Fe3 O4 nanoparticles coated with polyhedral oligomeric silsesquioxanes and ß-cyclodextrin for magnetic solid-phase extraction of carbaryl and carbofuran.

In this study, porous sandwich structure Fe3 O4 nanoparticles coated by polyhedral oligomeric silsesquioxanes and ß-cyclodextrin were prepared by surface polymerization and were used as the magnetic solid phase extraction adsorbent for the extraction and determination of carbaryl and carbofuran. The Fe3 O4 nanoparticles coated with polyhedral oligomeric silsesquioxanes and ß-cyclodextrin were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, and scanning electron microscopy. After optimizing the extraction conditions, a method that combined magnetic solid phase extraction with high-performance liquid chromatography was developed for the determination of carbaryl and carbofuran in apple. The method exhibited a good linearity in the range of 2-400 µg/kg for carbaryl and carbofuran (R2  = 0.9995), respectively. The limits of detection were 0.5 µg/kg of carbaryl and 0.7 µg/kg for carbofuran in apple, respectively. Extraction recoveries ranged from 94.2 to 103.1% with the preconcentration factor of 300 and the relative standard deviations were less than 5.9%. These results indicated that the method combined magnetic solid phase extraction with high-performance liquid chromatography and was promising for the determination of carbaryl and carbofuran at trace amounts.

A molecularly imprinted organic-inorganic hybrid monolithic column for the selective extraction and HPLC determination of isoprocarb residues in rice.

An IPC-imprinted (IPC is isoprocarb) poly(methacrylic acid)/SiO2 hybrid monolithic column was prepared and applied for the recognition of the template. The hybrid monolithic column was synthesized in a micropipette tip using methyltrimethoxysilane as the inorganic precursor, 3-(methacryloxy)propyltrimethoxysilane as the coupling agent, and ethylene glycol dimethacrylate as the cross-linker. The synthesis conditions, including the porogenic solvent, coupling agent, volume ratio of the inorganic alcoholysate and organic part, were optimized. The prepared monolithic column was characterized by SEM and FTIR spectroscopy. A simple, rapid, and sensitive method for the determination of IPC in rice using the imprinted monolithic column microextraction combined with HPLC was developed. Several parameters affecting the sample pretreatment were investigated, including the eluent, washing solution, and loading sample volume. The linearity of the calibration curve was observed in the range of 9.0-1000 µg/kg for IPC in rice with the correlation coefficient (r2) of 0.9983. The LOD was 3.0 µg/kg (S/N = 3). The assay gave recovery values ranging from 91 to 107%. The proposed method has been successfully applied for the selective extraction and sensitive determination of IPC in rice and a satisfactory result was obtained.

A novel ratiometric electrochemical sensing platform combined with molecularly imprinted polymer and Fe-MOF-NH2/CNTs-NH2/MXene composite for efficient detection of ofloxacin.

BACKGROUND: Ofloxacin (OFL) is often abused in medicine and animal husbandry, which poses a great threat to human health and ecological environment. Therefore, it is necessary to establish efficient method to detect OFL. Electrochemical sensor has attracted widespread attention due to the advantages of low cost and fast response. However, most electrochemical sensors usually use one response signal to detect the target, which makes it sensitive to the variable background noise in the complex environment, resulting in low robustness and selectivity. The ratio detection mode and employing molecularly imprinted polymer (MIP) are two strategies to solve these problems. RESULTS: A novel molecular imprinting polymer-ratiometric electrochemical sensor (MIP-RECS) based on Fe-MOF-NH2/CNTs-NH2/MXene composite was prepared for the rapid and sensitive detection of OFL. The positively charged Fe-MOF-NH2 and CNTs-NH2 as interlayer spacers were introduced into the negatively charged MXene through a simple electrostatic self-assembly technique, which effectively prevented the agglomeration of MXene and increased the electrocatalytic activity. A glass carbon electrode was modified by the composite and a MIP film was electropolymerized on it using o-phenylenediamine and ß-cyclodextrin as bifunctional monomers and OFL as template. Then a MIP-RECS was designed by adding dopamine (DA) into the electrolyte solution as internal reference, and OFL was quantified by the response current ratio of OFL to DA. The current ratio and the concentration of OFL displayed a satisfying linear relationship in the range of 0.1 µM-100 µM, with a limit of detection (LOD) of 13.2 nM. SIGNIFICANCE: Combining molecular imprinting strategy and ratio strategy, the MIP-RECS has impressive selectivity compared with the non-imprinted polymer-RECS, and has better repeatability and reproducibility than non-ratiometric sensor. The MIP-RECS has high sensitivity and accuracy, which was applied for the detection of OFL in four different brands of milk and was verified by HPLC method with satisfactory results.

