Junping Wang

Preparation of iminodiacetic acid functionalized multi-walled carbon nanotubes and its application as sorbent for separation and preconcentration of heavy metal ions

In this paper, a novel material was prepared with functionalizing multi-walled carbon nanotubes (MWCNTs) using iminodiacetic acid (IDA) and characterized by FT-IR. Isotherm and kinetics of adsorption were studied and the experimental data fitted the Langmuir model and pseudo-second-order equation very well. An on-line method for simultaneous determination of trace V (V), Cr (VI), Pb (II), Cd (II), Co (II), Cu (II) and As (III) in biological samples was developed using this material as sorbent coupled with inductively coupled plasma mass spectrometry (ICP-MS). A series of experimental parameters, including sample pH, sample flow rate and loading time, eluting solution and the effect of interfering ions have been investigated systematically. Under the optimum experimental conditions, the enrichment factors for above metal ions were ranged from 66 to 101. Detection limit (3 s) was achieved at 1.3, 1.2, 0.70, 0.40, 2.5, 3.4, 0.79 ng L(-1), respectively. At the 1.0 μg L(-1) level, the precision (RSD, %) for 11 replicate measurements was from 1.0 to 4.0. In spiked biological samples, good recoveries (n=3) were obtained in the range of 90-110%. These results had proved that the proposed method was with good accuracy and could be applied to the analysis of trace metal ions in biological samples.

N-Methylimidazolium ionic liquid-functionalized silica as a sorbent for selective solid-phase extraction of 12 sulfonylurea herbicides in environmental water and soil samples

A novel material for solid-phase extraction (SPE) was synthesized by chemical immobilization of a functionalized N-methylimidazolium ionic liquid on silica gel. Cartridges packed with the synthetic material were successfully applied to the pre-concentration of trace-level thifensulfuron-methyl, metsulfuron-methyl, chlorsulfuron, sulfometuron-methyl, rimsulfuron, ethametsulfuron, tribenuron-methyl, bensulfuron-methyl, prosulfuron, pyrazosulfuron, chlorimuron-ethyl and primisulfuron from environmental water and soil samples. The 12 sulfonylurea herbicides (SUs) obtained a good resolution in less than 50 min using HPLC with a UV detector. The recovery studies using the ionic liquid-functionalized silica as a sorbent were performed by three consecutive extractions of water and soil samples at two spiked levels. The average recovery for each analyte was in the range of 53.8-118.2% for the water samples and 60.9-121.3% for the soil sample, with RSDs lower than 11.3% in all cases. The ionic liquid-functionalized silica cartridges showed higher selectivity for the SUs than commercially available C(18) cartridges did.

Multi‐residue determination of organophosphorus and organochlorine pesticides in environmental samples using solid‐phase extraction with cigarette filter followed by gas chromatography–mass spectrometry

A solid-phase extraction (SPE) method was developed to extract 14 pesticides simultaneously from environment samples using cigarette filter as the sorbent before gas chromatography-mass spectrometry (GC-MS) analysis. Parameters influencing the extraction efficiency, such as the sample loading flow rate, eluent and elution volume, were optimized. The optimum sample loading rate was 3 mL/min, and the retained compounds were eluted with 6 mL of eluent at 1 mL/min under vacuum. Good linearity was obtained for all the 14 pesticides (r(2) >0.99) from 0.1 to 20 μg/L for water and from 2 to 400 μg/kg for soil samples. The detection limits (signal-to-noise=3) of the proposed method ranged from 0.01 to 0.20 μg/L for water samples and from 0.42 to 6.95 μg/kg for soil samples. The developed method was successfully applied for determination of the analytes in real environmental samples, and the mean recoveries ranged from 76.4 to 103.7% for water samples and from 79.9 to 105.3% for soil samples with the precisions (relative standard deviation) between 2.0 and 13.6%.

