Affinity liquid membrane introduction mass spectrometry Original Research Article

A mass-spectrometer membrane introduction system, modeled after affinity chromatography, utilizes chemically modified low vapor-pressure liquids to selectively bind and release aryl aldehydes from multi-component aqueous sample streams. Polyphenyl ether, a slightly polar liquid, was admixed with an optimum loading of 10% octadecylamine (w/w) and coated on a microporous support to create a hydrophobic, semipermeable membrane containing primary amine functionalities. A 1.9-cm2 surface-area membrane interface was built in-house for these experiments and optimized for temperature (71°C), flow rate (1 ml/min), additive loading, and thickness (0.10 mm). Benzaldehyde was selectively bound to this membrane under standard operating conditions with an efficiency of ca. 50%, defined as analyte response during release from the membrane (pH 1) as compared to response during loading (pH 7.8). Analytes were introduced into an ion-trap mass spectrometer in a helium stream via a jet separator. Total analysis periods were ca. 20 min for concentrations between 50 ppb and 50 ppm, with a standard deviation of 7% for similar concentration samples. Selective liquid-membrane interfaces represent new technology for membrane introduction mass spectrometry.