Migration behavior of metal complexes in capillary zone electrophoresis. Interpretation in terms of quantitative structure-mobility relationships

An overview of the methods for analyzing the chemical forms of metals in plants

Currently, the occurrence of toxic levels of metals in soils is a serious environmental issue worldwide. Phytoremediation is getting much attention to control metals soil pollution because it is economic and environmentally friendly. However, the methods used to detect metals in plants are not uniform and have depicted poor comparability of the research investigations. Therefore, the present overview is designed to discuss the possible chemical forms of metals in various environmental matrixes and the detection methods employed to identify the chemical forms of metals in plants. Moreover, the in situ and indirect methods to detect metals in plants have also been discussed herein. In addition, the pros and cons of the available techniques have also been critically analyzed and discussed. Finally, key points/challenges and future perspectives of these methods have been highlighted for the scientific community.Novelty statementIn the current review, the possible chemical forms of metals in various environmental matrixes are discussed in detail. Various extraction agents and their efficiency for extracting metals from plants have been clearly illustrated. Further, all the available methods for analyzing the chemical forms of metals in plants have been compared.

Development of quantitative structure–activity relationships for interpretation of the migration behavior of neutral platinum(II) complexes in microemulsion electrokinetic chromatography

Metal-ligand complexes present an important group of analytes in capillary electrophoresis (CE) utilized as an analytical tool for metal ion analysis, metal speciation studies, and characterization of metal complexes of pharmaceutical or industrial importance. In the majority of CE techniques but not yet in microemulsion electrokinetic chromatography (MEEKC), the migration behavior of metal complexes has been well described using the formalism of quantitative structure-activity relationships (QSARs). To fill this gap, a number of migration models, operating with the fundamental properties of analytes as molecular descriptors, were derived and tested for platinum(II) complexes with cyclohexanediamine and its alkylsubstituted derivatives as variable ligand. It was demonstrated that the complexes under examination are consistent with respect to the experimental versus calculated values of n-octanol-water partition coefficients (log P). Meaningful two-parametric regressions between the retention factors and the analyte structural descriptors, such as log P, molecular volumes or surface areas and dipole moments, were obtained. In addition, statistically significant correlations between k' of the platinum(II) complexes and their theoretical binding energies onto a hydrophobic surface were established. The validity of the QSAR modeling approach allowed the authors to postulate that it can be applied to the investigation of binding phenomena for neutral metal complexes to a microdroplet pseudostationary phase.

Capillary electrophoresis of inorganic ions: An update

This review as a sequel of three earlier similar reports gives a summary of the progress and significant methodological developments, starting from 2002, in the use of capillary electrophoresis (CE) for inorganic ion analysis. As substantiated by the illustrative number of relevant references, improvements in sensitivity achieved both in and outside a CE system, advances in manipulating the separation selectivity, novel hardware configurations, and system performance innovations are continually being reported over the review period. Specifically viewed are the recent advancements in elemental (bio)speciation analysis, which remains one of the most fertile areas of CE research, as well as in three recently booming research topics: contactless conductivity detection, separations on microchips, and transient isotachophoretic preconcentration. A state-of-the-art picture of technique's potentialities within the field of interest presented here demonstrates that CE has become recognized and is growing in acceptance as a reliable alternative to traditional analytical methods such as high-performance liquid chromatography (HPLC).

Determination of equilibrium constants from chromatographic and electrophoretic measurements

Chemical interactions, such as acid-base, complex-forming, ion association and other equilibria, are widely exploited to improve the separation efficiency in liquid chromatography as well as in electrophoresis. On the other hand, these techniques can be advantageously used to study the chemical equilibria affecting the separations. If the equilibium is sufficiently fast in comparison with the separation process, then the retention characteristics in chromatography (retention factors) or the migration characteristics in electrophoresis (effective mobilities) may be expressed as functions of the composition of mobile phase or background electrolyte (BGE), respectively. Using a proper experimental arrangement, the dependencies of retention (migration) characteristics on the mobile phase (background electrolyte) composition can be measured and utilized to calculate the equilibrium constants for equlibria taking place in the mobile phase (background electrolyte). Although principles of these measurements have been known for a long time, only more recent studies utilizing HPLC and capillary electrophoretic techniques are reviewed in this paper.

Study on the quantitative relationship between the structures and electrophoretic mobilities of flavonoids in micellar electrokinetic capillary chromatography

Quantitative structure-mobility relationship (QSMR) models were developed between the structures of flavonoids and their eletrophoretic mobilities in micellar electrokinetic capillary chromatography. Molecular descriptors calculated from structure alone are used to represent molecular structures, moreover, Nt was defined by ourselves. Multiple linear regression and radial basis function neural networks (RBFNNs) are utilized to construct the linear and nonlinear prediction model, respectively. The optimal QSMR model developed was based on a 3-10-1 RBFNNs architecture. The root mean square errors in mobilities predictions for the data set was 0.1083 mobility unit (10(-4) cm2 V(-1) s(-1)). The prediction results were in good agreement with the experimental values.

