286 

 microscale purge and trap GC/MS applied to skin emanations for this project are 

 preliminary; microscale purge and trap experiments have shown that the 

 composition of components desorbed from beads is similar to that from the enclosed 

 hand in a Tedlar bag. The difference between these two sample introduction 

 methods lies mainly in the markedly different relative intensities of some 

 components. Further studies involving quantitation will be required to confidently 

 report the differences. 



The negative ion fragmentations, attachments, and oligomerization 

 (polymerization) of lactic acid, the only previously known attractant for Ae. aegypti, 

 were examined in Chapter 3. Negative ions are typically not employed for structural 

 information; however, lactic acid can be readily identified via NCI. Oligomerization 

 reactions, as well as chloride ion attachment, provide easily detectable ions in the 

 NCI mass spectrum of lactic acid. Although lactic acid is one of the major 

 components found emanating from the skin, the determination of its presence by EI 

 is not achievable due to the absence of the M"^' ion and the resultant low mass 

 fragments. 



Altering the matrix conditions by adding acid or base to lactic acid affected 

 the attraction oiAe. aegypti. The observed effects have been rationalized to result 

 from simple acid-base dissociation equilibria. The addition of acid enhanced the 

 attraction of mosquitoes to the sample; the addition of base decreased the 

 attraction. The addition of acid to various lactic acid esters and methyl isovalerate 



