On-capillary sample cleanup method for the electrophoretic determination of carbohydrates in juice samples

On many occasions, sample treatment is a critical step in electrophoretic analysis. As an alternative to batch procedures, in this work, a new strategy is presented with a view to develop an on-capillary sample cleanup method. This strategy is based on the partial filling of the capillary with carboxylated single-walled carbon nanotube (c-SWNT). The nanoparticles retain interferences from the matrix allowing the determination and quantification of carbohydrates (viz glucose, maltose and fructose). The precision of the method for the analysis of real samples ranged from 5.3 to 6.4%. The proposed method was compared with a method based on a batch filtration of the juice sample through diatomaceous earth and further electrophoretic determination. This method was also validated in this work. The RSD for this other method ranged from 5.1 to 6%. The results obtained by both methods were statistically comparable demonstrating the accuracy of the proposed methods and their effectiveness. Electrophoretic separation of carbohydrates was achieved using 200 mM borate solution as a buffer at pH 9.5 and applying 15 kV. During separation, the capillary temperature was kept constant at 40 degrees C. For the on-capillary cleanup method, a solution containing 50 mg/L of c-SWNTs prepared in 300 mM borate solution at pH 9.5 was introduced for 60 s into the capillary just before sample introduction. For the electrophoretic analysis of samples cleaned in batch with diatomaceous earth, it is also recommended to introduce into the capillary, just before the sample, a 300 mM borate solution as it enhances the sensitivity and electrophoretic resolution.     

MgNb2O6 Modified K0.5Na0.5NbO3 Eco-Piezoceramics: Scalable Processing,Structural Distortion and Complex Impedance at Resonance

In this work, piezoceramics of the lead-free composition K_0.5Na_0.5NbO₃ with an increasing amount of MgNb₂O₆ (0, 0.5, 1, 2 wt.%) were prepared through conventional solid-state synthesis and sintered in air atmosphere at 1100 °C. The effect of magnesium niobate addition on structure, microstructure and piezoelectric properties was evaluated. The ceramics maintain the orthorhombic Amm2 phase for all compositions, while an orthorhombic Pbcm secondary phase was found for increasing the concentration of MgNb₂O₆. Our results show that densification of these ceramics can be significantly improved up to 94.9 % of theoretical density by adding a small amount of magnesium-based oxide (1 wt.%). Scanning electron microscopy morphology of the 1 wt.% system reveals a well-packed structure with homogeneous grain size of ∼2.72 μm. Dielectric and piezoelectric properties become optimal for 0.5–1.0 wt.% of MgNb₂O₆ that shows, with respect to the unmodified composition, either higher piezoelectric coefficients, lower anisotropy and relatively low piezoelectric losses (d₃₃=97 pC N⁻¹; d₃₁=−36.99 pC N⁻¹ and g₃₁=−14.04×10⁻³ mV N⁻¹; Q_p(d₃₁)=76 and Q_p(g₃₁)=69) or enhanced electromechanical coupling factors (k_p=29.06 % and k₃₁=17.25 %).     

Is there any bona fide example of O-H...F-C bond in solution? The cases of HOC(CF3)2(4-X-2,6-C6H2(CF3)2) (X = Si(i-Pr)3, CF3)

The reinvestigation of the title compounds, which are the only examples reported to show experimentally (by NMR) O-H...F-C bonds in solution proves that the NMR data were misinterpreted and the restrictions to rotation of one CF(3) group are due to crowding, not to intramolecular O-H...F-C bond.     

Determination of trace levels of dinitrophenolic compounds by microporous membrane liquid-liquid extraction in environmental water samples

A fast and simple hollow fibre-based microporous membrane liquid-liquid extraction (MMLLE) method is proposed for the determination of trace levels of dinitrophenolic compounds in water samples. The optimization step was performed using a three-variables Doehlert matrix design, involving the fibre length, the quantity of trioctylphosphine oxide (TOPO) in the acceptor phase and the extraction time. Using the established experimental conditions, some other parameters such as stirring speed, salt content, humic acids and different organic solvents as the acceptor phase were studied. Validation of the method included calibration experiments, linearity studies and determination of method LOD (MLD). The RSD was around 11% in all the experiments on different days at different concentrations. Separation and detection of four dinitrophenols were performed in 10 min with an RP-LC and a C(8 )column ACN-citric buffer gradient elution and diode array detection.     

