Volt-ampere method for measuring total acid content based on p-benzoquinone electrochemical reduction

Abstract

The invention belongs to the technical field of electrochemical detection, and particularly relates to a voltammetry for determining the total acid content based on p-benzoquinone electrochemical reduction. In the proton coupling electron transfer reaction, the mixed acid can generate a wide new peak or a plurality of new peaks in a voltammogram when being used as a proton donor for electrochemical reduction of p-benzoquinone, the peak area and the peak current of the new peak are both related to the total acid concentration of the mixed acid, and the peak area is more suitable for accurately detecting the total acid content. A three-electrode system is adopted, a standard curve and a linear regression equation of the concentration of a mixed acid standard solution and the peak area of a new peak are established through differential pulse voltammetry, the total acid content of a sample (sports beverage) is measured by measuring the peak area of the new peak caused by a to-be-measured sample (sports beverage) solution, and the result is consistent with that of an acid-base titration method. The method does not need complex sample pretreatment, and has the advantages of simplicity in operation, high analysis speed, low cost, high accuracy and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical detection, and particularly relates to a voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone. BACKGROUND

[0002] Organic acids such as acetic acid, lactic acid, tartaric acid, malic acid, succinic acid and citric acid can be formed in the fermentation process of specific foods or plants. The content of total acid affects the sensory properties of foods, including aroma, color and flavor, stability and microbial control. Some inorganic and organic acids are common beverage additives, but acidic substances such as carbonic acid, phosphate, malic acid and citric acid are also corrosive agents. Excessive intake of acidic substances by the human body can cause irritation and damage to organs such as teeth and digestive tract. Therefore, the determination of total acid content is crucial for the quality control of related foods such as beverages.

[0003] There are many methods for determining total acid content, such as traditional acid-base titration, near-infrared spectroscopy, high-performance liquid chromatography and headspace gas chromatography. However, these methods have the disadvantages of low precision, complicated operation, long analysis time and high analysis cost to varying degrees.

[0004] Electrochemical detection is a method that uses the redox properties of substances to measure the electrical signal changes of the solution, and then determines the characteristic information of the measured substance in the solution. This method has the advantages of simple operation, low cost, high sensitivity and fast analysis speed, and is increasingly widely used in the fields of chemistry, food, medicine and cosmetics.

[0005] Voltammetry based on electrochemical reduction of p-benzoquinone has been developed to determine the content of a single acid. As a proton donor, a single acid will produce a new cathodic peak in the voltammogram of p-benzoquinone, and the peak potential depends on the p K a value of the acid, and the peak height is proportional to the concentration of the acid. When the p K a values of mixed acids are similar, the total acid content of mixed acids can be determined by using the peak current of the new peak; but when the p K a values of mixed acids are quite different, a wide new peak or multiple new peaks will be produced in the voltammogram, and the above method cannot accurately determine the total acid content of mixed acids. Therefore, it is necessary to establish a simple, reliable, inexpensive and fast electrochemical method for detecting total acid content. SUMMARY

[0006] In view of the problems existing in the prior art, the purpose of the present application is to provide a detection method for determining total acid content based on electrochemical reduction of p-benzoquinone, which is more accurate, simple and efficient for determining the total acid content in actual samples containing multiple organic acids.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] A voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, comprising the following steps:

[0009] 1) Preparation of mixed acid standard solution: accurately pipette different volumes of standard solution stock of glacial acetic acid, DL-malic acid, potassium dihydrogen phosphate and citric acid into a volumetric flask, add p-benzoquinone and potassium chloride, and dilute to volume with double distilled water to prepare mixed acid standard solutions with different concentrations.

[0010] 2) Pretreatment of bare glassy carbon electrode: polish the bare glassy carbon electrode on a polishing cloth with alumina powder with particle sizes of 1.0 μm and 0.3 μm, respectively, wash the electrode with double distilled water, and then ultrasonically treat it in double distilled water for 30 seconds, and finally wash it again with double distilled water.

