Ruthenium and ruthenium dioxide-modified graphite–ethylene/propylene/diene and graphite–Teflon composite electrodes as amperometric flow detectors. Application to the determination of methionine

Abstract

The flow injection amperometric performance of solid composite graphite electrodes with ethylene/propylene/diene (EPD) or Teflon as binding agents, and with Ru or RuO₂ particles as electrocatalytic modifiers has been compared. Both, Ru and RuO₂ modified electrodes exhibited electrocatalytic properties on the methionine oxidation process in alkaline media. The electrodes composition and the hydrodynamic and chemical variables were optimized. Graphite–EPD (GEPD) electrodes showed a better analytical performance than graphite–Teflon (GPTFE) electrodes. Furthermore, a better sensitivity, repeatability and reproducibility was observed for RuO₂–GEPD electrodes when compared with Ru–GEPD electrodes. At an applied potential of +0.50 V, a detection limit for methionine of 4.8×10^–5 mol L^–1, similar to those reported in the literature for other RuO₂-modified electrodes, was obtained. The analytical applicability of RuO₂–GEPD electrodes was demonstrated by determining methionine in a complex pharmaceutical formulation.