1、Designation: E1588 16E1588 16aStandard GuidePractice 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,
2、in the case of 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 guide covers the analysis of gunshot residue (GSR) by scanning electron micr
3、oscopy/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 system software, or in an automated fashion, where some amount of theanalysis is controlled by pre-set softw
4、are functions.1.2 Since software and hardware formats vary among commercial systems, guidelines will be offered in the most general termspossible. For proper terminology and operation, consult the SEM/EDS system manuals for each system.1.3 The values stated in SI units are to be regarded as standard
5、. No other units of measurement are included in this standard.1.4 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 standard to establish appropriate safety and health practices and determine the applica
6、bility of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 major, adjelement whose main peak
7、 height is greater than 13 of the peak height of the strongest peak in the spectrum.Wallace 1984 (15)33.1.2 minor, adjelement whose main peak height is between 110 and 13 of the peak height of the strongest peak in thespectrum. Wallace 1984 (15)3.1.3 trace, adjelement whose main peak height is less
8、than 110 of the peak height of the strongest peak in the spectrum.Wallace 1984 (15)4. Summary of Practice4.1 From the total population of particles collected, those that are detected by SEM to be within the limits of certain parameters(for example, atomic number, size, or shape) are analyzed by EDS
9、(1-3). Typically, particles composed of high mean atomicnumber elements are detected by their SEM backscattered electron signals and an EDS spectrum is obtained from each. The EDSspectrum is evaluated for constituent elements that may identify the particle as being consistent with or characteristic
10、of GSR, orboth.5. Significance and Use5.1 This document will be of use to forensic laboratory personnel who are involved in the analysis of GSR samples bySEM/EDS (4).1 This guidepractice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommi
11、ttee E30.01 on Criminalistics.Current edition approved March 1, 2016May 1, 2016. Published March 2016July 2016. Originally approved in 1994. Last previous version approved in 20102016 asE1588 10E1588 16.1. DOI: 10.1520/E1588-16.10.1520/E1588-16A.3 For referencedASTM standards, visit theASTM website,
12、 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.2 The boldface numbers in parentheses refer to a list of references at the end of this standard.This document is no
13、t 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 editions as appropriat
14、e. 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 States15.2 SEM/EDS analysis of GSR is a non-destructive method that provid
15、es (5, 6) both morphological information and theelemental profiles of individual particles.5.3 Particle analysis contrasts with bulk sample methods, such as atomic absorption spectrophotometry (AAS) (7), neutronactivation analysis (NAA) (8), inductively coupled plasma atomic emission spectrometry (I
16、CP-AES), and inductively coupledplasma mass spectrometry (ICP-MS), where the sampled material is dissolved or extracted prior to the determination of totalelement concentrations, thereby sacrificing morphological information and individual particle identification.5.4 X-ray fluorescence spectrometry
17、(XRF) is a technique that has been used to map the placement and distribution of GSRparticles surrounding bullet holes in order to establish shooting distances (9). Unlike the solution-based bulk methods of analysis,XRF is non-destructive; however, XRF still does not provide morphological informatio
18、n and is incapable of individual GSRparticle identification.6. Sample Preparation6.1 Once the evidence seal is broken, care should be taken so that no object touches the surface of the adhesive SEM/EDSsample collection stub and that the stub is not left uncovered any longer than is reasonable for tr
19、ansfer, mounting, or labeling.6.2 Label the sample collection stub in such a manner that it is distinguishable from other sample collection stubs withoutcompromising the sample; for example, label the bottom or side of the stub.6.3 If a non-conductive adhesive was used in the sample collection stub,
20、 the sample will need to be coated to increase itselectrical conductivity, unless an environmental SEM or variable-pressure/low-vacuum SEM is used for the analysis. Carbon is acommon choice of coating material, since it will not interfere with X-ray lines of interest. For high-vacuum SEM, coat the s
21、amplesufficiently to eliminate charging of the sample.6.4 Observe the appropriate procedures for handling and documentation of all submitted samples as described in PracticeE1492.7. Sample Area7.1 Sample collection stubs for SEMs typically come in one of two diameters: 12.7 mm or 25.4 mm, which yiel
22、d surface areasof 126.7 mm2 and 506.7 mm2 respectively.7.2 Manual analysis of the total surface area of the stub is prohibitively time-consuming. Because the particles are collected ontoan adhesive surface in a random manner and the particles do not tend to cluster, it is reasonable to analyze a por
23、tion of the stubsurface by employing an appropriate sampling and analytical protocol (6, 10).7.3 Automated SEM/EDS analysis can enable data collection from nearly the entire surface area of the sample collection stub.Due to the disparity between the shape of the sample collection stub (round) and th
24、e SEM field of view search area (square orrectangular), analysis of 100 % of the sample collection area may not be possible in some systems.7.3.1 Analysis of the maximum allowable surface area of the sample is recommended, however, many automated systems canbe programmed to terminate the analysis of
25、 a stub or series of stubs once a pre-established number of particles with specifiedclassification(s) have been detected. The decision as to how many particles satisfy the requirements of a particular case is a matterfor the analyst to decide but should be subject to guidelines set out in the labora
26、torys standard operating procedures.8. Instrument Requirements and Operation8.1 General:8.1.1 Most commercial-grade SEM/EDS systems should be adequate for GSR analysis.8.1.2 Automated data collection of GSR involves some portion of the data collection being controlled by pre-set softwarefunctions. T
27、he extent to which the SEM and EDS systems communicate and are integrated varies according to the manufacturersinvolved and the capabilities of the hardware/software architecture.8.2 Scanning Electron Microscope (SEM):8.2.1 The SEM, operating in the backscattered electron imaging mode, must be capab
