ASTM E1588-95
(Guide)Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy-Dispersive Spectroscopy
Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy-Dispersive Spectroscopy
SCOPE
1.1 This guide covers the analysis of gunshot residue (GSR) by scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) by manual and automated methods. The analysis may be performed "manually," with the operator manipulating the microscope stage controls and the EDS system software, or in an automated fashion, where some amount of the analysis is controlled by pre-set software functions requiring little or no operator intervention.
1.2 Since software and hardware formats vary among commercial systems, guidelines will be offered in the most general terms possible. Each system's software manuals should be consulted for proper terminology and operation.
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Standards Content (Sample)
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Designation: E 1588 – 95
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Guide for
Gunshot Residue Analysis by Scanning Electron
Microscopy/ Energy—Dispersive Spectroscopy
This standard is issued under the fixed designation E 1588; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope elements in question are not distinguishable from non-GSR
,
3 4
sources.
1.1 This guide covers the analysis of gunshot residue (GSR)
by scanning electron microscopy/energy-dispersive spectrom-
5. Sample Preparation
etry (SEM/EDS) by manual and automated methods. The
5.1 Once the evidence seal is broken, care should be taken
analysis may be performed “manually,” with the operator
so that no object touches the surface of the collection stub and
manipulating the microscope stage controls and the EDS
that the specimen stub is not left uncovered any longer than is
system software, or in an automated fashion, where some
reasonable for transfer or mounting.
amount of the analysis is controlled by pre-set software
5.2 Label the stub in such a manner that it is distinguishable
functions requiring little or no operator intervention.
from other specimen stubs without compromising the sample’s
1.2 Since software and hardware formats vary among com-
analysis, that is, label the bottom or side of the stub.
mercial systems, guidelines will be offered in the most general
5.3 If a non-conductive adhesive was used in the collection
terms possible. Each system’s software manuals should be
device, the sample will need to be coated to increase its
consulted for proper terminology and operation.
electrical conductivity. Carbon is a common choice of evapo-
2. Referenced Documents rant, since it will not be detected with a beryllium window EDS
detector and, thus, will not interfere with X-ray lines of
2.1 ASTM Standard:
interest. A thickness of between 5 and 50 nm is typical, with
E 876 Practice for Use of Statistics in the Evaluation of
more non-conductive samples requiring a thicker coat.
Spectrometric Data
6. Sample Area
3. Summary of Practice
6.1 Sample stubs for SEMs typically come in one of two
3.1 Particles composed of high mean atomic number ele-
diameters: 12.7 mm (0.5 in.) or 25.4 mm (1 in.); these yield
ments are detected by their backscattered electron signals and
2 2
surface areas of, respectively, 126.7 mm and 506.7 mm .To
an EDS spectrum is obtained from each. The elemental profile
manually analyze the total surface area of the stub is prohibi-
is evaluated for constituent elements which may identify the
tively time-consuming; since the distribution of particles col-
particle as being unique to or indicative of GSR.
lected onto an adhesive surface is random and the particles do
,
4 5
4. Significance and Use
not tend to cluster, appropriate sampling regimes may be
employed.
4.1 This document will be of use to forensic laboratory
6.2 This relationship may also be expressed in terms of the
personnel who are involved in the analysis of GSR samples by
portion of the area that must be searched to ensure the finding,
SEM/EDS.
with some arbitrary certainty, of at least one GSR particle,
4.2 Analysis of GSR by SEM/EDS currently provides a
,
3 4
based on a predetermined population on a stub:
highly definitive method of identification, because it assigns
1/N
an elemental profile to a particular particle. This contrasts with
p 5 | 2 p (1)
a bulk sample method, such as atomic absorption or neutron
Thus, for example, if a jurisdiction required the identifica-
activation analysis, where the total measured levels of the
tion of a minimum of 5 GSR particles on a stub for a positive
finding for GSR, a search of 45 % of the stub area that yielded
This guide is under the jurisdiction of ASTM Committee E-30 on Forensic
no particles would indicate with 95 % certainty that further
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
searching would be unlikely to provide a positive finding. A
Current edition approved March 15, 1995. Published May 1995. Originally
search of 60 % of the stub with no GSR particles observed
published as E 1588 – 94. Last previous version E 1588 – 94.
increases this certainty to 99 %.
Annual Book of ASTM Standards, Vol 03.06.
Krishnan, S. S., “Detection of Gunshot Residue: Present Status,” Forensic
Science Handbook, Volume I, Prentice Hall, Inc., Englewood Cliffs, NJ, 1982.
4 5
Wolten, G. M., Nesbitt, R. S., Calloway, A. R., Loper, G. L., and Jones, P. F., Halberstam, R. C., “A Simplified Probability Equation for Gunshot Primer
“Final Report on Particle Analysis for Gunshot Residue Detection,” Report ATR-77 Residue (GSR) Detection,” Journal of Forensic Sciences, V36, N3, pp. 894–897,
(7915)-3, Aerospace Corporation, Segundo, CA, 1977. 1991.
E 1588
7. Operating Parameters is also related to the electron beam current and the particle’s
size. As the beam current increases, the amount of signal each
7.1 Scanning Electron Microscope (SEM) Parameters:
particle produces also increases.
7.1.1 Most commercial-grade SEMs should suffice for
8.1.1 The brightness and contrast settings on the backscat-
manual GSR analysis. The SEM/EDS system must, however,
tered electron detector determine the limits of detection and
meet the following performance specifications:
discrimination of particles whose mean atomic number exceed
7.1.1.1 The instrument must be capable, operating in the
the minimum setting but fall below the maximum setting.
backscattered mode, of detecting potential GSR particles down
Controls for the backscattered electron signal should be set on
to 0.5 μm in diameter.
a particulate sample of known origin at the same parameters as
7.1.1.2 The instrument must be capable, operating with the
will be used for the questioned sample analysis; this calibration
EDS unit, of producing a signal-to-noise ratio no less than 3:1
sample should, if possible, be in the microscope chamber at the
for the Pb La line from a lead particle no greater than 1 μm in
same time as the unknown samples to be analyzed.
diameter.
8.1.2 The backscattered electron detector’s brightness and
7.1.1.3 The EDS detector must be capable of resolving
contrast should be set to include those particles of interest and
clearly the Ba La ,Lb , and Lb peaks.
1 1 2
exclude particles that are not of interest. Typically, high
7.1.2 From a practical standpoint, these performance re-
contrast and low brightness settings provide an adequate range
quirements indicate that the SEM/EDS system must be capable
between thresholds for ease of detection. If the beam current is
of a minimum accelerating voltage of 20 keV; higher acceler-
changed or drifts, the threshold detection limits, which were
ating voltages should result in improved analytical sensitivity.
based on the previous beam current, may no longer be
The EDS system will typically have a resolution of less than
compatible with the new beam current. Analysis shall not begin
150 eV, measured as the full width at half the maximum height
until the beam current is stable to within 61 % of its measured
of the Mn Ka peak; lower resolutions will provide improved
value. The beam current may be measured with a Faraday cup,
discrimination of adjacent and/or overlapping peaks. Display
a specimen current meter or by comparing the integrated
of the EDS output must cover the range of 0-20 keV.
counts within the same peak in sequentially collected spectra.
7.2 Energ
...
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