A strategy to differentiate dopamine and levodopa based on their cyclization reaction regulated by pH

Levodopa is often used to treat Parkinson?s disease. It coexists with dopamine in human fluids and is electrochemically oxidized at the same potential as dopamine. Differentiating levodopa from dopamine is difficult via electrochemical techniques. Taking advantage of the differences in the rate constants of levodopa and dopamine for the intramolecular cyclization reaction, we observed that the cyclization reaction of dopamine-quinone was completely suppressed under pH 4.8, while that of levodopa-quinone occurred. The product of cyclization caused a new cathodic peak at negative potential. Its peak current was dependent on the concentration of levodopa but not that of dopamine. As a result, we developed a method of detecting levodopa in the presence of dopamine with a bare glassy carbon electrode. Levodopa is often used to treat Parkinson?s disease. It coexists with dopamine in human fluids and is electrochemically oxidized at the same potential as dopamine. Differentiating levodopa from dopamine is difficult via electrochemical techniques. Taking advantage of the differences in the rate constants of levodopa and dopamine for the intramolecular cyclization reaction, we observed that the cyclization reaction of dopamine-quinone was completely suppressed under pH 4.8, while that of levodopa-quinone occurred. The product of cyclization caused a new cathodic peak at negative potential. Its peak current was dependent on the concentration of levodopa but not that of dopamine. As a result, we developed a method of detecting levodopa in the presence of dopamine with a bare glassy carbon electrode. ? 2021 Elsevier B.V. All rights reserved.

Automated summary

Levodopa is often used in treating Parkinson's disease and is difficult to differentiate from dopamine via electrochemical techniques. By taking advantage of the differences in rate constants between levodopa and dopamine, a method was developed to detect levodopa in the presence of dopamine, ignoring the interference from dopamine at pH 4.8.