Simultaneous determination of ingredients in an ointment by hydrophobic interaction electrokinetic chromatography

Hydrophobic interaction electrokinetic chromatography was used to simultane ously determine seven active ingredients (diphenhydramine hydrochloride, di bucaine hydrochloride, chlorhexidine hydrochloride, phenylephrine hydrochlo ride, hydrocortisone acetate, allantoin and tocopherol acetate) in an ointm ent. Not only hydrophobic but also ionic compounds were successfully separa ted by use of a separation solution composed of acetonitrile-water (80:20, v/v), tetradecylammonium salt and ammonium chloride. The migration behavior of the hydrophobic compound depended on tetradecylammonium concentration, while that of the ionic compounds depended on ammonium chloride concentrati on. An addition of triethylamine to the separation solution markedly improv ed the reproducibility of the peak areas of cations with a relative standar d deviation (RSD) of less than 1.7% (n=6). The established method was valid ated and confirmed to be applicable to the determination of the active ingr edients in a commercial ointment. Sample preparation was performed by liqui d-liquid extraction and no interference from the formulation excipients was observed. Good linearities were obtained, with correlation coefficients ab ove 0.999. Recoveries and precisions ranged from 98.0 to 100.8%, and from 0 .4 to 2.9% RSD, respectively. These results suggest that hydrophobic intera ction electrokinetic chromatography can be used for the determination of io nic compounds as well as hydrophobic compounds in ointment. (C) 2001 Elsevi er Science B.V. All rights reserved.