Exploring Inter-Sample Variability of Malaysian Gasoline Using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and Multivariate Exploratory Methods for Forensic Investigation

Abstract

Determination of the source origin of fuel plays a paramount role in forensic investigations. The most probable location for selling questioned fuel seized from a crime scene can be inferred by determining the brand and quality grade of the fuel. In other words, insights into inter- and intra-sample variations of gasoline sold within a country could potentially contribute to developing reliable procedures for identifying gasoline sources. The current work aims to explore inter-gasoline variation based on their infrared (IR) fingerprints using multivariate exploratory tools. A total of 48 samples representing four brands (i.e., BHP, PET, PNAS, and S) with two different research octane numbers (RON95 and RON97) were purchased from eight pump stations in Selangor, Malaysia, over three different periods. The organic components of gasoline samples were analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy with minimal sample preparation. Multivariate exploratory tools, including principal component analysis and hierarchical clustering analysis, were applied to reveal variations by brand, RON grade, pump station, and sampling period. Results showed that IR fingerprints of gasoline varied by the four source origins. BHP gasoline emerged as the most discriminative sample, associated with lower inter-sampling period variation. On the other hand, PET and PNAS were highly similar, with PET showing pronounced inter-pump station variation. In particular, S gasoline was readily discriminated by sampling periods and pump stations. In conclusion, coupling ATR-FTIR spectroscopy with chemometric techniques is potentially useful for determining gasoline source origins.