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Encyclopedia of Physical Science and Technology EN002E-79 May 17, 2001 20:28

368 Capillary Zone Electrophoresis

micelle concentration (CMC); surfactant monomers are in flow when a voltage is applied to the system, pumping
equilibrium with micelles. The most widely used MEKC mobile phase through the column. Since EOF is plug-like
system employs sodium dodecylsulfate (SDS) as the sur- rather than laminar in nature, efficiencies in CEC can be
factant. The sulfate groups of SDS are anionic, so both sur- much higher than in HPLC. In contrast to pressure-driven
factant monomers and micelles have electrophoretic mo- capillary liquid chromatography, which requires pressures
bility counter to the direction of EOF. Sample molecules of several thousand psi to pump mobile phase through
will be distributed between the bulk aqueous phase and the the column, CEC generates no column backpressure. Like
micellar phase, depending upon their hydrophobic char- MEKC, CEC is used primarily for small molecules.
acter. Hydrophilic neutral species with no affinity for the
micelle will remain in the aqueous phase and reach the
detector in the time required for EOF to travel the effec- SEE ALSO THE FOLLOWING ARTICLES
tive length of the column. Hydrophobic neutral species
will spend varying amounts of time in the micellar phase ELECTROPHORESIS • LIQUID CHROMATOGRAPHY • MASS
depending on their hydrophobicity, and their migration SPECTROMETRY
will therefore be retarded by the anodically moving mi-
celles. Charged species will display more complex behav-
ior, and their migration will include contributions from BIBLIOGRAPHY
electrophoretic mobility and electrostatic interaction with
the micelles in addition to hydrophobic partitioning. The Camilleri, P., ed. (1993). “Capillary Electrophoresis: Theory and Prac-
selectivity of MEKC can be expanded with the introduc- tice,” CRC Press, Boca Raton, FL.
Deyl, Z., and Struzinsky, R. (1991). J. Chromatogr. 569, 63.
tion of chiral selectors to the system. MEKC is used al-
Grossman, P. D., and Colburn, J. C., eds. (1992). “Capillary Elec-
most exclusively for small molecules such as drugs and trophoresis: Theory and Practice,” Academic Press, San Diego, CA.
metabolites, pesticides, herbicides, vitamins, etc. Guzman, N. A. (1993). “Capillary Electrophoresis Technology,” Dekker,
New York.
Kuhr, W. G. (1990). Anal. Chem. 62, 403R.
Kuhr, W. G., and Monnig, C. A. (1992). Anal. Chem. 64, 389R.
X. CAPILLARY ELECTROKINETIC
Landers, J. P., ed. (1996). “Handbook of Capillary Electrophoresis,” 2nd
CHROMATOGRAPHY ed., CRC Press, Boca Raton, FL.
Li, S. F. Y. (1992). “Capillary Electrophoresis: Principles, Practice, and
Like MEKC, capillary electrokinetic chromatography Applications,” Vol. 52, Elsevier Science, Amsterdam.
(CEC) is a chromatographic technique performed with CE Lunte, S. M., and Radzik, D. M., eds. (1996). “Pharmaceutical and
Biomedical Applications of Capillary Electrophoresis: Progress in
instrumentation. It employs fused silica capillaries packed
Pharmaceutical and Biomedical Analysis,” Vol., Elsevier Science,
with 1.5- to 5-µm microparticulate porous silica beads, Oxford.
usuallyderivatizedwithahydrophobicligandsuchasC18. Monnig, C. A., and Kennedy, R. T. (1994). Anal. Chem. 66, 280R.
ı
Mobile phases are similar to those used for conventional Wehr, T., Rodriguez-D´az, R., and Zhu, M. (1998). “Capillary Elec-
reversed-phase HPLC (e.g., mixtures of aqueous buffers trophoresis of Proteins,” Dekker, New York.
Weinberger, R. (1992). “Practical Capillary Electrophoresis,” Academic
and an organic modifier such as acetonitrile). The silica
Press, Boston, MA.
surface of the derivatized beads has sufficient densities of Vindevogel, V. (1992). “Introduction to Micellar Electrokinetic Chro-
ionized silanol groups to generate a high electroosmotic matography,” H¨uthig, Heidelberg.