Validation of a micellar electrokinetic capillary chromatography method for the determination of imidurea, methyl and propylparabens in a pharmaceutical ointment Original Research Article

The quantitative aspects of a micellar electrokinetic chromatographic (MEKC) method for the determination of three preservatives (imidazolidinyl urea, methyl and propylparabens) in a pharmaceutical ointment are presented. Separation was carried out in a 31.2 cm long (21 cm to the detection window) × 50 μm i.d. fused silica capillary at an electric field of 960 V/cm and 25 °C. The electrolyte was 10 mM sodium dihydrogenophosphate containing 40 mM sodium dodecylsulfate (SDS) and adjusted to pH 6.1. Sample preparation consisted of a simple dispersion of the ointment in an internal standard solution (ethylparaben in the electrolyte). A 3.5 nl volume of the sample solution was introduced hydrodynamically into the capillary. The compounds detected at 200 nm were separated within 1.6 min. The method was validated with respect to specificity, linearity, accuracy, repeatability according to the International Conference on Harmonisation guidelines. Calibration curves were found to be linear for each compound (r2>0.999). Recovery studies performed by spiking an ointment placebo with the preservatives between 50 and 150% of their target concentration on 3 different days gave satisfactory results (mean recovery at each of the five concentrations ranging from 99.23 to 101.40%). The repeatability of sample preparation (n=6) was better than 2% for each of the preservatives.