Colorimetric and fluorimetric methods for the determination of some antihistaminics using acid dyes and charge transfer techniques

The acid dyes eosin B and tropeolin oo were used for the determination of terfinadine, astemizole and acrivastine in the presence of McIlvain buffer of a suitable pH. The formed ion-pairs were extracted with chloroform and the absorbances were measured at 530-535 nm and 410 nm in the case of eosin B and tropeolin oo, respectively. In addition terfinadine, astemizole and acrivastine were determined fluorimetrically using eosin B. The fluorescence intensity was measured at 480 nm excitation and 555 nm emission. Conformity with Beer's law was evident over a concentration range of 2-20 mu g/ml in the colorimetric methods and of 0.16 - 0.96 mu g/ml in the fluorimetric methods. The charge transfer technique was also applied for the determination of astemizole and acrivastine using iodine and 2,3 dichloro, 5, 6 - dicyano - p-benzoquinone (DDQ). Absorbances were measured at 286 nm and 292 nm, respectively, in the iodine method and at 461 nm in the DDQ method. Conformity with Beer's law was evident over concentration range of 1 - 12 mu g/ml and 20 - 200 mu g/ml in iodine and DDQ methods respectively. The precision of the proposed methods was tested by applying them for the determination of pure samples of terfinadine, astemizole and acrivastine. The mean percentage recovery of terfinadine, astemizole and acrivastine lies in the range 99.49-100.72% in eosin B method, 94.79-100.16% in tropeolin oo method 100.01-101.00% in the fluorimetric method. In the charge transfer methods the mean percentage recovery of astemizole and acrivastine lies in the range 99.61-100.40% and 100.02-100.30% in iodine and DDQ methods respectively. The proposed methods were successfully applied for the determination of the drags in their pharmaceutical dosage forms and their validities were ascertained by applying the standard addition technique.