Synthesis and characterization of a molecularly imprinted polymer and its application as SPE enrichment sorbent for determination of trace methimazole in pig samples using HPLC-UV

A novel molecularly imprinted polymer that could be applied as enrichment sorbent was prepared using methimazole (MMZ) as the template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker. Though evaluated by static, kinetic and competitive adsorption tests, the polymer exhibited high adsorption capacity, fast kinetics and good selective ability. A method for determination of trace MMZ was developed using this polymer as enrichment sorbent coupled with high performance liquid chromatography focusing on complex biological matrices. Under the optimum experimental conditions, the MMZ standard is linear within the concentration range studied, that is, from 0.5 microg L(-1) to 150 microg L(-1) (r2=0.9941). Lower limits of detection (LOD, at S/N=3) and quantification (LOQ, at S/N=10) in pig samples were 0.63 microg kg(-1) and 2.10 microg kg(-1) for kidney, 0.51 microg kg(-1) and 1.70 microg kg(-1) for liver, 0.56 microg kg(-1) and 1.86 microg kg(-1) for muscle, respectively. Recoveries and relative standard deviation (RSD, n=9) values for precision in the developed method were from 71.14% to 88.41% and from 2.53% to 6.18%.

Metal-organic frameworks supported surface-imprinted nanoparticles for the sensitive detection of metolcarb.

A novel approach to synthesize molecularly imprinted polymer (MIP) nanoparticles using a MIL-101 support (a type of metal-organic framework) is reported herein for the first time; the sample is referred as MIL@MIP. The nanoparticles were well distributed within the polymer film, and exhibit an octahedral shape, satisfied thermal stability, and a high specific surface area (SSA) of 1579.43 m(2)g(-1). The adsorption behavior of MIL@MIP toward metolcarb in aqueous solution was subsequently examined. The synthesized MIL@MIP displayed satisfactory high transfer mass rates and a high selective adsorption affinity for metolcarb. Based on these results, a quartz crystal microbalance (QCM) sensor based on MIL@MIP was subsequently constructed and examined for the sensitive detection of metolcarb. Under optimal conditions, the detection limit of the system assessed in pear juice was 0.0689 mg L(-1) within a linear concentration range of 0.1-0.9 mg L(-1). MIL@MIP-QCM system combines the advantages of MIL-101 and molecularly imprinted technology (MIT), thereby achieving high detection sensitivity and selectivity. The current findings suggest the potential of MIL@MIP for detecting trace level pesticides and veterinary drugs for food safety and environmental control.

Determination of V, Cr, Cu, As, and Pb Ions in Water and Biological Samples by Combining ICP-MS with Online Preconcentration Using Impregnated Resin.

A method was developed for detection of V, Cr, Cu, As, and Pb in water and biological samples by combining online flow injection and preconcentration with inductively coupled plasma-MS. The 2-nitroso-1-naphthol-4-sulfonic acid (Nitroso-S) impregnated MCI GEL CHP20P resin was prepared as an enrichment sorbent. Some parameters affecting the efficiency of the preconcentration process were investigated in the experiment, including the pH and volume of sample solution, the flow rate for sample loading, the type and concentration of eluent, and the influence of co-existing ions. Under the optimal experimental conditions, the enrichment factor and LOD (3s) of chosen metal ions V, Cr, Cu, As, and Pb were in the ranges of 71-268 and 4.89-23.76 ng/L, respectively. Based on 11 repeated measurements of standard solutions (1.0 μg/L), the RSD of the ions ranged from 1.2 to 2.9%. The detection procedure was also performed for analyzing two certified reference materials, GBW 08607 (water) and GBW 10052 (green tea), as well as environmental water and biological samples. Good agreement with certified values and high recoveries have demonstrated improved accuracy of the proposed method.

One-step post-imprint modification achieve dual-function of glycoprotein fluorescent sensor by "Click Chemistry"

A novel molecular imprinting fluorescent sensor synthesized avoiding complicated design and synthesis of a fluorescent functional monomer, and without the extra cost of additional fluorescence materials (quantum dots, carbon dots and fluorescein), only by a click reaction making the common protein imprinting polymers upgraded to a fluorescent sensing material which can be applied to the fast detection of glycoproteins. In this study, a common protein imprinted polymer (protein-IP) which containing a disulfide bond in the imprinted cavities was first synthesized, then the disulfide linkage was cleaved by reduction, the exposed thiol groups were used for the click reaction to introduce 4-vinyl phenylboronic acid to improve the imprinted recognition for glycoproteins and convert recognition behavior into fluorescent signal simultaneously in one-step site-specific post-imprinting modifications (PIMs). Good linear relationship was obtained in the range of 0.1-10mgmL-1 by fluorescence assay, comparison of the adsorption capacity of the MIPs before and after modification proved that the method has no negative impact on the imprinting effect and exhibit good imprinting effect for glycoproteins of different molecular size and weight.

