1、Designation: E1588 10Standard 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 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.1. Scope1.1 This guide covers the analysis of gunshot residue (GSR)by scanning electron microscopy/energy-disp
3、ersive 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 some amount ofthe analysis is controlled by pre-set software functions.1.2 Si
4、nce 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 values stated in SI units are to be regarded asstandard. No other units of m
5、easurement 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 safety and health practices and determine the applica-bility of regulatory
6、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) areanalyzed by EDS (1-3).2Typically, particles composed of highmean atomic numb
7、er 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 characteristic of GSR, or both.3. Significance and Use3.1 This document wi
8、ll 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 theelemental profiles of individual particles.3.3 Particle analysis contrasts with
9、 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 spectrometry (ICP-MS), where thesampled material is dissolved or extracted prior to
10、 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 placement and distribution ofGSR particles surrounding bullet holes in order
11、 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 identification.4. Sample Preparation4.1 Once the evidence seal is broken, care shoul
12、d 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 collection stub in such a manner that itis distinguishable from other sample coll
13、ection stubs withoutcompromising the sample; for example, label the bottom orside of the stub.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 S
14、EM is used for the analysis.Carbon is a common choice of coating material, since it will1This guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved June 1, 2010. Published June 2010
15、. 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 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Un
16、ited States.not 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 diameters: 12.7 mm or 25.4 mm, which yield surfaceareas of 126.7 mm2and 506.7 mm2
17、respectively.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, it is reasonable to analyze aportion of the stub surface by employing an ap
18、propriatesampling 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 samplecollection stub (round) and the SEM field of view search area(square or r
19、ectangular), 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 programmed to terminate the analysis of a stub orseries of stubs once a pre-establ
20、ished 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 guidelines set out in the laboratorys standard operatingprocedures.6. Instrume
21、nt 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 pre-setsoftware functions. The extent to which the SEM and EDSsystems communi
22、cate 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 electronimaging mode, must be capable of detecting particles down toat least 0.5 m in d
23、iameter.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 control. The systemshould have the ability to recall stage locations of part
24、icles 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 the Mn Ka peak.6.3.2 At a minimum, the EDS spectrum should be acquiredat 20
25、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 specified collection time ortotal X-ray counts.6.3.5 It is desirable that the
26、 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 the stubs (sample andstandard/reference stubs) on the SEM stage when the s
27、amplesare 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 of each stub and aligning it with marks on themicroscope stage or by havin
28、g 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 intensity. The absolute signal intensity that aparticle produces is relate
29、d 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 meanatomic number composition.As the beam current increases, theamount of signal eac
30、h 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 mean atomic number exceed the minimum thresholdsetting but fall below the
31、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 parameters that will be used for the sampleanalysis. This calibration sampl
32、e 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 interest and exclude low atomic number particlesthat are not of interest. Typ
33、ically, 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 based on the previous beam current, may no longer becompatible with the new con
34、ditions and should be readjusted.The beam current may be measured with a Faraday cup, aspecimen current meter, or monitored by comparing the inte-grated counts within the same peak in sequentially collectedspectra from a known standard.6.6 Quality Control:6.6.1 When conducting automated analysis of
35、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 basis.E1588 1026.6.1.2 Monitor the EDS X-ray energy calibration and SEMbeam current s
36、tability 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 regularintervals in order to test the accuracy of particle detection andidentifica
37、tion, 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 asample of GSR from a known source (caliber of weapon,ammunition manufactur
38、er, 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, asynthetic, simulated-GSR reference sample may be used forthis purpose. The freq
39、uency 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 analytical protocol is recommended in order tomonitor the cleanliness of th
40、e 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 from the sampling or analytical environment(exposed to the air or as a direc
41、t 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 m and 5.0 m in diameter; the remainder are irregular inshape or vary from 1
42、 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 knownprimer GSR residues. Since morphology can vary greatly, itshould never be cons
43、idered 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 composition of the recovered par-ticulate can be compared with case-specific
44、 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, the elemental compositions of these par-ticles should be compared to case-sp
45、ecific 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:7.1.3.1 Lead, antimony, barium.7.1.3.2 It is common for additional elements to bec
46、omeincorporated 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), nickel, copper, zinc,zirconium, and tin.7.1.4 Particles consistent with GS
47、R (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 or without a trace ofsulfur);7.1.4.2 Antimony, barium (15) (with no more tha
48、n 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 7.1.3 and 7.1.4);7.1.4.7 Antimony (only in the presence of particles withcomp
49、ositions 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) Gallium, copper, tin (19).7.1.5.2 Particles that have a composition that is simila
