Fast and energy-effective deep eutectic solvent-based microextraction approach for the ICP-OES determination of catalysts in biodiesel

Abstract

In this research a reversed-phase deep eutectic solvent-based air-assisted dispersive liquid-liquid microextraction approach was presented for the first time and applied to the determination of catalysts (sodium, potassium, calcium and magnesium) in biodiesel samples by the inductively coupled plasma-optical emission spectroscopy. Catalysts in samples were extracted with the hydrophilic deep eutectic solvent with the assistance of air. The obtained extract phase after phase separation was analyzed by the spectral method. In this procedure the natural three-component deep eutectic solvent based on choline chloride, lactic acid and water provided fast (15 instant extraction cycles) and effective mass-transfer (extraction recovery 95-98 %). Lactic acid as precursor of the deep eutectic solvent in the presence of water provided an effective condition for separation of doubly charged metal ions. Choline chloride acted as water-soluble hydrogen bond acceptor for the deep eutectic solvent formation. The developed procedure was utilized for analysis of different nature biodiesel samples and certified reference material. It was evaluated, that the procedure is sensitive (limits of detection 3 µg kg−1), well reproducible (RSD < 7%), green (no hazardous organic solvents and mineral acids) and energy-effective (no microwave digestion of samples).