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). In these experiments, we compare the sensitivity of a poly(dimethylsiloxane) (PDMS) membrane and an allyl alcohol (AA) membrane to the detection of methanol. In MIMS, the membrane serves as the interface between the sample and the vacuum of the mass spectrometer. Membrane-diffused water was used as the reagent ion (H3O+) for chemical ionization of methanol in an ion trap mass spectrometer. Linear calibration curves have been obtained for methanol using both PDMS and AA membranes. For PDMS, detection limits of methanol are 14 ppmv and 5 ppm in air and water, respectively. For AA, detection limits are 3.3 ppmv and 2 ppm in air and water, respectively. We demonstrate that the sensitivity of the analysis can be altered by the chemistry of the membrane. When the AA membrane is used, the sensitivity of MIMS 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.