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

The direct spectrophotometric method has been developed for the simultaneou s determination of nitrite and nitrate by flow-injection analysis. The meth od is based on the catalytic effect of nitrite on the oxidation of pyrogall ol red (PGR) by bromate in acidic media and the decrease in absorbance of t he 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 absorbanc e at 465 nm is due to the nitrite. The other stream is passed through a red uctor micro column containing copperized-cadmium, where nitrate reduces to nitrite and than the sample was treated with the mixed reagents and was pas sed through the same cell of the spectrophotometer. The total nitrite conce ntration initially plus that produced was determined. The influence of reag ents concentrations and manifold parameters were studied. The effect of pot ential interfering ions was examined. Nitrite and nitrate can be determined for the range of 0.003-2.00 and 0.030-2.00 mug ml(-1), respectively. The s ampling rate of analyses was 20 +/- 3 h(-1), with detection limits 0.001 an d 0.010 mug ml(-1) for nitrite and nitrate, respectively. Nitrite and nil:r ate were determined in food and water samples by the proposed method with s atisfactory results. (C) 2001 Elsevier Science B.V. All rights reserved.