Accurate measurement of O2, N2, and Ar gases in water and the solubility of N2

The degree of atmospheric saturation for O2, Ar, and N2 gases in water can be determined to accuracies of ±0.1–0.3% using mass spectrometry to determine the gas ratios and Winkler titrations for oxygen analysis. We describe methods used to obtain this level of accuracy and precision. Oxygen accuracy of ±0.1% can be obtained by careful attention to standardization using KIO3 standards that have been corrected for impurities. Accurate O2/Ar and O2/N2 gas ratios (±0.1–0.2%) are obtainable by measuring the mass ratios against the atmosphere if the effect of different gas concentrations on the performance of the mass spectrometer are taken into account. Oxygen and argon saturation values have been determined previously to accuracies of less than or equal to ±0.1%, but published estimates of the saturation value for nitrogen differ by more than 1%. We have redetermined the N2 saturation value at 19°C and zero salinity to be 0.92% greater than the results reported in the work of Weiss (1970).