Abstract
A metal-mediated molecularly imprinted polymer (MMIP) monolithic column was prepared as the stationary phase for high-performance liquid chromatography (HPLC) and applied to the enantiomeric separation of rac-citronellal. MMIP column was prepared through in situ copolymerizations with the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate/[BMIM][BF4] as the primary pore-forming agent and cobalt(II) acetate as the metal pivot. Interactions between polymer components in the synthesized monolith were assessed by FTIR to identify the functional groups. The monolith morphology was characterized with SEM, and the template removal was detected by UV Spectrophotometry at 253 nm. In this study, (R)-(+)-citronellal was used as a template, whereas 4-vinylpyridine (4-VP) was employed as the functional monomer with two monomer crosslinkers, trimethylolpropane trimethacrylate (TRIM), and ethylene glycol dimethacrylate (EDMA). The ternary mixture of porogenic solvent consisted of [BMIM][BF4], dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) with the applied ratio of 1 : 1:1 (v/v) and 10 : 1:5 (v/v) for the preparation of MMIP using TRIM and EDMA crosslinkers, respectively. Co(II) ion was added to the porogenic solvent before being mixed with the functional monomer and the crosslinker mixtures. Separating the rac-citronellal was achieved on the synthesized MMIP, showing better selectivity than the monolithic metal-mediated nonimprinted polymer (MNIP), nonimprinted polymer (NIP), and molecularly imprinted polymer (MIP).
Highlights
Monoliths have an excellent ability to separate isomers, especially as chiral stationary phase (CSP) in high-performance liquid chromatography (HPLC). ey have porous structures with sizes between micro and macro; they may provide good pressure reduction and increase the mass transfer kinetics facilitating higher flow rates [1, 2].monolith materials could reduce the length of the diffusion path while providing flow resistance [3–5].Molecularly imprinted polymer (MIP), as one of the techniques for the synthesis of stationary phases for chromatography, is increasingly in demand for separating enantiomer compounds [6–9]. e stationary phase is prepared by a hollow polymer formation after template e Scientific World Journal removal from the polymer structure
Using metal pivot will keep the monomer in the template vicinity by preventing the free motion of functional groups involved in the reaction, by decreasing nonspecific binding sites, and by increasing selectivity towards analytes [12, 13]
Silicosteel column was pretreated in advance through silanization before it was used as the column housing for Molecularly Imprinted Polymer (MMIP), mediated nonimprinted polymer (MNIP), molecularly imprinted polymer (MIP), and nonimprinted polymer (NIP) monoliths. e silanization process was carried out by hydrolyzing the column with acid and base solutions (NaOH and hydrochloric acid (HCl))
Summary
Monoliths have an excellent ability to separate isomers, especially as chiral stationary phase (CSP) in high-performance liquid chromatography (HPLC). ey have porous structures with sizes between micro and macro; they may provide good pressure reduction and increase the mass transfer kinetics facilitating higher flow rates [1, 2]. It was found that adding a template and Co(II) for the synthesis of the stationary phase leads to a longer retention time when methyl gallate is eluted Based on these results, Co(II) is deemed as the crucial factor in the separation process. DMF and DMSO dissolve the metal pivot and regulate template retention in MMIP and MIP. We apply similar monomers, porogen, and metal pivot, the MMIP polymerization in this study was carried out in situ inside a 1.0 mm i.d. microbore silicosteel column with the template of (R)-(+)-citronellal, which is smaller than those employed by Bai et al, 4.6 mm i.d. with the template of mandelic acid [10], and Bodoki et al, 2.1 mm i.d. with the template of atenolol [12]. Larger diameter monolithic columns are less homogeneous, due to differential heating across the tube diameter and because of the rising gravitational settling effect during the exothermic polymerization process [1, 24]
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