Pretreatment method of iodine-containing substance and determination method of iodine content in iodine-containing substance
The method of thermal combustion and pH-adjusted reduction in a sealed environment effectively converts iodine into iodide ions for accurate quantification, addressing low recovery and detection challenges in existing iodine measurement techniques.
Patent Information
- Application Number
- CN202510469446.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-15
- Publication Date
- 2025-07-15
AI Technical Summary
Existing methods for determining iodine content in substances face challenges such as low recovery rates, incomplete combustion of samples, and difficulty in detecting iodate due to its presence in organic forms, especially for samples with low thermal values.
A method involving thermal combustion of iodine-containing substances in a sealed environment followed by pH adjustment and reduction to convert iodine into iodide ions, using a basic solution and a reducing agent, and subsequent iodide quantification by automatic potentiometric titration.
Achieves high iodine recovery rates and accurate quantification with a relative deviation of less than 0.8% for different sample weights, overcoming the limitations of previous methods.
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Figure CN120314028A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of chemical analysis, and particularly relates to a pretreatment method for iodine-containing substances and a method for determining the iodine content in iodine-containing substances. Background Art
[0002] Iodine has multiple valence states in nature and exists in organic and inorganic forms, so it cannot be directly determined. Currently, the determination of iodine content is divided into two steps. First is the pretreatment, the purpose of which is to convert organic iodine into inorganic iodine, and then the iodine content in the substance is determined by detecting the inorganic iodine.
[0003] Currently, the main pretreatment methods are as follows:
[0004] (1) Oxygen bomb combustion: That is, oxygen is filled into the bomb, and then the sample is ignited by a ignition wire. The inorganic iodine obtained by combustion is absorbed by placing an absorbent solution in the bomb. The disadvantages of this method are: 1) When the bomb is opened to release gas later, the gaseous target substance is likely to escape, resulting in a low recovery rate; 2) The sample weighing amount in this method generally requires to be between 0.2 g and 0.5 g, otherwise it is easy to have incomplete combustion, and for some samples that are not easy to burn, it is also likely to cause a low recovery rate; 3) Part of the iodine in the absorbent solution exists in the form of iodate, which increases the difficulty of subsequent inorganic iodine determination; 4) It is not suitable for samples with low calorific value and not easy to burn.
[0005] (2) High-temperature alkali fusion: That is, the sample is added to a crucible and covered with sodium hydroxide flakes, and then melted at a high temperature in a muffle furnace. This method is suitable for high-boiling substances. For low-boiling substances such as organic solvents, since the heating process is not a sealed system, iodine is likely to sublime, resulting in a low recovery rate.
[0006] (3) Sodium hydroxide-zinc powder reflux: That is, the sample is added to a flask, and then sodium hydroxide and zinc powder are added, and then heated for condensation reflux. This method has cumbersome operations and a long reflux time. It relies on alkali to hydrolyze iodine in the organic matter, and at the same time reduces the high-valence iodine through zinc powder. However, because the hydrolysis reaction is an equilibrium reaction, the final iodine conversion rate is limited. Summary of the Invention
[0007] The purpose of the present invention is to provide a pretreatment method for iodine-containing substances and a method for determining the iodine content in iodine-containing substances. The pretreatment method provided by the present invention can fully convert the organic iodine in the iodine-containing substance into iodide ions, and the conversion recovery rate of iodine is high.
[0008] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:
[0009] The present invention provides a pretreatment method for iodine-containing substances, including the following steps:
[0010] (1) Thermally combust the iodine-containing substance and oxygen in a closed environment, and introduce all the resulting gas into an absorption solution for absorption to obtain an initial test solution to be measured; the temperature of the thermal combustion is 800°C to 950°C;
[0011] (2) Adjust the pH value of the initial test solution obtained in step (1) to <7, and then add a reducing agent for a reduction reaction to obtain a test solution.
[0012] Preferably, the time of thermal combustion in step (1) is 5 min to 15 min.
[0013] Preferably, the absorption solution in step (1) is an alkaline solution.
