Design of a Microprocessor Controlled Short Path Thermal Desorption Autosampler


Vinod T. Das and Thomas T. Hartmen of Cook College, Rugers University and John Manos, John Manura and Christopher Baker of Scientific Insturment Services.

Volatile and semivolatile organic compounds (VOC's) are of interest to many industries. Short Path Thermal Desorption (SPDT) is a technique that is used to introduce VOC's to the front of a gas chromatograph. The method involves purging and trapping VOC's from the analyte onto custom made glass lined stainless steel (GLT) tubes which are packed with commercially available adsorbent resins. The tubes are then heated in a custom apparatus which thermally desorbs the trapped VOC's onto the GC column with the aid of a carrier gas such as helium. In a method called Direct Thermal Extraction (DTE) the GLT tubes are packed with the analyte of interest and VOC's are transferred to the GC column in one step.

Presiously only one sample could be analyzed at a time making analysis slow and limited to applications such as quality control. The autosampler that is described here is a novel improvement on SPTD; it has the capacity to handle 12 samples (SPTD, DTE, or both). Once the unit is loaded and set up, the process of injecting the trap, heating, desorbing and reloading is automated and requires minimal attention. The microprocessor allows the user to control parameters such as the heater block temperature ramp (during desorption), desorption time and temperature of each sample. Also the user can control carrier gas flow rates and dry purge times for each sample. In addition, the unit is capable of operating directly on top of the GC with little or no modification. Finally cross contamination is minimized due to a separate "short path" for every sample that is loaded into the instrument.