Galina V. Burmakina

System peaks in capillary zone electrophoresis of anions with negative voltage polarity and counter‐electroosmotic flow

The system peaks that often appear on electropherograms in anion separation by CE with indirect spectrophotometric detection, negative voltage polarity and cathodic EOF are studied. The system peaks are shown to correspond to the zones with the changed concentration of the BGE constituents; they appear while the zone of each analyte anion passes through the outlet end of the capillary and are transported to the detector by EOF. An equation is suggested for predicting migration times of the system peaks with an error of 1%. The ratios of the system peak area to the analyte peak area are found to amount to 20%. It is shown that it is possible to avoid overlapping of the system peaks and analyte peaks by controlling the EOF velocity owing to hydrodynamic pressure. Using the mathematical simulation of CE shows that the system peaks and baseline shift can result from changing the transference numbers of the BGE ions and analyte ions at the capillary edge. The cases when the system peak may be incorrectly identified as the peak of analyte ion are considered. In order to avoid such errors, some practical recommendations are given.

Hydrodynamic suppression of the electroosmotic flow in capillary electrophoresis with indirect spectrophotometric detection

A version of capillary electrophoresis with indirect spectrophotometric detection and the hydrodynamic suppression of electroosmotic flow is studied. It is shown that, to improve the reliability of ion identification, one should calculate electrophoretic mobilities of ions or migration times corrected with regard to the electroosmotic flow rate. Correlations between electrophoretic peak areas of ions and their electrophoretic mobilities are derived. In the studied version of capillary electrophoresis, the accuracy of measuring anion concentrations can be improved using the internal standard method.

System peaks and optimization of anion separation in capillary electrophoresis with non-reversed electroosmotic flow

We studied system peaks present in the electropherograms obtained in the separation of anions by capillary electrophoresis with indirect spectrophotometric detection and cathode electroosmotic flow (EOF) with a chromate background electrolyte. The system peaks correspond to the zones with changed concentration of the background electrolyte; they formed when the zones of each analyte passed through the outlet of the capillary and then moved towards the EOF detector. It has been revealed that the height and area of the system peaks linearly depends on the concentration of the corresponding anion and the areas of the system peaks can achieve 10% of the anion peak area. An algorithm has been proposed for the determination of the optimal conditions for anion separation using hydrodynamic pressure for the regulation of the EOF flow rate. This algorithm prevents the overlapping of the anion and system peaks.

Chemistry of vinylidene complexes XII. Transmetalation of the μ-vinylidene ligand in the reaction of Cp(CO)2MnPt(μ-CCHPh)(dppp) with Fe2(CO)9. Formation of new PtFe, PtFe2 and PtFe3 complexes

Abstract The reaction between [Fe 2 (CO) 9 ] and [Cp(CO) 2 MnPt(μ-C CHPh)(dppp)] ( 1 ), where dppp is Ph 2 P(CH 2 ) 3 PPh 2 , proceeds stepwise, initially through transmetalation of the bridging vinylidene ligand, i.e. with replacement of the [Mn(CO) 2 Cp] fragment by the [Fe(CO) 4 ] group, to produce the novel binuclear μ-vinylidene complex [(dppp)PtFe(μ-C CHPh)(CO) 4 ] ( 2 ), which reacts further with [Fe 2 (CO) 9 ] to yield the tetranuclear cluster [(dppp)PtFe 3 (μ 4 -C CHPh)(CO) 9 ] ( 3 ) and the trinuclear complex [(dppp)PtFe 2 (CO) 8 ] ( 4 ). The IR and 1 H, 13 C and 31 P NMR data for the new complexes are reported and discussed.

Determination of iron and copper ions in cognacs by capillary electrophoresis

A method is developed for the determination of iron(III) and copper(II) in cognacs by capillary electrophoresis (CE) with diode array detection with limits of detection 0.06 and 0.6 mg/L, respectively. Foreign substances present in cognac do not interfere with the determination. The accuracy of the results of analysis was confirmed by the added-found method. The method was applied to the analysis of seven cognac samples. The data obtained by CE are in a good agreement with the results of inductively coupled plasma mass spectrometry.

Determination of stability constants of inclusion complexes of betulin derivatives with β-cyclodextrin by capillary electrophoresis

67 Betulin and its derivatives relating to pentacyclic triterpenoids of lupan series exhibit pharmacological activity including human immunodeficiency virus inhibition, as well as antibacterial, antimalarial, anti inflammatory, antioxidant, and anticancer activity [1–3]. However, their medical application is rather limited because of their low solubility in water, which hampers the preparation of formulation for injection in humans.

