Electrochemical Behaviour Study and Sensitive Determination of Dopamine on Cathodically Pretreated Boron-doped Diamond Electrode

Research Article

Austin J Anal Pharm Chem. 2014;1(1): 1004.

Electrochemical Behaviour Study and Sensitive Determination of Dopamine on Cathodically Pretreated Boron-doped Diamond Electrode

Sochr J, Cinkova K and Svorc L*

Department of Chemical and Food Technology, Slovak University of Technology, Slovak Republic

*Corresponding author: :Svorc L, Institute of Analytical Chemistry, Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovak republic.

Received: June 29, 2014; Accepted: July 08, 2014; Published: July 08, 2014


An unmodified and cathodically pretreated boron-doped diamond (BDD) electrode was used as a sensitive electrochemical sensor for the determination of dopamine (DA) using differential pulse (DPV) and square-wave voltammetry (SWV). Cyclic voltammetric studies indicated a quasi-reversible behaviour of DA in acetate buffer solution at pH 3 with well-defined oxidation and reduction peak at +0.66 and +0.07 V vs. Ag/AgCl/3 M KCl, respectively. The electrode reaction of DA was shown to be a two-electron diffusion-controlled process. With optimized experimental parameters, the current response of DA was proportionally linear in the concentration range from 0.3 to 100μM and 0.7 to 100μM with low detection limits of 0.09 and 0.04μM as well as good repeatability (relative standard deviation of 3.5 and 3.3 %) for DPV and SWV, respectively. The influence of possible interfering compounds was also studied. The practical applicability of the developed method was demonstrated on the determination of DA in model human urine and water samples, with results similar to those obtained by a spectrophotometric method. The proposed electrochemical methodology is simple, inexpensive and rapid with no need of tedious sample pretreatment. In this way, BDD electrode may represent an efficient alternative to widely used modified electrodes in the determination of DA.

Keywords: Dopamine; Catecholamine; Boron-doped diamond electrode; Detection limit; Recovery


Dopamine (3,4-dihydroxyphenethylamine, DA) is a biologically active compound belonging to the group of catecholamine. As a hormone it mediates a variety of the central nervous system functions including emotions, memory and endocrine regulation. DA is secreted in hypothalamus by regular physical activities such as eating, sports and especially during sex [1]. As a neurotransmitter, DA participates in the transfer of nervous signals between dendrites. Moreover, it allows the induction of some reactions (muscle contraction, emptying of the gland). Low concentration values of DA reflect mainly Parkinson’s and Alzheimer’s disease, rarely depression and anhedonia [2]. In contrary, higher concentrations are monitored in the case of long-term smoking, which may lead to dependency and taking hard drugs [3]. Therefore, a reliable determination of DA in the body fluids is important in clinical practice, particularly in diagnostics of the health state.

Instrumental analytical methods for the selective and sensitive detection and quantification of DA in mixtures containing also other compounds in various matrices (human urine, blood, vegetables, plants, etc.) are generally based on utilization of separation and spectral methods such as high-performance liquid chromatography coupled with UV [4], gas chromatography [5,6], capillary electrophoresis [7], fluorescence [8], UV/VIS [9,10] and NMR detection [11]. Nevertheless, these methods require sophisticated and expensive instrumentation, complicated sample pretreatment (preconcentration and/or purification step), long analysis time and extensive consumption of chemicals. In this sense, the development of novel, simple, low-cost and rapid analytical methods for the determination of DA in different matrices is still needed.

