High oxygen content graphene oxide functionalized with magnetite (GO@Fe3O4) via magnetic solid phase extraction and capillary electrophoretic determination of tetracyclines in milk.
Abstract
The present work describes the synthesis and application of magnetite-functionalized graphene oxide with higher oxygen content (GO@Fe3O4) as an adsorbent in the analysis of four tetracyclines: tetracycline (TC), chlortetracycline (CT), oxytetracycline (OT), and doxycycline (DT) in milk samples by magnetic solid phase extraction (MSPE) coupled with capillary electrophoresis (CE). Graphene oxide (GO) was synthesized by the Tour method, employing three different H2SO4/H3PO4 ratios to evaluate the oxidation degree. The GO synthesized with higher oxygen content was functionalized with magnetite (Fe3O4) using tetramethyl orthosilicate (TMOS) and 3-aminopropyltriethoxysilane (APTES) via the sol-gel methodology. Under the optimal conditions for MSPE (pH = 8.0, amount of adsorbent: 10.0 mg, and contact time: 5.0 min), the methodology provides a satisfactory extraction percentage. The adsorbent was characterized using SEM-EDS, FTIR spectroscopy, XRD, and TGA. The adsorption process was investigated with adsorption isotherms based on Langmuir, Freundlich, and Dubinin-Radushkevich models and Scatchard analysis. The developed adsorbent presents maximum extraction capacities of 1.17 to 7.66 mg g-1. The proposed methodology provides limits of detection (LODs) and limits of quantification (LOQs) of 33, 44, and 32 µg L-1 and 100, 135, and 98 µg L-1 for TC, OT, and DT, respectively, with inter- and intraday repeatability achieving % RSD < 10.0% in all cases. The accuracy was evaluated by determining the recovery percentages of blank milk samples that were spiked at three concentration levels: 100.0, 150.0, and 250.0 µg L-1. The recovery percentages range from 91.3 to 106.2% with % RSD values between 1.3 and 7.7%. The proposed methodology was applied in the analysis of 10 commercial milk samples from different brands.
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