Simultaneous electrochemical determination of dopamine, melatonin, methionine and caffeine

• A ZnO nanorods modified carbon paste electrode have been fabricated.
• This electrode reduced the oxidation potential of dopamine.
• It resolved the voltammetric waves of dopamine, melatonin, methionine and caffeine.

A novel carbon paste electrode modified with ZnO nanorods and 3-(4′-amino-3′-hydroxy-biphenyl-4-yl)-acrylic acid (3,4′AAZCPE) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of dopamine, is described. It has been found that the oxidation of dopamine at the surface of modified electrode occurs at a potential of about 180 mV less positive than that of an unmodified carbon paste electrode. The detection limit of 5.6 × 10−8 M for dopamine was obtained using square wave voltammetry (SWV). In addition, this modified electrode was used for simultaneous determination of dopamine, melatonin, methionine and caffeine. Finally, the modified electrode was used for determination of dopamine, melatonin, methionine and caffeine in human blood serum and urine samples.