Retention behaviour of the sulphoxide, sulphone and 2-aminosulphone metabolites of albendazole in ion-pair liquid chromatography

The chromatographic behaviour of the sulphoxide, sulphone and 2-aminosulphone metabolites of albendazole has been investigated as a function of the pH and the type and concentration of the pairing ions added to the mobile phase. Experiments were carried out using both tetrabutylammonium cations and octanesulphonate anions as pairing agents. The results showed that improvements of peak shape and marked differences in selectivity with alterations in elution order can be achieved by changing the ionisation state of the solutes and the type and the concentration of the pairing ion in the mobile phase. Although it was clear that at pH 2.3 the tetrabutylammonium cations exerted the conventional effect of a competing base whereas the octanesulphonate anions the conventional effect of a pairing agent, the lack of quantitative correlation and the exceptions at pH 7.4 indicated that the retention mechanisms may be more complex.