[0014] Preferably, the concentration of the alkaline substance in the absorption solution in step (1) is 0.1 mol / L to 0.5 mol / L.
[0015] Preferably, the reducing agent in step (2) is a sulfite or a thiosulfate.
[0016] Preferably, the reducing agent in step (2) is added in the form of an aqueous solution of the reducing agent, and the mass concentration of the aqueous solution of the reducing agent is 5% to 15%.
[0017] Preferably, oxygen is continuously introduced during the thermal combustion process in step (1), and the flow rate of the oxygen is 100 mL / min to 200 mL / min.
[0018] Preferably, a sulfuric acid solution is used to adjust the pH value of the initial test solution in step (2).
[0019] The present invention also provides a method for determining the iodine content in an iodine-containing substance, including: pretreating the iodine-containing substance using the pretreatment method described in the above technical solution to obtain a test solution; performing automatic potentiometric titration on the test solution to obtain the iodine content in the test solution, and calculating the iodine content in the iodine-containing substance; the titration solution used in the automatic potentiometric titration is a silver nitrate standard solution.
[0020] Preferably, the concentration of the silver nitrate standard solution is 0.01 mol / L to 0.1 mol / L.
[0021] The present invention provides a pretreatment method for iodine-containing substances, comprising the following steps: (1) thermally burning the iodine-containing substance and oxygen in a closed environment, and passing all the obtained gases into an absorption liquid for absorption to obtain an initial test liquid; the temperature of the thermal combustion is 800°C to 950°C; (2) adjusting the pH value of the initial test liquid obtained in step (1) to less than 7, and then adding a reducing agent for reduction reaction to obtain the test liquid. The present invention thermally burns the iodine-containing substance in a closed environment, which can force the iodine in the sample to be converted into iodine element, thereby avoiding the low iodine conversion rate caused by the non-flammable sample; the iodine recovery rate can be improved by passing the gas generated by the combustion into the absorption liquid, and fully contacting and absorbing the absorption liquid in a foaming manner; the oxidizing property of iodate under acidic conditions is utilized to react with the reducing agent to generate iodide ions, thereby avoiding the problem that iodate is difficult to detect.
[0022] The method for determining the iodine content in the iodine-containing substance provided by the present invention uses an automatic potentiometric titration method, and can use standard solutions of different concentrations for titration according to the iodine content, thereby meeting the detection needs of different iodine contents. The results of the embodiment show that the determination method provided by the present invention can accurately detect the iodine content in naphthalene iodine and potassium iodide, with an accuracy of 98.7%; the relative deviation of the same sample after multiple determinations is less than 0.8%. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 This is a schematic diagram of the device structure used in Example 1 of the present invention. DETAILED DESCRIPTION
[0024] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.
[0025] The present invention provides a method for pre-treating an iodine-containing substance, comprising the following steps:
[0026] (1) thermally burning an iodine-containing substance and oxygen in a closed environment, and passing all the resulting gas into an absorption liquid for absorption to obtain an initial test liquid; the temperature of the thermal combustion is 800° C. to 950° C.;
[0027] (2) adjusting the pH value of the initial test solution obtained in step (1) to less than 7, and then adding a reducing agent to carry out a reduction reaction to obtain the test solution.
[0028] The invention thermally burns the iodine-containing substance and oxygen in a closed environment.
[0029] The present invention has no particular requirements on the type of the iodine-containing substance, and any type of iodine-containing substance can be subjected to the pretreatment method of the present invention. In an embodiment of the present invention, the iodine-containing substance is naphthalene iodine, potassium iodide or iodine-containing solid waste.
[0030] The present invention has no special requirements for the sample amount of the iodine-containing substance, and the sample amount can be adjusted according to the detection needs. As an embodiment of the present invention, a sufficient amount of sample can be added at one time; for samples with low iodine content, multiple injections can be performed for thermal combustion, while the absorption liquid remains unchanged, to achieve accurate detection of low-concentration samples.
