1、Designation: E2926 13E2926 17Standard Test Method forForensic Comparison of Glass Using Micro X-rayFluorescence (-XRF) Spectrometry1This standard is issued under the fixed designation E2926; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONOne objective of a forensic glass examination is to compare glass specimens to determine if theyca
3、n be discriminated using their physical, optical or chemical properties (for example, color, refractiveindex (RI), density, elemental composition). If the specimens are distinguishable, except foracceptable and explainable variations, in any of these observed and measured properties, it may beconclu
4、ded that they did not originate from the same source of broken glass. If the specimens areindistinguishable in all of these observed and measured properties, the possibility that they originatedfrom the same source of glass cannot be eliminated. The use of an elemental analysis method such asmicro X
5、-ray fluorescence spectrometry (-XRF) yields high discrimination among sources of glass.1. Scope1.1 This test method is for the determination of major, minor, and trace elements present in glass fragments. The elementalcomposition of a glass fragment can be measured through the use of -XRF analysis
6、for comparisons of glass.1.2 This test method covers the application of -XRF using mono- and poly- capillary optics, and an energy dispersive X-raydetector (EDS).1.3 This test method does not replace knowledge, skill, ability, experience, education, or training and should be used inconjunction with
7、professional judgment.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this s
8、tandard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE2330 Test Method for Determination of Concentration
9、s of Elements in Glass Samples Using Inductively Coupled Plasma MassSpectrometry (ICP-MS) for Forensic Comparisons3. Summary of Test Method3.1 -XRF is a nondestructive elemental analysis technique based on the emission of characteristic X-rays following theexcitation of the specimen by an X-ray sour
10、ce using capillary optics. Simultaneous multi-elemental analysis is typically achievedfor elements of atomic number eleven or greater.3.2 Glass fragments usually do not require sample preparation prior to analysis by -XRF. Cleaning of specimens may beperformed to remove any surface debris.1 This tes
11、t method is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved June 15, 2013Feb. 1, 2017. Published July 2013February 2017. Originally approved in 2013. Last previous edition approved in
12、 2013 as E2926 13. DOI: 10.1520/E2926-13.10.1520/E2926-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.Thi
13、s document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editio
14、ns as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.3 Specimens are mounted and placed into the instr
15、ument chamber and subjected to an X-ray beam. The characteristic X-raysemitted by the specimen are detected using an energy dispersive X-ray detector and displayed as a spectrum of energy versusintensity.3.4 Qualitative analysis is accomplished by identifying elements present in the specimen based o
16、n their characteristic X-rayenergies.3.5 Semi-quantitative analysis is accomplished by comparing the relative area under the peaks of characteristic X-rays of certainelements.3.6 Spectral and elemental ratio comparisons of the glass specimens are conducted for source discrimination or association.4.
17、 Significance and Use4.1 -XRF provides a means of simultaneously detecting major, minor, and trace elemental constituents in small glass fragmentssuch as those frequently examined in forensic case work. It can be used at any point in the analytical scheme without concern forchanging sample shape or
18、sample properties, such as RI, due to its totally nondestructive nature.4.2 Limits of detection (LOD) are dependent on several factors, including instrument configuration and operating parameters,sample thickness, and atomic number of the individual elements.Typical LODs range from parts per million
19、 (gg-1) to percent (%).4.3 -XRF provides simultaneous qualitative analysis for elements having an atomic number of eleven or greater. Thismulti-element capability permits detection of elements typically present in glass such as magnesium (Mg), silicon (Si), aluminum(Al), calcium (Ca), potassium (K),
20、 iron (Fe), titanium (Ti), strontium (Sr), and zirconium (Zr), as well as other elements that maybe detectable in some glass by -XRF (for example, molybdenum (Mo), selenium (Se), or erbium (Er) without the need for apredetermined elemental menu.4.4 -XRF comparison of glass fragments provides additio
