Thermodynamic behaviour in capillary electrochromatography

Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, Laboratory of Instrumental Analysis, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Journal of Separation Science (Impact Factor: 2.74). 06/2002; 25(9):569 - 576. DOI: 10.1002/1615-9314(20020601)25:9<569::AID-JSSC569>3.0.CO;2-3


The thermodynamic behaviour of solutes was examined on four reversed-phase (RP) stationary phases under pressure-driven (viz. high performance liquid chromatography, HPLC) and electro-driven (viz. capillary electrochromatography, CEC) conditions. Thermodynamic constants such as standard enthalpy, entropy, and Gibbs free energy were compared for both separation modes. Differences and/or similarities observed were used as a tool in gaining a better understanding of the separation mechanism in CEC compared to HPLC. In addition, effects of temperature on the magnitude of electroosmotic flow (EOF) are explained in detail.

4 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Capillary electrochromatography (CEC) is a miniaturized separation technique that combines aspects of both interactive chromatography and capillary electrophoresis. In this chapter, the theory of CEC and the factors affecting separation such as the stationary phase and mobile phase parameters have been discussed. The chapter focuses on the types and preparation of columns for CEC and describes the progress made in the development of open-tubular, particle-packed, and monolithic columns. The detection techniques in CEC such as the traditional UV detection and improvements made in coupling with more sensitive detectors such as mass spectrometry are also described. The chapter provides a summary of some applications of CEC in the analysis of pharmaceuticals and biotechnology products.
    No preview · Article · Jan 2008 · Separation Science and Technology
  • [Show abstract] [Hide abstract]
    ABSTRACT: A mathematical modelling approach for open-tubular capillary electrochromatography is presented. The spatially one-dimensional model takes into account (i) a coupling of (non)linear adsorption of positively or negatively charged analyte molecules (at a negatively charged capillary inner surface) with the equilibrium electrokinetics at this solid-liquid interface, (ii) mobile phase transport by electroosmosis and pressure-driven flow, as well as (iii) transport of species by electrophoresis and molecular diffusion. Under these conditions the local zeta-potential and electroosmotic mobility become a function of the concentration of the charged analyte. The resulting inhomogeneity of electroosmotic flow through the capillary produces a compensating pore pressure as requirement for incompressible mobile phase flow (i.e., for constant volumetric flow along the capillary). The results of the simulations are discussed in view of the surface-to-volume ratio of the capillary lumen, the analyte concentration (in combination with a Langmuir isotherm for the adsorption process), and buffer effects.
    No preview · Article · Feb 2003 · Electrophoresis
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The behavior of neutral sample solutes in pressurized flow driven electrochromatography using a mixed stationary phase, which consisted of ODS and anion-exchange (ODS-SAX), was studied. Applications of both positive and negative voltage on a column induced increases in retention factors of sample solutes. The direction of an electroosmotic flow under applications of positive and negative voltage were the same, therefore, the sign of the surface charge density under positive and negative voltage was opposite. We proposed a new equation for the relationship between applied voltage and surface charge density, and the practical electroosmotic flow conformed to this equation. Studying the electroosmotic flow using our proposed equation revealed that the applied negative voltage accelerates the protonation of the quaternary ammonium group and dissociation of the silanol group on packing materials. The retention behavior of a neutral solute was affected by the existence of the charged functional groups. We propose that this phenomenon is applicable to the control of the retention behavior of a sample solute using an electric field.
    Full-text · Article · Jun 2003 · Journal of Chromatography A
Show more