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A New Analytical Method for the Kinetic Spectrophotometric Determination of Trace Amounts of Nitrite in Some Environmental Water Samples

Nitrite is a characteristic pollutant ion, which is ubiquitous within environmental and physiological systems, and occurs in water as an intermediate during the nitrogen cycle. Therefore, the detection and determination of its concentration at trace levels is extremely important in biological and environmental studies. A simple, sensitive and rapid kinetic spectrophotometric method for the determination of nitrite in different natural and wastewater samples is presented. The reaction is initiated by adding the known volumes of a nitrite ion solution of identified concentration to acid solutions of Cresyl violet perchlorate, which the color of indicator reagent changes to yellow with time. Then, the absorbance changes are monitored spectrophotometrically at λmax= 585 nm for the concentration range of 0.01-2 µg mL -1 and at λmax= 409 nm for the concentration range of 0.5-5 µg mL -1 of nitrite ion at 40 o C. The detection limit and quantification limit of the proposed kinetic method were 0.00627 and 0.0188 µg mL -1 respectively. The RSDs for the determination of 0.2 and 1.5 µg ml –1 of nitrite were 4.98% and 2.08% for five replicate measurements, respectively. The effect of possible interfering ions on the determination of nitrite is described. Many of cations and anions have no interfering effect but Fe 3+ , Fe 2+ , Cd 2+ , I - , N3 - , WO4 2- , S 2- , SO3 2- and S2O3 2- ions do interfere. The accuracy and validity of the proposed kinetic method was established by studying recovery of spiked nitrite ion and by parallel determination using a standard method based on diazo-coupling reaction. The method was successfully applied to the determination of nitrite in various natural and wastewater samples.