Graphene-derivatized silica as an efficient solid-phase extraction sorbent for pre-concentration of fluoroquinolones from water followed by liquid-chromatography fluorescence detection

tThis work presents a novel analytical method based on graphene for the determination of five widelyused fluoroquinolones (FQs) in aqueous matrices. The procedure entails solid-phase extraction (SPE) ongraphene-derivatized silica (200 mg), followed by liquid chromatography with fluorescence detection.Monolayer graphene oxide (GO) flakes were covalently bonded onto aminopropyl silica microparticles,and then treated with aqueous hydrazine to obtain the reduced GO (RGO). The final material (RGO–silica)was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BETanalysis, and for the first time evaluated as mixed-mode sorbent for the SPE of FQs from natural waters.Accuracy was studied on tap/raw river water in the concentration range 5–10,000 ng L−1, obtaining meanabsolute recoveries from 72 to 118%. The inter-day precision was good, showing relative standard devi-ations (RSDs) in the range 5–15%. Sample volumes up to 1 L provided enrichment factors up to 1000,achieving accurate quantification of concentrations as low as 5 ng L−1. The analytes were simultaneouslyand quantitatively eluted from the RGO–silica cartridge in a single fraction by using acetonitrile com-bined with aqueous tetrabutyl ammonium hydroxide. The batch-to-batch reproducibility was verified onthree independently prepared RGO–silica samples. RGO–silica was advantageous in terms of adsorptioncapacity and reusability with respect to commercial sorbents; the cartridge proved to be reusable forat least 10 consecutive extractions, with no significant loss of efficiency (recovery >70%). The analyticalprocedure was applied to the determination of FQs in actual environmental waters.