USE OF DETERGENTS AND HIGH CONTENTS OF ORGANIC-SOLVENTS FOR SIMULTANEOUS QUANTITATION OF IONIC AND NONIONIC DRUGS BY ELECTROKINETIC CHROMATOGRAPHY

Buffers containing high percentages of organic solvents, typically 50% of acetonitrile and/or methanol, together with sodium dodecyl sulfate (SDS) are employed for the separation and quantitation by electrokine tic chromatography (EKC) of analytes found in a nasal spray. Solutes c onsist of benzalkonium chloride, a family of highly positive compounds , and 2-phenylethanol and beclomethasone dipropionate, which are elect rically neutral and poorly soluble in aqueous buffers. It is observed that the effect of both concentration of SDS and temperature on the se paration depends on the organic solvent used and the solute nature. It is also observed that SDS-solute interaction for neutral and cationic compounds are weaker in the presence of high contents of acetonitrile than in methanol. Concentration of SDS, temperature, and organic solv ent nature and content, allow one to modify the selectivity of the sep aration when neutral and ionic species have to be simultaneously deter mined. The optimization of EKC conditions enables the analysis of comp ounds in less than 5 min. A one-step sample treatment consisting of ce ntrifugation of the nasal spray solved in acetonitrile, together with the referenced optimum separation conditions enable the reproducible q uantitation of the analytes. Relative standard deviation values of int er-day migration times lower than 2.45% are obtained (R.S.D.(n=12)), w hile R.S.D.(n=12) values for inter-day peak areas were lower than 6.32 %. (C) 1998 Elsevier Science BV. All rights reserved.