This work demonstrates experimentally the use of mass spectrometry (MS) for on-line, quantitative monitoring of organophilic pervaporation processes operated not only under variable conditions of temperature of condensation/downstream pressure but also when using complex multi-component feed streams. Due to its high sensitivity, mass spectrometry is particularly suitable for on-line monitoring of aromas in dilute streams under reduced pressure, as happens with natural aromas in permeate streams. Mass spectrometry is also suitable for on-line monitoring of solvent and co-solvent permeants (water and ethanol in the selected case study), enabling for on-line determination of selectivity of the solutes of interest. A new method of calibration is proposed and validated, which correlates the intensity of the characteristic mass peak m(i)/z for each compound of interest with its partial pressure in the permeate stream. Moreover, mass spectrometry proves to be a powerful tool for studying the fractionation of aromas, recovered by integrated pervaporation-condensation processes, allowing on-line monitoring of each solute vapour in the permeate stream. Additionally, this technique enables for accurate transient studies due to the possibility of acquiring one data point every 12-15 s (potentially less, if desired) in real-time. (C) 2009 Elsevier B.V. All rights reserved.