190 

 displayed in figure 4-6. The mass spectrum contains the m/z of ions passed by Ql 



into Q2, which fragmented by collision-induced dissociation to form ions detected by 



Q3 as 18 Da lower in mass than the ions transmitted by Ql. The actual assignment 



of the m/z 199 to be the [M-H]^ ion of dodecanoic acid could only be speculated at 



the time these experiments were conducted. The confirmation, both by GC retention 



time and by PCI and EI spectra is located in Chapter 5. Note that in addition to the 



[M-H]"^ ion, PCI of dodecanoic acid produces a number of other ions which undergo 



a neutral loss of H^O, including the [M+H]+, [M-H-(CH2)„]- [M-H-HP]" and [M- 



H-H20-(CH2)J~ ions at m/z 201, the series of m/z 185,171,157, . . ., the m/z 181 ion, 



and the series of m/z 167, 153, 139, 125, . . ., respectively. 



The last peak in the neutral loss of 18 Da chromatogram (scan number 2780) 

 is also presented in this chapter as figure 4-7. As with the previous case, knowledge 

 of retention time as well as information from Chapter 5 aids in drawing the 

 conclusion that this peak is due to octadecanoic acid. This is the last visible peak 

 in the chromatogram; therefore, additional acids of higher m/z in this series are 

 either absent or are at a trace level not detectable by these experiments. 



The identification of the peak corresponding to lactic acid was straightforward, 

 even without confirmation from GC/MS. Lactic acid has been used throughout this 

 dissertation as the model or target compound for various applications due mainly to 

 its characteristic being the only previously known attractant to Aedes aegypti. 

 Additionally, it is typically the most abundant compound found emanating from the 

 skin throughout the work for this dissertation. The neutral loss spectra examined in 



