1、Designation: E1588 16aE1588 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 th
2、e 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 practice covers the analysis of gunshot residue (GSR) by scanning electron micros
3、copy/energy-dispersive X-rayspectrometry (SEM/EDS) using 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 soft
4、ware functions. This practice refers to the analysis of electron microscopy stubs and does notaddress sample collection (1).21.2 Since software and hardware formats vary among commercial systems, guidelines will be offered in the most general termspossible. For proper terminology and operation, cons
5、ult the SEM/EDS system manuals for each instrument.1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.4 This practice offers a set of instructions for performing one or more specific operations. This practice cannot replace
6、knowledge, skill, or ability acquired through appropriate education, training, and experience and should be used in conjunctionwith sound professional judgment.1.5 This practice does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the us
7、er when applying this practice to establish appropriate safety and health practices and determine the applicability ofregulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Labor
8、atory3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 stub, nsample device with an adhesive surface used to collect materials for SEM/EDS analysis.3.1.2 characteristic particles, nparticles that have compositions rarely found in particles from any other source.3.1.3 major, cons
9、istent particles, adjnelement whose main peak height is greater thanparticles that have compositions thatare also found 13 of the peak height of the strongest peak in the spectrum.in particles from a number of relatively common,non-firearm sources. Particles within this group are produced through th
10、e operation of a variety of processes, equipment, or devicesand can be found in the environment with varying levels of frequency.Wallace, 1984 (2)3.1.4 minor, commonly associated particles, adjnelement whose main peak height is betweenparticles have compositionsthat are also commonly found in enviro
11、nmental particles from numerous sources. However, when present, in addition to particlesthat are characteristic of, and/or consistent with GSR, these particles can be of significance in the interpretation of a populationof particles and, consequently, the likelihood that that population is GSR. 110
12、andIn isolation, 13 of the peak height of the strongestpeak in the spectrum.however, such particles have little significance in examinations for GSR.Wallace, 1984 (2)1 This practice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee
13、E30.01 on Criminalistics.Current edition approved May 1, 2016Feb. 1, 2017. Published July 2016February 2017. Originally approved in 1994. Last previous version approved in 2016 asE1588 16. DOI: 10.1520/E1588-16A.2 The boldface numbers in parentheses refer to a list of references at the end of this s
14、tandard.3 For referencedASTM standards, visit theASTM website, 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.This document is not an ASTM standard and is intended
15、 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 appropriate. In all cases only the current v
16、ersionof 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 States13.1.5 trace,morphology, adjn; element whose main peak height is less than 110 of the peak height of t
17、he strongest peak in thespectrum.Wallace, 1984morphological, adj (referring to2) size,shape, structure, and texture.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, siz
18、e, or shape) are analyzed by EDS (3-2-54). 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 maycould identify the particle as
19、 being consistent with or characteristic of GSR,or both. See Section 9 for discussion on classification of particles.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 (65).5.2 SEM/EDS analysis of GSR is
20、a non-destructive method that provides (76, 87) both morphological information and theelemental profiles of individual particles.5.3 Particle analysis contrasts with bulk sample methods, such as atomic absorption spectrophotometry (AAS) (98), neutronactivation analysis (NAA) (109), inductively coupl
21、ed plasma atomic emission spectrometry (ICP-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 informationsize, shape, and individual particl
22、e identification.5.4 X-ray fluorescence spectrometry (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 (11). Unlike the solution-based bulk methods of analysis,XRF is non-destructive; howeve
23、r, XRF still does not provide morphological information 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 n
24、ot left uncovered any longer than is reasonable for transfer, mounting, or labeling.6.2 Label the The sample collection stub shall be labeled in such a manner that it is distinguishable from other sample collectionstubs without compromising the sample; for example, label the bottom or side of the st
25、ub.6.3 If a non-conductive adhesive was used in the sample collection stub, 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
