Solubility of Nifedipine and Lacidipine in Supercritical CO2: Measurement and Correlation

Abstract

Solubilities of two calcium channel blockers, nifedipine and lacidipine, were measured in supercritical carbon dioxide at T = (313, 323, and 333) K over the pressure range (12.0–36.0) MPa using a dynamic-analytical apparatus. The solubility values obtained are in the range of (0.18–7.05) × 10−5 mol·mol−1. The solubilities of the two solids show similar trends with a crossover region of the respective isotherms in the range 18.0–21.0 MPa. The experimental solubility data were correlated with several different models. The semi-empirical density-based models provided satisfactory correlation results with AARD values lower than 10%. According to the results of the Mendez-Santiago and Teja models, the measured solid solubility data are quite consistent at all experimental conditions, which indicates the reliability of the data. The compressed gas model of the Peng–Robinson equation of state, combined with the two parameter van der Waals mixing rule (PR-EoS-VDW2) model, gives better correlation results than the PR-EoS-VDW1 model. The expanded liquid model based on Scatchard–Hildebrand regular solution theory can be used for solubility prediction, but the correlation results for nifedipine and lacidipine by the model are inferior to the compressed gas models in this work.