An electrolyte for detecting cobalt element by anodic stripping voltammetry and a method for detecting cobalt element

Abstract

This application relates to the technical field of water quality monitoring, and specifically discloses an electrolyte for detecting cobalt element by anodic stripping voltammetry and a method for detecting cobalt element. An electrolyte for detecting cobalt element by anodic stripping voltammetry contains the following substances: 0.1 - 1 mol / L of ammonium chloride, 20 - 80 g / L of an additive, and 7 - 49 mL / L of concentrated ammonia water. Its detection method is: detecting and calculating the concentration of cobalt element in the sample by using a three-electrode system. The electrolyte of this application can be used for the detection of cobalt element, and has the advantages of strong anti-interference ability, excellent reproducibility, low cost, and simple operation.

Description

Technical Field

[0001] This application relates to the technical field of water quality monitoring, and particularly to a method for continuously, accurately, simply and rapidly detecting cobalt elements in water bodies by anodic stripping voltammetry; specifically, it is an electrolyte for detecting cobalt elements by anodic stripping voltammetry and a method for detecting cobalt elements. Background Art

[0002] Cobalt (Co) is one of the essential trace elements for the human body. It can stimulate hematopoiesis, affect lipid metabolism, participate in the synthesis of protein amino coenzymes and lipoproteins, etc., and is closely related to human health. Lack of cobalt in the human body will affect the formation of red blood cells and cause megaloblastic anemia. Of course, the intake of cobalt is not the more the better. Excessive intake of cobalt and cobalt compounds through respiratory tract, esophagus, skin, blood and other channels can cause allergic asthma, gastrointestinal dysfunction, irritant dermatitis and polycythemia. In the carcinogenic list announced by the World Health Organization, cobalt and cobalt compounds are classified as Group 2B carcinogens.

[0003] The concentration of cobalt in natural water bodies is very low. Wastewater from non-ferrous metal smelting and cobalt-containing material processing enterprises often contains high concentrations of cobalt. If it is discharged into the environment without proper treatment, it will affect and even endanger human life and health. At present, the determination of cobalt is involved in the investigation of pollution status in surface water sources, groundwater and soil monitoring of drinking water.

[0004] At present, the mainstream methods for determining cobalt are atomic absorption method, inductively coupled plasma mass spectrometry and spectrophotometry. The first two are relatively mature, but the instrument consumables are expensive; the latter is simple to operate and the detection is rapid, but the detection limit is high and the selectivity is poor. In addition, stripping voltammetry has the characteristics of low cost, high sensitivity and rapid detection. Its principle is to concentrate the extremely trace analyte in the electrolyte on the electrode by electrolysis, and then scan with a reverse potential to dissolve the component and record the voltammogram. Qualitative analysis is based on the position of the stripping potential, and quantitative analysis is based on the magnitude of the stripping current.

[0005] In the reports on the determination of cobalt elements by stripping voltammetry, there are: ① a hanging mercury electrode with an ammonium chloride-dimethylglyoxime system electrolyte; ② a glassy carbon electrode with a sodium hydroxide-5-Br-PADAP system electrolyte; ③ a carbon paste electrode with an ammonium chloride-o-phenanthroline system electrolyte; ④ a Nafion-modified glassy carbon electrode with a sodium nitrate electrolyte. These methods essentially belong to cathodic stripping methods. The electrode surface involves adsorption or catalytic processes. Most of them require electrode modification, and the reproducibility of the results is very poor. This has high requirements for the mass production of electrodes. Considering from both cost and operation aspects, it is not very suitable for wide application. Therefore, for the determination of cobalt, developing a test method with strong anti-interference ability, good reproducibility, low cost and simple operation has high application prospects. Summary of the Invention

[0006] In order to obtain a cobalt element testing method with strong anti-interference ability, good reproducibility, low cost, and simple operation, the present application provides an electrolyte for detecting cobalt element by anodic stripping voltammetry and a cobalt element detection method.

[0007] In the first aspect, the present application provides an electrolyte for detecting cobalt element by anodic stripping voltammetry, adopting the following technical solution:

[0008] An electrolyte for detecting cobalt element by anodic stripping voltammetry contains the following substances: 0.1 - 1 mol / L of ammonium chloride, 20 - 80 g / L of an additive, and 7 - 49 mL / L of concentrated ammonia water (every 30 mL of concentrated ammonia water with a mass fraction of 25% - 28% is diluted to 1000 mL of water).

