Electrocatalytic oxidation of sulfur containing amino acids at renewable Ni-powder doped carbon ceramic electrode: Application to amperometric detection L-cystine, L-cysteine and L-methionine

Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple due to Ni(II)/Ni(III) system with surface confined characteristics. The modified electrode shows excellent catalytic activity toward L-cystine, L-cysteine and L-methionine oxidation at reduced overpotential in alkaline solutions. In addition the antifouling properties at the modified electrode toward the above analytes and their oxidation products increases the reproducibility of results. L-cystine, L-cysteine and L-methionine were determined chronoamperometricaly at the surface of this modified electrode at pH range 9-13. Under the optimized conditions the calibration curves are linear in the concentration range 1-450 mu M, 2-90 mu M and 0.2-75 mu M for L-cystine, L-methionine and L-cysteine determination, respectively. The detection limit and sensitivity were 0.64 mu M, 3.8 nA/ mu M for L-cystine, 2 mu M, 5.6 nA/ mu M for L-methionine and 0.2 mu M and 8.1 nA/mu M for L-cysteine. The advantageous of this modified electrode is high response, good stability and reproducibility, excellent catalytic activity for oxidation inert molecules at reduced overpotential and possibility of regeneration of the electrode surface by potential cycling for 5 minutes. Furthermore, the modified electrode has been prepared without using specific reagents. This sensor can be used as an amperometric detector for disulfides detection in chromatographic or flow systems.