Electrocatalytic oxidation and determination of homocysteine at nanotubes-modified carbon paste electrode using dopamine as a mediator

A carbon paste electrode modified with multiwall carbon nanotubes (MWCNTPE) was prepared to study the electrocatalytic activity of dopamine (DP) in the presence of homocysteine (HCy) and it was used for the determination of HCy. The diffusion coefficient of HCy (D = 6.79x10(-6) cm(2) s(-1)), and the kinetic parameters of its oxidation, such as electron transfer coefficient (alpha = 0.46), and rate constant (k(h) = 7.44x10(2) dm(3) mol(-1) s(-1)) were also determined using electrochemical approaches. Under the optimum pH of 5.0, the peak current of oxidation of HCy at MWCNTPE in the presence of DP occurred at a potential of about 530 mV and the results showed that the oxidation peak current of HCy at the modified carbon nanotubes electrode was higher than on the unmodified electrode. The peak current of differential pulse voltammograms of HCy solutions increased linearly in the range 3.0-600 mu M HCy with a detection limit of 2.08 mu M HCy. This method was also examined for determination of HCy in physiological serum and urine. samples.