Solution thermodynamics and preferential solvation of sulfamethazine in ethylene glycol + water mixtures

Abstract

The solubility of sulfamethazine (SMT) in ethylene glycol (EG) + water (W) cosolvent mixtures was determined at nine temperatures (278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K) by means of the stirring method. From the solubility data, the thermodynamic functions of solution, transfer and mixing were calculated using the Gibbs and van´t Hoff equations. On the other hand, the preferential solvation parameters of SMT were determined by means of the method of the inverse integrals of Kirkwood-Buff (IKBI). In general terms, the solubility of SMT is favored by the increase in temperature and the decrease in the polarity of the cosolvent system, thus the maximum solubility is reached in pure EG at 318.15 K and the minimum in pure water at 278.15 K. Gibbs energy is positive in all cases, with a higher contribution from the energy component (enthalpy of solution). Regarding enthalpy-entropic compensation, the process is driven in all cases by the enthalpy of solution. Finally, SMT is preferentially solvated by water in mixtures with higher polarity and by EG in less polar mixtures.