1、Designation: E2926 13Standard 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 revision,
2、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 theycan be dis
3、criminated 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 beconcluded that
4、 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-ray flu
5、orescence 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. Theelemental composition of a glass fragment can be measuredthrough the use of -XRF analysis for compar
6、isons of glass.1.2 This test method covers the application of -XRF usingmono- and poly- capillary optics, and an energy dispersiveX-ray detector (EDS).1.3 This test method does not replace knowledge, skill,ability, experience, education, or training and should be used inconjunction with professional
7、 judgment.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to esta
8、blish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE2330 Test Method for Determination of Concentrations ofElements
9、in Glass Samples Using Inductively CoupledPlasma Mass Spectrometry (ICP-MS) for Forensic Com-parisons3. Summary of Test Method3.1 -XRF is a nondestructive elemental analysis techniquebased on the emission of characteristic X-rays following theexcitation of the specimen by an X-ray source using capil
10、laryoptics. Simultaneous multi-elemental analysis is typicallyachieved for elements of atomic number eleven or greater.3.2 Glass fragments usually do not require sample prepara-tion prior to analysis by -XRF. Cleaning of specimens may beperformed to remove any surface debris.3.3 Specimens are mounte
11、d and placed into the instrumentchamber and subjected to an X-ray beam. The characteristicX-rays emitted by the specimen are detected using an energydispersive X-ray detector and displayed as a spectrum ofenergy versus intensity.3.4 Qualitative analysis is accomplished by identifyingelements present
12、 in the specimen based on their characteristicX-ray energies.3.5 Semi-quantitative analysis is accomplished by compar-ing the relative area under the peaks of characteristic X-rays ofcertain elements.3.6 Spectral and elemental ratio comparisons of the glassspecimens are conducted for source discrimi
13、nation or associa-tion.1This test method is under the jurisdiction ofASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved June 15, 2013. Published July 2013. DOI: 10.1520/E2926-13.2For referenced ASTM standards, vis
14、it the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-29
15、59. United States14. Significance and Use4.1 -XRF provides a means of simultaneously detectingmajor, minor, and trace elemental constituents in small glassfragments such as those frequently examined in forensic casework. It can be used at any point in the analytical schemewithout concern for changin
16、g sample shape or sampleproperties, such as RI, due to its totally nondestructive nature.4.2 Limits of detection (LOD) are dependent on severalfactors, including instrument configuration and operatingparameters, sample thickness, and atomic number of theindividual elements. Typical LODs range from p
17、arts permillion (gg-1) to percent (%).4.3 -XRF provides simultaneous qualitative analysis forelements having an atomic number of eleven or greater. Thismulti-element capability permits detection of elements typi-cally present in glass such as magnesium (Mg), silicon (Si),aluminum (Al), calcium (Ca),
18、 potassium (K), iron (Fe), tita-nium (Ti), strontium (Sr), and zirconium (Zr), as well as otherelements that may be detectable in some glass by -XRF (forexample, molybdenum (Mo), selenium (Se), or erbium (Er)without the need for a predetermined elemental menu.4.4 -XRF comparison of glass fragments p
19、rovides addi-tional discrimination power beyond that of RI or densitycomparisons, or both, alone.4.5 The method precision should be established in eachlaboratory for the specific conditions and instrumentation inthat laboratory.4.6 When using small fragments having varying surfacegeometries and thic
20、knesses, precision deteriorates due to take-off-angle and critical depth effects. Flat fragments with thick-ness greater than 1.5 mm do not suffer from these constraints,but are not always available as questioned specimens receivedin casework.As a consequence of the deterioration in precisionfor sma
21、ll fragments and the lack of appropriate calibrationstandards, quantitative analysis by -XRF is not typically used.4.7 Appropriate sampling techniques should be used toaccount for natural heterogeneity of the material, varyingsurface geometries, and potential critical depth effects.4.8 Inductively C
22、oupled Plasma-Optical Emission Spec-trometry (ICP-OES) and Inductively Coupled Plasma-MassSpectrometry (ICP-MS) may also be used for trace elementalanalysis of glass and offer lower minimum detection levels andthe ability for quantitative analysis. However, these methodsare destructive, and require
23、larger sample sizes and muchlonger sample preparation times (Test Method E2330).4.9 LaserAblation-Inductively Coupled Plasma-Mass Spec-trometry (LA-ICP-MS) uses comparable specimen sizes tothose used for -XRF but offers better LODs, quantitativecapability and less analysis time. LA-ICP-MS drawbacks
24、aregreater instrument 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 usefor forensic glass source discrimination due to poor detectionlimits for higher atomic number elements present in glass attrace
25、 concentration levels. However, discrimination of sourcesthat have indistinguishable RIs and densities may be possible.5. Interferences5.1 Peak overlaps occur in various regions of the EDSspectrum.3In glass, such interferences include the overlap ofcharacteristic X-ray lines (for example, Ti K-serie
26、s and BaL-series), sum peaks, primary X-ray source excitation peaks(for example, Rh), and escape peaks. In general, automateddeconvolution algorithms are included in data processingsoftware that adequately address such overlaps. EDS spectrashall be manually inspected to ensure that potential peakove
27、rlaps are considered and addressed.6. Apparatus6.1 A -XRF spectrometer with an EDS detector is em-ployed. Most commercial-grade -XRF systems with EDSdetectors should be adequate for forensic analysis of glass. The-XRF system must, however, meet the following performancespecifications:6.1.1 The spot
28、size(s) must be within the range(s) ofapproximately 10 m to 2 mm; the spot size used may beadjustable to different sizing for instruments with appropriateoptics.6.1.2 The instrument must be capable of operating at anaccelerating voltage of 35 kV or greater.6.1.3 The EDS detector must be capable of a