Strategy for non-target ionic analysis by capillary electrophoresis with ultraviolet detection

AbstractA strategy for non-target analysis of samples with unknown composition by capillary electrophoresis (CE) with ultraviolet (UV) detection is suggested. The strategy is based on the preliminary identification of analytes and further optimization of the conditions for their separation using the developed computational tool set ElphoSeparation. It is shown that, in order to record electrophoretic peaks with the mobilities from the maximum to minimum possible values, the positive and negative voltage polarity and hydrodynamic pressure should be used. To choose the optimal separation conditions, dynamic maps of electrophoretic separation (DMES) are suggested. DMES is a bar chart with theoretical resolutions of adjacent peaks presented in ascending order of the migration time. The resolution is calculated as the division of the difference of the effective electrophoretic mobilities of adjacent analytes by their average peak width in terms of electrophoretic mobility. The suggested strategy is tested by the example of the analysis of herbal medicine (Holosas) on the basis of rose hips. The approach should be used to analyze samples with not very complex composition, such as environmental water and precipitation samples, process liquors, some vegetable extracts, biological fluids, food, and other samples for the determination of widespread compounds capable of forming ionic species. For samples with complex composition, the approach used together with other techniques may produce advantageous information due to specificity of the method, particularly it can be useful for determination of compounds suffering from low volatility or thermal stability, and for analysis of samples with difficult matrices. Graphical AbstractThe scheme of performing the non-target ionic analysis by capillary electrophoresis with ultraviolet detection

Influence of Analyte Concentration on Stability Constant Values Determined by Capillary Electrophoresis

The influence of analyte concentration when compared with the concentration of a charged ligand in background electrolyte (BGE) on the measured values of electrophoretic mobilities and stability constants (association, binding or formation constants) is studied using capillary electrophoresis (CE) and a dynamic mathematical simulator of CE. The study is performed using labile complexes (with fast kinetics) of iron (III) and 5-sulfosalicylate ions (ISC) as an example. It is shown that because the ligand concentration in the analyte zone is not equal to that in BGE, considerable changes in the migration times and electrophoretic mobilities are observed, resulting in systematic errors in the stability constant values. Of crucial significance is the slope of the dependence of the electrophoretic mobility decrease on the ligand equilibrium concentration. Without prior information on this dependence to accurately evaluate the stability constants for similar systems, the total ligand concentration must be at least >50-100 times higher than the total concentration of analyte. Experimental ISC peak fronting and the difference between the direction of the experimental pH dependence of the electrophoretic mobility decrease and the mathematical simulation allow assuming the presence of capillary wall interaction.

Electrochemical study of heteronuclear complex [Cp(CO)2MnCu(μ-C=CHPh)(μ-Cl)]2

The electrochemical behavior of the heteronuclear dimeric vinylidene complex [Cp(CO)2MnCu(μ-C=CHPh)(μ-Cl)]2 (I) is studied using polarography, cyclic voltammetry, and controlled-potential electrolysis on mercury and platinum electrodes in acetonitrile. The dimer is reduced in two two-electron stages: at the first stage, metal-halogen bonds are broken and binuclear monomers [Cp(CO)2MnCu(μ-C=CHPh)(Cl)]− are formed; at the second stage, mononuclear manganese complexes Cp(CO)2Mn=C=CHPh, metallic copper, and chloride ions are formed. The two-electron oxidation of dimer [Cp(CO)2MnCu(μ-C=CHPh)(μ-Cl)]2 also results in the formation of binuclear monomers, which decompose to complex Cp(CO)2Mn=C=CHPh, Cu2+ ions, and Cl− ions.

Composition and stability constants of copper(II) complexes with succinic acid determined by capillary electrophoresis

Abstract The advantage of capillary electrophoresis was demonstrated for studying a complicated system owing to the dependence of direction and velocity of the electrophoretic movement on the charge of complex species. The stability constants of copper(II) complexes with ions of succinic acid were determined by capillary electrophoresis, including the 1 : 2 metal to ligand complexes which are rarely mentioned. The measurements were carried out at 25 °C and ionic strength of 0.1, obtained by mixing the solutions of succinic acid and lithium hydroxide up to pH 4.2–6.2. It was shown that while pH was more than 4.5 the zone of copper(II) complexes with succinate moves as an anion. It is impossible to treat this fact using only the complexes with a metal-ligand ratio of 1 : 1 (CuL0, CuHL+). The following values of stability constants were obtained: log β(CuL) = 2.89 ± 0.02, log β(CuHL+) = 5.4 ± 0.5, log β(CuL22−) = 3.88 ± 0.05, log β(CuHL2−) = 7.2 ± 0.3.