Effect of Counter-Anions on the Retention of Zwitterionic Quinolones in Reversed-Phase Liquid Chromatography.

The effects of counter-anions on the reversed-phase HPLC retention of zwitterionic quinolones were studied. Four counter-anions, perchlorate, tetrafluoroborate, trifluoroacetate, and dihydrogenphosphate, were used as mobile phase additives. HPLC analysis was performed at a mobile phase pH 3, to ensure the complete protonation of the piperizine ring and to suppress the ionization of the carboxylic acid groups of the analytes. Results showed that retention factors of all analytes increased to varying degrees with increasing counter-anion concentration. The increase in retention of the analytes is attributed to the chaotropic effect exhibited by the counter-anions. Complete separation of all the studied compounds was achieved by varying the type and amount of counter-anions present in the mobile phase. The changes in selectivity offered by these counter-anions would be beneficial, especially for developing chromatographic methods for the analysis of quinolones in different sample matrices. [ABSTRACT FROM AUTHOR]