Liquid-liquid extraction followed by solid-phase extraction for the determination of lipophilic pesticides in beeswax by gas chromatography-electron-capture detection and matrix-matched calibration

Analytical methods for the simultaneous analysis of lindane, chlorpyriphos, z-chlorfenvinphos, endosulfan A and B, 4,4'-DDE, 4,4'-TDE, acrinathrine, bromopropylate, tetradifon, coumaphos and fluvalinate in pure beeswax samples are studied. For the analysis of bleached beeswaxes, a liquid-liquid extraction with acetonitrile followed by a clean-up on polymeric cartridges is the best option in terms of recovery and precision. However, some interferences that hinder the identification and quantification of important varroacides are found when non-bleached beeswaxes are analyzed. The analysis of all compounds in the latter samples require a clean-up by coupling an ODS cartridge before the polymeric cartridge. Considerations about the influence of the matrix in the quantitative analysis by a classical external standard calibration are also made and the use of a matrix-matched calibration is advised. Recoveries resulted to be about 100% with coefficients of variation between 10% and 20% (n = 5) for concentrations of 0.5 and 5 mg/kg.     

Magnetic alignment in nominally non-magnetic hexagonal metal hydrides: NMR

Powders of three hexagonal metal-hydrides or -deuterides are found to align in 4.4–8.3 T magnetic fields used for NMR. The field-alignment is unexpected, since all three systems have very small susceptibilities, as demonstrated by sharp NMR lines. The extent of alignment runs from nearly complete to barely detectable in ZrBe₂(H,D)_x, LuD₃, and YD₃, respectively. The preferred alignment direction in ZrBe₂(H,D)_x is with the crystallites’ c-axis perpendicular to B, while the c-axis and B tend to be parallel in LuD₃ and YD₃. The susceptibilities χ_|| and χ are determined from bulk magnetization measurements in aligned ZrBe₂H_1.4 powder. The alignment must be considered for proper analysis of NMR spectra in these and related materials.     

Powder MAS NMR lineshapes of quadrupolar nuclei in the presence of second-order quadrupole interaction

We derive a complete analytical solution for the powder magic angle spinning (MAS) nuclear magnetic resonance (NMR) lineshape in the presence of second-order quadrupole interaction, considering a radiofrequency (rf) pulse of finite width, a finite MAS frequency, and a non-zero asymmetry parameter. I_x is calculated using two approaches. The first applies time-dependent perturbation theory in the presence of the rf pulse and stationary perturbation theory (SPT) in its absence. The second is based on the Magnus expansion of the density matrix in the interaction representation during the pulse and SPT in its absence. We solve the problem in the laboratory frame using the properties of the Fourier transform and spin operators. Diagonalisation is not required. Both approaches agree well with each other under all conditions and also with the transition probability approach for the central transition. The Magnus expansion exists at all times and the effect of the non-secular terms is negligible. We describe an analytical method of averaging I_x over the Euler angles and simulate the ¹¹B MAS NMR lineshapes for crystalline and vitreous B₂O₃. A critical analysis is given of all earlier calculations of the MAS NMR lineshape.     

无溶剂顶空气相色谱法测定盐酸左氧氟沙星残留溶剂

采用无溶剂-顶空-气相色谱直接测定盐酸左氧氟沙星中残留溶剂乙醇、甲苯、二甲基亚砜(DMSO)等.各残留溶剂的检出限分别在0.007-0.032 μg,6次测定的相对标准偏差RSD在1.84%-1.92%,加标回收在90.9%-110%.方法简便、快速、灵敏,可应用于其他药品中残留溶剂的分析.     

Total analysis of surface structure and properties by UHV transfer system

We have developed an ultrahigh-vacuum (UHV) complex sample preparation and analysis system, which realizes a reliable surface science analyzing various characters on an identical surface. The system contains three sample-preparation-and-characterization chambers and five analysis chambers. They are (1) an electronic-properties-characterization chamber, (2) a magnetic-properties-characterization chamber, (3) an organic-molecule chamber, (4) UHV SEM, (5) a high-energy-resolution angle-resolved photoelectron spectrometer, (6) a high-energy-resolution display-type spherical mirror analyzer, (7) a room-temperature (RT) STM, and (8) an optical-properties characterization chamber. A special sample holder is used with six electrodes on it, which enables accurate temperature measurement of a sample by connecting a thermocouple directly to the sample even if it is transferred. Four other electrodes can be used for construction of various circuits including evaporators. Some examples are shown.     

