How can I prevent high air/water background when using a thermal desorber with GC–MS analysis?
Markes’ thermal desorbers use high-quality O-rings to create a strong seal around the sample tubes and cold trap, and therefore the air/water background should be similar to that observed with conventional GC injector systems.
However, as with all split GC injectors it is recommended that a flow of at least 10 mL/min is maintained through the split vent when the system is in standby, to prevent back-diffusion of air through the split. Markes’ TD software provides a ‘Split on in Standby’ option to facilitate this, and should give acceptable air/water levels.
Note that other thermal desorption systems may automatically switch the split flow off during analysis, leading to high air/water levels when the system has been in standby for some time.