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Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
39, Number 10, October 2001, pp. 411-419
Optimization Strategies and Modeling of Separations of Dansyl-Amino
Acids by Cyclodextrin-Modified Capillary Electrophoresis
James P. Schaeper, Shannon B. Fox, and Michael J. Sepaniak*
Department of Chemistry, University of Tennessee, Knoxville, TN 37996
Presented in this study is an approach to optimize conditions
for capillary electrophoresis separations of multianalyte enantiomeric pairs
(D- and L-dansyl (Dns)-amino acids) that involves the rational use of combinations
of cyclodextrins (CDs) as enantioselective running buffer additives. Migration
data is experimentally obtained for a range of concentrations for native CDs
used individually and employed to determine inclusion constants for the Dns-amino
acids of interest. An expression for the mobility of the amino acids when multiple
(two in this work) CDs are present in the running buffer is used to simulate
separations for more complex CD systems. A chromatographic response function
involving predicted resolution is generated to gauge the quality of these separations.
Simplex methods are then employed for the first time to optimize conditions
for the separation of amino acid enantiomers. The validity of this approach
is demonstrated for separations of five Dns-amino acid enantiomers using g-
and b-CDs at various concentrations. Extending the dual-CD approach to other
CDs and increasing the number of CDs beyond two should be possible. To this
end, preliminary experiments are performed by using several available single-isomer,
derivatized CDs (individually) to determine if they have potential for further
studies. Although results with these particular derivatized CDs are not encouraging,
we did find that molecular mechanics modeling is useful in interpreting those
cases in which low inclusion constants possibly contributed to the ineffectiveness
of the CDs.
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