RU2610220C1 - Method for determining ascorbic acid and dopamine in water at joint presence using modified electrodes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrochemical analysis and is intended for the qualitative and quantitative determination of ascorbic acid and dopamine using voltammetric method in a wide range of objects (food, pharmaceuticals, environmental objects, biological objects, et al.) A method for determining ascorbic acid and dopamine content at their joint presence using modified carbon-contained electrodes, wherein refined nanoparticles of Au, Pt, Ni, Cu metals are used as modificators injected by depositing (not less than 5 minutes) from their dispersions (with a concentration not less than 0.05 g / l), produced by laser ablation of metal targets in pure solvents.

EFFECT: invention provides solution to the problem of complexity and labour intensity of the electrode modification process for the simultaneous determination of ascorbic acid and dopamine, as well as the need for polymers and graphene with its derivatives which is expensive and difficult to handle and store.

9 dwg, 8 ex

Description

The invention relates to the field of electrochemical analysis and is intended for the qualitative and quantitative determination of ascorbic acid and dopamine by the voltammetric method in a wide range of objects (food products, pharmaceuticals, environmental objects, biological objects, etc.) using glassy carbon electrodes modified with metal nanoparticles ( Au, Pt, Ni, Cu).

Ascorbic acid (AK) and dopamine (DA) are some of the most important biologically active substances. Dopamine is a neurotransmitter, it plays an important role in the normal functioning of the human body. Ascorbic acid is a water-soluble vitamin that is present in many foods, as well as added to foods as an antioxidant and as a preservative to increase their shelf life. These substances are simultaneously present in the intracellular fluid of the central nervous system and in blood serum. Deviation from the normal content of these substances in the body leads to serious diseases, therefore reliable, reliable and rapid methods for their determination with joint presence are required.

Electrochemical methods of analysis have several advantages over other known methods (optical, titrimetric, etc.). They are distinguished by high sensitivity, rapidity, are simple in laboratory design, do not require highly qualified personnel, have low detection limits and low cost. Ascorbic acid and dopamine are electroactive compounds with similar electrochemical properties, they are oxidized on the surface of the indicator electrode, giving a signal. The signal is the peak of electrooxidation, the value of which is proportional to the concentration of the analyte in the solution. However, both substances have close oxidation potentials, which leads to overlapping signals of these analytes. The consequence of this is the practical impossibility of quantitative determination of these substances when they are present together or the low sensitivity of their joint determination [Article: Graphite electrodes modified with multi-walled carbon nanotubes in polystyrene sulfonate for the simultaneous determination of ascorbic acid, dopamine and uric acid / Kumar S.P. and [et al.] // Journal. electrochemistry. 2013.V. 49, no. 4. S. 339-347]. To separate voltammetric peaks of these substances, modified indicator electrodes can be used.

The known method [Article: Voltammetric simultaneous determination of glucose, ascorbic acid and dopamine on glassy carbon electrode modified byNiNPs @ poly 1,5-diaminonaphthalene // Hathoot AA, Yousef US, Shatla AS, Abdel-Azzem M. Electrochimica Acta V.85 2012 . P.531-537] joint determination of AK and DA using glassy carbon electrodes modified with nickel nanoparticles dispersed in poly-diaminonaphthalene. The polymer was used to attach nanoparticles to the electrode surface and to increase the conductivity of the system. The inclusion of metal nanoparticles in the conductive matrix of the polymer was carried out in the process of its electropolymerization. The authors performed a simultaneous determination of AK and DA in the concentration range of 1 × 10 ^-4 ÷ 5 × 10 ^-4 M. The correlation coefficient during calibration for each analyte was 0.999. The use of the described modified electrode made it possible to separate the close peaks of the analytes to obtain two separate ones that can be used to determine the concentration of each analyte.

A significant drawback of this method is the use of an organic compound - a polymer - to modify the surface of the electrode. Polymer materials have their own specifics of work, they are quite demanding on the conditions for the analysis and on the conditions for their storage. The service life of the electrodes described in the above method is not more than 5 days. In addition, the presence of organic compounds in the analysis of organic analytes, such as ascorbic acid and dopamine, can introduce an additional error, affect the response of the system as a whole and metal nanoparticles in particular.

