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71.
72.
A weak anion-exchange type chiral stationary phase (CSP) based on tert.-butylcarbamoylquinine as chiral selector and silica as chromatographic support was applied to non-aqueous capillary electrochromatography. The mobile phases used consisted of acetonitrile and methanol as organic solvents, and acetic acid and triethylamine were added as background electrolytes. The influence of several experimental parameters (electrolyte concentration, acetic acid-triethylamine ratio, acetonitrile-methanol ratio and temperature) was evaluated in order to obtain improved enantioselectivity and efficiency as well as short run times for the enantiomeric separation of negatively charged chiral analytes including benzyloxycarbonyl, N-(3,5-dinitrobenzyloxycarbonyl, 9-fluorenylmethoxycarbonyl, benzoyl, acetyl and N-(2,4-dinitrophenyl) derivatized amino acids and profens. Solvent composition of acetonitrile-methanol (80:20) and enhanced electrolyte concentrations up to 600 mM acetic acid at a constant acid-base ratio of 100:1 with high applied voltages of -25 kV proved to be optimum regarding short retention times and improved efficiencies. For example, the enantiomers of Fmoc-Leu could be separated in less than 10 min with a resolution factor of 6.9 and about 100000 theoretical plates per meter. 相似文献
73.
A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are252Cf and224Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:224Ra with ethyl radicals, and252Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas. 相似文献
74.
While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post
heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates
during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids
are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the
lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined
the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation
as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content)
of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture,
thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated
in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration
of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak
was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature
was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature
of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose. 相似文献
75.
Helvi Hödrejärv 《Analytical and bioanalytical chemistry》1997,357(2):191-196
The history of analytical chemistry, started in 1802, can be divided into different periods: 1802–1892 the Baltic German period in Universitas Dorpatensis, 1892–1917 the period of russification in the University, 1918–1939 the independent Estonian University of Tartu and opening of the chair of inorganic and analytical chemistry at Tallinn Technical University, 1940–1944 loss of independence and years of war, 1945–1991 the years in the Soviet Union, 1991-up to now the re-establishment of independence. The first chemical laboratory was founded at Universitas Dorpatensis by Prof. Ph. Arzt in 1802. The first practice in analytical chemistry was opened in 1847 by Prof. C. Göbel. The chair of chemistry was separated from pharmacy in 1850. A separate chair of analytical chemistry was opened at Tartu University in 1947. 相似文献
76.
Several attempts to produce conducting polymer based all-solid-state reference electrodes are presented. Open circuit potential of conducting polymers is redox sensitive and Donan equilibrium dependent. Therefore, more sophisticated constructions are necessary. Most promising were bilayers composed of conducting polymers with different ion-exchanger properties. 相似文献
77.
Zusammenfassung Die Möglichkeit einer Verbesserung der Wasserlöslichkeit sowie der Löslichkeit in anderen Lösungsmitteln von Medikamenten durch Verwendung metastabiler (instabiler) Modifikationen wurde aufgezeigt. Bei Sulfathiazol und Tromexan liegt die relative Zunahme der Wasser-Löslichkeit der metastabilen Modifikation gegenüber der stabilen Modifikation in Abhängigkeit vom pH zwischen 72 und 80%, bei Sulfuno ist der Effekt geringer, er liegt zwischen 8,4 und 15,2%. DiepK
s
- Werte der beiden Modifikationen sind sowohl für Sulfathiazol als auch für Sulfuno innerhalb der Fehlergrenze identisch. Für Sulfathiazol wurde die Löslichkeitskurve der beiden Modifikationen in Wasser und Isopropanol bestimmt.
Summary The possibility was shown of improving the water-solubility as well as the solubility in other solvents of medicaments through employment of metastable (unstable) modifications. In the case of sulfathiazole and also of tromexan the relative increase of the water-solubility of the metastable modification as compared with the stable modification is between 72 and 80% depending on the pH the effect is less for sulfuno where it lies between 8.4 and 15.2%. ThepK s values of the two modifications are identical both for sulfathiazole as for sulfuno, within the limits of error. The solubility curve of sulfathiazole was determined for both modifications in water and in isopropanol.
Résumé On présente la possibilité d'améliorer la solubilité de médicaments dans l'eau ainsi que dans d'autres solvants, par emploi de modifications métastables (instables). Dans le cas du sulfathiazole et du «Tromexan», l'augmentation relative de la solubilité dans l'eau de la modification métastable par rapport à celle qui est stable est fonction du pH entre 72 et 80%, pour le «Sulfuno» l'effet est moindre, entre 8,4 et 15,2%. Les valeurs dupK s des deux modifications sont identiques tant pour le sulfathiazole que pour le «Sulfuno» dans les limites d'erreurs. La courbe de solubilité des deux modifications a été déterminée pour le sulfathiazole dans l'eau et dans l'isopropanol.相似文献
78.
Johannes Häusler 《Monatshefte für Chemie / Chemical Monthly》1982,113(10):1213-1216
Meldrum's acid (2) is acylated by diketen affording the acylMeldrum's acid3. In aqueous bicarbonate its 3-oxogroup is selectively reduced by sodium tetrahydroborate giving the alcohol4, which readily undergoes cyclization in refluxing dioxane leading to the title pyrone7. Under identical conditions3 produces the pyrone6 with the pyrone carboxylic acid5 as intermediate. 相似文献
79.
The hydrogen peroxide is oxidized at + 1.5 V vs. SCE at a glassy carbon electrode of the wall-jet type. The samples are diluted about 100 times in a dispersion coil before entering the amperometric detector. The calibration curve is linear from 10?4 to 1 M H2O2, when 5-μl samples are used. With 50-μl samples the detection limit decreases to 10?6 M H2O2. Neither metal ions (Cu2+, Zn2+, Ni2+, Al3+) up to 0.5 M nor changes in the sulfuric acid concentration of the samples between 0.1 and 1 M interfere with the hydrogen peroxide determination. About 75 samples can be analyzed per hour. 相似文献
80.
W. Sänger 《Zeitschrift für Physik B Condensed Matter》1984,55(1):13-16
The isothermal magnetic susceptibility (x) of the completely miscible liquid Pd1–x
Si
x
alloy system shows a rapid monotonous decrease withx from strong paramagnetism to weaklyx-dependent diamagnetism. The measured susceptibility isotherm at 1825 K is analysed within 0x1 by using a semiphenomenological method of decomposing the magnetic susceptibility into its constituent parts. Because of the empirical similarity between liquid and glassy metals this interpretation also provides assertions about the magnetism of glassy Pd1–x
Si
x
aroundx=0.2. 相似文献