Determination of ethambutol by ion-pair reversed phase liquid chromatography with UV detection

An ion-pair reversed phase liquid chromatography method for the antituberculosis drug ethambutol hydrochloride was developed using sodium 1-heptanesulfonate (4.0 mg/ml) as an ion-pairing (IP) reagent. To enable detection of the ethambutol with a UV detector without sample pretreatment, the pH 4,5 aqueous tetrahydrofuran (THF) (25%, v/v) mobile phase contained 1.0 mM Cu(II), which forms a UV-absorbing complex with the analyte. At a column temperature of 35 degreesC, ethambutol gives a symmetrical peak with a retention time of 5 min. Chromatographic conditions were optimized through study of the effects of mobile phase composition and pH, Cu(II) and IP reagent concentration, and column temperature. The method is shown to be simple, precise, efficient, robust, linear up to at least 0.25 mg/ml, and to have a limit of quantitation of 6 mug/ml. (C) 2002 Elsevier Science B.V. All rights reserved.