Fast capillary electrochromatographic analysis of parabens and 4-hydroxybenzoic acid in drugs and cosmetics.

A fast reversed phase capillary electrochromatographic method was developed for the analysis of parabens preservatives in drugs and cosmetics in the presence of their main metabolite and/or impurity 4-hydroxybenzoic acid. The separation was optimised in 75 mm i.d. capillary, fully packed with 5 mm C18 stationary phase in our laboratory with a very well experienced methodology, studying the effects of mobile phase pH and composition (buffer type and organic solvent content). The mobile phase 5 mM ammonium formate pH 3.0 containing 65% of acetonitrile allowed us to obtain the baseline separation of methyl-, ethyl-, propyl-, butyl- and benzyl- parabens in mixture in less than 2.5 min with repeatability and linearity using the short end injection method (separation capillary effective length: 8 cm). Under the optimum experimental conditions the method provided high separation efficiency for parabens, in the range of 129,312-140,325 number of theoretical plates per meter, and analytes quantitation limits (LOQs) in the range 1.25-2.50 mg/mL. The method was successfully applied to the quantitative analysis of paraben preservatives in pharmaceutical and cosmetic industrial samples with direct injection or after a much reduced sample pretreatment.