Analysis of Metal Ions by Sweeping via Dynamic Complexation and Cation-Selective Exhaustive Injection in Capillary Electrophoresis

To improve the detection sensitivity of metal ions in capillary zone electrophoresis (CZE), a novel method that combines complex formation and on-line sample preconcentration by sweeping was developed. Sweeping is defined as the picking and accumulating of analytes by a carrier in the background solution, with which they have considerable affinity. In this sweeping method, using ethylenediaminetetraacetic acid as carrier, dynamic complexation to form a UV-absorbing chelate and on-line preconcentration occur simultaneously during a run. The technique was validated in terms of the limit of detection, reproducibility, and sensitivity enhancement. Detection responses of some divalent metal ions, in terms of peak heights, were improved from 60- to 180-fold, relative to conventional CZE which employed precapillary complexation. The limits of detection were in the range of (1.8-23.4) x 10(-8) M. This method was applied to the analysis of trace metal ions in factory wastewater. Furthermore, sweeping in conjunction with sample stacking accompanying electrokinetic injection, cation-selective exhaustive injection (CSEI-sweeping), was also examined. Up to 140 000-fold improvement in detector responses for some divalent and trivalent metal ions was realized by CSEI-sweeping. The limits of detection were in the range (2.4-25.2) x 10(-11) M.

Light-emitting diode-based indirect fluorescence detection for simultaneous determination of anions and cations in capillary electrophoresis

This report presents simultaneous analysis of cations and anions by capillary electrophoresis (CE) in conjunction with indirect fluorescence detection using a blue light-emitting diode (LED), based on the displacement of fluorescein with anionic EDTA-metal complexes and anions. A new focusing system combined with a plastic lens and a 40x objective was developed and used effectively to focus the diverging beam of the LED on the capillary. The optimum compositions for simultaneous analysis of metal ions and anions are the samples prepared in 5 mM borate, pH 9.2, containing 2 mM EDTA and the background electrolytes (BGEs) consisting of 5 mM borate buffer, 5 microM fluorescein, and 1 microM NaCl at pH 9.2. Using this pre-capillary complexation method, the analysis of a sample containing five metal ions and eight anions was accomplished in 8 min, with the relative standard deviation values for the migration times less than 2.0%. The peak heights against the concentrations of the metal ions and anions are linear in 10-1000 and 50-2000 microM, with correlation coefficients better than 0.998, and 0.982, respectively. The limits of detection at a signal-to-noise ratio 3 of up to 14.6 microM for formate and as low as 3.7 microM for Ni2+. The results of the analyses of pond water and a Chinese herbal soup present the advantages of this method, including simplicity, rapidity, reproducibility, and low costs.

Electrophoretic behavior of alprenolol in mixed solvent electrolyte systems

The electrophoretic mobilities of alprenolol have been determined in a mixed solvent background electrolyte system containing sodium acetate (40 mM)+acetic acid (40 mM) as buffering agent and different volume fractions of water, methanol and ethanol using capillary electrophoresis. The mobility of alprenolol has been used to test the prediction capability of a model trained by previously reported mobility data of five beta-blocker drugs at the same electrophoretic conditions. The average percentage mean deviations (APMD) between experimental and predicted values were used as an accuracy criterion. The APMD (+/-SD) obtained for alprenolol data in binary/ternary solvent electrolyte system employing the mobility values in mono-solvent buffers was 4.37 (+/-3.50)% and the corresponding value for an ab initio prediction method was 7.65 (+/-4.30)%.

Capillary electrophoresis of platinum-group elements. Analytical, speciation and biochemical studies

A great deal of research has been carried out in recent years on developing high-efficiency capillary electrophoresis (CE) techniques that are able to separate rapidly and selectively ionic platinum metal species in a wide variety of their complexed forms. Using a range of illustrative examples, this review examines the potential and utilization of various CE separation approaches and detection modes in this expanding area. Also covered are CE procedures suitable for solving practical analytical problems and for platinum metal speciation purposes. Presenting a comprehensive treatise on the evolving practices of CE concerning platinum anticancer drugs--in particular, the examination of the stability of intact drugs, the separation and identification of products of their metabolism and interactions with biomolecules (including kinetic studies of the binding behavior)--this paper witnesses a welcome shift of the main research activities to those performed under physiological conditions.