THE QUANTITATIVE DETERMINATION OF HYDROGEN PEROXIDE BY VOLTAMMETRY ON THE CARBOSITALL ELECTRODE

The electrochemical behaviour of hydrogen peroxide (H2O2) has been studied using the alternating current voltammetry with square wave modulation in the potential range of +1.0...–1.0 V on the carbositall electrode as a working and auxiliary electrode (vs Ag,AgCl/KСl(sat)). The peak was obtained at Ep = +0.16 V on the background of 0.1 Mol L–1 Na2SO4 and 0.01 Mol L–1 KHSO4 (pH≈2.4) with its height rising proportionally to the increase of H2O2 concentrations. The linear dependence was observed in the H2O2 concentration range of (1.7-10.2)×10–5 Mol L–1, the calibration curve equation was Ip = (8.6±0.7)×103с (r = 0.998); LOD = 6.16×10–6 Mol L–1, LOQ = 2.05×10–5 Mol L–1. To determine H2O2 in solutions of antiseptic drugs the standard addition method was used.

The electrochemical behaviour of hydrogen peroxide (H 2 O 2 ) has been studied using the alternating current voltammetry with square wave modulation in the potential range of +1.0…-1.0V on the carbositall electrode as a working and auxiliary electrode (vs Ag,AgCl/KСl(sat)).The peak was obtained at E p = +0.16 V on the background of 0.1 Mol L -1 Na 2 SO 4 and 0.01 Mol L -1 KHSO 4 (pH≈2.4)with its height rising proportionally to the increase of H 2 O 2 concentrations.The linear dependence was observed in the H 2 O 2 concentration range of (1. 7-10.2)×10 - Mol L -1 , the calibration curve equation was I p = (8.6±0.7)×10 3 с (r = 0.998); LOD = 6.16×10 -6 Mol L -1 , LOQ = 2.05×10 -5 Mol L -1 .To determine H 2 O 2 in solutions of antiseptic drugs the standard addition method was used.
Hydrogen peroxide (H 2 O 2 ) is one of the most versatile oxidants, which oxidizing activity exceeds the known oxidizing agents -chlorine, chlorine dioxide and potassium permanganate; as a result of catalysis, H 2 O 2 can be transformed into the hydroxyl radical (OH•), which is the second after Fluorine by its reactivity.In addition to the oxidizing properties (H 2 O 2 +2H + +2e -→2H 2 O, Еº = 1.78 V) it can be used as a reducing agent (H 2 O 2 + 2OH -→ O 2 + 2 H 2 O + 2e -, Еº = -0.15V) [22].
Thus, H 2 O 2 is widely used in various industrial processes, such as the textile and paper industries for bleaching materials [20], and promotes controlled fibre swelling [22].In the work [17] H 2 O 2 was used to enhance the oxidizing potential in remediation of soil and aquifer layers, and it was also reported to be a source of oxygen for biological treatment of environmental objects [13,24,25].H 2 O 2 is used for decontamination (detoxification) of organic pollutants (formaldehyde, phenol, amine, penicillins, surface-active substances (surfactants), herbicides, etc.) [3,4,18].
For the overall assessment of the residual toxicity of the treated water it is necessary to consider the content of H 2 O 2 since such an assessment is carried out by biological organisms, which are quite sensitive to it and, therefore, should continuously monitor its concentration in the aquatic environment [8,14,18,28].
Probably, H 2 O 2 is used most widely in medicine and pharmacy as an active ingredient of many antiseptics and disinfectants (the pharmacotherapeutic group: Antiseptics and disinfectants; ATC code D08А Х01), such as 3%, 6% solutions for external use, Hydroperite, Grillen, Peramine, PEMOS-1, Perkat.Recently, the more advanced forms of these drugs have appeared.For example, there is drug "Peroxygel" (3% gel) with the bactericidal, mild cauterizing and hemostatic effect.The product contains H 2 O 2 with the concentration of 3% as an active substance.
In the aqueous medium under the action of catalase it breaks down to water and atomic oxygen.This reaction is accelerated in the presence of traces of hemoglobin of the blood, pus, and necrotic tissues; the foam formed in this reaction loosens the eschar, mechanically cleanses the wound, and after drying and/or removal of the necrotic tissue, pus, etc., a protective film protecting the wound from the secondary infection is formed.
"Peroxygel, 3.0%" is a colourless or pale white, odourless disperse system.It has the thermoplastic quality: at temperatures below 20°C and above 45°C it is liquid, but once applied to the skin (i.e. at a temperature of about 36.6°C) it takes the form of a gel.It is contained in a 15 g aluminium tube with a protective membrane and with a polyethylene bouchon in a cardboard box.
The most selective, simple and rapid in performance, as well as economically viable electrochemical methods are considered.For example, to determine H 2 O 2 the direct oxidation on the working electrode (e.g.platinum or carbon) is widely used.Such methods were described in more detail in our review published earlier [1].However, there are relatively few methods, in which the H 2 O 2 quantitative determination is performed by reduction on solid electrodes.
Therefore, as can be seen from the above data, development of analytical methods for the H 2 O 2 quantitative determination is of a great practical importance for various applications, including pharmaceutical analysis.Practical requirements for methods of the H 2 O 2 concentration determination include such criteria as selectivity, high sensitivity and speed of analysis, simplicity, cheapness, and the possibility of their application to standardization of antiseptics and disinfectants.
The aim of the present work is to determine the feasibility of the H 2 O 2 quantitative determination in a standard pharmacopoeian solution and preparations by cathodic voltammetry using the carbositall rotation electrode (CE) as an indicating electrode.

