Microwave-assisted extraction and determination of enrofloxacin and danofloxacin photo-transformation products in soil

Here we describe the extraction from soil of the major photo-transformation products (PTPs) of enrofloxacin (ENR) and danofloxacin (DAN), two fluoroquinolones (FQs) widely used in veterinary medicine and of growing environmental concern, because their PTPs have been shown to retain high antibacterial activity. The microwave-assisted extraction (MAE) technique developed previously for determination of FQs, and based on use of an alkaline aqueous solution of Mg2+ as a complexing agent for the analytes, was applied to agricultural soil samples fortified with different amounts of the PTPs and residues of the parent compounds (53-1000 ng g(-1) for ENR, 24-148 ng g(-1) for DAN). The PTPs, obtained by irradiation of thin layers of the two drugs, were, after extraction, separated and quantified by HPLC-FD. Good recovery (70-130 %) and precision (RSDs 1-6 % for repeatability and 9-22 % for reproducibility) were obtained by use of the overall analytical procedure. The method was applied for the first time to study the in-soil lifecycle of ENR and DAN PTPs, generated in the matrix by irradiation under natural sunlight, at environmentally significant concentrations. Results indicated that soil-adsorbed FQ PTPs are themselves liable to photodegradation and have lifetimes comparable with those of parent compounds.