[0011] 3) Establishment of mixed acid standard curve and linear regression equation: use the bare glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Hg / Hg2Cl2 as the reference electrode to construct a three-electrode system; place the three-electrode system in an electrolytic cell, connect it with an electrochemical workstation, use the mixed acid standard solution in step 1) as the electrolyte, scan the mixed acid standard solutions with different concentrations by differential pulse voltammetry, and determine the new peak area of the mixed acid standard solutions with different concentrations; use the concentration of the mixed acid standard solution as the abscissa and the new peak area as the ordinate to establish a mixed acid standard curve and a linear regression equation.

[0012] 4) Preparation of sample solution: accurately pipette the sample to be tested into a volumetric flask, add p-benzoquinone and potassium chloride, and dilute to volume with double distilled water to prepare the sample solution to be tested.

[0013] 5) Determination of sample solution: use the bare glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Hg / Hg2Cl2 as the reference electrode to construct a three-electrode system; place the three-electrode system in an electrolytic cell, connect it with an electrochemical workstation, use the sample solution to be tested prepared in step 4) as the electrolyte, scan the sample solution to be tested by differential pulse voltammetry, and determine the new peak area of the sample solution to be tested; and calculate the total acid content of the sample solution to be tested according to the mixed acid standard curve and the linear regression equation established in step 3).

[0014] Further, in step 1) of the above voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, the final concentrations of p-benzoquinone and potassium chloride in the mixed acid standard solution are 1.0 mmol / L and 0.1 mol / L, respectively.

[0015] Further, in the step 1) of the above-mentioned voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, the molar ratio of the mixed acid standard solution is glacial acetic acid: DL-malic acid: potassium dihydrogen phosphate: citric acid = 1: 1: 2: 1.

[0016] Further, in the step 1) of the above-mentioned voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, the concentration of the mixed acid standard solution is 0.05 mmol / L to 1.50 mmol / L.

[0017] Further, in the step 1) of the above-mentioned voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, the mixed acid standard solution prepared in the step 1) and the sample solution to be determined prepared in the step 4) are deoxygenated by high-purity nitrogen before electrochemical determination.

[0018] Further, in the step 3) and the step 5) of the above-mentioned voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone, the parameters of the differential pulse voltammetry are as follows: scanning voltage: -0.4V to 0.4V, scanning speed: 0.1 V / s, pulse width: 200 ms, and amplitude: 50 mV.

[0019] The above-mentioned voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone is applied to detecting total acid content of food.

[0020] Further, in the above-mentioned application, the food is a sports drink containing multiple organic acids.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1. The present application uses a bare glassy carbon electrode as a working electrode without any modification, and the sample preparation does not require a complex pretreatment process, thus having the advantages of simple operation, low cost, and fast analysis speed.

[0023] 2. The present application determines the total acid content of the sample by measuring the peak area of the new peak of the sample solution to be determined in the p-benzoquinone voltammogram, thus having high accuracy and good stability.

[0024] 3. The present application has strong anti-interference ability, and sample additives such as vitamin B 12 , glucose, and sodium chloride have no effect on the determination of the total acid content of the sample. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a cyclic voltammogram of p-benzoquinone and mixed acids in water.

[0026] Figure 2 is a p-benzoquinone differential pulse voltammogram of four single acids.

[0027] Figure 3 is the differential pulse voltammogram of p-benzoquinone with different concentrations of mixed acid standard solution.

[0028] Figure 4 is the standard curve of mixed acid concentration and new peak peak area.

[0029] Figure 5 is the standard curve of mixed acid concentration and new peak peak current.

[0030] Figure 6 is the differential pulse voltammogram of p-benzoquinone with different concentrations of mixed acid standard solution.

[0031] Figure 7 is the differential pulse voltammogram of p-benzoquinone with different concentrations of mixed acid standard solution. DETAILED DESCRIPTION

[0032] The following examples are all deoxygenated with high-purity nitrogen before electrochemical determination.

