Novel recyclable acidic hydrophobic deep eutectic solvents for highly efficient extraction of calcium dobesilate in water and urine samples

Deep eutectic solvents (DESs) have been considered to be one of the most promising green alternatives of conventional volatile solvents for liquid-liquid separation. However, acidic hydrophobic DESs have been less studied although they are of great importance for the extraction of compounds which are unstable in alkaline conditions. In this study, a novel family of acidic hydrophobic deep eutectic solvents was designed and prepared from methyl trioctyl ammonium chloride and a series of haloacetic acids. For the first time, the obtained DESs were used for extraction and determination of calcium dobesilate, which is an extensively used medicine for treating vascular diseases, but it can be easily oxidized under alkaline and neutral conditions. The factors influencing extraction process including pH, temperature, extract time, inorganic salts and organic coexistence were systematically investigated. It is found that these DESs exhibited outstanding extraction performance towards calcium dobesilate. The extraction equilibrium time was only 3 min in a wide range of pH (1.2–9.2) at room temperature and the extraction capacity was up to 504 mg/g. The detection limit of calcium dobesilate extracting from water samples was 0.05 μg/L and the limit of quantification was 0.5 μg/L. A variety of inorganic salts with the concentration up to 1.0 mol/L and common coexisting organic compounds, such as glucose and starch, with the concentration more than 1000 times higher than the target analyte had no obvious impact on the extraction efficiency. The relative recovery for real samples ranged from 93.2% to 108.6%. Furthermore, the DESs could be recycled and regenerated through back extraction. After fifteen cycles, the extraction efficiency was still up to 99%. Finally, the extraction and back extraction mechanism was discussed in detail.