Facile synthesis of amino-modified magnetic covalent organic framework for the efficient extraction and determination of anionic azo dyes in carbonated beverages.

In this work, a novel magnetic covalent organic framework (COF (TpPa-NH2) @ Fe3O4) was prepared via two step by simple solvent method for the extraction of anionic azo dye residues in food. The as-prepared COF (TpPa-NH2) @ Fe3O4 nanocomposite was characterised by scanning electron microscope, transmission electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, it was used as magnetic adsorbent for magnetic solid-phase extraction (MSPE) to extract and pre-concentrate three anionic azo dyes in carbonated beverage samples. The several key extraction and desorption parameters affecting the extraction recovery rate were investigated, including extraction time, pH of the solution, amount of material, adsorption time, elution solvent, pH of elution solvent, type of elution solvent, elution volume and elution time. Under optimised conditions, this method has good linearity between 5 and 500 µg L-1 (correlation coefficient > 0.9986). The limit of detection was 2.3-3.4 µg L-1. The recoveries of the samples were between 87.5 and 96.9%, and the relative standard deviation lower than 4.6%. The developed method has broad application prospects for the analysis of anionic azo dyes in carbonated beverages.

Magnetic covalent organic framework nanocomposites as a new adsorbent for the determination of polycyclic aromatic hydrocarbons in water and food samples.

A magnetic covalent organic framework nanocomposite (Fe3O4@COF(Tp-NDA)) was synthesized via a solvothermal method, used as a magnetic adsorbent for the extraction of polycyclic aromatic hydrocarbons (PAHs) from lake water, tea, coffee, and fried chicken, and detected using a high performance liquid chromatography-ultraviolet detector. The synthesized magnetic adsorbent was characterized via transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption isotherm analysis and vibrating sample magnetometry. Parameters that affected the extraction conditions and desorption conditions were optimized. Adsorption equilibrium could be attained within 3 min. The prepared magnetic material could be reused 10 times. The limits of detection and quantification were 0.05-0.25 µg L-1 and 0.17-0.83 µg L-1, respectively. The recovery was 74.6-101.8% with a relative standard deviation of below 4.2%. The method was successfully used to detect PAHs in various samples.

Ratiometric fluorescence detection of sulfide ions based on lanthanide coordination polymer using guanosine diphosphate as ligand.

The efficiency of energy transfer from guanine nucleotide to terbium ion (Tb3+) is affected by the phosphate group significantly. Compared with the biomolecules 5'-GMP (guanosine monophosphate), guanosine diphosphate (GDP) exhibits better sensitize ability to Tb3+ ions luminescence. Assisted with the carboxycoumarin ligand, we synthesized a more stable optical Coumarin@GDP-Tb polymer with the characteristic emission peaks located on 440 nm and 545 nm in this work. The Coumarin@GDP-Tb polymer is not only rich in metal binding sites, but also maintains a moderate ionic binding force, which helps metal ions to bind or leave it easily. Experiment result shows that Coumarin@GDP-Tb polymer has the appropriate binding force for Fe2+ ions, which can be destroyed by sulfur ions (S2-) as the formation of FeS precipitation. Based on this, Coumarin@GDP-Tb was designed as the ratio fluorescence probe for sulfur ions detection, where the fluorescence at 545 nm can be selectively quenched by Fe2+ ions, while that at 440 nm was unaffected, in the presence of S2- ions, the quenched fluorescence can be recovered remarkably. With the increasing S2- ions from 0.1-45 µM, the ratio of fluorescence intensity at 545 nm to 440 nm (F545/F440) is linear to S2- concentration, and the detection limit of S2- was calculated to be 0.073 µM. Contrast to those fluorescence probes with single wavelength emission, Coumarin@GDP-Tb displays a comparable sensitivity, the introduced self-adjust wavelength improved the detection accuracy efficiently. The above 98.1 % recovery rates of S2- ions in the actual water sample demonstrated the practicability of Coumarin@GDP-Tb fluorescence probe.

Praseodymium selective fluorescence recognition based on GdPO4: Tb3+ probe via energy transfer from Tb3+ to Pr3+ ions.

A novel strategy is proposed based on the efficient energy transfer from Tb3+ to Pr3+ for the sensitive and selective discrimination of praseodymium ions due to the matched energy levels of 5D4 (Tb3+) and 3P0 (Pr3+). The electron of Tb3+ transfers from the ground state to the excited state under the excitation of ultraviolet light and relaxes to the 5D4 level. In the presence of Pr3+ the electron has no time to return to the ground state, thus it transfers to the 3P0 level of Pr3+ resulting in the quenching of Tb3+ luminescence. In the case of GdPO4: Tb3+ nanowire, its fluorescence intensity at 545 nm linearly decreased when Pr3+ concentration ranged from 1 × 10-7 to 1 × 10-5 M, and the detection limit was 75 nM. To further investigate the sensing mechanism, CePO4: Tb3+, YPO4: Tb3+, and YBO3: Tb3+ nanoparticles were also synthesized for Pr3+ ion detection. For all materials, similar fluorescence quenching by Pr3+ ions occurred, which confirmed the efficient energy transfer from Tb3+ to Pr3+ ions. Utilizing the matched energy levels of 5D4 (Tb3+) and 3P0 (Pr3+), for the first time, we proposed a novel strategy (taking GdPO4: Tb3+ probe as the example) based on the efficient energy transfer from Tb3+ to Pr3+ for the sensitive and selective discrimination of praseodymium ions.

Oreocharis jasminina (Gesneriaceae), a new species from mountain tops of Hainan Island, South China.

A new species of Gesneriaceae, Oreocharis jasminina S.J.Ling, F.Wen & M.X. Ren from Hainan Island, south China, is highlighted and described. The new species is distinguished by its actinomorphic corolla, narrow floral tube and ovate anthers hidden in the floral tube. The new species also showed clear geographic and altitudinal isolation from the three currently-recognised Oreocharis species on the Island. Molecular phylogenetic analysis, based on nuclear ITS1/2 and plastid trnL-trnF sequences, supported the delimitation of the new species, which forms a single lineage with all the other Oreocharis species from Hainan Island. The roles of geographic and floral isolation in the evolution of the new species and its affinities are discussed.

Use of a magnetic covalent organic framework material with a large specific surface area as an effective adsorbent for the extraction and determination of six fluoroquinolone antibiotics by HPLC in milk sample.

A magnetic covalent organic framework material was synthesized with a core-shell structure using a simple solvothermal method. It was prepared with Fe3 O4 as the magnetic core, covalent organic framework as the shell, which synthesized from 1,3,5-triformylphloroglucinol and p-phenylenediamine by Schiff base reaction. Transmission electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, vibrating sample magnetometry, and nitrogen adsorption-desorption were used to characterize magnetic adsorbent. It has showed a large specific surface area (505.6 m2 /g), which can provide many adsorption sites. Moreover, the saturation magnetization value was 48.4 emu/g enough to be separated by external magnet. Six kinds of fluoroquinolones (enoxacin, fleroxacin, ofloxacin, norfloxacin, pefloxacin, and lomefloxacin) were extracted by magnetic solid phase extraction with the magnetic adsorbent. High-performance liquid chromatography detects the entire adsorption and desorption process to further evaluate the optimal extraction and desorption conditions. Under the optimal chromatographic conditions, this method showed a low detection limit (0.05 to 0.20 µg/L), good linearity in the range of 0.5 to 200 µg/L, and the enrichment factor reaches 115.5-127.3. The spiked recovery of the fluoroquinolones in milk sample ranged from 90.4 to 101.2%.