Influence of Diene Rubber Combustion Residue on the Identification of Gasoline in Fire Debris

Abstract

The identification of accelerant about gasoline and other ignited liquids in arson has always been a difficult problem in the field of physical evidence identification. How to avoid “false positive” and “false negative” results is a key issue. To study the interference of diene rubber on gasoline identification from two aspects of “false positives” and “false negatives”, and to explore its degree when gasoline was mixed with diene rubber in different proportions, the combustion residues obtained from cis-polybutadiene rubber, isobutylene isoprene rubber and styrene butadiene rubber after loading different amounts of gasoline were compared using gas chromatography-mass spectrometry (GC-MS). The results showed that alkanes, alkenes/cycloalkanes, aromatic-alkylbenzenes, homologs of indenes and indanes, alkylnaphthalenes and polycyclic aromatic hydrocarbons were detected in the combustion residues of the three kinds of diene rubber samples before and after gasoline loading, which was consistent with gasoline in terms of the characteristic components categories and had strong interference with gasoline identification. After loading 0.05 mL and 0.1 mL gasoline respectively into 5 g rubber sample, there was no significant changes in the characteristic components of cycloalkanes/alkenes, alkylnaphthalenes, and polycyclic aromatic hydrocarbons in the rubber combustion residues. The number and relative peak area ratio of characteristic peaks corresponding to aromatic-alkylbenzenes, homologs of indenes and indanes changed to different degrees, while the changes of alkylbenzenes were more representative. Loading gasoline or not had little effect on the ratio of the characteristic peaks of C2 benzene components in the combustion residues of cis-polybutadiene rubber. The ratio among three characteristic peaks of C2 benzene components in the combustion residues of isobutylene isoprene rubber and styrene butadiene rubber samples changed significantly when the gasoline loading amount reached 0.1 mL. This study can provide important references for the gasoline identification when there is a presence of diene rubber matrix in practical work.

Keywords

• diene rubber
• false positive
• false negative
• combustion residues
• gas chromatography-mass spectrometry (gc-ms)
• evidence identification