Electrocatalytic and selective determination of d ‐penicillamine in the presence of tryptophan using a benzoylferrocene‐modified carbon nanotube paste electrode

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 × 10−6 to 8.0 × 10−4 m with a detection limit of 1.3 × 10−7 m for D‐PA. Finally, the proposed method was applied to the determination of D‐PA in a D‐PA capsule.