Development of capillary electrophoresis methods for the analysis of fluoroquinolones and application to the study of the influence of humic substances on their photodegradation in aqueous phase

Analytical techniques in capillary zone electrophoresis (CZE) and capillary electrokinetic chromatography (MEKC) were developed for the analysis of fl uoroquinolone carboxylic acids (norfloxacin, ciprofloxacin, ofloxacin, enro floxacin, danofloxacin) and their major degradation products. The theoretic al determination of the charge densities of the studied compounds allowed t he rapid development of the separation buffer conditions. These rapid estim ations can be used as an effective screening tool in capillary electrophore sis (CE) method development. The two CE methods were applied to follow the photostability of enrofloxacin with and without humic substances under natu ral sunlight conditions. Enrofloxacin showed an average half-life of 2.0 h under summer sunlight conditions and the photolysis kinetic decreased in th e presence of humic acids. The presence of humic substances in irradiated s olution caused changes in the measured photodegradation product profile. St udies in affinity capillary electrophoresis (ACE) of enrofloxacin and its d egradation products with the dissolved humic acids showed a lower adsorptio n potential of enrofloxacin to the humic phase than the degradation product s, The adsorption of some photodegradation products to the dissolved humic matrix may explain the differences in the measured photodegradation product s concentration in irradiated solutions. ACE turned out to be a rapid scree ning tool for the comparison of the adsorption potential of active ingredie nts and their degradation products to dissolved organic phases using very s mall amounts of sample. (C) 1999 Elsevier Science B.V. All rights reserved.