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Abstract. Simple and sensitive spectrophotometric methods for the determination of labetalol hydrochloride are described. The first two are based on the oxidative coupling reaction of labetalol hydrochloride with p-N,N-dimethylphenylenediamine dihydrochloride (method A, 2m~ x 685 rim) and 3-methyl-2-benzothiazolinone hydrazone hydroclhloride (method B, 2ma x 545 rim) in the presence of sodium hypochlorite and ceric ammonium sulphate as oxidants, respectively. The third depends on the formation of an ion-association complex of labetalol hydrochloride with suprachen violet 3B at pH 1.3, which is extracted into chloroform (method C, 2m, x 565 rim). The methods obey Beer's law and the precision and accuracy of the methods were checked against the B.P. reference method and the relative standard deviations were in the range 0.35-0.52%. These methods are applied to the determination of labetalol in dosage forms. Key words: spectrophotometry, labetalol hydrochloride, p-N,N-dimethyl-phenylenediamine dihydrochloride, 3-methyl-2-benzothiazolinone hydrazone hydrochloride, suprachen violet 3B, oxidative coupling reaction, ion-association complex.Labetalol hydrochloride (LBL 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl) amino] ethyl] benzamide hydrochloride), is an antihypertensive drug [1] with many desirable characteristics. This drug exhibits both ~-and /3-blocking actions and thus yields a faster antihypertensive effect than/~-blockers alone and is official in B.P. 1-2-] and U.S.P. [3]. Only a few spectrophotometric methods 1-4, 5] have been reported for the determination of LBL in pure and dosage forms. It is therefore of interest to develop fast and simple procedures for quantification of LBL.

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