Spectrophotometric Study of Stability Constants of Metal Complexes of Promethazine at Different Temperatures

The complexation reactions between Cu2+, Pd2+ and Ni2+ metal ions with promethazine (PM) in water or DMF were studied by the spectrophotometric methods at [(15, 25,35 and 45±0.1) °C]. The complexation process was optimized in terms of pH, temperature and contact time. The stoichiometry of the complex was found to be 1:1 (metal ion/ligand). The formation constants of the resulting complexes were determined from computer fitting absorbance-mole ratio data. The values of the thermodynamic parameters for complexation reactions were obtained from the temperature dependence of the stability constants. The proposed method was successfully applied for the determination of PM in their dosage forms.