In 1951, the University of Denver held perhaps the world's first one-day symposium on the application of X-rays to the study of materials and the importance of X-rays in research. The Annual Conference on Applications of X-ray Analysis, as it was known, grew and continues to flourish as the world's leading forum for scientists working in the field of X-ray materials analysis. The Denver X-ray Conference (DXC) still provides a unique mixture of sessions on training and education, applications, and papers containing details about state-of-the-art techniques and future developments in X-ray analysis. Another important part of the meeting is the presence of leading manufacturers of X-ray equipment who exhibit their most recent offerings and have their technical people available to offer suggestions on how one might use their equipment to solve problems. 

As a service to those planning on attending the conference, 

 presents the following preview of products scheduled to be on display at DXC 2005, as well as an overview of the courses, workshops, and lectures that will be offered during the five-day event. 

While every effort has been made to present as comprehensive a listing as possible, this article cannot be considered a complete record of every product scheduled to be shown at the conference. 

) PX4 combines a digital pulse processor, a power supply, a shaping amplifier, and an MCA. It is compatible with the company's XR-100 detectors and detectors from other manufacturers. The PX4 is software driven and has 24 programmable peaking times between 0.8–102 µs. 			

) is characterized by its compact all-in-one design with an integrated touch screen, a printer, and a vacuum pump. Based upon Peltier-cooled detector technology, the spectrometer now also includes EQUA ALL, a universal calibration feature that, according to the company, automatically handles the corrections for all line overlaps without any adjustments. 

) automatic balance, TheAnt, is designed to eliminate weighing manipulations. According to the company, TheAnt allows users to automatically attain the sample/flux ratio with an accuracy of a tenth of a milligram. Designed for labs that prepare samples by fusion, TheAnt reportedly weighs at a rate of 30–60 samples per hour. 

The Eagle III micro-XRF elemental analyzer from 

) uses capillary optics, CCD video imaging cameras, and a motorized xyz stage for nondestructive small-spot analysis correlated with video imaging. Features include simultaneous detection of elements ranging from Na through U, and little or no sample preparation requirements. Typical applications include forensics, failure analysis, coating thickness-composition measurement, quality control, and chemical imaging. 

) is a SWAXS system designed for small-angle and wide-angle X-ray scattering applications. The non-synchrotron system reportedly provides automated, real-time measurements and efficient speed. 

) is an analytical XRF microscope designed to provide fast, elemental characterization with spot sizes down to 10 µm. Featuring the mono-capillary X-ray Guide Tube, which reportedly provides the ultra-narrow beam with high x-ray intensity and excellent beam quality, the XGT-5000 offers a choice of beam sizes available from 1.2 mm to 10 µm, with up to two configurable on one instrument, reportedly allowing for fast switching between micro and macro measurements. Typical applications include forensics (glasses, paints, gun shot residues, fingerprints etc), geology (mineral identification, composition etc), electronics (circuit board analysis, defects, soldering, WEEE/RoHS lead free compliance), pharmaceutical (tablet formulations, foreign object identification etc), materials (concrete/cement, metals, fillers), and biology and medicine (tissue analysis, element accumulation, biomaterials and structure, etc). 

) reportedly perform elemental analysis from Chlorine to Uranium, use collimated beams of 13-0.1 mm diameter with laser beam focusing, and are designed for testing small or nonhomogeneous samples. Applications range from the analysis of lead-free solders for electrons, circuit boards, and chip studies to precious metals, bronzes, and alloys. Featuring X-ray tube technology that reportedly eliminates radioactive isotopes, the bench-top instrument incorporates a Silicon-PiN Diode detector, and features an optional xyz stage for measurements during batch operations. 

— The Alpha Series of handheld analyzers provide on-the-spot elemental analysis from phosphorous to uranium. Featuring a removable handle that allows it to fit into tight spaces, the Alpha Series analyzers use high Si PiN diode detectors for eliminating radioactive isotopes. Typical applications span material identification for new product quality control and assurance, recycling of metals, and checking levels of impurities. 

) features a 50-µm polycapillary focused X-ray beam, coupled with a transmission X-ray detector, which reportedly allows for high-speed mapping of elemental concentration, while concurrently collecting an X-ray optical image of the internal structure of components. This, coupled with the dual-zoom, orthogonal camera, allows for graphic presentation of results using the built-in reporting features of the software. 

— Shimadzu EDXRF spectrometers are Si:Li or SDD spectrometers that incorporate primary filters in their standard configuration, and employ FP methods using these filters. The optional collimators and CCD reportedly allow for defect/small area analyses for rapid determination of contaminant particulates, while the large analysis chamber allows for the easy analysis of nonconventional XRF samples without preparation.  

