Hongyuan Yan

Imidazolium embedded C8 based stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new imidazolium embedded C8 based stationary phase (SIL-MPS-VOL) was facilely prepared by two steps and characterized by Fourier transform infrared spectrometry and thermogravimetric analysis. Due to the introduction of quaternary imidazolium group to the traditional C8 stationary phase, the developed SIL-MPS-VOL column demonstrated both reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention mechanisms. A series of hydrophobic and hydrophilic test samples, including benzene homologues, anilines, positional isomers, nucleosides and nucleotides, were used to evaluate the developed SIL-MPS-VOL stationary phase. A rapid separation time, high separation efficiency and planar selectivity were achieved, compared with the commercially available C8 column. Moreover, the developed stationary phase was further used to detect and separate of melamine in powdered infant formula and high polar component of secondary metabolites of Trichoderma, and improved separation efficiency was achieved, indicating the potential merits of the developed SIL-MPS-VOL stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.

Hydrophilic Molecularly Imprinted Resorcinol–Formaldehyde–Melamine Resin Prepared in Water with Excellent Molecular Recognition in Aqueous Matrices

Hydrophilic molecularly imprinted resorcinol-formaldehyde-melamine resin (MIRFM) is synthesized in water and shows excellent molecular recognition in aqueous matrices. The double functional monomers resorcinol and melamine, and the cross-linker formaldehyde, are all hydrophilic, and then the hydrophilic groups (such as hydroxyls, imino groups, and ether linkages) can be introduced into MIRFM, which make the material compatible with aqueous samples. The general principle is demonstrated by the synthesis of MIRFM using sulfanilamide as a dummy template for the selective recognition to sulfonamides (SAs) in milk samples. Resorcinol and melamine can interact with the template mainly by hydrogen bonding and π-π interaction, which makes MIRFM and the analytes have strong affinity. Besides, melamine can improve the rigidity of MIRFM and accelerate the polymerization process, so there is no need to add base or acid as a catalyst, which guarantees the success of molecular imprinting. MIRFM shows higher recovery and improved purification effect for SAs, in comparison to silica, HLB, C18, and SCX. Because of its excellent hydrophilicity and specificity, MIRFM is promising to be applied in biological, environmental, and clinical fields.

Novel imidazolium-embedded N,N-dimethylaminopropyl-functionalized silica-based stationary phase for hydrophilic interaction/reversed-phase mixed-mode chromatography

AbstractA novel imidazolium-embedded N,N-dimethylaminopropyl-functionalized silica-based stationary phase (Sil-ImCl) was prepared and further used for hydrophilic interaction/reversed-phase mixed-mode chromatography. The Sil-ImCl stationary phase was respectively characterized by Fourier transform infrared spectrometry, thermogravimetric analysis, and element analysis. A variety of hydrophilic or hydrophobic compounds were used to evaluate the retention mechanisms of the developed stationary phase, and the effects of buffer salt concentration and pH of mobile phase on the retention of these compounds were also investigated. The developed stationary phase was successfully applied for separation of nucleosides and nucleic acid bases, water-soluble vitamins, phenols, and positional isomers. Moreover, simultaneous separation of polar and nonpolar compounds was also achieved with high resolution, outperforming the commercially available C8 column and amino column. Furthermore, the Sil-ImCl stationary phase has been successfully applied for separation of secondary metabolites of Hansfordia sinuosae. All these results demonstrate that the Sil-ImCl stationary phase might be promising for separation of complex polar and nonpolar compounds with high efficiency, especially in biological industry. Graphical AbstractNovel imidazolium-embedded N,N-dimethylaminopropyl-functionalized silica-based stationary phase for HILIC/RPLC mixed-mode chromatography

Hydrophilic molecularly imprinted melamine-urea-formaldehyde monolithic resin prepared in water for selective recognition of plant growth regulators

New hydrophilic molecularly imprinted melamine-urea-formaldehyde monolithic resin (MIMR) is synthesized using dopamine hydrochloride as a dummy template via in-situ polymerization directly within pipette tips and it presents special molecular recognition to plant growth regulators in aqueous matrices. Hydrophilic groups (such as hydroxyl groups, imino groups, and amino groups) can be introduced into MIMR by melamine- urea-formaldehyde resin, which make MIMR materials compatible with aqueous media and show their specific molecular recognition in aqueous sample solutions. Meanwhile, monolithic structures avoid the influence of uneven filling on the extraction efficiency. Various parameters affecting the selective recognition of MIMR have been optimized, such as molar ratio of melamine to urea, molar ratio of melamine and urea to formaldehyde, the amount of template and porogen. The prepared MIMR is applied as the sorbents of solid phase extraction (SPE) for sensitive and selective recognition of three plant growth regulators (p-chlorophenoxyacetic acid, 1-naphthaleneacetic acid and 2.4-dichlorophenoxyacetic acid) in bean sprouts. Considering its excellent hydrophilicity and specificity, MIMR-SPE is promising to be a potential pretreatment strategy in biological, environmental, and clinical fields.

Water-compatible dummy molecularly imprinted resin prepared in aqueous solution for green miniaturized solid-phase extraction of plant growth regulators.

A water-compatible dummy molecularly imprinted resin (MIR) was synthesized in water using melamine, urea, and formaldehyde as hydrophilic monomers of co-polycondensation. A triblock copolymer (PEO-PPO-PEO, P123) was used as porogen to dredge the network structure of MIR, and N-(1-naphthyl) ethylenediamine dihydrochloride, which has similar shape and size to the target analytes, was the dummy template of molecular imprinting. The obtained MIR was used as the adsorbent in a green miniaturized solid-phase extraction (MIR⬜mini-SPE) of plant growth regulators, and there was no organic solvent used in the entire MIR⬜mini-SPE procedure. The calibration linearity of MIR⬜mini-SPE⬜HPLC method was obtained in a range 5⬜250ngmL(↙1) for IAA, IPA, IBA, and NAA with correlation coefficient (r) Ⱕ0.9998. Recoveries at three spike levels are in the range of 87.6⬜100.0% for coconut juice with relative standard deviations Ⱔ8.1%. The MIR⬜mini-SPE method possesses the advantages of environmental friendliness, simple operation, and high efficiency, so it is potential to apply the green pretreatment strategy to extraction of trace analytes in aqueous samples.

