Sequential flow injection spectrophotometric determination of nitrite and nitrate in various samples

A direct spectrophotometric method has been developed for the sequential determination of nitrite and nitrate by flow injection analysis (FIA). The method is based on the reaction of nitrite with safranine O to form a diazonium salt which caused the reddish-orange dye colour of the solution to be changed to blue in acidic media, and which absorbs at 520 nm. The injected sample in the flow injection system is split in two streams. One of the streams is transported through a reductor microcolumn containing copperised cadmium, where nitrate is reduced to nitrite. The two streams are then mixed and treated with the appropriate reagents. The influence of reagent concentrations and manifold parameters was studied. The effect of potentially interfering ion was examined and procedures for elimination of interfering cations are proposed. Nitrite and nitrate can be determined in the range 0.0001-3.00 and 0.005-3.40 mug ml(-1), respectively, with a sampling rate of 20 +/- 3 h(-1). Detection limits (3 sigma) of 0.5 and 3 ng ml(-1) were obtained for nitrite and nitrate, respectively. Nitrite and nitrate were determined in food samples by the proposed method with satisfactory results. (C) 2001 Elsevier Science B.V. All rights reserved.