The known method [Article: Gold nanoparticle-decorated MoS2 nanosheets for simultaneous detection of ascorbic acid, dopamine and uric acid // Sun H., Chao J., Zuo X., Su S., Liu X., Yuwen L., Fan C ., Wang L. RSC Adv. 2014. V. 4. P. 27625-27629] determination of dopamine and ascorbic acid using a glassy carbon electrode modified with a nanocomposite consisting of gold nanoparticles embedded in a MoS ₂ structure-forming matrix. The composite was obtained by electrochemical deposition of gold nanoparticles on the surface of an SCE with a previously synthesized layer of molybdenum sulfide deposited. The simultaneous determination of AK and DA using the obtained modified electrode was carried out in the concentration range of 1 × 10 ^-3 ÷ 7 × 10 ^-2 M and 5 × 10 ^-5 ÷ 4 × 10 ^-3 M, respectively. The calibration correlation coefficient for each analyte was 0.99.

This method eliminates the need for polymer, however, its significant disadvantage is the complexity and complexity of the modifier preparation process, as well as the use of toxic reagents in the process of modifier synthesis.

The known method [Article: Synergistic electrocatalytic effect of graphene / nickel hydroxidecomposite for the simultaneous electrochemical determination of ascorbic acid, dopamine and uric acid // Mary Nancy TE, Anitha Kumary V. Electrochimica Acta V.133 2014. P. 233-240], where a composition of graphene and NiO was used as a modifier for SCE. Such an electrode allows analysis of solutions for the content of AA and DA by the method of differential pulse voltammetry in the concentration ranges 5 × 10 ^-5 ÷ 4.5 × 10 ^-4 M and 4.4 × 10 ^-7 ÷ 1.1 × 10 ^-5 M respectively. However, in this case, there is also a drawback described for previous systems - the procedure for modifying the electrode is quite complex and time-consuming, and the cost of the final electrode increases due to the use of graphene.

Also known is a method [Article: A facile electrochemical sensor based on reduced graphene oxide and Au nanoplates modified glassy carbon electrode for simultaneous detection of ascorbic acid, dopamine and uric acid / / Wang C., Du J., Wang H., Zou C. , Jiang F., Yang P., Du Y. Sensors and Actuators B V. 204. 2014. P. 302-309] determination of AA and DA using a GEM modified with a composition of oxidized graphene and gold nanoparticles. Gold nanoparticles were electrodeposited onto an electrode coated with oxidized graphene from HAuCl ₄ in H ₃ PO ₄ at a constant potential. This electrode maintains stability for up to 7 days at a storage temperature of 4 ° C. To analyze AK and DA solutions, the method of differential pulsed voltammetry was used. Simultaneous determination was carried out in the concentration ranges of 2.4 × 10 ^-4 ÷ 1.5 × 10 ^-3 M and 6.8 × 10 ^-6 ÷ 4.1 × 10 ^-5 M, respectively.

The main disadvantages of the method proposed in this work include the difficulty of preparing a modified electrode, including oxidized graphene, and the need to create special conditions for storing modified electrodes.

In a known method [Article: The simultaneous electrochemical detection of ascorbic acid, dopamine, and uric acid using graphene / size-selected Pt nanocomposites / / Sun C., Lee H., Yang J., Wu C. Biosensors and Bioelectronics V.26 . 2011. P. 3450-3455] for the simultaneous determination of AK and DA, electrodes modified with a nanocomposite of graphene and platinum nanoparticles were used. Pt nanoparticles were prepared by chemical deposition from PtCl ₄ , then graphene and platinum inks were prepared using a rather laborious and lengthy procedure. To modify the SCE (glassy carbon electrode), 10 μl of ink was applied to the cleaned surface of the electrode and dried at room temperature. The authors studied the simultaneous determination of AA and DA in the concentration ranges of 1.5 × 10 ^-7 ÷ 3.4 × 10 ^-5 M and 3 × 10 ^-8 ÷ 8.1 × 10 ^-6 M, respectively. The calibration correlation coefficient for each analyte was 0.99.

