A Sensitive Spectrofluorimetric Method for the Determination of Nitrite in Agricultural Samples

A simple, selective, and very sensitive spectrofluorimetric method was developed for the determination of nitrite in vegetables. The method is based on the reaction between nitrite and 4-amino-3-hydroxynaphthalene-1-sulfonic acid (AHNSA) which results in the quenching of the fluorescence of AHNSA. Optimal values of the factors influencing the reaction between nitrite and AHNSA were explored by central composite design (CCD). The factors were pH of the acidic solution and concentration of AHNSA. In optimal conditions, difference between fluorescence intensity of AHNSA and its fluorescence intensity in the presence of nitrite at 442 nm was selected as the analytical signal. The relation between signal and concentration of nitrite was linear in the range of 0.005-0.500 mg L-1. A detection limit of 2.5 x 10(-3) mg L-1 was obtained for the determination of nitrite by the proposed method. Using the proposed method, it is possible to determine trace amounts of nitrite in vegetable samples with relative errors lower than 6 %. The relative standard deviation (RSD) values of the method for the determination of nitrite in cucumber, cabbage, lettuce, and tomato samples were 0.12, 0.20, 0.86, and 0.13 %, respectively. Moreover, the proposed method was validated by comparison with a standard method.