Table I.

Electrochemical Characteristic of Insulin-Containing Amino Acids

Amino acids (0.1 mmol/l)	Structural groups	Anodic peaks
Cystine	Sulfur containing amino acids	1.03 V, 1.18 V
Phe, Tyr	Aromatic amino acids	None
Gly, Val, Leu, Ile, Glu, Pro, Ala	Aliphatic amino acids
Lys, Arg, Gln, Asn, His	Amide containing amino acids
Ser, Thr	Hydroxyl containing amino acids

The anodic peak of cystine near 1.18 V is much higher than that of phosphate buffer, suggesting new oxidation product formed; the anodic and cathodic peaks of other amino acids are close to that of phosphate buffer, thus these peaks should be attributed to the redox processes of Au electrode.

Conditions: initial potential −0.5 V; scan range −0.5–1.6 V; scan rate 100 mV/s; pH = 2.50; temperature 20°C.