174 

 section). Additionally, both compounds undergo neutral losses of CO (28 Da) and 



H2CO (30 Da), further confirming the presence of a carboxylic acid functional group 



for both species. 



Compounds identified or suspected by tandem mass spectrometric analysis are 

 listed in table 4-1. Most of the compounds found to be present by analysis of 

 daughter spectra were carboxylic acids. The saturated and unsaturated acids are well 

 known to be present on the skin [30,31]. These compounds were readily identifiable; 

 the most abundant species found when desorbed skin emanations are sampled from 

 glass beads are carboxylic acids as shown in this chapter and Chapters 2 and 5. Due 

 to the presence of methane CI adduct ions from lower carbon-number carboxylic 

 acids continually being transferred to the ion source, interpretation of daughter 

 spectra of the [M-t-H]"*^ ions of carboxylic acids consisting of ten or greater carbons 

 was ambiguous and speculative. 



In addition, substituted acids, such as lactic acid, were found to be present. 

 Lactic acid was the most abundant compound found in these analyses. Pyruvic acid 

 was also suspected to be present. In negative ion analyses (NCI), the [M-H]~ ion 

 of lactic acid will undergo elimination of Hj to form an ion at m/z 87, identical in 

 m/z value to the pyruvate ion, the [M-H]~ ion of pyruvic acid. Inspection of mass 

 chromatograms from NCI with single stage detection clearly showed that the thermal 

 desorption profile of m/z 87 contained the profile of the m/z 87 ion produced from 

 the lactic acid deprotonated molecule (m/z 89) as well as a profile depicting m/z 87 

 resulting from an additional source. Analysis of this region by NCI combined 



