Electro-analytical Characterization and Method Validation of Cysteine by Cyclic Voltammetry

This study investigates the electrochemical behavior of L-cysteine using cyclic voltammetry (CV) on a glassy carbon electrode (GCE) in aphosphate buffer solution (pH 8.0). Cysteine, a biologically significant thiol-containing amino acid, exhibits an irreversible oxidation peakcorresponding to the electrooxidation of its -SH group, following a diffusion-controlled mechanism. The influence of scan rate (10–70 mV/s)and pH (4.0–9.0) on the redox process was systematically examined, revealing a proton-coupled electron transfer (PCET) mechanism. Themethod was validated as per ICH guidelines, demonstrating excellent linearity (10–50 x10-3 M, R² = 0.9752), precision (%RSD < 1.12%),accuracy (recovery 98.64–103.06%), and sensitivity (LoD = 0.192 x10-2 M, LoQ = 0.582 x10-2 M). Robustness studies confirmed methodstability under slight pH variations. These findings establish CV as a rapid, sensitive, and cost-effective alternative for cysteine quantificationin biochemical and nutritional analysis.