Studies on solubility measurement of codeine phosphate (pain reliever drug) in supercritical carbon dioxide and modeling

Abstract In this study, the solubilities of codeine phosphate , a widely used pain reliever, in supercritical carbon dioxide (SC-CO 2 ) were measured under various pressures and temperature conditions. The lowest determined mole fraction of codeine phosphate in SC-CO 2 was 1.297 × 10 −5 at 308 K and 12 MPa, while the highest was 6.502 × 10 −5 at 338 K and 27 MPa. These measured solubilities were then modeled using the equation of state model, specifically the Peng-Robinson model . A selection of density models, including the Chrastil model , Mendez-Santiago and Teja model , Bartle et al. model , Sodeifian et al. model , and Reddy-Garlapati model , were also employed. Additionally, three forms of solid–liquid equilibrium models, commonly called expanded liquid models ( ELMs ), were used. The average solvation enthalpy associated with the solubility of codeine phosphate in SC-CO 2 was calculated to be − 16.97 kJ/mol. The three forms of the ELMs provided a satisfactory correlation to the solubility data, with the corresponding average absolute relative deviation percent (AARD%) under 12.63%. The most accurate ELM model recorded AARD% and AICc values of 8.89% and − 589.79, respectively.

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