Method for detecting ammonia content in a solution containing sulfurous acid

Abstract

The present application relates to a kind of ammonia content detection method in sulfurous acid-containing solution, belong to material detection technical field.The ammonia content detection method in sulfurous acid-containing solution of the present application, comprising the following steps: (1) adding potassium hydrogen persulfate to be measured sulfurous acid-containing ammonia solution and reacting with sulfurous acid, obtain the test solution;(2) using indigo phenol blue spectrophotometry to determine the ammonia content in the test solution obtained in step (1), i.e.the ammonia content in sulfurous acid-containing solution is obtained.The present application first adds oxidizing agent potassium hydrogen persulfate solution as pretreatment reagent, and reacts with sulfurous acid, eliminates sulfurous acid, while it will not produce interference factors affecting ammonia content determination.The ammonia concentration standard curve obtained by the test method of the present application, the R 2 of fitting curve has reached 0.999, which indicates that ammonia signal intensity and the concentration of standard solution have good linear relationship, further indicating that the ammonia content detection method of the present application has good detection reliability and accuracy.

Description

Technical Field

[0001] This invention belongs to the field of material detection technology, specifically relating to a method for detecting ammonia content in a solution containing sulfite. Background Technology

[0002] Currently, the commonly used method for qualitative analysis of ammonia is nuclear magnetic resonance spectroscopy (using isotopes). 15 Quantitative analysis of ammonia (using nitrogen as a nitrogen source) and infrared spectroscopy includes nuclear magnetic resonance spectroscopy, ion-selective electrode methods, ion chromatography, and spectrophotometry (including the indophenol blue method and Nessler's reagent method). Different catalytic reaction systems require specific calibration characteristics when selecting the appropriate detection method. Quantitative analysis of ammonia is a significant challenge in the development of photocatalytic ammonia synthesis technology. For spectrophotometry, the Nessler's reagent method is time-efficient and requires less sample, but has lower sensitivity; in contrast, the indophenol blue method has higher sensitivity but suffers from poor stability. Compared to the two colorimetric methods mentioned above, ion chromatography and nuclear magnetic resonance spectroscopy offer advantages such as shorter testing time, smaller sample volume, higher sensitivity, and continuous detection; however, both suffer from inconvenience, inability to monitor promptly, and high testing costs.

[0003] Regarding the performance and cost-effectiveness of photoelectrocatalytic ammonia synthesis, even though the various ammonia content detection methods mentioned above can show considerable consistency and high precision in the detection of ammonia concentration under ideal conditions, when dealing with complex chemical environments (such as harsh pH conditions, impurities and other nitrogen-containing contaminants), especially under extremely low ammonia concentration conditions, special attention needs to be paid to the different drawbacks of each method in verifying the effectiveness and accuracy of ammonia concentration.

[0004] In recent years, sacrificial agents have often been used to promote charge separation. For example, sulfides, which have shown promising performance in photocatalytic water splitting, are generally used as sacrificial agents when applied to photocatalytic ammonia synthesis. However, in the presence of sacrificial agents, the above-mentioned ammonia content testing methods are affected by the sacrificial agents, resulting in inaccurate tests and making it difficult to properly evaluate the ammonia synthesis performance of the catalyst. Therefore, the rationality and accuracy of ammonia production remains an issue to be addressed. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for detecting the ammonia content in a solution containing sulfite.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for detecting ammonia content in a solution containing sulfite, comprising the following steps:

[0008] (1) Add potassium persulfate to the ammonia solution containing sulfite to react with the sulfite to obtain the test solution;

[0009] (2) The ammonia content in the test solution obtained in step (1) was determined by indophenol blue spectrophotometry, which yielded the ammonia content in the solution containing sulfite.

