Determination of alkyl gallates in vegetable oils by deep eutectic solvent based microextraction method

Deep eutectic solvents (DES) are regarded as new generation green solvents because of their attractive properties such as easy synthesis, low cost, low volatility, high biodegradability and feasibility of structural design. A DES is typically prepared by mixing an appropriate amount of a hydrogen bond acceptor and a hydrogen bond donor. The resulting mixture has a lower melting point than that of each individual component, which makes the mixture liquid at room temperature. Due to their unique physicochemical characteristics, DESs constitute an alternative to molecular organic solvents in separation and extraction processes. In this study, a DES-based analytical method has been proposed for the microextraction of alkyl gallates (propyl gallate and octyl gallate) in vegetable oils. A hydrophilic DES was prepared by mixing choline chloride with ethylene glycol, and used in the microextraction step. The method involved the vortex mixing of the 1.0 g of oil sample with 120 µL of DES for 5 min, subsequent centrifugation for the phase separation, and direct analysis of the DES phase by liquid chromatography with ultraviolet detection. Some important parameters affecting the extraction efficiency such as type of DES, volume of diluent solvent, volume of DES and vortex stirring time have been optimized. Under optimal extraction conditions, the extraction recoveries for propyl gallate and octyl gallate were 93 % and 73 %, respectively. The method detection limits for propyl gallate and octyl gallate were 2,1 μg/kg and 4,6 μg/kg, respectively. Relative standard deviations obtained for the alkyl gallates were less than 6,4 % and 7,5 % for intra-day and inter-day precisions, respectively. The microextraction of related alkyl gallates from vegetable oil samples was carried out efficiently. The recoveries obtained from spiked oil samples were in the range of 78–106 %.