Electrochemical characterisation of nanoparticulate zirconium dioxide-on-gold electrode for electrochemical detection in flow-based analytical systems

The modification of gold (Au) electrode using zirconium dioxide nanoparticles (ZrO₂ NPs) has been investigated for enhanced electrochemical (EC) detection in flow-based analytical systems. The average size of ZrO₂ NPs deposited in a facile procedure on the Au electrode surface was calculated as 22.5 ± 7 nm. Redox behaviour of a test solute, ferrocyanide [Fe(CN)₆]^4-, on the bare- and ZrO₂-Au electrodes was initially investigated using cyclic voltammetry. From the voltammograms of bare- and ZrO₂-Au electrodes, the EC reversibility values and effective surface area were experimentally determined for the first-time in this study. Further, EC reversibility and 100% increase in effective electrode surface area were confirmed in ZrO₂-Au electrode through investigating the detection response (current). The EC performance of the ZrO₂-Au electrode was then investigated in amperometric detection of selected electroactive solutes separated by reversed-phase HPLC. The limits of detection (LODs), based upon an injection volume of 10 μL for ascorbic acid, 2,3-dihydroxybenzoic acid and pyrocatechol were 0.09 μM, 0.04 μM, and 0.10 μM, respectively (RSD 2.5%, <i>n</i> = 9, r² = 0.99 for concentration range 1-100 μM). These LODs for the ZrO₂-Au electrode were 2-times lower for 2,3-DHBA, and pyrocatechol than the lowest LODs reported in the literature for EC detection in HPLC. The ZrO₂-Au electrode demonstrated satisfactory repeatability of preparation, detection reproducibility and high stability (8.5 h) during continuous-flow in FIA and 45 days during intermittent use with HPLC, at flow rate of 0.6 mL min^-1. This work has demonstrated a comprehensive EC characterisation of Au electrode with nanoparticulate ZrO₂ for flow-based analytical systems.