Analysis method for cooperatively controlling total iron content in ferrous oxalate based on oxidation masking method

Abstract

According to the analysis method for cooperatively controlling the total iron content in the ferrous oxalate based on the oxidation masking method, the accuracy and repeatability of iron content determination are ensured through multi-step cooperative control, and the analysis method is suitable for industrial quality inspection and scientific research analysis. According to the method, an ammonium persulfate-mixed acid system is adopted, Fe is completely oxidized into Fe under the heating condition, errors caused by incomplete oxidation of Fe are eliminated, a nitrilotriacetic acid masking agent is added, free Fe in a sample is complexed, and hydrolytic precipitation of Fe is prevented. And carrying out potentiometric titration by adopting an EDTA standard solution until a potential jump point appears, so as to eliminate human judgment errors. The method can be applied to the fields of lithium battery positive electrode materials, mineral analysis, environment monitoring and the like, and is particularly suitable for accurate detection of a Fe / Fe coexistence system.

Description

Technical Field

[0001] The present invention belongs to the field of chemical analysis technology, and specifically relates to a method for realizing the total iron (Fe) in ferrous oxalate (FeC2O4) by combining oxidation masking with complexometric titration synergistic control strategy. 2+ with Fe 3+ It is a precise determination method for the total amount of PEG, suitable for quality control in the fields of battery materials, pharmaceutical intermediates, etc. Background Art

[0002] Ferrous oxalate is a key precursor of functional materials, and its accurate analysis of composition is the core link of product quality control. Traditional titration methods (such as potassium permanganate method) often have the following problems when determining ferrous oxalate: First, the Fe content in ferrous oxalate is 2+ Easily oxidized to Fe 3+ , only Fe 2+ , ignoring Fe 3+ content, which will lead to a low total iron result; secondly, oxalate and Fe 2+ When they coexist, they interfere with the color development reaction or the determination of the redox endpoint. Thirdly, conventional masking agents (such as sodium fluoride) lack selectivity for multivalent iron and the operation steps are cumbersome. In addition, existing detection methods lack oxidative stability, anti-interference ability, and ease of operation. There is an urgent need to develop an analytical method that is highly selective, rapid, and environmentally friendly. A new detection strategy based on the combination of oxidation-masking-complexometric titration is expected to significantly improve the accuracy and repeatability of total iron analysis, providing reliable technical support for the industrial application of ferrous oxalate and related materials. Summary of the Invention In view of the above, the present invention provides a method for quantitatively detecting total iron in ferrous oxalate, comprising the following steps: S1: Weigh a certain amount of ferrous oxalate, add ammonium persulfate to the sulfuric acid-phosphoric acid medium, and heat to boil to make Fe 2+ Completely oxidized to Fe 3+ , cooled to room temperature; S2: Add nitrilotriacetic acid masking agent to complex the free Fe in the sample 3+ , to prevent Fe 3+ Hydrolysis occurs; S3: Adjust the test solution to an acidic environment with a pH of 1.5-2.5, heat at 50-60℃ to promote the reaction, and titrate Fe with EDTA standard solution using potentiometric titration. 3+ The endpoint is titration until the potential jump point appears.

[0003] S4: Calculate the total iron content in ferrous oxalate according to the following formula:

[0004] Wherein, C1 is the molar concentration of EDTA standard solution; V1 is the volume of EDTA standard solution consumed; M=55.845g / moL is the molar mass of iron; and m is the mass of ferrous oxalate.

[0005] The purity of the ferrous oxalate described in step S1 is not less than 98%, wherein the iron content is 28-33%.

[0006] The volume fraction of sulfuric acid-phosphoric acid mixed acid (volume ratio of sulfuric acid-phosphoric acid is 1:2-3) mentioned in step S1 is 20-30%, and the amount added is 10-20 mL. The amount of ammonium persulfate solid added is 3-5 times the mass of the sample, the purpose of which is to remove Fe 2+ Completely oxidized to Fe 3+ , eliminating Fe in the subsequent titration process 2+ Errors caused by spontaneous oxidation.