[0031] In the present invention, the temperature of the thermal combustion is 800° C. to 950° C., preferably 850° C. to 900° C.; as an embodiment of the present invention, the temperature of the thermal combustion may be 810° C., 830° C., 840° C., 860° C., 880° C., 910° C., 920° C., 930° C. or 940° C. When the temperature of the thermal combustion is within the above range, the iodine in the iodine-containing substance can be forcibly converted into elemental iodine, thereby avoiding the low iodine conversion rate caused by the sample being difficult to burn.
[0032] In the present invention, the thermal combustion time is preferably 5 min to 15 min, more preferably 8 min to 12 min; as an embodiment of the present invention, the thermal combustion time can be 6 min, 7 min, 9 min, 10 min, 11 min, 13 min or 14 min. The thermal combustion time within the above range is conducive to the full combustion of the sample and further improves the recovery rate of iodine.
[0033] The present invention has no special requirements for the closed environment, as long as the gas generated by combustion does not escape. As an embodiment of the present invention, the thermal combustion can be carried out in a tubular combustion furnace, and the sample is sent into the tubular combustion furnace through a quartz boat.
[0034] In the present invention, oxygen is preferably continuously introduced during the thermal combustion process. By continuously introducing oxygen into a closed environment, the present invention can ensure that the iodine-containing substance is fully burned under thermal conditions, and can also be used as a carrier gas for combustion gas, which is conducive to the full contact and absorption of combustion gas with the absorption liquid, and further improves the recovery rate of iodine.
[0035] In the present invention, the flow rate of the oxygen is preferably 100mL / min to 200mL / min, more preferably 130mL / min to 170mL / min; as an embodiment of the present invention, the flow rate of the oxygen can be 110mL / min, 120mL / min, 140mL / min, 150mL / min, 160mL / min, 180mL / min or 190mL / min. The flow rate of oxygen within the above range is conducive to controlling the combustion temperature and further improving the recovery rate of iodine.
[0036] In the present invention, all gases obtained from thermal combustion are introduced into an absorption liquid for absorption to obtain an initial liquid to be tested.
[0037] In the present invention, the absorption liquid is preferably an alkaline solution. The present invention has no particular requirements for the specific type of the alkaline solution, as long as it can quickly absorb iodine. As an embodiment of the present invention, the alkaline solution can be a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution. The alkaline solution can react quickly with the iodine element, which is beneficial to the absorption of iodine and further improves the recovery rate of iodine.
[0038] In the present invention, the concentration of the alkaline substance in the absorption liquid is preferably 0.1mol / L to 0.5mol / L, more preferably 0.2mol / L to 0.4mol / L; as an embodiment of the present invention, the concentration of the alkaline substance in the absorption liquid can be 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L or 0.5mol / L. The concentration of the alkaline substance in the absorption liquid within the above range is conducive to the rapid absorption of iodine and further improves the recovery rate of iodine.
[0039] As an embodiment of the present invention, the gas obtained from thermal combustion can be introduced into a single foaming absorption tube through a connecting device for absorption, or a foaming absorption tube can be connected in series behind the tubular combustion furnace to directly introduce the combustion gas into the foaming absorption tube for absorption; all pipelines are connected by glass to reduce iodine adsorption losses.
[0040] After obtaining the initial test solution, the present invention adjusts the pH value of the initial test solution to less than 7, and then adds a reducing agent to perform a reduction reaction to obtain the test solution.
[0041] In the present invention, it is preferred to use a sulfuric acid solution to adjust the pH value of the initial test solution. The present invention has no particular requirements for the concentration of the sulfuric acid solution, and the conventional sulfuric acid solution concentration in the art can be used. In an embodiment of the present invention, the concentration of the sulfuric acid solution is 10% by mass. Iodate has oxidizing properties under acidic conditions and can react with a reducing agent to generate iodide ions, thereby avoiding the problem that iodate ions are difficult to measure.
[0042] In the present invention, the reducing agent is preferably sulfite or thiosulfate. As an embodiment of the present invention, the reducing agent can be sodium sulfite or sodium thiosulfate.
