Improvement of Standard Method IDF 95A: 1984 for Determination of the Nitrate and Nitrite Contents of Dried Milk

Despite major developments in chromatographic techniques, spectrophotometric methods are still used for quantitative analysis of nitrates and nitrites, as they are both specific and simple to apply. Official methods described in the literature lack precision, particularly as regards the final determination stage. This may lead to significant nitrite losses during measurement, thus considerably reducing sensitivity and reliability. In order to improve the accuracy and precision of standard methods, a number of points need to be modified: (1) during determination, the contact time between the solution to be analyzed and the first reagent should be nil; (2) the two determination reagents (HCI and sulfanilamide) should be added in reverse order; (3) the pH of the solution to be analyzed should be between 7.0 and 8.0; and (4) the entire determination process should take place in darkness. By systematically including these four points in the application of standard methods, highly satisfactory results with good repeatability are obtained.