—The Shimadzu XRD-7000 is a new Theta-Theta geometry diffractometer designed for powder diffraction, as well as sample analyses applications. The XD-7000 reportedly allows for the direct analyses of large structural components with no need to cut certain parts, thus leaving the local stress/strain environment unchanged.  

) Epsilon 5 EDXRF spectrometer is designed for low-level detection of heavy elements. Reportedly able to detect elements in solid, pressed-powder, granule, liquid, thin-film, and loose material samples, the Epsilon 5 is designed to support applications in geology, agriculture, land reclamation, fossil and secondary fuel usage, and catalyst production.  

The Vortex 60EX and 90EX silicon multi-cathode detectors from 

) reportedly have an active area of ~50 mm

, a resolution of 130 eV, and a count rate of > 1 Mcps. Designed for XRD/XRD/Synchrotron applications, the detectors can reportedly be cycled with cool down times of < 3 min.  

) is a 4kW WDXRF spectrometer with a thin end-window tube (30 µm) and the analytical capability for Be

. The tube-above ZSX Primus II reportedly integrates a newly designed sample-handling system, flexible changeover between helium and vacuum environments, and versatile, modular software. In addition to the components mentioned above, the ZSX Primus II features a mapping system and small sampling capabilities that can be field upgraded according to a user's changing needs. 

) is a polarized XRF analyzer for multi-element analysis of solids, powders, and liquids. The analyzer features C-force optics, which reportedly deliver levels of sensitivity for elements like Na, Mg, Al, Si, P, S and CL. Specific packages are available for the analysis of additives in oils, cement, slags, and refractories, as well as a "low S" version of the analyzer for the analysis of low sulfur in fuels. 

— SPECTRO also will showcase the latest models in its PHOENIX Series of compact, general-purpose analyzers. The PHOENIX Series XRF spectrometers are designed for both qualitative and quantitative non-destructive analyses of liquids, solids, powders, pastes, slurries, films, coatings, and other materials. Features include: optional tunable technology that reportedly permits optimum excitation of selected elements; automatic stabilization that reportedly eliminates drift and ensures smooth operation; a standardization feature to reduce calibration frequency; and optional data logging and networking software. 

On the heels of its recent acquisition of NITON LLC (

) will be showcasing both NITON and Thermo products. 

The NITON XLt 800 SY alloy analyzer features targeted X-ray tube excitation combined with a newly developed Super PiN detector, which reportedly improves minimum detection limits for chromium, copper, nickel, molybdenum, and other trace elements in alloy material. According to the company, these new features now enable the use of portable XRF as part of the Flow Accelerated Corrosion (FAC) — a source of problems in nuclear and fossil-fuel power plants — inspection protocol. 

— Thermo's ARL QUANT'X is an EDXRF instrument that utilizes a Peltier cooled Si(Li) detector and Digital Pulse Processing (DPP) technology for multi-element analysis of environmental and industrial applications, such as air particulates, soil contamination, toxic elements in plastic, and forensic science. According to the company, The ARL QUANT'X has been primarily developed to satisfy the analytical needs of laboratories dealing with unpredictable samples, government and military facilities, environmental laboratories monitoring urban and industrial air quality, and steel mills analyzing slags. 

— The ARL 9900 is an X-ray system that combines XRF and XRD technologies in one instrument. According to the company, the ARL 9900 has been developed to meet the increasing demand for chemical analysis in the metals industry, to satisfy the process-related analytical requirements in the cement industry, and to provide solutions for quality control in the copper and mining industries.  

) line of digital pulse processing electronics now includes the DXP-xMap and the microDXP. Designed for high-speed scanning applications, the DXP-xMAP contains four digital spectrometer channels in a compact PXI/cPCI module. Each channel reportedly offers efficient noise performance, resulting in energy dispersive X-ray measurements over the extended range of 0.2–100 keV. 

The microDXP is a complete low-power digital spectrometer that is reported to be the size of a credit card. It incorporates both a digital spectroscopy amplifier and MCA functionality, and is designed for both handheld and tabletop applications. 

A better understanding of the Rietveld method as applied to structural characterization and quantitative phase analysis will be emphasized. A brief introduction to the Rietveld method will start the workshop. 

This workshop covers recent progress in two-dimensional X-ray diffraction in terms of detector technology, geometry, and configuration of the two-dimensional diffractometer and various applications, such as phase ID, texture, stress, crystallinity, combinational screening, and thin film analysis. 

A Continuation of Rietveld Applications I—Beginner. 

Diffraction Analysis of Stress and Strain

This will introduce engineers to practical stress/strain analysis with diffraction. Basic theory, data acquisition and analysis tips, instrumental and statistical errors, as well as a few case studies will be covered. 

Line Profile Analysis by the Whole Powder Pattern Fitting

The workshop will focus on the determination of these properties by Rietveld refinement and other Whole Powder Pattern Fitting (WPPF) programs. A brief theoretical overview will be followed by a practical tutorial with recipes and examples of the determination of crystallite-size distribution and dislocation density in different materials. 

