Polyetherimide-silicone: a 10 mu m ultrathin composite membrane for fasterand more sensitive membrane introduction mass spectrometry analysis

A polyetherimide (polyester)/silicone (PEI/S) sheet composite membrane with a 10 mu m thick cross-linked silicone layer is found to display the requir ed mechanical properties to work efficiently as the solution/high vacuum in terface in membrane introduction mass spectrometry (MIMS) analysis of volat ile organic compounds (VOC) in water. Owing to much shorter response and re covery times, the PEI/S membrane allows much faster analysis and calibratio n procedures as compared to the 250 mu m silicone membrane usually used in MIMS, When using EI, owing to excessive water permeation, responses (signal intensity) for the PEI/S membrane are not always superior, being analyte-d ependent, For the more polar VOCs, however, the PEI/S membrane shows 2-3 ti mes greater responses, improving their relatively poor MIMS detection limit s, When water-methane chemical ionization is applied, the problem of excess ive water permeation is attenuated, and the PEI/S membrane displays greatly superior responses.