[0033] Example 1: A voltammetry method for determining total acid content based on electrochemical reduction of p-benzoquinone

[0034] Preparation of glacial acetic acid standard solution: transfer 1.15 mL of glacial acetic acid to a 200 mL volumetric flask, and dilute to volume with double distilled water to prepare a 100 mmol / L glacial acetic acid standard solution stock solution; transfer 1.00 mL of the 100 mmol / L glacial acetic acid standard solution stock solution to a 10 mL volumetric flask, and dilute to volume with double distilled water to prepare a 10.0 mmol / L glacial acetic acid standard solution stock solution; transfer 1.00 mL of the 10.0 mmol / L glacial acetic acid standard solution stock solution to a 10 mL volumetric flask, and dilute to volume with double distilled water to prepare a 1.00 mmol / L glacial acetic acid standard solution stock solution.

[0035] Preparation of DL-malic acid standard solution: weigh 0.0335 g of DL-malic acid into a small beaker, add a small amount of double distilled water to dissolve, transfer to a 25 mL volumetric flask, rinse the beaker with double distilled water three times, transfer all the rinsing solution to the volumetric flask, dilute to volume with double distilled water to prepare a 10.0 mmol / L DL-malic acid standard solution stock solution; transfer 1.00 mL of the 10.0 mmol / L DL-malic acid standard solution stock solution to a 10 mL volumetric flask, and dilute to volume with double distilled water to prepare a 1.00 mmol / L DL-malic acid standard solution stock solution.

[0036] Preparation of potassium dihydrogen phosphate standard solution: weigh 0.0342 g of potassium dihydrogen phosphate into a small beaker, add a small amount of double distilled water to dissolve, transfer to a 25 mL volumetric flask, rinse the beaker with double distilled water three times, transfer all the rinse liquid to the volumetric flask, and dilute to volume with double distilled water to prepare a 10.0 mmol / L potassium dihydrogen phosphate standard solution stock solution; take 1.00 mL of the 10.0 mmol / L potassium dihydrogen phosphate standard solution stock solution into a 10 mL volumetric flask, dilute to volume with double distilled water to prepare a 1.00 mmol / L potassium dihydrogen phosphate standard solution stock solution.

[0037] Preparation of citric acid standard solution: weigh 0.0483 g of citric acid into a small beaker, add a small amount of double distilled water to dissolve, transfer to a 25 mL volumetric flask, rinse the beaker with double distilled water three times, transfer all the rinse liquid to the volumetric flask, and dilute to volume with double distilled water to prepare a 10.0 mmol / L citric acid standard solution stock solution; take 1.00 mL of the 10.0 mmol / L citric acid standard solution stock solution into a 10 mL volumetric flask, dilute to volume with double distilled water to prepare a 1.00 mmol / L citric acid standard solution stock solution.

[0038] Preparation of mixed acid standard solution: glacial acetic acid: DL-malic acid: potassium dihydrogen phosphate: citric acid = 1:1:2:1 (molar ratio).

[0039] (1) Redox reaction of p-benzoquinone with mixed acid

[0040] 1.1) Pretreatment of working electrode: use a bare glassy carbon electrode as the working electrode, polish it on a polishing cloth with alumina powder of particle sizes of 1.0 μm and 0.3 μm, respectively, rinse the electrode with double distilled water, ultrasonicate it in double distilled water for 30 seconds, and then rinse it again with double distilled water.

[0041] 1.2) Preparation of electrolysis solution: prepare three 10 mL volumetric flasks, add potassium chloride, p-benzoquinone, and mixed acid standard solution, and dilute to volume with double distilled water to obtain the electrolysis solution.

[0042] Electrolysis solution 1: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone;

[0043] Electrolysis solution 2: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid;

[0044] Electrolysis solution 3: 0.1 mol / L potassium chloride + 0.8 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid.

