The impact of time and storage conditions on samples containing OC pepper sprays on the quantitative ratios of capsaicinoids

Pepper sprays of the OC type constitute the majority of self-defense sprays available on the market. The active ingredient in these preparations is pepper extract: Oleoresin Capsicum, which contains capsaicinoids - natural compounds with irritant properties. Preparations from OC pepper sprays can be distinguished based on differences in the quantitative ratios of four main capsaicinoids: capsaicin, dihydrocapsaicin, nordihydrocapsaicin, and nonivamide. This raises the question whether information on the quantitative ratios of capsaicinoids can also provide answers to questions regarding comparisons of traces of OC preparations, such as whether traces revealed on the clothing of the victim could originate from an OC spray secured from the suspect, or whether traces on the clothing of the suspect and the victim could come from the same pepper spray. Such comparisons would be viable only if the capsaicinoid profile remained unchanged during evidence storage and as a result of solvent extraction from the tested material. The aim of the presented research was to determine if this is indeed the case. Model aging experiments were conducted to examine whether the capsaicinoid profile in traces of OC preparations changed over time and whether solvent extraction affected this profile. Samples of five different OC preparations were applied to cotton swabs, which, after the evaporation of volatile solvents, were placed in three types of packaging with varying levels of tightness and transparency (tight amber vials, polyethylene bags, paper envelopes). These prepared samples underwent solvent extraction with methanol and analysis using gas chromatography – mass spectrometry, after 28, 84, 147, 196, 252, and 301 days from preparation. The likelihood ratio (LR) was applied as a statistical tool to investigate the data obtained. The LR model was computed using the three variables based on the relative content of nordihydrocapsaicin, nonivamide, and dihydrocapsaicin. The cotton swabs used in the experiments served as a model for both the swabs used by the police for securing liquid evidence and the cotton clothing of individuals sprayed with OC pepper sprays. The findings of the conducted studies suggest that the quantitative relationships of capsaicinoids indeed change over time, both in preparations stored in original containers and in traces of these preparations present on clothing. For traces of OC preparations secured on swabs or present on clothing, these changes are more significant the longer the sample is stored and the less airtight the packaging used.