28、le of detecting particles down to at least0.5 m in diameter.8.2.2 The SEM must be capable of an accelerating voltage of at least 20 kV.8.2.3 Automated SEM/EDS systems include: communication and control between the SEM and EDS system, and a motorizedstage with automated stage control. The system shou
29、ld have the ability to recall stage locations of particles for verification andsoftware for particle recognition.8.3 Energy Dispersive Spectrometry (EDS):8.3.1 The detectors resolution should be better (less) than 150 eV, measured as the full width at half the maximum height ofthe Mn Ka peak.8.3.2 A
30、t a minimum, the EDS spectrum should be acquired at 20 eV per channel.8.3.3 Display of the EDS output must encompass the X-ray lines of analytical utility, with a minimum range of 015 keV.E1588 16a28.3.4 Automated systems will also include software capable of acquiring X-ray spectra for a specified
31、collection time or totalX-ray counts.8.3.5 It is desirable that the spectrum obtained from the analysis of each particle of interest be stored. At a minimum, anautomated system must be capable of storing all of the particle location coordinates.8.4 Sample Placement:8.4.1 Record the positions of the
32、stubs (sample and standard/reference stubs) on the SEM stage when the samples are inserted.8.4.2 If it is anticipated or required that additional analyses will be needed, it is desirable that the stub can be returned to thesame orientation as before its removal. This may consist of marking the side
33、of each stub and aligning it with marks on themicroscope stage or by having stubs that fit into the stage in only one position (for example, stubs with a pin that is a half-circlein cross section).8.5 Detection and Calibration:8.5.1 Particles of GSR are detected by their backscattered electron signa
34、l intensity. The absolute signal intensity that a particleproduces is related to the electron beam current, mean atomic number, and size of the particle (for particle sizes on the order ofthe beam diameter). Particles whose mean atomic numbers are high will appear brighter than those of lower mean a
35、tomic numbercomposition. As the beam current increases, the amount of signal each particle produces also increases (11).8.5.2 The brightness and contrast settings (low and high thresholds) of the backscattered electron detector system determine thelimits of detection and discrimination of particles
36、whose mean atomic number exceed the minimum threshold setting but fall belowthe maximum threshold setting. Threshold settings for the backscattered electron signal should be done with a suitable referencesample of known origin (often supplied by the EDS manufacturer) or pure element standards at the
37、 same parameters that will beused for the sample analysis. This calibration sample should, if possible, be in the microscope chamber at the same time as thesamples to be analyzed.8.5.3 The backscattered electron detectors brightness and contrast should be set to include the high atomic number partic
38、lesof interest and exclude low atomic number particles that are not of interest. Typically, high contrast and low brightness settingsprovide an adequate range between threshold limits for ease of detection. If the beam current is changed or drifts, the brightnessand contrast threshold limits, which
39、were based on the previous beam current, may no longer be compatible with the newconditions and should be readjusted. The beam current may be measured with a Faraday cup, a specimen current meter, ormonitored by comparing the integrated counts within the same peak in sequentially collected spectra f
40、rom a known standard.8.6 Quality Control:8.6.1 When conducting automated analysis of GSR, special measures have to be chosen in order to meet common qualitymanagement demands. Therefore, as minimum conditions:8.6.1.1 Establish a protocol to confirm optimum instrument operation parameters on a routin
41、e basis.8.6.1.2 Monitor the EDS X-ray energy calibration and SEM beam current stability regularly. This may be facilitated by the useof appropriate standards or reference samples, or both.8.6.1.3 Analyze a reference sample (positive control) with particles of known size, range, and composition at re
42、gular intervalsin order to test the accuracy of particle detection and identification, whether by automated or manual analysis. It is recommendedthat a reference sample has been prepared and mounted in a manner comparable to the collection method in use by the submittingagency. The reference sample
43、may be a sample of GSR from a known source (caliber of weapon, ammunition manufacturer,number of rounds fired, collected area from shooter, or a synthetic GSR standard). Additional environmental particles may beadded to ensure the inclusion or exclusion of particular classes of particles. Alternativ
44、ely, a synthetic, simulated-GSR referencesample may be used for this purpose. The frequency of analysis of this sample is a matter for the analyst to decide and is subjectto guidelines set out in the laboratorys standard operating procedures.8.6.1.4 The incorporation of environmental or control samp
45、les into the analytical protocol is recommended in order to monitorthe cleanliness of the sampling or analytical system, or both. An environmental sample may be prepared in a number of ways: forexample, it may be an unused stub that has been prepared contemporaneously with the questioned samples or
46、a sample taken fromthe sampling or analytical environment (exposed to the air or as a direct sampling of clean workspace), or both.9. Data Analysis9.1 Definition and Classification:9.1.1 Morphology:9.1.1.1 Particles identified as characteristic or consistent with GSR using this method are often sphe
47、roidal, noncrystallineparticles between 0.5 m and 5.0 m in diameter; the remainder are irregular in shape or vary from 1 to 100+ m in size, or both(5, 12, 13). In general, it is not consistent with the mechanisms of GSR formation to find particles with crystalline morphology.However, such particles
48、have occasionally been observed in known primer GSR residues. Since morphology can vary greatly, itshould never be considered as the only criterion for identification of GSR.9.1.2 Elemental Composition:E1588 16a39.1.2.1 The elemental composition is the most diagnostic property to determine if a part
49、icle may be GSR (14). Whenappropriate, the elemental composition of the recovered particulate can be compared with case-specific known source items, suchas the recovered weapon, cartridge cases, or victim-related items.9.1.2.2 Occasionally, GSR particles with apparent unusual elemental compositions may be encountered in case work. In thiscircumstance, the elemental compositions of these particles should be compared to case-specific sources, such as cartridges orammunition/weapon test fire deposits.9.1.3 Particles characteristic of GSR (that is, most likely ass
