1、Designation: E1588 17Standard Practice 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
2、 revision, 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 practice covers the analysis of gunshot residue(GSR) by scanning electron microscopy/energ
3、y-dispersiveX-ray spectrometry (SEM/EDS) using manual and automatedmethods. The analysis may be performed manually, with theoperator manipulating the microscope controls and the EDSsystem software, or in an automated fashion, where someamount of the analysis is controlled by pre-set softwarefunction
4、s. This practice refers to the analysis of electronmicroscopy stubs and does not address sample collection (1).21.2 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/E
5、DS system manuals for each instrument.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This practice offers a set of instructions for performingone or more specific operations. This practice cannot replaceknowledge, skill
6、, or ability acquired through appropriateeducation, training, and experience and should be used inconjunction with sound professional judgment.1.5 This practice does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user when applying t
7、his practice toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principl
8、es for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3E1492 Practice for Receiving, Documenting, Storing, andRetrieving Evidence in a Forensic Science
9、Laboratory3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 stub, nsample device with an adhesive surface usedto collect materials for SEM/EDS analysis.3.1.2 characteristic particles, nparticles that have compo-sitions rarely found in particles from any other source.3.1.3 consis
10、tent particles, nparticles that have composi-tions that are also found in particles from a number ofrelatively common, non-firearm sources. Particles within thisgroup are produced through the operation of a variety ofprocesses, equipment, or devices and can be found in theenvironment with varying le
11、vels of frequency.3.1.4 commonly associated particles, nparticles havecompositions that are also commonly found in environmentalparticles from numerous sources. However, when present, inaddition to particles that are characteristic of, and/or consistentwith GSR, these particles can be of significanc
12、e in theinterpretation of a population of particles and, consequently,the likelihood that that population is GSR. In isolation,however, such particles have little significance in examinationsfor GSR.3.1.5 morphology, n; morphological, adjreferring to size,shape, structure, and texture.4. Summary of
13、Practice4.1 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 (2-4). Typically, particles composed of highmean atomic number elements are detected by their SEM1T
14、his practice is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Feb. 1, 2017. Published February 2017. Originallyapproved in 1994. Last previous version approved in 2016 as E1588 16a.
15、DOI:10.1520/E1588-17.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to t
16、he standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in
17、the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1backscattered electron signals and an EDS spectrum is ob-tained from each. The EDS spectrum is evaluated for consti
18、tu-ent elements that could identify the particle as being consistentwith or characteristic of GSR, or both. See Section 9 fordiscussion on classification of particles.5. Significance and Use5.1 This document will be of use to forensic laboratorypersonnel who are involved in the analysis of GSR sampl
19、es bySEM/EDS (5).5.2 SEM/EDS analysis of GSR is a non-destructive methodthat provides (6, 7) both morphological information and theelemental profiles of individual particles.5.3 Particle analysis contrasts with bulk sample methods,such as atomic absorption spectrophotometry (AAS) (8), neu-tron activ
20、ation analysis (NAA) (9), inductively coupled plasmaatomic emission spectrometry (ICP-AES), and inductivelycoupled plasma mass spectrometry (ICP-MS), where thesampled material is dissolved or extracted prior to the deter-mination of total element concentrations, thereby sacrificingsize, shape, and i
21、ndividual particle identification.6. Sample Preparation6.1 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
22、.6.2 The sample collection stub shall be labeled in such amanner that it is distinguishable from other sample collectionstubs without compromising the sample; for example, label thebottom or side of the stub.6.3 If a non-conductive adhesive was used in the samplecollection stub, the sample will need
23、 to be coated to increase itselectrical conductivity, unless an environmental SEM orvariable-pressure/low-vacuum SEM 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 el
24、iminate charging of thesample.6.4 Observe the appropriate procedures for handling anddocumentation of all submitted samples, for example PracticeE1492.7. Sample Area7.1 Sample collection stubs for SEMs typically come in oneof two diameters: 12.7 mm or 25.4 mm, which yield surfaceareas of 126.7 mm2an
25、d 506.7 mm2respectively.7.2 Manual analysis of the total surface area of the stub isprohibitively time-consuming. It may be reasonable to analyzea portion of the stub surface by employing an appropriatesampling plan and analytical protocol assuming a randomdistribution of particles on the stub surfa
26、ce (7, 10).7.3 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 rectangular), analysis of 100 % of the s
27、amplecollection area may not be possible in some systems.7.3.1 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-established number of particles havebeen dete
28、cted. The decision as to how many particles satisfythe requirements of a particular case should be set out in thelaboratorys standard operating procedures.8. Instrument Requirements and Operation8.1 General:8.1.1 Most commercial-grade SEM/EDS systems should beadequate for GSR analysis.8.1.2 Automate