[0043] In the present invention, the reducing agent is preferably added in the form of a reducing agent aqueous solution, and the mass concentration of the reducing agent aqueous solution is preferably 5% to 15%, more preferably 8% to 12%; as an embodiment of the present invention, the mass concentration of the reducing agent aqueous solution can be 6%, 7%, 9%, 10%, 11%, 13% or 14%. The reducing agent is added in the form of an aqueous solution, and the concentration of the reducing agent aqueous solution is limited to the above range, which is conducive to the reaction of the reducing agent with iodate, and further improves the conversion rate of iodate.
[0044] The present invention performs thermal combustion on an iodine-containing substance in a closed environment, so that the iodine in the sample can be forcibly converted into elemental iodine, thereby avoiding a low iodine conversion rate caused by the non-flammability of the sample; the gas generated by the combustion is passed into an absorption liquid, and the gas is fully contacted and absorbed with the absorption liquid in a foaming manner, thereby avoiding the escape of iodine caused by the automatic contact and absorption of the generated gas with the absorption liquid, and thereby improving the iodine recovery rate; the oxidizing property of iodate radical under acidic conditions is utilized to react with a reducing agent to generate iodide ions, thereby avoiding the problem that iodate radical is difficult to detect.
[0045] The present invention also provides a method for determining the iodine content in an iodine-containing substance, comprising: pre-treating the iodine-containing substance using the pre-treatment method described in the above technical solution to obtain a test liquid; performing automatic potentiometric titration on the test liquid to obtain the iodine content in the test liquid, and calculating the iodine content in the iodine-containing substance; the titration solution used in the automatic potentiometric titration is a silver nitrate standard solution.
[0046] In the present invention, the concentration of the silver nitrate standard solution is preferably 0.01mol / L to 0.1mol / L, more preferably 0.03mol / L to 0.06mol / L; as an embodiment of the present invention, the concentration of the silver nitrate standard solution can be 0.02mol / L, 0.04mol / L, 0.05mol / L, 0.07mol / L, 0.08mol / L or 0.09mol / L. The concentration of the silver nitrate standard solution within the above range is conducive to the determination of different concentrations of the test solution, further improving the detection accuracy.
[0047] The present invention has no special requirements for the specific operation of the automatic potentiometric titration, and the conventional automatic potentiometric titration method in the art can be used.
[0048] The method for determining the iodine content in an iodine-containing substance provided by the present invention uses an automatic potentiometric titration method, and can use standard solutions of different concentrations for titration according to the iodine content, thereby meeting the detection needs of different iodine contents.
[0049] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0050] Example 1
[0051] A pretreatment method for iodine-containing substances, using the device as shown in Figure 1 The specific steps are as follows: Take an appropriate amount of sample and place it in a quartz boat, then push it into the combustion furnace. The central temperature of the combustion furnace is 800 °C, and oxygen is introduced into the combustion furnace at a flow rate of 160 mL / min. A foaming absorption tube is connected in series behind the combustion furnace. There is 30 mL of 0.2 mol / L sodium hydroxide solution in the absorption tube. After burning for 10 minutes, disconnect the connection between the combustion furnace and the absorption tube, transfer the solution in the absorption tube to a 100 mL beaker, and rinse the foaming absorption tube with 5 mL of water. Combine the cleaning solution into the beaker to obtain the initial test solution. Add 5 mL of 10% sulfuric acid solution to the initial test solution to adjust the solution to acidity, and then add 1 mL of 10% sodium sulfite solution to obtain the test solution.
[0052] The details of the samples are recorded in Table 1.
[0053] Example 2
[0054] A pretreatment method for iodine-containing substances, using the device of Example 1. The specific steps are as follows: Take an appropriate amount of sample and place it in a quartz boat, then push it into the combustion furnace. The central temperature of the combustion furnace is 950 °C, and oxygen is introduced into the combustion furnace at a flow rate of 120 mL / min. A foaming absorption tube is connected in series behind the combustion furnace. There is 30 mL of 0.2 mol / L sodium hydroxide solution in the absorption tube. After burning for 10 minutes, disconnect the connection between the combustion furnace and the absorption tube, transfer the solution in the absorption tube to a 100 mL beaker, and rinse the foaming absorption tube with 5 mL of water. Combine the cleaning solution into the beaker to obtain the initial test solution. Add 5 mL of 10% sulfuric acid solution to the initial test solution to adjust the solution to acidity, and then add 1 mL of 10% sodium sulfite solution to obtain the test solution.