The basics of XRF sample preparation considerations starting with a discussion of the error involved in theoretical and practical instances that sample preparation can overcome or reduce, followed by an overview of sampling techniques and equipment needed for sampling in nature and in the lab will be addressed. This session will highlight the cleaning and polishing procedures needed to extend the life of the crucibles and molds. The effect of thickness, age, and degree of wear will be discussed with respect to length of service and performance. 

				A Continuation of Specimen Preparation I

 This workshop will concentrate on the practical aspects of Monte Carlo simulation for XRF applications. This will include how an individual particle or photon is tracked in a sample from emission to detection, how tallies pertinent to XRF predictions are obtained, statistical aspects of the Monte Carlo predictions, geometry considerations, random number generation in computers, cross section accessing, and variance reduction techniques. A review also will be given of the capabilities of the most popular general-purpose codes like MCNP for XRF use. 

Articles

Spectroscopy previews products and sessions for attendees to see and participate in at the 54th Annual Denver X-Ray Conference, to be held August 1–5 in Colorado Springs, CO.

DXC: The World's Leading Forum for X-Ray Materials Analysis

Scientists from the University of California working at Los Alamos National Laboratory (LANL, Los Alamos, NM) have developed, through the use of micro-X-ray fluorescence (MXRF), a novel technique that detects fingerprints based upon the chemical elements — salts excreted in sweat — mainly present in fingerprint residue. 

The MXRF technique, which is based upon elemental composition, detects the sodium, potassium, and chlorine elements in these salts, as well as many other elements, if they are present. These elements are detected as a function of their location on a surface, reportedly making it possible to see a fingerprint where the salts have been deposited in the patterns of fingerprints —the lines forensic scientists call friction ridges.

"It worked better than I would have guessed. I was afraid that the method's detection limits, typically parts-per-million levels, combined with loss in signal when restricting the X-ray beam to a small spot, would result in poor signal to noise and prevent the detection of trace levels of inorganic residue in fingerprints," explained Christopher Worley, a scientist at LANL, who led the project. "While this was true for some prints that were examined, others appeared to contain enough residue to detect the print friction ridges." 

When using the MXRF technique, a micro-focused X-ray beam irradiates the sample, and X-rays are emitted from the irradiated spot. The energies of the emitted X-rays correspond to the elements present in that spot, and the number of X-ray photons emitted correlates with the amount of that element present. Then, by moving the beam across the sample both horizontally and vertically, a two-dimensional image for a given element is collected depicting relative differences in concentration of that element dispersed across the surface. According to Worley, the time to acquire an image depends upon the amount of detectable material present in the fingerprint and the level of image pixel resolution desired.  

"For the majority of prints examined with the instrumentation in our labs, a typical analysis time was 10 to 20 hours – depending on the sample," Worley said. "The image was collected in an automated fashion, however, so this was just the waiting time before an image was complete. With the development of an instrument specifically designed to analyze elements commonly found in prints, such as those in body salts, I can envision the acquisition time being reduced to a few hours or less, perhaps much less with improvements in detector electronics." 

According to Worley, MXRF offers some advantages over traditional fingerprint techniques. First, MXRF does not require the application of powders, vapors, or chemicals, and uses a low power X-ray source, so it is nondestructive and does not alter the fingerprint. Because inorganic elements present in the print residue are detected by MXRF, the presence of certain elements could provide clues as to what an individual had been touching before leaving the fingerprint. Also, salts left on a surface in the pattern of a fingerprint should remain on the surface and detectable by MXRF indefinitely if left undisturbed. Finally, prints on multicolored backgrounds potentially can be difficult to detect by traditional methods, but the background color is irrelevant with MXRF. 

Despite these advantages, however, Worley stresses that he does not envision MXRF replacing those traditional fingerprint methods. 

"Dusting and chemical treatments will always be important in fingerprint detection. Dusting, in particular, is fast and easy to do at a crime scene," Worley said. "Traditional methods also detect organic constituents in fingerprints, but MXRF cannot detect the carbon, hydrogen, nitrogen, and oxygen present in organic compounds. I see MXRF complementing current methods rather than replacing them." 

And while it may make its mark in forensics, in the future, MXRF also could be used in two other important applications: homeland security and child-abduction cases. 

"Everyone has a unique fingerprint, and MXRF expands the ability to detect fingerprints in certain situations over current techniques," Worley said. "So I think this method could be useful in the detection of prints in terrorist-related cases. 

"Children's prints are typically difficult to detect by conventional means after aging," he continued. "However, inorganic components found in saliva or certain foods that might be present on a child's finger and left in a fingerprint pattern should be detectable for much longer periods of time, perhaps for many years." 

