Improved colorimetric method for determining nitrate and nitrate in foods

Abstract

A method is described for determining nitrate and nitrite in cured meat products, cheeses, and vegetables. The nitrite is determined colorimetrically by diazotization of sulfanilic acid and subsequent coupling with N-(1-naphthyl)-ethylenediamine. The concentration of nitrate plus nitrite is determined similarly but after reduction of the nitrate to nitrite on a cadmium column. The difference of the 2 values is a measure of the nitrate concentration. The main improvements are replacing the Griess reagent, which contains a carcinogen, with a mixture of sulfanile acid and N-(1-naphthyl)-ethylenediamine, providing for adjustment of pH of the sample suspension during extraction and digestion by heating, and maintaining constant pH by controlled addition of buffers and acids during color development. The method was successfully applied to the analysis of 15 samples of meat products, 23 cheeses, and 6 different vegetables. The average recovery of sodium nitrite added at levels ranging from 10 to 30 ppm was 95% and recovery of sodium nitrate added at levels from 30 to 400 ppm was 94% (corrected for cadmium column efficiency).