Spectrophotometric determination and thermodynamic studies of the charge transfer complexation of emedastine difumarate with some π-acceptors

Spectrophotometric procedures were presented for the determination of antihistaminic drug, emedastine difumarate. The methods are based on the charge transfer complexation reaction of the drug with π-acceptors; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), chloranilic acid (CA) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Different charge-transfer complexes and colored radical anions were obtained. The formations of the colored complexes were utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of emedastine in drug substance and products. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9996-0.9999) were found between the absorbance at the relevant maxima and the concentrations of emedastine in the range of 0.8-200 μg mL−1. The limits of detection ranged from 0.06 to 0.76 μg mL−1. The molar absorptivities and association constants for the colored complexes were evaluated using the Benesi-Hildebrand equation. The free energy change (ΔG°) and the enthalpy of formation (ΔH°) as well as the entropy (ΔS°) were also determined. The methods were successfully applied to analyze the drug formulation with mean recovery percentages ± RSD% of 100.04 ± 0.59-100.22 ± 0.72. The results were compared favorably with the official and reported methods.