104 



from m/z 87, respectively. Additionally, there is presence of an ion at m/z 85 from 



the neutral loss of H,. 



A summary of the fragmentation pathways for negative ions of lactic acid 

 examined by NCI MS/MS is presented in figure 3-3. There are two points about this 

 figure which warrant mentioning. The first is that ions shown in the figure represent 

 a selection according to threshold conditions for these experiments. This chosen 

 threshold was that the abundance of these ions be greater than or equal to 1% of the 

 base peak intensity in each daughter spectrum. The second point concerning figure 

 3-3 is that the structures listed are postulated from losses and reasonable 

 fragmentations and rearrangements [75-78]. Additional measures, such as the use 

 of high resolution mass spectrometry and isotopic labeling, were not employed to 

 confirm these structures. 



The trend via losses of H, is apparent; this loss most likely occurs by cleavage 

 of the hydrogen from the a-hydroxy group and a y-hydrogen from the terminal 

 methyl group. This process occurs through a four-centered intermediate ring state 

 [79]. This same cleavage most likely produces the species at m/z 85 from the m/z 87 

 ion. Due to the absence of sufficient hydrogens, the m/z 85 species does not undergo 

 a further neutral loss of Hj. The availability of hydrogens limit the possible 

 fragments resulting from precursors in other cases. Examination of the loss of water 

 from the m/z 89 and m/z 87 species reinforce this. Both these ions will undergo a 

 neutral loss of water, while m/z 85 will not. The fragments formed (m/z 71 and m/z 

 69) show this trend. 



