SPECTROPHOTOMETRIC ANALYSIS OF SOME GUANIDINO DRUGS BY ACID-DYE AND CHARGE-TRANSFER COMPLEXATION METHODS

Two spectrophotometric methods are described for the determination of guanethidine sulphate (I), guanfacine hydrochloride (II), guanoclor su lphate (III), guanoxan sulphate (IV) and debrisoquine sulphate (V). Th e first method involves ion-pair formation of the selected compounds ( I-V) with bromocresol purple at pH 3.8. The yellow ion pair is extract ed with chloroform and the absorbance is measured at about 415 nm. The second method is based on the reaction of the basic guanidino compoun ds (I, III-V) with iodine in chloroform to give molecular charge-trans fer complexes with maximum absorbance at 292 and 345 nm. Beer's law wa s obeyed for both methods and the relative standard deviations were fo und to be less than 2%. The apparent molar absorptivities were found t o be 2.1 x 10(4) to 6.9 x 10(4) l mol-1 cm-1 using bromocresol purple and 0.7 x 10(4) to 2.4 x 10(4) l mol-1 cm-1 using iodine. The investig ated drugs were assayed in tablets. The mean percentage recoveries wer e found to be 99.8-100.8% by the acid-dye method and around 100.4% by the charge-transfer complexation method.