Indirect detection in reversed-phase liquid chromatography: Ion-pair retention models for cations on polystyrene polymers |
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Authors: | E Arvidsson J Crommen G Schill D Westerlund |
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Institution: | (1) Department of Analytical Pharmaceutical Chemistry, Uppsala University, Biomedical Center, P.O. Box 574, S-751 23 Uppsala, Sweden;(2) Institute of Pharmacy, University of Liège, Rue Fusch 5, 4000 Liège, Belgium |
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Abstract: | Summary The distribution equilibria of cationic compounds in reversed-phase chromatographic systems (ion-pair chromatography) have
been studied on the basis of their effect on a detectable mobile phase component. The solid phase was a polystyrene-divinylbenzene
copolymer and the detectable component, a quaternary ammonium ion, 1-methylpyridine. The solutes were mono- and divalent amines
and quaternary ammonium ions.
The cations can be retained by ion-pair adsorption and ion exchange. Expressions for the ion-pair retention of the solutes
and the mobile phase cation (system peak) have been developed assuming Langmuir distribution of ion pairs to a solid phase
with one kind of binding site. The validity of the expressions has been tested by evaluation of ion-pair distribution constants
using non-linear curve fitting techniques. Good agreement for the constants of common ion pairs was obtained from different
kinds of capacity ratio expressions.
Ion exchange retention can appear beside ion-pair retention, and it has been observed in the pH range 1.6–6.1. The effect
depends not only on cations in the mobile phase, but also on the nature of the buffering systems. |
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Keywords: | Column liquid chromatography Polystyrene polymers Ion-pair retention model Indirect detection |
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