1、Designation: E1588 101Standard Guide forGunshot Residue Analysis by Scanning ElectronMicroscopy/Energy Dispersive X-Ray Spectrometry1This standard is issued under the fixed designation E1588; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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.1NOTESections 7.1.5.2 and 7.2.1.2 were editorially corrected in July 2010.1. Scope1.1 This guide covers the a
3、nalysis of gunshot residue (GSR)by scanning electron microscopy/energy-dispersive X-rayspectrometry (SEM/EDS) by manual and automated methods.The analysis may be performed manually, with the operatormanipulating the microscope controls and the EDS systemsoftware, or in an automated fashion, where so
4、me amount ofthe analysis is controlled by pre-set software functions.1.2 Since software and hardware formats vary among com-mercial systems, guidelines will be offered in the most generalterms possible. For proper terminology and operation, consultthe SEM/EDS system manuals for each system.1.3 The v
5、alues stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 establish appro-priate
6、safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Summary of Practice2.1 From the total population of particles collected, thosethat are detected by SEM to be within the limits of certainparameters (for example, atomic number, size, or shape) area
7、nalyzed by EDS (1-3).2Typically, particles composed of highmean atomic number elements are detected by their SEMbackscattered electron signals and an EDS spectrum is ob-tained from each. The EDS spectrum is evaluated for constitu-ent elements that may identify the particle as being consistentwith or
8、 characteristic of GSR, or both.3. Significance and Use3.1 This document will be of use to forensic laboratorypersonnel who are involved in the analysis of GSR samples bySEM/EDS (4).3.2 SEM/EDS analysis of GSR is a non-destructive methodthat provides (5, 6) both morphological information and theelem
9、ental profiles of individual particles.3.3 Particle analysis contrasts with bulk sample methods,such as atomic absorption spectrophotometry (AAS) (7), neu-tron activation analysis (NAA) (8), inductively coupled plasmaatomic emission spectrometry (ICP-AES), and inductivelycoupled plasma mass spectrom
10、etry (ICP-MS), where thesampled material is dissolved or extracted prior to the deter-mination of total element concentrations, thereby sacrificingmorphological information and individual particle identifica-tion.3.4 X-ray fluorescence spectrometry (XRF) is a techniquethat has been used to map the p
11、lacement and distribution ofGSR particles surrounding bullet holes in order to establishshooting distances (9). Unlike the solution-based bulk methodsof analysis, XRF is non-destructive; however, XRF still doesnot provide morphological information and is incapable ofindividual GSR particle identific
12、ation.4. Sample Preparation4.1 Once the evidence seal is broken, care should be takenso that no object touches the surface of the adhesive SEM/EDSsample collection stub and that the stub is not left uncoveredany longer than is reasonable for transfer, mounting, orlabeling.4.2 Label the sample collec
13、tion stub in such a manner that itis distinguishable from other sample collection stubs withoutcompromising the sample; for example, label the bottom orside of the stub.1This guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E3
14、0.01 on Criminalistics.Current edition approved June 1, 2010. Published June 2010. Originallyapproved in 1994. Last previous version approved in 2008 as E1588 08. DOI:10.1520/E1588-10.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.1Copyright ASTM Intern
15、ational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 If a non-conductive adhesive was used in the samplecollection stub, the sample will need to be coated to increase itselectrical conductivity, unless an environmental SEM orvariable-pressure/low-vacuum SE
16、M is used for the analysis.Carbon is a common choice of coating material, since it willnot interfere with X-ray lines of interest. For high-vacuumSEM, coat the sample sufficiently to eliminate charging of thesample.5. Sample Area5.1 Sample collection stubs for SEMs typically come in oneof two diamet
17、ers: 12.7 mm or 25.4 mm, which yield surfaceareas of 126.7 mm2and 506.7 mm2respectively.5.2 Manual analysis of the total surface area of the stub isprohibitively time-consuming. Because the particles are col-lected onto an adhesive surface in a random manner and theparticles do not tend to cluster,
18、it is reasonable to analyze aportion of the stub surface by employing an appropriatesampling and analytical protocol (6, 10).5.3 Automated SEM/EDS analysis can enable data collec-tion from nearly the entire surface area of the sample collectionstub. Due to the disparity between the shape of the samp
