The Bay Instruments membrane inlet mass spectrometer (MIMS) is the de facto standard for denitrification studies which demand the highest precision for N2 and N2Ar ratios. Our MIMS is the instrument of choice for government and academic researchers, oceanographers, and environmental scientists who require precise measurements of dissolved gases in water. Our applications have grown over the last 25+ years to encompass denitrificaton, ecosystem oxygen studies, trace environmental gases, and stable isotope studies. Our MIMS provides high precision, rapid analysis, and small sample size capabilities with a small footprint that makes it an excellent candidate for field applications.