On-line monitoring of nitrite in fertilizer process streams, natural and waste water effluents with sequential injection analysis

A sequential injection system for the online monitoring of nitrite in fertilizer process streams, natural and waste water effluents is proposed. Nitrite is diazotised in the SIA system with N-(1-naphthyl) ethylenediammonium dichloride to form a highly coloured azo dye which is measured at 525 nm. The proposed system is fully computerised and is able to monitor nitrite at a frequency of 49 samples per hour with a relative standard deviation of < 2.7%. The calibration curve is linear up to 5 mg/l. The detection limit is 0.053 mg/l.