Dynamic computer simulations of the influence of injection conditions on capillary zone electrophoretic stacking of preparative free-flow zone electrophoresis fractions of peptides

Dynamic computer simulations were carried out to investigate the effect of residual acetic acid content on the initial stacking conditions of oligoglycine samples during the analytical CE run. These simulations were carried out with both individual peptides and with their equimolar mixtures. Results indicate that optimum acetic acid conditions were in the range of equimolar values

Discontinuities of pH at zone boundaries in isotachophoretic systems with poorly buffering leading electrolytes

Discontinuities of pH at zone boundaries of strong ion sample zones in isotachophoretic systems with poorly buffering leading electrolytes have been discovered by dynamic computer simulations of isotachophoretic separations with uncommon electrolyte systems. When using a salt solution containing a strong cation (anion) as leading ion and a weak anion (cation) as counterion for the isotachophoretic separation of strong cations (anions), severe pH discontinuities are present at zone boundaries of these cations (anions). The magnitude of these pH discontinuities has been investigated as a function of several parameters, namely counter ion/leading ion concentration ratio of the leading electrolyte, pK values, and mobilities of sample ions and counterion

Enantiomeric separation of mirtazapine and its metabolites by using nano-liquid chromatography

Mirtazapine (MIR) and two of its main metabolites, namely, 8-hydroxymirtazapine and N-desmethylmirtazapine, were separated in totheir enantiomers by nanoLC in a laboratory-made fused-silica capillary column (75 \ub5m ID) packed with a vancomycin modified silica stationary phase. The simultaneous separation of the three couples of the studied enantiomers was achieved in less than 33 min, using an experimentally optimized mobile phase delivered in the isocratic mode. Optimization of the mobile phase composition was achieved by testing the influence of the buffer pH and concentration, the water concentration, the organic modifier type and concentration, and on the retention and resolution of the analytes. The optimum mobile-phase composition contained 500 mM ammonium acetate pH 4.5/water/MeOH/MeCN, 1:14:40:45 v/v/v/v. Using a UV detector at 205 nm, the method was validated studying several experimental parameters such as LOD and LOQ, intraday and interday repeatability, and linearity. Good results were achieved: LOD and LOQ were in the range 5\u201315 and 10\u201340 \ub5g/mL, respectively (the highest value was obtained for the DEMIR enantiomers); correlation coefficients, 0.9993\u20130.9999; the intraday and interday precision was acceptable (RSD < 2%) using an internal standard. The method was tested for the separation of the studied enantiomers in an extracted (solid-phase) serum sample spiked with standard racemic mixture of MIR and its two metabolites. Finally, the nanoLC system was connected to a mass spectrometer through a nanoelectrospray interface and the MS, MS2, and MS3 spectra were acquired showing the potential of the system used for characterization and identification of the separated analytes

Vyvoj palestinsko-izraelskeho miroveho procesu v 80. a 90. letech 20. stoleti.

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