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991.
The separation, characterization, and determination of mixtures of alkyl ether sulfates (AES) and fatty acids (C10-C16) in background electrolytes (BGEs) containing acetonitrile (ACN)-water mixtures is addressed. Due to inhibition of the ionization of the carboxylate groups, the migration time and the resolution between the fatty acids decreased when the water content of the BGE was reduced, but efficiency and resolution between the AES oligomers improved. The migration times increased and resolution improved by substituting 5% ACN by an equivalent amount of dioxane. A complete separation of the two surfactant classes, up to the AES oligomers with 8 ethylene oxide units (EOs) with respect to C10, with excellent resolution between the AES oligomers, while preserving a satisfactory resolution between the fatty acids, was achieved with a BGE containing 5 mM trimethoxybenzoic acid, 7 mM dipentylamine, 85% ACN, 5% dioxane, and 10% water. The two surfactant classes were increasingly resolved by further reducing the water content of the BGE. Thus, C2 (acetate) was resolved from the AES oligomers up to 7 EOs using 90% ACN and 5% dioxane, but the resolution between the heavier fatty acids was poor with this BGE. Identification of the AES oligomers was eased by the excellent regularity of the successive migration times; thus, within each AES subclass or series of oligomers with the same number of carbon atoms in the alkyl chain, the migration times decreased following a mild curve as the number of EOs increased. The way how the data obtained by indirect photometry (corrected peak areas that are proportional to the molar concentrations) should be managed to avoid systematic error when the calibration curve is constructed using an AES standard with an oligomer distribution different from that of the samples is discussed and equations are given. Decyl sulfate was successfully used as internal standard. The detection limits (S/N = 3) were of ca. 2 microM for individual AES oligomers. 相似文献
992.
The asymmetric reduction of benzophenones p-X-C6H4-CO-C6H5 (X = CH3, OCH3, Br, CF3) and p-CF3-C6H4-CO-C6H4-p'-Z (Z = CH3, Br) by chiral Grignard reagents p-Y-C6H4-CH(C2H5)CH2MgCl (Y = OCH3, CF3) gives benzhydrols of optical purities which can reach 37%. The absolute configuration of the alcohol depends on the nature of substituents. The substituent effect is discussed through donor-acceptor interactions between the aromatic nuclei in the diastereoisomeric transition states. 相似文献
993.
Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations
of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous
precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride
ions the application of crystalline, easily filtrable Ca(COO)2·H2O or CaCO3, and in the case of tungstate ions the application of CaWO4 precipitate improves the filtration properties of45CaF2 and45CaWO4, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations
were carried out with 0.05M and 0.005M CaCl2 solutions, labelled with45Ca. 相似文献
994.
Thérèse Dupuis 《Mikrochimica acta》1967,55(3):461-464
Résumé Dans le spectre d'absorption infrarouge de l'iodatochromate de potassium K[(CrO3)(IO3)], on peut identifier la présence de bandes de vibration de valence de ponts Cr-0-I à 508 et680 cm–1.
Summary The infrared absorption spectrum of potassium iodatochromate K(CrO3)(IO3) contains vibration bands of the valence bridges Cr-O-I at 508 and 680 cm–1.
Zusammenfassung Im Infrarot-Absorptionsspektrum des Kaliumjodatochromats lassen sich Banden der Valenzschwingungen der Atomgruppe Or-O-J bei 508 und 680 cm–1 nachweisen.相似文献
995.
Fehr C Chaptal-Gradoz N Galindo J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):853-858
Two efficient enantioselective syntheses of the more active (S,S)-enantiomer of the powerful musk odorant Vulcanolide are described. In both syntheses, the key step is an enantioselective protonation of a ketone enolate. A third enantioselective protonation, of a thiol ester enolate, was applied for the determination of the absolute configuration of Vulcanolide by comparison with a known compound. 相似文献
996.
de la Fuente JM Eaton P Barrientos AG Menéndez M Penadés S 《Journal of the American Chemical Society》2005,127(17):6192-6197
Thermodynamic evidence for the selective Ca(2+)-mediated self-aggregation via carbohydrate-carbohydrate interactions of gold glyconanoparticles functionalized with the disaccharides lactose (lacto-Au) and maltose (malto-Au), or the biologically relevant trisaccharide Lewis X (Le(X)-Au), was obtained by isothermal titration calorimetry. The aggregation process was also directly visualized by atomic force microscopy. It was shown in the case of the trisaccharide Lewis X that the Ca(2+)-mediated aggregation is a slow process that takes place with a decrease in enthalpy of 160 +/- 30 kcal mol(-)(1), while the heat evolved in the case of lactose and maltose glyconanoparticles was very low and thermal equilibrium was quickly achieved. Measurements in the presence of Mg(2+) and Na(+) cations confirm the selectivity for Ca(2+) of Le(X)-Au glyconanoparticles. The relevance of this result to cell-cell adhesion process mediated by carbohydrate-carbohydrate interactions is discussed. 相似文献
997.
A set of amino-group possessing cyanine dyes is obtained from their N-acetyl derivatives via deprotection with boron trifluoride-methanol complex in good yields. 相似文献
998.
Y. Marcus 《Journal of solution chemistry》1991,20(9):929-944
Taft and Kamlet's -scale of solvent hydrogen bond donation ability is reexamined with regard to its correlations with three widely used polarity scales: Dimroth and Reichardt's E
T
(30), Kosower's Z and Mayer's A
N
, as well as with the m values of the solvents when present as monomeric solutes. The correlation with E
T
serves to extend the solvent -scale according to the expression:
相似文献
999.
J. L. Gascón M. T. Crespo M. L. Aceña 《Journal of Radioanalytical and Nuclear Chemistry》1990,139(2):249-254
In this paper the authors present a study of the adsorption of thorium on manganese dioxide by batch equilibration and cartridge experiments. Some anomalies in the use of MnO2 to concentrate thorium have been found. So the use of this technique is limited for the determination of thorium in natural waters. 相似文献
1000.
Pérez Pavón JL Guerrero Peña A García Pinto C Moreno Cordero B 《Journal of chromatography. A》2004,1047(1):101-109
The direct coupling of a headspace sampler with a mass spectrometer is proposed as a screening tool for the rapid detection of soil pollution by hydrocarbons from petroleum and derivatives. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of the sample analysed. Suitable treatment of the signal by chemometric techniques allows unequivocal characterisation of the different types of sample. The use of fast gas chromatography with a mass spectrometer detector coupled to the headspace sampler allows identification of the major hydrocarbons present in the mineral and organic polluted samples, interpretation of the results obtained, and demonstrates the analytical potential of headspace-mass spectrometry coupling. 相似文献
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