Direct interface of chemistry to microbiological systems: membrane inlet mass spectrometry.

Direct measurement of dissolved gases and low molecular weight volatiles through permeable membranes (e.g. 50-μm-thick silicone rubber), provides an invaluable tool for the investigation of the activities of microorganisms in the laboratory and in their natural environments. Multiple molecular species are monitored at a single point. Fast response times (t90%<1 min) and long-term stability, (<1% week−1); high specificity and high sensitivity (e.g. 0.2 μM for O2, <0.5 mM for ethanol), provides a technique that can provide information on the kinetics of processes over many decades (100–106) of minutes. Spatial resolution of <1 mm enables 3D mapping of gases in complex ecosystems (sediments, peat, soils, biofilms, foodstuffs). Results with membrane inlet mass spectrometry (MIMS) when used in conjunction with confocal scanning laser microscopy, provides a powerful approach to the analysis of kinetic and spatial aspects of natural environments. Examples discussed are peat cores and cheese.