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.

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.

Electrocatalytic reduction of chloramphenicol at multiwall carbon nanotube-modified electrodes.

A multiwall carbon nanotube-modified glassy carbon (GC) electrode was employed for the investigation of chloramphenicol (CAP) reduction. Carbon nanotube coating can greatly lower the overpotential of the electrochemical reduction of CAP and promote the electrode reaction. CAP undergoes an irreversible reduction process in phosphate buffer by the modified electrode. The reduction peak current (Ip) was significantly increased. Effects of some important factors, including pH, scan rate, and amount of modifier, on the determination of CAP were investigated. In the range of 3 x 10(-7) to 1.2 x 10(-5) M, the reduction peak current (Ip) has a good linear relationship with the concentration of CAP. When the signal-to-noise ratio is 3, the detection limit is 4.5 x 10(-8) M. The relative standard deviation of 10 measurements for 3 x 10(-6) M CAP is 5.3%, suggesting an excellent reproducibility of the modified electrode. Interfering experiments show that the modified electrode has excellent selectivity for the detection of CAP. The modified electrode was used to determine CAP in eyedrops, and the recoveries were approximately 100%.

The effect of cetyltrimethyl ammonium bromide on the electrochemical determination of thyroxine.

Electrochemical behavior of thyroxine at a polyvinylpyrrolidone modified carbon paste electrode in the presence of cetyltrimethyl ammonium bromide was described. Thyroxine underwent totally irreversible oxidation at this system and a well-defined peak at 0.42 V was obtained. The influence of various surfactants on the oxidation of thyroxine was examined by cyclic voltammetry. Chronocoulometry was also used to investigate the electrode process. In the range 2 x 10(-7) to 9 x 10(-6)mol/l, the thyroxine concentration was linear with the oxidation peak current and a low detection limit of 8 x 10(-8) mol/l was obtained for 5 min accumulation.

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).