Determination of uric acid in human serum by capillary electrophoresis with polarity reversal and electrochemical detection

Capillary zone electrophoresis (CE) under conditions of reversed polarity is used in conjunction with electrochemical detection (EC) at carbon fiber microcylinder electrodes for the selective and sensitive determination of uric acid in human blood serum. Comigration of anions with the electroosmotic flow is accomplished with reversed polarity and the buffer additive cetyltrimethylammonium bromide (CTAB) in a 2-(N-morpholino)ethanesulfonic acid (MES) buffer system, giving rise to rapid and sensitive analyses. Optimal buffer conditions (pH 7.0), detection potential (0.80 V vs. Ag/AgCl), and electrokinetic injection are employed to allow for maximal resolution and signal intensity. Amperometric end-column detection with a carbon fiber microcylinder electrode results in lower limits of detection for uric acid of about 25 nM (ca. 140 amol injected) without the need for decoupling. Linear calibration plots using uric acid standards in water and serum are obtained over a linear range from 5.00 x 10(-4) M to 2.50 x 10(-7) M. Uric acid concentrations obtained for human sera using the CE-EC approach described here are shown to compare favorably to the accepted laboratory values.     

On-line Surface Area Measurement of Concentrated Slurries using low field spin-lattice relaxation NMR

A method for the rapid on-line determination of surface area and solids content in flowing concentrated slurries using low field NMR spin-lattice relaxation measurements has been developed and demonstrated. The relationship between flow and spin-lattice relaxation time (T₁) of protons in water at 20 MHz was examined using aqueous copper sulfate solutions. The ability to measure surface area and solids concentration in both stagnant (stopped flow) and flowing systems via NMR was demonstrated using several different concentrated aqueous titania and glass slurries (20 to 80 weight percent) for which the dried powder surface area was previously determined via nitrogen adsorption/BET analysis and the solids content determined gravimetrically. Surface areas were also calculated from particle size analysis and found to vary by up to an order of magnitude from the adsorption and NMR results.     

Chemical assembly of TiO2 and TiO2@Ag nanoparticles on silk fiber to produce multifunctional fabrics

Activated carbon fibers (ACFs) were prepared by chemical activation of poly(p-phenylene terephthalamide (PPTA) with phosphoric acid, with a particular focus on the effects of impregnation ratio and carbonization temperature on both surface chemistry and porous texture. Thermogravimetric studies of the pyrolysis of PPTA impregnated with different amounts of phosphoric acid indicated that this reagent has a strong influence on the thermal degradation of the polymer, lowering the decomposition temperature and increasing the carbon yield. As concerns surface chemistry, TPD and chemical analysis results indicated that the addition of phosphoric acid increases the concentration of oxygenated surface groups, with a maximum at an impregnation ratio of 100 wt.%. The resulting materials present uncommon properties, namely a large amount of oxygen- and phosphorus-containing surface groups and a high nitrogen content. Porosity development following H(3)PO(4) activation was very significant, with values close to 1700 m(2)/g and 0.80 cm(3)/g being reached for the BET surface area and total pore volume, respectively. The pore size distributions remained confined to the micropore and narrow mesopore (<10 nm) range.     

Anisotropy of the electron mean free path in the thermal conductivity of very pure gallium

In order to determine the anisotropy of the bulk mean free pathl _b, we have measured the thermal conductivity of 6–9's pure gallium single crystals as a function of size and crystal orientation between 1.4 and 4.2°K. The results were analyzed by adapting the existing theory for the electrical conductivity of thin wires to the thermal case. The results show that the reciprocal of the bulk mean free path can be expressed as a linear function ofT ³ for all three orientations. The residual contributions to this quantity are highly anisotropic, as expected. The electron-phonon contributions are, on the other hand, nearly equal in magnitude and exhibit a ratio of 3:4:4 for the A:B:C axis, respectively. In addition, an unusual dependence upond ⁻², whered is the specimen diameter, was observed for the C-axis. It is possibly related to the fact that for this direction only 6% of the entire free electron Fermi surface takes part in conduction which, as a consequence, may be largely dominated by Umklapp scattering. Research sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force under Grant No. AF-AFOSR 1051-66.     

Lattice vibration and optical properties of crystalline Nd:KLu(WO4)2

Crystalline Nd:KLu(WO₄)₂ has been grown by the top-seeded-solution growth (TSSG) method. The polarized Raman spectrum, infrared spectrum, polarized absorption spectrum and fluorescence spectrum have been recorded at room temperature. The lattice vibration modes were calculated using space group theory and the infrared transmission spectrum was used as a supplement to the Raman spectrum to assign the modes more accurately. The Judd–Ofelt theory was used to study some important spectroscopic parameters, which were also compared with some other Nd³⁺ doped double tungstates.     

Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.     

Inhomogeneity of composition in near‐stoichiometric LiNbO3 single crystal grown from Li rich melt

A near‐stoichiometric LiNbO₃ single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li₂O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO₃ crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of the boys and Pipek–Mezey localizations in the local correlation approach and automatic virtual basis selection

Our implementation of Pipek–Mezey population localization is described. It is compared with other localization schemes and its use in the framework of the local correlation method is discussed. For such use, this localization is shown to be clearly superior to Boys in the case of physically well-localized systems. Our current algorithm for selection of local virtual spaces is also described. © 1993 John Wiley & Sons, Inc.     

Synthesis of Bi2Se3 thermoelectric nanosheets and nanotubes through hydrothermal co-reduction method

Bi₂Se₃ nanosheets and nanotubes were prepared by a hydrothermal co-reduction method at 150, 180, 200, and 210 °C. Bi₂Se₃ nanosheets, nanobelts and nanotubes were obtained. The Bi₂Se₃ nanoflakes are 50-500 nm in width and 2-5 nm in thickness. The Bi₂Se₃ nanotubes are 5-10 nm in diameter, 80-120 nm in length, and 1.3 nm in wall thickness. X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and electron diffraction were employed to characterize the products. Experimental results showed that the nanosheets and the nanotubes are hexagonal in structure with a=4.1354 Å and c=27.4615 Å. A possible formation and crystal growth mechanism of Bi₂Se₃ nanostructures is proposed.