[0010] Na₂SO₃, used as a sacrificial agent, has reducing properties. If the test solution is directly standardized using the indophenol blue method, it will react with the strongly oxidizing NaClO first, affecting the final standardization result. When directly using the indophenol blue spectrophotometric method to determine the ammonia content in a solution system containing sulfite as a sacrificial agent, the reducing properties of sulfite will cause it to react with the strongly oxidizing NaClO first, affecting the final standardization result. Therefore, this invention adds potassium persulfate (KHSO₅) solution as an oxidizing agent to the test solution as a pretreatment reagent to react with sulfite, eliminating sulfite and avoiding interference factors that affect the ammonia content determination. The ammonia concentration standard curve obtained by the method of this invention has an R-value of [missing value]. 2 The value has reached 0.999, which indicates a good linear relationship between the ammonia signal intensity and the concentration of the standard solution, further demonstrating that the ammonia content detection method of the present invention has good detection reliability and accuracy.

[0011] In a preferred embodiment of the method for detecting ammonia content in a sulfite-containing solution according to the present invention, in step (1), the molar ratio of sulfite in the ammonia solution containing sulfite to potassium persulfate is 1:(0.3-0.8).

[0012] Preferably, the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.6.

[0013] The present invention has found through research that treating sulfite with the above-mentioned ratio of oxidant can improve the accuracy of the ammonia content detection method of the present invention.

[0014] As a preferred embodiment of the method for detecting ammonia content in a solution containing sulfite according to the present invention, in step (2), the method for determining ammonia content by indophenol blue spectrophotometry is as follows: a colorimetric agent, an oxidant, and a catalyst are added sequentially to the test solution obtained in step (1), mixed and allowed to stand, the absorbance is tested, and compared with the standard curve to obtain the ammonia content in the solution containing sulfite.

[0015] In a preferred embodiment of the method for detecting ammonia content in a sulfite-containing solution according to the present invention, the pH value of the colorimetric reagent is 13.1-13.5.

[0016] In a preferred embodiment of the method for detecting ammonia content in a sulfite-containing solution according to the present invention, the colorimetric reagent is a mixed solution of salicylic acid, sodium hydroxide and sodium citrate.

[0017] In a preferred embodiment of the method for detecting ammonia content in a sulfite-containing solution according to the present invention, the oxidant is sodium hypochlorite.

[0018] In a preferred embodiment of the method for detecting ammonia content in a sulfite-containing solution according to the present invention, the catalyst is sodium nitroprusside.

[0019] The indophenol blue spectrophotometric method is based on the Bethlot reaction, involving the reaction of ammonia with salicylic acid and hypochlorite under alkaline conditions to produce a yellow-green product. The working principle of each substance in the indophenol blue spectrophotometric method for testing ammonia content in this invention is as follows: First, ammonia reacts with the oxidant sodium hypochlorite to produce monochloramine, which is the first stage of the reaction mechanism. Adding the colorimetric agent before the oxidant ensures the formation of indophenol and accurate color development. Adding the oxidant hypochlorite first introduces excess chlorine, affecting the final ammonia concentration used for calibration. In the presence of a catalyst, salicylic acid reacts with the generated monochloramine to produce quinone chloroimine, which then reacts with another salicylic acid molecule, oxidizing to produce the final product, blue indophenol. Sodium citrate acts as a masking agent to mask interfering ions, especially cations in the reagent. NaOH is used to adjust the pH. The stability of monochloramine, the initial product of the reaction, comes from the catalyst. In the presence of the catalyst, indophenol is produced in maximum quantities at pH values ​​between 9.8 and 10.4. The reaction catalyzed by sodium nitroprusside produces a basically stable color at pH values ​​between 11.4 and 12.4, but becomes unstable at pH values ​​above 12.7. When using salicylates, the optimal pH value for color development is even higher. It has been verified that the test results are most stable when the final pH value of the color developer is between 13.1 and 13.5.

[0020] This invention does not limit the concentration of each reagent when testing ammonia content using the indophenol blue spectrophotometric method. The indophenol blue spectrophotometric method for determining ammonia content has been widely used in the field, and conventional indophenol blue spectrophotometric methods can achieve the ammonia content determination of this invention.