21、nal discrimination power beyond that of RI or density comparisons,or both, alone.4.5 The method precision should be established in each laboratory for the specific conditions and instrumentation in thatlaboratory.4.6 When using small fragments having varying surface geometries and thicknesses, preci
22、sion deteriorates due to take-off-angleand critical depth effects. Flat fragments with thickness greater than 1.5 mm do not suffer from these constraints, but are not alwaysavailable as questioned specimens received in casework. As a consequence of the deterioration in precision for small fragmentsa
23、nd the lack of appropriate calibration standards, quantitative analysis by -XRF is not typically used.4.7 Appropriate sampling techniques should be used to account for natural heterogeneity of the material, varying surfacegeometries, and potential critical depth effects.4.8 Inductively Coupled Plasm
24、a-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrom-etry (ICP-MS) may also be used for trace elemental analysis of glass and offer lower minimum detection levels and the ability forquantitative analysis. However, these methods are destructive, and require larger sa
25、mple sizes and much longer sample preparationtimes (Test Method E2330).4.9 Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) uses comparable specimen sizes to thoseused for -XRF but offers better LODs, quantitative capability and less analysis time. LA-ICP-MS drawbacks are grea
26、terinstrument cost and complexity of operation.4.10 Scanning Electron Microscopy with EDS (SEM-EDS) is also available for elemental analysis, but it is of limited use forforensic glass source discrimination due to poor detection limits for higher atomic number elements present in glass at traceconce
27、ntration levels. However, discrimination of sources that have indistinguishable RIs and densities may be possible.5. Interferences5.1 Peak overlaps occur in various regions of the EDS spectrum.spectrum (1).3 In glass, such interferences include the overlapof characteristic X-ray lines (for example,
28、Ti K-series and Ba L-series), sum peaks, primary X-ray source excitation peaks (forexample, Rh), and escape peaks. In general, automated deconvolution algorithms are included in data processing software thatadequately address such overlaps. EDS spectra shall be manually inspected to ensure that pote
29、ntial peak overlaps are consideredand addressed.3 Available from X-ray Transition Energies Database, National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070,http:/physics.nist.gov/PhysRefData/XrayTrans/Html/search.html.3 Latkoczy, C., Becker, S.
30、Ducking, M., Gunther, D., Hoogewerff, J.A., Almirall, J., Buscaglia, J., Dobney, A., Koons, R., Montero, S., van der Peijl, G., Stoecklein, W.,Trejos, T., Watling, J.R., and Zdanowicz, V., “Development and evaluation of a standard method for the quantitative determination of elements in float glass
31、samples byLA-ICP-MS,” Journal of Forensic Sciences, Vol 50, No. 6, 2005, pp. 13271341.The boldface numbers in parentheses refer to a list of references at the end of this standard.E2926 1726. Apparatus6.1 A -XRF spectrometer with an EDS detector is employed. Most commercial-grade -XRF systems with E
32、DS detectorsshould be adequate for forensic analysis of glass. The -XRF system must, however, meet the following performancespecifications:6.1.1 The spot size(s) must be within the range(s) of approximately 10 m to 2 mm; the spot size used may be adjustable todifferent sizing for instruments with ap
33、propriate optics.6.1.2 The instrument must be capable of operating at an accelerating voltage of 35 kV or greater.6.1.3 The EDS detector must be capable of a resolution that is typically less than 180 eV, measured as the full width at half themaximum height of the Mn K peak; better resolutions will
34、provide improved discrimination of adjacent or overlapping peaks,or both.6.1.4 A calibrated, scaled display of energy units (keV) and the ability to identify and label X-ray lines is required for the EDSsystem.6.2 Energy Calibration MaterialCapable of calibrating the EDS detector at both the low (6
35、keV) X-rayspectral regions.6.3 An X-ray source that does not yield significant spectral interferences with the characteristic X-ray lines for the elementstypically found in glass is required. Several X-ray sources are available; a rhodium X-ray source is preferred for appropriateexcitation energy an
