Polyetherimide–silicone: a 10 µm ultrathin composite membrane for faster and more sensitive membrane introduction mass spectrometry analysis

A polyetherimide (polyester)/silicone (PEI/S) sheet composite membrane with a 10 µm thick cross-linked silicone layer is found to display the required mechanical properties to work efficiently as the solution/high vacuum interface in membrane introduction mass spectrometry (MIMS) analysis of volatile organic compounds (VOC) in water. Owing to much shorter response and recovery times, the PEI/S membrane allows much faster analysis and calibration procedures as compared to the 250 µm 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-dependent. For the more polar VOCs, however, the PEI/S membrane shows 2–3 times greater responses, improving their relatively poor MIMS detection limits. When water–methane chemical ionization is applied, the problem of excessive water permeation is attenuated, and the PEI/S membrane displays greatly superior responses.