[0021] In one specific embodiment of the present invention, when determining the ammonia content by indophenol blue spectrophotometry, 1 mL of colorimetric reagent, 0.5 mL of oxidant, and 0.1 mL of catalyst are added sequentially to 1 mL of the test solution. After shaking and standing for 1 hour, the absorbance is measured. The preparation methods of each reagent are as follows:

[0022] Colorimetric reagent: Weigh 5g NaOH and prepare it in a 100mL volumetric flask (concentration of 1mol·L-1). Transfer the solution to a 150mL beaker, weigh 5g salicylic acid and 5g sodium citrate, and dissolve them by magnetic stirring.

[0023] Oxidizing agent: Pipette 4 mL of NaClO (≥5%) into a 100 mL beaker, add 50 mL of ultrapure water, and dissolve by magnetic stirring.

[0024] Catalyst: Take 0.1g of sodium nitroferricyanide / sodium nitroprusside in a 20mL beaker, add 10mL of ultrapure water, and dissolve by magnetic stirring.

[0025] Another object of the present invention is to provide the application of the method for detecting the ammonia content in the sulfite-containing solution in photocatalytic ammonia synthesis.

[0026] The ammonia content detection method of this invention can eliminate the interference of sulfite sacrificial agent and can accurately determine the ammonia content when applied in the photocatalytic ammonia synthesis experiment.

[0027] The present invention has the following beneficial effects: By selecting a suitable oxidant KHSO5 solution as a pretreatment reagent to treat sulfite ions, the present invention can effectively block SO3 in the sacrificial agent. 2- The impact on subsequent indophenol blue spectrophotometry was investigated to ensure normal colorimetric development and effective calibration of ammonia content in the test solution. A suitable mixing ratio was designed, the pH range of the test solution was further confirmed, and an ammonia concentration standard curve was obtained. The R-squared value of the fitted curve was determined. 2 The value reached 0.999, indicating a good linear relationship between the ammonia signal intensity and the concentration of the standard solution. This invention solves the problem of the indophenol blue spectrophotometric calibration of ammonia content failing due to the presence of the strong reducing agent Na2SO3 in the ammonia synthesis reaction caused by sulfide photocatalysts, thus ensuring the colorimetric effect, calibration accuracy, and reliability. Attached Figure Description

[0028] Figure 1 This is a normally colored optical photograph taken when measuring ammonia content using the ammonia content detection method of Embodiment 1 of the present invention.

[0029] Figure 2 The ultraviolet absorption spectra of three colorimetric experiments in Example 1 of this invention;

[0030] Figure 3 This is the standard curve obtained from three color development experiments in Example 1 of the present invention;

[0031] Figure 4 This is an optical photograph of Indophenol Blue that could not be properly developed by spectrophotometry under conditions without oxidant pretreatment, as shown in Comparative Example 1.

[0032] Figure 5 The external standard curves obtained by treating the test solution with different concentrations of oxidant KHSO5 in the detection method of this invention are R values. 2 With slope;

[0033] Figure 6The UV-Vis absorption spectra obtained by treating the test solution with an ammonia content of 4 ppm by different concentrations of oxidant KHSO5 in the detection method of the present invention are as follows:

[0034] Figure 7 The external standard curve Ri is obtained by treating the test solution under different pH conditions of the chromogenic reagent in the detection method of this invention. 2 With slope;

[0035] Figure 8 The UV-Vis absorption spectra are obtained by treating the test solution with an ammonia content of 4 ppm under different pH conditions of the colorimetric reagent in the detection method of the present invention. Detailed Implementation

[0036] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0037] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0038] Example 1

[0039] This invention verifies the accuracy of its method for detecting ammonia content in sulfite-containing solutions by measuring standard ammonia solutions. The test method is as follows:

[0040] Na2SO3 (0.06 mol·L) -1 Using NH3 solution as background and (NH4)2SO4 as ammonia source, standard solutions of NH3 at different concentrations (0.2ppm, 2ppm, 4ppm, 6ppm, 8ppm) were prepared.

