Specific rotation measurements from peak height data, with a Gaussian peak model

A method is described whereby a sensitive laser-based polarimeter can be used to make very accurate and precise specific rotation measurements on microgram quantities of optically active materials. Flow-injection or liquid chromatography systems provide reproducible introduction of the sample into the polarimetric system. If a Gaussian distribution of the analyte concentration is assumed, the peak height can be used in the determination of specific rotation. This method provides a direct calibration with an absolute standard which yields more accurate and precise results than those obtainable by using peak area.     

Über die verteilung von metall-8-oxychinolinverbin-dungen zwischen wasser und organischen lösungsmitteln : Mitt. untersuchungen über 8-oxychinolin und scandium-oxinat im system wasser-benzol1

The distribution of 8-hydroxyquinoline and scandium oxinate between water and benzene as a function of the pH of the aqueous phase has been studied. The distribution coefficient and the dissociation constants of the oxine are calculated from its distribution curve.Scandium oxinate is quantitatively extractable in the pu range 9.7 – 10.5 if at least 20 molecules of oxine per 1 atom scandium are used. In the presence of smaller quantities of oxine hydrolysis of tile scandium oxinate occurs on shaking. Directions arc given for the photometric determination of small quantities of scandium.     

Contribution au microdosage titrimétrique de l'iode organique

Simultaneous microdetermination of carbon, hdrogen and iodine in organic substances is practically possible on a five milligramme sample. The two first mentioned elements are gravimetrically deetermined, iodine being titrated. The available results are quite good.New calibration technique of capillary instruments enables precise titration of very small quantities of Iodine. It will help to improve precision of this determination.     

Precise titrimetric determination of uranium in high-purity uranium compounds

A procedure has been developed for the very precise determination of uranium in high-purity uranium compounds. Uranium(VI) is reduced in a strong hydrochloric acid solution with aluminium in the presence of cadmium ions to uranium(III). It is oxidised to uranium(IV) in the presence of excess orthophosphoric acid and then quantitatively oxidised to uranium(VI) with potassium dichromate using a potentiometric end-point detection. The coefficient of variation based on 20 analyses is -/+ 0.003%.     

Die erlangungsfähigkeit des gleichgewichtes in systemen,die aus flüssigkeit und wenigstens aus einer festen phase gebildet sind

The difficulties associated with the precise determination of the freezing temperature of different systems containing one, two, or several solid phases are discussed. The “thermal sensitivity test” is suggested for testing whether the precision with which the thermodynamic liquid-solid phase equilibrium, is restored is quite satisfactory.The static method makes it possible to introduce or to remove very small quantities of heat and to observe whether or not the restoration of the phase equilibrium takes place. If a kinetic method is applied, the “thermal sensitivity” of the system may be tested by comparing the solidification and the melting curves determined at different crystallization or melting velocities.     

Determination of aprotinin by titration with bovine trypsin with end-point detection by high-performance liquid chromatography

A method for the determination of aprotinin (bovine pancreatic trypsin inhibitor, BPTI) is described. The procedure involves the formation of the BPTI-trypsin complex in the presence of an excess of BPTI, quantitative separation of the residual BPTI from the mixture by affinity chromatography and identification and evaluation of the residual BPTI by reversed-phase high-performance liquid chromatography. The method is precise with a mean coefficient of variation of 4.0 and 4.3% for intra- and inter-assay runs, respectively, and has a limit of determination of 3.0 micrograms of aprotinin. The proposed method can be applied to commercial samples, even in very dilute solutions, for the standardisation of aprotinin.     

Morphological analysis of polymer systems with broad particle size distribution

This contribution is focused on precise determination of particle size distribution in polymer blends with complex morphology by means of our new program called MDISTR. Standard determination of the particle size distribution is usually achieved by measurement of particle sizes in (a single set of) electron micrographs. We show why this method fails for two frequent cases: (i) blends with very broad particle size distribution and (ii) blends that are composed of domains with different particle sizes. On real-life examples, we demonstrate that program MDISTR yields accurate particle size distributions in both the above-mentioned cases, while the standard image analysis gives average particle sizes differing by >100 % from the correct result. We describe MDISTR calculations which are based on a linear combination of standard particle size distributions from two (or more) sets of micrographs with different magnifications, different locations within the sample and precisely defined statistical weights.     

