Biomedical subjects

E Kenndler

Publications and source records attributed to E Kenndler.

At least 37 records · Page 2Linked to original sources

PubMed2000

Recent innovation in capillary electrokinetic chromatography with replaceable charged pseudostationary phases or additives.

Recent developments of separation of neutral analytes in capillary systems with the mobile phase driven by the electroosmotic flow (EOF) and charged additives acting as a pseudostationary phase are reviewed. As pseudostationary phases a number of additives are used. Soluble polymers, either anionic or cationic, were applied as alternatives to micelles. Monomeric charged additives are also intended to form associates with the analytes, leading to selective retention and separation in a similar way as the polymeric pseudostationary phases. Dendrimers, spherical macromolecules with highly branched chains and charged terminal groups, are successfully applied for the separation of lipophilic analytes. Polymers with covalently stabilized structures are introduced in the form of permanent micelles and are therefore insensitive to the mobile phase composition, enlarging the applicability of micellar electrokinetic capillary chromatography (MEKC).

Chemistry, Organic↗

PubMed2000

Dispersive phenomena in electromigration separation methods.

A review on dispersive effects and on peak broadening in electromigration separation methods (capillary electrophoresis and electrochromatography) is presented, mainly covering papers published between the beginning of 1997 and the beginning of 2000. Most attention is drawn to work dealing with nonlinear effects that cause anomalous electromigration dispersion in electrolyte systems with two or multiple coions. Further, topics cover the comparison of electroosmotic and pressure-driven modes in electrochromatography, dispersive effects due to nonhomogeneous velocity fields in packed electrochromatography columns, to nonuniform electroosmotic flow, to sorption of analytes (mainly proteins) at the column wall or the stationary phase, and due to the influence of the nonideal column geometry like coiling or irregularities in shape.

Adsorption↗

PubMed2000

Quantitation of olanzapine in tablets by HPLC, CZE, derivative spectrometry and linear voltammetry.

Four analytical methods have been developed for the quality control of pharmaceutical formulations containing the novel antipsychotic drug, olanzapine: high performance liquid chromatography (HPLC), capillary zone electrophoresis (CZE), derivative spectrometry and linear voltammetry. All methods require only a simple extraction procedure of olanzapine from the tablets before analysis. HPLC with ultraviolet detection at 260 nm is carried out with a C8 column and a mobile phase constituted of acetonitrile and aqueous tetramethylammonium perchlorate. CZE is performed in an uncoated capillary with phosphate buffer, pH 3.0, as the background electrolyte, with UV detection at 214 nm. Spectrophotometry uses the derivative of the spectrum at 298 nm. In linear voltammetric method (LSV) the current intensity of the oxidation wave at +495 mV is measured. All methods gave similar results in terms of precision and accuracy. For HPLC and CZE, repeatability and intermediate precision, expressed by the RSD was better than 1.8%. The accuracy, resulting from recovery experiments, was between 99.9 and 101.1%. Spectrometry and voltammetry gave slightly higher RSD values (up to 2.9%) and a larger variation of the accuracy (the recovery was between 97.8 and 102.6%). However, the requirements for quantitative analysis are fulfilled for all methods.

Antipsychotic Agents↗

PubMed1999

Separation and biospecific identification of subviral particles of human rhinovirus serotype 2 by capillary zone electrophoresis.

During infection, human rhinoviruses undergo structural rearrangements of their capsid proteins from D-antigenic native virus (sedimenting at 150S upon sucrose density gradient centrifugation) to C-antigenic A-particles (sedimenting at 135S) and B-particles (sedimenting at 80S); the latter remain after release of the viral genomic RNA into the cytosol. Subviral particles with very similar properties can also be produced in vitro upon exposure to elevated temperatures or to low-pH buffers. This paper reports on the successful separation of native virus and 80S B-particles by capillary zone electrophoresis. Separation was carried out in an untreated fused-silica capillary (50 microns i.d., total length 50.0 cm, effective length 41.5 cm) at 20 degrees C and monitored with UV detection. The separation buffer was 100 mmol/L boric acid/borate (pH 8.3) and contained 0.5% sodium deoxycholate, 0.05% SDS, and 0.5% Triton X100R; the detergents were required to prevent viral aggregation and adsorption to the capillary wall. The analytes were identified from their characteristic spectra as determined by fast spectral scanning. Final confirmation was obtained by comparison of electropherograms from samples prior and after immunodeplition with antibodies specifically precipitating D- or C-antigen. The present method enables one to easily monitor and quantify these structural changes and thus to determine the most favorable conditions for complete conversion of native virus to 80S B-particles.

Buffers↗

PubMed1999

Separation of antipsychotic drugs (clozapine, loxapine) and their metabolites by capillary zone electrophoresis.

