Forensic analysis of tetrahydrothiophene (THT) at gas explosion scenes: Adsorption–desorption dynamics on common substrates

Tetrahydrothiophene (THT) is a common odorant in natural gas and plays a crucial role as key chemical evidence in post-explosion investigations. However, there has been limited research on the detection of THT in samples collected from gas explosion scenes. Headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was employed to systematically investigate the adsorption and desorption behavior of THT on three common substrates: soil, sponge, and fabric. The results indicate that the physical and chemical properties of the substrate significantly influence the retention of THT. Polyurethane sponge and flax fiber exhibit the highest adsorption capacity, attributed to their larger specific surface area and porous structure. With soil as the representative substrate, humidity significantly reduces physical adsorption efficiency. Desorption kinetics exhibit significant temperature dependence: THT is released markedly faster as temperature rises, whereas storage under low-temperature conditions substantially prolongs its persistence on the substrate. The limit of detection (LOD) of the proposed method is 0.05 ng/g in soil, thus affording sufficient sensitivity for ultra-trace analysis. These findings provide a critical scientific basis for on-site evidence collection (prioritizing dry, porous materials), optimizing evidence preservation (immediate low-temperature storage), and enhancing the accuracy of forensic evidence interpretation in gas explosion cases.