Simultaneous determination of nitrite and nitrate in various samples using flow injection with spectrophotometric detection

A direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. The method is based on catalytic effect of nitrite on the oxidation of gallocyanine by bromate in acidic media and the decrease in absorbance of the system at 530 nm. The injected sample is split into two segments. One of the streams was directly treated with the above reagents and passed to the sample how cell of the spectrophotometer. The decrease in absorbance at 530 nm is due to the nitrite. The other stream was passed through a reductor minicolumn containing copperized-cadmium, where reduction of nitrate to nitrite occurs, and then the sample was treated with the mixed reagents and was passed through the same cell of the spectrophotometer. The total nitrite concentration initially plus that produced was determined. The influences of reagent concentration and manifold parameters were studied. The effect of potential interfering ions was examined. Nitrite and nitrate can be determined for the range of 0.010-2.500 mu g ml(-1) and 0.020-3.500 mu g ml(-1), respectively. The sampling rate of analysis was 20+/-3 h(-1), with 3 sigma detection limits of 0.001 and 0.002 mu g ml(-1) for nitrite and nitrate, respectively. Nitrite and nitrate were determined in food and water samples by the proposed method with satisfactory results. (C) 1999 Elsevier Science B.V. All rights reserved.