Precise determination of uranium in pure uranium and uranium compounds by constant-current coulomeric titration

A procedure is described for very precise determination of uranium in high-purity uranium and uranium compounds. Uranium(VI) is reduced in a concentrated hydrochloric acid solution by metallic aluminium in the presence of cadmium ions to uranium(III). This is oxidized to uranium(IV) by protons on addition of an excess of orthophosphoric acid, and then oxidized to uranium(VI) by adding a weighed quantity of potassium dichromate in small excess. The excess of potassium dichromate is determined by constant-current coulometry. The coefficient of variation does not exceed 0.003%.     

Sorption of radiocesium on soils in the presence of electrolytes

The influence of background electrolytes (KCl, NH₄Cl, CTABr) in different concentrations on the sorption ability of radiocesium by measuring the distribution coefficient has been studied. Sorption isotherms of cesium for characterization of soil sorption ability were used. Sorption of cesium depends on its concentration and at least three different sorption sites are active in the sorption process. In the case of low cesium concentration, two very selective sites with high distribution coefficients are responsible for the sorption. With increasing cesium concentration in the aqueous phase, distribution coefficient is decreasing. Frayed edge sites of illite in soil and exchangeable potassium are probably responsible for nonlinear isotherms at low cesium concentrations. From sorption isotherms and determination of potassium by activation analysis, it was found that the capacity of very selective sites for different concentrations of background electrolyte was up to 7 mmol·kg^–1.     

流动注射免疫比浊法测定血清中免疫球蛋白A

基于可溶性抗原和抗体在液相中特异性结合,形成一定大小的抗原-抗体免疫复合物,使反应液出现浊度。采用流动注射光度分析法联用单片机,优化了实验条件;采用合并带技术节省试剂与试样,寻找到了抗原抗体反应的最佳浓度比与最佳反应时机,从而建立了流动注射免疫比浊测定人体血清免疫球蛋白A(IgA)的新方法。整个测试系统联用单片机,使测试过程实现程序操作。本法简便、快速,节省试剂和试样,进样频率高,每小时进样40次。     

Mechanical and electrochemical effects on surface convection and on emulsification new criteria

Theoretical and experimental studies of surface instability for charged and polarized interfaces between two immiscible liquids are reviewed. A linear analysis of stability shows the role of mechanical and electrochemical para meters for the onset of interfacial convection. Three cases are studied: 1) For the restored Boltzman distribution in bulk phases, the stability is only governed by the interfacial tension through the composition between mechano-chemicaland electrical contributions to the surface free energy; 2) for the non-restored Boltzman distribution, the stability is also governed by the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical and electrical quantities (dielectric constant-solute concentration-diffusion coefficient, potential drop); and 3) for concentrated charged and dipolar monolayers, the convection criteria of stability are directly related to the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical quantities (dielectric constant).Additional experiments on emilsification and demulsification were performed in order to verify this last theoretical prediction.     

Quantitative determination of cristobalite by thermal methods

Cristobalite was quantitatively determined by quartz samples fired between 1350 and 1490°C by thermal methods and specific gravity measurements. The amount of cristobalite was calculated from the thermal expansion coefficient, the area of the differential thermal expansion together with specific heat measurements and specific gravity determinations. The calculated values from the expansion coefficient and specific gravity are misleaing due to the presence of tridymite and glass in the samples. The results of differential thermal expansion compare well with those of specific heat measurements. Therefore, this method could be taken as a very precise measure for the quantitative determination of cristobalite. Also, the temperature of the peak indicates whether ordered or disordered cristobalite is present.     

Effet de la température,de la pression et de la composition sur l'intensité diffusée par un mélange de deux polymères

Phase diagrams of polymer blends and solutions are usually studied by measuring the scattered intensity (by light or neutrons) as a function of composition, temperature and pressure. If one expands Flory's χ parameter as a function of the composition, one sees that in order to have deviations from Flory's laws, thermodynamic quantities such as volume, heat capacity or compressibility should vary with respect to composition by a power law of degree larger than two. In some cases, the direct measurement of these quantities could lead to a more precise and rapid determination of the miscibility conditions.     

Analytical investigations on cephalosporins--IV: application of Ellman's reagent

The application of 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman's reagent) for the determination of microgram quantities of various selected cephalosporins in aqueous solution is described. Cephalosporin derivatives (cephalothin sodium, cephacetrile sodium, cefamandole lithium and nafate, cefoperazone sodium and ceftizoxime sodium) have to be treated with 0.5N sodium hydroxide before determination with Ellman's reagent, which reacts with free thiol groups. An aliquot of the solution is reacted with Ellman's reagent in pH 7.2 phosphate buffer and the absorbance of the resulting yellow solution is measured at 410 nm. The method, which is simple and precise, has been applied to determination of those cephalosporins in formulations, the results being compared with those obtained by the Ni-hydroxylamine method.     

