ASTM E1588-20

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it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: E1588 − 17 E1588 − 20
Standard Practice for
Gunshot Residue Analysis by Scanning Electron
Microscopy/Energy Dispersive X-Ray Spectrometry
This standard is issued under the fixed designation E1588; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the analysis of gunshot residue (GSR) by scanning electron microscopy/energy-dispersive X-ray
spectrometry (SEM/EDS) using manual and automated methods. The analysis may be performed manually, with the operator
manipulating the microscope controls and the EDS system software, or in an automated fashion, where some amount of the
analysis is controlled by pre-set software functions.(SEM/EDS). The analysis is performed using automated software control of
both the SEM and EDS systems, to screen the sample for candidate particles that could be associated with GSR. Manual control
of the instrument is then used to perform confirmatory analysis and classification of the candidate particles. This practice refers
solely to the analysis of electron microscopy stubs and does not address sample collection (1).
1.2 Since software and hardware formats vary among commercial systems, guidelines will be offered in the most general terms
possible. For proper terminology and operation, consult 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
knowledge, skill, or ability acquired through appropriate education, training, and experience and should be used in conjunction
with sound professional judgment.
1.4 This standard cannot replace knowledge, skills, or abilities acquired through education, training, and experience (Practice
E2917), and is to be used in conjunction with professional judgment by individuals with such discipline-specific knowledge, skills,
and abilities.
1.5 This practicestandard does not purport to address all of the safety concerns, if any, associated with its use. It is the
responsibility of the user when applying of this practicestandard to establish appropriate safety safety, health, and healthenvi-
ronmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
This practice is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
Current edition approved Feb. 1, 2017Sept. 15, 2020. Published February 2017September 2020. Originally approved in 1994. Last previous version approved in 20162017
as E1588 – 16a.E1588 – 17. DOI: 10.1520/E1588-17.10.1520/E1588-20.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1588 − 20
E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory
E2917 Practice for Forensic Science Practitioner Training, Continuing Education, and Professional Development Programs
3. Terminology
3.1 Definitions of Terms Specific to This Standard:Definitions:
3.1.1 stub, n—sample device with an adhesive surface used to collect materials for SEM/EDS analysis.
3.1.2 characteristic particles, n—particles that have compositions rarely found in particles from any source other source.than
GSR.
3.1.3 consistent particles, n—particles that have compositions that are also found in particles from a number of relatively common,
non-firearm sources. Particles within this group are produced through the operation of a variety of processes, equipment, or devices
and can be found in the environment with varying levels of frequency.found in GSR and also arise from other non-firearm sources.
3.1.3.1 Discussion—
Particles within this group are produced through the operation of a variety of processes, equipment, or devices and can be found
in the environment with varying levels of frequency.
3.1.4 commonly associated particles, n—particles have compositions that are also commonly found in environmental particles
from numerous sources. However, when present, in addition to particles that are characteristic of, and/or consistent with GSR,
these particles can be of significance in the interpretation of a population of particles and, consequently, the likelihood that that
population is GSR. In isolation, however, such particles have little significance in examinations for GSR.
3.1.4.1 Discussion—
When present in addition to particles that are characteristic of, or consistent with, GSR, or both, these particles can be of use in
the interpretation of a population of particles and, consequently, the likelihood that that population is GSR. In isolation, however,
such particles have little use in examinations for GSR.
3.1.5 morphology, n; morphological, adj—referring to size, shape, structure, and texture.
4. Summary of Practice
4.1 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 Particles (2-4). Typically, particles composed of high mean
atomic number elements are detected by their SEM backscattered electron signals and an EDS spectrum is obtained from each.
The EDS spectrum is evaluated for constituent elements that could identify the particle as being consistent with or characteristic
of GSR,GSR or(2-4). both. See Section 9 for discussion on classification of particles.
5. Significance and Use
5.1 This document will be of use to forensic laboratory personnel who are involved in the analysis of GSR samples by SEM/EDS
(5).
5.2 SEM/EDS analysis of GSR is a non-destructive method that provides (6, 7) both morphological information and the elemental
profiles of constituent elements detected in individual particles.
5.3 Particle analysis contrasts with bulk sample methods, such as atomic absorption spectrophotometry (AAS) (8), neutron
activation analysis (NAA) (9), inductively coupled plasma atomic emission spectrometry (ICP-AES), and inductively coupled
plasma mass spectrometry (ICP-MS), where the sampled material is dissolved or extracted prior to the determination of total
element concentrations, thereby sacrificing size, shape, and individual particle identification.
6. Sample Preparation
6.1 Once the evidence seal is broken, care should be taken so that no object touches the surface of the adhesive SEM/EDS sample
collection stub and that the stub is not left uncovered any longer than is reasonable for transfer, mounting, or labeling.
E1588 − 20
6.2 The sample collection stub shall be labeled in such a manner that it is distinguishable from other sample collection stubs
without compromising 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, the sample will need to be coated to increase its electrical
conductivity, unless an environmental SEM or variable-pressure/low-vacuum SEM is used for the analysis. Carbon is a common
choice of coating material, since it will not interfere with X-ray lines of interest. For high-vacuum SEM, coat the sample
sufficiently to eliminate charging of the sample.
