226 

 allowed a 6-8 hour gap between handling time and analysis time. After each sample 



from the morning session was analyzed, the beads stored from the afternoon session 



were analyzed under the complementary ionization mode. 



The GC parameters were dependent upon the column employed. The 



columns and corresponding GC parameters were discussed previously (in the cryo- 



focused GC/MS section of this chapter). The mass spectrometer was operated in EI 



and PPINICI modes as previously discussed and reported in this chapter. A blank 



was not analyzed in the evening for studies involving beads which had been stored 



in tubes (open to ambient air) for over 6 hr. 



Case Study Comparison of Bio-assay to GC/MS Assay 



Cryo-focusing GC/MS 



Experiments were performed involving analyzing emanations collected from 

 one subject, each day, for five consecutive days. The collection process was similar 

 to that for the case study described for the comparison of subjects. In this case, Mr. 

 Ken Posey of the USDA served as the test subject. On each of the five days, a blank 

 was recorded in EI mode prior to analysis. The subject handled ten glass beads for 

 15 min; three beads were used for each analysis. The remaining beads were stored 

 for analysis with the complementary ionization mode. The cryo-focusing stage for 

 the first handled-bead analysis was initiated at approximately 8:40 am each day. 

 Upon completion of the this analysis, the mass spectrometer ion volume was 

 switched to allow for PPINICI. A blank was acquired and three beads were 



