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  • Author or Editor: Y. Gao x
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A novel multi-walled carbon nanotubes (MWCNTs) dispersive solid phase extraction (d-SPE) method which combined with gas chromatography (GC) coupled with electron capture detector (ECD) was developed for the determination of five pyrethroid pesticides in liquid milk for the first time. The effect of d-SPE conditions on the kinds of sorbent, MWCNTs and magnesium sulfate anhydro mass ratio, and extraction condition were researched, and then, the suitable method was found. Under the optimal conditions, the linear range was from 20 to 500 μg kg−1. The recoveries were from 81.8% to 112.1%, with the corresponding relative standard deviations (RSDs) less than 6%, correlation coefficients from 0.9978 to 0.9990, and limits of detection and quantification from 2.62 to 4.86 μg kg−1 and 8.73 to 16.2 μg kg−1. The proposed method is simple, fast, safe, and has high recovery and sensitivity applicable to analyze pyrethroid pesticides in liquid milk sample.

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Abstract  

We show that a monotonically normal space X is paracompact if and only if for every increasing open cover {U α: α < κ} of X, there is a closed cover {F : n < ω, α < κ} of X such that F U α for n < ω, α < κ and F F if αβ.

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Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants (IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0. The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry (DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and Rmax, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol−1 while it becomes 193.8 kJ mol−1 for EP containing IFR, decreased by 36.6 kJ mol−1, which shows that IFR can catalyze decomposition and carbonization of EP.

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The radiation effect of γ-ray on polyether-urethane foam was studied. The gas products from irradiated samples were analyzed quantitatively and qualitatively by gas chromatography, the thermal property and radical intensity were determined by differential thermal gravimetry and electron spin resonance. The dynamic mechanical property, compression and tensile properties were analyzed. Positron annihilation lifetime of irradiated samples was also measured at room temperature in vacuum. The results show that the general mechanical properties of ETPU sample irradiated by γ-rays at a dose of 8.0·105 Gy is excellent, but there are considerable gas products and a great deal of radicals created, which indicates that the sample has been damaged by radiation. Relatively, the thermal stability of the sample remained fine.

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Polyphenols in Chinese Kushui rose (Rosa sertata × Rosa rugosa) leaves were first extracted and analysed in this study. Among four fractions (ethyl ether, ethyl acetate, n-butanol, and water layer) of crude extracts, the ethyl acetate fraction showed the highest ABTS•+ scavenging activity, and the n-butanol fraction exhibited the maximum components in composition. On-line HPLC-ABTS•+ analysis indicated that there were more than 30 antioxidant compounds from Chinese Kushui rose leaves. The identified polyphenols could be classified into quercetin derivatives, gallic acid derivatives, and proanthocyanidins. Gallic acid was the most antioxidative compound.

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A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO3)]NO3·2H2O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=Ae−E/RT(1−α)2. The kinetic parameters (E, A), activation entropy ΔS # and activation free-energy ΔG # were also gained.

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Nano-ZnO flakes were synthesized by calcination of the precursor of Zn(OH)2 obtained via the reactive ion exchange method between an ion exchange resin and ZnSO4 solution at room temperature. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscope, UV-Vis diffuse reflection spectrum and Na2EDTA titration were used to characterize the structure features and chemical compositions of the as-prepared ZnO. The results show that the as-prepared ZnO flakes have uniform structure and high purity. Heat capacities in the temperature range of 83 to 396 K were measured. The measured heat capacities values were compared with those of coarse crystal powders and the difference between this two heat capacity curves was analyzed.

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The thermogenic curves of the aerobic metabolism of the three strains of Bacillus thuringiensis B.t. A, B.t. B and B.t. C have been determined by using an LKB-2277 BioActivity Monitor. B.t. A was the host bacterium without foreign gene. B.t. B and B.t. C were constructed by transforming different foreign genes into the host B.t. A, respectively. B.t. B expressed erythromycin resistant gene, while B.t. C expressed both erythromycin resistant gene and tyrosinase gene. The heat flow rate of these strains is B.t. A> B.t. B >B.t. C. These results indicated that there is obvious interrelation between expression of foreign genes and heat flow rate of B.t. strains.

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A novel complex, [Pr(5-nip)(phen)(NO3)(DMF)] (5-nip: 5-nitroisophthalic acid; phen: 1,10-phenanthroline, DMF: N,N-dimethylformamide), was prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectrum and DTG-DSC techniques. The results show that the crystal is monoclinic, space group P2(1)/n with a=11.0876(6) Å, b=12.8739(7) Å, c=16.9994(8) Å; β=91.193(4)°, Z=4, D c=1.822 Mg m–3, F(000)=1320. Each Pr(III) ion is nine-coordinated by one chelating bidentate and two monodentate bridging carboxylate groups, one chelating bidentate nitryl group, one DMF molecule and one 1,10-phenanthroline molecule. The complex is constructed with one-dimensional ribbons featuring dinuclear units and the one-dimensional ribbons are further assembled into two-dimensional networks by strong π–π stacking interactions. The complex has high stability up to 500°C. The enthalpy change of formation of the compound in DMF was measured using an RD496-III type microcalorimeter with the value of –9.214±0.173 kJ mol–1.

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