Characterization of a condensed-phase membrane introduction mass spectrometry (CP-MIMS) interface using a methanol acceptor phase coupled with electrospray ionization for the continuous on-line quantitation of polar, low-volatility analytes at trace levels in complex aqueous samples.

We report the development and application of a capillary hollow fibre membrane interface using methanol as an acceptor phase to deliver target analytes to an electrospray ionization source and a triple quadrupole mass spectrometer. Superior fluid handling systems lead to greater signal stability and membrane integrity for the continuous on-line monitoring of polar and charged analytes in complex aqueous samples with detection limits in the parts-per-trillion to parts-per-billion range. The system can be operated in either a continuous flow or a stopped acceptor flow mode - the latter giving rise to greater sensitivity. We report detection limits, enrichment factors and signal response times for selected analytes with polydimethylsiloxane and Nafion® polymer membrane interfaces. In addition, we demonstrate the use of this interface to detect pharmaceuticals and other contaminants in natural water and artificial urine. The improved sensitivity and analytical response times of our CP-MIMS system make it possible to continuously monitor dynamic chemical systems with temporal resolutions on the order of minutes. Presented is a comparison of the performance of CP-MIMS versus direct infusion electrospray ionization, demonstrating the potential advantages over direct infusion for trace analyte measurements in complex, high ionic strength samples. Furthermore, by continuously flowing a reaction mixture in a closed loop over the interface, we demonstrate the use of the system as an in situ reaction-monitoring platform for the chlorination of a model organic compound in aqueous solution.