Departments

Using MXRF, researchers have developed a novel method that detects fingerprints through the salts that are excreted in sweat.

End of the Spectrum: Revealing More Than Meets the Eye

Lead is an element of great environmental significance due to the fact that it is both highly toxic and serves no known biological function. There are many different sources of lead contamination in the environment, which include but are not specific to the following: mining, ore processing, coal combustion, automobile battery production and disposal, and acid mine drainage. Thus, an understanding of the coordination of lead to natural materials is needed in order to have a better understanding of the potential risks and remediation of lead in the environment. To understand the behavior and the possible interactions of lead with natural materials including peat moss and humic materials, a number of different spectroscopic techniques have been employed.  

In the determination of the total lead content in different materials techniques such as atomic absorption (AA), graphite furnace atomic absorption spectroscopy (GFAAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), and ICP-mass spectrometry (MS) have been used. All of the aforementioned instrumental techniques have been utilized to determine the lead concentration in drinking water, plant materials, soils, and wastes (1–5). However, the total concentration of an element is only part of the story when dealing with environmental pollution. There are two other very important factors, which are for the most part neglected in the analysis of many environmental samples. These two factors are the coordination and the speciation of the elements in question. There are several instrumental techniques that can be employed to investigate the coordination of an element. For example, infrared (IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy are all techniques that can provide invaluable information on metal coordination. All of these techniques have been used to study lead coordination in biological materials, synthetic materials, and environmental samples with a high degree of certainty in the results obtained (including humic materials) (6–9). However, the speciation of an element in a sample requires either the use of chemical extraction, followed by high performance liquid chromatography (HPLC)-ICP-MS (or some other hyphenated speciation technique), electrochemical techniques, or the use of X-ray near edge structure (XANES) spectroscopy. XANES spectroscopy provides one major advantage over chemical extraction because in this technique, no sample pretreatment is required (10–13). XANES has been used to perform speciation studies of lead, iron, gold, copper, and manganese, among other elements in many different sample matrices (14–16). 

In this study we used a combination of ICP-OES and X-ray absorption (XAS) spectroscopy to study the effect of pH on the coordination of lead to humin and peat moss. Through studying the effects of pH on the binding one can develop a better understanding of the behavior of lead in the environment. In conjunction with studying the binding characteristics with changing pH in this study, we also investigated the effect of pH on the coordination and speciation of lead binding to humic materials. 

First, we ground the sphagnum peat moss to pass through an 80 mesh sieve. After sieving, the peat moss was washed with dilute acid (0.01 M HCl) to eliminate interference in the studies from acid -soluble materials and debris. Then, we extracted the humin from the sphagnum peat moss by adjusting the pH to 13.5 and constantly stirring the material for 48 h (17). After 48 h the base-adjusted peat moss was centrifuged at 3000 rpm for 5 min, and the supernatant was discarded and the humin fraction was lyophilized. The whole peat moss and the humin fractions then were pH adjusted to pH 2, 3, 4, 5, and 6. We pH adjusted the material by weighing out 500 mg of the humin or sphagnum peat moss and washing as previously mentioned. The materials then were diluted to give a slurry concentration of 5 mg/mL.  			

The humin and peat moss were pH adjusted initially to pH 2, at which point three triplicate 4-mL aliquots were extracted. The materials were then pH adjusted to pH 3 using dilute base (0.01 M NaOH) and three triplicate 4-mL aliquots of the slurry were again extracted. This pH adjustment and extraction procedure was repeated for the subsequent pHs under investigation. The pH-adjusted slurries then were centrifuged at 3000 rpm for 5 min and the supernatants were discarded. To each of the pH-adjusted materials, we added 4 mL of pH-adjusted 0.20 mM lead solution. Then, the lead–humin and lead–peat moss slurries were reacted for 1 h, along with control solutions containing only the 0.20 mM lead solutions. After one hour of reaction, the samples were centrifuged again and the supernatants were kept for metal analysis using ICP-OES. 

In our XAS studies, we first washed 2.0 g of either the humin or peat moss as mentioned earlier and the humin and peat moss were reacted with a 1000 ppm lead solution for 1 h at pHs of 3 and 4. After the reaction with lead, the samples were centrifuged at 3000 rpm and the supernatants were discarded. The solid materials were then lyophilized and packed into 1.0-mm aluminum plates with Kapton tape windows for analysis at SSRL (Stanford Synchrotron Radiation Laboratories, Stanford, CA). The operation parameters of the beam line included a 1.0-mm slit, energy of 3 GeV, a current range of 60–100 mA, and a Si 111 double crystal monochromator (with a Φ 0 orientation). The XAS spectra were recorded using the lead L

 line with an internal lead foil standard (E

 13.035 keV) at room temperature. The data treatment for the XAS was performed using the standard data analysis techniques and the WinXAS software (18).

