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981.
The design and use of a two-channel fountain cell in potentiometric and voltammetric detection is described. The two flows produced two distinct sectors inside the thin layer region and one of the sectors was used as the internal electrolyte of a reference electrode built into the cell body and the other as the indicator/counter electrode section. The behavior of the flowthrough Ag/AgCl reference electrode was first investigated and found satisfactory and it was then employed as the reference electrode in the subsequent experiments. Continuous and flow-injection measurements were made using the Fe(III)/Fe(II) redox couple in potentiometry and the reduction of Fe(III) in voltammetry. 相似文献
982.
983.
984.
One more model of aq-harmonic oscillator based on theq-orthogonal polynomials of Al-Salam and Carlitz is discussed. The explicit form ofq-creation andq-annihilation operators,q-coherent states and an analog of the Fourier transformation are established. A connection of the kernel of this transform with a family of self-dual biorthogonal rational functions is observed. 相似文献
985.
Instability of the paramagnetic state towards incommensurate magnetic order in the 2-d Hubbard model
K. Doll M. Dzierzawa R. Frésard P. Wölfle 《Zeitschrift für Physik B Condensed Matter》1993,90(3):297-300
We determine the instability line separating the paramagnetic phase in the phase diagram of the 2-d Hubbard Model from a phase with incommensurate magnetic order. A mean-field approximation of the Kotliar-Ruckenstein slave boson representation is used to calculate the wave-vector dependent magnetic susceptibility. For largeU/t the instability occurs at a densityn0.37, and a wave-vector close toq=(0,). The dependence ofq onU andn is also given. 相似文献
986.
Determination of platinum and palladium in strongly acid solution by means of flow injection analysis 总被引:1,自引:0,他引:1
Microamounts of Pt(II/IV) (0.25–800 μg/ml) and Pd(II) (5–600 μg/ml) in> 0.5 M hydrochloric acid can readily be determined by means of a simple FIA method based on the selective reaction of tin(II)chloride with these metals. The FIA method has a high linear dynamic range, and is relatively free from interferences of many transition metals, with the exception of Au and Rh; small amounts of other PGMs can be tolerated. Determination of Pt on a hydrogenation catalyst by this method compares well with that found by flame atomic absorption spectroscopy. By monitoring at two or more wavelengths, Pt and Pd can be determined in mixtures by this means, to yield a simple, cost-effective FIA method for possible on-line determinations and quality control of, in particular, Pt containing acidic refinery and other process streams. 相似文献
987.
K. I. Dikovskaya I. V. Turovskii T. V. Mazur Ya. F. Freimanis 《Chemistry of Heterocyclic Compounds》1993,29(8):878-882
A study was made of the condensation of bicyclic -lactone I with furylacrolein and furylpropionic aldehyde. Significant differences were observed in the reactivity of the aldols obtained, and in the stereochemical trend of their dehydration reaction.For Communication 35, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1035–1039, August, 1993. 相似文献
988.
M. G. Voronkov V. N. Knutov O. N. Shevko M. K. Butin 《Chemistry of Heterocyclic Compounds》1993,29(1):115-118
The acid hydrolysis of 9,14-bis(2-methoxycarbonylethyl)-11-12-benzo-3,4-(4,5-dimethylbenzo)-10,13-dioxo-1,6-dithia-9,14-diazacyclohexadeca-3,11-diene leads to the corresponding 9,14-biscarboxy derivative. The reaction of 4,9,15,20-tetrakis-(2-methoxycarbonylethyl)-6,7,17,18-dibenzo-5,8,16,19-tetraoxo-1,12-dithia-4,9,15,20-tetraazacyclodocosa-6,17-diene with hydrazine hydrate and subsequent treatment with NaNO2 gave the corresponding tetraazide. The reaction of this tetraazide with histamine and histidine leads to macroheterocycles, containing exocyclic histamine and histidine fragments.For Communication 6, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 130–133, January, 1993. 相似文献
989.
G. K. Airapetyan M. G. Akopyan Zh. S. Arustamyan É. A. Markaryan 《Chemistry of Heterocyclic Compounds》1993,29(5):578-581
Methods have been developed for the synthesis of 1,4-benzodioxanyl-6-ethylamine with cyclopentyl and tetrahydropyranyl substituents in the -position. These compounds have been used as starting materials for the synthesis of new heterocyclic systems, the 4-spirocyclosubstituted dioxinoisoquinolines.For Communication 29, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 677–680, May, 1993. 相似文献
990.
K. Oxynos J. D. Schladot J. Schmitzer F. Backhaus A. Kettrup 《Fresenius' Journal of Analytical Chemistry》1993,345(2-4):238-239
Summary This paper describes the cryogenic preparation of 50 individual specimens of dab (Limanda limanda) from the Baltic Sea to produce a homogeneous fish material. 950 subsamples (8 g each) are stored in the gaseous phase over liquid nitrogen. Five series of analyses were randomly selected out of store. The results show that the obtained precision of 8 to 9% could be used as an indication unit for the deviation of the mean values of CHC concentrations from true values. If the analytical variability is 5%, the maximum inhomogeneity in the subsamples is 3–4%. It may be concluded that the subsamples of the candidate fish reference material (RM) are homogeneous enough for analytical purposes. Thus ESB (German Environmental Specimen Bank) material prepared in accordance with the standard operating procedure (SOP) [1] are valuable and appropriate reference materials. The prepared fish RM is suitable for the analysis of chlorinated hydrocarbons in fat containing marine samples. 相似文献