19、lecollection stub (round) and the SEM field of view search area(square or rectangular), analysis of 100 % of the samplecollection area may not be possible in some systems.5.3.1 Analysis of the maximum allowable surface area ofthe sample is recommended, however, many automated sys-tems can be program
20、med to terminate the analysis of a stub orseries of stubs once a pre-established number of particles withspecified classification(s) have been detected. The decision asto how many particles satisfy the requirements of a particularcase is a matter for the analyst to decide but should be subjectto gui
21、delines set out in the laboratorys standard operatingprocedures.6. Instrument Requirements and Operation6.1 General:6.1.1 Most commercial-grade SEM/EDS systems should beadequate for GSR analysis.6.1.2 Automated data collection of GSR involves someportion of the data collection being controlled by pr
22、e-setsoftware functions. The extent to which the SEM and EDSsystems communicate and are integrated varies according tothe manufacturers involved and the capabilities of thehardware/software architecture.6.2 Scanning Electron Microscope (SEM):6.2.1 The SEM, operating in the backscattered electronimag
23、ing mode, must be capable of detecting particles down toat least 0.5 m in diameter.6.2.2 The SEM must be capable of an accelerating voltageof at least 20 kV.6.2.3 Automated SEM/EDS systems include: communica-tion and control between the SEM and EDS system, and amotorized stage with automated stage c
24、ontrol. The systemshould have the ability to recall stage locations of particles forverification and software for particle recognition.6.3 Energy Dispersive Spectrometry (EDS):6.3.1 The detectors resolution should be better (less) than150 eV, measured as the full width at half the maximum heightof t
25、he Mn Ka peak.6.3.2 At a minimum, the EDS spectrum should be acquiredat 20 eV per channel.6.3.3 Display of the EDS output must encompass the X-raylines of analytical utility, with a minimum range of 015 keV.6.3.4 Automated systems will also include software capableof acquiring X-ray spectra for a sp
26、ecified collection time ortotal X-ray counts.6.3.5 It is desirable that the spectrum obtained from theanalysis of each particle of interest be stored.At a minimum, anautomated system must be capable of storing all of the particlelocation coordinates.6.4 Sample Placement:6.4.1 Record the positions of
27、 the stubs (sample andstandard/reference stubs) on the SEM stage when the samplesare inserted.6.4.2 If it is anticipated or required that additional analyseswill be needed, it is desirable that the stub can be returned tothe same orientation as before its removal. This may consist ofmarking the side
28、 of each stub and aligning it with marks on themicroscope stage or by having stubs that fit into the stage inonly one position (for example, stubs with a pin that is ahalf-circle in cross section).6.5 Detection and Calibration:6.5.1 Particles of GSR are detected by their backscatteredelectron signal
29、 intensity. The absolute signal intensity that aparticle produces is related to the electron beam current, meanatomic number, and size of the particle (for particle sizes on theorder of the beam diameter). Particles whose mean atomicnumbers are high will appear brighter than those of lower meanatomi
30、c number composition.As the beam current increases, theamount of signal each particle produces also increases (11).6.5.2 The brightness and contrast settings (low and highthresholds) of the backscattered electron detector system de-termine the limits of detection and discrimination of particleswhose
31、 mean atomic number exceed the minimum thresholdsetting but fall below the maximum threshold setting. Thresh-old settings for the backscattered electron signal should bedone with a suitable reference sample of known origin (oftensupplied by the EDS manufacturer) or pure element standardsat the same
32、parameters that will be used for the sampleanalysis. This calibration sample should, if possible, be in themicroscope chamber at the same time as the samples to beanalyzed.6.5.3 The backscattered electron detectors brightness andcontrast should be set to include the high atomic numberparticles of in
33、terest and exclude low atomic number particlesthat are not of interest. Typically, high contrast and lowbrightness settings provide an adequate range between thresh-old limits for ease of detection. If the beam current is changedor drifts, the brightness and contrast threshold limits, whichwere base
34、d on the previous beam current, may no longer becompatible with the new conditions and should be readjusted.The beam current may be measured with a Faraday cup, aE1588 1012specimen current meter, or monitored by comparing the inte-grated counts within the same peak in sequentially collectedspectra f
