PARTITION VERSUS ELECTROSTATIC MODEL APPLIED TO THE ION-PAIRING RETENTION PROCESS OF SOME GUANIDINE BASED COMPOUNDS.

Two models (partition and electrostatic) were utilized to explain the retention data of four polar compounds with guanidine or tertiary amine moieties (metformin, phenformin, tolylformin, and ranitidine) in ion-pairing liquid chromatography based on C18 stationary phase (Zorbax Eclipse XDB column). Mobile phase composition, concentration of the ion-pairing (alkylsulphonates with 5 – 8 carbon atoms), and pH of the aqueous component were varied to determine the corresponding dependence of the retention factors and explanation by one model. Good correlations were found for retention factor versus concentration of ion pairing alkyl sulfonates concentration with a slope similar to the predicted values by the electrostatic model and between retention factor and the content of methanol used as organic modifier in mobile phase. Some extrapolations of the linear dependences were used in estimating the hydrophobic character of the pair between analyte and alkyl sulfonate ions in accordance to the partition model. [ABSTRACT FROM PUBLISHER]