Voltammetry and amperometric detection of tetracyclines at multi-wall carbon nanotube modified electrodes

Abstract

The voltammetric behaviour and amperometric detection of tetracycline (TC) antibiotics at multi-wall carbon nanotube modified glassy carbon electrodes (MWCNT-GCE) are reported. Cyclic voltammograms of TCs showed enhanced oxidation responses at the MWCNT-GCE with respect to the bare GCE, attributable to the increased active electrode surface area. Hydrodynamic voltammograms obtained by flow-injection with amperometric detection at the MWCNT-GCE led us to select a potential value E _det = +1.20 V. The repeatability of the amperometric responses was much better than that achieved with bare GCE (RSD ranged from 7 to 12%), with RSD values for i _p of around 3%, thus demonstrating the antifouling capability of MWCNT modified electrodes. An HPLC method with amperometric electrochemical detection (ED) at the MWCNT-GCE was developed for tetracycline, oxytetracycline (OTC), chlortetracycline and doxycycline (DC). A mobile phase consisting of 18:82 acetonitrile/0.05 mol L⁻¹ phosphate buffer of pH 2.5 was selected. The limits of detection ranged from 0.09 μmol L⁻¹ for OTC to 0.44 μmol L⁻¹ for DC. The possibility to carry out multiresidue analysis is demonstrated. The HPLC-ED/MWCNT-GCE method was applied to the analysis of fish farm pool water and underground well water samples spiked with the four TCs at 2.0 × 10⁻⁷ mol L⁻¹. Solid-phase extraction was accomplished for the preconcentration of the analytes and clean-up of the samples. Recoveries ranged from 87 ± 6 to 99 ± 3%. Under preconcentration conditions, limits of detection in the water samples were between 0.50 and 3.10 ng mL⁻¹.