Materials and Methods
The standard solution of hydrogen peroxide (H 2 O 2 ).0.1700 Mol L −1 was freshly prepared and standardized permanganometrically.The stock solution was prepared by dissolving of 60% commercial preparation in a 100 mL volumetric flask by double distilled water.10.00 mL of 0.1700 Mol L -1 solution of H 2 O 2 was diluted in a 1000 mL volumetric flask with double distilled water to obtain The solution of potassium hydrogen sulphate.1 Mol L −1 (KHSO 4 ) was prepared by dissolving of 68.1 g of KHSO 4 in a 500 mL volumetric flask by double distilled water.
The solution of sodium sulphate.1 Mol L −1 (NaSO 4 ) was prepared by dissolving of 142.0 g of NaSO 4 in a 1000 mL volumetric flask by double distilled water.
The background solution consisted of the mixture of solutions of potassium hydrogen sulphate (KHSO 4 ) and sodium sulphate (Na 2 SO 4 ).
The model solution of "Hydrogen peroxide, 3%" antiseptic was prepared by dissolving of 1.0 mL of the preparation in a 100 mL volumetric flask by double distilled water to obtain 8.8×10 -3 Mol L -1 of H 2 O 2 solution (standardized permanganometrically).10.00 mL of this solution was diluted in a 100 mL volumetric flask with double distilled water to obtain 8.8×10 -4 Mol L -1 of H 2 O 2 solution.
The model solution of "Peroxygel, 3.0%" antiseptic was prepared by dissolving of 1.0 g of the preparation in a 100 mL volumetric flask by double distilled water.
The pH was measured using an ionmeter of І-160М type (Belarus) with a glass electrode of ESL-43-07 type paired with Ag, AgCl/KСl (sat) electrode.
Electrochemical measurements were carried out in an АVS-1.1 analyzer (Volta, St. Petersburg) with a threeelectrode scheme by alternating the current mode with a square wave modulation in the potential range of +1.0…-1.0V, W = 1000 rpm, the amplitude of 40 mV, ν = 65 Hz.The values of potential peaks directly at the maximum were measured by the electrochemical sensor "Module EM-04" with the accuracy of ±5 mV.CE was used as a working and an auxiliary electrode, and Ag,AgCl/KСl(sat) electrode type EVL-1М4 as a reference electrode.
The procedure for obtaining results of the calibration graph.The working solutions were prepared by diluting different volumes of the stock solution (0.5-3.0 mL) in a 50 mL volumetric flask with the background solution.25 mL of the working solution was transferred to the cell.The voltammograms were recorded by scanning the potential toward the negative direction in the potential range from +1.0 V to -1.0 V (vs Ag,AgCl/KСl(sat)).The graph was plotted in the following coordinates: the height of peaks I p in μA at E p = +0.16V on the ordinate axis and the corresponding concentration of Н 2 О 2 , c in Mol L -1 on the abscissa axis (Fig. 3).The graph equation coefficients were calculated by the least square method.