Two antipsychotic drugs (clozapine and loxapine) and six metabolites, N-demethylclozapine, clozapine N-oxide, N-demethylloxapine (amoxapine), 7-hydroxyloxapine, 8-hydroxyloxapine, 8-hydroxyamoxapine, were separated by capillary zone electrophoresis. Variation of pH and ionic strength of the acidic phosphate buffer (pH below 4) did not enable the separation of loxapine and one of its metabolites. Resolution of the single parent drugs and their metabolites was possible in background electrolytes (phosphate, pH 3.5, 60 mmol/l) containing either 0.2% (w/v) polyvinylpyrrolidone as replaceable pseudo-stationary phase, or 0.75 mmol/l beta-cyclodextrin added as complex-forming agent. Full separation of the mixture with baseline resolution of all analytes was obtained with a background electrolyte with heptakis-6-sulfato-beta-cyclodextrin added as negatively charged complexation agent with improved separation selectivity.

Antipsychotic Agents↗

PubMed1999

Capillary electrokinetic chromatography with polyethyleneimine as replaceable cationic pseudostationary phase. Influence of methanol and acetonitrile on separation selectivity.

The effect of methanol and acetonitrile, respectively, on the separation of neutral compounds (benzyl alcohol, phenols) is investigated in electrokinetic chromatographic (EKC) systems consisting of polyethyleneimine (PEI) as charged, polymeric, replaceable pseudostationary phase. The separation systems consist of a buffer solution (2-morpholinoethanesulfonic acid, pH 7.0, 20 mM) containing 0.3-0.9% (w/v) PEI as additive and a varying percentage of methanol (0-50%, v/v) or acetonitrile (0-30%, v/v). EKC is carried out in fused-silica capillaries [47.0 cm (effective length 40.3 cm) x 100 microns I.D.]. They are dynamically coated with PEI, resulting in an electroosmotic flow directed towards the anode. The neutral analytes are migrating with the electroosmotic flow, and are retarded by the electrically driven counterflow of PEI. Separation of the analytes follows in the sequence benzyl alcohol, phenol, resorcinol, pyrogallol, reflecting the increasing hydrogen bond acidity and polarity (polarizibility) of the solutes. However, addition of methanol or acetonitrile causes a drastic loss of resolution, whereby the relative retention of the separands (related to benzyl alcohol) indicates a decrease of retardation upon addition of the organic solvents.

Acetonitriles↗

PubMed1999

Separation of eleven central nervous system drugs by capillary zone electrophoresis.

Several strategies to improve the separation of 11 central nervous system drugs (antipsychotics and antidepressants) with capillary zone electrophoresis were applied: the variation of the pH of the buffering background electrolyte, its ionic strength, addition of inclusion-complex forming beta-cyclodextrin or polyvinylpyrrolidone (PVP), respectively, as a replaceable, soluble, polymeric pseudo-stationary phase. Best separation was achieved at pH 2.5 and 35 mmol/l ionic strength (phosphate buffer), with 0.5% (w/v) PVP.

Central Nervous System Agents↗

PubMed1999

Analysis of common cold virus (human rhinovirus serotype 2) by capillary zone electrophoresis: the problem of peak identification.

Different preparations of human rhinovirus serotype 2 (HRV2), a common cold virus, were analyzed by capillary zone electrophoresis (CZE) in untreated fused-silica capillaries using borate buffer (100 mmol/L, pH 8.3) and sodium dodecyl sulfate (10 mmol/L) as additive to prevent wall adsorption. The electropherograms showed one major peak at 205- and 254-nm detection wavelengths. The identity of the peak as originating from native virus was confirmed by several indirect methods. Heating to 56 degrees C is known to lead to release of the genomic RNA from the viral capsid; this treatment resulted in the disappearance of the major peak and the emergence of a new predominant peak that was identified as RNA by enzymatic digestion. As expected, RNase treatment of the unheated sample remained without effect as the viral genome is inaccessible in the native viral shell. A monoclonal, virus-aggregating antibody was used for immunodepletion of native virus; again, the major peak disappeared upon removal of viral aggregates by centrifugation prior to CZE analysis. In combination, these results allowed for the unambiguous identification of the main peak as native HRV2 and of the minor peaks as contaminants present in various amounts in the different viral preparations. It is demonstrated that CZE allows for an extremely easy and rapid assessment of conformational state and purity of virions in a given viral preparation.

Electrolytes↗

PubMed1999

Ionization constants of weak acids and bases in organic solvents.

A discussion of the influence of organic solvents on pKa values is presented. Enthalpy and entropy of ionization in organic solvents are compared with aqueous systems. The impact of the solvent on the ionization constants is interpreted based on the free energy of transfer applied to all particles involved in the ionization reaction of acids and bases, and the concept of the 'medium effect' on these species. The limitation of Born's approach (which takes into account only electrostatic effects on the ionization equilibrium) is demonstrated and the importance of solute-solvent interactions on the change of the pKa values emphasized.

