Nitrogen/argon ratios by difference thermal conductivity

A method has been developed for the precise determination of dissolved nitrogen/argon ratios in sea water for the purpose of evaluating small changes in the dissolved nitrogen content. Nitrogen and argon are extracted from sea water (in vacuo) and separated from water vapor, carbon dioxide and oxygen. The residual nitrogen-argon mixture is swept over a thermal conductivity detector with a carrier gas of the same composition, except for having a slightly different argon mole fraction. Calibration is carried out by equilibrating sea water at various temperatures with air. The technique has been used successfully in the analysis of N₂ Ar ratios from the intermediate depths of the eastern tropical Pacific Ocean and the Cariaco Trench. Precision is estimated at ± 0·2% at the 95% confidence level; the accuracy depends on the solubility tables used and the method of equilibration.