In the last decade, electrochemical methods may offer a useful alternative with favourable characteristics such as low expense of instrument, operation simplicity and lower sensitivity to matrix effects in comparison with chromatographic methods. Glassy carbon (GCE) and carbon paste electrodes (CPE) are commonly used in the determination of DA as the non-modified electrode surfaces [12,13]. Mahanthesha et al. [13] developed a method for the determination of DA with detection limit (LOD) of 0.2μM using DPV in phosphate buffer at pH 7. Cathodically pretreated CPE exhibited excellent selectivity in the presence of large excess of ascorbic (AA) and uric acid (UA). Various modifiers (carbon nanotubes (CNTs), graphenes, nanoparticles (NPs), polymer films and biocomponents) have been mainly applied to enhance sensitivity and in order to carry out the selective determination of DA in the presence of common urinary electroactive interferents such as AA, folic (FA) and UA. Shankar et al. [15] developed a method using CPE modified by do-decyl benzene sulfate (DDBS) for simultaneous determination of DA, AA and UA by DPV. The LOD was found to be 0.01μM for DA and the procedure was applied to the analysis of real samples with good recoveries. Voltammetric behaviour of DA on GCE modified by NiFe2O4 – MWCNTs was described by Ensafi et al. [16]. The oxidation of peak current was increased linearly in the wide concentration range of 0.05 – 6 and 6 – 100μM with LOD of 0.2μM using DPV. Applicability of the proposed method was evaluated on the analysis of the pharmaceuticals, human urine and blood serum samples. Golden nanoparticles (AuNPs) immobilized on a polycrystalline gold electrode (AuE) by Raj et al. [17] were used for the sensitive and selective determination of DA (LOD = 0.13 μM) in the presence of AA. The coexistence of AA did not interfere with the voltammetric sensing of DA. Moreover, modified AuE showed excellent antifouling properties.

Nowadays, the use of boron-doped diamond (BDD) electrode is very attractive in electroanalytical chemistry. This non-toxic electrode material has several unique properties such as high thermal conductivity, good mechanical and electrochemical stability in both alkaline and acidic media, low background current, wide potential range (up to 3.5 V) and low sensitivity on dissolved oxygen in aqueous solutions. Due to its high resistance to adsorption processes (presence of sp3 hybridized diamond carbon atoms) BDD differs from other conventional carbon electrodes [18,19]. Its properties can be influenced either by the structure (quantity of doping agents, presence of impurities) or by controllable (hydrogen or oxygen) surface termination. Consequently, BDD has been utilized as an effective alternative to traditional electrode materials in the determination of various biologically active compounds in the field of clinical [20,21] and environmental [22-24] trace analysis.

Electrochemical oxidation of DA and NADH was investigated by Fujishima et al. (1999) [25] using chronoamperometry (CA). Anodically pretreated BDD electrode was used to determine DA selectively with high sensitivity in the presence of large excess of AA in acidic media with a very low LOD = 50nM. BDD electrode was also applied in the investigation of DA oxidation in the study with surface modification based on the utilization of negatively charged AuNPs and polyelectrolyte. Multilayer sphere-modified electrodes showed high electrocatalytic activity and promote the oxidation of DA in the presence of AA with good selectivity. The peak current was linear for the concentration of DA in the range of 5 – 100μM and the LOD was found to be 0.8μM [26]. The BDD electrode modified with gold clusters [27] and AuNPs [28] were prepared and applied for the determination of DA by SWV with LOD = 0.1 and 0.03μM, respectively.

In this paper we describe the electrochemical behaviour of DA and the development of a novel, simple and sensitive voltammetric method for its determination using an unmodified and cathodically pretreated BDD electrode and its application to the analysis of model human urine and water samples. As stated above, the determination of DA has already been investigated by chronoamperometry using anodically pretreated BDD electrode [25]. However, the current work studies in detail the possibilities of a highly sensitive quantification of DA in voltammetric mode with the cathodic pretreatment of an electrode working surface. In this way, BDD offers an efficient modification-free alternative to widely used modified electrodes for a sensitive monitoring of DA.

Materials and Methods

Dopamine hydrochloride (p.a. purity ≥ 99.8 %) was obtained from Sigma-Aldrich Chemie GmbH (Germany) and used without any further purification. The acetate buffer solution (ABS) was prepared by mixing acetic acid (0.1 M) with sodium hydroxide (0.1 M) to the required pH value. A stock standard solution of DA (10mM) was prepared by dissolving 94.8 mg of its solid hydrochloride standard in 50 ml of deionized water and then stored in the refrigerator at +8OC. The working solutions of DA with lower concentrations were freshly prepared by dilution of respective volume of DA standard solution with supporting electrolyte. All other reagents were of analytical grade purity.

