Size-exclusion electrochromatography

In previous work [15,17,28] we have evaluated the relation between the flow ratio co, the pore size, and the ionic strength of the solution experimentally, by means of size-exclusion electrochromatography (SEEC). In SEEC the transport rates of the (neutral) macromolecules depend direcdy on co. As in conventional, pressure-driven SEC, the separation in SEEC is based on the differential accessibility of the (stagnant) mobile phase in the pores of the particles for macromolecules of different sizes. However, with increasing pore flow ratio in SEEC, the velocity difference between the mobile-phase fractions inside and outside the particles decreases. The retention ratio x (the retention time relative to a low-molecular-mass marker) for a probe molecule in SEEC is given by... 

Pore Flow Effects in Size-Exclusion Electrochromatography... 

The effects of pore flow in size-exclusion electrochromatography (SEEC) are even more apparent than in reversed-phase CEC. The solutes typically separated in SEEC are slowly diffusing macromolecules such as synthetic polymers. For these solutes the enhanced diffusion effect becomes relevant even at low pore flow velocities and at low pore-to-interstitial flow ratios. 

Stol, R., et al.. Application of size exclusion electrochromatography to the microanalytical determination of the molecular mass distribution of celluloses from objects of cultural and historical value. Anal Chem., 74, 2314, 2002. 

The separation scientist with experience gained from a LC background may tend to limit the modes of electrochromatography to reversed phase (RP), normal phase, ion-exchange and, maybe, size-exclusion. Analysts from an electrophoretic background typically use the term "CE" in a much broader sense to include the main modes of capillary zone electrophoresis, micellar electrokinetic chromatography, capillary gel electrophoresis, isoelectric focusing and isotachophoresis. 

Other detectors being developed at Sandia National Laboratory are based on miniaturizing standard laboratory separation techniques, such as capillary zone electrophoreses, size exclusion chromatography, and reverse phase and affinity electrochromatography coupled with fluorescence (Vitko and Kottenstette, 1998 Dulay et al., 1995 Ramsey et al.. 

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