Quantitative detection method for low-concentration urea in electrocatalytic synthesis urea solution

Abstract

The invention discloses a quantitative detection method for low-concentration urea in an electrocatalytic synthesis urea solution, and belongs to the technical field of urea detection. According to the method, the sample is subjected to vacuum freeze drying and concentration, the urea concentration amplification factor is flexibly controlled, the detection sensitivity limitation of a traditional diacetyl monooxime method is broken through, precise detection of trace urea in an electro-catalytic synthesis system is achieved, and the applicability and detection efficiency of the method are remarkably improved; meanwhile, an interferent scavenger is introduced into the detection solution, so that the interference of residual metal ions and byproducts in the electro-catalysis system on the chromogenic reaction is effectively eliminated, and the anti-interference capability of the detection method is greatly enhanced; in addition, according to the technology, key parameters such as the adding amount of the color developing reagent, the color developing reaction device, the heating / cooling mode and the heating time are systematically optimized, and the accuracy, stability and repeatability of the detection method are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of urea detection, and in particular relates to a quantitative detection method for low-concentration urea in an electrocatalytically synthesized urea solution. Background Art

[0002] Urea, with a nitrogen content of 46%, is an indispensable nitrogen fertilizer in agricultural production and is vital to global food production. However, with the continued growth of the global population and the urgent need for environmentally friendly production methods, the limitations of traditional urea synthesis processes are becoming increasingly prominent. Currently, the Bosch-Meiser process widely used in industry requires harsh conditions of high temperature and high pressure (~200°C and ~210 bar). It is energy-intensive and accompanied by a large amount of greenhouse gas emissions, which runs counter to the global "carbon neutrality" goal. In this context, electrocatalytic technology driven by renewable energy provides a promising alternative for sustainable urea synthesis, utilizing the abundant CO2 on the earth. 2 and nitrogen sources (such as N 2 ,NO,NO 2 ⁻And NO 2 ⁻) as raw materials, efficient and green urea synthesis can be achieved through CN coupling under mild conditions, opening up an innovative path to alleviate energy consumption and reduce carbon emissions.

[0003] At present, the research in the field of electrocatalytic CN coupling urea synthesis is progressing rapidly. However, due to the limitation of reaction kinetics, the urea yield in the reaction system is generally low (usually <10 mg / L), and a large amount of unconverted raw materials, by-products and metal ions coexist, which makes the quantitative analysis of urea face severe challenges and become a key bottleneck problem restricting the development of this field. Among the existing detection methods, the diacetyl monoxime method has the advantages of convenient operation and high sensitivity based on the principle of color development reaction, but it faces significant challenges in the practical application of electrocatalytic synthesis system - nitrite (NO 2 ⁻), metal ions (such as Ag + 、Ru 3+ The presence of urea in the presence of a small amount of urea (such as urea, urea, urea nitrate, etc.) will cause color interference, resulting in poor accuracy and repeatability, making it difficult to meet the needs of precise quantification. Therefore, it is urgent to establish a low-concentration urea quantitative detection method that is simple to operate, has rapid response capability, and high anti-interference ability. This has important scientific significance and practical application value for the reaction mechanism in the field of electrocatalytic urea synthesis, optimizing catalyst performance, and promoting industrial applications.

[0004] The national standard method (GB / T 18204.2-2014) and the three improved methods based on diacetyl monoxime disclosed in CN 115015142 A, CN 114544533 A, and CN111487209 A, although showing certain applicability in traditional urea detection, still have obvious deficiencies in the quantitative detection of low-concentration urea in the complex environment of the electrocatalytic urea synthesis system, and cannot meet the current needs. Therefore, how to achieve a urea quantitative method with simple operation, strong anti-interference ability and rapid response ability is a problem that needs to be solved urgently. Summary of the invention

[0005] In view of the above-mentioned prior art, the present invention provides a method for quantitatively detecting low-concentration urea in an electrocatalytic urea synthesis solution, so as to solve the technical problem of poor accuracy of quantitative detection of urea in an electrocatalytic urea synthesis system in the prior art.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for quantitatively detecting low-concentration urea in an electrocatalytically synthesized urea solution, comprising the following steps:

