Stir membrane liquid-phase microextraction based on milk fats hydrolysis and deep eutectic solvent formation: Determination of bisphenols.

In this paper, a stir membrane liquid-phase microextraction approach based on milk fats hydrolysis and in situ deep eutectic solvent formation was developed for the first time. The approach was applied to clean-up and preconcentrate bisphenols from milk samples. The procedure assumed alkaline hydrolysis of samples fats to obtain water-soluble salts of fatty acids that acted as precursors for the deep eutectic solvent formation. A stir membrane disk impregnated with menthol was placed into the sample solution. The formation of microdroplets of the hydrophobic fatty acids was observed under sample acidification. Collection of the extract phase on the disk was based on deep eutectic solvent formation. Under optimal conditions, the RSD was < 6 %, limits of detection for bisphenols were 0.3-0.5 μg kg. The extraction recoveries were in the range of 95-97 %, which indicated the excellent capability of the developed approach to extract hydrophobic analytes from complex matrices.