Biomedical subjects

E Kenndler

Publications and source records attributed to E Kenndler.

47 records · Page 3Linked to original sources

PubMed1995

Dynamics of peak dispersion in capillary zone electrophoresis including wall adsorption I. Theoretical model and results of simulation.

A mathematical model is described for the simulation of peak profiles in capillary zone electrophoresis taking wall adsorption into account. It is based on such physico-chemical relations as mass balance equations, sorption rate equations and appropriate boundary conditions. The numerical solution of the model is carried out, allowing the depiction of the concentration profile of the sample in the capillary as a result of the dynamics of the processes involved, which depend on a number of input parameters: rate constants, adsorption isotherms, column dimensions, field strength etc. Four cases are discussed in detail, namely those with either slow or fast adsorption kinetics and linear or nonlinear isotherms.

Adsorption↗

PubMed1995

Dynamics of peak dispersion in capillary zone electrophoresis including wall adsorption: II. Exact analysis of unsteady linear adsorptive dispersion.

An exact analysis of the unsteady axial dispersion of an analyte, undergoing a linear adsorption at the column wall in capillary zone electrophoresis, is presented. A system of partial differential equations--in which the radial coordinate is one of the independent variables--is taken as a model for linear wall adsorption. It is shown that the dispersion is a sum of two terms, one which depends linearly on time and whose exact form is generally known, and a non-linear one. The most interesting result of this work is that it derives another system of differential equations, which this nonlinear term is to satisfy. It makes it possible to present a closed formula for the asymptotic value of the nonlinear term, i.e., its limit for large time. Its behavior for times close to zero is also studied.

Adsorption↗

PubMed1994

Time course of formation of inositol phosphates during enzymatic hydrolysis of phytic acid (myo-inositol hexaphosphoric acid) by phytase determined by capillary isotachophoresis.

Capillary isotachophoresis with conductivity detection was applied to the investigation of the hydrolytic decomposition of phytic acid (myo-inositol hexaphosphoric acid) by phytase, and for the formation of the reaction products as a function of time. The quantitation of all analytes (besides phytic acid the mono- to penta-phosphorylated inositols and orthophosphate) can be carried out using two different buffer systems.

6-Phytase↗

PubMed1994

Improved separation of diastereomeric derivatives of enantiomers by a physical network of linear polyvinylpyrrolidone applied as pseudophase in capillary zone electrophoresis.

Diastereomeric analytes were separated using capillary zone electrophoresis with polyvinylpyrrolidone as polymeric additive to the buffer solution. As test substances derivatives of D- and L- alpha-amino and alpha-hydroxy acids formed by reaction with (+)-O,O'-diacetyl- and (+)-O,O'-dibenzoyl-L-tartaric anhydride, respectively, were used. The physical network formed by the linear polymer is supposed to act as a kind of pseudophase. It was found that the network affects the mobility of diastereomeric compounds to a different extent, enhancing the selectivity of the system. In nearly all cases of aromatic acids the diastereomer carrying the D-amino acid was more strongly retained than the L-isomer, as opposed to the situation with aliphatic acids.

Amino Acids↗

PubMed1993

Determination of ionic species formed during growth of Escherichia coli by capillary isotachophoresis.

The ionic species that are formed during the microbial growth of Escherichia coli were determined by capillary isotachophoresis as a function of the time of cultivation. This formation was indicated by the change in a sum parameter, the impedance of the nutrient broth, measured by a special electrode system. Based on the determination of the individual ions formed under the given conditions (identified as acetate, lactate, alpha-ketoglutarate, fumarate, ammonium and probably a simple amine), the change in conductivity was calculated and compared with that obtained by the impedance measurement of the bulk medium. From the results it can be concluded that the change in the sum parameter as a function of time is originated by the ions determined.

Electric Impedance↗

PubMed1979

Quantitation of the information content of multi-dimensional gas chromatography and low-resolution mass spectrometry in the identification of doping drugs.

On the basis of information theory, a comparison of the performance of the identification of compounds by multi-dimensional gas chromatography and binary-encoded low-resolution mass spectrometry is made for doping drugs. This group of compounds was not selected at random but according to their pharmocological effects. For these compounds it was observed that the m/e values of the peaks in the mass spectra are highly correlated, while a number of chromatographic columns can be found on which the retention data are only slightly correlated. As a result, the information content of two-dimensional gas chromatographic retention data on such columns equals the information content of binary-encoded low-resolution mass spectra. It is shown that the accuracy and precision of retention data in gas--liquid chromatography, and therefore the information content, can be significantly improved if the data are corrected for adsorption effects of the solid support and extrapolated to a limiting value in the case of asymmetric peaks.