Imidazolium-based iodoacetamide functional tags: design, synthesis, and property study for cysteinyl-peptide analysis by mass spectrometry

New types of imidazolium-based iodoacetamide tags were designed, synthesized and further exploited for cysteinyl-peptide analysis with superior labeling efficiency, high stability, improved ionization efficiency, and increased charge states by mass spectrometry. For the first time, the effects of these kinds of tags on the mass spectrometry performance of the derivatized peptides were investigated, which is of great importance to help us design more efficient tags for the analysis of peptides or proteins, especially for those with low abundance.

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

In this work, choline chloride (ChCl) 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 ChCl 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 ChCl-FA (1:1, mole ratio). For the purification step of the pretreatment, eight ChCl DES-modified adsorbents were prepared by hydrothermal polymerization and packed into solid-phase extraction (SPE) cartridges, and ChCl-Urea, ChCl-Gly, ChCl-FA, and water, were used as eluents. The ChCl 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 chromatograph-ultraviolet detection. The highest purification efficiency was obtained using the ChCl-Ph DES-modified adsorbent as the SPE packing material and ChCl-Urea-H2O (1:1:5, mole ratio), ChCl-Gly (1:1, mole ratio), ChCl-FA-H2O (1:1:5, mole ratio), and H2O as the eluents. Compared to conventional purification processes that employ commercial C18 or C8 SPE columns with organic solvents as eluents, the ChCl 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.

Ionic Liquid–Hybrid Molecularly Imprinted Material–Filter Solid-Phase Extraction Coupled with HPLC for Determination of 6-Benzyladenine and 4-Chlorophenoxyacetic Acid in Bean Sprouts

A new method involving ionic liquid-hybrid molecularly imprinted material-filter solid-phase extraction coupled to high-performance liquid chromatography (IL-HIM-FSPE-HPLC) was developed for the simultaneous isolation and determination of 6-benzyladenine (6-BA) and 4-chlorophenoxyacetic acid (4-CPA) in bean sprouts. Sample preconcentration was performed using a modified filter, with the new IL-HIM as the adsorbent, which shows double adsorption. The first adsorption involves special recognition of molecular imprinting, and the second involves ion exchange and electrostatic attraction caused by the ionic liquid. This method combines the advantages of ionic liquids, hybrid materials, and molecularly imprinted polymers and was successfully applied to determine 6-BA and 4-CPA in bean sprouts. The adsorption of 6-BA to IL-HIM is based on selective imprinted recognition, whereas the adsorption of 4-CPA is mainly dependent on ion-exchange interactions.

Development of a novel imidazolium-based aromatic quaternary ammonium tag: synthesis and application to the efficient analysis of cysteinyl-peptides by mass spectrometry.

RATIONALE Chemical derivatization is a very promising technique for improving analysis of peptides by mass spectrometry (MS). In this study, a novel kind of imidazolium-based aromatic quaternary ammonium tag, 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-3-butylimidazolium bromide (IPBI), designed with strong gas-phase basicity and a permanent positive charge, was firstly synthesized and further used for derivatization of cysteinyl-peptides with improved ionization efficiency and higher charge states. METHODS Both the model peptides and tryptic digests of proteins were used to evaluate the effect of IPBI derivatization on the MS performance of the derivatized peptides, and the results were further compared with the commonly used iodoacetamide (IAA) tag. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-MS and electrospray ionization (ESI)-MS were used to evaluate the ionization efficiency and charge states of the derivatized peptides. RESULTS With model peptides as samples, a nearly 100% derivatization efficiency and superior stability were achieved via IPBI derivatization. By further analysis of both standard peptides and tryptic protein digests, the ionization efficiency and charge states of IPBI-derivatized peptides could be remarkably improved. For example, for protein bovine serum albumin, compared with the commercial available IAA tag, the identification efficiency of cysteinyl-peptides was increased about 67% by combining with IPBI derivatization. CONCLUSIONS The results indicated that the novel tag is an effective derivatization reagent for cysteinyl-peptide identification. We hope it could be further used for high-efficiency cysteinyl-peptide identification in proteome research, especially those with low abundance and poor ionization efficiency.

One-pot synthesis of ethylenediamine-connected graphene/carbon nanotube composite material for isolation of clenbuterol from pork

A fluffy porous ethylenediamine-connected graphene/carbon nanotube composite (EGC), prepared by a simple and time-saving one-pot synthesis, was successfully applied as an adsorbent in pipette-tip solid-phase extraction (PT-SPE) for the rapid extraction and determination of clenbuterol (CLB) from pork. In the one-pot synthesis, carbon nanotubes were inserted into graphene sheets and then connected with ethylenediamine through chemical modification to form a three-dimensional framework structure to prevent agglomeration of the graphene sheets. Under the optimum conditions for extraction and determination, good linearity was achieved for CLB in the range of 15.0-1000.0ngg-1 (r=0.9998) and the recoveries at three spiked levels were in the range of 92.2-96.2% with relative standard deviation ≤9.2% (n=3). In comparison with other adsorbents, including silica, NH2, C18, and Al2O3, EGC showed higher extraction and purification efficiency for CLB from pork samples. This analytical method combines excellent adsorption performance of EGC and high extraction efficiency of PT-SPE.