218 

 cases, library searching failed to provide a reasonable compound choice for the 



unknown mass spectrum. When this occurred, r.^ information obtained from CI 



analyses was relied upon to further restrict the search. If this still failed to produce 



a reasonable selection, the mass spectra were manually examined. This involved a 



quick inspection for characteristic compound class fragments or McLafferty 



rearrangement ions. This information was then employed and library re-searched 



with new constraints. Compounds which remained unidentified are not listed in the 



tables contained throughout this chapter, although speculative identifications are 



listed and noted. The remainder of this introduction will address the characteristic 



fragments and McLafferty rearrangement ions which were examined in the 



interpretation used in this dissertation. 



Aliphatic acids show a characteristic McLafferty rearrangement ion at m/z 60. 



This rearrangement can occur for compounds with an available y-hydrogen and 



unsubstituted a-carbon [79,109,110]. For EI GC/MS analysis, mass chromatograms 



for this ion were examined to determine the location of the carboxylic acid series 



from propenoic acid up to octadecanoic acid. Fragment ions corresponding to [M- 



IS]"^, [M-28]"^, and [M-45]'^ were fairly common in these mass spectra. The possible 



presence of amines was determined by examining the mass chromatogram for an ion 



at m/z 58. Esters produce an m/z 74 ion when methyl substituted and an m/z 88 ion 



when ethyl substituted. Mass chromatograms for the m/z 58 and 74 ions were also 



examined in almost every case. 