[0007] The heating and boiling oxidation pretreatment in step S1 is performed at a temperature of 100-120°C for 10-15 minutes. Sufficient boiling time allows for the complete decomposition of excess ammonium persulfate, eliminating test errors caused by oxidation of EDTA or other reagents in subsequent steps.

[0008] Step S2 mentions the nitrilotriacetic acid masking agent, the concentration of which is generally in the range of 0.1 to 0.5 mol / L. The volume added is 10 to 20 mL to complex Fe 3+ And inhibit its hydrolysis and precipitation.

[0009] In step S3, the acidic environment is adjusted to a pH of 1.5 to 2.5 using hydrochloric acid, and a precision pH meter is used for accurate adjustment.

[0010] The concentration of the EDTA standard titration solution in step S3 is 0.02-0.1 mol / L, and its preparation method refers to the national standard GB / T601-2002 "Preparation of Standard Titration Solutions for Chemical Reagents".

[0011] The present invention provides an analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method, which has the following beneficial effects: the present invention solves the problem of Fe 2+ / Fe 3+ To solve the problem of coexistence and oxalate interference, phosphoric acid was used to replace the traditional hydrochloric acid medium to reduce Cl - Interference and toxic gas release, the use of potentiometric titration, eliminates human error judgment, improves detection sensitivity, and shortens the operation cycle. DETAILED DESCRIPTION

[0012] The following detailed description of the embodiments of the present invention provides a clear and complete description of the oxidation masking method provided by the present invention. However, the scope of protection of the present invention is not limited to the following specific embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0013] Example 1 An analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method specifically comprises the following steps: Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Boil at 110°C for 12 minutes and cool to room temperature.

[0014] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution in sequence and shake thoroughly. Adjust the pH of the solution to 2.0 with hydrochloric acid while monitoring with a precision pH meter and heat in a 60°C water bath for 15 minutes. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Stop the titration when the potential jump point appears on the potentiometric titrator. Finally, calculate Fe according to the formula 3+ The results of the content.

[0015] Example 2 An analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method specifically comprises the following steps: Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 10mL of a 30% (volume fraction) sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.6g of (NH4)2S2O8 (3 times the mass of the ferrous oxalate). Heat to a boil at 100°C for 10 minutes, then cool to room temperature.

[0016] Step S2: Add 10 mL of nitrilotriacetic acid masking agent to the above test solution and shake well. Adjust the pH of the solution to 1.5 with hydrochloric acid while monitoring with a precision pH meter. Heat in a 60°C water bath for 15 minutes. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Stop the titration when the potential jump point appears on the potentiometric titrator. Finally, calculate Fe according to the formula 3+ The results of the content.

[0017] Example 3 An analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method specifically comprises the following steps: Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 20mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 1.0g of (NH4)2S2O8 (5 times the mass of the ferrous oxalate). Boil the mixture at 120°C for 15 minutes and cool to room temperature.

[0018] Step S2: Add 20 mL of nitrilotriacetic acid masking agent to the above test solution and stir thoroughly for 5 minutes. Adjust the pH of the solution to 2.5 with hydrochloric acid while monitoring with a precision pH meter. Heat in a 60°C water bath for 15 minutes. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Stop the titration when the potential jump point appears on the potentiometric titrator. Finally, calculate Fe according to the formula 3+ The results of the content.

[0019] Example 4 An analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method specifically comprises the following steps: Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Boil the mixture at 110°C for 12 minutes and cool to room temperature.

[0020] Step S2: Add 20 mL of nitrilotriacetic acid masking agent to the above test solution in sequence and shake thoroughly. Adjust the pH of the solution to 1.8 with hydrochloric acid while monitoring with a precision pH meter and heat in a 60°C water bath for 15 minutes. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Stop the titration when the potential jump point appears on the potentiometric titrator. Finally, calculate Fe according to the formula 3+ The results of the content.

