AN AUTOMATED TECHNIQUE FOR THE MEASUREMENT OF DISSOLVED N2O IN NATURAL-WATERS

We have developed a fully automated technique for measuring dissolved N2O in freshwater and seawater. This analytical system can measure N2O at intervals as short as 6 min in a virtually continuous mode, and it provides for repeat analysis where greater precision is needed. The method, which employs a modified, automated headspace sampler, involves equilibrating a small (15 ml) sample with an inert headspace, subsampling the headspace, and injecting it into an electron capture-gas chromatograph configured for back-flushing. The method is precise to +/- 2% (1 SD) and has been used for more than 3000 measurements of N2O in the Pacific Ocean, Indian Ocean, and Black Sea. It also has been used to measure N2O dissolved in surface water and groundwater. On a recent cruise to the east Pacific Ocean, we were able to analyze up to 125 samples per day, limited mainly by the frequency of hydrocasts.