48 

 The canister manifold allowed for 70-100 mL of volatiles and residual air to 



be sampled by the ELA2000 concentrator. The concentrator consisted of three 



stages. The first stage employed a dryer with a gradient of large to small glass beads 



through the dryer. This served to remove most of the water in the sample. During 



concentration, this stage is set to -160°C for three minutes and heats up to -16°C as 



sample is transferred to the second stage. The second stage in these experiments 



was a Tenax trap. During concentration, the trap was set to -20°C and then heated 



to 156°C for desorption of trapped volatiles onto the focusing trap. Tlie cryo- 



focusing trap was set a -160''C for concentration and was heated ballistically 



(approximately 10 seconds) to 150°C to purge volatiles onto the head of the GC 



column. 



The GC employed was an HP5890 series I with a 30 m x 0.25 mm i.d. DB-1 

 column (df= 1 |j,m). For analyses involving glass beads, the column was initially cryo- 

 cooled at -35°C and held for 3.0 min. Subsequently, the column was ramped at 

 12°C/min up to 180°C, then ramped at 25°C/min from 180°C to 225''C and held for 

 5.0 min at 225°C. For analyses from the Tedlar bag, the column was held 6.0 min 

 at -35''C then ramped at 6°C/min to 180°C and 12°C/min from 180°C to 225°C, and 

 held for 10.0 min at 225''C. 



The mass spectrometer used for these studies was a Finnigan MAT Incos 50 

 single-stage quadrupole. The scan rate employed was 0.75 s per scan. The filament 

 emission current was set at 750 |j,A with an electron energy of 100 eV. The electron 

 multiplier was set to -1200 V. The ion source temperature was set at 180°C; there 



