321 

 range. Saturated conditions with methane as the reagent gas produces the m/z 89 

 [M-H]~ ion as the base peak and an intense ion at m/z 87 due to the elimination of 

 H2 from m/z 89, in the gas phase. For conditions below saturation, the m/z 87 ion 

 may be slightly lower in intensity; however, in all cases, the m/z 88 is present but in 

 very low abundance (less than 3% RA). 



The intensity of the m/z 88 ion, at greater intensity than seen throughout this 

 work, suggests that there is an alternative mechanism of ion formation occurring with 

 CO2 as the reagent gas. This alternative route did not occur to the extent seen here 

 for methane CI studies conducted previously. The best explanation for this is the 

 elimination of Hj prior to electron capture in the gas phase, presumably by a wall 

 reaction, followed by electron attachment to the neutral species forming the m/z 88 

 [M-H2]— ion. 



The most common detriment to this work involving CO2 for CE or ECNCI 

 was high ion source pressures resulting from the presence of the sample in the ion 

 source. An example mass spectrum of standard palmitic (hexadecanoic) acid 

 subjected to CE with 1200 mtorr COj is shown in figure A- 10. Although the M""* ion 

 is present at m/z 256, the base peak is the [M+H]"^ ion of hexadecanoic acid at m/z 

 257. The only route for production of this ion is via self-CI. An additional 

 interesting feature of this mass spectrum is the adduct ions present at m/z 271 and 

 m/z 285. The latter ion at m/z 285 is the typical [M+29]+ ion seen in methane CI 

 mass spectra. The [M+15]^ adduct ion at m/z 271 is fairly uncommon in methane 