The working solutions were prepared by diluting different volumes (1.00-2.00mL) of the test solution (≈1×10 -3 Mol L -1 ) with 2.00 mL of the stock solution of H 2 O 2 (1.7×10 -3 Mol L -1 ) in a 50 mL volumetric flask with the background solution.The voltammograms were recorded by scanning the potential toward the negative direction in the potential range from +1.0 V to -1.0 V (vs Ag,AgCl/KСl(sat)).The concentration of the test solution C x (Mol L -1 ) is calculated by the equation: It was found that the surface active substances (SAS) being a part of the test solution of the sample preparation had the catalytic effect (current increase).Therefore, it was decided to use the addition method for analysis of the preparation.
The procedure of the quantitative determination of Н 2 О 2 in "Hydrogen peroxide, 3%" antiseptic.A typical procedure involves preparing several solutions containing the same amount of the unknown solution, but different amounts of the standard solution.For example, three 50 mL volumetric flasks are filled with 1.00 mL of the unknown solution each, and then the standard solution is added in different amounts, such as from 0.50 to 2.00 mL.The flasks are then diluted to the volume and mixed well.25 mL of each solution prepared are transferred to the cell.The voltammograms are recorded by scanning the potential toward the negative direction in the potential range from +1.0 V to -1.0 V.
At first, the voltammogram of test solution is recorded, then the solution of the known aliquots of the standard solution of С st (Mol L -1 ) is added, and again the voltammogram is recorded.The concentration of the test solution C x (Mol L -1 ) is calculated by the equation: where: 34.01 -is the molar weight of H 2 O 2 , g Mol -1 ; V 0 -is the volumetric flask capacity; V -is the volume of the test solution; m -is the sample weight, g; 10 -is the volume of the stock solution; 100, 1000 -are volumetric flask capacities.
The procedure of the quantitative determination of Н 2 О 2 in "Peroxygel, 3.0%" gel.The working solutions are prepared by diluting different volumes (0.5-1.5 mL) of the stock solution with the same amount of the test solution of H 2 O 2 (1.7×10 -3 Mol L -1 ) in a 50 mL volumetric flask with the background solution.The voltammograms are recorded by scanning the potential toward the negative direction in the potential range from +1.0 V to -1.0 V (vs Ag,AgCl/KСl(sat)).The graph is plotted in the following coordinates: the height of peaks I p in μA at E p = +0.16V on the ordinate axis and the corresponding concentration of H 2 O 2 c in Mol L -1 on the abscissa axis (Fig. 1).
The mass fraction of H 2 O 2 (%) in the test solution is calculated by the equation: where: 34.01 -is the molar weight of H 2 O 2 , g Mol -1 ; V 0 -is the volumetric flask capacity; V -is the volume of the test solution; m -is the sample weight, g; C x -is the graph of the Н 2 О 2 (regression line equation) found concentration, Mol L -1 : у = ax + b where a, b -are the graph equation coefficients; у -I p (µA).