[0021] Comparative Example 1 The method and conditions were the same as in Example 1, except that ammonium persulfate was not added and titration was performed directly under masking.

[0022] Step S1: Accurately weigh 0.2000 g of ferrous oxalate (FeC2O4·2H2O) and add 15 mL of a 30% (volume fraction) sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Boil the mixture at 110°C for 12 minutes and then cool to room temperature.

[0023] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution in sequence and stir thoroughly for 5 minutes. Adjust the pH of the solution to 2.0 with hydrochloric acid while monitoring with a precision pH meter and heat in a 60°C water bath for 15 minutes. Potentiometric titration was performed using a 0.05 mol / L EDTA standard solution. The titration endpoint was unclear and the potential jump was not obvious. Fe 3+ The content of the measured value is low. The reason for the low result is free Fe 3+ Premature complexation with EDTA interferes with the determination of the endpoint.

[0024] Comparative Example 2 The method and conditions were the same as in Example 1, but the pH was adjusted to 3.5 (outside the range of 1.5-2.5).

[0025] Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Boil the mixture at 110°C for 12 minutes and cool to room temperature.

[0026] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution and shake well. Adjust the pH of the solution to 3.5 with hydrochloric acid and monitor with a precision pH meter. Heat in a 60°C water bath for 15 minutes until the solution becomes turbid. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Delay the titration endpoint. 3+ Incomplete complexation, Fe 3+ The content determination value is low. Because Fe 3+ It is easy to hydrolyze to form precipitates, reducing the reaction efficiency.

[0027] Comparative Example 3 The method and conditions were the same as in Example 1, except that the amount of ammonium persulfate added was 0.3 g (1.5 times the mass).

[0028] Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.3g of (NH4)2S2O8 (1.5 times the mass of the ferrous oxalate). Heat to a boil at 110°C for 12 minutes, then cool to room temperature.

[0029] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution and shake well. Adjust the pH of the solution to 2.0 with hydrochloric acid and monitor it with a precision pH meter. Heat in a 60°C water bath for 15 minutes. Use 0.05 mol / L EDTA standard solution for potentiometric titration. Stop titration when the potential jump point appears on the potentiometric titrator. The measurement result is abnormally high. 2+ Incomplete oxidation, residual Fe 2+ Reacts with EDTA, causing false positive interference.

[0030] Comparative Example 4 The method and conditions were the same as in Example 1, except that the boiling time was adjusted to 5 min.

[0031] Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Boil the mixture at 110°C for 5 minutes and cool to room temperature.

[0032] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution and shake thoroughly. Adjust the pH of the solution to 2.0 with hydrochloric acid while monitoring with a precision pH meter. Heat in a 60°C water bath for 15 minutes. Potentiometric titration using a 0.05 mol / L EDTA standard solution yielded a low value. Due to insufficient oxidation time, the ferrous iron was not completely oxidized to ferric iron.

[0033] Comparative Example 5 The method and conditions are the same as in Example 1, except that the heating temperature is 80°C.

[0034] Step S1: Accurately weigh 0.2000 g of ferrous oxalate (FeC2O4·2H2O) and add 15 mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8 g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Heat to a boil at 80°C for 12 minutes, then cool to room temperature.

[0035] Step S2: Add 15 mL of nitrilotriacetic acid masking agent to the above test solution and shake thoroughly. Adjust the pH of the solution to 2.0 with hydrochloric acid while monitoring with a precision pH meter. Heat in a 60°C water bath for 15 minutes. Potentiometric titration using a 0.05 mol / L EDTA standard solution reveals a low value. The low-temperature oxidation reaction kinetics are insufficient.

[0036] Comparative Example 6 The method and conditions were the same as in Example 1, except that the nitrilotriacetic acid masking agent was not added.

