Forensic Analysis of Trace Evidence Using Direct Solid-Sampling Techniques in Plasma Spectroscopy
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Authors
Moghadam, Kate
Date
2025-02-26
Type
Language
eng
Keyword
Forensic Science , Solid-Sampling , ETV , ICPOES , LIBS , LIBS/LA-ICPMS , Analytical Chemistry , Solder , Polymer
Alternative Title
Abstract
Locard’s Exchange Principle, which posits that “every contact leaves a trace”, has long guided the discovery and value of trace physical evidence in the investigation and adjudication of crime. In the modern forensic laboratory, elemental analyses provide a powerful way to identify, characterize, and differentiate recovered trace evidence. As technology and weapon systems evolve, there is an ongoing demand to enhance these analysis techniques to maintain forensic intelligence and support the judicial process. There is also a need to develop methods suitable for evidence available only in scarce quantities, as conventional methods require digestion of large amounts of material. This thesis will explore solid-sampling techniques for profiling two types of trace evidence encountered in Canadian casework.
Solder is one form of trace evidence that can be used to investigate improvised explosive devices (IEDs). Following the detonation of an IED, electrical components containing solder may be recovered and chemically associated to source materials or tools used in its construction. Electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICPOES) was used to quantify elements in solders and assess compositional changes during mock IED preparation scenarios. Utilizing a data processing strategy with background correction can improve figures of merit and increase efficiency for routine analyses.
Another approach combines laser induced breakdown spectroscopy/laser ablation with inductively coupled plasma mass spectrometry (LIBS/LA-ICPMS). This technique allows for rapid screening of solders and achieves quantification with only microscopic destruction to the sample. LIBS/LA-ICPMS is especially compelling for exhibits that must be preserved for casework and court testimony.
A method by LIBS is presented for the preliminary profiling of polymer filaments used in the fabrication of 3D-printed firearms (3DPFs). In this project, LIBS is used to characterize various classes and brands of black polymer filaments available on the commercial market (e.g., polylactic acid, etc.). Spectral features representative of additives, fillers, or species of the base polymer chain are sufficient to discriminate different filaments and associate traces of 3DPFs to specific filament sources. Outcomes demonstrate that the LIBS method is a quick, effective tool for analyzing black polymers and is a complementary tool to existing methods for 3DPF examination.