Simultaneous voltammetric detection of dopamine and ascorbic acid using didodecyldimethylammonium bromide (DDAB) film-modified electrodes

A voltammetric method using a surfactant didodecyldimethylammonium bromide (DDAB) film-modified electrode was developed for simultaneous measurement of various combinations of neurotransmitters and ascorbic acid. The DDAB-modified film has the positive charge and neurotransmitters (dopamine, norepinephrine, and epinephrine) existed as the positively-charged species in the neutral solution whereas AA (ascorbic acid) as a negatively-charged one. Both the cyclic voltammetry (CV) and square-wave voltammetry were used for the measurement of neurotransmitters by means of the DDAB/GC-modified electrode in phosphate buffer solution of pH 6.5. Well-separated voltammetric peaks were observed for dopamine and ascorbic acid at the DDAB/GC-modified electrodes. The oxidation potential of ascorbic acid was shifted to a more positive potential due to a positive electro-catalytic activity of the DDAB/GC-modified electrode while neurotransmitters such as dopamine or norepinephrine or epinephrine were oxidized at a more positive potential due to electrostatic repulsion. The rotating ring disk electrode (RRDE) method was applied to study the redox reaction mechanism of dopamine and ascorbic acid. The DDAB/GC electrode resolved the voltammetric signals of the above analytes successfully.