[0009] By adopting the above technical solution, the content of cobalt element is detected by anodic stripping voltammetry in the technical solution of the present application. The principle is to apply a constant voltage to the electrode immersed in a specific electrolyte. When the selected voltage reaches the electrolytic reduction potential of the cobalt ions (or complex ions) to be measured, the cobalt ions (or complex ions) will migrate to the electrode surface and undergo a reduction reaction, which is the enrichment stage. After a short rest after enrichment, the voltage on the electrode is increased in the reverse direction at a certain rate. The cobalt enriched on the electrode surface will undergo an oxidation reaction, dissolve out, and generate an oxidation current. Quantitative determination is carried out according to the magnitude of the peak current of the "stripping peak" in the current-voltage curve. The analysis method is very sensitive, and the detection limit can reach 10 -12 mol / L, and the detection accuracy for cobalt element is better.

[0010] In the present application, ammonium chloride and concentrated ammonia water are preferably used in combination as the electrolyte to form an NH 3 -NH 4 Cl buffer system. Under the action of an external electric field and specific electrochemical parameters, the cobalt element shows an anodic stripping peak on the voltammogram, which is convenient for calculating the content of cobalt element. Ammonium chloride has a certain influence on the stripping peak of cobalt element and can be used as a supporting electrolyte, making the potential difference of the stripping peaks of various ions larger and the sharpness of the peak shape higher, thereby improving the sensitivity of cobalt element monitoring.

[0011] Preferably, the additive is selected from any one or more of fluoride, amine compounds, or organic acids.

[0012] By adopting the above technical solution, in the technical solution of the present application, additives are added to the electrolyte. Fluorides, amine compounds, and organic acids can all be used as masking agents. Through complexation reactions, redox reactions, or precipitation reactions, iron ions, nickel ions, manganese ions, etc. in the sample are removed, and the influence of other metal ions in the sample on the detection of cobalt element is eliminated, thereby improving the accuracy of cobalt element detection. Moreover, fluorides, cyanides, and organic acids can cooperate with each other to improve the binding effect of the additive with iron ions, nickel ions, manganese ions, etc. in the sample, eliminate interference peaks, and improve the accuracy of the detection result.

[0013] Preferably, the organic acid is selected from any one of ascorbic acid, citric acid, oxalic acid, or glycine.

[0014] Preferably, the fluoride is selected from any one of sodium fluoride, potassium fluoride, ammonium fluoride, or ammonium bifluoride.

[0015] Preferably, the amine compound is selected from triethanolamine or hydroxylamine hydrochloride.

[0016] By adopting the above technical solution, in the technical solution of the present application, fluoride is preferably used as an electrolyte additive. Fluoride ions can undergo complexation reactions with other metal ions in the sample, such as iron ions, nickel ions, and manganese ions, etc., which can stably reduce the influence of other metal ions on the detection result of cobalt element, eliminate interference peaks, and improve the detection accuracy of cobalt element.

[0017] Preferably, the fluoride is ammonium fluoride.

[0018] By adopting the above technical solution, in the technical solution of the present application, ammonium fluoride is preferably used as an additive. Ammonium fluoride not only contains fluoride ions but also ammonium ions, which can effectively bind other metal ions in the sample and eliminate interference peaks. At the same time, to improve the sensitivity of cobalt element determination, the selected concentration of the electrolyte is relatively high. However, in a relatively high-concentration ammonia-ammonium chloride buffer system, ammonia is prone to volatilization, resulting in a decrease in the ammonium ion concentration in the electrolyte, that is, the conductivity effect of the electrolyte becomes poor. By adding ammonium fluoride, the ammonium ions in the electrolyte can be supplemented, maintaining the concentration stability of ammonium ions in the electrolyte, and keeping the accuracy, stability, and sensitivity of cobalt element detection at a relatively high level.

[0019] Preferably, it is made of substances including the following contents: 0.5 mol / L ammonium chloride, 30 mL / L concentrated ammonia water (every 30 mL of concentrated ammonia water with a mass fraction of 25% - 28% is diluted to 1000 mL of water), and 45 g / L ammonium fluoride.

