RETENTION BEHAVIOR OF NEUTRAL MOLECULES IN ION-INTERACTION CHROMATOGRAPHY

The retention behaviour of aprotic neutral molecules in Ion Interactio n Chromatography was investigated. The study demonstrates that their r etention, for an aqueous mobile phase (phosphate buffer pH 7.2-methano l, 85:15 v/v) containing the ion-interaction reagent (IIR) in the rang e 0-25 mM, decreases with increasing IIR concentration. Silanophilic i nteractions were accounted for by comparison of results obtained with either a silica based or a styrene-divinylbenzene based C-18 stationar y phase, under otherwise identical conditions. The retention behaviour of neutral molecules was elucidated on the basis of the exhaustive Io n Interaction retention model and evidence was obtained to support the proposition that the decreased retention is the result of an adsorpti on competition between tested analytes and ion-interaction reagent for inner layer sites on the stationary phase.