Sheet Materials for Use as Membranes in Membrane Introduction Mass Spectrometry

Several polymer sheets including silicone, latex, PVC, Teflon, polyurethane, polyimide, polyethylene, and nitrile were used as membranes for membrane introduction mass spectrometry (MI/MS). The relative performance of each material was explored for its potential utility in MI/MS analyses where samples are delivered via flow injection. Each of the membrane materials was tested by exposing it to separate aqueous solutions containing the analytes benzene and ethanol in order to represent the results that may be achieved for environmental analyses and fermentation monitoring, respectively. Flow injection delivery of these solutions was used to measure the relative analyte quantification limits, response times, and permeation of water as a function of temperature for each membrane material. It was observed that latex and polyurethane membranes yield MI/MS performance characteristics (in aqueous matrix) similar to those of the commonly used silicone membranes for both benzene and ethanol solutions. Polyethylene was observed to work well with benzene as an analyte and simultaneously provided improved selectivity over water. While the other materials allowed aqueous matrix MI/MS to be performed, poor quantification limits and/or slow response times made these materials undesirable for this purpose. Two membrane materials which showed especially low organic permeability and higher water permeability, polyimide and Teflon, were briefly tested with polar analytes and nonpolar solvent. For the polyimide material, the analytes acetone, acetic acid, chloroform, ethanol, ethyl acetate, and water were readily observed in hexane solvent.