The electrochemical analyzer Autolab PGSTAT-302N (Metrohm Autolab B.V., The Netherlands) potentiostat/galvanostat was applied for all electrochemical measurements, controlled with the NOVA 1.10 electrochemical software. The three electrode cell system was used with BDD as a working electrode (Windsor Scientific Ltd, UK) with 3 mm inner diameter of an active surface, resistivity of 0.075 O cm and boron content of 1000ppm, a platinum wire as a counter electrode and an Ag/AgCl/3 M KCl as a reference electrode. All pH values were measured by pH meter Model 215 (Denver Instrument, USA) with a combined electrode (glass-reference electrode). The pH meter was calibrated weekly with standard buffer solutions. All potentials mentioned in this paper are referred against Ag/AgCl/3 M KCl reference electrode. The spectral measurements were made using 6715 UV/VIS Spectrometer Jenway (Bibby Scientific Limited, UK).

Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square-wave voltammetry (SWV) were used as electrochemical techniques for the purpose of this work. Before measuring, dissolved oxygen was eliminated by gaseous nitrogen for 10 min. prior to use of BDD electrode at the beginning of every work day, it was rinsed with deionized water. Subsequently, it was cathodically pretreated by applying -1.5 V for 30 s in 0.1 M H2SO4 solution in order to predominantly reach hydrogen terminated surface. After optimizing the instrumental parameters of DPV and SWV, calibration curves were obtained by successive addition of aliquots of the DA stock standard solution into the electrochemical cell already containing 25mL of supporting electrolyte; each concentration was measured in six replicate. The linear least-square regression in OriginPro 8 (OriginLab Corporation, USA) was used for the evaluation of calibration curve and the relevant results (slope and intercept) were reported with 95 % confidence level. The detection limit (LOD) was calculated as the three times standard deviation for the blank solution divided by the slope of the calibration curve.

Drug-free human urine sample was obtained from a healthy non-smoking volunteer (man, 27 years) immediately before the experiments. The water samples were obtained from communal source of drinking water and from the river. Aliquot volume of fresh urine (1mL) and water (1mL) was placed into the electrochemical cell with 20mL of supporting electrolyte. Subsequently, this solution was suitably fortified with DA standard solution to achieve a required concentration. Analysis of all samples was performed by the standard addition method with respective volumes of 20, 40 and 60μL (n = 6).

The samples for the spectrophotometric method were prepared similarly according to the above mentioned process. Before the addition of acidic medium (ABS, pH 3) the same volume K4[Fe(CN)6] and FeCl3 (1 mL), both of 15 mM was added . After the reaction time of 35 min, the solution was subsequently 50-times diluted and theabsorbance of prepared solutions was measured at 725 nm. This procedure was undertaken according to Guo et al. (2009) [9].

Results and Discussion

First, the electrochemical behaviour of DA was studied in various electrolytes such as Britton-Robinson (BRBS), phosphate (PBS) and acetate (ABS) buffer in the pH range of 3–10 by CV on the cathodically pretreated BDD electrode (results not shown). The best results with the highest magnitude, low background and good repeatability were obtained in ABS. Hence, it was chosen as an optimal medium for further voltammetric studies in this work. Generally, DA is an electrochemically active substance which can transfer electrons from solution to the electrode. Figure 1 shows the representative CV voltammograms in the presence of 0.1mM DA in ABS at pH 3 (black curve). The well-defined oxidation peak of DA was observed on the forward scan at the potential of +0.66 V. On the reverse scan the corresponding cathodic peak was recorded at +0.07 V indicating the quasi-reversible character of electrode reaction of DA on BDD electrode. The electrochemical behaviour of DA well coincides with those previously reported in literature [14,15].