX or EDXRF)
The detector is used to record both: • the energy E and • the number Nof X-ray photons
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Sample
Wavelength-Dispersive XRF (WDX or WDXRF)
An analyzer crystal separates the various wavelengths, λ (energies)
The detector records only the number, N, of X-ray photons at a given wavelength (energy)
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Sample
Primary Signal: ED and WD
For both methods, the primary signal is the number of detected X-ray photons ("counts")
Counts are collected:
• as a function of the energy (EDX)
• as a function of the reflection angle 2θ (WDX)
E2θ
counts / Δ E
counts / Δ 2θ
38
Primary Signal: ED and WD
Resolution (separation of peaks)
Count rate (number of detected photons)
Background (scatter from sample)
E2θ
counts / Δ E
counts / Δ 2θ
39
X-ray Fluorescence Analysis: Energy-Dispersive XRF (EDX or EDXRF)
The detector is used to record both: • the energy E and • the number Nof X-ray photons
40
Sample
Traditional EDXRF
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EDXRF
Can detect multiple elements simultaneouslyExcitation can be controlled by selecting the current (number of photons) as well as high voltage (excitation energy)Beam filters allow selective absorption of the primary beam to “optimize” certain regions of the spectraUsing Silicon Drift (SDD) detectors allows for “quality” resolution of < 150 eV while capable of high total spectra count rate of > 100 000 counts per secondNO liquid nitrogen! NO carrier gasses!Instrument can operate under air, vacuum or heliumPower level 50 Watts; large irradiated bulk sample spots of 30-mm diameter
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Excitation of light elements
43
Excitation of heavy elements
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Benchtop EDXRF
e.g.
University Western Ontario
Murray State Univ
45
PXRF/ HH-XRFEDXRF in a small package
Tube (Rh, Ag)
Si-Pin Detector<170 eV(40 000cps)
IR SENSOR
FILTER /TARGETEXIT WINDOW
46
Point and Shoot vs. TRACER
e.g. Metals “SORTER” Point and shootFactory calibrationsPDA
Multi-calibrationMulti-filter and VacuumFactory AND user calibrationsPC software AND PDA
DEVELOPED WITH NASA
47
TRACER III-SD with X-Flash SDD Detector
48
Mobile use, stationary or even point and shoot
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The usage difference
TRACER III will let you adjust:• Voltage• Current• Filter• Secondary target• Variations of the above 4
Bruker Software(distributed with equipment)• Subtraction• Normalization• Analysis locations• Overlays and deconvolution
Perform the sample analysis • from back to front vice versa• Transmission test or calculations• Analyzed layer
50
X-ray Fluorescence Analysis Energy-Dispersive TXRF
Sample
Det
ecto
r
E, N
The detector is used to record both: • the energy E and • the number Nof X-ray photons
Monochromatic X-rays at low incidence angle to “skim” the very thin sample
51
TXRF low background = lowest LLD‘sPICOFOX does PICOgrams
Sample:1 ng NiTime: 100 sSensit.:37 cps/ngLLD: 0.95 pg
52
TXRF Applications: Chemotherapy
Sample preparation and analysisPt was analyzed in serum only centrifugation and separation of serumfor accurate analysis an external calibration, applying spiked samples and Compton-normalizationmeasurements: 50 kV/750 µA, Mo-excitation, 100 s
Data kindly supplied by E. Greaves, Universidad Simón Bolívar, Apartado89000, Caracas 1080A, Venezuela. E-mail: [email protected]
DL: 67 µg/l (100s)
53
Benchtop TXRF
e.g. Loyola University (filters), Lawrence Berkeley National Lab, British Columbia Institute of TechnologySee our extensive TXRF webinars posted on www.bruker-axs.com
54
Wavelength-Dispersive XRF (WDXRF)
An analyzer crystal separates the various wavelengths, λ (energies)
The detector records only the number, N, of X-ray photons at a given wavelength (energy)
55
Sample
EDXRF versus WDXRF
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Sample Preparation
Pressed Pellet – Black Shale
XRF for YOU Seminar Nashville, TNH. RoweAt that time U. Kentucky
57