[0020] By adopting the above technical solution, the composition and addition amount of the electrolyte are optimized in the technical solution of the present application. The appropriate addition amount of ammonium fluoride effectively masks metal ions such as iron ions, nickel ions, and manganese ions in the sample, has little effect on cobalt ions, and the cobalt element can stably move under the action of the electric field and precipitate at the anode. Moreover, the obtained voltammogram has better linearity, further improving the accuracy of cobalt element detection.

[0021] In a second aspect, the present application provides a method for detecting cobalt element, adopting the following technical solution:

[0022] A method for detecting cobalt element, which uses an anodic stripping voltammetry method to detect the electrolyte of cobalt element, includes the following steps:

[0023] A) Insert the counter electrode into the counter electrode socket.

[0024] B) Insert the reference electrode into the reference electrode socket.

[0025] C) First, polish the working electrode with a polishing solution containing alumina powder, then soak it in an alkaline cleaning solution containing sodium hydroxide, and after washing, insert it into the working electrode socket.

[0026] D) Rinse the inserted three-electrode system with deionized water, connect the measurement module to the heavy metal detector, connect the heavy metal detector to the PC terminal, and ensure the entire system is in a conductive state.

[0027] E) Take 3 clean measuring cups and label them as blank sample, standard sample, and sample to be measured. First, add the electrolyte to all 3 cups, then add deionized water, cobalt standard solution, and water sample to be measured respectively, mix well and set aside.

[0028] F) Enter the online software, create a new cobalt determination project, and set the detection parameters as follows;

[0029] G) After setting the parameters, insert the blank sample measuring cup into the measurement base, insert the three-electrode system into the measuring cup, ensure that the lower end of the electrode is immersed in the electrolyte, click "blank sample" on the PC terminal to start measuring the blank sample. After the blank sample measurement is completed, similarly, measure the standard sample and the sample to be measured in turn.

[0030] H) After the measurement of the sample to be measured is completed, view the voltammogram, record the potential range of the cobalt stripping peak of the standard sample, and calculate the concentration of cobalt element in the sample to be measured.

[0031] By adopting the above technical solution, a three-electrode system is used for the detection of cobalt element in the technical solution of the present application. This system not only has a large Faraday current, but also has an extremely small diffusion layer thickness around the electrode, separating the Faraday current from the convection effect and having a relatively stable mass transfer coefficient. In stripping analysis, it avoids errors caused by factors such as electrolyte disturbance, making the current proportional to the ion concentration of the solution to be measured to a great extent, resulting in a good linearity of the cobalt element detection method and improving the accuracy of the cobalt element detection method. At the same time, the silver / silver chloride reference electrode can provide a stable reference potential, and the saturated potassium chloride in the electrode acts as a salt bridge to eliminate or reduce the liquid junction potential; through certain treatment means, problems such as "zigzag" stripping peaks appearing in the voltammogram caused by concentration polarization can be eliminated, which can effectively improve the stability of the measurement result and enhance the precision of the detection method.

[0032] Preferably, the detection parameters are as follows: stirring potential (mV): -2500 to -1000; stirring time (s): 5 to 30; enrichment potential (mV): -2500 to -1000; enrichment time (s): 5 to 300; standing potential (mV): -2500 to -1000; standing time (s): 5 to 60; scanning start potential (mV): -1300 to -900; scanning end potential (mV): 300 to 800; scanning rate (mV / s): 500 to 1000; cleaning potential (mV): 800 to 1500; cleaning time (s): 10 to 60; sensitivity: 1.0×10 -4 。

[0033] By adopting the above technical solution, the detection parameters in the cobalt element detection in the technical solution of the present application are optimized. The appropriate detection parameters make the detection result more accurate and have better stability.

[0034] Preferably, the working electrode is selected from any one of a glassy carbon electrode, a hanging mercury electrode, or a carbon paste electrode.

[0035] Preferably, the working electrode is a glassy carbon electrode.

