Forensic comparison of unevaporated and evaporated automotive gasoline samples from Australia and New Zealand

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The comparison of two or more samples of gasoline (petrol) to establish a common origin is a difficult problem in the forensic investigation of arsons and suspicious fires. The high- boiling fraction of the gasoline was targeted with a view to apply the techniques described herein to evaporated gasoline samples in the future. A novel micro solid phase extraction technique using activated alumina was developed to isolate the polar compounds and the polycyclic aromatic hydrocarbons from a 200 µL sample of gasoline. This technique was applied to 35 randomly collected samples of unevaporated gasoline, covering three different grades (regular unleaded, premium unleaded and lead replacement), collected in Sydney, Australia. The samples were analysed using full-scan GC-MS; potential target compounds identified were the C0- to C2-naphthalenes. The samples were then re-analysed directly, without prior treatment, using GC-MS in selected ion monitoring (SIM) mode for target compounds that exhibited variation between gasoline samples. Multivariate statistical analysis (principal component and linear discriminant analysis) was applied to the chromatographic data. The first two principal components described approximately 90% of the variation in the data and showed that the majority of the 35 samples could be differentiated using the method developed. A comparison of unevaporated samples collected in Auckland, New Zealand to those collected in Sydney was also made. Most of the samples could be differentiated based on their country of origin. The variation of unevaporated regular unleaded and premium unleaded gasoline over time at three different service stations was studied. Ninety-six samples of gasoline were collected over a 16 week period and analysed for their C0- to C2-naphthalene content using the GC-MS (SIM) method that was developed. In most cases it was found that the C0- to C2-naphthalene profile in gasoline changed from week to week, and from station to station. Samples of 25%, 50%, 75% and 90% evaporated gasoline (w/w) were generated from the 35 randomly collected samples of unevaporated gasoline. The C0- to C2-naphthalene content of all unevaporated and evaporated gasoline samples was determined using the GC- MS (SIM) method. Analysis of the data by principal components followed by linear discriminant analysis showed that the 35 samples formed 18 unique groups, irrespective of the level of evaporation. The application of the method to forensic casework is discussed.
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