Forensic Applications of Gas Chromatography - Forensic Applications of Gas Chromatography - page 95

100

90

80

70

60

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40

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20

10

0

0 5 10 15

Time (min)

20 25 30

Figure 8.9 Total ion chromatogram for butobarbital, pentobarbital and
phenobarbital.

the analytes have a mass spectrum with both 141 and 156 Da as the prin-
cipal ions. Of the three barbiturates being analysed, all three have well-
documented mass spectra data and both butobarbital and pentobarbital have
principal ions of 141 and 156 Da. It is therefore virtually impossible to differ-
entiate between the two based on mass spectra alone. Normally, single drug
standards of the three analytes would be run to establish the retention times
of the analytes of interest. ( Note: There is some tailing on the three peaks
because the concentrations of each of the barbiturates in the mixture were
particularly high.)
By comparing the first two peaks and mass spectra to the third peak
(Figure 8.11), it is observed that this analyte has a mass spectrum with prin-
cipal ions of 204 and 117 Da; these are the principal ions associated with
phenobarbital.

8.3 Forensic Toxicology

8.3.1 Introduction to Forensic/Analytical Toxicology
A poison can be defined as follows: 'What is there that is not a poison? All
things are poison and nothing [is] without poison. Solely the dose determines
that a thing is not a poison' (Paracelsus 1493-1541).