54 

 molecular ion (M"^') of cholesterol and m/z 387, the carbon-13 isotope of the 



molecular ion. Positive identification of cholesterol during this initial phase was 



difficult to obtain due to the abundance of fragment ions from other species found 



in the mass spectrum over the selected peak; background subtraction was not able 



to fully remove the interferant masses due to the width of the desorption profiles. 



Trace components of lower m/z become increasingly difficult to identify due 

 to overlapping profiles of fragment ions when examining the mass chromatograms 

 for particular m/z values (see discussion of figure 2-8). Additionally, re-examination 

 of each mass over the entire scan range, or sections of the RIC devoid of discernible 

 peaks, makes identification a tedious process. The positive identification of 

 cholesterol was achieved in the work of Chapter 5. 



During this first series of experiments with a single bead, different subjects 

 were involved in handling the beads. Figure 2-6 is the RIC from the mass 

 spectrometric analysis of a single bead rubbed by Mr. Dan Smith; this individual has 

 been consistently found to be the most attractive person to mosquitoes in USDA 

 tests conducted with the olfactometer. Comparing figure 2-6 to figure 2-4 (the RIC 

 of a bead rubbed by the author of this dissertation) it is evident that the traces are 

 very similar. This comparison also demonstrates that examination of this nature is 

 insufficient to ascertain differences among people in terms of relating what 

 components and what abundance of components is present on the skin causing the 

 differentiation. 



