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 fluoroquinolone carboxylic acids (norfloxacin, ciprofloxacin, ofloxacin, enrofloxacin, danofloxacin) and their major degradation products. The theoretical determination of the charge densities of the studied compounds allowed the rapid development of the separation buffer conditions. These rapid estimations can be used as an effective screening tool in capillary electrophoresis (CE) method development. The two CE methods were applied to follow the photostability of enrofloxacin with and without humic substances under natural sunlight conditions. Enrofloxacin showed an average half-life of 2.0 h under summer sunlight conditions and the photolysis kinetic decreased in the presence of humic acids. The presence of humic substances in irradiated solution caused changes in the measured photodegradation product profile. Studies in affinity capillary electrophoresis (ACE) of enrofloxacin and its degradation products with the dissolved humic acids showed a lower adsorption potential of enrofloxacin to the humic phase than the degradation products, The adsorption of some photodegradation products to the dissolved humic matrix may explain the differences in the measured photodegradation products concentration in irradiated solutions. ACE turned out to be a rapid screening tool for the comparison of the adsorption potential of active ingredients and their degradation products to dissolved organic phases using very small amounts of sample. (C) 1999 Elsevier Science B.V. All rights reserved.