Forensic analysis of gasoline in molotov cocktail using gas chromatography-mass spectrometry and chemometric procedures
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Date
2014-10
Authors
Jamaluddin, Mohamad Ismail
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
There has been a significant increase in the number of seizure of Molotov cocktail by the Royal Malaysia Police (RMP) during street demonstrations, religious tensions and society conflicts in Malaysia recently. In a forensic science investigation, information gathered for intelligence purposes and investigation on the composition of a material of interest may serve as a link between different cases, or to a particular source or group of people involved. This thesis studies the variability (in term of chemical profiles) of gasoline commonly used as accelerant in Molotov cocktail using gas chromatography-mass spectrometry (GC-MS) coupled with chemometric techniques for advanced data analysis including principal component analysis (PCA) and hierarchical cluster analysis (HCA). A total of 27 samples of fresh gasoline were collected from different service stations. Collection of gasoline samples from two selected service stations at different time interval over 28 days was conducted to study their profiles changes over time. Two brands of gasoline were also used to investigate the profiles change after being subjected to evaporation and dissolution. All samples were analysed using GC-MS and selected peaks were used for subsequent data analysis. The results show that the GC-MS analyses were able to discriminate the fresh gasoline samples into two main groups on the basis of the different brands of gasoline. Using selected peaks from chromatogram, , the fresh samples collected over time from a particular service station were able to be
discriminated though some were tightly clustered. Both samples showed a predictable trend on PCA score plot that could possibly be used to estimate the extent of evaporation of a sample. The extracted ion chromatography data of the gasoline samples in contact with water appeared to be only slightly changed. The investigation of the recovery of accelerant on spent Molotov cocktail found that only 80% of the Molotov cocktails were completely combusted. Solvent rinse (of the recovered glass fragments) has shown negative result which could suggest that collection of glass fragment of exploded Molotov cocktail for accelerant recovery is not advisable unless for other forensic purposes such as fingerprint recovery. In conclusion, the fresh gasoline from different sources could be differentiated according to their different brands or into small clusters (within brand) using the chemometrics techniques. This information is useful for the investigation of seized Molotov cocktail cases. Evaporated samples are grouped differently by the chemometrics techniques however in a predictable manner while dissolution gave only slight change to the gasoline profiles. In the case of spent Molotov cocktail, accelerant would be lost due to evaporation as a result of intense burning and heat.
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Keywords
Molotov cocktail