Prediction of Retention Times for Compounds on Mixed Retention Mechanism Stationary Phases

Eduard Kolovanov, Vadim Tashlitsky, Michael McBrien, Edward H. Kravets, Yury Zelechonok

Abstract

Recently, liquid chromatographic stationary phases have been developed that demonstrate retention mechanisms combining both hydrophobic and ion-exchange characteristics. These characteristics are imparted by embedded ion-pairing reagents. The unique characteristics of these materials give very interesting selectivities for separations involving mixtures of acids, bases, and neutrals, but have provided a challenge for typical algorithms designed to predict retention times for given compounds based on predicted physicochemical parameters.

Advanced Chemistry Development has proposed a new parameter for the description of the chromatographic behavior of such columns. The ion-exchange character of the column is modeled by a conditional charge term, a function of the stationary phase material and of the solvent component. ACD/Labs has used this parameter in conjunction with its standard approach that employs algorithms that model hydrophobic and other interactions for these systems. These algorithms use prediction of LogP, LogD, and pK_a as well as some other physicochemical parameters. Examples will be shown that describe the accuracy of prediction for given compounds as well as the predicting the effects of pH on the separations.

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