6.4 Observe the appropriate procedures for handling and documentation of all submitted samples, for example Practice E1492.
7. Sample Area
7.1 Sample collection stubs for SEMs typically come in one of two diameters: 12.7 mm or 25.4 mm, which yield surface areas
2 2
of 126.7 mm and 506.7 mm respectively.
7.2 Manual analysis of the total surface area of the stub is prohibitively time-consuming. It may be reasonable to analyze a portion
of the stub surface by employing an appropriate sampling plan and analytical protocol assuming a random distribution of particles
on the stub surface (7, 10).
7.2 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 the SEM field of view search area (square or
rectangular), analysis of 100 % 100 % of the sample collection area mayis not bealways possible in some systems.
7.2.1 Analysis of the maximum allowable surface area of the sample is recommended, however, many automated systems can be
programmed to terminate the analysis of a stub or series of stubs once a pre-established number of particles have been detected.
The decision as to how many particles satisfy the requirements of a particular case should be set out in the laboratory’s standard
operating procedures.
8. Instrument Requirements and Operation
8.1 General:
8.1.1 Most commercial-grade SEM/EDS systems should be adequate for GSR analysis.analysis given that the criteria set forth in
8.2 and 8.3 are met.
8.1.2 Automated data collection of GSR involves some portion of the data collection being controlled by pre-set software
functions.instrument automation software. The extent to which the SEM and EDS systems communicate and are integrated varies
according to the manufacturers involved and the capabilities of the hardware/software architecture.hardware/software. The system
shall have the ability to recall stage locations of particles for verification and software for particle recognition.
8.2 Scanning Electron Microscope (SEM):
8.2.1 The SEM, operating in the backscattered electron imaging mode, shall be configured to detect particles down to at least 1.0
μm in diameter.
8.2.2 The SEM shall 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 SEM systems
shall include: a motorized stage with automated stage control. The system should have the ability to recall stage locations of
particles for verification and software for particle recognition.
8.3 Energy Dispersive X-Ray Spectrometry (EDS):
8.3.1 The detector shall be configured to produce a resolution of better (less) than 150 eV during analysis, measured or
extrapolated as the full width at half the maximum height of the Mn KaK peak (1).
a
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8.3.2 At a minimum, the EDS spectrum shouldshall be acquired at 20 eV 20 eV per channel.
8.3.3 Display of the EDS output shall encompass the X-ray lines of analytical utility, with a minimum range of 0–15 keV.
8.3.4 Automated systems will also include software capable of acquiring X-ray spectra for a specified collection time or total
X-ray counts.
8.3.5 It is recommended that the instrument The instrument shall be capable of recording spectra obtained from the analysis of
each particle of interest. candidate particles. At a minimum, an automated system shall be capable of storing all of the particle
location 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 the same
orientation as before its removal. This maycould consist of marking the side of each stub and aligning it with marks on the
microscope stage or by having stubs that fit into the stage in only one position (for example, stubs with a pin that is a half-circle
in cross section).
8.5 Detection and Calibration:
8.5.1 Particles of GSR are detected by their backscattered electron signal intensity. The absolute signal intensity that a particle
produces is related to the electron beam current, mean atomic number, and size of the particle (for particle sizes on the order of
the beam diameter). Particles whose mean atomic numbers are high will appear brighter than those of lower mean atomic number
composition. As the beam current increases, the amount of signal each particle produces also increases (1110).
8.5.2 The brightness and contrast settings (low and high thresholds) of the backscattered electron detector system determine the
limits of detection and discrimination of particles based on their mean atomic number. Threshold settings for the backscattered
electron signal should be done with a suitable reference sample of known origin (often supplied by the EDS manufacturer) or pure
element elemental standards at the same parameters that will be instrumental settings used for the sample analysis.analyses. This
reference sample should, if possible, be in the microscope chamber at the same time as the samples to be analyzed.
8.5.3 The backscattered electron detector’s brightness and contrast should be set to include the high atomic number particles of
interest and exclude low atomic number particles that are not of interest. Typically, high contrast and low brightness settings
provide an adequate range between threshold limits for ease of detection. If the beam current is changed or drifts, the brightness
and contrast threshold limits, which were based on the previous beam current, could no longer be compatible with the new
conditions and should be readjusted. The beam current may be measured with Beam current measurements can be taken with (but
are not limited to) a Faraday cup, a specimen current meter, or monitored by comparing the integrated counts within the same peak
in sequentially collected spectra 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 quality
management demands. The use of control charts or tracking of instrument parameters and quality control metrics, or both, is
recommended. Therefore, as minimum conditions:
8.6.1.1 Establish a protocol to confirm optimumappropriate instrument operation parameters on a routine basis.prior to sample
analysis.
8.6.1.2 Monitor the EDS X-ray energy calibration and SEM beam current stability regularly. This may be facilitated by the use
of appropriate reference materials.at least once per batch of samples using appropriate reference materials of known elemental
composition such as copper, cobalt, etc.
8.6.1.3 Analyze a reference material with particles of known size range and comp
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