Determination of preservatives in cosmetics and food samples by micellar liquid chromatography

An analytical procedure has been developed for the analysis of benzoic acid, p-hydroxybenzoic acid, methyl-, ethyl-, propyl-, isopropyl-, and butyl esters of p-hydroxybenzoic acid by micellar liquid chromatography. After dilution in n-propanol the sample was directly injected onto a Lichrosorb ODS, 5 microm (250 x 4.6 mm ID) column and eluted with aqueous 2% Brij-35 adjusted to pH 3.0 with phosphoric acid:propanol (80:20 v/v) at a flow rate of 1 mL min(-1) and UV detection at 254 nm. A linear calibration curve was obtained simultaneously for each component in the range of 50-500 microg mL(-1) for benzoic acid and 5-150 microg mL(-1) for the other components; detection limits were within 25-250 ng mL(-1) corresponding to 125-1250 pg per injection (5 microL). The reproducibility in terms of average peak area and average retention time was obtained with coefficients of variation (CV) of 1.2% and 0.5%. The method was applied to analysis of these compounds in cosmetics (shampoos, hand lotions, creams, and bath foam) and food samples.