Abstract
The origin and characteristics of the system peaks appearing in ion chromatography with dibasic acid eluent systems were extensively studied by computer simulation, theoretical considerations, and experiments. The functional relationships between the retention volume of the second system peak and chromatographic parameters have been derived for dibasic acid eluent systems. The functional relations reproduced the results by computer simulation of the chromatographic processes for dibasic acid eluent systems based on the plate theory and multiple chemical equilibria in each theoretical plate. Sample injection perturbs not only the partition equilibrium of the eluent acid between the mobile phase and the stationary phase, but also the concentration ratio of monovalent and divalent eluent ions on the ion-exchange site in the stationary phase. Therefore, the second system peak is caused mainly by the perturbation of the partition of the acid molecules in dibasic acid eluent systems, as in monobasic acid eluent systems. In addition, the ion-exchange reaction between HB- and B2- is another cause of the second system peak in dibasic acid eluent systems. The retention volume of the second system peak has been explicitly related to the elution parameters. The complicated retention of the second system peak observed by Jackson and Haddad with phthalate eluent was elucidated for the first time. By using the derived functional relationships, we can easily obtain the partition isotherm for the eluent acid from the retention volume data of the second system peak in the chromatographic measurements.