Black Shale AnalysisPressed Pellet
58
Calibration
Not so many standards for Black Shales!Need for mixing and matching (similar matrices)Need for developing standards
XRF for YOU Seminar Nashville, TNH. RoweAt that time U. Kentucky
59
Floor standing units (WDXRF)
e.g. University of Kentucky, Michigan State University, University of Wisconsin – MilwaukeeGeoscience applications
60
Summary
John Patterson
61
From Lab to FieldWhy Teaching XRF Matters
Conclusion:• XRF is an excellent technique for teaching atomic spectroscopy
and analytical techniques
• XRF provides an opportunity to engage the student and teach scientific reasoning
• XRF is suitable for use in almost any location so take the analysis to the samples rather than the reverse
• XRF is an important job skill – industry is always looking for trained operators; this will expand the resume of a recent graduate
62
Advantages of XRF for Teaching
• XRF can be completely nondestructive – leading to use of very
interesting and unusual samples
• There is little or no sample prep
• No dangerous chemicals to dispose of (acids)
• No expensive Argon or explosive gasses needed/No LN
• Low operating costs
• Direct analysis of solids, liquids and inert gasses (TRACER only)
• Multiple techniques to select from based on applications / funding
• PXRF/HH-XRF• EDX• TXRF• WDXRF
63
We want to make it easy to adapt
Educational package
• PPT and exercises (and solutions)
• Materials for calibration and “applications”
• Software package (SPECTRA/SpectraEDX) which can be freely distributed to students, faculty to use
• Networked units allow multiple users to use the unit, then crunch data and evaluate them offline
• Train the trainer by our experienced applications staff
• Priority applications support
64
We want to make it easy to adapt
• Alexander Seyfarth can provide all the Bruker AXS material and support (email to [email protected])
• Dr. Palmer’s XRF lecture materials and laboratory experiments are available on request (email to [email protected])
65
Any Questions?
Please type any questions you may have in the Q&A panel and then
click Send.
66
Where can you learn more about XRF?
University of Western OntarioXRF2010 Short Course• 2 weeks: May 31 – June 11, 2010
o 1st week is basicso 2nd week is quantification
2 topical workshops:• Sample Prep Workshop – June 4, 2010• 20th Anniversary Symposium: Practical
Applications of XRF in Industries
Charles Wu at [email protected]/earth/news/xrfcourse
67
Where can you learn more about XRF?
ICDD XRF Clinic - Practical X-ray Fluorescence5 days: May 3-7, 2010Newtown Square, PennsylvaniaTaught by a dedicated and experienced group of XRF specialistsLive instrumentation: WDXRF, EDXRF and more
www.icdd.com/education/xrf.htm
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Where can you learn more about XRF?
DXC 2010 WorkshopsMonday & Tuesday, August 2 & 3, 2010Denver Marriott Tech Center Hotel, Denver, COXRF Workshops:• Basic XRF• Trace Analysis• XRF Specimen Preparation• Quantitative Analysis• Standards and Advanced Sample Preparation for XRF Analysis
www.dxcicdd.com
69
Where can you learn more about XRF?
Bruker Training Central (BTC) – Online Training Courses2-hour web-based training courses delivered through your browserInclude slides, audio, video and participant Q&AUpcoming live:• April 22-23 – Ultra-Low Sulfur Determination by XRF• July 15-16 – XRF Standardless Analysis• September 9-10 – Getting the Most From Your WDXRF System
On-demand:• XRF Basics I: From Theory to Intensity• XRF Basics II: From Intensities to Concentrations• XRF Sample Preparation
www.brukersupport.com
70
Thank You for Attending!
Alexander SeyfarthProduct Manager , XRFBruker AXS [email protected]+1.608.276.3040
Dr. Peter PalmerProfessor, Analytical-Environmental ChemistrySan Francisco State [email protected]+1.415.338.7717
John Patterson, Ph.D.Director of Marketing and Product ManagementBruker [email protected]+1.609.847.9468
When you exit the webinar, please complete our brief survey.Your feedback is very important to us.
71
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