26、not interfere with X-ray lines of interest. For high-vacuum SEM, coat the samplesufficiently to eliminate charging of the sample.6.4 Observe the appropriate procedures for handling and documentation of all submitted samples as described in samples, forexample Practice E1492.7. Sample Area7.1 Sample
27、collection stubs for SEMs typically come in one of two diameters: 12.7 mm or 25.4 mm, which yield 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 surfac
28、e in a random manner and the particles do not tend to cluster, it is It may be reasonable to analyze a portionof the stub surface by employing an appropriate sampling plan and analytical protocol assuming a random distribution of particleson the stub surface (87, 1210).7.3 Automated SEM/EDS analysis
29、 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 the SEM field of view search area (square orrectangular), analysis of 100 % of the sample collection area may not be possible
30、 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 a stub or series of stubs once a pre-established number of particles with specifiedclassification(s) have been detected. T
31、he 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 should be set out in the laboratorys standard operating procedures.8. Instrument Requirements and Operation8.1 General:8.1.1 Most commercial-gra
32、de SEM/EDS systems should be adequate for GSR analysis.E1588 1728.1.2 Automated data collection of GSR involves some portion of the data collection being controlled by pre-set softwarefunctions. The extent to which the SEM and EDS systems communicate and are integrated varies according to the manufa
33、cturersinvolved 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 capable of detectingshall be configured to detectparticles down to at least 0.5 m 1.0 m in diameter.8.2.2 The
34、 SEM mustshall 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 should have the ability to recall stage locations of particles for v
35、erification andsoftware for particle recognition.8.3 Energy Dispersive Spectrometry (EDS):8.3.1 The detectors resolution should be detector shall be configured to produce a resolution of better (less) than 150 eV,measured 150 eV during analysis, measured or extrapolated as the full width at half the
36、 maximum height of the Mn Ka peak.peak(1).8.3.2 At a minimum, the EDS spectrum should be acquired at 20 eV per channel.8.3.3 Display of the EDS output mustshall encompass the X-ray lines of analytical utility, with a minimum range of 015 keV.8.3.4 Automated systems will also include software capable
37、 of acquiring X-ray spectra for a specified collection time or totalX-ray counts.8.3.5 It is recommended that the instrument be capable of recording spectra obtained from the analysis of each particle ofinterest. At a minimum, an automated system mustshall be capable of storing all of the particle l
38、ocation coordinates.8.4 Sample Placement:8.4.1 Record the positions of the 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 thesa
39、me orientation as before its removal. This may consist of marking the side 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 Calibratio
40、n:8.5.1 Particles of GSR are detected by their backscattered electron signal 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 m
41、ean atomic numbers are high will appear brighter than those of lower mean atomic numbercomposition. As the beam current increases, the amount of signal each particle produces also increases (1311).8.5.2 The brightness and contrast settings (low and high thresholds) of the backscattered electron dete
42、ctor system determine thelimits of detection and discrimination of particles based on their mean atomic number. Threshold settings for the backscatteredelectron signal should be done with a suitable reference sample of known origin (often supplied by the EDS manufacturer) or pureelement standards at
43、 the same parameters that will be used for the sample analysis. This reference sample should, if possible, bein the microscope chamber at the same time as the samples to be analyzed.8.5.3 The backscattered electron detectors brightness and contrast should be set to include the high atomic number par
44、ticlesof 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, whi
45、ch were based on the previous beam current, maycould 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 s
46、pectra from 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
47、a routine 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. reference materials.8.6.1.3 Analyze a reference sample (positive control) material with particles of kn
48、own size, range,size range and compositionat regular intervals in order to test the accuracy of particle detection and identification, whether by automated or manual analysis.It is recommended that athe reference samplematerial has been prepared and mounted in a manner comparable to the collectionme
49、thod in use by the submitting agency. The reference sample maymaterial can be a sample of GSR from a known source (caliberof weapon, ammunition manufacturer, number of rounds fired, collected area from shooter, or a synthetic GSR standard).Additional environmental particles may be added to ensure the inclusion or exclusion of particular classes of particles.Alternatively, a synthetic, simulated-GSR reference samplematerial may be used for this purpose. The frequency of analysis of thissample is a matter for the analyst to decide and is shall be subject to guideli
