Significance and Use
4.1 This guide provides guidance in the selection of appropriate sample preparation methods and instrumental parameters for the analysis, comparison, or identification of various polymeric materials by PGC and PGC/MS.
4.1.1 PGC/MS can differentiate between classes of fibers (for example, acrylic, polyester, nylon) and within classes of fibers (for example, acrylics) (1-3).5
4.1.2 Paint binders are differentiated based upon the variety of monomers used in paint formulations which could be difficult to identify by other analytical techniques. In addition, some additives can be detected or identified.
4.1.3 Differentiation can be achieved by the separation and identification of organic components in the adhesive portion of tapes (4, 5) and in the backings of electrical tapes (6).
4.1.4 PGC/MS can provide additional discrimination for other types of polymers such as automotive lenses, automotive body fillers, cosmetics, plastics, and rubbers (7-9).
4.2 Pyrolysis breaks a large molecule into many smaller molecules in a reproducible fashion through the breaking of bonds by means of the application of thermal energy. Analytical pyrolysis is used to provide chemical information on organic-containing solids that cannot be dissolved or otherwise introduced into a chromatographic system. It is also used to analyze and compare solvents bound in a solid material (such as tape adhesives) (10). When analyzed using a separation technique such as gas chromatography, the smaller molecules produced through the action of pyrolysis form a pattern of separated fragments. Mass and structural information indicative of the original molecule are also available when a mass spectral detector is used.
4.3 Although a destructive method, and therefore often placed at the end of an analytical scheme, the pyrograms produced from different polymer compositions form characteristic patterns that are useful for both identification of polymer type and comparisons between samples (4, 6, 9-23). When used for comparison purposes, the goal is to determine whether any exclusionary differences exist between the samples.
Scope
1.1 This guide covers information and recommendations for the selection and application of various PGC and PGC/MS procedures and methods in the forensic examination of polymeric materials (for example, fibers, paint, tape). PGC and PGC/MS methods are used for the identification and comparison of the organic components of these materials. Refer to Practice D3452 for further information on the preparation of the pyrolysis system for polymeric analyses.
1.2 This guide is to be used in conjunction with a broader analytical scheme such as Guides E1610 or E3260, or the SWGMAT Forensic Fiber Examination Guidelines.
1.3 This standard is intended for use by competent forensic science practitioners with the requisite formal education, discipline-specific training (see Practices E2917, E3233, E3234), and demonstrated proficiency to perform forensic casework.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
