Helical sorbent microtrap for continuous sampling by a membrane and trap interface for on-line gas chromatographic monitoring of volatile organic compounds.

A helical sorbent microtrap consisting of a helical sorbent fixed inside a silicosteel capillary tube is presented. The main parameters that affect the safe sampling time of the helical sorbent microtrap in continuous sampling by a membrane and trap interface for on-line gas chromatographic monitoring of organic volatiles in gaseous samples are examined, taking into account the helical configuration of the sorbent, the presence of the membrane in system, and the properties of the analytes. Thermal desorption of analytes from the helical sorbent trap was also examined having regard to the influence of the turbulent flow generated by the helical sorbent in the heat transfer and the effect of thermal backward flow on the peak shape. The practical application of the helical sorbent microtrap in a membrane and trap interface was demonstrated by on-line gas chromatographic monitoring of four volatile organic compounds in the fume hood air and of volatile organic compounds from a diesel engine exhaust. The limit of detection was in the picogram per milliliter range, depending on the time of trapping and the parameters that affect the permeation through the membrane.