Acids↗

PubMed1999

Capillary electrophoresis of small solutes in linear polymer solutions: relation between ionic mobility, diffusion coefficient and viscosity.

Electrophoretic mobilities, mu, and diffusion coefficients, D, of a small ion (molecular weight 579) were determined in dependence on the viscosity, eta, of aqueous buffer solutions containing ethylene glycol, or polyethylene glycol (PEG) with average molecular weights of 400, 20000, 100000 or 2000000, respectively, as additives. The values for mu and D are inversely proportional to the viscosity for the solutions with small-sized additives (ethylene glycol and PEG400), in accordance to Walden's rule. In contrast, for the longest polymers the mobilities and the diffusion coefficients approximate the values observed for pure water, and are nearly independent of the viscosity. This result agrees with the model of fractional free volume and the obstruction theory. For solutions with equal viscosity, three ranges can be differentiated for mu and D in relation to the size of the additive: for small additives, on the one hand, and the long-chained polymers, on the other hand, the values for mu and D are nearly independent of the size of the additive. In contrast, a pronounced increase of mu and D is found with increasing polymer size in the molecular weight range between 20000 and 100000. The ratio mu/D, occurring in a number of expressions for the plate height contributions, exhibits a remarkably small change over the entire polymer size and viscosity range (between 1 and 7 cP) under consideration. Consequently, the separation efficiency, expressed by the plate number, is found to be nearly constant, and is independent of viscosity.

Diffusion↗

PubMed1998

Separation of neutral compounds by capillary electrokinetic chromatography using polyethyleneimine as replaceable cationic pseudostationary phase.

Polyethyleneimine (PEI, molecular weight 6 x 10(5) - 1 x 10(6)) is applied as a positively charged pseudostationary phase for electrokinetic chromatography (EKC) of uncharged mono- and oligophenols. EKC is carried out in PEI-coated fused-silica capillaries (with electroosmotic flow directed towards the anode) in 2-(N-morpholino)ethanesulfonic acid (MES) buffer (pH 7.0, 20 mM) with PEI added to the solution in concentrations up to 0.70% w/v. The pseudostationary phase leads to a retardation of the solutes mainly according to the number (and the position) of the OH-groups of the separands, and is not influenced significantly by methyl groups. For 0.70% w/v PEI solution, for instance, the relative retention, rho, has values between 0.33 and 0.53. For the systems with the highest resolution of the separands (0.25-0.30% PEI) 190,000 plates per meter are observed. The results indicate that the separation selectivity is mainly caused by ion-dipole interactions between the OH-groups of the solutes and the pseudostationary phase.

Capillary Action↗

PubMed1997

Reduction of wall adsorption in capillary zone electrophoresis of a basic single-chain antibody fragment by a cationic polymeric buffer additive.

Reduction of adsorptive protein-wall interactions by poly(diallyldimethyl ammonium chloride), a permanently cationic polymer, at a concentration of 0.5% (w/v) is demonstrated for a basic single-chain antibody fragment (scFv, pI about 9.5) even in the range of physiological pH of around 7. The polymer additive forms a positively charged layer at the silica surface which reverses electroosmosis and leads to electrostatic repulsion of the positively charged basic protein.

Adsorption↗

PubMed1997

Trace determination of iron in water at the microgram/l level by on-line coupling of capillary isotachophoresis and capillary zone electrophoresis with UV detection of the EDTA-Fe (III) complex.

The determination of iron in water at the trace level by on-line coupled capillary isotachophoresis and capillary zone electrophoresis (CITP-CZE) with a commercial column coupling device is described. Iron is determined as the negatively charged complex with EDTA which is highly UV-absorbing and thus enables photometric detection at 254 nm. The analyses are performed using 10 mmol/l HCl + 20 mmol/l L-histidine + 0.1% hydroxypropylmethyl cellulose (pH 6.0), 5 mmol/l MES, and 25 mmol/l MES + 10 mmol/l bis-tris-propane (pH 6.6) which served as leading, terminating and background electrolyte, respectively. Samples are acidified with HNO3, diluted and EDTA added (to a final concentration of 10(-4) mol/l) prior to CITP-CZE analysis. The detection limit of Fe(III) is 10 micrograms/l, and is given by the chemical noise due to the impurities of the chemicals used enriched by the ITP preconcentration step. The precision of the CE measurement, expressed by the relative standard deviation, is about 3% (at the 400 micrograms/l level); the recovery is between 80 and 115% depending on the iron concentration level (40-400 micrograms/l).

