DIRECT DETECTION AND IDENTIFICATION OF VOLATILE ORGANIC-COMPOUNDS DISSOLVED IN ORGANIC-SOLVENTS BY REVERSED-PHASE MEMBRANE INTRODUCTION TANDEM MASS-SPECTROMETRY

A new technique is described for the direct detection and identification of volatile organic compounds dissolved In organic solvents. The method uses a porous membrane introduction system to a mass spectrometer and is capable of continuous on-line monitoring. The porous polypropylene membrane chosen for this work allows sufficient amounts of the solvent to penetrate into the ion source for chemical ionization (CI) to occur with the vaporized solvent acting as the reagent gas. Solute molecules permeate the membrane together with the solvent and can be analyzed by CI/MS and tandem mass spectrometry(MS/MS). In cases in which the solute cannot be chemically ionized by the vaporized solvent CI-plasma, it is possible to co-introduce a conventional CI reagent gas to achieve additional control of the ionization process. With this technique, a broad range of compounds dissolved in organic solvents can be detected in the sub-ppm range with rise and fall times faster than 10 s. Detection limits depend on the efficiency of ionization, not on the rate of passage through the membrane, and they can often be improved by using tandem rather than single-stage mass spectrometry. As an example of the application of the technique, the detection and identification of additives in gasoline samples is demonstrated.