The pH Influence on the HPLC-Retention of Chemotherapeutic Fluoroquinolone Derivatives

Abstract

The gyrase inhibitor fluoroquinolone derivatives were investigated by RP-HPLC methods in C₁₈/methanol-phosphate buffer system. Considering the amphoteric feature of the substances it was reasonable to study the relationship between their chromatographic behaviour vs. pH of the mobil phase. The formation of k¹ values was characterized by a maximum curve, and the retention maxima could be found close to or at the pH values of isoelectric point of the compounds. This may be explained by the presence of the zwitter ionic or the unionized form of the derivatives at this pH value.

By addition of ion-pairing (IP) agent (cetrimide or hexanesulfonic acid) in different concentration to the eluent a definite k' value increase (formation of a characteristic saturation type curve) was observed indicating an ion-pairing mechanism.

In case of IPHPLC significant correlation was found between the octanol-water partition coefficients measured at the isoelectric point or at pH 7. 4, and the retention values of the compounds.