[0036] By adopting the above technical solution, a glassy carbon electrode is preferably used as the working electrode in the technical solution of the present application. The glassy carbon electrode has good electrical conductivity and chemical stability, a small thermal expansion coefficient, a hard texture and good airtightness, and a long service life. Importantly, it can be mass-produced, with a low cost, and can meet the requirements of commercial mass production. The hanging mercury electrode is not only expensive, has certain toxicity, but also is not easy to be mass-produced, and is easily oxidized during use, which is likely to lead to poor reproducibility of test results. Although the carbon paste electrode has a high modifiability on the electrode surface, an excellent electrochemical window and low-cost raw materials, it is difficult to control the proportion of the binder during the production process. Too much binder will reduce the sensitivity; too little binder will result in poor connection between graphite particles, leading to an increase in resistance and also affecting the sensitivity. The raw material cost of the binder with less usage and good bonding effect doubles. In addition, its service life is also shorter than that of the glassy carbon electrode, and the obtained carbon paste electrodes have poor consistency, which is likely to lead to poor consistency and accuracy of measurement results.

[0037] In summary, the present application has the following beneficial effects:

[0038] 1. Since the present application preferably uses ammonium chloride and ammonia water in combination as the electrolyte to form an NH 3 -NH 4 Cl buffer system, under the action of an externally applied electric field and specific electrochemical parameters, the cobalt element shows an anodic stripping peak on the voltammogram, which is convenient for calculating the content of the cobalt element. Ammonium chloride has a certain influence on the stripping peak of the cobalt element and can be used as a supporting electrolyte, making the potential difference of the stripping peaks of various ions larger and the sharpness of the peak shape higher, thereby improving the sensitivity for monitoring the cobalt element.

[0039] 2. Ammonium fluoride is preferably used as an additive in the present application. Ammonium fluoride contains not only fluoride ions but also ammonium ions, which can effectively combine with other metal ions in the sample to eliminate interference peaks. At the same time, since the ammonia water in the high-concentration ammonia-ammonium chloride electrolyte is easily volatilized, the concentration of ammonium ions in the electrolyte decreases, that is, the conductivity effect of the electrolyte becomes worse. By adding ammonium fluoride, the ammonium ions in the electrolyte can be supplemented to maintain the concentration stability of ammonium ions in the electrolyte, so that the accuracy, stability and sensitivity of cobalt element detection are maintained at a high level.

[0040] 3. For the detection method of the present application, the cobalt element is detected through a three-electrode system. In the stripping analysis of the three-electrode system, errors caused by factors such as electrolyte perturbation are avoided, and the current is proportional to the ion concentration of the solution to be measured to a great extent, making the detection method of the cobalt element have good linearity and improving the accuracy of the cobalt element detection method. And while maintaining the stability of the reference voltage, the liquid junction potential can be eliminated or reduced, which can effectively improve the stability of the measurement results and the precision of the detection method.

[0041] 4. This application uses a glassy carbon electrode as the working electrode. The glassy carbon electrode has better reproducibility and stability, can be mass-produced, and has a lower cost, enabling test results with better consistency, repeatability, and stability to be obtained. Description of the Drawings

[0042] Figure 1 is the voltammogram of sample a in Example 1 of this application;

[0043] Figure 2 is the voltammogram of sample b in Example 1 of this application;

[0044] Figure 3 is the voltammogram of sample c in Example 1 of this application;

[0045] Figure 4 is the voltammogram of sample d in Example 1 of this application. Detailed Embodiments

[0046] The following further details this application in conjunction with examples.

[0047] In the embodiments of this application, the selected instrument and equipment are as follows, but not limited thereto:

[0048] Drugs and Instruments: The reagents used in this method and subsequent examples are all of analytical purity (AR). The equipment used is the Nanotek 2000 portable heavy metal determination solution provided by Shenzhen Longstone Scientific Instruments Co., Ltd., mainly including: a three-electrode system (glassy carbon electrode, silver / silver chloride reference electrode, and platinum counter electrode) measurement module, a handheld heavy metal detector, and PC-side online software.

[0049] Examples

[0050] Example 1

[0051] On the one hand, this application provides an electrolyte for detecting cobalt elements by anodic stripping voltammetry, containing 0.5 mol / L ammonium chloride, 30 mL / L concentrated ammonia water, and 45 g / L ammonium fluoride, and the mass fraction of concentrated ammonia water is 26%.

