Sequential injection analysis-based system for on-line monitoring of nitrite and nitrate in wastewaters

A sequential injection analysis system has been developed for on-line monit oring of nitrite and nitrate in wastewaters, based on the Griess-Llosvay re action and spectrophotometrical measuring of the absorbance at 543 nm. Nitr ate is previously reduced to nitrite in a copperized cadmium column and ana lyzed as nitrite. The proposed system is fully automatized and is able to m onitor nitrite and nitrate, simultaneously, in samples at a frequency of ab out 24 samples per hour with a relative standard deviation (RSD) better tha n 2.0% for nitrite and 1.3% for nitrate. The calibration graph was linear b etween 0.05 - 25 mg dm(-3) for nitrite and 0.05 - 15 mg dm(-3) for nitrate.