An evaluation of improvised sampling materials for the collection of chemical trace evidence

Melissa Payne

Trace chemical evidence can be identified in numerous crime-related scenarios, including crime scenes typical of assaults burglaries, etc., covert terrorist attacks, and clandestine illicit drug laboratories, and can provide valuable evidential links between a suspect and a crime scene. Sampling methods of such chemical traces, such as swabbing, and tape-lifting have been widely reviewed and established in the forensic science field. Forensic personnel are typically equipped with all requisite sampling equipment when responding to crime scenes, including during covert and deployed investigations; however, given the unpredictable circumstances and environments covert operations often encounter, personnel may not always have access to this equipment. In these types of scenarios easily accessible, commercially available materials, or improvised sampling materials (ISMs) can be implemented. In this study, seven chemicals of security concern (ammonium nitrate, potassium chlorate, potassium nitrate, potassium perchlorate, sodium azide, sodium chlorate, and sodium nitrate) were identified from the list of Chemicals of Security Concern as representative compounds and analysed in the milligram range using portable and laboratory-based Raman and infrared spectroscopy. Controlled quantities of these target analytes were deposited onto a polypropylene surface and collected using conventional sampling materials (swab wetted with sterile water and a gel lifter) and improvised sampling materials (Band-Aid ®, Post-It Note ® and alcohol wipe). Post-It Notes ® demonstrated a better overall performance in the ability to recover analytes and analyse without interfering peaks as a result of the adhesive. Band-Aids ®, due to the stronger adhesive, had more interfering peaks present in spectra, particularly those samples analysed on FTIR instruments. The alcohol wipe also demonstrated to have interfering peaks associated with the pre-wetting solvents, water and propan-2-ol. Overall, this novel approach demonstrated a simple yet effective sampling strategy, allowing for rapid collection from smooth, non-porous surfaces via adhesive and wipe improvised sampling materials.

An evaluation of improvised sampling materials for the collection of chemical trace evidence

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