Determination of Dissolved Nitrogen and Oxygen in Water by Headspace Gas Chromatography

摘要

Measurements of the dissolved gas status of streams and impoundments are of interest because of the relationship between oversaturation and gas embolism in fish. In this study dissolved oxygen and nitrogen were determined by shaking 20 to 25 ml of water with an equal amount of helium in a 50-ml gas-tight syringe and injecting 2 ml of the equilibrated headgas into a gas chromatograph. Oxygen and nitrogen were separated on a 5-A molecular sieve column at ambient temperature and detected with a hot wire detector using atmospheric air for calibration. Advantages of this method over previously reported methods are: (1) oxygen and nitrogen are determined in a single analysis, (2) no specifically fabricated stripping apparatus is needed, and (3) analysis can be done in the field with completely portable, battery-operated equipment. Analysis of a sample of laboratory distilled water by the described method gave values for O2 (corrected for argon) and N2 of 5.74 + or - 0.16 ml/l and 10.71 + or - 0.36 mil/l respectively. Calculated values for distilled water based on the literature were 5.71 ml/l for O2 and 10.76 ml/l for N2. Dissolved oxygen determined by the Winkler method was 5.64 ml/l. Therefore, the method appears to be accurate and reproducible. Several lake O2 and N2 profiles were obtained using this technique. The results for dissolved oxygen compared favorably with those obtained using either the Winkler method or the dissolved oxygen membrane probe. Dissolved nitrogen values were between 92% and 97% of saturation relative to surface water. (Author)