Environmentally friendly and non-polluting solvent pretreatment of palm samples for polyphenol analysis using choline chloride deep eutectic solvents

In this work, choline chloride (ChCI) deep eutectic solvents (DESs) were evaluated for the pretreatment of palm samples in the analysis of polyphenols, such as protocatechuic acid, catechins, epicatechin, and caffeic acid. During the enrichment step of the pretreatment, eight DESs comprising ChCI with ethylene glycol (EG), glycerol (Gly), xylitol (Xyl), phenol (Ph), formic acid (FA), citric acid (CiA), oxalic acid (OA), or malonic acid (MA), were prepared and applied to the reflux extraction of polyphenols from palm samples. All the DESs exhibited higher polyphenol extraction efficiency than methanol, and the highest extraction efficiency was obtained using ChCI-FA (1:1, mole ratio). For the purification step of the pretreatment, eight ChCI DES-modified adsorbents were prepared by hydrothermal polymerization and packed into solid phase extraction (SPE) cartridges, and ChCI-Urea, ChCI-Gly, ChCI-FA, and water, were used as eluents. The ChCI DES-modified adsorbents were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, and Brunauer-Emmett-Teller surface analysis, and the polyphenols were analyzed by mass spectrometry and high-performance liquid chromatographultraviolet detection. The highest purification efficiency was obtained using the ChCI-Ph DES-modified adsorbent as the SPE packing material and ChCI-Urea-H2O (1:1:5, mole ratio), ChCI-Gly (1:1, mole ratio), ChCI-FA-H2O (1:1:5, mole ratio), and H2O as the eluents. Compared to conventional purification processes that employ commercial C-18 or C-8 SPE columns with organic solvents as eluents, the ChCI DES-based SPE purification process successfully avoided the use of expensive commercial SPE columns and organic solvents. Furthermore, it isolated a larger amount of the target compounds under the same experimental conditions, and could be applied over five cycles with good reversibility. This work indicates that DESs as green solvents have great potential for the totally green pretreatment of samples during the enrichment and purification processes. (C) 2017 Elsevier B.V. All rights reserved.