Forensic Applications of Gas Chromatography - Forensic Applications of Gas Chromatography - page 112

(gasoline), lighter fluid, paint thinner and turpentine. Other less commonly
encountered ignitable liquids such as methylated spirits, diesel and toluene
may also be found.

8.4.2.1 Petrol
Petrol (also known as gasoline) is a complex mixture of chemicals obtained
from the distillation of crude oil with performance-enhancing chemicals
added by the company blending the product. Petrol is typically used as a
fuel for light road vehicles (e.g., cars) and small motorised devices (e.g., lawn
mowers) and is typically composed of hydrocarbons with chain lengths of
C 4 to C 12 .
When analysed by GC-MS, petrol produces a fairly characteristically
shaped chromatogram (Figure 8.24); however, petrol evaporates easily, so
what is generally found is that there will be very variable proportions of the
different peaks because of the ease of weathering. Weathering is a term used
to describe the evaporation effects of ignitable liquids. Weathering can be
controlled in a laboratory environment when an ignitable liquid will be left
until a certain volume of the liquid has evaporated. For example, if the start-
ing volume for petrol is 100 mL and 50 mL is left after evaporation, then
the liquid is 50% weathered. This is much more difficult to control and
understand in an actual fire scenario since there are many environmental

Abundance

1e+07

a

9000000

8000000

7000000

6000000

5000000

4000000

3000000

e

b

c

2000000

d

1000000

0

Time --> 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00

Figure 8.24 Total ion chromatogram of a pure petrol standard sampled by SPME.
Peak identification: (a) toluene, (b) ethylbenzene, (c) m,p-xylene, (d) o-xylene, (e)
1,2,4-trimethylbenzene.