Standard Practice for Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry
5.1 This document will be of use to forensic laboratory personnel who are involved in the analysis of GSR samples by SEM/EDS (6).
5.2 SEM/EDS analysis of GSR is a non-destructive method that provides (7, 8) both morphological information and the elemental profiles of individual particles.
5.3 Particle analysis contrasts with bulk sample methods, such as atomic absorption spectrophotometry (AAS) (9), neutron activation analysis (NAA) (10), 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 morphological information and individual particle identification.
5.4 X-ray fluorescence spectrometry (XRF) is a technique that has been used to map the placement and distribution of GSR particles surrounding bullet holes in order to establish shooting distances (11). Unlike the solution-based bulk methods of analysis, XRF is non-destructive; however, XRF still does not provide morphological information and is incapable of individual GSR particle identification.
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. This practice refers to the analysis of electron microscopy stubs and does not address sample collection (1).2
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.
1.5 This practice 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 this practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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