195 

 this section exhibit the most abundant peaks to be those of fatty acids rather than 



lactic acid. It is known from previous work in Chapter 3 that lactic acid will undergo 



a neutral loss of 18 Da (H2O) from the [M+H]"^ ion. Therefore, the presence of an 



ion at m/z 91 in the neutral loss (of 18 Da) spectra from these analyses should be 



readily be observed. Figure 4-8 reveals the location of what is suspected to be lactic 



acid in these experiments. This can be confirmed by comparing the retention times 



to those acquired under the same GC conditions in Chapter 5. It is interesting to 



note (from the RIC trace in figure 4-8), that lactic acid appears to be less abundant 



than the fatty acids. The experiments for figures 4-5 through 4-7 were conducted in 



December, a relatively cold month. Therefore, lactic acid may not be as prevalent 



on the skin as it would be were the temperature warmer. 



These experiments were repeated a month later under warmer weather 



conditions as well as after physical exertion to produce a greater amount of 



perspiration on the skin for subsequent sampling. Comparing the RIC for a neutral 



loss of 18 Da in figure 4-9 (bottom trace) to that of figure 4-8 (bottom trace), it is 



quite evident that lactic acid is the most abundant compound in this second sample. 



Included at the top of figure 4-9 is the chromatogram for the neutral loss of 28 Da 



(CO) from the m/z 91 ion, additionally providing confirmation that this is lactic acid. 



The final figure (4-10) confirms this; this is the neutral loss of 44 Da mass spectrum 



in the negative ion mode from the peak centered around scan 1480. Present are the 



[M-H]~ ion of lactic acid at m/z 89, which loses CO2 to form m/z 45, as well as the 



