Authors: Emma R. Calabrese1 and Dr. Lauryn E. DeGreeff1

1Florida International University, Department of Chemistry and Biochemistry,
Global Forensic and Justice Center, 11200 SW 8th St, Miami, FL 33199

Explosives, drugs, and other contraband are often packaged with the intent of concealing their presence. These attempts to avoid detection are often ineffective when up against well-trained detection canines who are able to sniff out the volatile organic compounds (VOCs) emanating from the target. The transport of VOCs from a hidden target is obstructed by the products used to wrap or contain it due to limited transport through the material, as well as losses due adsorption/absorption. This research focuses on the latter, wherein the degree of analyte lost is impacted by the chemical properties of both the containment material and the target analyte involved. Our work sought to gain a better understanding of the adsorptive and absorptive properties of commonly used materials – metal, glass, plastic, and cardboard – as they were exposed to certain explosives and drugs. Trinitrotoluene, triacetone triperoxide, ammonium nitrate, and cocaine each have a single dominant analyte in their headspace thus classifying them as having a simple vapor profile, whereas hexamethylene triperoxide diamine has a mixture of VOCs comprising its headspace and making it a complex vapor profile [1-5]. For the simple vapor profiles, vapor sorption would merely result in a lower concentration of analyte found in the headspace than expected based on the quantity of the bulk material. However, for the complex vapor profile, preferential sorption of certain VOCs can alter the expected concentration ratios that makes up their distinctive and anticipated headspace causing more sever detection complications.
Complementary methods of adsorption/desorption affinity through the use of a quartz crystal microbalance (QCM) and headspace analysis by way of solid phase microextraction with gas chromatography and either a mass spectrometer or electron capture detector (SPME-GC/MS or SPME-GC/ECD) were implemented. The QCM allowed for the measurement of nanogram level mass changes as vapor from each analyte was flowed over and interacted with sensors coated with stainless steel, silicon dioxide, polystyrene, and cellulose to simulate metal, glass, plastic, and cardboard, respectively. The use of SPME-GC/MS(ECD) revealed losses of the headspace concentration of each analyte over time when surface areas of either 50cm2 or 100cm2 of each material were introduced. In addition to validating the anticipated behavior of containment material when exposed to specific explosives and drugs, the results also identify situations in which the loss of certain VOCs to certain containment material is more likely to hinder detection efforts. In particular, cardboard demonstrated higher levels of analyte interaction leading to a diminished concentration in the headspace over time. In contrast, the trials in which stainless steel was used resulted in minimal variation of the headspace and a limited increase in the mass adsorbed onto the QCM sensor. Overall, the most significant amount of sorption occurred within the first hour of exposure to each material.

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[2] DeGreeff, L.E.; Peranich, K. (2021) Forensic Chemistry, 25, 100342.
[3] Oxley, J.C.; Smith, J.L.; Shinde, K; Moran, J. (2005) Propellants, Explos., Pyrotech., 30(2), 127-130.
[4] Furton, K.G.; Hsu, Y.L.; Luo, T.Y.; Alvarez, N; Lagos, P. (1997) Forensic Evidence Analysis and Crime Scene Investigation, 2941, 56-62.
[5] DeGreeff, L.E.; Cerreta, M; Katilie, C.J. (2017) Forensic Chemistry, 4, 41-50.