130 

 abundance than m/z 89 ion. The m/z 177 dimer ion abundance is approximately 



equal to that of the m/z 179 dimer ion. The presence of the trimer and tetramer 



ions at m/z 268 and 357 can also be seen. Although the source is not yet fully 



saturated, the increased pressure leads to oligomerization reactions from lactic acid. 



Examination of NCI mass spectrum of lactic acid after saturation has occurred 



(figure 3-12) shows increased m/z 179 relative to m/z 89, as well as loss of H2O (m/z 



161) from esterification. The relative abundance of m/z 177 is increased with respect 



to m/z 179. Also, the trimer ions now include both oligomerization ions and 



esterification ions due to a single loss of HjO; the tetramer ion at m/z 323 



corresponds to the loss of two molecules of water, [M4-H-2H20]". As expected, 



dimer ion formation is more prevalent at higher pressures. Additionally, the ions 



formed indicate that esterification becomes more prominent with respect to 



oligomerization as the source pressure is increased due to greater abundance of 



neutral lactic acid. The oligomerization and esterification reactions are similar to 



solution-phase reactions addressed earlier in this section. 



Altering Attraction 



Experiments in this section involve analysis of methanolic lactic acid solutions 

 modified by the addition of acid or base. Samples were initially examined by an 

 olfactometer to determine the attraction of Ae. aegypti to these solutions. Mass 

 spectrometric analysis was employed as a complementary technique for the 

 identification of species present in these solutions. The mass spectrometric results 