 Figure 1. pH profile for 0.20 mM lead(II) binding to humin and peat moss from pH 2 to pH 6.			

Briefly, the data reduction consisted of averaging two or three spectra of each of the samples and model compounds. The energy calibration of the spectra was based upon the energy of the internal lead(0) foil using a second-degree derivative of the absorption edge. Then the samples were background corrected using polynomial fittings to the pre-edge and post-edge regions and normalized to one absorption unit. The XANES spectra were then extracted at this point in the data analysis by sectioning the XAS spectra from 12.95 keV to 13.15 keV. The LC-XANES fittings were then performed on these spectra using procedures previously published (16, 18). The spectra then were converted into wave vector space (or k space Å

) based upon the energy of the photoelectron ejected from the sample using a second-degree derivative of the sample edge. Subsequently, the EXAFS of the samples were extracted from the spectra using a spline of 4 knots and a k weight of 2, and Fourier transformed from 2.0 to 10.0 Å

. The spectra then were back transformed to include the first and second shells of neighboring atoms. Then, the spectra were fitted using FEFF 8.00 and least-squared fittings of the data obtained from the calculations of the FEFF program (19). The parameters calculated using the least-squared fittings of the back transforms were: the interatomic distances, the coordination numbers, and the Debye-Waller factors. The input files for the FEFF program were created using the ATOMS software from crystallographic data of the model compounds (20).

Figure 2. Lead LIII XANES (12.96-13.15 keV) of the reaction of lead(II) with peat moss and humin at pH 3 and pH 4.			

Figure 1 shows the pH dependency of lead binding to both the humin and the peat moss. As can be seen in this figure, there is a direct relationship between the increase in lead binding and the increase in pH. This behavior has been observed for lead binding to several different biological materials (15, 21–23). This binding trend has been explained in the literature to be related to the pK

s of the different carboxylic acid functional groups on the different materials, which for the most part they are protonated at pH values around 2 and become deprotonated at pHs in the 3.0–4.5 range. Thus, the binding increases drastically above pH 2 and then becomes stable at approximately pH 4. From the data presented in the pH profile we are proposing that the binding of the lead to both the humin and peat moss is occurring through different carboxyl groups present on the materials. 

Figure 3. Lead LIII XANES spectra (12.96-13.15 keV) of the lead model compounds showing the difference in the structures that occur in similar lead compounds.						

Figures 2 and 3 show the XANES of the lead reacted with the humin and peat moss and the model compounds, respectively. These figures show that lead binds as Pb(II) to both humin and peat moss. To corroborate this we also used LC-XANES fittings, which are shown in Table I. LC-XANES has been used to determine the geometry and the oxidation state of elements in a plethora of different materials. More specifically, the XANES analysis has been used to determine the oxidation state of manganese in soot emitted from engines, the oxidation state of chromium in coal, plants, and minerals, and the oxidation state of gold in different biological materials (16). As can be seen in Table I, the LC-XANES fittings of lead bound to the humin and peat moss most closely resembles the spectra of disodium lead(II) ethylenediaminetetraacetate ((Na

)), which has a four coordinate system in the solid state (24). As observed in this table, approximately 80–100% of the lead bound to both the humin and peat moss is found in the same configuration as lead(II) ethylenediaminetetraacetate. This suggests that Pb(II) is coordinating through carboxyl groups. This binding configuration has been suggested in the literature for the binding of lead to similar materials (21–23).

Table I. LC-XANES fittings of lead(II) reacted with humin and peat moss at pH 3 and pH 4.			

The Fourier-transformed EXAFS of the samples, with the exception of the lead bound to peat moss at pH 3 (which was too dilute to obtain EXAFS spectra), are presented in Figure 4. Also included in this figure is the Fourier-transformed EXAFS of the model compound disodium lead(II) ethylenediaminetetraacetate. The fittings of the backtransformed EXAFS are presented in Table II. As can be seen in Figure 4, the Fourier-transformed EXAFS of the samples and the model compound are very similar, indicating that the samples have practically the same coordination. The FEFF fittings of the samples in Table II show that the samples have approximately four oxygen atoms coordinated to the lead with interatomic distances ranging from 2.49 Å to 2.53 Å in the first shell, and in the second shell the interaction is with carbon atoms at approximately 2.90 Å. This coordination is very similar to that of the disodium lead(II) ethylenediaminetetraacetate which has four oxygen atoms at approximately 2.53 Å in the first coordination shell and two carbon atoms in the second coordination shell at approximately 3.23 Å The information obtained from our results of the XANES and EXAFS studies compliment each other, indicating that the coordination of the lead to humin and peat moss is four coordinate and occurs through oxygen atoms, most likely carboxyl groups.

