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

An SIA systems proposed for the determination of oxidised nitrogen (nitrate + nitrite as N) in natural waters. A cadmium reductor, made of cadmium gra nules, 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) eth ylene diammoniumdichloride to form a highly coloured azo dye which is detec ted 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.