The integration of organophilic pervaporation into processes of varying feed concentration, such as bioconversions, chemical reactions, or analytical sample preparation, requires not only the understanding of mass transport phenomena across the membrane under steady-state conditions, but also the insight into the transient response of the pervaporation membrane to changes as they occur in practice. For this purpose, a laboratory-scale pervaporation unit was coupled to a mass spectrometer for on-line permeate analysis, maintaining the overall pervaporation operating conditions controllable independently, and without introducing any inert gases for sample transfer. The experimental set-up was employed for investigating the transport of aroma compounds across a POMS-PEI composite membrane, focusing in particular on the so-called "membrane conditioning"; the possible synergetic effect of ethanol on the flux of one model aroma compound, ethyl hexanoate; the application of the system proposed to the rapid screening of the effect of the hydrodynamic upstream conditions on the degree of concentration polarisation. The method proposed proved to be robust and flexible, not only allowing insights into transient mass transport phenomena otherwise not attainable, but also reducing experimental workload significantly when characterising the effect of varying operating conditions on the pervaporation performance. (C) 2004 Elsevier B.V. All rights reserved.