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

A direct spectrophotometric method for the simultaneous determination of ni trite and nitrate by flow-injection analysis has been developed. The method is based on catalytic effect of nitrite on the oxidation of gallocyanine b y bromate in acidic media and the decrease in absorbance of the system at 5 30 nm. The injected sample is split into two segments. One of the streams w as directly treated with the above reagents and passed to the sample how ce ll of the spectrophotometer. The decrease in absorbance at 530 nm is due to the nitrite. The other stream was passed through a reductor minicolumn con taining copperized-cadmium, where reduction of nitrate to nitrite occurs, a nd then the sample was treated with the mixed reagents and was passed throu gh the same cell of the spectrophotometer. The total nitrite concentration initially plus that produced was determined. The influences of reagent conc entration and manifold parameters were studied. The effect of potential int erfering ions was examined. Nitrite and nitrate can be determined for the r ange 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 limi ts of 0.001 and 0.002 mu g ml(-1) for nitrite and nitrate, respectively. Ni trite and nitrate were determined in food and water samples by the proposed method with satisfactory results. (C) 1999 Elsevier Science B.V. All right s reserved.