82 

 experiments. Additionally, the top trace on figure 2-16 is that of the molecular ion 



of cholesterol at m/z 386. Tlie major peaks found in the RIC of these figures are 



aliphatic fatty acids; the examination of the cholesterol molecular ion demonstrates 



the ability to detect trace components. TTie quality of figures 2-15 and 2-16 are 



similar (although slightly lower) to that of the subsequent cryo-focused analyses 



found for studies in Chapter 5. 



Purge and Trap/GC Separation 



Thermal desorption/purge and trap has been used previously for studies such 

 as identification of fruit fragrances and analysis of volatiles from smoke [69,71]. 

 However, purge and trap was initially avoided in this study due to the possibility of 

 sample discrimination by the trap, i.e. being unable to desorb some volatiles back off 

 of the trap for analysis. However, upon analysis via a three-stage microscale purge 

 and trap GC/MS system, it was found that a great number of trace components could 

 be concentrated and identified, as readily seen in the RIC traces for figures 2-17 and 

 2-18. Data for figure 2-17 were acquired from rubbed beads and data for figure 2-18 

 (using a heating rate approximately half of that for figure 2-17) were acquired from 

 direct introduction of volatiles from the skin by sampling a Tedlar bag with the hand 

 contained therein. 



The microscale purge and trap system does not allow for detection of the 

 acids and other polar compounds; they are lost somewhere in the system, possibly 

 in the nickel-plated lines or perhaps in the first drying trap. The removal of the 



