Simultaneous determination of l‑DOPA, l‑tyrosine and uric acid by cysteic acid - modified glassy carbon electrode.

Electrochemical oxidation of l‑cysteine resulted in the formation of a film on glassy carbon electrode. In a solution of levodopa (l‑DOPA), l‑tyrosine (Tyr) and uric acid (UA), three separated intense anodic peaks were appeared in differential pulse voltammetry regime. Experimental conditions were optimized for simultaneous determination of the three compounds. All experiments were carried out in phosphate buffer solution (0.1 M, pH 8). Calibration curves were obtained in the presence of various concentrations of l‑DOPA, Tyr, and UA. Linear concentration ranges were 0.65-22 μM for l‑DOPA, 3.5-96 μM for Tyr, and 1.0-19 μM for UA. The limits of detection (LODs) were calculated as 0.2, 1.1 and 0.36 μM for l‑DOPA, Tyr, and UA, respectively. The electrochemical sensor was used successfully for the simultaneous determination of l‑DOPA, Tyr, and UA species in human blood serum samples.