Abstract: In its simplest sense the invention is an expansion chamber device that allows a sample to be purged and trapped for analysis without removal of the sample from the common field sample vial (VOA vial) storing the sample. The expansion chamber generally comprises an expansion chamber tube of transparent material having a top end adapted for gas tight fit in a compression fitting of a host purge and trap instrument, a bottom end including an external flange, and a central passage for fluid communication between a sample vial top opening and a host purge and trap instrument. A connector cap has a bottom end having internal threads for mating with external threads on a sample vial and a top end having an internal flange for bearing down on the expansion chamber tube bottom end external flange. An inert gasket forms a positive pressure seal between the expansion chamber tube bottom end and the sample vial.