Chemistry Reference
In-Depth Information
sample is quickly heated in a pyrolysis unit in the absence of air and is then
directly transferred by an inert carrier stream to the inlet of the GC-MS. The
output from the py-GC is called a pyrogram. The smaller molecules formed
in the pyrolysis of the paint sample can be identified by mass spectrometry
and the paint polymer can also be identified by understanding the chemistry
of the thermal decomposition of the components.
Consider an example where the green paint analysed by FTIR was col-
lected from a scene where a painted monument to soldiers who died in World
War II was vandalised. A suspect was apprehended shortly after the crime
took place and was found to be carrying a crow bar/jemmy with small chips
of green paint attached. Some very small chips of paint were also found in the
inside jacket pocket of the suspect. When FTIR analysis was carried out, it
appeared that the spectra of the chips were very similar to those of the FTIR
of the paint collected from the monument. However, the results from colour
analysis and FTIR were not conclusive enough to provide an interpretation;
therefore, py-GC was carried out.
The pyrogram of the green paint is shown in Figure 8.37. This pyrogram
shows peaks for benzene and acetic acid. These compounds are typical of
bergene
105
322
100
95
90
85
80
75
70
65
60
55
50
45
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35
30
25
20
15
10
5
0
201
vinyl versatate
components
14.93
14.69
15.06
14.57
215
14.45
13.45
13.68
15.48
15.56
15.74
16.17
7.33
7.38
226
6.84
871
8.80
13.35
7.52
9.06
12.04
309
5.54
6.09
9.39
10.33
459 485
2
3
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9 10
Time (min)
11
12
13
14
15
16
17
Figure 8.37
Pyrogram of green paint from WW2 monument.
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