A sensitive colorimetric method for the determination of trace amounts of nitrate in various environmental samples

A simple and sensitive spectrophotometric procedure for the determination of nitrate has been developed using a new reagent system. Nitrate is first reduced to nitrite with zinc in alkaline medium. The reduced nitrite reacts with p-nitroaniline in presence of hydrochloric acid to form diazonium cation which is subsequently coupled with phloroglucinol (1,3,5-trihydroxy benzene) to form a stable yellow orange azo dye, the absorbance of which is measured at 444 nm. Various analytical parameters such as effect of pH, sample size, time, temperature, reagent concentration and interfering species were studied. Beers law is obeyed over the concentration range of 0.5 mu g - 5.0 mu g of nitrate (NO3) per 25 mi of solution (20.0 mu g L-1 - 200 mu g L-1). The method has been successfully applied to water samples and certain commercial samples such as baby food, cheese etc. The results obtained are reported and discussed.