[0055] The details of the samples are recorded in Table 1.
[0056] Application Examples 1-2
[0057] Use an automatic potentiometric titrator to titrate the test solutions obtained in Example 1 and Example 2. The titration solution is 0.02988 mol / L AgNO3 solution, and the iodine contents in the samples of Example 1 and Example 2 are obtained and recorded in Table 1.
[0058] Table 1 Record Table of Example Samples and Test Data
[0059] / Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Sample Name Naphthalene Iodine Potassium Iodide Solid Waste Sample 1# Solid Waste Sample 2# Solid Waste Sample 3# Solid Waste Sample 4# Sample Type High-Purity Reagent High-Purity Reagent Actual Sample Actual Sample Actual Sample Actual Sample Sample Quantity / g 0.04625 0.03578 0.5562 1.0114 1.5536 2.0059 Theoretical Iodine Content / % 49.9 76.4 / / / / Measured Iodine Content / % 49.3 75.4 1.25 1.27 1.26 1.26
[0060] As can be seen from the test results in Table 1, the pretreatment method of the iodine-containing substance provided by the present invention can efficiently extract iodine into the test solution, and the detection accuracy reaches 98.7%.
[0061] Examples 3 to 6
[0062] According to the pretreatment method of Example 1 and the determination method of the application example, the iodine content of a certain iodine-containing solid waste sample was determined. The solid waste sample was divided into 4 parts, and the sample conditions and test results were recorded in Table 1. As can be seen from the determination results in Table 1, the pretreatment method and determination method provided by the present invention can precisely detect samples of different weights, and the relative deviation is less than 0.8%.
[0063] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.
Claims
1. A pretreatment method for iodine-containing substances, comprising the following steps: (1) Thermally combust the iodine-containing substance and oxygen in a closed environment, and introduce all the obtained gas into an absorption liquid for absorption to obtain an initial test solution; the temperature of the thermal combustion is 800°C to 950°C; (2) Adjust the pH value of the initial test solution obtained in step (1) to <7, and then add a reducing agent for a reduction reaction to obtain a test solution.
2. The preprocessing method according to claim 1, characterized in that The time of thermal combustion in step (1) is 5 min to 15 min.
3. The preprocessing method according to claim 1, wherein The absorption liquid in step (1) is an alkaline solution.
4. The pre-treatment method according to claim 1 or 3, characterized in that The concentration of the alkaline substance in the absorption liquid in step (1) is 0.1 mol / L to 0.5 mol / L.
5. The pretreatment method according to claim 1, wherein The reducing agent in step (2) is a sulfite or a thiosulfate.
6. The pre-treatment method according to claim 1 or 5, characterized in that, The reducing agent in step (2) is added in the form of an aqueous solution of the reducing agent, and the mass concentration of the aqueous solution of the reducing agent is 5% to 15%.
7. The preprocessing method according to claim 1, characterized in that, During the thermal combustion process in step (1), oxygen is continuously introduced, and the flow rate of the oxygen is 100 mL / min to 200 mL / min.
8. The preprocessing method according to claim 1, wherein In step (2), a sulfuric acid solution is used to adjust the pH value of the initial test solution.
9. A method for determining the iodine content in an iodine-containing substance, characterized in that, Including: Pretreat the iodine-containing substance using the pretreatment method according to any one of claims 1 to 8 to obtain a test solution; Automatically potentiometric titrate the test solution to obtain the iodine content in the test solution, and calculate the iodine content in the iodine-containing substance; the titration solution used for the automatic potentiometric titration is a silver nitrate standard solution.
10. The detection method according to claim 9, wherein The concentration of the silver nitrate standard solution is 0.01 mol / L to 0.1 mol / L.