Page 204 - Multidimensional Chromatography

Multidimensional Chromatography
Edited by Luigi Mondello, Alastair C. Lewis and Keith D. Bartle
Copyright © 2002 John Wiley & Sons Ltd
ISBNs: 0-471-98869-3 (Hardback); 0-470-84577-5 (Electronic)

9 Multidimensional Electrodriven
Separations

MARTHA M. DEGEN and VINCENT T. REMCHO
Oregon State University, Corvallis, OR, USA

9.1 INTRODUCTION

Multidimensional separations allow for the analysis of complex mixtures, such as
those from biological matrices with thousands of components that would be difficult
or impossible to separate by utilizing only one method. Electrodriven separations
have been employed to separate biological molecules for many years, due to the
charged nature of amino acids and nucleic acids. The addition of an electrodriven
component to a multidimensional separation is therefore desirable, especially for the
separation of biological mixtures.
This chapter will first cover the nature of electrophoretic separations, especially
those concerning capillary electrophoresis. Comprehensive multidimensional sepa-
rations will then be defined, specifically in terms of orthogonality and resolution.
The history of planar and non-comprehensive electrodriven separations will then be
discussed. True comprehensive multidimensional separations involving chroma-
tography and capillary electrophoresis will be described next. Finally, the future
directions of these multidimensional techniques will be outlined.

9.2 ELECTROPHORETIC SEPARATIONS

Zone electrophoresis is defined as the differential migration of a molecule having a
net charge through a medium under the influence of an electric field (1). This tech-
nique was first used in the 1930s, when it was discovered that moving boundary elec-
trophoresis yielded incomplete separations of analytes (2). The separations were
incomplete due to Joule heating within the system, which caused convection which
was detrimental to the separation.
Charged macromolecules, such as proteins or polymers, are often separated elec-
trophoretically. The rate of migration through an electric field increases with net
charge and field strength. Molecular size of analytes and viscosity of separation
media both have inverse relationships with rate of migration. These variables must
all be taken into account in order to optimize the conditions for an efficient elec-
trophoretic separation.