A description is given of a process and an apparatus for the qualitative and/or quantitative monitoring of starting material in the form of substances in a liquid phase which are taken up in a carrier gas and fed to an analyser, possibly via a gas-chromatographic capillary column. In order to be able to analyse the spectrum of the substances being monitored with as low loss as possible, a defined amount of starting material is fed into a narrow extractor space (7) which is elongated in an essentially vertical direction, the carrier gas is allowed to bubble from below through the liquid starting material in the extractor space and the loaded carrier gas is fed to an evaporator tube (15) which can be cooled and heated and whose temperature setting is such that a liquid phase it contains retains the substances to be monitored, while entrained evaporated starting-material liquid phase is removed, at least predominantly, with the carrier gas. The substances retained in the evaporator tube are then released by heating the evaporator tube with free access to the capillary column (17) or to the analyser and are fed into the capillary column or the analyser by means of the carrier gas. <IMAGE>