Deep eutectic solvent in ultrasound-assisted liquid-phase microextraction for determination of vanadium in food and environmental waters

A method based on ultrasound-assisted liquid-phase microextraction (UA-LPME) was developed for the determination of vanadium in food and environmental water samples. Preconcentration is based on the extraction of V(V) ions in a deep eutectic solvent (DES), composed of choline chloride and phenol at a molar ratio of 1:2. Vanadium is extracted in the form of a complex consisting of V(V) and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP). The extraction solvent is dispersed in the aqueous solution using ultrasound. Tetrahydrofuran (THF) is used to aid dispersion. Detection was performed directly in the solvent after centrifugation and removal of the rich phase by digital image colorimetry (DIC). Under optimized conditions, the method presented a limit of detection of 0.3 μg L−1 and an enrichment factor of 50. The procedure was successfully applied to determine V(V) and V(IV) species in environmental water. Total vanadium was also determined in food samples. The proposed method follows the principles of green chemistry, as it uses an alternative solvent and generates few residues.