The Thermal Desorption Autosampler (TDAS) was developed by CHROMTECH for fully automated thermal desorption. The system works as follows: First, desorption vials, crimped with regular caps, are transported from the sample tray to the heater inlet port by the PAL’s injection unit. As soon as the vial is placed into the heater, the injection unit pushes the vial and heater downwards, piercing both vial ends. The bottom of the heater, which is fitted with a syringe needle, injects the sample into the PTV when the heater is pushed down. The carrier gas flow then switches direction, passing through the desorption vial and onto the cooled PTV.

All analytes are thereby refocused onto the cooled liner. After a 3 – 5 minute desorption at a high temperature, the PAL moves the thermal desorption unit out of the inlet. At that point, the flow is redirected back to the inlet, so that it no longer passes through the sample. After a short equilibration time, the PTV inlet heats rapidly to its maximum temperature. Doing the heating while the PTV is in splitless mode will provide maximum sensitivity.