| The environmental impact of pharmaceutical chemicals has been the focus of great concern in recent years. Antibiotics, such as fluoroquinolones, have attracted attention since these drugs are often prescribed in relatively high doses of which only a percentage of the active drug is metabolized. Although antibiotics have a low toxicity to humans, in the environment they have the potential to induce antibiotic resistance in pathogenic and non-target microorganisms. While several studies have reported the presence of the pharmaceuticals in the environment, little has been done to identify the pathways resulting in their attenuation and fate in surface waters.; A series of systematic laboratory and field scale experiments have been implemented to identify the prominent mechanism for the attenuation of the fluoroquinolones ciprofloxacin and enrofloxacin in surface waters at environmentally relevant concentrations and to elucidate the structures of the major products formed. To facilitate these investigations, solid phase extraction was used to prepare the samples collected from natural water matrices, while HPLC-UV/VIS-MS was used to monitor the loss of the parent drugs and identify the transformation products formed. The studies showed that the disappearance of ciprolloxacin and enrofloxacin in surface water is driven primarily by photochemical degradation, except in the presence of high concentrations of particulate organic carbon where the mechanism was dominated by adsorption.; While adsorption resulted in removal of the ciprofloxacin from solution, photodegradation lead to the destruction of the parent compound and the formation of several products, including two unique compounds TP-245 and TP-270. Prior to its application to the complex mixture of ciprofloxacin degradation products, the newly acquired on-line HPLC 1H-NMR system was optimized through the study of the isomerization of two alachlor-ethane sulfonic acid isomers through a series of stopped-flow experiments. The stopped-flow HPLC-NMR instrument was then used to measure one and two dimensional 1H NMR spectra for ciprofloxacin and a number of its transformation products. Assessment of the 1H NMR and MS/MS data acquired for ciprofloxacin and several known transformation products allowed for the unequivocal structure elucidation of TP-245 and a proposed structure for TP-270. |
