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101.
Suppressed ion chromatography with a highly selective and high capacity anion-exchange column is used for the determination
of anionic compounds in ten commercially available toothpastes. Minimal sample preparation is needed, requiring only dilution
and filtration over a solid-phase extraction cartridge. Quantitative analysis of fluoride and monofluorophosphate, as well
as chloride, nitrate, orthophosphate, and sulfate is achieved in one chromatographic run with a total analysis time of 25
minutes.
Optimized analytical conditions are validated in terms of accuracy, precision, and total uncertainty, and the results demonstrate
the reproducibility of ion chromatography. The coefficient of determination for the anions ranges from 0.9896 to 0.9997. The
spiked recoveries for the anions are 88–108%. The change in the fluoride content of the toothpaste with storage time is investigated. 相似文献
102.
The phase transition, bulk and lattice thermal expansion behaviour of the strontium and neodymium substituted lanthanum chromites have been studied by dilatometry and high temperature X-ray powder diffractometry from room temperature to 1123 and 1073 K, respectively, in static air. The studies revealed that the temperature of the orthorhombic to rhombohedral phase transition, which occurred at 550 K in undoped LaCrO3, decreased on substitution of Sr2+ ions and increased on substitution of Nd3+ ions, systematically. However, the coefficients of average linear and volume thermal expansion (l and v) of LaCrO3 showed a marginal increase on Sr2+ substitution to different extent, whereas a reverse trend was observed with Nd3+ substitution. The phase transition temperatures and l and v of the compounds as determined by dilatometric and high temperature X-ray diffractometric methods are reported. 相似文献
103.
Hart JM Kennedy SD Mathews DH Turner DH 《Journal of the American Chemical Society》2008,130(31):10233-10239
As the rate of functional RNA sequence discovery escalates, high-throughput techniques for reliable structural determination are becoming crucial for revealing the essential features of these RNAs in a timely fashion. Computational predictions of RNA secondary structure quickly generate reasonable models but suffer from several approximations, including overly simplified models and incomplete knowledge of significant interactions. Similar problems limit the accuracy of predictions for other self-folding polymers, including DNA and peptide nucleic acid (PNA). The work presented here demonstrates that incorporating unassigned data from simple nuclear magnetic resonance (NMR) experiments into a dynamic folding algorithm greatly reduces the potential folding space of a given RNA and therefore increases the confidence and accuracy of modeling. This procedure has been packaged into an NMR-assisted prediction of secondary structure (NAPSS) algorithm that can produce pseudoknotted as well as non-pseudoknotted secondary structures. The method reveals a probable pseudoknot in the part of the coding region of the R2 retrotransposon from Bombyx mori that orchestrates second-strand DNA cleavage during insertion into the genome. 相似文献
104.
Yelamaggad CV Mathews M Hiremath US Rao DS Prasad SK 《Chemical communications (Cambridge, England)》2005,(12):1552-1554
The first mesoionic nematic and smectic A mesogens derived from sydnones that are characterized by both covalent and ionic features have been synthesized and evidenced by optical, calorimetric and X-ray diffraction studies. 相似文献
105.
V.E. Bondybey J.H. English C.Weldon Mathews R.J. Contolini 《Journal of Molecular Spectroscopy》1982,92(2):431-442
Infrared and uv absorption spectra of the CHNO isomers in rare gas matrices and their photolysis products by ultraviolet light were studied. The most efficient processes occurring in the matrix involve isomerization between the CHNO species. The NCO free radical is the only fragment appearing in the ir spectrum. The diatomic fragments CN, NH, and OH are also observable in the uv spectrum of photolyzed samples. 相似文献
106.
A recently-formulated residue-squaring method for perturbation problems is subjected to an exacting test in its application
to the problem of diagonalising the Hamiltonian of the nonlinear oscillator with quartic anharmonicity. Unlike other methods,
this new iterative diagonalisation method enables several eigenvalues to be calculated simultaneously with little more labour
than for a single eigenvalue. Values obtained for the four lowest even-parity levels of the anharmonic oscillator from just
two or three iterations are shown to agree well with earlier accurate calculations. An approximate analytical formula for
the energy levels is also presented. 相似文献
107.
108.
Rate coefficients and ion product distributions have been determined for the gas phase reactions of C3H3+ with several homocyclic and heterocyclic molecules in a selected ion flow tube (SIFT) at 298 K. The rate coefficients for both the linear and cyclic isomers of C3H3+ are given. l-C3H3+ reacts by association in the majority of the reactions. c-C3H3+ is shown to be more reactive than previously suggested by low pressure experiments. In fact, the cyclic isomer reacts at the gas kinetic rate when the reaction involves a nitrogen containing cyclic compound but is less reactive with oxygen containing cyclic compounds. It is noted this reactivity of both the cyclic and linear isomer should be included when modeling the atmosphere of Titan due to the large number of nitrogen containing molecules that are considered to be present. Currently, the models consider electron recombination to be the only loss channel for c-C3H3+. 相似文献
109.
Absence of emission concentration quenching accompanied by high emission efficiency in a solid state is highly challenging though very attractive, for example, for fabrication of solid state light emitters or fluorescent organic nanoparticles (FONs). Here, formation of FONs based on novel p-phenylenediacetonitrile derivatives by re-precipitation method in aqueous solutions is demonstrated. The exceptionality of the derivatives employed is manifested by nitrile groups-induced steric hindrance effects inhibiting concentration quenching of emission. Consisting of different size and polarity end-groups, phenyl groups in one compound and hexyl-carbazolyl in another, the derivatives were examined and compared in regard to nanoparticle formation morphology, size tunability, spectral signatures, and fluorescence turn-on efficiency. The variation of solvent/non-solvent ratio allowed to achieve tuning of the FON sizes from 55?nm up to 360?nm and resulted in maximal fluorescence on/off ratio of 38. Spectrally resolved confocal fluorescence microscopy revealed somewhat different molecule arrangement in different FONs suggesting dominant amorphous-like phase, which was confirmed by small angle X-ray scattering measurements. The FONs were verified to be stable against degradation or conglomeration into larger clusters at least over a couple of months thus implying their feasibility for practical applications. Finally, potential application of the fluorescent p-phenylenediacetonitrile nanoparticles for organic vapor sensing via fluorescence on/off switching was demonstrated. 相似文献
110.
S. Tripura Sundari N.C. RautTom Mathews P.K. AjikumarS. Dash A.K. TyagiBaldev Raj 《Applied Surface Science》2011,257(17):7399-7404
TiO2 thin films were synthesized on quartz substrates at substrate temperatures of 350 °C and 450 °C by thermal spray pyrolysis technique using titanium oxy-acetyl acetonate as a precursor. The optical properties of the thin films were characterized by a Spectroscopic Ellipsometer (SE). The surface morphology of the thin films was studied using Atomic Force Microscopy (AFM). The surface roughness values obtained using AFM and SE was compared. The refractive indices of the films were computed using a point by point ellipsometric data extraction procedure. The porosity of the films were modeled from the optical data by effective medium approximation and corroborated from empirical relations. Using Forouhi-Bloomer optical dispersion model, further treatment of SE data was carried out. The experimental investigations and modeling of the data were directed towards optical benchmarking of spray pyrolyzed titania thin films. 相似文献