The disadvantage of this method, as well as the previous ones, is the complexity, complexity and high duration of the process of preparing graphene and platinum inks used to modify the electrode.

The closest to the method proposed by the authors for determining AK and DA is described in [Article: Hydrothermal synthesis of one-dimensional assemblies of Pt nanoparticles and their sensor application for simultaneous determination of dopamine and ascorbic acid // Wang W., Wang O., Zhang Z . J Nanopart Res 2008. V 10. P.255-262]. This method is based on the use of an electrode modified with Pt nanoparticles. Platinum nanoparticles were prepared by hydrothermal synthesis, by mixing H ₂ PtCl ₆ with a starch solution (template for forming the structure) and intensive mixing. The resulting homogeneous solution was transferred to Teflon autoclaves, sealed and kept at 160 ° C for 24 hours. Then the product was centrifuged, washed and redispersed in ethanol to obtain a colloidal solution of Pt, which was then applied to the cleaned surface of the SCE. The applied modifier was dried at room temperature to evaporate the solvent. Modified electrodes were used to analyze AK and DA. Before each experiment, the electrode was placed in a cell with 0.02 M phosphate buffer (pH 7.4) and scanned at a potential of –0.30 and +0.70 V at a scan rate of 50 mV / s to stabilize the CVA (cyclic voltammogram). In this work, using an electrode modified according to the described scheme, it was possible to shift the peak of AA electrooxidation to the negative region, and the DA peak to a more positive one, thereby solving the problem of overlapping analyte data signals. However, the data are presented for only one solution containing 2 × 10 ^-3 M ascorbic acid and 1 × 10 ^-4 M dopamine; ranges of concentrations determined using the described modified electrode are not indicated.

Although this method does not use polymers and is expensive and picky about graphene, the modification procedure itself involves quite laborious and lengthy stages and requires special equipment. The analysis process is also complicated by the need to maintain a constant pH. In addition, the analytical characteristics of the method are not described.

The present invention solves the problem of the complexity and complexity of the process of modifying the electrode to simultaneously determine ascorbic acid and dopamine, as well as the need for polymers and the expensive and picky handling and storage of graphene and its derivatives.

The objective of the invention is the creation of a simple, reagent-pure, not complicated by the need to use high temperatures and toxic organic substances method of preparing carbon-containing electrodes modified with metal nanoparticles (Au, Pt, Ni), for simultaneous voltammetric determination of ascorbic acid and dopamine.

A positive result is achieved by the fact that:

- Charge-stabilized finished dispersions of metal nanoparticles (Au, Pt, Ni, Cu) obtained by laser ablation of bulk metal targets in a pure solvent - ethanol in the absence of stabilizing or encapsulating agents are used as modifiers of the electrode surface. Particle size is governed by the conditions for obtaining their dispersions [Article: Synthesis of metal nanoparticles during laser ablation of solids in liquids by nanosecond radiation of the 2nd harmonic of an Nd-YAG laser // Svetlichny VA, Isaak TI, Babkina OV, Shabalina A.V. University News. Physics. 2009, No. 12/2].

- Modification of the surface of the SCE is carried out by keeping the electrode in a colloidal solution of nanoparticles, followed by drying in air at room temperature.

The main feature of the proposed method is the use of pure metal nanoparticles (Au, Pt, Ni, Cu) from 2 to 200 nm in size as a modifier, as well as a simplified method of applying the modifier to the electrode surface, as compared with the described ones, which can significantly reduce time and financial costs for the analysis of AK and DA solutions.

The proposed method is illustrated by a diagram (Figure 1), which shows the process of modifying the electrode.

(1) Prepared surface of the carbon-containing electrode (a - contact; b - electrode body; c - working surface of the electrode);

(2) Holding the electrode in a dispersion of nanoparticles;

(3) Drying to remove solvent from the work surface and rinsing with distilled water;

(4) Insertion of an electrode into an electrochemical cell with an analyzed solution containing analytes in a background electrolyte solution - 0.1 M sulfuric acid, an auxiliary electrode and a reference electrode, connection to a potentiostat and activation;

(5) Obtaining a cyclic voltammogram in the potential range 0 ÷ 1.2 V with a potential change rate of 30 mV / s;

(6) Determining the current value of the analytical peak of each analyte and calculating their concentration according to the equation of the calibration function.

