Selective determination of dopamine in the presence of ascorbic acid at the carbon atom wire modified electrode

Selective recognition of 5-hydroxytryptamine and dopamine on a multi-walled carbon nanotube-chitosan hybrid film-modified microelectrode array

It is difficult to determine dopamine (DA) and 5-hydroxytryptamine (5-HT) accurately because of the interference of ascorbic acid (AA) in vitro, which has a high concentration and can be oxidized at a potential close to DA and 5-HT at a conventional electrode, combined with the overlapping voltammetric signal of DA and 5-HT at a bare electrode. Herein, chitosan (CS) was used as a stabilizing matrix by electrochemical reaction, and multi-walled carbon nanotubes (MWCNTs) were modified onto the microelectrode array (MEA). The CS-MWCNT hybrid film-modified MEA was quite effective at simultaneously recognizing these species in a mixture and resolved the overlapping anodic peaks of AA, DA and 5-HT into three well-defined oxidation peaks in differential pulse voltammetry (DPV) at −80 mV, 105 mV and 300 mV (versus Ag|AgCl), respectively. The linear responses were obtained in the range of 5 × 10⁻⁶ M to 2 × 10⁻⁴ M for DA (r = 0.996) and in the range of 1 × 10⁻⁵ M to 3 × 10⁻⁴ M for 5-HT (r = 0.999) using the DPV under the presence of a single substance. While DA coexisted with 5-HT in the interference of 3 × 10⁻⁴ M AA, the linear responses were obtained in the range of 1 × 10⁻⁵ M to 3 × 10⁻⁴ M for selective molecular recognition of DA (r = 0.997) and 5-HT (r = 0.997) using the DPV. Therefore, this proposed MEA was successfully used for selective molecular recognition and determination of DA and 5-HT using the DPV, which has a potential application for real-time determination in vitro experiments.

Flow injection-chemiluminescence determination of dopamine using potassium permanganate and formaldehyde system

A simple and sensitive flow injection-chemiluminescence method for the determination of dopamine has been proposed. The method is based on the enhancing effect of dopamine on the chemiluminescence emission generated by the reaction of potassium permanganate with formaldehyde in an acidic medium. The proposed procedure allows the determination of dopamine over the concentration range of 3.1×10(-8)-1.7×10(-5) mol/L and with a detection limit of 1.0×10(-8) mol/L. The linear regression equation was F=44.4912+1.07×10(9)(*)C (correlation coefficient, r(2)=0.9998). The relative standard deviation is 2.1% for the determination of 1.0×10(-8) mol/L dopamine (n=11). The method was successfully applied to the determination of dopamine in pharmaceutical preparation with satisfactory results. The recoveries were found in the range of 96.5-101.3%.

Differential pulse voltammetric determination of dopamine with the coexistence of ascorbic acid on boron-doped diamond surface

Electrochemical determination of dopamine (DA) in the presence of ascorbic acid (AA) was achieved on boron-doped diamond (BDD) film electrode by differential pulse voltammetry. The experimental results indicated that the oxidative peaks of DA and AA could be separated completely on anodically-treated (BDD) electrode without further modification, although these two peaks can not be separated on glassy carbon electrode. The peak separation of DA and AA was developed to be 0.44 V. High sensitivity was obtained to determine DA selectively with the coexisting of a large excess of AA in acidic media by DPV. The detection limit of DA was achieved to be 1.1 × 10-6 M in the presence of AA with the concentration of 200 times more than DA. This technique was also applied to the determination of DA in real samples.

Spectrofluorimetric Determination of Dopamine Using Chlorosulfonylthenoyltrifluoroacetone–Europium Probe

A new spectrofluorimetric method was developed for the determination of trace amounts of dopamine (DA). Using chlorosulfonylthenoyltrifluoroacetone (CTTA)-europium ion (Eu(3+)) as a fluorescent probe, in a buffer solution at pH = 10.0, DA can remarkably enhance the fluorescence intensity of the CTTA-Eu(3+) complex at lambda = 612 nm; the enhanced fluorescence intensity of Eu(3+) is proportional to the concentration of DA. Optimum conditions for the determination of DA were also investigated. The linear range and detection limit for the determination of DA were 5.0 x 10(-8) approximately 1.6 x 10(-5) mol/l and 3.2 x 10(-8) mol/l. This method is simple, practical and relatively free of interference from coexisting substances, and can be applied to assess DA in injection and human serum samples with good precision and accuracy.

Experimental and theoretical study of the electrochemical behavior of N-protonated dopamine at Nafion multiwalled carbon nanotubes (MWNTs) modified glassy carbon (GCE) electrode

The electrochemistry of N-protonated dopamine (DAH+) was studied by cyclic voltammetry (CV) at a glassy carbon electrode modified by Nafion multiwalled carbon nanotubes (MWNTs) in phosphate buffers (pH 5.50) and the results show that the standard electrode potential of half reaction for DAH+(O),H+/ DAH+(R) is 0.74 V. Calculations are performed using DFT B3LY/6-31G(d,p) for nine conformers of N-protonated dopamine (DAH+(R)) and three conformers of oxidized N-protonated dopamine (DAH+(O)). The energies of solvation and sum of electronic and thermal free energies of DAH+(R), DAH+(O), p-benzoquinone (p-BQ), and p-hydroquinone (p-HQ) are calculated at same level. The theoretical weighted average of the standard electrode potential (0.732 V) for DAH+(O),H+/ DAH+(R), using the transformed Gibbs free energies of the stable DAH+(R) and DAH+(O) with a p-BQ, H+/p-HQ reference electrode, is consistent with the experimental one of 0.74 V.Key words: dopamine, DFT, cyclic voltammetry, standard electrode potential.

Sodium dodecyl sulfate-modified carbon paste electrodes for selective determination of dopamine in the presence of ascorbic acid

A carbon paste electrode (CPE) modified by a monolayer film of sodium dodecyl sulfate (SDS) was used for detection of dopamine (DA). Cyclic voltammetry demonstrated improved response of the DA sensor. This suggests the effectivity of surface modification of CPE by SDS. Impedance spectroscopy was used for the characterization of CPE surface properties. The effect of SDS concentration on the electrode quality also reveals that SDS formed a monolayer on CPE surface with a high density of negative-charged end directed outside the electrode. As a result, the carbon paste electrode modified with SDS (SDS/CPE) exerted discrimination against ascorbic acid in physiological circumstance. Thus, it can selectively determine dopamine even in the presence of 220-fold AA combined with differential pulse stripping voltammetry. In pH 7.40 phosphate buffer solution, the oxidation peak current on differential pulse voltammograms increases linearly with the concentration of DA in the range of 5.0 x 10(-7) to 8.0 x 10(-4) mol . L(-1) with a detection limit of 5.0 x 10(-8) mol . L(-1). Satisfying results are achieved when detecting the DA in injection and simulated biology sample.