29、 resolution thatis typically less than 180 eV, measured as the full width at halfthe maximum height of the Mn K peak; better resolutions willprovide improved discrimination of adjacent or overlappingpeaks, or both.6.1.4 A calibrated, scaled display of energy units (keV) andthe ability to identify an
30、d label X-ray lines is required for theEDS system.6.2 Energy Calibration MaterialCapable of calibratingthe EDS detector at both the low (6 keV)X-ray spectral regions.6.3 An X-ray source that does not yield significant spectralinterferences with the characteristic X-ray lines for the ele-ments typica
31、lly found in glass is required. Several X-raysources are available; a rhodium X-ray source is preferred forappropriate excitation energy and minimal spectral interfer-ences for elements in glass. Other X-ray sources such as MoX-ray tubes cause interferences with discriminating elementssuch as Zr.6.4
32、 A vacuum sample chamber, sample stage, and visual-ization system are required.6.5 The sample holder, sample support film, and mountingmaterial (for example, adhesive with low trace elements) mustprevent background interferences.3Available from X-ray Transition Energies Database, National Institute
33、ofStandards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD20899-1070, http:/physics.nist.gov/PhysRefData/XrayTrans/Html/search.html.E2926 1327. Hazards7.1 The X-ray sources emit radiation when energized. Foroperator safety, appropriate shielding and safety interlocksmust be in pl
34、ace and operational.8. Calibration and Standardization8.1 ApparatusThe instrument must be optimized as inaccordance with manufacturers instruction.8.1.1 Energy Calibrationcalibrate the X-ray energy scaleto characteristic X-ray emission lines by either measuring thecentroid energy of a low- (6 keV) e
35、nergypeak or by using software provided by the instrument manu-facturer. 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 pointanalysis, initialize the stage position to assure that the stagecoordinates
36、 accurately reflect the stage position.8.1.3 Optical Alignment:8.1.3.1 Align X-ray optics to obtain the maximum countrate.8.1.3.2 Align visualization optics to ensure that the visualtarget area coincides with the X-ray beam position.8.1.4 Spot Size MeasurementDetermine spot size of theX-ray beam at
37、the focal point of the visualization optics. Forinstruments with continuous variable spot size options, deter-mine the spot size at multiple settings and interpolate theothers.8.1.5 Reference MaterialsAnalyze a glass certified refer-ence material (CRM) (for example, NIST SRM 1831) to verifythe calib
38、ration of X-ray energy lines for elements present inglass and determine if the instrument response is withinacceptable limits. Measure this glass CRM using the sameanalysis parameters as the glass specimens. Use this referenceglass sample to normalize element ratios for interlaboratorycomparisons, i
39、ntralaboratory data collection from differentanalytical runs, and databasing applications to improve preci-sion.8.1.6 BlanksCollect a spectrum of a specimen devoid ofelements having an atomic number of 11 or greater, such as theplastic stage plate or an area of the support material having noglass pr
40、esent. Record any system peaks present for futurereference.8.2 Quality Assurance:8.2.1 The performance of the instrument must be monitoredroutinely and the frequency and tolerances should be set byeach laboratory.8.2.1.1 Check the system calibration prior to the perfor-mance of an analysis.8.2.1.2 C
41、heck the performance of the X-ray source using aknown element standard (for example, Cu). Maximum countsfor the system should be obtained utilizing system operatingparameters established by the laboratory. Maximum countsshould not show appreciable drift from acceptable parametersestablished by the l
42、aboratory or analyst for this procedure (10% tolerance is recommended).8.2.2 Demonstrate that Ti and Sr have LOD in a soda-limeglass matrix of 75 ppm or less (as described in 11.1) for theinstrumental parameters used for collection of spectra from theglass specimens. NIST SRM 1831 is a suitable samp
43、le for thispurpose.9. Procedure9.1 Specimen Preparation:9.1.1 Examine glass fragments using stereomicroscopy todetermine an appropriate preparation method for the specimen.9.1.2 If necessary, clean the specimen to remove any surfacecontamination. Cleaning may include washing specimens withsoap and w
44、ater, with or without ultrasonication, and rinsing indeionized water, followed by rinsing in acetone, methanol, orethanol, and drying. Soaking in various concentrations of nitricacid for 30 minutes or longer, rinsing with deionized water andethanol, and drying prior to analysis removes most surfacec
45、ontamination without affecting the measured concentrationsof elements inherent in the glass. However, the use of nitricacid 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 thesample size and shape, beam size,
46、 X-ray fluorescence spec-trometer chamber design and purpose of the examination.9.1.3.2 Raise specimens off the surface of the stage foranalysis using an X-ray transparent sample holder or support-ive X-ray film, or both. This positioning reduces X-ray scatteroff of the surface of the stage and, hen
47、ce, improves samplesignal-to-noise. Because analysis is performed under vacuum,ensure that specimens retain their position on the sample holderby securing with adhesive. Prior to analysis, analyze a smallamount of the adhesive to determine the presence of anyelements that could interfere with those
48、in the specimen. Whensmall amounts of adhesive are used and beam overspill (X-raybeam extending beyond the perimeter of the specimen) isavoided, little to no interference from the adhesive will beobserved.9.1.3.3 Position specimens to present as flat a surface aspossible to the impinging excitation
49、X-ray beam. If necessary,use a small amount of adhesive to facilitate this positioning.9.1.3.4 For comparisons, glass specimen should be of simi-lar size, shape, and thickness to each other. For full thicknessfragments of float glass, comparisons should be made betweensimilar surface types (for example, non-float surface to non-float surface).9.1.4 Place sample(s) in the instruments analysis chamber.For automated multiple point analyses, it may be necessary tosecure the sample/sample holder to the instrument stage.9.1.5 Evacuate the chamber; samples shoul
