Magnetic Solid-phase Extraction with Fe3O4/Molecularly Imprinted Polymers Modified by Deep Eutectic Solvents and Ionic Liquids for the Rapid Purification of Alkaloid Isomers (Theobromine and Theophylline) from Green Tea

Abstract

Different kinds of deep eutectic solvents (DES) based on choline chloride (ChCl) and ionic liquids (ILs) based on 1-methylimidazole were used to modify Fe3O4/molecularly imprinted polymers (Fe3O4/MIPs), and the resulting materials were applied for the rapid purification of alkaloid isomers (theobromine and theophylline) from green tea with magnetic solid-phase extraction (M-SPE). The M-SPE procedure was optimized using the response surface methodology (RSM) to analyze the maximum conditions. The materials were characterized by Fourier transform infrared spectroscopy (FI-IR) and field emission scanning electron microscopy (FE-SEM). Compared to the ILs-Fe3O4/MIPs, the DESs-Fe3O4/MIPs were developed for the stronger recognition and higher recoveries of the isomers (theophylline and theobromine) from green tea, particularly DES-7-Fe3O4/MIPs. With RSM, the optimal recovery condition for theobromine and theophylline in the M-SPE were observed with ratio of methanol (80%) as the washing solution, methanol/acetic acid (HAc) (8:2) as the eluent at pH 3, and an eluent volume of 4 mL. The practical recoveries of theobromine and theophylline in green tea were 92.27% and 87.51%, respectively, with a corresponding actual extraction amount of 4.87 mg·g−1 and 5.07 mg·g−1. Overall, the proposed approach with the high affinity of Fe3O4/MIPs might offer a novel method for the purification of complex isomer samples.

Involvement of Deep Eutectic Solvents in Extraction by Molecularly Imprinted Polymers—A Minireview

“…The best system for the extraction of the target substances theophylline, theobromine, (+)-catechin hydrate, and caffeic acid from green tea [49] was Fe O 4 -ChCl:oxalic acid:polypropylene glycol-MMIPs (5.82; 4:32; 18.36 and 3.96 mg/g, respectively). For the binary system [48], ChCl: urea, and Fe 3 O 4 @MMIPs [48], the extraction amounts of theobromine and theophylline reached 4.87 mg/g and 5.07 mg/g green tea, respectively.…”

“…To investigate the kinetics of the adsorption process, the pseudo-first order, pseudo-second order models, and intraparticle diffusion model are used [38,39]. The latest results published in the last five years and evaluating the state-of-the-art of methods and technologies applied in the field of DES-MIPs utilization document a wide potential range of these systems in obtaining and/or purifying value-added substances [32,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] (Table 1). Extraction methods using DES-MIPs show excellent adsorption ability and selectivity for the selection of templates or target compounds in case studies.…”

“…In addition to the possibilities offered by MIPs and DES-MIPs, invention of a new class of MIPs-magnetic MIP (further on MMIPs)-has opened and expanded the possibilities of extraction, isolation and analysis of the desired compounds from materials of biological origin as well as separation of MIPs from reaction systems. DES-MMIPs can contain various magnetic parts as carrier, such as Fe 3 O 4 @3-aminopropyltriethoxysilane [37], Fe 3 O 4 @SiO 2 [38]; Fe 3 O 4 @MoS 2 [39]; Fe 3 O 4 @acrylic acid [40]; Fe 3 O 4 [48]; Fe 3 O 4 @SiO 2 [49]. MIPs are imprinted on the surface of magnetic parts and have usually a core-shell structure, of which the magnetic phase is the core and the polymeric phase acts as the shell [31].…”

“…The adsorption capacity of the DES-MMIPs and DES-MNIPs with a different amount of monomer were compared, and the results suggested that DES-MIPs had approximately three times higher absorption capacity than DES-MNIPs. The extraction method using DES-MMIPs for the determination of target compounds from green tea was used with carriers Fe 3 O 4 @MIPs [48] and Fe 3 O 4 @SiO 2 [49]. In the case of Fe 3 O 4 @MIPs [48], MIPs modified by binary DESs such as ChCl:ehylene glycol; ChCl:glycerol; ChCl: 1,4-butanediol, ChCl:urea, ChCl:formic acid, ChCl:acetic acid, ChCl:propionic acid were used.…”

“…The extraction method using DES-MMIPs for the determination of target compounds from green tea was used with carriers Fe 3 O 4 @MIPs [48] and Fe 3 O 4 @SiO 2 [49]. In the case of Fe 3 O 4 @MIPs [48], MIPs modified by binary DESs such as ChCl:ehylene glycol; ChCl:glycerol; ChCl: 1,4-butanediol, ChCl:urea, ChCl:formic acid, ChCl:acetic acid, ChCl:propionic acid were used. The authors of the paper [49] described magnetic polymers modified by ternary DESs, namely ChCl:oxalic acid:ethylene glycol; ChCl:oxalic acid:glycerol; ChCl:oxalic acid:propylene glycol; ChCl:caffeic acid:ethylene glycol.…”