162 

 Each standard was injected and analyzed three times in order to obtain daughter 



spectra for the [M+H]"^ and [M-H]"^ ions in positive ion mode, and the [M-H]~ ion 



in the negative ion mode. 



Compound Class Screening 



Volatiles desorbed from 8 glass beads rubbed in the palms of the hands for 

 5 minutes by the author of this dissertation were analyzed by cryo-focused GC/MS. 

 The beads were placed in a reversed fritted injection port liner and replaced into the 

 GC injection port (set at 25°C). The cap, septum, and needle guide were replaced 

 on the injection port. Liquid nitrogen in a 12 oz. styrofoam cup was placed in the 

 column oven and approximately 8 cm of column (starting approximately 15 cm into 

 the oven) was placed into the cup, as described in the experimental section on cryo- 

 focusing in Chapter 2. The helium pressure was increased from to 20 psig before 

 initiating the cryo-focusing of desorbed volatiles. The cryo-focusing consisted of a 

 20 min injection port ramping program downloaded from the TSQ70. The program 

 consisted of a ramping the injection port from 25°C to 250°C over 7.5 min and then 

 holding at 250°C for 12.5 min. Throughout cryo-focusing, the GC oven was set at 

 25°C and the transfer line was set at 40°C. Liquid nitrogen was added to the cup as 

 needed to compensate for evaporation. 



After the cryo-focusing stage was completed, a new program was downloaded 

 to the GC. The cup containing the liquid nitrogen was removed and the analysis 

 started. The GC program consisted of an initial 1.0 min hold at 40°C, an 18 min 



