142 

 Analysis by methane PCI of the peak suspected to be methyl lactate provided 



the mass spectrum found in figure 3-17. The ions at m/z 105 and m/z 77 correspond 



to the [M + H]^ and [M + H-CO]^ CI ions, indicating a possible relative molecular 



mass of 104 Da (that of methyl lactate). For comparison, figure 3-18 shows the 



methane PCI mass spectrum of standard methyl lactate in methanol. 



Addition of acid or base to esters 



The confirmation of the presence of methyl lactate in lactic acid solutions 



prompted the testing of methyl lactate and two additional esters for attraction. The 



previous knowledge gained from acidification of solutions was also incorporated into 



the experiment; the results are displayed in figure 3-19. There are two evident 



trends. The first is that as esters increasingly differ structurally from lactic acid, the 



attraction decreases. The second trend is that upon addition of acid, all solutions 



increase in attraction. Acidification of lactic acid was addressed in the previous 



section. Acidification of ethyl lactate and methyl lactate may lead to partial 



hydrolysis of the esters, producing lactic acid, thus enhancing attraction. Note that 



isovalerate exhibits no response until acidified. Partial hydrolysis of the ester to form 



isovaleric acid may be the reason for the increased attraction oiAe. aegypti. 



Analysis of Methanolic Perspiration Solution 



This final section is focused upon a brief extension of condensed-phase work 

 to human emanations. Previous olfactometer studies have shown little attraction 

 when attractants are dissolved in solution. The attraction was only found to be 



