Highly Sensitive Square Wave Adsorptive Stripping Voltammetric Determination of Dopamine in Human Plasma Using a Cytosine-Modified Pencil Graphite Electrode.

Dopamine (DA) is an essential neurotransmitter in the central nervous system, playing a vital role in the human brain. A simple, facile, fast, and low-cost method based on the cytosine-modified pencil graphite electrode (CT/PGE) was developed to determine dopamine (DA) by using the square wave adsorptive stripping voltammetry (SWAdSV) technique. The cytosine (CT) was modified on the bare pencil graphite electrode (PGE) by conducting cyclic voltammetry (CV) over a potential range between +0.7 and +1.9 V for 10 cycles. A number of techniques including CV, electrochemical impedance spectroscopy (EIS), and field-emission scanning electron microscopy (FE-SEM) were used to characterize the CT/PGE. The impact of varying pH values (6.4, 6.8, 7.2, 7.6, and 8.0) and phosphate buffer solution (PBS) on the DA determination was studied using the square wave voltammetry (SWV) technique. The basic voltammetric techniques SWV, SWAdSV, differential pulse voltammetry (DPV), and differential pulse adsorptive stripping voltammetry (DPAdSV) were used to determine the most suitable method for analytical applications. The accumulation time was optimized using the SWAdSV technique on the CT/PGE, within a potential range of -0.4 to +0.4 V. The CT/PGE was evaluated in the presence of several interferents, such as urea, ascorbic acid, and uric acid. Under optimum conditions, the CT/PGE exhibited a well-defined linear relationship for DA across the concentration ranges of 0.1 mM to 0.5 μM and 0.1 μM to 7.5 nM, with a limit of detection (LOD) of 2.28 nM and a limit of quantification (LOQ) of 6.85 nM. The suggested method was effectively applied to the determination of DA in human plasma serum samples to evaluate its suitability.