36、d minimal spectral interferences for elements in glass. Other X-ray sources such as Mo X-ray tubes causeinterferences with discriminating elements such as Zr.6.4 A vacuum sample chamber, sample stage, and visualization system are required.6.5 The sample holder, sample support film, and mounting mate
37、rial (for example, adhesive with low trace elements) mustprevent background interferences.7. Hazards7.1 The X-ray sources emit radiation when energized. For operator safety, appropriate shielding and safety interlocks must bein place and operational.8. Calibration and Standardization8.1 ApparatusThe
38、 instrument must be optimized as in accordance with manufacturers instruction.8.1.1 Energy CalibrationcalibrateCalibrate the X-ray energy scale to characteristic X-ray emission lines by either measuringthe centroid energy of a low- (6 keV) energy peak or by using software provided by the instrumentm
39、anufacturer. For example, the aluminum (1.486 keV) and copper (Cu) (8.040 keV) K-X-ray energy lines may be used.8.1.2 Stage CalibrationFor automated or multiple point analysis, initialize the stage position to assure that the stagecoordinates accurately reflect the stage position.8.1.3 Optical Align
40、ment:8.1.3.1 Align X-ray optics to obtain the maximum count rate.8.1.3.2 Align visualization optics to ensure that the visual target area coincides with the X-ray beam position.8.1.4 Spot Size MeasurementDetermine spot size of the X-ray beam at the focal point of the visualization optics. Forinstrum
41、ents with continuous variable spot size options, determine the spot size at multiple settings and interpolate the others.8.1.5 Reference MaterialsAnalyze a glass certified reference material (CRM) (for example, NIST SRM 1831) to verify thecalibration of X-ray energy lines for elements present in gla
42、ss and determine if the instrument response is within acceptable limits.Measure this glass CRM using the same analysis parameters as the glass specimens. Use this reference glass sample to normalizeelement ratios for interlaboratory comparisons, intralaboratory data collection from different analyti
43、cal runs, and databasingapplications to improve precision.8.1.6 BlanksCollect a spectrum of a specimen devoid of elements having an atomic number of 11 or greater, such as the plasticstage plate or an area of the support material having no glass present. Record any system peaks present for future re
44、ference.8.2 Quality Assurance:8.2.1 The performance of the instrument must be monitored routinely and the frequency and tolerances should be set by eachlaboratory.8.2.1.1 Check the system calibration prior to the performance of an analysis.8.2.1.2 Check the performance of the X-ray source using a kn
45、own element standard (for example, Cu). Maximum counts forthe system should be obtained utilizing system operating parameters established by the laboratory. Maximum counts should notshow appreciable drift from acceptable parameters established by the laboratory or analyst for this procedure (10 % to
46、lerance isrecommended).8.2.2 Demonstrate that Ti and Sr have LOD in a soda-lime glass matrix of 75 ppm or less (as described in 11.1) for theinstrumental parameters used for collection of spectra from the glass specimens. NIST SRM 1831 is a suitable sample for thispurpose.E2926 1739. Procedure9.1 Sp
47、ecimen Preparation:9.1.1 Examine glass fragments using stereomicroscopy to determine an appropriate preparation method for the specimen.9.1.2 If necessary, clean the specimen to remove any surface contamination. Cleaning may include washing specimens withsoap and water, with or without ultrasonicati
48、on, and rinsing in deionized water, followed by rinsing in acetone, methanol, orethanol, and drying. Soaking in various concentrations of nitric acid for 30 minutes or longer, rinsing with deionized water andethanol, and drying prior to analysis removes most surface contamination without affecting t
49、he measured concentrations ofelements inherent in the glass. However, the use of nitric acid may remove any surface coating that may be present.9.1.3 Mount the specimen for analysis.9.1.3.1 The specimen mounting technique depends on the sample size and shape, beam size, X-ray fluorescence spectrometerchamber design and purpose of the examination.9.1.3.2 Raise specimens off the surface of the stage for analysis using an X-ray transparent sample holder or supportive X-rayfilm, or both. This positioning reduces X-ray scatter off of the surface of the st
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