29、d data collection of GSR involves someportion of the data collection being controlled by pre-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.8.2 Sc
30、anning Electron Microscope (SEM):8.2.1 The SEM, operating in the backscattered electronimaging mode, shall be configured to detect particles down toat least 1.0 m in diameter.8.2.2 The SEM shall be capable of an accelerating voltageof at least 20 kV.8.2.3 Automated SEM/EDS systems include: communica
31、-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 particles forverification and software for particle recognition.8.3 Energy Dispersive Spectrometry (EDS):8.3.1 The detector shall be con
32、figured to produce a resolu-tion of better (less) than 150 eV during analysis, measured orextrapolated as the full width at half the maximum height of theMn Ka peak (1).8.3.2 At a minimum, the EDS spectrum should be acquiredat 20 eV per channel.8.3.3 Display of the EDS output shall encompass the X-r
33、aylines of analytical utility, with a minimum range of 015 keV.8.3.4 Automated systems will also include software capableof acquiring X-ray spectra for a specified collection time ortotal X-ray counts.8.3.5 It is recommended that the instrument be capable ofrecording spectra obtained from the analys
34、is of each particle ofinterest. At a minimum, an automated system shall be capableof storing all of the particle location coordinates.8.4 Sample Placement:8.4.1 Record the positions of the stubs (sample andstandard/reference stubs) on the SEM stage when the samplesare inserted.8.4.2 If it is anticip
35、ated 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 having stubs that fit into the stage inE1588 1
36、72only one position (for example, stubs with a pin that is ahalf-circle in cross section).8.5 Detection and Calibration:8.5.1 Particles of GSR are detected by their backscatteredelectron signal intensity. The absolute signal intensity that aparticle produces is related to the electron beam current,
37、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 each particle produces also increas
38、es (11).8.5.2 The brightness and contrast settings (low and highthresholds) of the backscattered electron detector system de-termine the limits of detection and discrimination of particlesbased on their mean atomic number. Threshold settings for thebackscattered electron signal should be done with a
39、 suitablereference sample of known origin (often supplied by the EDSmanufacturer) or pure element standards at the same param-eters that will be used for the sample analysis. This referencesample should, if possible, be in the microscope chamber at thesame time as the samples to be analyzed.8.5.3 Th
40、e 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. Typically, high contrast and lowbrightness settings provide an adequate range between thresh-old limits for
41、ease of detection. If the beam current is changedor drifts, the brightness and contrast threshold limits, whichwere based on the previous beam current, could no longer becompatible with the new conditions and should be readjusted.The beam current may be measured with a Faraday cup, aspecimen current
42、 meter, or monitored by comparing the inte-grated counts within the same peak in sequentially collectedspectra from a known standard.8.6 Quality Control:8.6.1 When conducting automated analysis of GSR, specialmeasures have to be chosen in order to meet common qualitymanagement demands. Therefore, as
43、 minimum conditions:8.6.1.1 Establish a protocol to confirm optimum instrumentoperation parameters on a routine basis.8.6.1.2 Monitor the EDS X-ray energy calibration and SEMbeam current stability regularly. This may be facilitated by theuse of appropriate reference materials.8.6.1.3 Analyze a refer
44、ence material with particles ofknown size range and composition at regular intervals in orderto test the accuracy of particle detection and identification,whether by automated or manual analysis. It is recommendedthat the reference material has been prepared and mounted in amanner comparable to the
45、collection method in use by thesubmitting agency. The reference material can be a sample ofGSR from a known source (caliber of weapon, ammunitionmanufacturer, number of rounds fired, collected area fromshooter, or a synthetic GSR standard). Additional environmen-tal particles may be added to ensure
46、the inclusion or exclusionof particular classes of particles. Alternatively, a synthetic,simulated-GSR reference material may be used for this pur-pose. The frequency of analysis of this sample shall be subjectto guidelines set out in the laboratorys standard operatingprocedures.8.6.1.4 The incorpor
47、ation of environmental or controlsamples into the analytical protocol is recommended in order tomonitor the cleanliness of the sample collection or analyticalsystem, or both. An environmental sample may be prepared ina number of ways: for example, it may be an unused stub thathas been prepared conte
48、mporaneously with the questionedsamples or a sample taken from the sample collection oranalytical environments (exposed to the air or as a directsample collection from clean workspace), or both.9. Data Analysis9.1 Definition and Classification:9.1.1 Morphology:9.1.1.1 Particles identified as charact
49、eristic of or consistentwith GSR using this method are often spheroid particles,typically between 0.5 m and 5.0 m in diameter; the remain-der are irregular in shape or vary from 0.5 m to 100+ m insize, or both (6, 12, 13). In general, it is not consistent with themechanisms of GSR formation to find particles by SEM-displaying crystalline morphology. However, such particleshave occasionally been observed in known primer GSR resi-dues. Since morphology can vary greatly, it should never beconsidered as the only criterion for identification of GSR.9.1.2 Elemental
