113 



the m/z 125 parent ion. The daughter spectrum of m/z 127 consisted of the expected 



daughter ions at m/z 37 and 89. 



Chloride ion attachment spectra are useful for applications involving detection 

 of organic compounds with acidic protons [81]. This attachment is somewhat 

 selective for specific classes of compounds which meet this criteria. Typically, 

 methylene chloride is used as the reagent gas to effect the attachment in the ion 

 source. In the instrument employed for this work, residual chloride ions are always 

 present in the negative ion background and, as demonstrated, can undergo ion- 

 molecule reactions even in the presence of additional reagent gas. This reaction 

 itself is of secondary importance in the work for this dissertation rather than a 

 primary mode of identification. 



Negative ions which undergo a neutral loss of 90 Da (i.e. lactic acid) are 

 presented in figure 3-6. The chloride attachment ion at m/z 125 was previously 

 shown (figure 3-5) to undergo a neutral loss of 90 Da. The other ions found in this 

 neutral loss spectrum are at m/z 179 and m/z 177. The lactic acid-lactate dimer ion 

 at m/z 179 was pointed out in figure 3-4. Additionally, dimer formation can result 

 from the combination of a neutral lactic acid molecule and the hydrogen-eliminated 

 lactate ion (m/z 87) to produce a dimer at m/z 177. Experimental data not shown 

 indicate that the m/z 177 dimer can also undergo losses of 88 Da and 92 Da to form 

 ions at m/z 89 and m/z 85, respectively. Additional data will be presented later in 

 this chapter (figure 3-10). 