[0037] Step S1: Accurately weigh 0.2000g of ferrous oxalate (FeC2O4·2H2O) and add 15mL of a 30% volume fraction sulfuric acid-phosphoric acid mixture (volume ratio of sulfuric acid to phosphoric acid is 1:2). Add 0.8g of (NH4)2S2O8 (4 times the mass of the ferrous oxalate). Heat to a boil at 110°C for 12 minutes, then cool to room temperature.

[0038] Step S2: Adjust the solution pH to 2.0 with hydrochloric acid while monitoring with a precision pH meter. Heat in a 60°C water bath for 15 minutes. The solution becomes turbid. Potentiometric titration using a 0.05 mol / L EDTA standard solution reveals a low endpoint potential with a minimal change. Omission of sulfosalicylic acid results in oxalate interference with endpoint determination.

[0039] Comparative Example 7 The total iron content in ferrous oxalate was determined using the traditional potassium dichromate method.

[0040] The same batch of samples was tested according to the GB / T223.7-2002 method. This method requires complex treatments such as zinc powder reduction and the use of sodium diphenylamine sulfonate as an indicator. This method takes longer to perform a single test, and the presence of oxalate can lead to higher results.

[0041] Table 1 Test values, theoretical values and deviations of total iron content of Examples 1-4 and Comparative Examples 1-7

[0042] As shown in Table 1, Example 1 is by the steps such as optimization, masking, pH control, and result is completely consistent with standard value.Example 2-4 proves that method is effective within the patent parameter range, verifies the reliability of method.Comparative Example 1-6 results show that: ammonium persulfate dosage, heating temperature, boiling time, masking agent and pH range are key parameters, and any one deviation all causes result significant deviation.Comparative Example 7 adopts traditional potassium dichromate method to carry out the mensuration of total iron content in ferrous oxalate, and oxalate radical also can react with potassium dichromate, causes titrant consumption to increase, and result is higher.In summary, the detection method of total iron content in ferrous oxalate of the present invention can significantly improve the accuracy of iron content test, while avoiding human error.

[0043] As described above, the above embodiments are only for illustrating the technical concept and features of the present invention, and those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and purpose of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. An analytical method for collaboratively controlling the total iron content in ferrous oxalate based on an oxidation masking method, characterized in that: The following steps are involved: S1: Weigh a certain amount of ferrous oxalate, add ammonium persulfate to the sulfuric acid-phosphoric acid medium, and heat to boil to make Fe 2+ Completely oxidized to Fe 3+ , cooled to room temperature; S2: Add masking agent to complex the free Fe in the sample 3+ , to prevent Fe 3+ Hydrolysis occurs; S3: Adjust the test solution to an acidic environment, heat to promote the reaction, and titrate Fe with EDTA standard solution using potentiometric titration. 3 + , titrate until the potential jump point appears, which is the end point; S4: Calculate the total iron content in ferrous oxalate according to the following formula: Wherein, C1 is the molar concentration of EDTA standard solution; V1 is the volume of EDTA standard solution consumed; M=55.845g / moL is the molar mass of iron; and m is the mass of ferrous oxalate.

2. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The purity of the ferrous oxalate described in step S1 is greater than 98%, wherein the iron content is 28-33%.

3. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The volume fraction of sulfuric acid-phosphoric acid mixed acid is 25-30%, the addition amount is 10-20 mL, and the addition amount of ammonium persulfate solid is 0.5-1.0 times the mass of the sample.

4. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The heating and boiling for oxidation pretreatment in step S1 is performed at a temperature of 100-120° C. and a boiling time of 10-15 minutes.

5. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The masking agent in step S2 is nitrilotriacetic acid, and its concentration range is 0.1-0.5 mol / L.

6. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The concentration range of the preparation described in step S2 is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L.

7. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: In step S4, the acidic environment is adjusted to a pH of 1.5 to 2.5 using hydrochloric acid.

8. The method for analyzing the total iron content in ferrous oxalate based on the oxidation masking method according to claim 1, wherein: The concentration of the EDTA standard solution in step S4 is 0.02-0.1 mol / L.

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