[0045] 1.3) A three-electrode system was constructed using a bare glassy carbon electrode as the working electrode, a platinum electrode as the counter electrode, and Hg / Hg2Cl2 as the reference electrode. This three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The electrolyte solution from step 1.2) was used as the electrolyte, and cyclic voltammetry was employed to scan it. The scanning voltage was -0.4V to 0.4V, and the scanning rate was 0.1 V / s. The results are as follows: Figure 1 As shown.

[0046] Depend on Figure 1 It can be seen that the reduction peak (peak I) of p-benzoquinone in water has a peak potential of -0.18 V. After the addition of mixed acid, a new peak (peak II) appears in the p-benzoquinone voltammogram at the corrected potential. This is because when p-benzoquinone undergoes electrochemical reduction at the electrode surface, it preferentially accepts protons released by the mixed acid. When the mixed acid on the electrode surface is depleted, the pH changes abruptly, resulting in a new reduction peak. When the concentration of p-benzoquinone decreases and the concentration of mixed acid remains constant, the peak area of ​​peak I decreases and the peak current decreases, while the peak current and peak area of ​​peak II remain unchanged. This indicates that the new reduction peak is not related to the concentration of p-benzoquinone but to the concentration of mixed acid, and can be used to determine the total acid content of the mixed acid.

[0047] (II) Relationship between new reduction peaks and acid characteristics

[0048] 2.1) Pretreatment of working electrode: Using bare glassy carbon electrode as working electrode, polish it on polishing cloth with alumina powder with particle size of 1.0 μm and 0.3 μm in sequence. After rinsing the electrode with double distilled water, it is ultrasonicated in double distilled water for 30 seconds, and finally rinsed with double distilled water again.

[0049] 2.2) Preparation of electrolyte solution: Prepare four 10 mL volumetric flasks, add potassium chloride, p-benzoquinone and glacial acetic acid / DL-malic acid / potassium dihydrogen phosphate / citric acid standard solution, and dilute to volume with double-distilled water to obtain the electrolyte solution.

[0050] Electrolyte 1: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.3 mmol / L glacial acetic acid;

[0051] Electrolyte 2: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.3 mmol / L DL-malic acid;

[0052] Electrolyte 3: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.3 mmol / L potassium dihydrogen phosphate;

[0053] Electrolyte 4: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.3 mmol / L citric acid.

[0054] 2.3) A bare glassy carbon electrode was used as the working electrode, a platinum electrode as the counter electrode, and a Hg / Hg2Cl2 electrode as the reference electrode to construct a three-electrode system. The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The electrolyte was the electrolytic solution prepared in step 2.2). Differential pulse voltammetry was used to scan the working electrode, with a scanning voltage of -0.4 V to 0.4 V, a scanning speed of 0.1 V / s, a pulse width of 200 ms, and an amplitude of 50 mV. The results are shown in FIG. 2. Figure 2

[0055] As can be seen from FIG. 2, the acetic acid (p Figure 2 K a = 4.75), DL-malic acid (p K a = 3.5 and 4.4), potassium dihydrogen phosphate (p K a = 7.2), and citric acid (p K a = 3.1, 4.8, and 6.4) produced different new peaks (peak II) in the voltammogram, with peak potentials of 0.228 V, 0.256 V, 0.1 V, and 0.24 V, respectively. The ternary weak acid citric acid also had a weaker new peak at 0.16 V, which may correspond to the release of the third proton (p K a = 6.4) of citric acid. It can be seen that the peak potential of the new reduction peak is related to the strength of the corresponding acid and depends on the p K a value. Although the concentrations of the four single acids are the same, the peak currents of the new peaks are different. At a potential of 0.256 V, DL-malic acid can provide protons to reduce p-benzoquinone, while potassium dihydrogen phosphate cannot, so the peak current at 0.256 V is only related to the concentration of DL-malic acid and is not related to the concentration of potassium dihydrogen phosphate. It can be seen that the peak current may not accurately determine the total acid content of the mixed acid system.

