Voltammetric determination of cysteine using carbon paste electrode modified with Co(II)-Y zeolite.

A novel zeolite modified electrode for use in voltammetric determination of l-cysteine (CySH) was described. The electrode comprises a Co(II)-exchanged zeolite Y as modifier in carbon paste matrix. First, the electrochemical behavior of Co(II) in modified carbon paste electrode was studied. The results demonstrated that diffusion can control the redox process of cobalt cations at the surface of the modified electrode. Then, the behavior of the electrode in the presence of CySH was studied by using cyclic voltammetry and a novel behavior was observed. In high concentration of CySH (above 10 mmol L(-1)), one pair of semi-reversible electrochemical extra peak was observed which was assigned to the processes of oxidation-reduction of CySH at the unmodified and modified electrode. Acidic conditions with respect to the neutral one cause an increase in the electrode response. The modified electrode showed a suitable linear calibration graph in the concentration range of 1.0×10(-9)-1.0×10(-3)mol L(-1) cysteine with a detection limit of 2.37×10(-10)mol L(-1). The influence of potential interfering substances on the peak current was studied and the results showed that the method was highly selective for determination of CySH. Thus, the proposed electrode was used for the determination of CySH in real samples including human blood serum, urine, N-acetylcysteine tablet and powdered poultry feed and the satisfactory results were obtained. Typical features of the sensor can be summarized as: low cost, simple preparation, fast response, good stability and selectivity, wide linear range, low detection limit and high reproducibility.