Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume 37, Number
11, November 1999, pp. 413-422
Benzene
Oligocarboxylic Acids: Characterization by Isocratic, Linear Gradient, and Frontal
Anion-Exchange Chromatography
Hong
Li, Leo Lue, and Costas S. PatrickiosA
series of nine benzene oligocarboxylic acids is characterized using anion-exchange
chromatography to determine the steric mass-action affinity parameters: the characteristic
charge, the equilibrium ion-exchange constant (and the corresponding Gibbs free
energy of ion-exchange), and steric factor. Isocratic elution under various concentrations
of sodium chloride in the mobile phase provides the characteristic charge and
the ion-exchange constant. The former agrees closely with the number of carboxylic
acid groups in the sample, and the latter seems to be strongly influenced by the
relative positions of the carboxylic acid groups on the benzene ring. Analysis
of all samples under a linear salt gradient provides retention times that follow
the same order as the ion-exchange constants determined isocratically. Using an
appropriate model, along with the isocratically determined characteristic charge
and ion-exchange constant, the linear gradient retention times are predicted theoretically
and agree well with the experimental times. Frontal experiments led to the calculation
of the characteristic charge and the steric factor. The former agrees well with
the value determined isocratically. For most samples, the steric factor increases
slowly with the characteristic charge.
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