Viktoria V. Sursyakova

New peak broadening parameter for the characterization of separation capability in capillary electrophoresis

The influence of separation conditions on peak broadening is usually estimated by the number of theoretical plates. Using the data available in literature and experimental data, it is shown that in pressure-assisted capillary electrophoresis the plate number is not directly related to the separation capability of conditions used. The experiments at different electrolyte flow velocities demonstrate that a higher plate number (the best separation efficiency) can be obtained with a lower peak resolution. Since ions are separated by electrophoresis due to the difference in electrophoretic mobilities, the peak width in terms of electrophoretic mobility is suggested as a new peak broadening parameter describing the separation capability of the conditions used. The parameter can be calculated using the tailing factor and the temporal peak width at 5% of the peak height. A simple equation for the resolution calculation is derived using the parameter. The advantage of the peak width in terms of mobility over other parameters is shown. The new parameter is recommended to be used not only in pressure-assisted capillary electrophoresis but also in general capillary electrophoresis when in a number of runs the virtual separative migration distance and separation capability of the conditions used change widely.

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.

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.

Stability constants of adducts of succinate copper(II) complexes with β-cyclodextrin determined by capillary electrophoresis

Cyclodextrins (CD) form inclusion complexes with different “guests” owing to the fact that the shape of the CD molecule is a truncated cone with a hydrophobic cavity. The adducts of CD with metal complexes remain scantily explored. In this study, the stability constants of the adducts between succinate copper(II) complexes and β‐CD was determined using capillary electrophoresis. The β‐CD concentration in background electrolytes (BGE) was found to influence on the effective electrophoretic mobility of the copper(II) complexes in succinate BGEs. It was shown that succinic acid and its anions and copper(II) ions did not form a significant amount of the inclusion complexes with β‐CD and the mobility change was caused by the adduct formation between succinate copper(II) complexes and β‐CD. The stability constants of these adducts were determined at 25°С and ionic strength of 0.100 M: log β(CuL22−/β‐CD) = 1.76 ± 0.06, log β(CuL0/β‐CD) = 0.98 ± 0.09. The [CuHL]+ and [CuHL2]− species were found to do not form adducts with β‐CD.

Combination of phase-solubility method and capillary zone electrophoresis to determine binding constants of cyclodextrins with practically water-insoluble compounds

HIGHLIGHTSCombination of phase‐solubility technique and electrophoresis was suggested.Mode allows to determine binding constants of CD complexes with insoluble compounds.Background electrolyte for CE should contain ethanol and cyclodextrin if necessary.Binding constants between betulinic/betulonic acids and hydroxypropyl‐cyclodextrin. ABSTRACT The combined method based on phase‐solubility technique and capillary zone electrophoresis (PS‐CZE) was suggested for the determination of binding (stability) constants of cyclodextrins (CD) complexes with water‐insoluble organic compounds that have no or weak UV chromophores. In this method, the insoluble compounds are agitated at the desired temperature in CD solutions with different concentration up to the attainment of equilibrium and then CZE is used to determine the concentration of the compounds that have passed into the solutions. To avoid precipitation and complex dissociation, the background electrolyte (BGE) for CZE should contain ethanol and, if necessary, cyclodextrin. The samples should be diluted with the BGE without CD so that the CD concentrations in BGE and samples were equal to preclude a baseline shift. Using the suggested approach, the inclusion complexes between betulinic and betulonic acids, pentacyclic lupane‐type triterpenes, and hydroxypropyl‐&bgr;‐ and &ggr;‐cyclodextrins (HP‐&bgr;‐CD and HP‐&ggr;‐CD) were studied. It was found that solubility of the acids studied in HP‐&bgr;‐CD solutions did not differ from their solubility in pure water. That is, the HP‐&bgr;‐CD complexes of the acids studied were not formed in noticeable amount. At the same time, the acids formed inclusion complexes with HP‐&ggr;‐CD, what possibly was caused by the greater size of the HP‐&ggr;‐CD molecule as compared to HP‐&bgr;‐CD. To determine binding constants by Higuchi and Connors method, the acids solubility was determined by CZE after their agitation in the solutions of HP‐&ggr;‐CD (with 0.6 molar substitution) at 25 °C for 3 days. The dependences of acids solubility on HP‐&ggr;‐CD concentration deviated from straight line in the range of high concentration (AN mode). This can be explained by a self‐association of HP‐&ggr;‐CD molecules. Using the linear segment of the solubility dependences on CD concentration, the binding constants were determined. Their logarithms for the HP‐&ggr;‐CD complexes with betulonic and betulinic acids were 3.88 ± 0.14 and 3.82 ± 0.12, respectively.

Interfering Influence of Organic Acids Anions on the Determination of Fluoride Ions by Capillary Electrophoresis Using Chromate Background Electrolyte

The interfering influence of the anions of typical low-molecular organic acids (citric, formic, maleic, fumaric, tartaric, succinic, and malic) on the determination of fluoride ions by capillary electrophoresis with using chromate background electrolyte was studied. For low concentration of fluoride ions, it was found that the peaks of anions of citric, maleic, and fumaric acids were well separated from the peak of fluoride ions. The peak of succinic acid was nearly baseline separated from the peak of fluoride ions. The peaks of anions of malic and formic acids were poorly separated from the peak of fluoride ions. The peak of tartaric acid was not separated from the peak of fluoride ions. It is shown that the anions of studied acids were baseline separated with the peak of fluoride ions when the difference between their effective electrophoretic mobility and mobility of fluoride ions was above or equal to 1.5·10-9 m2·V-1·s-1.

Solubility Study of Betulonic Acid in the Presence of Hydroxypropyl-γ-cyclodextrin by Capillary Electrophoresis

Olesya V. Popovaa, Viktoria V. Sursyakova*a, Galina V. Burmakinaa, b Nikolay G. Maksimova, Vladimir A. Levdanskya and Anatoly I. Rubayloa, b, c aInstitute of Chemistry and Chemical Technology SB RAS FRC “Krasnoyarsk Science Center SB RAS” 50/24 Akademgorodok, Krasnoyarsk, 660036, Russia bSiberian Federal University 79 Svobodny, Krasnoyarsk, 660041, Russia cKrasnoyarsk Scientific Centre, SB RAS 50 Akademgorodok, Krasnoyarsk, 660036, Russia