Yunkai Lv

Application of accelerated solvent extraction in the analysis of organic contaminants, bioactive and nutritional compounds in food and feed

Accelerated solvent extraction (ASE) has become a popular green extraction technology for different classes of organic contaminants present in numerous kinds of food and feed for food safety. The parameters affecting ASE efficiency and application advancement of ASE in the analysis of organic contaminants, natural toxins compounds as well as bioactive and nutritional compounds in animal origin food, plant origin food and animal feed are reviewed in detail. ASE is a fully automated and reliable extraction technique with many advantages over traditional extraction techniques, so it could be especially useful for routine analyses of pollutants in food and feed.

Synthesis and application of molecularly imprinted poly(methacrylic acid)-silica hybrid composite material for selective solid-phase extraction and high-performance liquid chromatography determination of oxytetracycline residues in milk.

A novel molecularly imprinted organic-inorganic hybrid composite material (MIP-HCM) was developed based on molecular imprinting technique in combination with hybrid composite synthesis and sol-gel technology for selective solid-phase extraction (SPE) of tetracyclines residues in milk. The MIP-HCM was prepared using oxytetracycline as the template, methacrylic acid as organic functional monomer, tetraethoxysilane as inorganic precursor and methacryloxypropyltrimethoxysilane as the coupling agent. Synthesis conditions are optimized by changing some factors to obtain sorbent with the controllable adsorption capacity, selectivity, hardness and toughness. Binding study demonstrated that the imprinted hybrid composites showed excellent affinity and high selectivity to oxytetracycline. An enrichment factor of 18.8 along with a good sample clean-up was obtained under the optimized SPE conditions. The average recoveries of three tetracyclines antibiotics spiked milk at 0.1, 0.2 and 0.5 mg kg⁻¹ were in the range of 80.9-104.3% with the precision of 1.5-5.0%. The limits of detection and quantitation of the proposed method were in a range of 4.8-12.7 μg kg⁻¹ and 16.0-42.3 μg kg⁻¹, respectively.

Ultrasound-assisted dispersive liquid–liquid microextraction coupled with capillary gas chromatography for simultaneous analysis of nine pyrethroids in domestic wastewaters

A simple and rapid ultrasound-assisted dispersive liquid-liquid microextraction method coupled with GC-flame ionization detection was developed for simultaneous determination of nine pyrethroids in domestic wastewater samples. An ultrasound-assisted process was applied to accelerate the formation of the fine cloudy solution using small volume of disperser solvent, which markedly increased the extraction efficiency and reduced the equilibrium time. Various parameters affecting the extraction efficiency were investigated, including the type and volume of extraction solvent and disperser solvent, extraction and ultrasonic time. Good linearity was obtained for all analytes in the range of 0.8-100 microg/L with the correlation coefficient (r(2)) > or = 0.998. The recoveries at three spiking levels ranged from 75.3 to 101.2% with the RSD less than 8.7% (n=5). Under the optimum condition, the enrichment factors for the nine pyrethroids ranged from 728- to 1725-fold. This method offered a good alternative for routine analysis due to its simplicity and reliability.

Interaction of Avelox with Bovine Serum Albumin and Effect of the Coexistent Drugs on the Reaction

The interaction between Avelox and bovine serum albumin (BSA) was investigated at different temperatures by fluorescence spectroscopy. Results showed that Avelox could quench the intrinsic fluorescence of BSA strongly, and the quenching mechanism was a static quenching process with Förester spectroscopy energy transfer. The electrostatic force played an important role on the conjugation reaction between BSA and Avelox. The order of magnitude of binding constants (K a) was 104, and the number of binding site (n) in the binary system was approximately equal to 1. The binding distance (r) was less than 3 nm and the primary binding site for Avelox was located in subdomain IIA of BSA. Synchronous fluorescence spectra clearly revealed that the microenvironment of amino acid residues and the conformation of BSA were changed during the binding reaction. In addition, the effect of some antibiotics on the binding constant of Avelox with BSA was also studied.

