title: Investigation of the retention/pH profile of zwitterionic fluoroquinolones in reversed-phase and ion-interaction high performance liquid chromatography.
abstract: The retention/pH profiles of three fluoroquinolones, ofloxacin, norfloxacin and ciprofloxacin, was investigated by means of reversed-phase high performance liquid chromatography (RP-HPLC) and reversed-phase ion-interaction chromatography (RP-IIC), using an octadecylsilane stationary phase and acetonitrile as organic modifier. Sodium hexanesulphonate and tetrabutylammonium hydroxide were used as sources of counter ions in ion-interaction chromatography. The retention/pH profiles under in RP-HPLC were compared to the corresponding lipophilicity/pH profiles. Despite the rather hydrophilic nature of the three fluoroquinolones positive retention factors were obtained while there was a shift of the retention maximum towards more acidic pH values. This behavior was attributed mainly to non-hydrophobic silanophilic interactions with the silanized silica gel material of the stationary phase. In ion-interaction chromatography the effect of counter ions over a broad pH range was found to be ruled rather by the ion pair formation in the mobile phase which led to a drastic decrease in retention as a consequence of the disruption of the zwitterionic structure and thereupon the deliberation of a net charge in the molecules. At pH values at which zwitterionic structure was not favored both the ion-exchange and ion pair formation mechanisms were assumed to contribute to the retention.
authors.affiliation: Division of Pharmaceutical Chemistry, Department of Pharmacy, University of Athens, Panepistimiopolis, Zografou 15771, Greece.
authors.forename: C
authors.initials: C
authors.lastname: Pistos
authors.forename: A
authors.initials: A
authors.lastname: Tsantili-Kakoulidou
authors.forename: M
authors.initials: M
authors.lastname: Koupparis
mesh_terms: D000097:Acetonitriles / Q000032:analysis; D000838:Anions; D000975:Antioxidants / Q000737:chemistry; D002021:Buffers; D002626:Chemistry, Pharmaceutical / Q000379:methods; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D004345:Drug Industry / Q000379:methods; D004563:Electrochemistry / Q000379:methods*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D024841:Fluoroquinolones / Q000032:analysis* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D009643:Norfloxacin / Q000032:analysis; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D000838:Anions; D000975:Antioxidants; D002021:Buffers; D004791:Enzyme Inhibitors; D024841:Fluoroquinolones; D007477:Ions; D000644:Quaternary Ammonium Compounds; D012822:Silicon Dioxide; C009405:tetrabutylammonium; D009643:Norfloxacin; C032159:acetonitrile