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

A direct spectrophotometric method has been developed for the sequential de termination of nitrite and nitrate by flow injection analysis (FIA). The me thod is based on the reaction of nitrite with safranine O to form a diazoni um salt which caused the reddish-orange dye colour of the solution to be ch anged to blue in acidic media, and which absorbs at 520 nm. The injected sa mple in the flow injection system is split in two streams. One of the strea ms is transported through a reductor microcolumn containing copperised cadm ium, where nitrate is reduced to nitrite. The two streams are then mixed an d treated with the appropriate reagents. The influence of reagent concentra tions and manifold parameters was studied. The effect of potentially interf ering ion was examined and procedures for elimination of interfering cation s 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 f or nitrite and nitrate, respectively. Nitrite and nitrate were determined i n food samples by the proposed method with satisfactory results. (C) 2001 E lsevier Science B.V. All rights reserved.