(CdSe/ZnS QDs)-ionic liquid-based headspace single drop microextraction for the fluorimetric determination of trimethylamine in fish

Here, we propose the use of ionic liquid-modified QDs for the combination of ionic liquid-based headspace single drop microextraction technique (IL-HS-SDME) and QD-based fluorimetric detection. In that way, we exploit the advantages of ILs as extractant solvent and the use of QDs as fluorescence detection probe. After in situ generation of volatile trimethylamine (TMA) from fish samples, the analyte was extracted and preconcentrated directly onto a (QD)IL microdrop by HS-SDME. Then, TMA was quantified through the enhancing effect produced on the initial fluorescence of the (QD)IL dispersion. The working conditions for the (QD)IL-HS-SDME procedure were: 20 μL microdrop of (QD)IL exposed for 2 min to the headspace of a 5 mL aqueous sample (0.2 g of fish in 10 M NaOH) placed in a 10 mL vial with stirring and thermostatted at 50-60 °C. For the detection, the microdrop was transferred to a microcuvette with 300 μL of acetonitrile and the fluorescence was recorded (λ(em) = 570 nm, λ(exc) = 400 nm). Under the selected conditions, the analytical response was linear over the range from 0.05 to 0.25 mg L(-1) (R(2) = 0.997) with a detection limit of 0.014 mg L(-1) (0.35 μg TMA per gram of fish) and the relative standard deviation was 3.5% (n = 5). The proposed method was applied to the determination of TMA in hake fish samples with satisfactory results.     

Relativistic perfect fluids in local thermal equilibrium

Every evolution of a fluid is uniquely described by an energy tensor. But the converse is not true: an energy tensor may describe the evolution of different fluids. The problem of determining them is called here the inverse problem. This problem may admit unphysical or non-deterministic solutions. This paper is devoted to solve the inverse problem for perfect energy tensors in the class of perfect fluids evolving in local thermal equilibrium (l.t.e.). The starting point is a previous result (Coll and Ferrando in J Math Phys 30:2918–2922, 1989) showing that thermodynamic fluids evolving in l.t.e. admit a purely hydrodynamic characterization. This characterization allows solving this inverse problem in a very compact form. The paradigmatic case of perfect energy tensors representing the evolution of ideal gases is studied in detail and some applications and examples are outlined.     

CEMS spectra of non-spherical nanoparticles in oxidized iron thin films

The polycrystalline stannide SmRhSn was prepared by arc melting of the elements in an argon atmosphere. The title compound crystallizes with the ZrNiAl type structure (space group $P\bar{6}2m)$ with the lattice parameters: a?= 739.6(1) and c?= 406.9(1) pm. The magnetic and electronic properties of SmRhSn were investigated in detail by magnetic susceptibility measurements and ¹¹⁹Sn Mössbauer spectroscopy. A transition from a paramagnetic to a ferromagnetic state was determined to be T _C?= 14.5(1) K. The ¹¹⁹Sn Mössbauer spectrum recorded in T?= 4.2 K was fitted using single component, but with a broad quasi-distribution of magnetic hyperfine fields.     

Ionic liquids and CE combination

This paper reviews and discusses the analytical combination of ionic liquids (IL) with CE. On the one hand, it shows CE as a powerful technique to separate impurities from IL as well as being capable to determine physical and chemical properties of IL. On the other hand, it also shows how IL are employed in CE separations to enhance resolution, peak efficiency and peak symmetry. Specifically, IL are used as additives in CZE, NACE, and MEKC and as support coatings of the capillary wall in electrochromatography. The integrity of the IL in the electrophoretic system as well as the roles of the cations and anions of the IL in the electrophoretic separation are also discussed.     

New supported liquid membrane-capillary electrophoresis in-line arrangement for direct selective analysis of complex samples

An in-line coupling of a micro-membrane extraction unit, based on supported liquid membrane, with commercially available capillary electrophoresis equipment is described. A main characteristic of this micro-membrane device, made from a simple Eppendorf tube, is that it permits the application of voltage in the acceptor solution to be applied during the extraction process. This has been shown as an alternative to enhance sensitivity, as the analytical signal achieved by applying 10 kV for 20 min was similar to that obtained without the application of voltage and with extraction time of 60 min. In addition, the design has been made permitting both in-line hydrodynamic and electrokinetic sample introduction into the electrophoretic capillary. The analytical potential of the proposed system has been demonstrated by the direct determination of nitroimidazoles from pig liver tissue. The high efficiency of the proposed system allowed the extraction and the determination of the analytes to be performed from a simple tissue homogenate obtained in water. The precision of the analysis of spiked samples, expressed in terms of relative standard deviation, was better than 4.8%.     

Influence of alloying elements and etching treatment on the passivating films formed on aluminium alloys

This paper studies the characteristics of aluminium oxide layers present on the surface of commercial aluminium specimens after thermomechanical processing and after subsequent etching in an alkaline solution, highlighting the main differences observed. An attempt is made to establish possible relationships between alloying elements and the characteristics of these layers. Copyright © 2006 John Wiley & Sons, Ltd.