64 

 ions (M"^') of aliphatic fatty acids, some of these ions may be due to fragment ions 



from higher molecular weight compounds (e.g. longer chain fatty acids in the same 



series). 



Thermal Desorption from Multiple Beads 



The first approach to improving identification of components was to develop 

 methods of increased sample size to obtain greater ion signal for the identification 

 of trace components. The apparatus initially constructed for this purpose was 

 described in the experimental section and depicted in figure 2-3. Figure 2-10 is an 

 illustration of the NCI results of thermal desorption from multiple beads in a round 

 bottom flask. In this case, the 100 handled beads were spiked with additional lactic 

 acid prior to heating and analysis of the beads. Tliere is an erratic response of the 

 RIC past scan number 1100. This problem was characteristic for the analysis of a 

 large number of beads. This may arise from saturation of the electron-capture/NCI 

 process in the ion source due to the increased abundance of sample components 

 from the large number of beads. Alternatively, this problem could arise from the 

 desorption of volatiles from the surface of the beads, where non-uniform heating 

 produces warm spots and "burping" occurs from volatiles escaping around the beads. 



The problems associated with the analysis of a large number of beads were 

 rectified by reducing the number of beads and size of the sample container used to 

 hold the sample in the GC oven. The RIC in figure 2-11, obtained by using 5 

 rubbed beads in a small tube, demonstrates that the erratic fluctuations in the RIC 