[0056] (Three) Establishing a standard curve and linear regression equation for determining the total acid content of the mixed acid

[0057] 3.1) Pretreatment of the working electrode: A bare glassy carbon electrode was polished with alumina powder with particle sizes of 1.0 μm and 0.3 μm on a polishing cloth, respectively. After rinsing with double distilled water twice, the electrode was ultrasonicated in double distilled water for 30 seconds and then rinsed with double distilled water again.

[0058] 3.2) Preparation of the electrolytic solution: Seven 10 mL volumetric flasks were prepared, and potassium chloride, p-benzoquinone, and the mixed acid standard solution were added. The volume was adjusted with double distilled water to obtain the electrolytic solution.

[0059] ​​Electrolyte solution 1: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.05 mmol / L mixed acid;

[0060] Electrolyte solution 2: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.10 mmol / L mixed acid;

[0061] Electrolyte solution 3: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.20 mmol / L mixed acid;

[0062] Electrolyte solution 4: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.50 mmol / L mixed acid;

[0063] Electrolyte solution 5: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.75 mmol / L mixed acid;

[0064] Electrolyte solution 6: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 1.00 mmol / L mixed acid;

[0065] Electrolyte solution 7: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 1.50 mmol / L mixed acid.

[0066] 3.3) A bare glassy carbon electrode was used as the working electrode, a platinum electrode as the counter electrode, and a Hg / Hg2Cl2 electrode as the reference electrode to construct a three-electrode system. The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The electrolyte solution in step 3.2) was used as the electrolyte, and differential pulse voltammetry was used for scanning, with a scanning voltage of -0.4 V to 0.4 V, a scanning speed of 0.1 V / s, a pulse width of 200 ms, and an amplitude of 50 mV. The results are shown in Figure 3 .

[0067] As can be seen from Figure 3 , the mixed acid standard solution produced two distinct new peaks (peaks II and III) in the voltammogram. As the concentration of mixed acid increased, the new peak area and peak current gradually increased, indicating that the new peak area and peak current were related to the concentration of mixed acid. Considering that the peak potential of peak III gradually moved to the negative direction, and peak II remained unchanged, the concentration of the mixed acid standard solution was used as the horizontal coordinate, and the peak area of the new peak (peaks II and III) and the peak current of the new peak II were used as the vertical coordinate. The standard curve of mixed acid concentration-new peak area and the linear regression equation of mixed acid concentration-new peak II peak current were established, and the results are shown in Figure 4 and Figure 5 .

[0068] As can be seen from Figure 4It can be seen that there is a certain linear relationship between the concentration of the mixed acid and the peak area of ​​the new peak in the range of 0.05 mmol / L to 1.50 mmol / L.

[0069] Its linear regression equation is AREA = 0.0279 + 2.0277 C, R 2 = 0.995,

[0070] In the formula, AREA is the peak area of ​​the new peak (μA*s), and C is the concentration of the mixed acid (mmol / L).

[0071] Depend on Figure 5 It can be seen that there is a certain linear relationship between the concentration of the mixed acid and the peak current of the new peak in the range of 0.05 mmol / L to 1.50 mmol / L.

[0072] Its linear regression equation is I = -1.416 - 8.707 C, R 2 = 0.978,

[0073] In the formula, I is the peak current of the new peak II (μA), and C is the concentration of the mixed acid (mmol / L).

[0074] Depend on Figure 4 and Figure 5 It can be seen that the area of ​​the new peak (R) 2 = 0.995) compared to the new peak current (R) 2 = 0.978) is more suitable for determining the total acid content of mixed acids.

[0075] Example 2: Application of the method for determining total acid content based on the reduction of p-benzoquinone

[0076] (I) The effect of sports drink additives on the determination of total acid content

[0077] 1.1) Pretreatment of working electrode: Using bare glassy carbon electrode as working electrode, polish it on polishing cloth with alumina powder with particle size of 1.0 μm and 0.3 μm in sequence. After rinsing the electrode with double distilled water, ultrasonically immerse it in double distilled water for 30 seconds, and finally rinse it with double distilled water again.

