182 

 neutral loss data from selected parent ions; the parent ions surveyed are the 



methane CI produced [M + H]"^, [M-H]^, and [M-H]~ ions of each tested compound. 



The inclusion of information in the table is by no means a statement that all 



compounds within a class will exhibit the same trend. Additionally, the trends 



observed here were determined for a specific set of CID conditions. Exclusion of 



trends from the table for a parent ion of a class of compounds is due to the inability 



to find an observable trend and/or due to insufficient data from the analyses. The 



purpose of this table is to provide a foundation for screening different classes within 



a sample. Identification of compounds can then be carried out by GC/MS employing 



CI and EI analysis with the screening information aiding as a preview of classes 



present. 



The first two classes listed in table 4-2 are the alkanes and alkenes. The 



information for their inclusion in the table was derived from the MS/MS analyses of 



straight chain aliphatics as well as compounds containing an alkyl chain attached to 



a functional group. One of the more significant indications of the presence of these 



classes is the existence of the [M + H]^ ion under PCI and the inability to form the 



deprotonated [M-H]~ ion under NCI conditions. Simple alkanes and alkenes are not 



easily deprotonated, even by the strongest reagent bases, due to their weakly acidic 



nature [74,96]. In these experiments, proton abstraction from simple alkanes did not 



occur with methane reagent gas. An additional characteristic is the successive 



neutral losses of approximately 14 Da. This trend is also observed for alkyl chains 



attached to various functional groups. There are mass spectrometric methods for 



