Solubility Determination and Correlation of Gatifloxacin, Enrofloxacin, and Ciprofloxacin in Supercritical CO2

Abstract

The solubilities of gatifloxacin, enrofloxacin, ciprofloxacin in SC–CO2 were determined by the dynamic method under pressures of 12–36 MPa and temperature of 313, 323, and 333 K. The consistency of the resulting solubility data was verified by the Mendez-Santiago and Teja model, Chrastil model, Bartle model, and K-J model and these models give comparable AARDs (between 6.70% and 13.51%). The compressed gas model and modified expanded liquid model were also used to correlate the resulting solubilities of the three fluoroquinolone drugs. By introducing the reference solubility and calculating the fugacity coefficient of the solute using the Carnahan–Starling-VDW hard sphere equation of state (CS-VDW EoS), the compressed gas model gives the AARDs between 0.86% and 23.65%. The intrinsic proximity of the model parameters in this model is also confirmed for the structurally similar fluoroquinolone drugs. This intrinsic proximity can be used in mutual solubility prediction between the fluoroquinolone drugs once the reference solubilities were known. The modified expanded liquid model gives the AARDs between 10.88% and 16.65% in solubility correlation. However, the predictive capability of the modified expanded liquid model based on the group contribution method needs to be improved further.