Evaluation of Rice Husk for SPE of Fluoroquinolones from Environmental Waters Followed by UHPLC-HESI-MS/MS

Untreated rice husk (RH) was evaluated as solid-phase extraction (SPE) sorbent for Fluoroquinolone antibiotics (FQs). This natural material, made of cellulose, hemicellulose, lignin and silica, and containing various functional groups, i.e., carboxyl, hydroxyl, and amidogen residues, is a potential sorbent material for polar aromatics like FQs. First, the RH capability to adsorb FQ species from water was studied by batch sorption experiments in tap and river waters, and the experimental data, fitted by the Langmuir model, gave adsorption capacities up to 32 mg g(-1). Then, RH was tested as column-packed sorbent for pre-concentration of tap and not tampered river waters spiked with six widely employed FQs, i.e., Ciprofloxacin, Danofloxacin, Enrofloxacin, Levofloxacin, Marbofloxacin, and Norfloxacin. The analytes were quantitatively adsorbed on the RH cartridge at the native pH, simultaneously eluted by NH3-MeOH mixture, separated in an 8 min ultrahigh-performance liquid chromatography run and quantified/confirmed by electrospray ionization tandem mass spectrometric detection in single reaction monitoring mode. Recoveries in the range 71-120% were observed (RSD < 15%, n = 3) for 75-1000 ng L-1 spikes. Method detection limits were in the range 25-33 ng L-1. The batch-to-batch reproducibility was assessed, and the analytical procedure was applied to the determination of FQs in actual environmental waters.