Calibration↗

PubMed1997

Size-based separation of polyelectrolytes by capillary zone electrophoresis: migration regimes and selectivity of poly(styrenesulphonates) in solutions of derivatized cellulose.

The migration regimes and the separation selectivity of linear poly(styrenesulfonates) (PSS) were investigated in solutions of linear polymeric hydroxyethylcellulose (HEC). Variable parameters were the number of PSS monomer units (in the range of 25-6520), HEC concentration (below and above the entanglement threshold), molecular mass of HEC (between 35900 and 438000 Da) and electric field strength (from 190 to 1140 V/cm). Besides those regimes which are known for migration of polyelectrolytes in physical networks (Ogston sieving, reptation without and with orientation), the observed separation below the entanglement threshold indicates an effect of solute-chain interactions similar to that observed for the separation of double-stranded DNA. From the dependence of the separation selectivity on HEC concentration and molecular weight it was found that both parameters increase the separation. The selectivity of the solutions of higher concentrated low molecular HEC was compared to lower concentrated high molecular HEC, which has a similar bulk viscosity, and therefore obeys comparable peak dispersion due to thermal broadening. At high field strengths (preferably used in capillary electrophoresis) the former gave better separation only for shorter PSS molecules. For separation of longer PSS molecules, only high molecular HEC is applicable due to the deformation of the low molecular matrix by large analyte molecules.

Cellulose↗

PubMed1997

Chiral interactions in capillary zone electrophoresis: computer simulation and comparison with experiment.

Chiral interaction in capillary electrophoresis can be modeled using pK values, mobilities of analytes, and their formation constants with the chiral selector. An existing steady-state simulation program for CE (HPCESIM) was recently extended with a chiral submenu involving the chiral parameters listed above. These were experimentally determined in both our laboratories for mandelic acid and terbutaline using hydroxypropylated beta-cyclodextrin as chiral selector. A comparison was made between both sets of parameters and between experimental electropherograms and those obtained from simulation. Error analysis of the results indicate the sensitivity of the obtained results.

Computer Simulation↗

PubMed1997

Peak broadening in capillary zone electrophoresis.

A review on peak broadening in capillary zone electrophoresis in free solutions is given which covers a selection of the literature published on this topic over the period mainly between 1992 and the beginning of 1997 (consisting of 71 publications). The contributions to peak dispersion from extracolumn effects (e.g. due to the finite length of the injection zone, or the aperture of the detector), from longitudinal diffusion, Joule heating, electromigration dispersion (concentration overload), a different path length of the solute ions, wall adsorption, laminar flow and the (longitudinally) homogeneous or nonhomogeneous electroosmotic flow are described. The latter may also occur when a longitudinally nonhomogeneous radial electric field is applied. Peak dispersion is depicted either by the plate-height model, or the concentration of the solute as a function of space and time is calculated either analytically or numerically by solving the equation of continuity with appropriate initial and boundary conditions and possibly completed by equations governing further quantities.

Electrophoresis, Capillary↗

PubMed1996

Determination of the pI of human rhinovirus serotype 2 by capillary isoelectric focusing.

Capillary isoelectric focusing was applied to determine the pI value of human rhinovirus serotype 2 (HRV 2), a picornavirus of about 8,500,000 Da in size. Using fused silica capillaries dynamically coated with hydroxypropylmethyl cellulose (added at 0.08% to the catholyte), the virus zone failed to reach the steady state position in the pH gradient within times usually employed in focusing experiments, as the electroosmotic flow (EOF) pushed the analyte zone past the detector. Therefore, the residence time of the zones in the separation capillary was extended by applying hydrodynamic pressure at the detector side during focusing, thus pneumatically counteracting the EOF. After completion of focusing, the zones were mobilized by pressure maintaining the high voltage. For calibration of the pH gradient, low molecular mass pI marker substances were employed. Using the relation between the apparent pI value of the virus and the focusing time under counter pressure, the actual pI of HRV2 was determined as 6.8 by extrapolating to infinite time.

Electrophoresis, Capillary↗

PubMed1996

Influence of transference number on migration and deformation of concentration boundaries in capillary zone electrophoresis.

The change of the position and shape of a concentration boundary existing in the background electrolyte in capillary zone electrophoresis is treated theoretically. Such boundaries may occur when the ionic concentration, c, of the sample differs from that of the background electrolyte. Both mathematical treatment and numerical simulation lead to the result that when an (initially symmetrical) concentration boundary migrates in the capillary it becomes nonsymmetrical. The reason for this is the nonsymmetry of the function, which is obtained as the difference of the transference number (which is a function depending on c) and its linear approximation at the average value of the concentration. Numerical simulations for capillary zone electrophoresis with LiI or potassium benzorate as a hypothetical background electrolyte show the formation of asymmetrical plugs for samples of more diluted electrolyte solutions.

Computer Simulation↗