The proposed method is as follows and includes the steps:

1. Preparation of the surface of carbon-containing electrodes for applying the modifier by grinding and polishing with abrasive materials, filter paper.

2. Activation of glassy carbon electrodes in a 0.1 M sulfuric acid solution by scanning the potential in the range from –0.8 to +1.8 V at a speed of 30 mV / s.

3. Application of metal nanoparticles (Au, Pt, Ni, Cu) on the working surface of carbon-containing electrodes by keeping at least 5 minutes of the working surface of the indicator electrode in an alcohol dispersion of metal nanoparticles with a concentration of at least 0.05 g / l.

4. Drying in air at room temperature until the solvent is completely removed from the electrode surface.

5. Rinsing with distilled water and re-drying.

6. The introduction of a modified electrode into an electrochemical cell with a background electrolyte (0.1 M H ₂ SO ₄ ), an auxiliary electrode and a reference electrode, and connection to a potentiostat.

7. Surface activation of the modified indicator electrode by a single scan in the potential region from –0.8 to +1.8 V, in the background electrolyte (in a 0.1 M sulfuric acid solution).

8. Obtaining a cyclic voltammogram in the potential range 0 ÷ 1.2 V with a potential change rate of 30 mV / s.

9. Determination of the current value of the analytical peak of each analyte and calculation of their concentration according to the equation of the calibration function in the ranges: 1 × 10 ^-5 ÷ 0.49 × 10 ^-3 M for dopamine, 1 × 10 ^-5 ÷ 0.97 × 10 ^{- 3} M for ascorbic acid.

Example 1

Platinum nanoparticles from an alcohol dispersion with a concentration of 0.2 g / L were applied to the prepared and activated surface of the GEM for 10 minutes. This was followed by air drying and washing. Then, the electrode was re-activated by anodic polarization in a 0.1 M sulfuric acid solution at potentials from –0.8 to +1.8 V at a speed of 30 mV / s. To build a calibration dependence, 10 μl of analytes were simultaneously introduced into the background solution from the initial solutions to obtain solutions in the concentration range 1 × 10 ^-5 ÷ 4.9 × 10 ^-4 M for dopamine, 1 × 10 ^-5 ÷ 9.7 × 10 ^-4 M for ascorbic acid. On the obtained CVA, two anode peaks characteristic of the oxidation of AA and DA were observed (Figure 2a). The dependence of the peak value of analyte oxidation peak on the concentrations of the compounds to be determined in solution is linear for each of these compounds in the following concentration ranges: dopamine 5 × 10 ^-5 ÷ 0.37 × 10 ^-3 M, ascorbic acid 9 × 10 ^-5 ÷ 7.3 × 10 ^-4 M (Figure 2b - calibration dependences of the current of analytical peaks obtained on Pt / SUE in the concentration ranges: dopamine 5 × 10 ^-5 ÷ 0.37 × 10 ^-3 M, ascorbic acid 9 × 10 ^-5 ÷ 7, 3 × 10 ^-4 M). The correlation coefficient for each analyte was 0.996.

A metrological analysis of the developed methodology was carried out using the input-found method. In a 0.1 M sulfuric acid solution, a known amount of AA and YES was introduced. Next, cyclic voltammograms were obtained in the potential range from 0 to +1.2 V, the sweep speed was 30 mV / s. After processing the results containing the entered and calculated number of analytes, it was determined that the relative standard deviation for the analysis of AK is 0.015, the relative measurement error was 0.99%. In the case of YES, the relative measurement error was 0.97%, and the relative standard deviation Sr was 0.04.

