Evaluation of Cross-Contamination of Unlined Metal Cans with Fire Debris Containing Petrol

Abstract

Metal cans are one of the regularly utilized containers for fire debris sampling. When lined cans are used, co-extraction of interfering compounds from the can’s lining may cause false data interpretation. Accordingly, unlined metal cans are recommended to avoid this potential problem. Since unlined metal cans are not vapor tight, heavy loaded volatile matter can escape easily and even trace quantities can leak during the extraction procedure. Therefore, this research was carried out (a) to examine the potential crosscontamination and (b) to interpret data correctly when such cross contaminations occur through unlined metal cans. Volatile compounds were solvent extracted using heated passive headspace adsorption by charcoal strips followed by acetone. Analyses were done using gas chromatography/mass spectrometry (GC/MS) and the data were interpreted was carried out by visual comparison of the total ion chromatograms or extracted ion profiling (EIP), considering target compounds concerning the reference chromatogram. Petrol-free cans, which were kept closely with cans containing known volumes of spiked petrol from 1 µL – 50 µL, eluted all the target compounds. But the eluting patterns of chromatograms were different from reference petrol. Typically, 1,2,4-trimethylbenzene is the prominent peak of the reference petrol chromatogram. In cross contaminations, the co-eluting peak of 1-ethyl-3-methylbenzene/1-ethyl-4-methylbenzene appeared tallest, which is second prominent peak in the reference located in the castle group, at low quantities of spiked petrol samples. Considering high quantities of spiked petrol samples, both co-eluting peak and 1,2,4-trimethylbenzene appeared with almost the same peak heights or prominent peak height for the 1,2,4-Trimethylbenzene. Therefore, misinterpreting of false-positive results can be avoided by examining these pattern distortions. Further, comparison samples should be examined for background interference prior to concluding as cross-contamination since they can distort peak patterns