Determination of ofloxacin and lomefloxacin in chicken muscle using molecularly imprinted solid-phase extraction coupled with liquid chromatography.

A new molecularly imprinted solid-phase extraction (MISPE) procedure combined with liquid chromatography was developed for the simultaneous selective extraction and determination of ofloxacin (OFL) and lomefloxacin (LOM) in chicken muscle samples. The water-compatible molecularly imprinted microspheres (MIMs) were synthesized by aqueous suspension polymerization using 2-hydroxy-3-naphthoic acid and 1-methylpiperazine as mimic templates. The MIMs applied as selective sorbents in SPE method showed high selectivity and affinity to OFL and LOM in complex biological matrices. Good linearity was obtained in a range of 0.025-2.0 μg/g, and the average recoveries of OFL and LOM at three spiked levels ranged from 94.4 to 96.9%, respectively, with the relative standard deviation ≤4.7%. The developed MISPE-HPLC method was successfully applied to the isolation of OFL and LOM in chicken muscles, which demonstrated the potential ability of the novel MIMs for selective extraction of fluoroquinolones in biological samples.

Layer-by-layer fabrication of restricted access media-molecularly imprinted magnetic microspheres for magnetic dispersion microextraction of bisphenol A from milk samples

A novel restricted access media-molecularly imprinted magnetic microsphere (RAM-MIMM) was prepared through layer by layer modification. The magnetic nanoparticles were coated with silica gel, modified with the amino group, coated by BPA-imprinted sol–gel film and grafted with the epoxy silane coupling agent. The RAM-MIMMs were characterized by SEM, TEM, FT-IR and adsorption experiments. The RAM-MIMMs were prepared with the average diameters of around 300 nm and the coating thickness in the range of 10–15 nm, and exhibited high selectivity (2.54) of the imprinted cavities and hydrophilicity of the external surface with water compatibility and exclusion biomacromolecules. The RAM-MIMMs were used for magnetic dispersion microextraction of BPA from milk samples. The average recoveries were obtained in the range of 85.2–98.6% with a precision of 2.2–4.6%. The limits of detection and quantitation of the proposed method were in the range of 4.70–10.51 μg kg−1 and 15.65–35.02 μg kg−1, respectively.

Adsorption-controlled preparation of molecularly imprinted hybrid composites for selective extraction of tetracycline residues from honey and milk

Molecularly imprinted organic–inorganic hybrid composite materials (MIP-HCMs) with controlled swelling and adsorption properties were prepared through copolymerization and the sol–gel process by using doxycycline (DC) as the template molecule, methacrylic acid (MAA) as a functional monomer, methacryloxypropyltrimethoxysilane (KH-570) as a coupling agent and TEOS as an inorganic precursor. By means of changing polymerization conditions as well as the copolymerization ratio of the inorganic precursor and the organic functional monomer, the properties of sorbents can be adjusted for different needs. So the effect of preparation conditions on the structure of the material was studied. The polymer group, thermal stability, adsorption and selectivity characteristics, and the volume swelling degree of the MIP-HCMs were characterized by FTIR, TGA, and dynamic adsorption and swelling experiments, respectively. It was observed that the MIP-HCMs exhibited the highest selectivity (4.9), maximum adsorption capacity (58.2 mg g−1) and good thermal stability. The obtained MIP-HCM was used as an adsorbent for solid-phase extraction of tetracyclines from the milk and honey samples. The average recoveries of three tetracycline antibiotics (DC, tetracycline and chlortetracycline) were obtained in the range of 74.7–115.5% with the precision of 2.1–4.9%. The limits of detection and quantitation of the proposed method were in the range of 4.9–15.3 μg kg−1 and 16.6–51.0 μg kg−1 for the milk samples, and 8.3–15.1 μg kg−1 and 18.3–50.2 μg kg−1 for the honey samples, respectively.