Example 2

Nickel nanoparticles were applied to the prepared surface of the SCE by keeping them for 15 minutes in an alcohol dispersion with a concentration of 0.1 g / L. After drying and washing, a potential scan was performed in the range from –0.8 to +1.8 V (at a speed of 30 mV / s) in 0.1 M sulfuric acid. Then, in a background electrolyte solution, at the same time, 10 μl portions of analytes were added from the initial solutions in the concentration range 1 × 10 ^-5 ÷ 0.49 × 10 ^-3 M for dopamine, 1 × 10 ^-5 ÷ 0.97 × 10 ^-3 M for ascorbic acid to build calibration dependencies. Filmed cyclic voltammograms in the range from 0 to +1.2 V at a speed of 30 mV / s.

Two peaks characteristic of the oxidation of AA and DA are visible in the obtained CVA (Fig. 3a). A pronounced separation of analyte oxidation peaks occurs at ascorbic acid concentrations from 1.7 × 10 ^-4 to 4.1 × 10 ^-3 M, and for dopamine from 9 × 10 ^-5 M to 2.1 × 10 ^-4 M. Figure 3b shows the calibration dependence of the peak value of the oxidation current of AA and DA on the concentration of these compounds on Ni / SCE. The dependence is linear, the correlation coefficient is 0.996.

The correctness of the methodology was checked by the "entered-found" method, for which an unknown amount of AA and DA was simultaneously introduced into the solution of the background electrolyte. As a result of the determination, it was found that the relative standard deviation for determining AK is 0.05, and the relative measurement error is 0.99%. For YES, the relative measurement error was 0.97%, and the relative standard deviation Sr was 0.05.

Example 3

Gold nanoparticles from an alcohol dispersion of 0.4 g / l were deposited on the cleaned and activated surface of the SCE for 5 minutes. After drying and washing, a potential scan was performed in the range from –0.8 to +1.8 V (at a speed of 30 mV / s) in the background electrolyte. Then, a portion of DA was introduced into the background electrolyte solution once, so that the dopamine concentration in the solution was 1 × 10 ^-5 M. After that, 10 μl portions of AA were successively added to the resulting solution in order to construct a calibration dependence in the concentration range of ascorbic acid 1 × 10 ^-5 ÷ 0.97 × 10 ^-3 M. Cyclic voltammograms were taken in the range of potential values from 0 to +1.2 V at a speed of 30 mV / s.

The obtained CVA shows (Figure 4a) that the modification of the SCE by gold nanoparticles allows one to separate the oxidation peaks of AA and DA in the case of a sequential increase in the concentration of AA from 1 × 10 ^-5 M to 9.7 × 10 ^-4 M, when the concentration of DA is constant and minimal (0.01 × 10 ^-3 M). With an increase in AA concentration, a linear increase in the peak current value occurs (Figure 4b shows the calibration dependences of the current of the analytical peak of AA obtained on Au / SCE with a DA content of 1 × 10 ^-5 M in the concentration range of ascorbic acid 1 × 10 ^-5 M to 9, 7 × 10 ^-4 M), the correlation coefficient is 0.991. According to the results of the quantitative determination of AK and YES, an input-found test was performed. For this, an unknown amount of AA and DA was simultaneously introduced into the background electrolyte solution. According to the results of the determination, it was found that in the case of ascorbic acid determination, the relative standard deviation is 0.05, the relative measurement error was 0.94%. The relative measurement error in the case of dopamine was 0.96%, the relative standard deviation Sr is 0.04.

Example 4

On the surface of the glassy carbon electrode, previously prepared by grinding and polishing, platinum nanoparticles from an alcohol dispersion (0.2 g / l) were deposited for 10 minutes. This was followed by air drying and washing with distilled water. To activate the electrode surface, a single potential scan was performed in 0.1 M sulfuric acid in the range from –0.8 to +1.8 V at a speed of 30 mV / s. Further, CVA was obtained in the analyzed solution (Figure 5). As a result of determining the content of ascorbic acid and dopamine with their simultaneous presence, it was found from the values of the analytical peaks that the concentration of AA was (2.5 ± 0.07) × 10 ^-4 M, and the concentration of DA was (1.3 ± 0.05) × 10 ^-3 M.

