Capillary electrochromatography

The capillary electrochromatography (engl. Capillary electrochromatography , CEC) is a biochemical method for the separation of molecules in the stationary phase of a chromatographic separation column by electroosmosis . It is a combination of capillary electrophoresis and high-performance liquid chromatography .

principle

Construction of a CEC apparatus

At an alkaline pH , the silanol groups on the surface of the inside of the capillary and the stationary phase are negatively charged. Positive charges accumulate on it to balance the charge, which is referred to as an electrochemical double layer . When an electrical field is applied, an electroosmotic flow builds up in capillaries , with the cations migrating along these layers towards the cathode . The migration of the cations leads to a flow of liquid via their hydrate shells . Due to the different net charges of the analytes and their different degrees of interaction with the stationary phase leads to a separation of the migrating particle. The sample is introduced into the capillary by capillary action. By avoiding high pressure as in HPLC, the capillary is less prone to clogging, since the electroosmotic flow does not depend on the diameter and length of the column. The particle size of the column material can therefore be selected more freely.

theory

The thickness of the electric double layer δ is defined with the dielectric constant ε _r , the electric field constant ε ₀ , the universal gas constant , the absolute temperature , the molar concentration and the Faraday constant as follows: ${\displaystyle R}$ ${\displaystyle c}$ ${\displaystyle F}$

${\displaystyle \delta ={\sqrt {\frac {\varepsilon _{\mathrm {r} }\varepsilon _{0}RT}{2cF^{2}}}}}$

According to the Smoluchowski equation , the linear velocity of the liquid flow depends, among other things, on the zeta potential ζ, the electric field strength E and the viscosity η of the medium. ${\displaystyle u}$

${\displaystyle u=\varepsilon _{r}\varepsilon _{0}\zeta E\eta }$

literature

• Norman Smith: Capillary ElectroChromatography . Beckman Coulter, Fullerton, CA 1999 ( beckmancoulter.com [PDF]).
• Keith D. Bartle, Peter Myers (eds.): Capillary ElectroChromatography (= RSC Chromatography Monographs. Vol. 7). The Royal Society of Chemistry, Cambridge 2001, ISBN 0-85404-530-9 .
• František Švec, Zdeněk Deyl (ed.): Capillary ElectroChromatography (= Journal of Chromatography Library. Vol. 62). Elsevier Science, Amsterdam et al. 2001, ISBN 0-444-50432-X .

Individual evidence

1. ↑ Maria G. Cikalo, Keith D. Bartle, Mark M. Robson, Peter Myers, Melvin R. Euerby: Tutorial Review Capillary electrochromatography. In: Analyst . Vol. 123, 1998, pp. 87R-102R, doi: 10.1039 / A801148F .
2. ↑ Keith D. Bartle, Peter Myers: Theory of capillary electrochromatography. In: Journal of Chromatography A . Vol. 916, No. 1/2, 2001, pp. 3-23, PMID 11382305 , doi: 10.1016 / S0021-9673 (01) 00709-9 .