[0052] On the other hand, this application provides a method for detecting cobalt elements, including the following steps:

[0053] A) Insert the platinum counter electrode into the counter electrode socket;

[0054] B) Insert the silver / silver chloride reference electrode into the reference electrode socket;

[0055] C) First, polish the glassy carbon electrode with a polishing solution containing alumina powder, then soak it in an alkaline cleaning solution containing sodium hydroxide (1 mol / L), and after washing, insert it into the working electrode socket;

[0056] D) Rinse the inserted three - electrode system thoroughly with deionized water, connect the measurement module to the heavy metal detector, and connect the heavy metal detector to the PC terminal to ensure the entire system is in a conductive state;

[0057] E) Take clean measuring cups and label them as blank sample, standard sample, and sample to be measured. First, add electrolyte to each cup, then add deionized water, cobalt standard solution, and the sample to be measured respectively, and mix well for later use;

[0058] Add liquid to 4 clean measuring cups respectively in the following ways:

[0059] Sample a: 10 mL of deionized water + 10 mL of cobalt standard solution (1 mg / L);

[0060] Sample b: 10 mL of cobalt electrolyte (0.5 mol / L ammonium chloride, 30 mL / L concentrated ammonia water) + 10 mL of deionized water;

[0061] Sample c: 10 mL of cobalt electrolyte (0.5 mol / L ammonium chloride, 30 mL / L concentrated ammonia water) + 10 mL of cobalt standard solution (1 mg / L); Sample d: 10 mL of cobalt electrolyte (0.5 mol / L ammonium chloride, 30 mL / L concentrated ammonia water) + 10 mL of cobalt standard solution (1 mg / L) + 0.1 mL of cobalt additive (ammonium fluoride at 45 g / L);

[0062] F) Enter the online software, create a new cobalt measurement project, and set the detection parameters as follows:

[0063] Stirring potential (mV): - 2200;

[0064] Stirring time (s): 17;

[0065] Enrichment potential (mV): - 2200;

[0066] Enrichment time (s): 10;

[0067] Resting potential (mV): - 2200;

[0068] Resting time (s): 20;

[0069] Scanning start potential (mV): - 1200;

[0070] Scanning end potential (mV): 550;

[0071] Scanning rate (mV / s): 850;

[0072] Cleaning potential (mV): 1100;

[0073] Cleaning time (s): 35;

[0074] Sensitivity: 1.0×10 -4 .

[0075] G) After setting the parameters, insert the blank sample measuring cup into the measuring base, insert the three-electrode system into the measuring cup, ensure that the lower end of the electrode is immersed in the electrolyte, click "Blank Sample" on the PC side to start measuring the blank sample. After the blank sample measurement is completed, similarly, measure the standard sample and the sample to be measured in sequence;

[0076] H) After the measurement of the sample to be measured is completed, view the voltammogram, record the potential range of the cobalt stripping peak of the standard sample, and calculate the concentration of cobalt element in the sample to be measured.

[0077] Prepare 7 cobalt standard solutions with a concentration of 0.4 mg / L as Samples 1 - 7 according to the liquid addition method of Sample d. Select the "area method", with the integration window range of -750 to -50 mV. Continuously measure one of the samples 6 times according to the above method, record the concentration measured each time and calculate the measurement precision (i.e., relative standard deviation RSD), and the specific values are shown in Table 1; then measure and record the concentrations of 7 parallel samples, namely Samples 1 - 7 in sequence, and further calculate the indication error, and the specific values are shown in Table 2.

[0078] Table 1 Test Results of Samples in Example 1

[0079]

[0080] Table 2 Test Results of Samples 1 - 7 in Example 1

[0081]

[0082] Example 2

[0083] The difference from Example 1 is that the enrichment time is set to 300 s. Prepare 6 cobalt standard solutions with a concentration of 0.01 mg / L as Samples 8 - 13 according to the liquid addition method of Sample d in Example 1. Select the "area method", with the integration window range of -750 to -50 mV, test the concentrations of Samples 8 - 13, and calculate the detection limit, and the specific data are shown in Table 3.

[0084] Table 2 Test Results of Samples 8 - 13 in Example 2

[0085]

[0086] Example 3

[0087] On the one hand, the present application provides an electrolyte for detecting cobalt element by anodic stripping voltammetry, which contains 0.1 mol / L ammonium chloride, 7 mL / L concentrated ammonia water and 20 g / L ammonium fluoride, and the mass fraction of concentrated ammonia water is 25%.