[0007] S1: dissolve diacetyl monoxime and thiosemicarbazide in water to obtain color developer A; dissolve phosphoric acid, sulfuric acid, and iron salt in water to obtain color developer B;

[0008] S2: amplifying the urea concentration in the electrocatalytic synthesis urea solution by N times by concentrating, drying and then re-dissolving, and then adding an interference scavenger to the re-dissolved urea solution, mixing, filtering, and obtaining a test solution; the interference scavenger includes zinc powder and aminosulfonic acid, or the interference scavenger is composed of ascorbic acid and aminosulfonic acid, or the interference scavenger is composed of ascorbic acid and hydroxylamine;

[0009] S3: Add color developer A and color developer B to the solution to be tested, mix well, heat to 90-120°C in a sealed condition, keep warm for 10-30 minutes, and then cool to room temperature;

[0010] S4: The absorbance of the solution obtained in S3 was measured at 525 nm using a UV-visible spectrophotometer;

[0011] S5: preparing a urea standard solution with a concentration gradient, measuring the absorbance of the urea standard solution according to the method in S2 to S4, and drawing a standard curve;

[0012] S6: Calculate the concentration of urea in the electrocatalytic urea synthesis solution according to the absorbance value and concentration magnification of the solution to be tested.

[0013] Based on the above technical solution, the present invention can also be improved as follows.

[0014] Furthermore, the concentrations of diacetyl monoxime and thiosemicarbazide in the color developer A are 5 mg / mL and 0.1 mg / mL, respectively; the ratio of phosphoric acid, sulfuric acid, iron salt and water in the color developer B is 1 mL: 3 mL: 1 mg: 6 mL.

[0015] Furthermore, the iron salt is ferric chloride.

[0016] Furthermore, the method for amplifying the urea concentration in S2 includes the following steps: drying N mL of electrocatalytically synthesized urea solution by a vacuum freeze-drying process, and then dissolving the dried product in 1 mL of water; N is greater than 1; the vacuum degree of the vacuum freeze-drying process is 0.01~0.05MPa, and the temperature is -50℃~-75℃.

[0017] Furthermore, the interferent scavenger comprises 1-5 parts by mass of zinc powder and 1-5 parts by mass of aminosulfonic acid; or the interferent scavenger is composed of ascorbic acid and aminosulfonic acid or hydroxylamine in a mass ratio of 1-5:1-5.

[0018] Furthermore, the interferent scavenger includes 1 part by mass of zinc powder and 4 parts by mass of aminosulfonic acid; or the interferent scavenger is composed of ascorbic acid and aminosulfonic acid or hydroxylamine in a mass ratio of 1:4.

[0019] Furthermore, the volume ratio of the color developer A and color developer B added in S3 to the solution to be tested is 1:2:1.

[0020] Furthermore, the final heating temperature in S3 is 100° C. and the insulation time is 20 min.

[0021] The beneficial effects of the present invention are:

[0022] 1. The detection method of the present invention breaks through the sensitivity limit of the traditional diacetyl monoxime method (LOD=0.01mg / L), and realizes the accurate detection of trace urea in the electrocatalytic synthesis system; at the same time, by vacuum freeze-drying and concentrating the sample, the urea concentration magnification factor can be flexibly controlled, which significantly improves the applicability and detection efficiency of the method.

[0023] 2. The detection method of the present invention effectively eliminates the interference of residual metal ions and by-products in the electrocatalytic system on the color development reaction by introducing an interference scavenger, thereby greatly enhancing the anti-interference ability of the detection method.

[0024] 3. The technology of the present invention systematically optimizes key parameters such as the amount of color reagent added, color reaction device, heating / cooling method and heating time, which significantly improves the accuracy, stability and repeatability of the detection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the urea concentration detection method in the present invention;

[0026] Figure 2 It is the visible absorption spectrum of urea standard solution;

[0027] Figure 3 To prepare the standard curve;

[0028] Figure 4 This is a comparison chart of the anti-interference effects of the experimental group and the control group on metal ions. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0030] Example 1

[0031] A quantitative detection method for low-concentration urea in an electrocatalytically synthesized urea solution, the process flow is as follows Figure 1 As shown, the specific steps include:

[0032] (1) Prepare color developer A and color developer B: add 200 mL of deionized water, 1 g of diacetyl monoxime and 20 mg of thiosemicarbazide into a brown reagent bottle, and mix them evenly by ultrasonication to obtain color developer A; slowly add 120 mL of sulfuric acid into 240 mL of deionized water, and then add 40 mL of phosphoric acid and 40 mg of ferric chloride in sequence, and mix them evenly by ultrasonication to obtain color developer B; keep color developer A and color developer B away from light for future use;

[0033] (2) 4 mL of the electrocatalytically synthesized urea solution was subjected to vacuum freeze drying to achieve sample concentration; during this process, the vacuum degree of the dryer was 0.01 MPa and the cold trap temperature was -75 °C; then, 1 mL of deionized water was added to the dried sample to redissolve it and transfer it to an 8 mL screw-capped glass pressure tube; then, 4 mg of zinc powder was added, the mixture was shaken and mixed for 5 min, and then filtered; then, 16 mg of aminosulfonic acid was added to the filtrate, the mixture was shaken and mixed for 5 min, and then filtered to obtain the test solution;

[0034] (3) Add 1 mL of color developer A and 2 mL of color developer B to the test solution obtained in step 2 and mix well; then, transfer the solution to a high-power water bath, heat to 100°C with the tube mouth sealed, and maintain this temperature for 20 minutes; after the reaction is completed, place the solution in a constant temperature device at 25°C and quickly cool to room temperature;

[0035] (4) Using a UV-visible spectrophotometer, measure the absorbance of the solution at 525 nm;

[0036] (5) Prepare a urea standard solution with a concentration gradient (the concentration range of the urea standard solution is 0-0.5 mg / L), and process it according to the above steps (the concentration multiple of the standard solution is 4 times), and measure the absorbance of the standard solution (parallel test three times). The results are as follows: Figure 2 As shown; and a standard curve is drawn with the measured absorbance values ​​and the corresponding concentrations. The results are shown in Figure 3 As shown, from Figure 3 It can be seen that there is a good linear relationship between urea concentration and absorbance, and the correlation coefficient (R 2 ) is 0.9999;

[0037] (6) Calculate the actual urea concentration of the sample based on the absorbance value and concentration magnification of the sample.

[0038] Example 2

[0039] A quantitative detection method for low-concentration urea in an electrocatalytically synthesized urea solution, the process flow is as follows Figure 1 As shown, the specific steps include:

[0040] (1) Prepare color developer A and color developer B: add 200 mL of deionized water, 1 g of diacetyl monoxime and 20 mg of thiosemicarbazide into a brown reagent bottle, and mix them evenly by ultrasonication to obtain color developer A; slowly add 120 mL of sulfuric acid into 240 mL of deionized water, and then add 40 mL of phosphoric acid and 40 mg of ferric chloride in sequence, and mix them evenly by ultrasonication to obtain color developer B; keep color developer A and color developer B away from light for future use;

[0041] (2) 4 mL of the electrocatalytically synthesized urea solution was subjected to vacuum freeze drying to achieve sample concentration; during this process, the vacuum degree of the dryer was 0.01 MPa and the cold trap temperature was -75 °C; then, 1 mL of deionized water was added to the dried sample to redissolve it and transfer it to an 8 mL screw-capped glass pressure tube; then, 20 mg of an interference scavenger was added, the interference scavenger component being composed of ascorbic acid and aminosulfonic acid in a mass ratio of 1:4, and the mixture was shaken and mixed for 5 minutes and then filtered to obtain a test solution;

[0042] (3) Add 1 mL of color developer A and 2 mL of color developer B to the test solution obtained in step 2 and mix well; then, transfer the solution to a high-power water bath, heat to 100°C with the tube mouth sealed, and maintain this temperature for 20 minutes; after the reaction is completed, place the solution in a constant temperature device at 25°C and quickly cool to room temperature;

[0043] (4) Using a UV-visible spectrophotometer, measure the absorbance of the solution at 525 nm;

[0044] (5) Calculate the actual urea concentration of the sample to be tested based on the absorbance value and concentration magnification of the sample to be tested and the standard curve drawn in Example 1.