Example 5

Nickel nanoparticles from an alcohol dispersion (0.1 g / l) were applied to the cleaned and activated surface of the SCE for 15 minutes. After drying and washing with distilled water, a potential scan was performed in the range from –0.8 to +1.8 V (sweep speed 30 mV / s) in the background electrolyte — 0.1 M sulfuric acid. According to the obtained values of the current of analytical peaks in the analyzed solution (Figure 6), it was found that the concentration of AA in the test sample is (1.7 ± 0.1) × 10 ^-4 M, and the value of the concentration of DA (8.7 ± 0, 05) × 10 ^-5 M.

Example 6

Gold nanoparticles were deposited on the prepared surface of the SCE for 5 minutes, keeping in the alcohol dispersion at a concentration of 0.4 g / l. After drying and washing with distilled water, a potential scan was performed in the range from –0.8 to +1.8 V (at a speed of 30 mV / s) in the background electrolyte — 0.1 M sulfuric acid. Next, CVA was obtained for a solution with an unknown content of AA and DA (Figure 7). The values of analytical peaks allowed us to calculate the concentration of analytes, which were: (1.6 ± 0.1) × 10 ^-4 M for ascorbic acid and (8.6 ± 0.04) × 10 ^-5 M for dopamine.

Example 7

Copper nanoparticles from an alcohol dispersion with a concentration of 0.3 g / L were applied to the prepared and activated surface of the SCE for 10 minutes. After air drying and washing, the electrode was re-activated by anodic polarization in a 0.1 M sulfuric acid solution (from –0.8 to +1.8 V, 30 mV / s). To build the calibration dependence, portions of dopamine were added to the background solution containing 9.7 × 10 ^-4 M ascorbic acid to obtain solutions in the concentration range 1 × 10 ^-5 ÷ 0.49 × 10 ^-3 M. Two voltammograms were observed on the obtained voltammograms anode peaks characteristic of the oxidation of AA and DA (Figure 8a - CVA of the joint solutions of AA and DA obtained for Cu / SUE with a content of 9.7 × 10 ^-4 M ascorbic acid and changes in the concentration of DA in the range 1 × 10 ^-5 ÷ 0.49 × 10 ^-3 M). The dependence of the current value of the peak of dopamine oxidation on its concentration in the solution in the presence of ascorbic acid (in a higher concentration) has two linearity ranges (Figure 8b - calibration dependences of the current of the analytical peak obtained on Cu / SUE at a content of 9.7 × 10 ^-4 M ascorbic acid and a change in the concentration of DA in the range of 1 × 10 ^-5 ÷ 0.49 × 10 ^-3 M). The correlation coefficient for each of the ranges was 0.998.

A metrological analysis of the developed methodology was carried out using the input-found method. In a 0.1 M sulfuric acid solution, known amounts of AA and DA were introduced. Next, cyclic voltammograms were obtained in the potential range from 0 to +1.2 V, the sweep speed was 30 mV / s. After processing the results, it was determined that the relative standard deviation for the analysis of AK is 0.009, the relative measurement error was 0.99%. In the case of YES, the relative measurement error in both ranges of linearity of the calibration function was 0.98%, the relative standard deviation Sr was 0.02 and 0.013.

Example 8

Copper nanoparticles were applied to the prepared surface of the SCE for 10 minutes, keeping in an alcohol dispersion at a concentration of 0.3 g / l. Then the electrode was dried and washed with distilled water. Then, the potential was scanned at a speed of 30 mV / s in the range from –0.8 to +1.8 V in 0.1 M sulfuric acid. By cyclic change of potential from 0 to +1.2 V, CVA was obtained for a solution with an unknown content of AA and DA (Figure 9). By measuring the values of analytical peaks, analyte concentrations were calculated. It was found that the concentration of ascorbic acid in solution was (9.7 ± 0.05) × 10 ^-4 M, and the concentration of dopamine was (9.0 ± 0.09) × 10 ^-5 M.

Claims (1)

A method for determining the concentration of ascorbic acid and dopamine when they are together using modified carbon-containing electrodes, characterized in that pure nanoparticles of Au, Pt, Ni, Cu metals introduced by precipitation (time of at least 5 minutes) from their dispersions are used as modifiers with a concentration of at least 0.05 g / l) obtained by laser ablation of metal targets in pure solvents.

Images