Parabens determination with a hybrid FIA/HPLC system with ultra-short monolithic column

The combination of an ultra-short C18 monolithic column (5 mm long) with a flow injection analysis (FIA) scheme results in a versatile and efficient system that has been used for the chromatographic determination of four preservatives — methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is carried out by using two carriers, A and B, consisting of a mixture of ACN: water in different proportions. The described procedure is able to separate the analytes in only 150 s. The applicable concentration range, detection limit and the relative standard deviation were the following: for MP from 1.6 × 10^-5 to 1.1 × 10^-3 M; 4.8 × 10^-4 M; 0.65%; for EP between 3.7 × 10^-5 and 2.0 × 10^-3 M; 1.2 × 10^-5 M; 1.2%; for PP between 3.9 × 10^-5 and 2.0 × 10^-3 M; 1.2 × 10^-5 M; 1.2%; and for BT between 6.0 × 10^-5 and 2.0 × 10^-3 M; 1.8 × 10^-5 M; 1.8%. The method was applied and validated satisfactorily for the determination of these parabens in commercial cosmetics samples, comparing the results with those obtained by HPLC reference method.