35、rom a known standard.6.6 Quality Control:6.6.1 When conducting automated analysis of GSR, specialmeasures have to be chosen in order to meet common qualitymanagement demands. Therefore, as minimum conditions:6.6.1.1 Establish a protocol to confirm optimum instrumentoperation parameters on a routine
36、basis.6.6.1.2 Monitor the EDS X-ray energy calibration and SEMbeam current stability regularly. This may be facilitated by theuse of appropriate standards or reference samples, or both.6.6.1.3 Analyze a reference sample (positive control) withparticles of known size, range, and composition at regula
37、rintervals in order to test the accuracy of particle detection andidentification, whether by automated or manual analysis. It isrecommended that a reference sample has been prepared andmounted in a manner comparable to the collection method inuse by the submitting agency. The reference sample may be
38、 asample of GSR from a known source (caliber of weapon,ammunition manufacturer, number of rounds fired, collectedarea from shooter, or a synthetic GSR standard). Additionalenvironmental particles may be added to ensure the inclusionor exclusion of particular classes of particles. Alternatively, asyn
39、thetic, simulated-GSR reference sample may be used forthis purpose. The frequency of analysis of this sample is amatter for the analyst to decide and is subject to guidelines setout in the laboratorys standard operating procedures.6.6.1.4 The incorporation of environmental or controlsamples into the
40、 analytical protocol is recommended in order tomonitor the cleanliness of the sampling or analytical system, orboth. An environmental sample may be prepared in a numberof ways: for example, it may be an unused stub that has beenprepared contemporaneously with the questioned samples or asample taken
41、from the sampling or analytical environment(exposed to the air or as a direct sampling of clean workspace),or both.7. Data Analysis7.1 Definition and Classification:7.1.1 Morphology:7.1.1.1 GSR particles detected and analyzed using thismethod are often spheroidal, noncrystalline particles between0.5
42、 m and 5.0 m in diameter; the remainder are irregular inshape or vary from 1 to 100+ m in size, or both, (5, 12, 13).In general, it is not consistent with the mechanisms of GSRformation to find particles with crystalline morphology. How-ever, such particles have occasionally been observed in knownpr
43、imer GSR residues. Since morphology can vary greatly, itshould never be considered as the only criterion for identifi-cation of GSR.7.1.2 Elemental Composition:7.1.2.1 The elemental composition is the most diagnosticproperty to determine if a particle may be GSR (14). Whenappropriate, the elemental
44、composition of the recovered par-ticulate can be compared with case-specific known sourceitems, such as the recovered weapon, cartridge cases, orvictim-related items.7.1.2.2 Occasionally, GSR particles with apparent unusualelemental compositions may be encountered in case work. Inthis circumstance,
45、the elemental compositions of these par-ticles should be compared to case-specific sources, such ascartridges or ammunition/weapon test fire deposits.7.1.3 Particles characteristic of GSR (that is, most likelyassociated with the discharge of a gun) will have the followingelemental composition:7.1.3.
46、1 Lead, antimony, barium.7.1.3.2 It is common for additional elements to becomeincorporated into particles containing these elements. Suchparticles may contain but not be limited to one or more of theelements: aluminum, silicon, phosphorus, sulfur (trace), chlo-rine, potassium, calcium, iron (trace)
47、, nickel, copper, zinc,zirconium, and tin.7.1.4 Particles consistent with GSR (that is, may be associ-ated with the discharge of a gun but could also originate fromother sources unrelated to a gun discharge) will have one of thefollowing elemental compositions:7.1.4.1 Barium, calcium, silicon (with
48、or without a trace ofsulfur);7.1.4.2 Antimony, barium (15) (with no more than a trace ofeither iron or sulfur (16);7.1.4.3 Lead, antimony;7.1.4.4 Barium, aluminum (with or without a trace ofsulfur);7.1.4.5 Lead, barium;7.1.4.6 Lead (only in the presence of particles with compo-sitions mentioned in 7
49、.1.3 and 7.1.4);7.1.4.7 Antimony (only in the presence of particles withcompositions mentioned in 7.1.3 and 7.1.4);7.1.4.8 Barium (with or without a trace of sulfur); or7.1.4.9 Particles with the above compositions may alsocontain any one or several of the elements listed in 7.1.3.2.7.1.5 The following compositions have been observed fromdifferent kinds of ammunition with “lead-free/non-toxic” prim-ers (17, 18).7.1.5.1 Particles that have a composition characteristic ofGSR, will have one of the following elemental compositions:(1) Gadolinium, titanium, zinc (19);or(2) Ga
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