A new fabrication strategy of the graphene-coated solid-phase microextraction (SPME) fiber is developed. Graphite oxide was first used as starting coating material that covalently bonded to the fused-silica substrate using 3-aminopropyltriethoxysilane (APTES) as cross-linking agent and subsequently deoxidized by hydrazine to give the graphene coating in situ. The chemical bonding between graphene and the silica fiber improve its chemical stability, and the obtained fiber was stable enough for more than 150 replicate extraction cycles. The graphene coating was wrinkled and folded, like the morphology of the rough tree bark. Its performance is tested by headspace (HS) SPME of polycyclic aromatic hydrocarbons (PAHs) followed by GC/MS analysis. The results showed that the graphene-coated fiber exhibited higher enrichment factors (EFs) from 2-fold for naphthalene to 17-fold for B(b)FL as compared to the commercial polydimethylsioxane (PDMS) fiber, and the EFs increased with the number of condensed rings of PAHs. The strong adsorption affinity was believed to be mostly due to the dominant role of π-π stacking interaction and hydrophobic effect, according to the results of selectivity study for a variety of organic compounds including PAHs, the aromatic compounds with different substituent groups, and some aliphatic hydrocarbons. For PAHs analysis, the graphene-coated fiber showed good precision (<11%), low detection limits (1.52-2.72 ng/L), and wide linearity (5-500 ng/L) under the optimized conditions. The repeatability of fiber-to-fiber was 4.0-10.8%. The method was applied to simultaneous analysis of eight PAHs with satisfactory recoveries, which were 84-102% for water samples and 72-95% for soil samples, respectively.

No abstract

Surface-enhanced Raman scattering (SERS) signals strongly rely on the interactions and distance between analyte molecules and metallic nanostructures. In this work, the use of a gold nanoparticle (AuNP)-embedded metal-organic framework was introduced for the highly sensitive SERS detection. The AuNPs were in situ grown and encapsulated within the host matrix of MIL-101 by a solution impregnation strategy. The as-synthesized AuNPs/MIL-101 nanocomposites combined the localized surface plasmon resonance properties of the gold nanoparticles and the high adsorption capability of metal-organic framework, making them highly sensitive SERS substrates by effectively preconcentrating analytes in close proximity to the electromagnetic fields at the SERS-active metal surface. We discussed the fabrication, physical characterization, and SERS activity of our novel substrates by measuring the Raman signals of a variety of model analytes. The SERS substrate was found to be highly sensitive, robust, and amiable to several different target analytes. A SERS detection limit of 41.75 and 0.54 fmol for Rhodamine 6G and benzadine, respectively, was demonstrated. The substrate also showed high stability and reproducibility, as well as molecular sieving effect thanks to the protective shell of the metal-organic framework. Subsequently, the potential practical application of the novel SERS substrate was evaluated by quantitative analysis of organic pollutant p-phenylenediamine in environmental water and tumor marker alpha-fetoprotein in human serum. The method showed good linearity between 1.0 and 100.0 ng/mL for p-phenylenediamine and 1.0-130.0 ng/mL for alpha-fetoprotein with the correlation coefficients of 0.9950 and -0.9938, respectively. The recoveries ranged from 80.5% to 114.7% for p-phenylenediamine in environmental water and 79.3% to 107.3% for alpha-fetoprotein in human serum. These results foresee promising application of the novel metal-organic framework based composites as sensitive SERS-active substrates in both environmental and clinical samples.

The use of microwave heating for preparation in organic synthesis has been accepted as an effective technique in synthesis due to the significant advantages over the conventional method. In the present work, microwave heating was applied to the preparation of atrazine (template molecule) magnetic molecularly imprinted polymer (mag-MIP) beads by suspension polymerization. The term of the polymerization was dramatically shortened by using microwave heating in polymerization, which was less than (1)/(10) that by conventional heating. The resultant polymers incorporating molecular recognition and magnetic separation can provide a highly selective material for trace analysis in complicated samples. The mag-MIP beads were demonstrated with a narrow diameter distribution (80-250 microm) and cross-linking, spherical shape, and porous morphologies and exhibited magnetic property (M(s) = 0.491 emicro/g) and thermal stability under 260 degrees C. An improvement of imprinted efficiency is obtained in comparison to the mag-MIP beads prepared by conventional heating. A method for the determination of triazines in complicated samples by the mag-MIP beads extraction coupled with high-performance liquid chromatography (HPLC) was developed. The results indicated that the mag-MIP beads can be favorably used for the extraction of the triazines in spiked soil, soybean, lettuce, and millet samples. The reused beads displayed a long-term stability after undergoing extraction of 100 times.

No abstract

No abstract

A facile and efficient strategy about the synthesis of a novel kind of hybrid magnetic metal-organic framework (MOF)-5 via chemical bonding assembly was reported. The covalent bonding established between the amino functionalized Fe3O4 nanoparticles and the surface of the metal organic framework improved the chemical stability and structure uniformity of the hybrid microcrystals. Combination of MOF-5 with Fe3O4 nanoparticles allows for facile withdrawal of the porous materials by magnetic decantation. The powder X-ray diffraction patterns of the hybrid magnetic MOF-5 showed the structure of the metal organic framework was not disturbed with the decoration of magnetic nanoparticles. The as-synthesized materials combine the favorable attributes of both magnetic characteristics of Fe3O4 nanoparticles and high porosity of metal organic framework, making them excellent candidates as adsorbents for magnetic enrichment of trace analytes. Their potential applications were explored by preconcentrating polycyclic aromatic hydrocarbons and gibberellic acids from environmental, food, and plant samples prior to gas chromatography-mass spectrometry (GC/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively. The results showed that the magnetic MOF-5 exhibited superior enrichment capacity for both of these nonpolar and polar analytes. The method demonstrated good precision (relative standard deviations (RSDs) of 1.7-9.7%), low detection limits (0.91-1.96 ng·L(-1) for polycyclic aromatic hydrocarbons and 0.006-0.08 μg L(-1) for gibberellic acid), and good linearity (correlation coefficients higher than 0.9949). The RSDs of batch-to-batch extraction were 2.9-11.2%. The magnetic MOF-5 was robust enough for repeatable use without damage of extraction performance.

No abstract