Central Nervous System Stimulants↗

PubMed1978

[A method for differentiating between vinegar produced by fermentation and vinegar made from synthetic acetic acid based on the determination of the specific 3H-radioactivity (author's transl)].

The applicability of the specific 3H-radioactivity for the distinction of synthetic and biogenic vinegar was tested. The acetic acid was isolated from the vinegar as calcium acetate, and the calcium acetate was combusted at 830 degrees C to CO2 and H2O. The water was measured either after two destillation steps by liquid scintillation counting or after reduction to hydrogen and reaction to ethane in a gas proportional counter. The difference in the 3H-content between the two types of vinegar in Austria is about 80--100 T.U. Since the level of activity is subject to appreciable annual fluctuations a series of synthetic and biogenic comparison samples always has to be included.

Acetates↗

PubMed1977

[A contribution to the distinction of biogenic vinegar and vinegar made from synthetic acetic acid by determining the specific 14C-radioactivity (author's transl)].

The method of Simon et al. [2] for the separation of the acetic acid from vinegar prior to the determination of the specific 14C-radioactivity has been modified. The precipitation as calcium acetate and the preparation of free acetic acid by addition of diphosphoric acid has been replaced by an extraction procedure with diisopropylether which is faster and cheaper. On the Austrian market glacial acetic acid (Merck, p.A.) having the natural spezific 14C-radioactitivity was found. The natural specific 14C-radioactivity is therfore necessary but not sufficient to prove the biogenic origin of vinegar.

Acetates↗

PubMedDate not supplied

Determination of 1,2,4-trimethylbenzene (pseudocumene) in serum of a person exposed to liquid scintillation counting solutions by GC/MS.

1,2,4-Trimethylbenzene (pseudocumene) is often used as the solvent for liquid scintillation counting solutions. In the present work, the determination of 1,2,4-trimethylbenzene in the serum of a person exposed to the solvent vapor during the handling of liquid scintillation counting cocktails is described. The identification of 1,2,4-trimethylbenzene was carried out by GC/MS. The analyte was quantified by GC with flame ionization detection. The detection limit of the method is 0.01 ppm. Two hours after exposure of a person to the solvent vapor, the concentration of 1,2,4-trimethylbenzene in her serum was found to be 0.20 ppm.

Benzene Derivatives↗

PubMedDate not supplied

Capillary electrophoresis in mixed aqueous-organic solvents: effect of aprotic dipolar N,N-dimethylformamide and N,N-dimethylacetamide on acidity constants of substituted aromatic acids.

The change in the pKa values of substituted benzoic acids in binary mixtures of water with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA), respectively, was determined up to a concentration of 80% (vol/vol) organic cosolvent. Such solvents are applied as media of the background electrolyte in capillary electrophoresis, with the intention of increasing the analyte solubility and the separation selectivity. The pKa values increase nonlinearly with increasing DMF and DMA concentration, and reach values between 2.5 and 3.7 pK units higher than in water at 80% organic solvent content. This change is discussed based on the concept of the medium effect, taking into account the particular stabilization of the species involved in the protolysis equilibria of the acids: HA, A-, and H+, in the different solvents. The contribution of the medium effect of the individual neutral acid HA on the delta pKa values is determined by solubility measurements. The increase in the delta pKa values, averaged for all five acids investigated, is compared in different mixed aqueous-organic media, consisting of methanol, ethanol, 1-propanol, acetonitrile, DMF, and DMA, respectively. The comparison is based on the third-order polynomial fit of the delta pKa versus organic solvent concentration data. It is found that, in this respect, acetonitrile resembles the lower alcohols, and is dissimilar to the other dipolar, aprotic solvents, DMF and DMA. The similarity of the solvent systems is depicted by cluster analysis.

Acetamides↗

PubMedDate not supplied

Effect of electroosmotic flow on selectivity, efficiency, and resolution in capillary zone electrophoresis expressed by the dimensionless reduced mobility.

A dimensionless number, the reduced mobility, mu i, of separand, i, defined by mu i = ueff,i/(Ueff,i + Ueo) (with the specific effective mobility, Ueff,i, and the unspecific electroosmotic mobility, Ueo), permits expressing the effect of the electroosmotic flow (EOF) in capillary zone electrophoresis (CZE) on all relevant separation parameters, such as selectivity, efficiency, and resolution. A detailed discussion is given for the extent of the effect of the EOF on both cations and anions. The gain and loss of separation performance by application of an EOF is described quantitatively by expressions consisting solely of the reduced mobility.

Anions↗