Simultaneous spectrophotometric determination of nitrite and nitrate in a flow-injection system

A spectrophotometric flow-injection method based on a diazo-coupling reaction is proposed for the simultaneous determination of nitrite and nitrate. Nitrate is reduced to nitrite by using a reductor column which is formed by filling part of the sample loop with copperized cadmium. The flow system produces a signal of which the height of a shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The method is suitable for the simultaneous determination of both ions in natural waters. The detection limit is 0.1 mg 1−1 for nitrite and 0.5 mg 1−1 for nitrate. Up to 22 samples can be analyzed per hour with a relative precision of ca. 1–2%.