Results and Discussion
The effect of the nature and pH of the background solution.The effect of the pH on the reduction process was studied by recording voltammograms of Н 2 О 2 in the concentration of 6.8×10 -5 Mol L -1 at several pH values ranging from 1.4 to 4.5 (Fig. 2).The mixture of 0.1 Mol L -1 Na 2 SO 4 + 0.01 Mol L -1 KHSO 4 was used as a background solution, and the pH of the solution was changed when gradually adding NaOH 0.2 Mol L -1 .
As can be seen from the graph (Fig. 2), the height of the H 2 O 2 reduction peak decreases, and the potential of the reduction peak is shifted toward more electronegative values with increasing the background electrolyte pH from 1.4 to 4.5.The maximum peak (I p ) is at the pH of approximately 2.2 and at a the pH around 4 the analytical signal almost disappears.The effect of the pH on the peak potential (E p ) shows the following: when the pH value increases in the interval from 2 to 3, E p remains almost constant, but E p decreases sharply to a negative value with the pH increasing over 3.5.Therefore, the optimal peak for the analysis (E p = +0.16V) was obtained at pH≈2.2-2.4 on the background of Na 2 SO 4 and Mol L -1 KHSO 4 .
For the quantitative determination of H 2 O 2 in a standard pharmacopoeian solution the calibration curve method was used.The calibration curve equation was I p = (8.6±0.7)× 10 3 ×с (r = 0.998) (Fig. 3).The results obtained are summarized in Tab. 1.
The high sensitivity of this method is accompanied by very good reproducibility.The reproducibility was evaluated from 5 repeated electrochemical signal measurements of model solutions with Н 2 О 2 concentrations of 5.10×10 -5 , 6.80×10 -5 and 8.50×10 -5 Mol L -1 .Precision of the method developed with reference to the relative standard deviation (RSD) was 4.24%, 3.27% and 2.30%, respectively (n = 5, P = 0.95).The results obtained are summarized in Tab. 2.
Precision and accuracy of the voltammetric determination of Н 2 О 2 in the model solution of preparations were studied by analyzing five replicates of the sample 1.The graph of the Н 2 О 2 reduction current peak vs. the concentration on the background of 0.1 Mol L -1 Na 2 SO 4 and 0.01 Mol L -1 KHSO 4 (pH≈2.4)on CE (vs Ag,AgCl/KСl(sat)); E p = +0.16V. solutions at three concentration levels.The results obtained are summarized in Tab. 3. CONCLUSIONS Thus, a new voltammetric method of the Н 2 О 2 determination in a standard pharmacopoeian solution and the model solution of preparations, such as antiseptics "Hydrogen peroxide, 3.0%" and "Peroxygel, 3.0%" using CE as an indicating electrode has been developed, and the possibility of its quantitative determination has been shown.The linear dependence is observed in the concentration ranges of the pure substance from 1.70×10 -5 to 10.20×10 -5 Mol L -1 .The calibration curve equation is I p = (8.6±0.7)×10 3 ×с (r = 0.998); LOD = 6.16×10 -6 Mol L -1 , LOQ = 2.05×10 -5 Mol L -1 .To determine Н 2 О 2 in preparations the standard addition method was used.The RSD was 2.11% (δ = -1.56%)for "Hydrogen peroxide, 3.0%" and 2.45% (δ = -0.67%)for "Peroxygel, 3.0%", respectively.Note: * -The calculation was made according to the average content determined by the pharmacopeian procedure.Table 2 The assessment of accuracy and precision of the Н 2 О 2 voltammetric determination procedure in the model solution of the standard pharmacopoeian solution (n = 5; P = 0.95%)
x -is the current peak of the test solution; I x+stis the current peak of the test solution with addition of a standard substance.The mass fraction of H 2 O 2 (w, %) in the test solution is calculated by the equation:

Fig. 2 .
Fig. 2. The effect of the pH on the current peak intensity (a) and the peak potential (b)of the reduction process of Н 2 О 2 on CE (vs Ag,AgCl/KСl(sat)).

Table 3
The results of voltammetric determination of Н 2 О 2 in the model solution of preparations (n = 5; P = 0.95%)

Table 1
Analytical characteristics of the calibration graph of the Н 2 О 2 voltammetric determination procedure in a standard pharmacopoeian solution (y = ax + b)