[0041] The preparation methods for each reagent in the indophenol blue spectrophotometric method for determining ammonia content are as follows:

[0042] Colorimetric reagent: Weigh 5g NaOH and prepare it in a 100mL volumetric flask (concentration 1mol·L⁻¹). -1 The solution was transferred to a 150mL beaker, and 5g of salicylic acid and 5g of sodium citrate were weighed and dissolved by magnetic stirring. The pH value of the colorimetric reagent was 13.14.

[0043] Oxidizing agent: Pipette 4 mL of NaClO (≥5%) into a 100 mL beaker, add 50 mL of ultrapure water, and dissolve by magnetic stirring.

[0044] Catalyst: Take 0.1g of sodium nitroferricyanide / sodium nitroprusside in a 20mL beaker, add 10mL of ultrapure water, and dissolve by magnetic stirring.

[0045] The present invention provides a method for detecting ammonia content in a solution containing sulfite, comprising the following steps:

[0046] (1) Potassium persulfate is added to standard ammonia solutions containing sulfite of different concentrations to react with sulfite to obtain the test solution; the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite is 1:0.6.

[0047] (2) Add 1 mL of colorimetric reagent, 0.5 mL of oxidant and 0.1 mL of catalyst to 1 mL of the test solution in sequence. Shake well and let stand for 1 h. Then test the absorbance at 650 nm to obtain the ammonia content in the solution containing sulfite.

[0048] Three colorimetric experiments were conducted using the ammonia content detection method of this embodiment. The optical images of the color development are as follows: Figure 1 As shown, from Figure 1 As can be seen, this invention enables the test solution to develop color normally after pretreatment with a KHSO5 solution of appropriate ratio. The ultraviolet absorption spectra of the three color development experiments are as follows: Figure 2 As shown, the standard curve obtained from the data of three colorimetric experiments is as follows: Figure 3 As shown, from Figure 2 and Figure 3 As can be seen, the ammonia content detection method of the present invention can make it develop color normally, and Figure 3 The standard curve shows that the detection method of the present invention can accurately calibrate the ammonia yield in ammonia synthesis experiments with interference from sulfite ions.

[0049] Example 2

[0050] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.3; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0051] Example 3

[0052] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.4; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve... 2 and slope display Figure 5In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0053] Example 4

[0054] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.5; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0055] Example 5

[0056] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.7; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0057] Example 6

[0058] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.8; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0059] Example 7

[0060] The difference between the ammonia content detection method in this embodiment and Example 1 is that the pH value of the colorimetric reagent is adjusted to 13.31 by adjusting the amount of sodium hydroxide added, and no 8 ppm NH3 standard solution is used; otherwise, it is the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0061] Example 8

[0062] The difference between the ammonia content detection method in this embodiment and Example 1 is that the pH value of the colorimetric reagent is adjusted to 13.44 by adjusting the amount of sodium hydroxide added, and no 8 ppm NH3 standard solution is used; otherwise, it is the same as in Example 1. The standard curve obtained by the detection method in this embodiment has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0063] Comparative Example 1

[0064] This comparative example uses the traditional indophenol blue spectrophotometric method to perform a single colorimetric experiment on ammonia solutions of different standard concentrations. That is, compared with Example 1, only step (2) is performed to determine the ammonia content. The colorimetric results obtained are as follows: Figure 4 As shown, Figure 4 The results show that without oxidant treatment of the solution, the indophenol blue spectrophotometric method could not produce a normal color development. Furthermore, the UV-Vis absorption spectrum showed no obvious absorption peaks.

[0065] Comparative Example 2

[0066] The difference between this comparative method for detecting ammonia content and Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.1; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by this comparative method has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0067] Comparative Example 3

[0068] The difference between this comparative method for detecting ammonia content and Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.2; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by this comparative method has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0069] Comparative Example 4

[0070] The difference between the ammonia content detection method in this embodiment and that in Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:0.9; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by this comparative detection method has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0071] Comparative Example 5

[0072] The difference between this comparative method for detecting ammonia content and Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite to be tested is 1:1.0; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by this comparative method has a good linear relationship. The R of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0073] Comparative Example 6

[0074] The difference between this comparative method for detecting ammonia content and Example 1 is that, in step (1), the molar ratio of sulfite to potassium persulfate in the ammonia solution containing sulfite is 1:1.1; there is no 8 ppm NH3 standard solution; the rest are the same as in Example 1. The standard curve obtained by this comparative method has a good linear relationship. The R value of the standard curve is... 2 and slope display Figure 5 In the middle, the ultraviolet-visible absorption spectrum shows Figure 6 middle.

