Spectrophotometric determination of trace amounts of nitrates and nitritesby the modified Griess-Ilosvay method - Application in analysis of hard cheese

Nitrates and nitrites in natural samples are determined by ion chromatograp hy and spectrophotometric methods. The spectrophotometric method most often used for the determination of nitrites is the Griess-Ilosvay one, based on the reaction of diazotization of the primary aromatic amines followed by c oupling of diazonium salts yielding azo dye. The same method can be used fo r the determination of nitrates, after their reduction to nitrites. In this study the Griess-Ilosvay method was applied with different diazotizing and coupling reagents. The diazotizing reagents were the sulfonamides: sulfame thazine, sulfacetamide, sulfamethizole, sulfadimethoxine and sulfisomidine. The coupling reactions were carried out using either 1-naftol-4-sulfonic a cid (NSA) or 8-amino3-naphthalenesulfonic acid (CA). Basic studies were per formed in order to establish the conditions of diazotization and coupling. The limits of determination, the range of linearity, accuracy and precision of the method and molar absorption coefficients were determined. The syste m sulfamethazine-Ca was used for the determination of nitrates and nitrites in hard cheese. In 8 selected kinds of hard cheese the concentration of ni trite nitrogen varied in the range from 0.052 to 0.356 mug g(-1) and that o f nitrate nitrogen - from 0.212 to 8.559 mug g(-1). The method applied was shown to be characterised by good accuracy and precision.