Development of water-compatible molecularly imprinted solid-phase extraction coupled with high performance liquid chromatography–tandem mass spectrometry for the detection of six sulfonamides in animal-derived foods

A water-compatible molecularly imprinted polymer (MIP) was prepared by combining reversible addition-fragmentation chain transfer (RAFT) with reflux precipitation polymerization (RPP) for solid-phase extraction (SPE) coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to detect six sulfonamides (SAs) in animal-derived foods and water samples. The SEM images indicated the spherical structure of MIP materials. In water medium, MIPs still performed good specific adsorption for SAs. Under the optimized detection conditions, the proposed method offered good linearity (R2 > 0.996) for the six SAs with relative standard deviation (RSD) for ten replicate extractions of 1.64%-4.68%, limits of detection (S/N = 3) of 0.02 μg L-1-0.1 μg L-1 and recoveries of 63.49%-115.72%. Besides, the whole extract process avoided organic solvent consumption, and trace sulfadiazine residues were found in the pork sample at similar concentration of 3.57 and 3.79 μg kg-1 using the MIP-SPE method and commercial Oasis HLB cartridge, respectively. It is confirmed the method could be applied to quantitative detect the trace residue sulfonamides in animal-derived samples and water samples.

Development and Validation of a Reproducible and Label-Free Surface Plasmon Resonance Immunosensor for Enrofloxacin Detection in Animal-Derived Foods

This study describes the development of a reproducible and label-free surface plasmon resonance (SPR) immunosensor and its application in the detection of harmful enrofloxacin (ENRO) in animal-derived foods. The experimental parameters for the immunosensor construction and regeneration, including the pH value (4.5), concentration for coating ENRO-ovalbumin conjugate (ENRO-OVA) (100 μg·mL−1), concentration of anti-ENRO antibody (80 nM) and regeneration solution (0.1 mol·L−1 HCl) were evaluated in detail. With the optimized parameters, the proposed SPR immunosensor obtained a good linear response to ENRO with high sensitivity (IC50: 3.8 ng·mL−1) and low detection limit (IC15: 1.2 ng·mL−1). The proposed SPR immunosensor was further validated to have favorable performances for ENRO residue detection in typical animal-derived foods after a simple matrix pretreatment procedure, as well as acceptable accuracy (recovery: 84.3–96.6%), precision (relative standard deviation (n = 3): 1.8–4.6%), and sensitivity (IC15 ≤ 8.4 ng·mL−1). Each SPR chip for analysis can be reused at least 100 times with good stability and the analysis cycle containing the steps of sample uploading/chip regeneration/baseline recovery can be completed within 6 min (one cycle) and auto-operated by a predetermined program. These results demonstrated that the proposed SPR immunosensor provided an effective strategy for accurate, sensitive, and rapid detection for ENRO residue, which has great potential for routine analysis of large numbers of samples for measuring different types of compounds.

Synthesis of artificial chaperones in a novel type of Pickering emulsion for glycoprotein

Novel particles of poly(DVB-co-PBA) were synthesized by a one-step solvothermal route instead of distillation precipitation polymerization (DPP), which was simple to operate. The poly(DVB-co-PBA) showed excellent versatility in the preparation of functional materials. On the one hand, it could be applied to the preparation of a sugar fluorescent sensor due to the features of molecular recognition of cis-diol-containing compounds and fluorescence; on the other hand, it showed flexibility in the preparation of a Pickering emulsion. Further, the core–shell microspheres named W-type and W-II type were synthesized in emulsions of water-in-toluene and water-in-chloroform with stabilizers of poly(DVB-co-PBA), respectively. The core–shell microspheres named O-type were synthesized in the emulsion of oil-in-water with stabilizers poly(DVB-co-PBA)@L-Cys. The W-type polymer microspheres were used as thermally stable materials for the glycoprotein of horseradish peroxidase (HRP) to study the change of conformation and catalytic activity of HRP under heat stress through methods of UV-vis spectrophotometry, circular dichroism spectroscopy, ANS probe, chromogenic substrates, FITC fluorescence labelling, TEM and enzyme catalysis reaction. The results showed the W-type polymer microspheres with a core of hydrophilic/hydrophobic moieties reaching 2/1 could effectively maintain the natural conformation of HRP and longer catalytic activity under heat stress.