[0078] 1.2) Preparation of electrolyte solution: Prepare four 10 mL volumetric flasks, add potassium chloride, p-benzoquinone, mixed acid standard solution and vitamin B. 12 The solution is prepared by mixing glucose and sodium chloride with double-distilled water to obtain an electrolyte solution.

[0079] Electrolyte 1: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid + 0.066 mmol / L vitamin B 12 ;

[0080] Electrolyte solution 2: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid + 0.259 mol / L glucose;

[0081] Electrolyte solution 3: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid + 0.4 mmol / L sodium chloride;

[0082] Electrolyte solution 4: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.4 mmol / L mixed acid.

[0083] 1.3) A bare glassy carbon electrode was used as the working electrode, a platinum electrode as the counter electrode, and a Hg / Hg2Cl2 as the reference electrode to construct a three-electrode system. The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The electrolyte solution in step 1.2) was used as the electrolyte, and differential pulse voltammetry was used for scanning with a scanning voltage of -0.4 V to 0.4 V, a scanning speed of 0.1 V / s, a pulse width of 200 ms, and an amplitude of 50 mV. The results are shown in Figure 6 .

[0084] As can be seen from Figure 6 , when the mixed acid solution is added with the additives vitamin B 12 / glucose / sodium chloride, the peak area of peak II remains basically unchanged, indicating that the above additives have no effect on the determination of total acid content, and the anti-interference ability of the method is strong.

[0085] (II) Determination of total acid content of three sports drinks

[0086] 2.1) Pretreatment of working electrode: a bare glassy carbon electrode was used as the working electrode, which was polished with alumina powder with particle sizes of 1.0 μm and 0.3 μm on a polishing cloth, respectively. After rinsing with double distilled water twice, the electrode was ultrasonicated in double distilled water for 30 seconds, and then rinsed with double distilled water again.

[0087] 2.2) Preparation of electrolyte solution: six 10 mL volumetric flasks were prepared, and potassium chloride, p-benzoquinone and (or) sports drink 1 / sports drink 2 / sports drink 3 were added, and then double distilled water was added to make up the volume to obtain the electrolyte solution.

[0088] Electrolyte solution 1: 0.1 mol / L potassium chloride + 0.3 mL sports drink 1;

[0089] Electrolyte solution 2: 0.1 mol / L potassium chloride + 0.1 mL sports drink 2;

[0090] Electrolyte solution 3: 0.1 mol / L potassium chloride + 0.2 mL sports drink 3;

[0091] Electrolyte solution 4: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.3 mL sports drink 1;

[0092] Electrolyte solution 5: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.1 mL sports drink 2;

[0093] Electrolyte solution 6: 0.1 mol / L potassium chloride + 1.0 mmol / L p-benzoquinone + 0.2 mL sports drink 3.

[0094] 2.3) A bare glassy carbon electrode was used as the working electrode, a platinum electrode as the counter electrode, and a Hg / Hg2Cl2 as the reference electrode to construct a three-electrode system. The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The electrolyte solution in step 2.2) was used as the electrolyte, and differential pulse voltammetry was used to scan it. The scan voltage was -0.4 V to 0.4 V, the scan speed was 0.1 V / s, the pulse width was 200 ms, and the amplitude was 50 mV. The results are shown in Figure 7 .

[0095] As can be seen from Figure 7 , when there is only a sports drink sample in the solution, no new peak is generated in the voltammogram, indicating that the sample itself does not have electrochemical activity. The new peak area of the sample solution to be tested is substituted into the linear regression equation: AREA = 0.0279 + 2.0277 C, where AREA is the new reduction peak area (μA*s) and C is the mixed acid concentration (mmol / L). The total acid content of the sports drink is obtained, and compared with the mature potential titration method in the prior art, the results are shown in Tables 1 and 2.