A very precise high-performance liquid chromatographic procedure for the determination of cefmenoxime, a new cephalosporin antibiotic, in plasma

A simple and very precise high-performance liquid chromatographic procedure has been developed for the determination of cefmenoxime, a new broad spectrum cephalosporin antibiotic, in plasma. The workup procedure involves ultrafiltration of samples which have been treated with sodium dodecyl sulfate to displace the drug from its binding sites on plasma proteins. The ultrafiltrates are then directly injected into a high-performance liquid chromatographic system utilizing a reversed-phase analytical column, and an ultraviolet spectrophotometric detector. The mean assay coefficient of variation over a concentration range of 0.5-200 micrograms/ml is slightly greater than 1% when either p-nitrobenzoic or p-anisic acid is used as the internal standard. Recoveries of drug are essentially quantitative at all levels investigated; hence the calibration curves are rectilinear from the limit of quantification (about 0.05 microgram/ml) to at least 200 micrograms/ml.     

Polymerization and reptation,an analytical treatment

Free-radical polymerization without crosslinking is considered. By taking the chain length as a continuous variable the reaction kinetics is treated in a simple way for the stationary state. Equations for instantaneous average degrees of polymerization and related quantities are generalized to allow for chain-length dependence of the termination rate constant. For the Ito model, which treats reptation-controlled termination, approximate versions of these equations are derived in the limits of low and high conversion. The observed structure in the peak of the gel permeation chromatograms is shown not to be related to the bimodality in the instantaneous molecular weight distribution. None of the results is very sensitive to the precise reptation behavior.     

Exact distribution functions in two-dimensional lattice polymers. Comparison with maximum entropy distributions

Toeplitz matrices are used to calculate the complete distribution functions for such quantities as the fraction of a particular conformational state and the end-to-end distance in 2-dimensional lattice polymer models with a finite range of intrachain correlation. These are compared with approximate distribution functions obtained using the maximum entropy principle. The two-parameter maximum entropy distribution (giving the exact first and second moments) in most cases gives a good approximation to the exact distribution and always gives a better approximation than a simple Gaussian approximation. We illustratesome extreme forms of the distribution functions when the intrachain interactions are either very attractive or very repulsive.     

Sensitive kinetic-spectrophotometric determination of iodate in iodized table salt based on its accelerating effect on the reaction of bromate with chloride ion in the presence of hydrazine.

A simple, precise, sensitive and accurate method was developed for rapid determination of trace quantities of iodate. The method is based on the accelerating effect of iodate on the reaction of bromate and chloride acid in the presence of hydrazine in acidic media. The decolorization of Methyl Orange with the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. Iodate could be determined in the concentration ranges of 0.03 - 1.2 microg ml(-1). The relative standard deviation for ten replicate determinations of 0.3 microg ml(-1) of iodate was 1.65%. The proposed method was applied to the determination of iodate in table salts with satisfactory results.     

Rapid gas analyses for the investigation of spontaneous combustion using capillary gas chromatography

A simple and fast but sensitive and precise gas chromatographic method is described for the quantitative determination of O(2), N(2), CO, CO(2), C1 and C2-hydrocarbons for coal research. Gas analyses are necessary to obtain parameters for modelling spontaneous combustion and to predict long term coal behaviour. The method is based on a single PLOT-type capillary column in a single channel gas chromatograph. Using a micro-volume TCD coupled in series with a FID detector containing a capillary methanizer it is possible to determine high and trace level gases simultaneously. Trace quantities of CO and CO(2) can be determined with a single analysis and the detection limits are improved significantly using the capillary methanizer. The detection limit of the described method is approximately ten parts per million CO(2) and one part per million CO. Using the same instrument configuration the O(2)/N(2) ratios (major components), as parameter for coal reactivity, are also determined. The proposed approach is restricted to the determination of gases evolved during coal studies and the application to other gas mixtures is not considered.     

Bestimmung sehr kleiner mengen kohlendioxyds und die analytische anwendung des verfahrens

A volumetric method for the determination of very small quantities carbon dioxide is described. The procedure gives very satisfactory results and can be applied for the determination, of carbon in organic compounds.