A systematic comparison of the extraction and adsorption of theophylline by new amino acid ester-based ionic liquids

Abstract

For the extraction of theophylline from a water phase, four hydrophobic ionic liquids (ILs) were designed and synthesized which included various amino acid ester cations and the same bis(trifluoromethyl)sulfonimide anion. After screening, L-phenylalanine ethyl ester bis(trifluoromethyl)sulfonimide ([PheC₂][Tf₂N]) showed the highest distribution coefficient and it was then applied to further investigations focused on the extraction conditions. It was also immobilized through a simple procedure and used for the adsorption of theophylline for comparison. The new sorbent was characterized via infrared spectroscopy (IR), scanning electron microscopy (SEM), elemental analysis, thermogravimetric analysis, and particle size analysis. In addition, thorough investigations into the adsorption conditions, kinetics, isotherms, and thermodynamics were carried out, together with selective separation studies. The post-treatment and reuse of the IL were also explored using the two separation approaches. A comprehensive comparison was made between these approaches and reported methods.