Fabrication and application of Zn5 functionalized copolymer monolithic column for pipette tip micro-solid phase extraction of 4 polycyclic aromatic hydrocarbons in edible oil.

The contamination of polycyclic aromatic hydrocarbons (PAHs) in edible oil is a health threat. Thus, trace analysis of PAHs is of high necessity. Based on the efficient adsorption of PAHs on Zn5 metal cluster, a Zn5 functionalized copolymer monolithic column was rationally designed for pipette tip micro-solid phase extraction (µ-SPE). The modified Zn5 improved the adsorption selectivity and capacity of the monolith for naphthalene, phenanthrene, fluoranthene and pyrene. Chemical doping and copolymerization stabilized the monolith with a long life. Under optimal extraction conditions, a µ-SPE-high performance liquid chromatography with ultraviolet detector method was established for the detection of 4 PAHs in edible oils. The method yielded detection ranges of 0.15-250 µg L-1 (R2 > 0.997), detection limits of 0.050-1.5 µg L-1, satisfactory recoveries (86.3-101.5 %), and high precisions (RSDs < 7.9 %). The results indicated that the Zn5 functionalized copolymer monolithic column was an ideal separation medium for the detection of PAHs residues in edible oils.

Selective determination of trace thiamphenicol in milk and honey by molecularly imprinted polymer monolith microextraction and high-performance liquid chromatography.

A novel solid-phase microextraction (SPME) method based on molecularly imprinted polymer (MIP) monolith as the sorbent for the selective extraction of thiamphenicol (TAP) in milk and honey was developed. The newly developed MIP monolith was produced using TAP as the template molecule, 4-vinylpyridine (4-VP) as the functional monomer. The TAP-MIP monolith synthesized in a micropipette tip could be connected with syringes in different sizes simply to perform SPME process without any other treatment. The derivated MIP monolith showed high selectivity and enrichment ability for TAP. A simple, rapid and sensitive method for the determination of TAP in milk and honey using polymer monolith microextraction (PMME) based on the MIP monolith combined with high-performance liquid chromatography-photodiodes array detector was developed. Several parameters affecting MIP monolith microextraction were investigated, including the flow rate, volume, pH and salt concentration of sample, the type and volume of washing solution, the type and flow rate of eluent. The recovery of this method for TAP was investigated and high recoveries of 92.9-99.3% from milk and honey were obtained with relative standard deviations less than 4.9%.

Preparation and application of a nanocomposite of dopamine modified zirconium metal organic framework and polythiophene for solid-phase microextraction/gas chromatography of phenols released from polycarbonate materials.

The zirconium metal-organic framework (MOF) UiO-66 was modified by dopamine (DA) and electrodeposited with Poly (3,4-ethylenedioxothiophene) (PEDOT) on an etched stainless steel wire to prepare a UiO-66-DA/PEDOT nanocomposite coating. The coating was characterized by scanning electron microscopy, energy dispersive spectrometer, Fourier transform infrared and thermogravimetric analysis, respectively. The coating has high specific surface area and more porous structure, which can be used to extract eight phenols, including 2-chlorophenol, o-cresol, m-cresol, 2, 4-dichlorophenol, 4-tert-butylphenol, 4-chlorophenol, 4-tert-octylphenol and α-naphthol. The adsorption behavior of the phenols on the UiO-66-DA/PEDOT coating had significant correlation with Langmuir isothermal model. A determination method for the eight phenols was established by combining with direct immersion solid-phase micro extraction and gas chromatography. Under the optimal experimental conditions, the detection linear range (LRs) was 0.05-50 µg mL-1 and the detection limit (LODs) was 0.01-0.08 µg mL-1 (S/N = 3). The method was applied for the migration detection of eight phenols in polycarbonate cups, which showed satisfactory recovery.

