Application of Ion Associate Formation for Conductimetric Determination of Dothiepin Hvdrochloride in Pharmaceutical Formulations by Using Trioxalato Complexes

A simple titrimetric method is described for the determination of dothiepin hydrochloride. The method is based on titrating the cited drug with potassium salts of trioxalato-ferrate (III) (TOXFe), trioxalato-chromate (III) (TOXCr), trioxalatoaluminate (III) (TOXAI) and trioxalato-cobaltate (III) (TOXCo). The end point was located conductimetrically. The effect of solvent, molar ratio, reagent concentration and temperature were studied. Based on conductimetric measurements at 25 °C, the solubility, solubility product, free energy (ΔG) and entropy changes (ΔS) of the ion associates were calculated. Calculations of the enthalpy change (ΔH) are based on atomic absorption measurements of the solubility of the ion associates at different temperatures. The method allowed the determination of 6.63-29.87, 3.31-49.78, 9.95-49.78 and 3.31-33.19 mg of the studied drug using TOXFe, TOXCr, TOXAl and TOXCo, respectively. The method was further applied successfully to some dosage forms containing the cited drug, and the obtained results were compared favorably with those previously given by the official method.