Study of solubility and thermodynamic properties of amlodipine besylate in solvent mixtures of polyethylene glycol 400 and ethanol at different temperatures

Abstract

Solubility is one of the most important physicochemical properties of medicinal substances, which is very important in the process of drug discovery and development. Solubility data provide important and useful information for the preparation of pharmaceutical formulations, the development of pharmaceutical analyses, recrystallization in the purification process, and solid phase properties and extraction. Aim: In the current research, the solubility and density of the amlodipine besylate in the solvent mixture of PEG400+ethanol in the temperature range of 293.2 to 313.2 K has been studied. Also, the correlation between the obtained data and different solubility models has been investigated. Method: In this study, the solubility of amlodipine besylate in the binary solvent system of PEG400 and ethanol was measured using the shake-flask method. For this purpose, different mixtures of PEG400 and ethanol were prepared with mass intervals of 10% and excess amounts of drug are dispensed into it, and after centrifugation of the solution and appropriate dilution, the absorption of the solutions was measured at 239 nm using a UV spectrophotometer and the concentrations were calculated using a plotted calibration curve. This process was repeated for 5 temperatures and all data were used to find an equation to predict solubility. Results: The obtained results indicate that the solubility of amlodipine besylate increases with the increase of the mass fraction of PEG400, until it reaches its maximum value at w1 = 0.7. Then, by adding more amounts of PEG400, the solubility decreases. In addition, the solubility of amlodipine besylate increases with temperature increase in each mass fractions.Conclusion:Solubility data showed an upward trend with the increase of PEG400 up to 0.7 fraction. We also saw an upward trend in solubility with increasing temperature. The obtained data were fitted to different models and the constants of each model were calculated.