[0045] Example 3

[0046] A quantitative detection method for low-concentration urea in an electrocatalytically synthesized urea solution, the process flow is as follows Figure 1 As shown, the specific steps include:

[0047] (1) Prepare color developer A and color developer B: add 200 mL of deionized water, 1 g of diacetyl monoxime and 20 mg of thiosemicarbazide into a brown reagent bottle, and mix them evenly by ultrasonication to obtain color developer A; slowly add 120 mL of sulfuric acid into 240 mL of deionized water, and then add 40 mL of phosphoric acid and 40 mg of ferric chloride in sequence, and mix them evenly by ultrasonication to obtain color developer B; keep color developer A and color developer B away from light for future use;

[0048] (2) 4 mL of the electrocatalytically synthesized urea solution was freeze-dried in a vacuum to achieve sample concentration; during the process, the vacuum degree of the dryer was 0.01 MPa and the cold trap temperature was -75 °C; then, 1 mL of deionized water was added to the dried sample to redissolve it and transfer it to an 8 mL screw-capped glass pressure tube; then, 20 mg of an interference scavenger was added, the interference scavenger component being composed of ascorbic acid and hydroxylamine in a mass ratio of 1:4, and the mixture was shaken and mixed for 5 minutes and then filtered to obtain a test solution;

[0049] (3) Add 1 mL of color developer A and 2 mL of color developer B to the test solution obtained in step 2 and mix well; then, transfer the solution to a high-power water bath, heat to 100°C with the tube mouth sealed, and maintain this temperature for 20 minutes; after the reaction is completed, place the solution in a constant temperature device at 25°C and quickly cool to room temperature;

[0050] (4) Using a UV-visible spectrophotometer, measure the absorbance of the solution at 525 nm;

[0051] (5) Calculate the actual urea concentration of the sample to be tested based on the absorbance value and concentration magnification of the sample to be tested and the standard curve drawn in Example 1.

[0052] Comparative Example 1

[0053] A method for quantitatively detecting low-concentration urea in an electrocatalytically synthesized urea solution comprises the following steps:

[0054] (1) Prepare color developer A and color developer B: add 200 mL of deionized water, 1 g of diacetyl monoxime and 20 mg of thiosemicarbazide into a brown reagent bottle, and mix them evenly by ultrasonication to obtain color developer A; slowly add 120 mL of sulfuric acid into 240 mL of deionized water, and then add 40 mL of phosphoric acid and 40 mg of ferric chloride in sequence, and mix them evenly by ultrasonication to obtain color developer B; keep color developer A and color developer B away from light for future use;

[0055] (2) Transfer 1 mL of the electrocatalytically synthesized urea solution to an 8 mL screw-capped glass pressure tube; then, add 4 mg of zinc powder, shake and mix for 5 min, and filter; then, add 16 mg of aminosulfonic acid to the filtrate, shake and mix for 5 min, and filter to obtain the test solution;

[0056] (3) Add 1 mL of color developer A and 2 mL of color developer B to the test solution obtained in step 2 and mix well; then, transfer the solution to a high-power water bath, heat to 100°C with the tube mouth sealed, and maintain this temperature for 20 minutes; after the reaction is completed, place the solution in a constant temperature device at 25°C and quickly cool to room temperature;

[0057] (4) Using a UV-visible spectrophotometer, measure the absorbance of the solution at 525 nm;

[0058] (5) According to the absorbance value and concentration magnification of the sample to be tested, the actual urea concentration of the sample to be tested is calculated using the standard curve obtained in Example 1.

