Renewable sol–gel carbon ceramic electrodes modified with a Ru-complex for the amperometric detection of l-cysteine and glutathione

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A renewable three-dimensional chemically modified carbon ceramic electrode containing Ru [(tpy)(bpy)Cl] PF 6 was constructed by sol–gel technique. It exhibits an excellent electro-catalytic activity for oxidation of l-cysteine and glutathione at pH range 2–8. Cyclic voltammetry was employed to characterize the electrochemical behavior of the chemically modified electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for l-cysteine and glutathione by hydrodynamic amperometry. Optimum pH value for detection is 2 for both l-cysteine and glutathione. The catalytic rate constants for l-cysteine and glutathione were determined, which were about 2.1×10 3 and 2.5×10 3 M −1 s −1, respectively. Under the optimized condition the calibration curves are linear in the concentration range 5–685 and 5–700 μM for l-cysteine and glutathione determination, respectively. The detection limit (S/N=3) and sensitivity is 1 μM, 5 nA/μM for l-cysteine and 1 μM, 7.8 nA/μM for glutathione. The relative standard deviation (RSD) for the amperogram's currents with five injections of l-cysteine or glutathione at concentration range of linear calibration is <1.5%. The advantages of this amperometric detector are: high sensitivity, good catalytic effect, short response time ( t<3 s), remarkable long-term stability, simplicity of preparation and reproducibility of surface fouling (RSD for six successive polishing is 3.31%). This sensor can be used as a chromatographic detector for analysis of l-cysteine and glutathione.