Preparation and evaluation of a novel molecularly imprinted hybrid composite monolithic column for on-line solid-phase extraction coupled with HPLC to detect trace fluoroquinolone residues in milk

A novel molecularly imprinted organic–inorganic hybrid composite monolithic column (MIP-HCMC) was prepared in a stainless-steel chromatographic column for the determination of fluoroquinolone residues in milk by on-line solid-phase extraction coupled with HPLC. The MIP-HCMC was prepared using enrofloxacin as the template, methacrylic acid and 2-hydroxyethyl methacrylate as functional monomers, tetraethoxysilane as inorganic precursor and methacryloxypropyltrimethoxysilane as coupling agent, toluene and polyethylene glycol as porogenic solvents, and ethylene glycol dimethacrylate as the cross-linking agent. The synthetic conditions were optimized. The chemical group, morphology, thermal stability, dynamic adsorption characteristic and swelling of the monolithic column were characterized by IR, SEM, TG, dynamic binding tests and swelling tests, respectively. An enrichment factor (EF) of 18.5 along with a good sample clean-up effect was obtained under the optimized conditions when the method was applied to milk sample analysis only after centrifugation. The average recoveries of four fluoroquinolones from milk spiked at 0.05, 0.1 and 0.25 mg kg−1 were in the range of 89.1–99.2% with the precision of 3.55–4.32%. The limits of detection and quantification of the proposed method were 1.69 and 5.63 μg kg−1 for ofloxacin, 1.63 and 5.43 μg kg−1 for lomefloxacin, 3.74 and 12.5 μg kg−1 for ciprofloxacin, 1.37 and 4.56 μg kg−1 for enrofloxacin, respectively. The proposed method was successfully applied to on-line extraction and determination of fluoroquinolone antibiotics in milk.

Determination of Tetracyclines Residues in Egg, Milk, and Milk Powder by Online Coupling of A Precolumn Packed with Molecular Imprinted Hybrid Composite Materials to RP-HPLC-UV

A rapid, specific, and sensitive method was developed for determination of tetracyclines (TCs) in egg, milk, and milk powder samples by online molecularly imprinted solid-phase extraction (MISPE) coupled to a reversed-phase high-performance liquid chromatography (HPLC). A molecularly imprinted polymer hybrid composite material (MIP-HCM) was prepared using TC as the template, methacrylic acid as the functional monomer, tetraethoxysilane as inorganic precursor, and methacryloxypropyltrimethoxysilane as the coupling agent. A new technique of online solid-phase extraction (SPE) coupled with HPLC was established. The conditions of online SPE were optimized. Under the optimal conditions, three TCs residues in egg, milk, and milk powder were separated and detected by the proposed method with better clean-up and recoveries. The recoveries of TCs ranged from 85.3% to 98.3%. The limits of detection and quantitation of the proposed method were in the range of 0.76–1.13 µg/kg and 2.53–3.77 µg/kg, respectively. The MIP-HCM was first used as online SPE packing and the hyphenated technique is promising as a general strategy for direct determination of veterinary drug residues in milk and other biological samples.

Synthesis and evaluation of dummy molecularly imprinted microspheres for the specific solid-phase extraction of six anthraquinones from slimming tea

Dummy molecularly imprinted microspheres with danthron as template were synthesized and their performance was evaluated. Accelerated solvent extraction can rapidly and effectively remove template molecules from the microspheres. The microspheres were applied as a specific sorbent for solid-phase extraction of six anthraquinones from slimming tea, showing excellent affinity and high selectivity to danthron and the target analytes. The molecular recognition mechanisms were discussed by the experimental validation with IR spectroscopy. The sample was treated using accelerated solvent extraction followed by dummy molecularly imprinted microspheres solid-phase extraction. Under the optimized ultra high performance liquid chromatographic conditions, the six target analytes can be baseline separated in 8 min, and good linearity was obtained in a range of 0.1-40 μg/mL with the correlation coefficient (r(2)) of ≥0.9998. The method limit of quantification was in a range of 1-2 mg/kg, it can ensure analysis of anthraquinones at mg/kg level. The intra- and interday precision (RSD, n = 6) for the analysis of the six analytes in a slimming tea was less than 4.5 and 5.4%, respectively. The developed method can be applied for the selective extraction, effective separation, and rapid determination of six anthraquinones in slimming tea.