[0088] On the other hand, the present application provides a method for detecting cobalt element, including the following steps:

[0089] A) Insert the platinum counter electrode into the counter electrode socket;

[0090] B) Insert the silver / silver chloride reference electrode into the reference electrode socket;

[0091] C) First polish the glassy carbon electrode with a polishing solution containing alumina powder, then soak it in an alkaline cleaning solution containing sodium hydroxide (1 mol / L), and after washing, insert it into the working electrode socket;

[0092] D) Rinse the inserted three-electrode system with deionized water, connect the measurement module to the heavy metal detector, connect the heavy metal detector to the PC terminal, and ensure the entire system is conductive;

[0093] E) Take clean measuring cups and label them as blank samples, standard samples, and samples to be measured. First add electrolyte to the cups, then add deionized water, cobalt standard solution, and the sample to be measured respectively, and mix well for later use;

[0094] F) Enter the online software, create a cobalt measurement project, and set the detection parameters as follows:

[0095] Stirring potential (mV): -1000;

[0096] Stirring time (s): 30;

[0097] Enrichment potential (mV): -1000;

[0098] Enrichment time (s): 300;

[0099] Static potential (mV): -1000;

[0100] Static time (s): 60;

[0101] Scanning start potential (mV): -900;

[0102] Scanning end potential (mV): 800;

[0103] Scanning rate (mV / s): 500;

[0104] Cleaning potential (mV): 800;

[0105] Cleaning time (s): 10;

[0106] Sensitivity: 1.0×10 -4 .

[0107] G) After setting the parameters, insert the blank sample measuring cup into the measuring base, insert the three - electrode system into the measuring cup, ensure that the lower end of the electrode is immersed in the electrolyte, click "Blank Sample" on the PC side to start measuring the blank sample. After the blank sample measurement is completed, similarly, measure the standard sample and the sample to be measured in sequence;

[0108] H) After the measurement of the sample to be measured is completed, view the voltammogram, record the potential range of the cobalt stripping peak of the standard sample, and calculate the concentration of cobalt element in the sample to be measured.

[0109] Sample d: 10 mL of cobalt electrolyte (0.1 mol / L ammonium chloride, 7 mL / L concentrated ammonia water) + 10 mL of cobalt standard solution (1 mg / L) + 0.1 mL of cobalt additive (20 g / L ammonium fluoride);

[0110] According to the liquid - adding method of sample d, prepare 7 cobalt standard solutions with a concentration of 0.4 mg / L as samples 1 - 7. Select "area method", the integration window range is - 750~ - 50 mV, continuously measure one of the samples 6 times according to the above method, calculate the measurement precision (i.e., relative standard deviation RSD), and the specific values are shown in Table 4; then measure 7 parallel samples in sequence and calculate the indication error, and the specific values are shown in Table 4.

[0111] Example 4

[0112] On the one hand, the present application provides an electrolyte for detecting cobalt element by anodic stripping voltammetry, which contains 1 mol / L ammonium chloride, 49 mL / L concentrated ammonia water and 80 g / L ammonium fluoride, and the mass fraction of concentrated ammonia water is 28%.

[0113] On the other hand, the present application provides a method for detecting cobalt element, including the following steps:

[0114] A) Insert the platinum counter electrode into the counter - electrode socket;

[0115] B) Insert the silver / silver chloride reference electrode into the reference - electrode socket;

[0116] C) First, polish the glassy carbon electrode with a polishing solution containing alumina powder, then soak it in an alkaline cleaning solution containing sodium hydroxide (1 mol / L), and after washing, insert it into the working - electrode socket;

[0117] D) Rinse the inserted three - electrode system with deionized water, connect the measurement module to the heavy - metal detector, connect the heavy - metal detector to the PC side, and ensure the entire system is in a conductive state;

[0118] E) Take a clean measuring cup, and label it as blank sample, standard sample and sample to be measured. First, add electrolyte to the cups evenly, then add deionized water, cobalt standard solution and sample to be measured respectively, mix well and set aside;

[0119] F) Enter the online software, create a new cobalt determination project, and set the detection parameters as follows:

[0120] Stirring potential (mV): -2500;

[0121] Stirring time (s): 5;

[0122] Enrichment potential (mV): -2500;

[0123] Enrichment time (s): 5;

[0124] Resting potential (mV): -2500;

[0125] Resting time (s): 5;

[0126] Scanning start potential (mV): -1300;

[0127] Scanning end potential (mV): 800;

[0128] Scanning rate (mV / s): 1000;

[0129] Cleaning potential (mV): 1500;

[0130] Cleaning time (s): 60;

[0131] Sensitivity: 1.0×10 -4 .

