Optimization of a Py-GC/MS method for silicone -based lubricants analysis

Condom evidence can be analysed using several analytical techniques, such as FTIR, MALDI-MS or DART-TOF-MS, but the only one that was used on real samples for transfer and persistence studies in the context of sexual assault or rape cases was Py-GC/MS. However, there has been no study to identify which specific pyrolysis parameters were the most suitable for the analysis of silicone-based lubricants, especially in terms of repeatability of the analyses. This study looked at the different reported pyrolysis parameter with the aim of optimizing these parameters for polydimethylsiloxane (PDMS) analysis and detection. Experimental parameters were refined while performing a full factorial experimental design (FFD) for the screening, extended to a face centered central composite design (FCCD) for the optimisation. Analyses were led on standard PDMS reference material for the optimisation. Two-way ANOVA statistics and surface responses were used to define the most adequate parameters for the analysis. The adequate parameters were then applied to five condom extracts that were analysed in replicates. Chemometrics was used to evaluate within and between sample variations. Separation of the samples was investigated and was not found to be applicable to the limited set of samples. Issues in reproducibility were highlighted and further investigation on different instruments are necessary to improve the reported study.