Determination of astemizole, terfenadine and flunarizine hydrochloride by ternary complex formation with eosin and lead(II).

A simple and sensitive spectrophotometric method has been established for the determination of astemizole(I), terfenadine(II) and flunarizine hydrochloride(III) based on ternary complex formation with eosin and lead(II). The method does not involve solvent extraction. The colour of the produced complex is measured at 547.5 nm for (I) and (III), while (II) is measured at 540.7 nm. Appropriate conditions were established for the colour reaction and for the eosin: Pb(II): drug ratio to obtain maximum sensitivity. Under the proposed conditions, the method is applicable over concentration range of 4.1-37.6, 11.8-47.2 and 2.4-19.1 microg x ml(-1) with mean percentage recovery of 99.20+/-0.63, 99.76+/-0.39 and 99.60+/-0.47% for (I), (II) and (III), respectively. The suggested method was applied for determination of (I), (II) and (III) in pharmaceutical preparations. Through the use of a non-ionic surfactant (methylcellulose), prior extraction of the drugs was unnecessary. The results obtained demonstrated that the method is equally accurate, precise and reproducible as the official or reported methods. For the purpose of enhancing the sensitivity, a fluorescence quenching method for determination of the studied drugs via ternary complex formation was also investigated. The detection limit for the studied drugs (I), (II) and (III) was 0.94-7.1 microg x ml(-1) with mean percentage recovery of 99.84+/-0.29, 99.24+/-0.36 and 99.34+/-0.26%, respectively. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by official or reference methods. Unlike other reported ion-pair techniques, the suggested methods have the advantage of being applicable for the determination of the three drugs in their pharmaceutical dosage forms without prior extraction. They are recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical techniques are of great importance.