137 

 reaction between lactic acid and methanol via acid-catalyzed or base-catalyzed 



esterification was examined by mass spectrometry. There are two purposes behind 



the selection of mass chromatograms displayed in figure 3-15. The first purpose is 



the verification that masses corresponding to the protonated molecular species of 



lactic acid and methyl lactate are indeed present (in this case, under basic 



conditions). The additional mass chromatogram (m/z 73) displayed in the figure 



explains additional peaks found in the RIC which are not attributable to either lactic 



acid or methyl lactate. A fragment ion at m/z 73 is characteristic of siloxanes from 



GC analysis. 



The second purpose behind selecting these data was to illustrate a 

 phenomenon which can occur for these compounds. The data were acquired under 

 El conditions; however, a significant abundance of the protonated molecular species 

 occurs rather than the molecular ion. It was previously mentioned that lactic acid 

 does not form a molecular ion under EI conditions; however, the formation of 

 [M-l-H]^ is relatively facile by self-induced chemical ionization due to high ion source 

 concentrations and pressure. Reactions of similar compounds at high ion source 

 pressure under EI conditions support this supposition [82]. 



Verification that the peak found at scan number 320 is indeed lactic acid can 

 be found in figure 3-16. The data for this figure were acquired under NCI 

 conditions; this clearly depicts the characteristic chloride ion attachment and 

 oligomer ions formed by lactic acid. Confirmation of the presence of methyl lactate 

 by NCI is not possible since it does not readily form an [M-H]~ ion. 