[0075] Comparative Example 7

[0076] The difference between this comparative method for ammonia content detection and Example 1 is that the amount of sodium hydroxide added was adjusted to adjust the pH of the colorimetric reagent to 5.41, and no 8 ppm NH3 standard solution was used; all other aspects are the same as in Example 1. The UV-Vis absorption spectrum obtained by this comparative method shows... Figure 8 middle.

[0077] Comparative Example 8

[0078] The difference between this comparative method for ammonia content detection and Example 1 is that the amount of sodium hydroxide added was adjusted to change the pH of the colorimetric reagent to 12.47, and no 8 ppm NH3 standard solution was used; all other aspects are the same as in Example 1. The standard curve obtained by this comparative method shows good linearity. The R-squared value of the standard curve is...2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0079] Comparative Example 9

[0080] The difference between this comparative method for ammonia content detection and Example 1 is that the amount of sodium hydroxide added was adjusted to change the pH of the colorimetric reagent to 12.84, and no 8 ppm NH3 standard solution was used; all other aspects are the same as in Example 1. The standard curve obtained by this comparative method shows good linearity. The R-squared value of the standard curve is... 2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0081] Comparative Example 10

[0082] The difference between this comparative method for ammonia content detection and Example 1 is that the amount of sodium hydroxide added was adjusted to change the pH of the colorimetric reagent to 13.56, and no 8 ppm NH3 standard solution was used; all other aspects are the same as in Example 1. The standard curve obtained by this comparative method shows good linearity. The R-squared value of the standard curve is... 2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0083] Comparative Example 11

[0084] The difference between this comparative method for ammonia content detection and Example 1 is that the amount of sodium hydroxide added was adjusted to change the pH of the colorimetric reagent to 13.64, and no 8 ppm NH3 standard solution was used; all other aspects are the same as in Example 1. The standard curve obtained by this comparative method shows good linearity. The R-squared value of the standard curve is... 2 and slope display Figure 7 In the middle, the ultraviolet-visible absorption spectrum shows Figure 8 middle.

[0085] This invention uses Na2SO3 (0.06 mol·L⁻¹) -1 Using NH3 solution as background and (NH4)2SO4 as ammonia source, different concentrations of KHSO5 solution were added to standard solutions of NH3 (0.2ppm, 2ppm, 4ppm, 6ppm) of different concentrations. Examples 1-6 and Comparative Examples 2-6 used different concentrations of KHSO5 oxidant with a molar ratio of sulfite to potassium persulfate of 1:(0.1-1.1) in the ammonia solution containing sulfite to be tested for pretreatment of the test solution in step (1), and standard curves were plotted. All showed good linearity. The R value of the obtained curves was calculated. 2 Plotting the slope summation, the results are displayed... Figure 5 middle, Figure 6 The UV-Vis absorption spectra are obtained after treating the test solution with different concentrations of oxidant KHSO5 and an ammonia content of 4 ppm. Figure 5 and Figure 6 In the middle, the R of the external standard curve obtained from the results 2 By comparing the slope and the peak value of the UV-Vis absorption spectrum, it is determined that when the molar ratio of sulfite to potassium peroxymonosulfate in the ammonia solution containing sulfite is 1:(0.3-0.8), the detection method of the present invention can eliminate the interference of sulfite on the detection of ammonia content and has high accuracy.

