ASTM E1588-95(2001)
(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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Designation:E1588–95 (Reapproved 2001)
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 a bulk sample method, such as atomic absorption or neutron
activation analysis, where the total measured levels of the
1.1 This guide covers the analysis of gunshot residue (GSR)
elements in question are not distinguishable from non-GSR
by scanning electron microscopy/energy-dispersive spectrom-
,
3 4
sources.
etry (SEM/EDS) by manual and automated methods. The
analysis may be performed “manually,” with the operator
5. Sample Preparation
manipulating the microscope stage controls and the EDS
5.1 Once the evidence seal is broken, care should be taken
system software, or in an automated fashion, where some
so that no object touches the surface of the collection stub and
amount of the analysis is controlled by pre-set software
that the specimen stub is not left uncovered any longer than is
functions requiring little or no operator intervention.
reasonable for transfer or mounting.
1.2 Since software and hardware formats vary among com-
5.2 Label the stub in such a manner that it is distinguishable
mercial systems, guidelines will be offered in the most general
from other specimen stubs without compromising the sample’s
terms possible. Each system’s software manuals should be
analysis, that is, label the bottom or side of the stub.
consulted for proper terminology and operation.
5.3 If a non-conductive adhesive was used in the collection
2. Referenced Documents device, the sample will need to be coated to increase its
electrical conductivity. Carbon is a common choice of evapo-
2.1 ASTM Standard:
rant,sinceitwillnotbedetectedwithaberylliumwindowEDS
E 876 Practice for Use of Statistics in the Evaluation of
detector and, thus, will not interfere with X-ray lines of
Spectrometric Data
interest. A thickness of between 5 and 50 nm is typical, with
3. Summary of Practice
more non-conductive samples requiring a thicker coat.
3.1 Particles composed of high mean atomic number ele-
6. Sample Area
ments are detected by their backscattered electron signals and
6.1 Sample stubs for SEMs typically come in one of two
an EDS spectrum is obtained from each. The elemental profile
diameters: 12.7 mm (0.5 in.) or 25.4 mm (1 in.); these yield
is evaluated for constituent elements which may identify the
2 2
surface areas of, respectively, 126.7 mm and 506.7 mm.To
particle as being unique to or indicative of GSR.
manually analyze the total surface area of the stub is prohibi-
4. Significance and Use tively time-consuming; since the distribution of particles col-
lected onto an adhesive surface is random and the particles do
4.1 This document will be of use to forensic laboratory
,
4 5
not tend to cluster, appropriate sampling regimes may be
personnel who are involved in the analysis of GSR samples by
employed.
SEM/EDS.
6.2 This relationship may also be expressed in terms of the
4.2 Analysis of GSR by SEM/EDS currently provides a
,
3 4
portion of the area that must be searched to ensure the finding,
highly definitive method of identification, because it assigns
with some arbitrary certainty, of at least one GSR particle,
an elemental profile to a particular particle. This contrasts with
based on a predetermined population on a stub:
1/N
p 5 | 2 p (1)
This guide is under the jurisdiction of ASTM Committee E30 on Forensic
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
Thus, for example, if a jurisdiction required the identifica-
Current edition approved March 15, 1995. Published May 1995. Originally
tion of a minimum of 5 GSR particles on a stub for a positive
published as E 1588 – 94. Last previous version E 1588 – 94.
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 ParticleAnalysis 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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1588
finding for GSR, a search of 45 % of the stub area that yielded 8. Manual Analysis
no particles would indicate with 95 % certainty that further
8.1 Detection and Calibration—Particles of GSR are de-
searching would be unlikely to provide a positive finding. A
tected by their backscattered electron signal intensity, which is
search of 60 % of the stub with no GSR particles observed
proportionaltoatomicnumber.Particlesofhighermeanatomic
increases this certainty to 99 %.
number are brighter than those of lower atomic number
composition. The absolute signal intensity a particle produces
7. Operating Parameters
is also related to the electron beam current and the particle’s
7.1 Scanning Electron Microscope (SEM) Parameters: size.As the beam current increases, the amount of signal each
7.1.1 Most commercial-grade SEMs should suffice for particle produces also increases.
manual GSR analysis. The SEM/EDS system must, however,
8.1.1 The brightness and contrast settings on the backscat-
meet the following performance specifications:
tered electron detector determine the limits of detection and
7.1.1.1 The instrument must be capable, operating in the discrimination of particles whose mean atomic number exceed
backscattered mode, of detecting potential GSR particles down
the minimum setting but fall below the maximum setting.
to 0.5 µm in diameter. Controls for the backscattered electron signal should be set on
7.1.1.2 The instrument must be capable, operating with the
a particulate sample of known origin at the same parameters as
EDS unit, of producing a signal-to-noise ratio no less than 3:1 willbeusedforthequestionedsampleanalysis;thiscalibration
for the Pb La line from a lead particle no greater than 1 µm in
sampleshould,ifpossible,beinthemicroscopechamberatthe
diameter. same time as the unknown samples to be analyzed.
7.1.1.3 The EDS detector must be capable of resolving
8.1.2 The backscattered electron detector’s brightness and
clearly the Ba La,Lb , and Lb peaks.
contrast should be set to include those particles of interest and
1 1 2
7.1.2 From a practical standpoint, these performance re- exclude particles that are not of interest. Typically, high
quirements indicate that the SEM/EDS system must be capable
contrast and low brightness settings provide an adequate range
of a minimum accelerating voltage of 20 keV; higher acceler- between thresholds for ease of detection. If the beam current is
ating voltages should result in improved analytical sensitivity.
changed or drifts, the threshold detection limits, which were
The EDS system will typically have a resolution of less than
based on the previous beam current, may no longer be
150 eV, measured as the full width at half the maximum height
compatiblewiththenewbeamcurrent.Analysisshallnotbegin
of the Mn Ka peak; lower resolutions will provide improved
until the beam current is stable to within 61 % of its measured
discrimination of adjacent and/or overlapping peaks. Display
value. The beam current may be measured with a Faraday cup,
of the EDS output mu
...
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