[0059] Comparative Example 2

[0060] A method for quantitatively detecting low-concentration urea in an electrocatalytically synthesized urea solution comprises the following steps:

[0061] (1) Prepare color developer A and color developer B: add 200 mL of deionized water, 1 g of diacetyl monoxime and 20 mg of thiosemicarbazide into a brown reagent bottle, and mix them evenly by ultrasonication to obtain color developer A; slowly add 120 mL of sulfuric acid into 240 mL of deionized water, and then add 40 mL of phosphoric acid and 40 mg of ferric chloride in sequence, and mix them evenly by ultrasonication to obtain color developer B; keep color developer A and color developer B away from light for future use;

[0062] (2) 4 mL of the electrocatalytically synthesized urea solution was subjected to vacuum freeze drying to achieve sample concentration; during this process, the vacuum degree of the dryer was 0.01 MPa and the cold trap temperature was -75 °C; then, 1 mL of deionized water was added to the dried sample to redissolve it, and the sample was transferred to an 8 mL screw-capped glass pressure tube to obtain a test solution;

[0063] (3) Add 1 mL of color developer A and 2 mL of color developer B to the test solution obtained in step 2 and mix well; then, transfer the solution to a high-power water bath, heat to 100°C with the tube mouth sealed, and maintain this temperature for 20 minutes; after the reaction is completed, place the solution in a constant temperature device at 25°C and quickly cool to room temperature;

[0064] (4) Using a UV-visible spectrophotometer, measure the absorbance of the solution at 525 nm;

[0065] (5) According to the absorbance value and concentration magnification of the sample to be tested, the actual urea concentration of the sample to be tested is calculated using the standard curve obtained in Example 1.

[0066] Experimental example

[0067] The detection results of the detection methods in Examples 1 to 3 of the present invention are similar. Taking Example 1 as an example, the detection effect of the detection method is described in detail.

[0068] 1. Limit of detection (LOD) of the quantitative detection method of urea of ​​the present invention

[0069] The LOD of the analytical method is calculated from the standard working curve as follows:

[0070]

[0071]

[0072] Where: Slope is the slope of the standard working curve; Y i is the analytical signal measured by this method; Y r,i is the analytical signal predicted by the standard working curve; n is the number of data points.

[0073] The linear regression equation, correlation coefficient and detection limit of the standard curve drawn by the urea quantitative detection method of the present invention are shown in Table 1. As can be seen from the table, there is a good linear relationship between urea concentration and absorbance, and the correlation coefficient (R 2 ) is 0.9999, and the detection limit of this quantitative detection method is 0.01 mg / L, indicating that this method has a high urea detection sensitivity and a strong linear response characteristic even in a lower urea concentration range.

[0074] Table 1 Standard curve and detection limit of low concentration urea

[0075]

[0076] 2. Repeatability test of urea quantitative detection method

[0077] According to the urea quantitative detection method described in Example 1, the urea standard solution and the electrocatalytic synthesis urea solution were repeatedly tested to evaluate the repeatability of the urea concentration determination, and the results are shown in Table 2. The relative standard deviation (RSD) value is less than 5%, indicating that the low-concentration urea detection technology of the present invention has good repeatability, especially suitable for low-concentration detection of the electrocatalytic synthesis urea system.

[0078] Table 2 Repeatability test results of urea quantitative detection method

[0079]

[0080] 3. Accuracy test of urea quantitative detection method

[0081] The sample spike recovery experiment was used to verify the accuracy of the quantitative detection method of urea of ​​the present invention. Three urea standard solutions with low (0.5 mg / L), medium (1 mg / L), and high (5 mg / L) concentrations were added to the sample solution, and each sample was measured 3 times. The steps of the detection method were the same as those in Example 1. The results showed that the recovery rate and relative standard deviation (RSD) met the requirements. The specific data are shown in Table 3.

[0082] Table 3 Spiked recovery of urea quantitative detection method (n=3)

[0083]

[0084] 4. Verification of the anti-interference ability of urea quantitative detection method on nitrite and metal ions

[0085] In the 0.5 mg / L standard urea sample, 10 mg / L interfering metal ions (such as Ru 3+ , Pd 2+ 、Ag + etc.) and 100mg / L NO 2 - The experimental group performed urea concentration detection according to the steps of Example 1 (including interference scavenger), while the control group (performing urea concentration detection according to the steps of Comparative Example 2) did not add any interference scavenger, and the remaining steps were the same. Figure 4 As shown. As can be seen from the figure, when the control group did not add the scavenger, the color development reaction was interfered by metal ions and nitrite, resulting in abnormal fluctuations in absorbance, and it was impossible to accurately quantify urea. The experimental group effectively eliminated the influence of coexisting interferents through the action of the interferent scavenger. The experimental results show that the quantitative detection method in the present invention significantly enhances the anti-interference ability of the method and significantly improves the reliability of urea detection in complex electrocatalytic systems.

