Voltammetric determination of tryptophan in the presence of uric acid and dopamine using carbon paste electrode modified with multi-walled carbon nanotubes

A carbon paste electrode modified with multi-walled carbon nanotubes (CPE-MWCNTs) was prepared for determination of tryptophan (Trp) in the presence of uric acid (UA) and dopamine (DA). Cyclic voltammetry, chronoamperometry and differential pulse voltammetry (DPV) techniques were used to investigate the modified electrode for the electrocatalytic oxidation of Trp, UA and DA in aqueous solutions. The separation of the oxidation peak potentials for Trp-UA and UA-DA by CPE-MWCNTs was 386 and 144 mV, respectively. The calibration curves obtained for Trp, UA and DA were in the range of 0.60-100.00, 0.40-100.00 and 2.00-170.00 μM, respectively. The detection limits (S/N = 3) were 6.50 × 10−8, 2.70 × 10−7 and 3.60 × 10−7 M for Trp, UA and DA, respectively. The diffusion coefficient for the oxidation of Trp at the surface of modified electrode was calculated as 1.00 × 10−5 cm2 s−1 by chronoamperometry. The chemically modified electrode was successfully used for the quantification of Trp in the presence of UA and DA in serum samples.