Parameters that affect the permeation of analytes across a thin (0.025 mm) flat membrane of polysiloxane in a membrane and trap interface coupled to a gas chromatograph are examined taking into account a mechanism of mass transport for porous and nonporous materials and the permeation of carrier gas in the direction opposite to that of the analytes. The best permeation rate was reached with hydrogen as carrier gas at a flow-rate between 3 and 5 ml/min, an agitation of analytes outside the membrane above 0.4 m/s and thin membrane. The parameters that affect the residual diffusion time of analytes in membrane were also examined. A practical application of the thin membrane in membrane and trap interface was demonstrated by gas chromatographic monitoring of six volatile organic compounds in air. The limit of detection is at the nmol/ml level depending on the time of trapping and the parameters that affect the permeation through the membrane.