Simultaneous multiresponse optimization applied to epinastine determination in human serum by using capillary electrophoresis

Experimental design and optimization techniques were implemented for the development of a rapid and simple capillary zone electrophoresis method (CZE) for the determination of epinastine hydrochloride in human serum. The effects of five factors were studied on the resolution between the peaks for the target analyte (epinastine hydrochloride) and lidocaine hydrochloride, used as internal standard, as well as on the analysis time. The factors were the concentration and pH of the buffer, the injection time, the injection voltage and the separation voltage. The separation was carried out by using an uncoated silica capillary with 50 microm i.d. and total length 64.5 cm (150 microm of path length) and UV detection (200 nm). Multiple response simultaneous optimization by using the desirability function was used to find experimental conditions where the system generates desirable results. The optimum conditions were: sodium phosphate buffer solution, 16.0 mmol L(-1); pH 8.50; injection voltage, 20.0 kV; injection time, 30 s; separation voltage, 26.7 kV. The method was confirmed to be linear in the range of 2.0-12 ng mL(-1). The injection repeatability of the method was evaluated by six injections at three concentration levels, while intra-assay precision was assessed by analysing a single concentration level, yielding a CV's of ca. 1% for standard and 2% for serum samples. Accuracy was evaluated by recovery assays and by comparing with an HPLC method, the results being acceptable according to regulatory agencies. The rudgeness was evaluated by means of an experimental Plackett-Burman design, in which the accuracy was assessed when small changes were set in the studied parameters. Clean-up of human serum samples was carried out by means of a liquid-liquid extraction procedure, which gave a high extraction yield for epinastine hydrochloride (93.00%).