[0096] Table 1 Determination of total acid content of sports drink by differential pulse voltammetry and potential titration method

[0097]

[0098] * n = 8

[0099] Table 2 Single factor variance analysis of determination results by differential pulse voltammetry and potential titration method

[0100]

[0101] From Tables 1 and 2, it can be seen that the standard deviation of the determination of the total acid content of the three sports drinks by the potential titration method is twice that of the present method. There is no statistical difference between the determination results of the present method and the potential titration method (P p > 0.05).

Claims

1. A voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone, characterized in that, Includes the following steps: 1) Preparation of mixed acid standard solutions: Accurately transfer different volumes of standard stock solutions of glacial acetic acid, DL-malic acid, potassium dihydrogen phosphate and citric acid into volumetric flasks, add p-benzoquinone and potassium chloride, and dilute to volume with double-distilled water to prepare mixed acid standard solutions of different concentrations. 2) Pretreatment of bare glassy carbon electrode: The bare glassy carbon electrode was polished on a polishing cloth with alumina powder with particle size of 1.0 μm and 0.3 μm in sequence. After rinsing with double-distilled water, the electrode was ultrasonicated in double-distilled water for 30 seconds, and finally rinsed with double-distilled water again. 3) Establishment of mixed acid standard curve and linear regression equation: A three-electrode system was constructed using a bare glassy carbon electrode as the working electrode, a platinum electrode as the counter electrode, and Hg / Hg2Cl2 as the reference electrode. The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The mixed acid standard solution in step 1) was used as the electrolyte. Differential pulse voltammetry was used to scan the mixed acid standard solutions of different concentrations and to determine the peak area of ​​the new peaks of the mixed acid standard solutions of different concentrations. A standard curve and linear regression equation for the mixed acid were established with the concentration of the mixed acid standard solution as the x-axis and the peak area of ​​the new peak as the y-axis. 4) Preparation of sample solution: Accurately transfer the sample to be tested into a volumetric flask, add p-benzoquinone and potassium chloride, and dilute to volume with double-distilled water to prepare the sample solution to be tested; 5) Determination of sample solution: A three-electrode system was constructed using a bare glassy carbon electrode as the working electrode, a platinum electrode as the counter electrode, and Hg / Hg2Cl2 as the reference electrode; The three-electrode system was placed in an electrolytic cell and connected to an electrochemical workstation. The sample solution to be tested prepared in step 4) was used as the electrolyte. The sample solution to be tested was scanned using differential pulse voltammetry to determine the peak area of ​​the new peak of the sample solution to be tested. The total acid content of the sample solution to be tested is calculated based on the mixed acid standard curve and linear regression equation established in step 3).

2. The voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone according to claim 1, characterized in that, In step 1), the final concentrations of p-benzoquinone and potassium chloride in the mixed acid standard solution are 1.0 mmol / L and 0.1 mol / L, respectively.

3. The voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone according to claim 1, characterized in that, In step 1), the mixed acid standard solution contains glacial acetic acid: DL-malic acid: potassium dihydrogen phosphate: citric acid in a molar ratio of 1:1:2:

1.

4. The voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone according to claim 1, characterized in that, In step 1), the concentration range of the mixed acid standard solution is 0.05 mmol / L to 1.50 mmol / L.

5. The voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone according to claim 1, characterized in that, Both the mixed acid standard solution prepared in step 1) and the sample solution to be tested prepared in step 4) were deoxygenated with high-purity nitrogen before electrochemical measurement.

6. The voltammetric method for determining total acid content based on the electrochemical reduction of p-benzoquinone according to claim 1, characterized in that, In steps 3) and 5), the parameters of the differential pulse voltammetry are: scanning voltage: -0.4V to 0.4V, scanning speed: 0.1 V / s, pulse width: 200 ms, amplitude: 50 mV.

7. The application of the voltammetric method based on the electrochemical reduction of p-benzoquinone for determining total acid content as described in any one of claims 1-6 in the detection of total acid content in food.

8. The application according to claim 7, characterized in that, The food product is a sports drink containing a variety of organic acids.

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