Table II. FEFF fitting results of room temperature EXAFS of lead reacted with peat moss at pH 4, humin at pH 3 and pH 4, and the fitting of disodium lead EDTA (Na2Pb((O2C)4(CH2)6N2)).Note: CN denotes the coordination number, R is the interatomic distance, ÃÂ2 is the Debye-Waller factor, and S02 is a goodness of fit parameter.			

We determined from our XANES spectroscopy investigations that lead was present as lead(II) in both the humin and the sphagnum peat moss. In addition, the results of the LC-XANES fittings of the samples showed that the sample's atomic geometry most closely resembled that of disodium lead(II) ethylenediaminetetraacetate ((Na

)), which has a four coordinate system. The EXAFS studies showed that the lead was coordinated to four oxygen ligands with an interatomic distance of approximately 2.50 Å as was suggested from the XANES studies. Our ICP-OES studies showed a direct pH dependency for lead binding. The increase in lead binding above pH 2 further strengthens our premise that the functional group responsible for lead binding on both materials is the carboxyl group. 

Figure 4. Fourier-transformed EXAFS of lead reacted with different humic substances and a lead(II) model compound. (a) Lead(II) reacted with peat moss at pH 4. (b) Lead(II) reacted with humin at pH 4. (c) Lead(II) reacted with humin at pH 3. (d) Fourier-transformed EXAFS of Na2Pb(EDTA). Note that the EXAFS of the lead(II) reacted with peat moss at pH 3 was too dilute to obtain EXAFS spectra.										

The authors would like to acknowledge the National Institutes of Health (grant S06 GM8012-33) and the University of Texas at El Paso's Center for Environmental Resource Management (CERM) through funding from the Office of Exploratory Research of the U.S. Environmental Protection Agency (cooperative agreement CR-819849-01). They also would like to thank the Southwest Center for Environmental Research and Policy (SCERP) program for financial support, and the HBCU/MI, Environmental Technology Consortium, which is funded by the Department of Energy. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the Department of Energy, Office of Biological and Environmental Research, and by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program. Dr. Gardea-Torresdey acknowledges the Dudley family for the Endowed Research Professorship in Chemistry and also funding from the NIEHS (grant R01ES11367-01). 				

 is in the environmental science and engineering Ph.D. program, and 

 are with the department of chemistry, at the University of Texas at El Paso (El Paso, TX). 

 is with both the environmental science and engineering Ph.D. program and the department of chemistry at the university. E-mail: 

1. R.J VanCott, B.J. McDonald, and A.G. Seelos, 

2. M.E. Soares, M.L. Bastos, F. Carvalho, and M. Ferreira, 

3. A. Sattar, M. Wahid, and S.K. Durrani, 

6. M.R. St John Foreman, M.J. Plater, and J.M.S. Skakle, 

7. E.S. Claudio, M.A. Ter Horst, C.E. Forde, C.L. Stern, M.K. Zart, and H.A. Godwin, 

9. I.V. Smirnov, F.W. Kotch, I.J. Pickering, J.T. Davis, and R.H. Shafer, 

10. A.L. Nolan, H. Zhang, and M.J. McLaughlin, 

12. A. Al-Rashdan, D. Heitkemper, and J.A. Caruso, 

13. J. Lecomte, P. Mericam, and M. Astruc, 

16. J.G Parsons, M.V. Aldrich, and J.L. Gardea-Torresdey, 

17. J.L. Gardea-Torresdey, L. Tang, and J.M. Salvador, 

19. A.L. Ankudinov, B.J. Ravel, J.J. Rehr, and S.D. Conradson, 

In this study X-ray absorption was used to determine the effect of pH on the coordination of lead to humin and sphagnum peat moss. The authors determined the oxidation state and the coordination of lead to both humin and sphagnum peat moss using X-ray near edge structure and extended X-ray absorption fine structure spectroscopy. In addition, inductively coupled plasma optical emission spectroscopy was used to determine the amount of lead bound to the humin and sphagnum peat moss in the pH range 2–6.

Using X-Ray Absorption Spectroscopy to Study the Speciation and Coordination of Lead Binding to Humic Materials

hysical evidence often is distributed widely when a crime is being committed. The smaller these suspect materials are, the more likely they will be transported from the crime scene undetected. For example, when glass is shattered, the fragments created can be less than a few hundred micrometers (<0.2 mm). These fragments can become attached to clothing and embedded in shoes, "tagging" the criminal with a unique marker. Another important factor for the forensic investigator is being able to present data clearly and unambiguously in a court of law.  

Traditional techniques for the analysis of forensic samples such as glass fragments include the determination of a number of physical properties, including refractive index (RI), wet chemistry, scanning electron microscopy (SEM), X-ray fluorescence (XRF), and optical microscopy (1). Although these techniques offer a high degree of differentiation with traditional glass, modern glass has a greater degree of chemical and physical similarity. The major and minor elemental composition and RI values of these new materials are becoming more difficult to discriminate. The histograms in Figures 1a and 1b show RI values for flat glass extracted from an FBI database for the periods of 1964–1979 and 1980–1997, respectively (2). Comparison of the two charts clearly shows the reduced opportunity for inter-sample discrimination using this technique. 

