Forensic comparison of unevaporated and evaporated automotive gasoline samples from Australia and New Zealand
- Publication Type:
- Thesis
- Issue Date:
- 2002
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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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