Simultaneous detection of eight phenols in food contact materials after electrochemical assistance solid-phase microextraction based on amino functionalized carbon nanotube/polypyrrole composite.

An electrochemical assistance solid-phase microextraction (EA-SPME) was developed based on amino functionalized multi-walled carbon nanotube/polypyrrole (MWCNTs-NH2/PPy) composite coating. It was applied for the extraction of eight phenols in food contact material, including 2-chlorophenol, o-cresol, m-cresol, 2,4-dichlorophenol, 4-tert-butylphenol, 4-chlorophenol, 4-tertoctylphenol and alpha-naphthol. MWCNTs-NH2/PPy coating was characterized by scanning electron microscopy, transmission electron microscope, X-ray energy spectrometer, X-ray diffraction, Fourier transform infrared and thermogravimetric analysis. The adsorption mechanism of phenols on the composite coatings was investigated. The coating modified steel-wire as an extraction fiber has good electroconductibility, reproducibility and long service life. A determination method for the eight phenols was established by EA-SPME coupled with gas chromatography-flame ionization detection. Under the optimal experimental conditions (extraction temperature: 40 °C; extraction time: 30 min; stirring rate: 600 rpm; NaCl concentration: 0.15 g mL-1; desorption temperature: 250 °C and desorption time: 4 min), the detection linear range was 0.005-50 µg L-1 (R2>0.99), and the detection limit was 0.001-0.1 µg L-1 (S/N = 3). For the quintuple analysis of 50 µg L-1 phenols, the single fiber RSDs were 2.2-12.4%, and the fiber-to-fiber RSDs were 1.9-10.5%. The method was used to detect the migration quantity of the eight phenols from five canned packaging materials, which showed satisfactory recovery 87.3-118.9%.

A polythiophene/UiO-66 composite coating for extraction of volatile organic compounds migrated from ion-exchange resins prior to their determination by gas chromatography.

A Poly (3,4-ethylenedioxothiophene) (PEDOT)/UiO-66 composite was electrodeposited on an etched stainless-steel wire as head-space solid-phase microextraction (HS-SPME) coating. A robust, well controlled thickness, and uniform coating of metal organic framework composites can be realized by the electrodeposited strategy. The incorporated UiO-66 not only enhanced the uniformity and stability of the composite coating, but also effectively decreased the stacking phenomenon of PEDOT and improved its extraction efficiency, which was over 100 times higher than that of the PEDOT coating without UiO-66. The composite coating was used to enrich seven types of volatile organic compounds (VOCs) in ion-exchange resins, including methyl cyclohexane, benzene, toluene, ortho-xylene, styrene, para-xylene and divinyl-benzene. The results of adsorption isotherm analysis showed that π stacking effect played dominant role between the composite coating and VOCs in the extraction process. The composite coating was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared and thermogravimetric analysis, respectively. A determination method for seven kinds of VOCs was established by HS-SPME coupled with gas chromatography-flame ionization detection (GC-FID). Under the optimal experimental conditions, the detection linear range (LRs) was 0.09-100 ng mL-1, and the detection limit (LODs) was 0.03-0.06 ng mL-1 (S/N = 3). The method was applied for the migration detection of VOCs in four types of ion-exchange resin, which showed satisfactory recovery (84.5-117.2%).

A Selective Joint Determination of Salicylic Acid in Actinidia chinensis Combining a Molecularly Imprinted Monolithic Column and a Graphene Oxide Modified Electrode.

A new combination between selective polymer monolith microextraction (PMME) and sensitive differential pulse voltammetry (DPV) was developed for the determination of the phytohormone salicylic acid (SA) in Actinidia chinensis. A molecularly imprinted monolithic column (MIMC) thermally in-situ polymerized in a micropipette tip by using SA as a template, 4-vinyl pyridine (4-VP) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the mixed porogen of toluene and dodecanol, was employed for the microextraction of SA. The prepared MIMC was characterized by a Fourier transform infrared spectrometer (FI-TR), scanning electron microscope (SEM) and thermo gravimetric analysis (TGA). The results confirmed the binary continuous structure of the porous network. The extracted SA was determined by DPV on a graphene oxide (GO) modified electrode. The joint conditions between MIMC and DPV were investigated practically. Under the optimum conditions, SA could be determined selectively and sensitively in a linear range from 0.1 to 60.0 µg g-1. The limit of detection was 0.03 µg g-1 and the recoveries were between 86.2 and 105.2%. The proposed joint method was successfully used to determine SA in Actinidia chinensis.