[0086] In order to fully demonstrate the superiority and interference ability of the urea quantitative detection method of the present invention in detecting low-concentration urea in electrocatalytic urea synthesis, multiple groups of tests were carried out using the national standard method (GB / T 18204.2-2014), the method in Example 1, and the methods in Comparative Examples 1 and 2, and the results are shown in Table 4.

[0087] Table 4 Comparison of experimental results of national standard method, embodiment and comparative example

[0088]

[0089] Note: RD is relative deviation, RSD is relative standard deviation, and concentration is mg / L.

[0090] The above results show that the urea quantitative detection method in the present invention is significantly superior to the traditional national standard method in terms of stability, accuracy and repeatability. The concentration process achieved by vacuum freeze drying effectively improves the accuracy of low-concentration urea quantification. In addition, the interference scavenger plays an irreplaceable key role in this method, which effectively eliminates interference, ensures the accuracy of low-concentration urea detection, and provides solid technical support for the accurate quantitative analysis of urea in electrochemical reactions.

[0091] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for quantitatively detecting low-concentration urea in an electrocatalytically synthesized urea solution, characterized in that: The following steps are involved: S1: dissolve diacetyl monoxime and thiosemicarbazide in water to obtain color developer A; dissolve phosphoric acid, sulfuric acid, and iron salt in water to obtain color developer B; S2: amplifying the urea concentration in the electrocatalytic synthesis urea solution by N times by concentrating, drying and then redissolving, then adding an interference scavenger to the redissolved urea solution, mixing, filtering, and obtaining a test solution; the interference scavenger comprises zinc powder and aminosulfonic acid, or the interference scavenger consists of ascorbic acid and aminosulfonic acid, or the interference scavenger consists of ascorbic acid and hydroxylamine; S3: Add color developer A and color developer B to the solution to be tested, mix well, heat to 90-120°C in a sealed condition, keep warm for 10-30 minutes, and then cool to room temperature; S4: The absorbance of the solution obtained in S3 was measured at 525 nm using a UV-visible spectrophotometer; S5: preparing a urea standard solution with a concentration gradient, measuring the absorbance of the urea standard solution according to the method in S2 to S4, and drawing a standard curve; S6: Calculate the concentration of urea in the electrocatalytic urea synthesis solution according to the absorbance value and concentration magnification of the solution to be tested.

2. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1, characterized in that: The concentrations of diacetyl monoxime and thiosemicarbazide in the developer A are 5 mg / mL and 0.1 mg / mL respectively; the ratio of phosphoric acid, sulfuric acid, iron salt and water in the developer B is 1 mL: 3 mL: 1 mg: 6 mL.

3. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1 or 2, characterized in that: The iron salt is ferric chloride.

4. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1, characterized in that: The urea concentration amplification method in S2 comprises the following steps: drying N mL of electrocatalytically synthesized urea solution by a vacuum freeze drying process, and then dissolving the dried product in 1 mL of water; wherein N is greater than 1; and the vacuum degree of the vacuum freeze drying process is 0.01-0.05 MPa, and the temperature is -50°C--75°C.

5. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1, characterized in that: The interfering substance scavenger comprises 1-5 parts by mass of zinc powder and 1-5 parts by mass of aminosulfonic acid; or the interfering substance scavenger is composed of ascorbic acid and aminosulfonic acid or hydroxylamine in a mass ratio of 1-5:1-5.

6. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 5, characterized in that: The interfering substance scavenger comprises 1 part by mass of zinc powder and 4 parts by mass of aminosulfonic acid; or the interfering substance scavenger consists of ascorbic acid and aminosulfonic acid or hydroxylamine in a mass ratio of 1:

4.

7. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1, characterized in that: The volume ratio of the color developer A and color developer B added in S3 to the solution to be tested is 1:2:

1.

8. The method for quantitatively detecting low-concentration urea in the electrocatalytic synthesis urea solution according to claim 1, characterized in that: The final heating temperature in S3 is 100°C and the insulation time is 20 minutes.

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