Analysis of parabens in cosmetics by low pressure liquid chromatography with monolithic column and chemiluminescent detection

This paper presents an application of chromatographic separation based on an ultra-short monolithic column and chemiluminescent detection in an FIA type instrument manifold for the determination of four paraben mixtures: methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is achieved in 150 s using two consecutive carriers: first 12% ACN:water that changes 75 s after injection to 27% ACN:water. The detection is based on the oxidation of the hydrolysis product of parabens, p-hydroxybenzoic acid, with Ce(IV) in the presence of Rhodamine 6G which evokes chemiluminescence of sufficient intensity to enable a sensitive determination of these species. After optimization of the variables involved, the analytical method is characterized, displaying the following values for concentration ranges, detection limits and precision, as relative standard deviation at low concentration (0.15 mg l−1)—MP: from 9.9 × 10−7 to 3.3 × 10−4 M; 1.9 × 10−8; 5.6%; EP: from 9.0 × 10−7 to 3.3 × 10−4 M; 2.8 × 10−8; 3.5%; PP: from 8.3 × 10−7 to 9.9 × 10−5 M; 2.3 × 10−8; 4.2%; and BP: from 7.7 × 10−7 to 9.9 × 10−5 M; 4.2 × 10−8 M; 6.2%. The method was applied and validated satisfactorily for the determination of these parabens in cosmetic samples, comparing the results against a liquid chromatography reference method.