Membrane extractors comprising a membrane houseinside of a valve have been developed to separate compounds of interest from a sample matrix and introducethese compounds into a mass spectrometer. Experimental control over parameters that affect permeability orthatmay damage the membrane, such as the membranetemperature, is provided with the valve. The valvewastested for response and response times with the valveseparated from the mass spectrometer by various interface tube lengths. Data for steady state response measurements showed no significant change with the valveat different distances from the ion source. Polar compounds show a strong response time dependency on theinterface tube length. This adsorption phenomenon isminimized by simply heating the interface tube. Otherfactors affecting the performance of the device are discussed.