[0132] G) After setting the parameters, insert the blank sample measuring cup into the measuring base, insert the three-electrode system into the measuring cup, ensure that the lower end of the electrode is immersed in the electrolyte, click "Blank sample" on the PC side to start measuring the blank sample. After the blank sample measurement is completed, similarly, measure the standard sample and the sample to be tested in sequence;

[0133] H) After the measurement of the sample to be tested is completed, view the voltammogram, record the potential range of the cobalt stripping peak of the standard sample, and calculate the concentration of cobalt element in the sample to be tested.

[0134] Sample d: 10 mL of cobalt electrolyte (1 mol / L ammonium chloride, 49 mL / L concentrated ammonia water) + 10 mL of cobalt standard solution (1 mg / L) + 0.1 mL of cobalt additive (80 g / L ammonium fluoride);

[0135] According to the liquid addition method of sample d, prepare 7 cobalt standard solutions with a concentration of 0.4 mg / L as samples 1 to 7. Select the "area method", and the integration window interval is -750 to -50 mV. Continuously measure sample 1 6 times according to the above method, and calculate the measurement precision (i.e., relative standard deviation RSD). The specific values are shown in Table 4; then measure the concentrations of samples 1 to 7 in sequence and calculate the indication error. The specific values are shown in Table 4.

[0136] Example 5

[0137] The difference from Example 1 is that in this example, sodium fluoride is used as an additive, the sample concentration is measured, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0138] Example 6

[0139] The difference from Example 1 is that in this example, ascorbic acid is used as an additive, the sample concentration is measured, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0140] Example 7

[0141] The difference from Example 1 is that in this example, hydroxylamine hydrochloride is used as an additive, the sample concentration is measured, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0142] Example 8

[0143] The difference from Example 1 is that in this example, a hanging mercury electrode is used as the working electrode, the sample concentration is measured, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0144] Example 9

[0145] The difference from Example 1 is that in this example, a carbon paste electrode is used as the working electrode, the sample concentration is measured, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0146] Comparative Example

[0147] Comparative Example 1

[0148] The difference between this comparative example and Example 1 is that in this comparative example, a hanging mercury electrode is paired with an ammonium chloride - dimethylglyoxime system electrolyte to replace the electrolyte and working electrode in Example 1, the sample is detected, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0149] Comparative Example 2

[0150] The difference between this comparative example and Example 1 is that in this comparative example, a glassy carbon electrode is paired with a sodium hydroxide - 5 - Br - PADAP system electrolyte to replace the electrolyte and working electrode in Example 1, the sample is detected, and the measurement precision and indication error values are calculated. The specific values are shown in Table 4.

[0151] Comparative Example 3

[0152] The difference between this comparative example and Example 1 is that in this comparative example, a carbon paste electrode is used in combination with an ammonium chloride - o - phenanthroline system electrolyte to replace the electrolyte and working electrode in Example 1, and the sample is detected to calculate the measurement precision and indication error value. The specific values are shown in Table 4.

[0153] Comparative Example 4

[0154] The difference between this comparative example and Example 1 is that in this comparative example, a Nafion - modified glassy carbon electrode is used in combination with a sodium nitrate electrolyte to replace the electrolyte in Example 1, and the measurement precision and indication error value are calculated. The specific values are shown in Table 4.

