Chemical Profiling and Persistence of Gasoline Residues on Natural and Synthetic Porous Substrates under Tropical Weathering Conditions

Understanding the persistence of gasoline residues on porous substrates is fundamental to arson investigations, which may provide critical evidence of malicious intent through the identification of ignitable liquid residues (ILRs). In forensic practice, delays between fire suppression and evidence collection frequently result in the recovery of weathered debris, where volatile organic compounds (VOCs) have been significantly depleted by environmental factors. In tropical regions such as Malaysia, high ambient temperatures and relative humidity are hypothesised to accelerate this evaporation process, potentially hindering residue recovery. This study evaluates the retention and chemical profiling of gasoline residues on natural (100% cotton) and synthetic (100% polyester) substrates subjected to outdoor tropical weathering. Following controlled ignition and suppression, samples were exposed to environmental conditions for durations ranging from 30 min to 960 min (16 h). Residues were extracted via passive headspace adsorption and analysed using gas chromatography–mass spectrometry (GC–MS) in strict accordance with American Standards for Testing and Materials (ASTM) E1618-19 standards. Nine diagnostic target compounds, including critical alkylbenzenes and indane, were consistently identified using the National Institute of Standards and Technology (NIST) library with a minimum match quality of 85%. The findings demonstrated that both natural and synthetic substrates successfully retained identifiable gasoline residues throughout the 960-minute exposure period, despite the aggressive tropical environment. This confirms a viable window for short-term ILR recovery in warm, humid climates and underscores the significance of substrate-environment interactions in environmental forensic investigations.