 Figure 1. Distribution of RI values from FBI database of flat glasses: (a) 1964-1979 and (b) 1980-1997.			

Quadrupole inductively coupled plasma mass spectrometry (ICP-MS) enables the analysis of elements across the periodic table with very low detection limits. Typically, samples are introduced into an ICP-MS by aspirating a solution of the sample. Often, liquid samples require little preparation, but without a solid sampling accessory, solid samples need to be dissolved. This process is time-consuming and often requires the use of acid-dissolution reagents and additional sample preparation apparatus. Adding chemicals such as hydrofluoric acid to dissolve the sample can give rise to matrix-based interferences forming in the plasma, as well as being a potential source of contamination. Additionally, aqueous analysis typically has minimum requirements for sampling mass. A 200-µm glass shard, entangled in clothing, is an insufficient quantity for reliable aqueous results of the trace elements. In contrast, combining ICP-MS with the direct solid-sample introduction technique of laser ablation (LA) requires minimal sample preparation. LA-ICP-MS provides an excellent and relatively nondestructive technique for elemental analysis of forensic samples that are difficult to digest, or where small fragments or inclusions must be analyzed. LA-ICP-MS is amenable particularly to time-resolved analysis (TRA); enabling direct comparison of samples in three dimensions. Combining such flexible data-handling capabilities with in-situ solid sampling enhances the discriminating power of samples with similar visual, physical, and chemical characteristics, strengthening the analyst's ability to determine the similarities and differences within large data sets. These attributes, combined with low levels of detection and high precision, explain the increasing acceptance of LA-ICP-MS for investigation of forensic samples. 

Figure 2. Schematic of Nd: YAG LA system (fifth harmonic: 213 nm) for ICP-MS.										

The sample surface is irradiated with deep-UV (213 nm) output from a frequency-quintupled Nd:YAG (neodymium doped yttrium aluminum garnet crystal) laser, as shown in Figure 2. The high-intensity pulsed ultraviolet (UV) beam is focused onto the sample surface in an ablation chamber or cell, which is purged with argon. The UV beam diameter can be accurately set by 12 software-controlled apertures to produce variable "spot" sizes from <5 µm to 300 µm depending upon the application. The high power, short-wavelength 213-nm laser couples directly with the sample matrix, with high absorption efficiency, reducing or eliminating plasma induced fractionation. The resultant laser-induced aerosol is then transported to the inductively coupled plasma in an argon carrier gas stream where it is decomposed, atomized and ionized, before extraction into the mass spectrometer vacuum system for analysis. Calibration typically is undertaken using a well-characterized synthetic solid material, such as NIST 612 Trace Elements in Glass or other suitable solid certified reference material (CRM).

Figure 3. LA-ICP-MS analytical hardware:  A = New Wave Research UP-213 AI high energy Nd:YAG (fifth harmonic) 213 nm LA system; B = Agilent 7500s ICP-MS system.						

All the analyses for these experiments were undertaken using an Agilent 7500s ICP-MS system (Agilent Technologies, Inc., Palo Alto, CA). Solid sampling was achieved by introducing a stream of particles generated in situ by direct coupling of short UV laser with the sample surface into the ICP using a stable flow of argon gas. The laser system used was a New Wave Research (Fremont, CA) UP-213AI Nd:YAG operating at the fifth harmonic frequency (213 nm). Due to the nature of LA solid sampling (that is, revealing sample microheterogeneity) and the desire for high spatial and temporal resolution, in situ, the most suitable ICP-MS system for coupling to a laser ablation sample introduction device must be capable of capturing these transient events. The photograph in Figure 3 shows the system used for this study. Operating parameters for each experiment are given in Table I.

Table I. LA-ICP-MS operating conditions for the analysis of glass fragments.						

Calibration of the LA-ICP-MS system was carried out using a glass standard obtained from National Institute of Science and Technology (NIST USA): NIST SRM 612: 50 µg/g nominal trace element concentration. Matrix elements: Si (SiO

Table II. Results for NIST SRM 612 major and trace multielements analyzed as a sample compared to certified values.										

NIST soda lime glass standards (620, 621 and 1831) were used as surrogates for clear forensic glass samples. It was possible therefore to check the accuracy and the precision of the calculated values by comparing them with the certified values given for the major elements (Table II). Each sample was placed in a separate, sealed plastic bag and shattered. The small fragments (0.5 mm to 2 mm) were attached to a petrographic slide using double-sided graphite tape. This process was repeated for all the surrogates, as well as the three headlamp samples (Figure 4). 

Figure 4. Sample mounting of glass fragments.			

