Extraction of ofloxacin from water using hydrophobic eutectic solvents

Wastewater treatment plants do not cope well with emerging micropollutants, such as pharmaceuticals, because they are not effective to remove them. Therefore, this work aims to develop a process for the extraction of ofloxacin (OFX) based on a liquid-liquid extraction using hydrophobic eutectic solvents (HES), coupled with the Conductor-like Screening Model for Real Solvent (COSMO-RS) for solvent screening. First, COSMO-RS was used to predict the partition coefficient of OFX for four HES families: L-menthol: fatty acid, L-menthol: fatty alcohol, fatty acid: fatty acid and fatty acid: fatty alcohols, at three different molar ratios (2:1, 1:1, and 1:2). These results showed that HES formed by fatty acids, especially those with a longer alkyl chain and a higher fatty acid molar ratio, were the most suitable solvents for OFX extraction. Then, the most promising HES to extract OFX was evaluated experimentally. The HES decanoic acid: dodecanoic acid (C10 acid: C12 acid) in a molar ratio of 2:1 being the system with best extraction results of OFX was selected to optimize the extraction conditions of OFX, namely pH, HES: water ratio (v/v), and OFX concentration, using a response surface methodology (RSM). The results obtained showed that at a pH of 5.2, HES-water ratio (v/v) of 1.3, and 2.5 mg/ml of OFX that an extraction efficiency of OFX of (98.8 ± 0.9)% could be achieved. The results show that one-step OFX extraction is possible, but is significantly influenced by both the extraction parameters and the hydrophobic properties of the HES.