An improved technique for the determination of oxidised nitrogen in natural waters with a sequential injection analysis (SIA) system

Abstract

An SIA system is proposed for the determination of oxidised nitrogen (nitrate + nitrite as N) in natural waters. A cadmium reductor, made of cadmium granules closely packed in a glass column reduces the nitrate to nitrite. The reduced nitrate and the nitrite present in the water samples is diazotised in the SIA system with sulphanilamide and coupled with N – (1-napthyl) ethylene diammoniumdichloride to form a highly coloured azo dye which is detected at 540 nm with a UV/Vis spectrophotometer. The proposed system is fully computerised and is able to monitor total oxidised nitrogen as nitrite at a frequency of 36 samples per hour with a standard deviation of < 1.2%. The calibration curve is linear up to 5 mg/l with a detection limit of 0.01 mg/l.

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