NIST 612 standard glass was used as a means of calibration and was analyzed repeatedly throughout the analysis procedure, bracketing each sample set. Each sample analysis was 115 s and consisted of a 20-s blank delay, a 60-s laser sampling period, followed by a 35-s washout period. Six repetitive data acquisitions over two separate rastor lines were collected for each sample. The data was imported into Glitter data reduction software (Macquarie University – GEMOC, Australia). Analyte and blank regions were defined within the Signal Selection Screen (Figure 5) and quantitative values were determined. The mean and standard deviation (SD) for each sample was then calculated (Table IIIa).

Figure 5. Signal selection screen, Glitter data reduction software. Traditionally used in geochronology, forensic data benefits from the ability of this software to enable easy isolation of changing data sets within a heterogeneous sample matrix. Each sample has its own associated blank, reducing memory effects.			

Three sets of automobile headlamp fragments and three sets of NIST soda lime glass standard fragments were chosen as forensic sample surrogates for this study. All glass samples were colorless to the naked eye. Time- resolved data was imported directly into Glitter data reduction software from the Agilent 7500s ICP-MS ChemStation software. Blank and sample integration areas were defined within the Signal Selection screen (Figure 5) and elemental concentrations were calculated using NIST 612 as the multi-element standard (Table III). Though the glass fragments were typically <1 mm, (Figure 4), elemental recoveries for the NIST certified values, information values, and literature values were very good and RSDs were <3% for many elements. NIST soda-lime glass standards 620 (flat glass), 621 (container glass), and 1831 (sheet glass) were used to emulate samples. The good agreement between the reference values and the returned values support the efficacy of the method used. Though the Mg values are consistently high by approximately 40%, the data suggests that this is likely due to a problem with the calibration standard either because of an inhomogeneous distribution of the element, or even possibly variation in the certified value. In this study, the literature value for Mg in NIST 612 was defined as 77.44 µg/g, 1σ = 30.15 µg/g (4). Another study published the NIST 612 Mg value as 64 µg/g, 1σ = 6 µg/g (5). 

Table IIIa. Glass data obtained from the analysis of standard glass fragments.										

Forensic data must be presented in the most accurate and clearly understandable format. Jurors with little or no scientific background must be able to decipher subtle chemical differences between evidentiary materials. Consequently, the glass data can be presented in two discriminating formats: numerically and stacked bar graphs (Tables IIIa and b and Figure 6). Stacked bar graphs are extremely effective in comparing different multicomponent data sets. We have therefore included the quantitative mean values with 1σ SD (Tables IIIa and b). Like gel electrophoresis, banding patterns within an elemental data set are easy to visualize and differentiate. Stacked bar charts can characterize clearly the elemental nature of a unique sample type. Notice the clear and even banding pattern of NIST 612 (first bar Figure 6). In NIST 612, all elements with the exception of Sr (76 ppm) are nominally at equal concentration (50 ppm), which the banding pattern clearly portrays. The NIST glass serves not only as a quantitative standard, but also demonstrates the effectiveness of the stacked bar chart in its ability to compare trace element constituents.

Figure 6. The mean data from Tables IIIa and IIIb are presented in a stacked bar chart format. This visual representation of the data aids data presentation in terms of clarity and relative simplicity.						

LA-ICP-MS is an effective tool for the analysis of a wide variety of forensic samples. This technique is particularly effective in overcoming the limitations associated with very small sample types or samples composed of chemically inert materials. Colorless glass fragments, indistinguishable to the naked eye and chemically identical at the ppm level, may be identified with good accuracy and precision, even at submillimeter dimensions. Due to the micro-destructive nature of this technique, forensic samples characterized by this method may also be available to alternative analysis if confirmation is required.

Table IIIb. Glass data obtained from headlight fragments.						

Often a clear visual representation of the data is produced using a suitable plotting program making it easier to discriminate samples with similar visual, physical, and chemical characteristics. By combining powerful, in situ microanalysis, low levels of detection, high precision, and clear and easily understandable diagrams, LA-ICP-MS is becoming an increasingly important weapon in the arsenal of forensic science. 

 is worldwide applications and marketing manager of laser ablation products at New Wave Research. E-mail: 

1. R.J. Watling, B.F. Lynch, and D. Herring, 

www.fbi.gov/hq/lab/fsc/backissu/jan2001/koons.htm

3. A. Dobney, W. Wiarda, P. de Joode, and G. van der Peijl, Forensic Tape Investigations, Presentation at 2nd EAFS Meeting, Sept. 24, 2000, Cracow. 

Laser ablation ICP-MS enables identification and comparison of physical crime-scene evidence. Discriminating elemental and isotopic differences of solid samples directly at the parts-per-billion level provides forensic scientists with a powerful analytical tool.

Spectroscopy-07-01-2005

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