Two amino acids – D-penicillamine (D-PA) and tryptophan (TRP) – could be simultaneously determined in an aqueous solution (pH 7.0) using a novel benzoylferrocene-modified carbon nanotube paste electrode. The results indicate that the electrode is efficient in terms of its electrocatalytic activity for the oxidation of D-PA, leading to an overpotential reduction by more than 155 mV. Using square wave voltammetry, measurement of D-PA and TRP in one mixture could be done independently from each other with a potential difference of about 205 mV. The proposed electrochemical sensor exhibited a linear calibration plot ranging from 1.0 106 to 8.0 104 M with a detection limit of 1.3 107 M for D-PA.
