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J. T. Hann 《Chromatographia》1987,24(1):510-512
Summary A quaternary mobile phase was optimized in conjunction with Fast LC techniques to separate α and β acids extracted from hops
in less than 4 minutes. The method is proposed for automated analysis of large numbers of hop samples and its usefulness is
demonstrated by comparing α-acid levels obtained by liquid chromatographic and conductometric techniques. Both assays provided
similar values for “fresh” hops but in “aged” hops liquid chromatography showed a lower level of α-acids. 相似文献
4.
Christina Haberhauer-Troyer Marizela Delic Brigitte Gasser Diethard Mattanovich Stephan Hann Gunda Koellensperger 《Analytical and bioanalytical chemistry》2013,405(6):2031-2039
A novel method for the simultaneous quantification of both glutathione (GSH) and its oxidized form glutathione disulfide (GSSG) by hydrophilic interaction chromatography–MS/MS has been developed and is critically discussed. Internal standardization based on isotopically labeled standards for both analytes is an absolute prerequisite for accurate quantification of this redox pair. Hence, a highly efficient and selective miniaturized procedure for the synthesis of isotopically labeled GSSG from commercially available glutathione-(glycine-13C2,15N) was established using H2O2 as oxidant and NaI as catalyst. Moreover, a tool is presented to monitor and hence uncover artifactual GSSG formation due to oxidation of GSH during sample preparation, which is the main source of systematic error in GSSG analysis. For this purpose, we propose to monitor the oxidation product formed by reaction of naturally occurring GSH with the isotopically labeled GSH used as internal standard. For the determination of GSH/GSSG ratios in yeast, different extraction methods based on (1) hot extraction with aqueous, acidic, or organic solvents, (2) mechanical cell lysis, and (3) extraction at subambient temperature were investigated in terms of recovery, extraction efficiency, and artifactual formation of GSSG. Total combined uncertainties of as low as 25–30 % (coverage factor?=?2) for the determination of GSH/GSSG ratios without derivatization were made possible by the addition of the internal standards early in the analytical procedure (before extraction) and immediate analysis of the analytes. 相似文献
5.
Dileep Kumar Kian-Eang Neo Malik Abdul Rub Ze Lene Tan Woan Lin Beh Hann Ling Wong 《Journal of Dispersion Science and Technology》2013,34(11):1657-1664
The present work is aimed at studying the interaction between copper-glycyltyrosine [(Cu(II)-Gly-Tyr)]+ and ninhydrin in water and in micelles formed by cetyltrimethylammonium bromide (CTAB) using spectrophometric measurements at 80°C and pH 5.0. The order of reaction remains the same in the two systems, that is, first- and fractional-order kinetics with respect to [Cu(II)-Gly-Tyr]+ and [ninhydrin], respectively, in the excess of ninhydrin over [Cu(II)-Gly-Tyr]+. It was observed that the product formed is same in both the media. The reaction is catalyzed by CTAB, and the maximum rate enhancement is about three fold. Quantitative kinetic analysis of kψ–[CTAB] data was explained in terms of pseudo-phase of the micelles (assuming the association/incorporation of both the reactants at the micellar surface). 相似文献
6.
Numerical modelling of the Gaussian beam diffraction by a wire near the Fraunhofer limit is presented. Two cases are considered: the case of the wire being on the axis of the beam and the case of the wire being off-axis. For the case where the wire is on the axis, the displacements of the diffracted minima are calculated. For the off-axis case, the changes in the positions of the maxima and minima and the power density are calculated. The conditions are determined at which the measurements made using a Gaussian beam can be calculated using the formula for plane waves. This work arises in connection with research being performed into the Doppler spectrum of big particles. 相似文献
7.
Certain anthracenophanes undergo photochemistry without light, sensitised by active oxalates. Although the quantum yield of sensitisation is extraordinarily high, no direct evidence for the expected radical cation intermediate has been found. 相似文献
8.
The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe). 相似文献
9.
R.A. Hann 《Chemical physics letters》1974,25(2):271-273
The large temperature dependence of the fluorescence maximum of (-)-bornyl 9-anthryl-3-propanoate is interpreted in terms of anharmonicity of thermally populated excimer vibrational levels. 相似文献
10.
Let R
8 denote the 8-element bounded tower. G. Tardos has shown that C(R
8), the clone of all monotone functions on R
8, is not finitely generated. In this paper we show that the clone of all nonsurjective functions is finitely generated. 相似文献