[0155] Table 4 Detection Results of Example 1, Examples 3 - 9, and Comparative Examples 1 - 4

[0156]

[0157] Combined with Figures 1-4 and the detection results in Table 4, it can be found that:

[0158] From Figures 1-3 comparison, it can be seen that the electrolyte configured by the technical solution of this application can indeed make an obvious stripping peak appear on the voltammogram of cobalt under the corresponding detection method, but there are also interference peaks beside it; through Figure 3 and 4 it can be known that the addition of the additive eliminates the interference peaks to a certain extent. Since the additive contains two common ligands, fluoride ions (F - ) and ammonium ions (NH 4 + ), which can mask these interference factors; at the same time, a high concentration of NH 4 + can also supplement part of the loss of the electrolyte due to the volatilization of ammonia water, synergistically improving the accuracy of the test results.

[0159] (1) By comparing Example 1, Examples 3 - 4, Examples 5 - 7, and Comparative Examples 1 - 4, it can be found that: the precision and indication error of the detection results obtained in Example 1 and Examples 3 - 5 are relatively small, which indicates that by using ammonium chloride and concentrated ammonia water in combination as the electrolyte in this application, NH 3 -NH 4The Cl buffer system, through the action of an external electric field and specific electrochemical parameters, makes the cobalt element show an anodic dissolution peak on the voltammetric curve, which makes it easier to calculate the content of the cobalt element. Ammonium chloride can be used as a supporting electrolyte to increase the potential difference of the dissolution peaks of each ion, improve the sharpness of the peak shape, and improve the sensitivity of cobalt element monitoring. The addition of ammonium fluoride not only eliminates interference peaks through the reaction of fluoride ions with other metal ions; it can also supplement the concentration of ammonium ions in the electrolyte, maintain the stability of the electrolyte, and synergistically improve the accuracy of the detection results.

[0160] (2) By comparing Example 1, Examples 8-9 and Comparative Examples 1-4, it can be found that the precision and indication error of the test results obtained in Examples 8-9 are relatively large, which shows that the present application uses a glassy carbon electrode as the working electrode. The glassy carbon electrode has good electrical conductivity and chemical stability, a small thermal expansion coefficient, a hard texture and good airtightness, and a long service life. What is important is that it can be mass-produced at a low cost, can meet the requirements of commercial mass production, and can obtain test results with good consistency, repeatability, and stability. Both suspended mercury electrodes or carbon paste electrodes are more likely to lead to poor reproducibility of test results, and have the defect of poor consistency of finished products, which in turn leads to large precision and indication errors in the detection results of the cobalt element.

[0161] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for detecting cobalt element by anodic stripping voltammetry, characterized in that: It includes the following steps: A) Insert the platinum counter electrode into the counter electrode socket; B) Insert the silver / silver chloride reference electrode into the reference electrode socket; C) First polish the working electrode with a polishing solution containing alumina powder, then soak it in an alkaline cleaning solution containing sodium hydroxide, and after washing, insert it into the working electrode socket; D) Rinse the inserted three-electrode system with deionized water, connect the measurement module to the heavy metal detector, connect the heavy metal detector to the PC terminal, and ensure the entire system is in a conductive state; E) Take 3 clean measuring cups and label them as blank sample, standard sample and sample to be measured. First add electrolyte to all 3 cups, then add deionized water, cobalt standard solution and water sample to be measured respectively, and mix well for later use; F) Enter the on-line software, create a cobalt determination project, and set the detection parameters; G) After setting the parameters, clip the blank sample measuring cup into the measuring base, insert the three-electrode system into the measuring cup, ensure that the lower end of the electrode is immersed in the electrolyte, click "blank sample" on the PC terminal to start measuring the blank sample. After the blank sample measurement is completed, similarly, measure the standard sample and the sample to be measured in turn; H) After the measurement of the sample to be measured is completed, view the voltammogram, record the potential range of the cobalt stripping peak of the standard sample, and calculate the concentration of cobalt element in the sample to be measured; The electrolyte for detecting cobalt element by anodic stripping voltammetry contains the following substances: 0.1 - 1 mol / L of ammonium chloride, 20 - 80 g / L of additive, and 7 - 49 mL / L of concentrated ammonia water; The additive is ammonium fluoride; The working electrode is a glassy carbon electrode.

2. The method for detecting cobalt element by anodic stripping voltammetry according to claim 1, characterized in that: The electrolyte for detecting cobalt element by anodic stripping voltammetry is made of the following content substances: 0.5 mol / L of ammonium chloride, 30 mL / L of concentrated ammonia water, and 45 g / L of ammonium fluoride.

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