Flow-injection catalytic spectrophotometric determination of nitrite using the redox reaction between naphthol green B and potassium bromate

A flow injection catalytic spectrophotometric method is proposed for the determination of nitrite based on its catalytic effect on the redox reaction between naphthol green B and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of naphthol green B at the maximum absorption wavelength of 722 nm. The detection limit is 0.5 ng cm(-3) in a sample volume of 90 mm(3). Up to 50 samples can be analyzed per hour with a relative precision of ca. 2%. The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural waters.