Buffer Capacity And Ascorbic Acid Effect The Cyclization Reaction Of Catecholamine And Its Application In The Detection Of Dopamine

Catecholamines are extremely important neurotransmitters in vivo. It is composed of amino chain connected to the catechol (benzene with two hydroxyl groups).They include the Dopamine (DA)、Levodopa (L-DOPA) and Adrenaline (AD) ect. Catecholamines have a widely adjustment to the nervous system and organs of the human body. Parkinson’s Disease (PD) is characterized by a progressive and massive loss of midbrain dopaminergic neurons. Several studies indicates catecholamine after oxidative polymerization can be formed to melanin. So it has important significance to study the cyclization reaction of catecholamine.Using the electrochemical method determine DA, the difficulty in the process of measurement is the interference of ascorbic acid (AA). A A and DA often coexist in the brain and body fluids, and have similar oxidation potential. So the electrochemical analysts have been very interested in how to measure the content of DA in the presence of high concentration of AA.In the present work, we study the buffer capacity and AA affect the cyclization reaction of DA、 L-DOPA and AD. The results show that, compared with the redox peak of catecholamine itself, the peak appeared in a more negative potential after the cyclization reaction. Buffer components in the buffer solution can accept the protons released by catecholamine during the oxidation process, it can suppress the decreasing of pH at the electrode surface and the protonation of amino group. So in dilute buffer solution, the concentration of the buffer solution can promote the cyclization reaction of DA and L-DOPA and AD. Due to the oxidation potential of AA is more negative than catecholamine, therefore AA can reduce the catecholamine-quinone at the electrode surface, it also suppresses the cyclization reaction. And AA more profoundly affects the extent of the cyclization reaction of DA, because the cyclization reaction rate of DA is more slowly than that of L-DOPA and AD.Then we use the electrochemical deposition method to polymerize L-DOPA on the glassy carbon electrode surface, which maked the electrode with negative charge. the modified electrode repels the AA which also has negative charge in the neutral solution, so it can absorb the DA to the electrode surface. we develop a new method that can detect DA in the presence of high concentration of AA. The reduction current is well linear with DA concentration in the range of 1.0× 10-7～1.0× 10-6 mol·L-1, detection limit is 0.5×10-8 mol·L-1. This method has the advantages of high sensitivity, strong anti-jamming capability.