Pervaporation in chemical analysis

Unlike thermal processes such as distillation, pervaporation relies on the relative rates of solute permeation through a membrane and is a combination of evaporation and gas diffusion. The analytical pervaporation systems consist of a membrane module suitable for liquid sample introduction and a vacuum (or a sweeping gas) on the permeate side. It has been used in a wide range of applications including the analysis of various organic and inorganic compounds, and sample concentration. It has been directly interfaced with gas chromatography, spectrophotometry, capillary electrophoresis, electrochemical detectors, liquid chromatography, and mass spectrometry. A wide range of liquids, slurries, and solids samples has been analyzed using these techniques. This review highlights the basic principles of the pervaporation and the state of its current development as applied to analytical chemistry.     

An ultra‐high temperature flow‐through capillary device for bacterial spore lysis

Rapid and specific characterization of bacterial endospores is dependent on the ability to rupture the cell wall to enable analysis of the intracellular components. In particular, bacterial spores from the bacillus genus are inherently robust and very difficult to lyze or solubilize. Standard protocols for spore inactivation include chemical treatment, sonication, pressure, and thermal lysis. Although these protocols are effective for the inactivation of these agents, they are less well suited for sample preparation for analysis using proteomic and genomic approaches. To overcome this difficulty, we have designed a simple capillary device to perform thermal lysis of bacterial spores. Using this device, we were able to super heat (195°C) an ethylene glycol lysis buffer to perform rapid flow‐through rupture and solubilization of bacterial endospores. We demonstrated that the lysates from this preparation method are compatible with CGE as well as DNA amplification analysis. We further demonstrated the flow‐through lysing device could be directly coupled to a miniaturized electrophoresis instrument for integrated sample preparation and analysis. In this arrangement, we were enabled to perform sample lysis, fluorescent dye labeling, and protein electrophoresis analysis of bacterial spores in less than 10 min. The described sample preparation device is rapid, simple, inexpensive, and easily integratable with various microfluidic devices.     

Properties of the density for a three-dimensional stochastic wave equation

We consider a stochastic wave equation in space dimension three driven by a noise white in time and with an absolutely continuous correlation measure given by the product of a smooth function and a Riesz kernel. Let pt,x(y) be the density of the law of the solution u(t,x) of such an equation at points (t,x)∈]0,T]×R³. We prove that the mapping (t,x)?pt,x(y) owns the same regularity as the sample paths of the process {u(t,x),(t,x)∈]0,T]×R³} established in [R.C. Dalang, M. Sanz-Solé, Hölder-Sobolev regularity of the solution to the stochastic wave equation in dimension three, Mem. Amer. Math. Soc., in press]. The proof relies on Malliavin calculus and more explicitly, the integration by parts formula of [S. Watanabe, Lectures on Stochastic Differential Equations and Malliavin Calculus, Tata Inst. Fund. Res./Springer-Verlag, Bombay, 1984] and estimates derived from it.     

Separation of alkylbenzyl quaternary ammonium compounds by capillary zone electrophoresis with sample stacking injection

Summary A systematic investigation of operational buffer systems, sample preparation and instrument parameters for achieving the best possible performance for determinating an homologous series of N-benzyl-N-alkyl-N,N-dimethylammonium chloride compounds by capillary zone electrophoresis with direct UV detection. The most effective separation was achieved within 3.5 min with the addition of acetonitrile (40%) in a phosphate buffer (20 mM pH 5.2) using a 40 cm fused-silica capillary operating at 25 KV and 20°C. Degassing of all electrolyte solutions and samples was very important. The linearity and repeatability for each compounds were satisfactory. To improve detection limits, on-column sample preconcentration, sample stacking, was investigated achieving a tenfold enrichment factor and quantitation limits about 10⁻⁷M.     

NMR analysis of multiple samples using parallel coils: improved performance using reference deconvolution and multidimensional methods

Improvements in the Multiplex Sample NMR method are investigated to explore its capabilities of analyzing multiple samples simultaneously. Issues of quantitation and resolution in the multiple-coil probe are examined in one- and two-dimensional experiments. Improvements in quantitation are shown to result from the use of reference deconvolution for one-dimensional experiments, while the use of two-dimensional methods has much improved resolution and shows the potential for significantly increased parallelism. A multiplicative scheme is shown to be an easily implemented, effective method for generating individual sub-spectra from individual samples.