Utilisation of crown ethers in microemulsion electrokinetic chromatography for the separation of inorganic cations

Recent trends in CE of inorganic ions: From individual to multiple elemental species analysis

The major methodological developments in CE related to inorganic analysis are overviewed. This is an update to a previous review article by the author (Timerbaev, A. R., Electrophoresis 2004, 25, 4008-4031) and it covers the review work and innovative research papers published between January 2004 and the first part of 2006. As was underlined in that review, a growing interest of analytical community in providing elemental speciation information found a sound response of the CE method developers. Presently, almost every second research paper in the field of interest deals with element species analysis, the use of inductively coupled plasma MS detection and biochemical applications being the topics of utmost research efforts. On the other hand, advances in general methodology traditionally centered on a CE system modernization for improvements in sensitivity and separation selectivity have attracted less attention over the review period. While there is no indication that inorganic ion applications would surpass by the developmental rate the more matured analysis of organic analytes, CE can now be seen as an analytical technique to be before long customary in a number of inorganic analysis arenas.

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.

Recent advances in the development and application of microemulsion EKC

Microemulsion EKC (MEEKC) is an electrodriven separation technique. Separations are typically achieved using oil-in-water microemulsions, which are composed of nanometre-sized oil droplets suspended in an aqueous buffer. The droplets are stabilised by a surfactant and a cosurfactant. The novel use of water-in-oil microemulsions has also been investigated. This review summarises the advances in the development of MEEKC separations and also the different areas of application including determination of log P values, pharmaceutical applications, chiral analysis, natural products and bioanalytical separations and the use of new methods such as multiplexed MEEKC and high speed MEEKC. Recent applications (2004-2006) are tabulated for each area with microemulsion composition details.