[0086] Examples 1, 7-8, and Comparative Examples 7-11 of this invention further adjusted the pH value of the colorimetric reagent by changing the amount of NaOH. Standard curves were plotted for each group of data, all showing a good linear relationship. The R-value of the obtained curves was... 2 Plotting the slope summation together yields the following results: Figure 7 As shown, Figure 8 The UV-Vis absorption spectra were obtained after treating test solutions with an ammonia content of 4 ppm at different pH values ​​(5.41-13.64). Figure 7 and Figure 8 In the middle, the R of the external standard curve obtained from the results 2 The accuracy of the detection method of the present invention is determined by comparing the slope and the peak value of the ultraviolet-visible absorption spectrum. When the pH value of the colorimetric reagent is 13.1-13.5, the detection method of the present invention has high accuracy.

[0087] This invention uses the oxidant KHSO5 for pretreatment of the test solution, which has significant advantages compared to other types of oxidants.

[0088] If dilute sulfuric acid is added to the test solution to react with sulfite ions, a pale yellow sulfur precipitate is observed in the solution. After centrifugation, the solution remains turbid, which affects the subsequent colorimetric reaction. Therefore, this method is not recommended.

[0089] If NaClO is used for pretreatment of the test solution, the amount used is difficult to control precisely, except when combined with SO3. 2- In addition to the reaction, excess ClO - Will with NH 4+ The above reaction occurs similarly to the classic breakpoint chlorination mechanism, where ammonia first reacts with an active chlorine substance (ClO). - The reaction proceeds stepwise to produce chloramines, namely monochloramine, dichloramine, and trichloramine, and finally nitrogen gas. Because the process continues to consume monochloramine after the first-stage product is produced, indophenol blue cannot be formed normally in the end.

[0090] If hydrogen peroxide is used, its concentration has no definite value, making it difficult to quantify. Furthermore, excessive hydrogen peroxide will react with ammonia to generate nitrogen gas, affecting the subsequent calibration of ammonia concentration.

[0091] Using potassium permanganate as a commonly used non-chlorine oxidant is also not advisable, because it is colored and will interfere with the normal color development of indophenol blue.

[0092] Therefore, this invention employs a suitable ratio (molar ratio of SO3). 2- :SO5 2- A KHSO5 solution of 1:[0.3,0.8] was used to pretreat the indophenol blue spectrophotometric method in a Na2SO3 sacrificial agent system to ensure proper color development and to generate a standard curve for calibrating ammonia yield in ammonia synthesis experiments. This invention further determines the optimal pH value of the display agent for the indophenol blue spectrophotometric method in a Na2SO3 sacrificial agent system, further ensuring the color development effect, calibration accuracy, and reliability.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for detecting the ammonia content in a sulfite-containing solution, characterized by, The method comprises the following steps: (1) adding potassium peroxymonosulfate to the ammonia solution containing sulfite to be tested to react with sulfite to obtain a test solution; (2) determining the ammonia content in the test solution obtained in step (1) by using an indigo blue spectrophotometry method to obtain the ammonia content in the solution containing sulfite.

2. The method of claim 1, wherein the sulfite-containing solution is a sulfite solution. In step (1), the molar ratio of sulfite in the ammonia solution containing sulfite to be tested to the potassium peroxymonosulfate is 1:(0.3-0.8).

3. The method of claim 1, wherein the sulfite-containing solution is a sulfite solution. In step (2), the method for determining the ammonia content by using the indigo blue spectrophotometry method is as follows: sequentially adding a color developing agent, an oxidizing agent and a catalyst to the test solution obtained in step (1), mixing, standing, testing the absorbance, comparing with a standard curve, and obtaining the ammonia content in the solution containing sulfite.

4. The method for detecting the ammonia content in a sulfite-containing solution according to claim 3, characterized by, The pH value of the color developing agent is 13.1-13.

5.

5. The method of claim 3, wherein the sulfite-containing solution is a sulfite solution. The color developing agent is a mixed solution of salicylic acid, sodium hydroxide and sodium citrate.

6. The method of claim 3, wherein the sulfite-containing solution is a sulfite solution. The oxidizing agent is sodium hypochlorite.

7. The method of claim 3, wherein the sulfite-containing solution is a sulfite solution. The catalyst is sodium nitroprusside.

8. Application of the method for detecting the ammonia content in the solution containing sulfite according to any one of claims 1-7 to photocatalytic synthesis of ammonia.

Images