45 

 tuned for Q3MS NCI mode via maximizing transmission of characteristic negative 



ions from PFTBA. 



Thermal Desorption from Multiple Beads/Cryo-focused GC Separation 



Heating of beads to desorb volatiles for cryo-focusing was accomplished by 

 loading the beads into the GC injection port. A Varian 3400 GC fritted glass 

 injection insert was inserted reversed into the injection port. This allowed for up to 

 12 beads to be placed between the frit (located approximately halfway down the 

 insert) and the GC septum sealing the injection port. The frit kept the beads from 

 dropping down onto the column entrance and provided a means for volatile 

 emanations to be loaded onto the column; the column entrance extends up into the 

 injector insert just below the frit. Operating the injection port in a entirely splitless 

 mode (i.e. it was not necessary to open the split valve due to the absence of solvent 

 in samples) for the duration of the experiment provides essentially only one exit for 

 volatiles, through the column. 



Beads were rubbed for 5 min prior to being placed into the injector insert. 

 Experiments were typically performed with 5 to 12 beads. After loading the beads 

 into the insert, the insert was placed into the injection port held at 25°C to minimize 

 sample loss from evaporation. Repetitive analyses required a method of cooling the 

 glass insert prior to subsequent analyses; Dust-Off (difluoroethane) was used for this 

 purpose. The cap, septum, and needle guide were replaced. TTiroughout the loading 

 process the head pressure of helium was set to psig to allow for proper alignment 



