A method for measuring nitrite in fresh vegetables

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Abstract
A method for the measurement of nitrite in fresh vegetables is described. Interference from ascorbic acid, tannins and nitrate reductase enzyme is limited by extracting the nitrite with zinc acetate at pH 7.2–7.5 in the presence of activated carbon. Using three types of activated carbon the mean overall recovery of 40 μg nitrite added to samples of five types of vegetables (equivalent to 0. 667 mg kg−1 nitrite fresh weight) was 35.84 μg (89.6%) SD 2.437, CV 6.8%. The spectrophotometric determination uses the diazotization/coupling reaction between sulphanilamide and N(l‐naphthyl)ethylenediamine. The precision and sensitivity is improved by controlling the test solution to pH 1.2 ± 0.1.