Abstract: An interface linking a mass spectrometer (MS) to a thermogravitational analyzer (TGA) for adjusting the concentration of volatiles entering the MS. The interface is preferably a capillary column provided with a dilution chamber having a inlet for gas insertion, with one end of the chamber connected to the TGA and the other to the capillary column having its other end directly attached to the MS. In a second embodiment, the interface bypasses the dilution chamber, and is made of a glass tubing protected by a stainless steel tubing, in turn surrounded by a temperature programmable sheath heater.