Efficiency of composite vs. conically shaped chromatographic columns

The theory of composite chromatographic columns has been re-examined and general equations relating their efficiency to those of individual columns were derived. The derivations were based on elementary principles without reference to the principle of variance additivity. Derived also, were general equations for the efficiency of columns with continuously varying diameters, HETP and other properties from which formulae for special cases of practical interest were deduced. An example comparing the efficiencies of two columns, one conical and the other composite was given. The calculations show clearly that the conical column is superior in efficiency for the same total length and total retention volume.     

Bestimmung von Melment in Zementmischungen durch UV-Spektralphotometrie

Ohne Zusammenfassung

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Determination of melment in cement mixtures by UV-spectrophotometry

     

The theoretical basis of column chromatography in multicomponent separations. Part 2: Peak capacity. Column systems with good selectivity

The selectivity of a column system, S, defined by equation 28, includes a variation coefficient (β) of plate number with capacity ratio which has a large influence on the peak capacity, as shown in Fig. 18. Some typical chromatograms are given. In order to predict S for a column system from Kovat's Index, equations 40 and 41 are given to calculate the constant of the carbon number rule for squalane at different temperatures or for different stationary phases. The specific retention value of heptane on squalane at different temperatures can be calculated from equation 42. The nonpolarity index, defined by equation 43, was used to calculate the retention value of heptane on various stationary phases. In liquid chromatography, the order of elution may be reversed by changing the composition of the eluent on the same chemically bonded silica (manufactured in China). The linear relations between the log retention values of different kinds of solutes or of a single solute on the silicas of different surface areas when using the same eluent are given.     

Solvent effects on 17O nuclear magnetic shielding: N-methylformamide in polar and apolar solutions

The solvent effect on ¹⁷O isotropic shielding was computed by different methods: the polarizable continuum model and a mixed approach, including a few real solvent molecules treated as the solute. The experimental data show that the behavior of protic and aprotic solvents is markedly different: we found that the continuum approach describes well the observed shielding at various dielectric constants for aprotic solvents, while the mixed procedure is needed when hydrogen bonds to the magnetic centre are present.Contribution to the Jacopo Tomasi Honorary Issue     

Nature of weak inter-and intramolecular interactions in crystals 6. Intramolecular O—H...O bond in enol forms of (phosphoryl)acylacetonitriles

The nature of the intramolecular O—H...O bond was studied and its energy was estimated by X-ray diffraction analysis and quantum-chemical calculations (B3LYP/6-311G**) of (diphenylphosphoryl)acylacetonitriles. The influence of the nature of the substituents at the double bond in the H-bonded ring and the crystal packing effects on the hydrogen bond were investigated. Dedicated to Corresponding Member of the Russian Academy of Sciences T. A. Mastryukova. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2406–2413, November, 2005.     

Gas-chromatographische Bestimmung von Glykokollbetain in Mischfuttermitteln

Zusammenfassung Es wird eine Methode zur gas-chromatographischen Bestimmung von Glykokollbetain in Mischfuttermitteln beschrieben. Die Extraktion erfolgt mit Alkohol, anschließend wird die Lösung über einen Kationenaustauscher gereinigt. Das Betain wird mit N-O-Bis-(trimethylsilyl)-trifluoracetamid und Acetonitril verestert und gas-chromatographisch bestimmt. Für die beschriebene Methode errechnete sich bei einem Mittelwert von 2309 ppm und 7 Parallelen ein Variationskoeffizient von 1,79%.

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Gas-chromatographic determination of glycocoll betaine in feeding-stuffs

The betaine is extracted with ethanol, purified by cation-exchange chromatography, esterified with N-O-bis-trimethylsilyl-trifluoracetamide and determined by gas chromatography. The coefficient of variation for the described method for 7 parallels and an average of 2309 ppm was 1.79%.

     

pH滴定-主成分回归法同时测定酚类同系物

本文利用pH滴定－主成分回归法同时测定了苯酚、邻苯二酚、邻苯三酚的混合物，结果良好。通过交差验证法，本文还对采样区间和采样间隔作了详细讨论。     

CLIMATIC CHANGE SINCE LITTLE ICE AGE RECORDED BY DUNDE ICE CAP

The climatic change since the Little Ice Age recorded in the Dunde Ice Cap is presentedin this paper. There have been three cold periods and three warm periods since 1400AD.Among them, the coldest one was in the 17th century. Many evidences verified the three coldand warm variations recorded in the Dundc Ice Cap. But it was found from the comparison between the Dunde Icc Cap climatic record and thewinter temperature record in Shanghai that there was a temporal dfference in climatic changebetween East China and West China. The general trend is that the cooling and warmingprocesses in West China were earlier than that in East China. In the Dunde Ice Cap, it isnow in an anomalous warm period, while it is not as warm as in Dunde Ice Cap recordaccording to the winter temperature in Shanghai. In addition to the possible cause of temporaldifference in climatic change between West China and East China, another possible cause isthat the greenhouse effect of CO_2 may already be recognizable in the Dunde Ice Cap a     

Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I

Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.     

Calculation of vertical ionization potentials of difluoramine by perturbation corrections to koopmans' theorem

The vertical ionization potentials of difluoramine are calculated by perturbation corrections to Koopmans' theorem. The calculation shows that difluoraimine has three overlapping bands between 15 and 16 eV. The calculated results compare well with the experimental values. The photoelectron spectrum of difluoramine is compared with that of OF₂ and CH₂F₂.