20 

 handled beads were placed in an enclosed glass container which was placed inside 



the GC oven; helium passed over the beads transferred sample to the ion source via 



a deactivated fused silica column (transfer line). This technique will be discussed in 



greater detail in Chapter 2. 



Separation methods . Complexity of the sample may dictate that a method of 

 separation is necessary in order to adequately resolve compounds whose thermal 

 desorption profiles overlap. The focus of this work is on volatiles; therefore, gas 

 chromatographic separation was chosen. The initial phases of this work employed 

 short columns for faster analyses. However, due to the number of components 

 desorbed, longer columns were employed for identification and case studies in the 

 final stages of this work. 



Volatiles desorbed from the glass beads have wide desorption profiles; thus, 

 some method of reducing bandwidth before chromatographic separation can 

 significantly improve chromatographic resolution. This was accomplished either by 

 cryo-focusing or by purge and trap. Cryo-focusing involves immersing a portion of 

 the column, just after the column exits the injection port, into liquid nitrogen to 

 collect volatiles and focus them into a narrow band [33]. After focusing, the column 

 is removed from the liquid nitrogen and GC separation is conducted. Purge and trap 

 is slightly more complex in that it typically contains an additional trap [33]. Prior to 

 GC analysis, the sample is collected onto a suitable trap (e.g. Tenax) to perform the 

 focusing operation. The trap is then heated to desorb volatiles which are then 

 focused onto a cyro-trap. 



