Spectrophotometric determination of some preservatives in milk

Benzoic acid, propyl p-hydroxybenzoate, and sorbic acid in milk have been determined by using the corresponding first derivative curves of absorption spectra of clarified milk samples. The delta A/delta lambda curves were computed and the concentration of each preservative was calculated using 1 point, 2 points, and/or 3 points. In all cases, the percentage error was within 2.4%.