Thermodynamic and Spectrophotometric Studies of Electron Donor-Acceptor Complexation Between Loratadine and Chloranilic Acid

Purpose: To developing a simple, rapid and reliable analytical method for loratadine based on charge transfer complexation with chloranilic acid. Methods: The complex between loratadine and the complexing agent, chloranilic acid, was formed by mixing appropriate volumes of their solutions in non-aqueous media. Some features of the formed complex, such as molar ratio of the reaction and effect of time, were determined spectrophotometrically. Thermodynamic parameters were determined as well, the method was utilized in the assay of the drug in both bulk and tablet dosage forms. Results: The complex showed a wavelength of maximum absorption (lambda(max)) at 527 nm (lambda(max) of loratadine alone was 440 nm). Beer's law was obeyed in the concentration range of 3.2 - 28.8 mg% (r(2) = 0.9997). The stoichiometry of the complex was 2:1 (loratadine: chloranilic acid) and the complex was stable for over 60 min. Thermodynamic results show that as temperature changed from 30 to 70 degrees C, enthalpy change (Delta H) was steady at -0.254 kcal.mol(-1) while the free energy (Delta G) changed from -3.904 to -4.450 kcal.mol(-1). The complex appeared to be more stable at the slightly elevated temperature of 50 degrees C with a value of 757.14 mol(-1). Analysis of the drug in both bulk and dosage forms showed good accuracy and precision with recovery ranging from 99.98 +/- 1.00 to 100.94 +/- 2.39 %. Conclusion: Charge transfer complexation method with chloranilic acid was successfully developed for the simple, rapid and accurate determination of loratadine.