An inexpensive and very reliable technique for the determination of nitrate and nitrite in seawater is based on the conventional method of reducing nitrate to nitrite and the colorimetric determination of the nitrite as an azo dye, with a modification of the technique of flow injection analysis used to automate the processing of samples. More than 75 determinations can be made per hour on a flowing stream of seawater, such as the effluent from an in situ pump. Discrete samples can be run at a rate of 30·h‒1 with duplicate determinations of each sample. The detection limit is 0.1 µM. Precision is better than 1% at concentrations >10 µM.

A modification of flow Injection analysis Is described that can Increase the sensitivity of an analysis. The technique was tested by using It for the determination of dissolved phosphate In seawater with the colorimetric phosphomolybdate complex method. The precision of the method Is 1.5% at the 3 µ level, and the detection limit Is 0.05 µ . Samples can be analyzed at rates exceeding 90 samples per hour.

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