Preparation and application of a novel electrochemical sensing material based on surface chemistry of polyhydroquinone.

A new analogue of polydopamine (PDA), i.e., polyhydroquinone (PH2Q), was polymerized and its surface chemistry was studied by different ways of characterization. PH2Q was produced by the self-polymerization of H2Q mediated by dissolved oxygen, and the self-polymerization process was strongly dependent on the type and the pH value of the buffer solutions. PH2Q can not only achieve surface hydrophilization of different substrates like polyethylene terephthalate (PET) film, graphite strip, C12SH/Au and wax slice, but also possess several unique properties like reversible adsorption, good solubility and low cost. These properties made PH2Q an ideal polymeric modifier for the noncovalent functionalization of some nanomaterials. By simply grinding with PH2Q, pristine multi-walled carbon nanotubes (MWNTs) can be readily dispersed in water with high solubility and good stability. The resulting MWNT-PH2Q composite exhibited excellent electrochemical performance, which was employed for the simultaneous determination of dopamine (DA) and uric acid (UA).

Preparation, characterization and application of organic-inorganic hybrid caffeine imprinted monolith.

The present work aims to synthesize an organic-inorganic hybrid caffeine imprinted monolith using one-step method. The synthesis conditions such as the type of inorganic precursor and porogenic solvent, the molar ratios of the monomer and cross-linker, the volume ratio of the inorganic alcoholysate and organic part were optimized. The morphology of the monolith was studied by scanning electron microscopy and Fourier transform infrared spectra. The imprinted factor of the monolith for caffeine reached 3.02. A simple, rapid and sensitive method for the determination of caffeine in children's milk using the organic-inorganic hybrid caffeine imprinted polymer monolith microextraction combined with high-performance liquid chromatography-photodiodes array detector was developed. Several parameters affecting the sample pretreatment were investigated, including the type, flow rate and volume of eluent, the flow rate and volume of sample solution. The assay exhibited a linear dynamic range of 8-500µgL(-1) with the correlation coefficient above 0.9987. Lower limits of detection (LOD, at S/N=3) and quantification (LOQ, at S/N=10) in children's milk samples were 2.7 and 8µgL(-1). Recoveries of caffeine from spiked children's milk ranged from 85 to 104% with relative standard deviations of less than 8.9%.

Preparation, evaluation and application of molecularly imprinted solid-phase microextraction monolith for selective extraction of pirimicarb in tomato and pear.

A simple, rapid and sensitive method for the determination of pirimicarb in tomato and pear using polymer monolith microextraction (PMME) based on the molecularly imprinted polymer (MIP) monolith combined with high-performance liquid chromatography-photodiodes array detector (HPLC-PAD) was developed. By optimizing the polymerization conditions, such as the nature of porogenic solvent and functional monomer, the molar ratio of the monomer and cross-linker, an pirimicarb MIP monolith was synthesized in a micropipette tip using methacrylic acid (MAA) as the functional monomer, ethylene dimethacrylate (EGDMA) as the cross-linker and the mixture of toluene-dodecanol as the porogenic solvent. The MIP monolith showed highly specific recognition for the template pirimicarb. The monolith was applied for the selective extraction of pirimicarb in tomato and pear. Several parameters affecting MIP-PMME were investigated, including the nature and volume of extraction solvent, sample volume, flow rate and sample pH. Under the optimum PMME and HPLC conditions, the linear ranges were 2.0-1400 µg/kg for pirimicarb in tomato and pear with the correlation coefficient of above 0.999. The detection limits (s/n=3) were both 0.6 µg/kg. The proposed method was successfully applied for the selective extraction and determination of pirimicarb in tomato and pear.