Chiral analysis of UV nonabsorbing compounds by capillary electrophoresis using macrocyclic antibiotics: 1. Separation of aspartic and glutamic acid enantiomers.

Glycopeptide antibiotics, namely vancomycin or teicoplanin, were evaluated in capillary electrophoresis for the analysis of UV nonabsorbing compounds such as aspartic and glutamic acid enantiomers. Electrophoretic runs were performed in laboratory-made polyacrylamide-coated capillaries using the partial filling-counter current method in order to avoid the presence on the detector path of the absorbing chiral selector. The background electrolyte consisted of an aqueous or aqueous-organic buffer in the pH range of 4.5-6.5 of sorbic acid/histidine and the appropriate concentration of chiral selector. Several experimental parameters such as antibiotic concentration and type, buffer pH, organic modifier, type and concentration of absorbing co-ion (for the indirect UV detection) were studied in order to find the optimum conditions for the chiral resolution of the two underivatized amino acids in their enantiomers. Among the two investigated chiral selectors, vancomycin resulted to be the most useful chiral selector allowing relatively high chiral resolution of the studied compounds even at low concentration. The optimized method (10 mM sorbic acid/histidine, pH 5, and 10 mM of vancomycin) was used for the analysis of real samples such as teeth dentine and beer.

Capillary electrophoresis of methylderivatives of quinolines. I.

Migration behavior of quinoline, isoquinoline and related methylderivatives has been investigated with respect to the influence of running buffer acidity and to the presence of polyethylene glycol (PEG) 2000 as additive. Dissociation constants and ionic mobilities were determined by capillary electrophoresis (CE). Mobility and viscosity measurements in PEG containing buffers show that analyte transport is not in accordance with Walden's rule and microviscosity plays the role in analyte retardation. Variation of pH and PEG concentration provides the optimal conditions for the CE separation of methylquinolines (0.0176 M acetate-Tris buffer, pH 5.5, 10% PEG 2000). Analysis of industrial mixture (isoquinoline fraction from distillation of coal tar) was performed and good agreement with gas chromatographic results was found.

Determination of dissociation constants of cytokinins by capillary zone electrophoresis.

A method for the pKa determination, based on mobility data measured by capillary zone electrophoresis, was applied to cytokinins and their analogs. The combination of charged mobility standards with an uncharged electroosmosis marker, injected in the uncoated capillary simultaneously with the measured substances, allows one to minimize the number of runs, reduce their duration and, in addition, to inform on the run-to-run stability of electroosmosis and on contingent side-effects. pKa values of investigated cytokinins and their analogs ranged from 2.8 to 4.0 at 25 degrees C in the phosphate and acetate buffers of ionic strength 0.015 M. Standard deviations of the constants, obtained by the non-linear fitting of equations for the pKa calculation, were 3-5-times lower than standard deviations from the linear fitting or from the point-to-point calculation utilizing the Hendersson-Haselbalch equation. The equation of Boltzman sigmoid offers two checks on reliability of effective mobilities that serve as the raw data in the pKa calculation.

Methamphetamine--properties and analytical methods of enantiomer determination.

Methamphetamine is one of the most frequently abused drugs of today. Due to its stereogenic center, it can exist as single enantiomer. Like many other chiral compounds, methamamphetamine enantiomers exhibit different pharmacological effects on living organisms. For this reason, it is necessary to develop enantioselective and sufficiently sensitive methods of determination. This review focuses on methamphetamine with an accent on analytical chemistry and especially on chiral separations of this toxicologically important compound.

Capillary electrophoretic enantioseparation of selegiline, methamphetamine and ephedrine using a neutral beta-cyclodextrin epichlorhydrin polymer.

This paper describes the development of a capillary zone electrophoretic method for chiral separation of three basic compounds of the selegiline synthetic pathway: ephedrine, methamphetamine and selegiline. The method developed allows one to separate the studied compounds in one run using a neutral beta-cyclodextrin epichlorhydrin polymer. The effect of various experimental parameters, such as chiral selector concentration, concentration and composition of background electrolyte, pH, temperature, and the addition of some organic solvents, on the resolution and migration time is discussed. For selegiline and methamphetamine, it is possible, under optimal conditions, to quantify less than 0.5% of the minor isomer in an excess of the major one.

Step change of counterion--a new option in capillary zone electrophoresis.

In contrast to common capillary zone electrophoresis, with a constant composition of the background electrolyte, a new method is described, based on a change of the ionic matrix composition during the migration of the sample components. The proposed method expands the scale of pK's of analyzed compounds in a single run and affords new potential for optimizing the separation. The step change of the ionic matrix composition was achieved by displacing the primary matrix by the modified ionic matrix (electrolyte) which migrated against the movement of the sample components. The separation thus proceeded in the primary ionic matrix (electrolyte) while the detection was performed in the modified matrix with resultant shortening of the analysis time and convenient quantitation. A model mixture of five compounds, with a difference of four units in pK could be well resolved.

Study of alkaline hydrolysis of the insecticide alphamethrine by isotachophoretic determination of decomposition products.

Alkaline hydrolysis of the pyrethroid insecticide alphamethrine has been studied. After hydrolytic cleavage at various temperatures and pH values, the degradation products, phenoxybenzoic acid and the dichloro derivative of chrysanthemic acid, were identified and determined by means of capillary isotachophoresis. Rate constants, activation energies and the reaction enthalpy and entropy were calculated.

The use of a bivalent counter anion to control the effective mobility of the hydrogen ion constituent in cationic isotachophoresis.

The use of a bivalent counter anion for cationic isotachophoresis was studied both theoretically and experimentally. A mathematical model was proposed and solved to give the effective mobility of the hydrogen ion constituent, uH,H, in the respective electrolyte systems. The theoretical values agreed well with the experimental data in a series of electrolyte systems. The dependence of uH,H on such parameters as pH of the leading electrolyte, ionic mobilities of leading and counter ions, and dissociation constants was calculated and discussed. A bivalent counter anion will prove useful for the separation of low mobility cations and weak bases, as shown for the separation of substituted anilines in a succinate electrolyte system.

Determination of trimecaine metabolites in blood plasma by capillary isotachophoresis.

A method is proposed for the determination of trimecaine (diethylglycylmesidide) and its de-ethylated metabolites (monoethylglycylmesidide and glycylmesidide) in blood plasma by capillary isotachophoresis. The deproteinated plasma is extracted into chloroform after alkalinization and the total solids in the organic layer are dissolved in acidified 25% 2-propanol. Subsequent isotachophoretic analysis is performed in an operational system consisting of potassium acetate buffer (pH 4.75) as the leading and beta-alanine as the terminating electrolyte. The order of the zones corresponds to the molecular weights of the separated compounds. The recovery of all substances of interest is 55% and the limit of determination is 0.05 micrograms of each substance in 1 ml of plasma.