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

A renewable three-dimensional chemically modified carbon ceramic electrode containing Ru [(tpy)(bpy)Cl] PF6 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 x 10(3) and 2.5 x 103 M-1 s(-1), respectively. Under the optimized condition the calibration curves are linear in the concentration range 5-685 and 5-700 muM for L-cysteine and glutathione determination, respectively. The detection limit (SIN = 3) and sensitivity is 1 muM, 5 nA/muM for L-cysteine and 1 muM, 7.8 - nA/muM 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. (C) 2003 Elsevier Science B.V. All rights reserved.