SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF NITRITE AND NITRATE IN A FLOW-INJECTION SYSTEM

A spectrophotometric flow-injection method based on a diazo-coupling r eaction is proposed for the simultaneous determination of nitrite and nitrate. Nitrate: is reduced to nitrite by using a reductor column whi ch is formed by filling part of the sample loop with copperized cadmiu m. The flow system produces a signal of which the height of a shoulder in the ascending part of the peak corresponds to the nitrite concentr ation and the maximum of the peak corresponds to nitrate plus nitrite. The method is suitable for the simultaneous determination of both ion s in natural waters. The detection limit is 0.1 mg l(-1) for nitrite a nd 0.5 mg l(-1) for niltrate. Up to 22 samples can be analyzed per hou r with a relative precision of ca. 1-2%.