MICROPORE MEMBRANE INLET MASS-SPECTROMETER PROBES SUITABLE FOR MEASUREMENT OF TISSUE SURFACE GAS TENSIONS

New membrane inlet mass spectrometer (MIMS) probes are described that feature a micropore in a flat metal surface filled with a polymer membrane (Krytox high-vacuum fluorinated grease). In vitro assessment of spatial resolution, time response, stirring effect and calibration are reported. The small membrane area for this MIMS results in spatial resolution of about 30 mu m, adequate for measuring gas tensions at an exposed tissue surface in experimental studies of tissue oxygenation and tissue gas exchange. These probes offer a unique combination of minimal stirring effect and rapid response speed for measurements of gas partial pressures in the per cent range in aqueous solutions. Several gases, including oxygen, carbon dioxide, helium, sulfur hexafluoride and argon, permeate the polymer membrane to give a detectable signal, and the membrane is highly impermeable to water. Membrane dimensions were calculated from time response characteristics and the measured gas sample rate for argon. The membrane area was independently confirmed by direct assessment of spatial resolution. This MIMS is highly linear, has an excellent signal-to-noise ratio and offers practical advantages over electrode approaches to the measurement of gas tensions in aqueous solution.