Simultaneous spectrophotometric determination of nitrate and nitrite in foodstuffs and water by flow injection analysis

A simple method is described for the simultaneous determination of nitrate and nitrite in foodstuffs and water. Cadmium is used to reduce nitrate to n itrite. Nitrite is diazotised in the FIA system with N-(l-naphthyl)ethylene diammonium dichloride to form the highly coloured ate-dye, which is measure d at 540 nm. The detection limit is 0.085 mu l(-1) for a sample injection o f 400 mu l. The sampling rate is about 50 samples per hour and the relative standard deviation is 1.56% and 0.77% for both nitrate and nitrites, respe ctively. The effect of pH, length of reductor column. and various types of cadmium reductor on the yield of nitrite is investigated. At pH above 8.05 a maximum yield of nitrite is obtained. Cadmium coarse powder and cadmium g ranules all give practically the same yield. The results of the variables m entioned are discussed thoroughly.