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

Abstract

The direct spectrophotometric method has been developed for the simultaneous determination of nitrite and nitrate by flow-injection analysis. The method is based on the catalytic effect of nitrite on the oxidation of pyrogallol red (PGR) by bromate in acidic media and the decrease in absorbance of the system at 465 nm. The injected sample is split into two streams. One of the streams is directly treated with the above reagents and then is passed to the sample flow cell of the spectrophotometer. The decrease in absorbance at 465 nm is due to the nitrite. The other stream is passed through a reductor micro column containing copperized-cadmium, where nitrate reduces to nitrite 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 influence of reagents concentrations and manifold parameters were studied. The effect of potential interfering ions was examined. Nitrite and nitrate can be determined for the range of 0.003–2.00 and 0.030–2.00 μg ml −1, respectively. The sampling rate of analyses was 20±3 h −1, with detection limits 0.001 and 0.010 μg ml −1 for nitrite and nitrate, respectively. Nitrite and nitrate were determined in food and water samples by the proposed method with satisfactory results.