Real-time analysis of methanol in air and water by membrane introduction mass spectrometry

We present results for the near-real-time, on-line detection of methanol in both air and water using membrane introduction mass spectrometry (MIMS). I n these experiments, we compare the sensitivity of a poly(dimethylsiloxane) (PDMS) membrane and an allyl alcohol (AA) membrane to the detection of met hanol. In MIMS, the membrane serves as the interface between the sample and the vacuum of the mass spectrometer. Membrane-diffused water was used as t he reagent ion (H3O+) for chemical ionization of methanol in an ion trap ma ss spectrometer. Linear calibration curves have been obtained for methanol using both PDMS and AA membranes. For PDMS, detection limits of methanol ar e 14 ppmv and 5 ppm in air and water, respectively. For AA, detection limit s are 3.3 ppmv and 2 ppm in air and water, respectively. We demonstrate tha t the sensitivity of the analysis can be altered by the chemistry of the me mbrane. When the AA membrane is used, the sensitivity of MINTS is enhanced over that of PDMS by a factor of 8.5 for methanol in air and by a factor of 23.4 for methanol in water.