Use of optimized 1H selTOCSY for identification and individualization of petrol samples from fire debris

Abstract

Detection and identification of ignitable liquids in fire investigation is ongoing challenge for forensics investigators. This study uses the analytical power of NMR analysis and permits the identification of trace amounts of olefinic compounds the complex mixture of petrol that aids the individualization of petrol sources. The ¹H selTOCSY NMR method has proven to be successful in the investigation of the four sets of alkenes namely: 3-methyl-1-butene (set 1), a mixture of 3-methyl-1-butene and 1-pentene (set 2), 2-methyl-2-butene (set 3) and a mixture of cis and trans-2-pentene (set 4) in petrol samples evaporated to different extents, simulating the action of weathering of actual casework samples, and still achieved significant discrimination of petrol brands at 25 % and 50 % evaporation. Discrimination of burned samples also proved possible, both of burnt petrol its own and then petrol burned on different substrates including wood, carpet, fabric, and paper materials representing common household fire debris residues. ¹H selTOCSY NMR experiments on these alkene signals remove most of the non-alkene-related signals from the spectra and thus provide additional clarity in heavily burnt and contaminated samples, increasing the capacity to discriminate between samples using the four alkene markers.