Continuous microwave-assisted extraction coupled with derivatization and fluorimetric monitoring for the determination of fluoroquinolone antibacterial agents from soil samples

Abstract

An automated screening approach for fluoroquinolone (FQ) antibiotics (norfloxacin and ciprofloxacin) in soil samples has been developed. The proposed approach consists on dynamic microwave-assisted extraction and subsequent real-time on-line monitoring of the analytes extracted; thus, the extraction is halted when complete leaching of the analytes has been reached (independently of the sample matrix), avoiding extraction times in excess. The end of the extraction allowed quantifying the total content of the analytes. The extraction was carried out using pure water as extractant and consisted of a number of extraction cycles (depending on the sample matrix) in which the sample was subjected to microwave irradiation while the direction of the extractant was changed in an iterative manner. The target analytes were fluorometrically monitored after derivatization with a terbium (Tb3+)/tri-n-octylphosphine oxide (TOPO)/cetylpyridinium chloride (CPCl)/acetate buffer solution. Optimum conditions for analytes extraction and formation of FQ–Tb3+–TOPO ternary complexes have been obtained using the experimental design methodology. The mean recoveries from soil samples spiked with 5 and 0.5μg/g of each analyte were (95.2±4.16%) and (98±5.21%), respectively. The within-laboratory reproducibility and repeatability, expressed as relative standard deviation, were 7.29 and 5.80%, respectively. The approach only allows monitoring of the overall content of the species that yield fluorescent complexes with the derivatizing reagent, so the use of chromatography is mandatory for individual separation/quantification of the target compounds.