Back titration detection method for chloride ion content in anti-freezing solution

Abstract

The invention relates to a back titration detection method for the content of chloride ions in an anti-freezing solution, which comprises the following steps: pre-treating the anti-freezing solution, then obtaining the dosage of each solution by using a back titration method, and calculating to obtain the content of chloride ions in the anti-freezing solution. According to the method, the content of the chloride ions in the anti-freezing solution can be accurately obtained through manual operation under the condition that equipment such as a point titrator is not used, and the error is small. The invention belongs to the field of chemical analysis.

Description

Technical Field

[0001] The invention relates to a method for detecting the chloride ion content in an antifreeze solution, in particular to a back titration detection method for the chloride ion content in an antifreeze solution. Background Art

[0002] Engine antifreeze is a coolant with antifreeze function, which is mainly used to protect the normal operation of the engine. The antifreeze circulates in the engine water tank to play the role of antifreeze, antirust, and anticorrosion. The chlorine content is an important indicator to detect whether the engine antifreeze is healthy. Chloride ions are a strong oxidant. If there are a large number of chloride ions, they will corrode the metal parts inside the engine, thus causing engine damage.

[0003] At present, there are many common detection methods, such as spectrophotometry, fluorescence detection, ion chromatography, spectroscopy and electrochemical detection, as well as visual turbidimetry. Among them, the silver nitrate standard solution determination method used in the Petrochemical Ministry Standard SH / T 0621-1995 "Determination of Chlorine Content in Engine Coolant" determines the chloride ion content in antifreeze, converts the chlorine content by the potential value and the corresponding titration volume, and requires a potentiometric titrator for titration, and the determination process is complicated and cumbersome. In addition, the above-mentioned other methods either require equipment support and high cost; or the operation is cumbersome and there are many interference factors; the titration results are inaccurate. Summary of the invention

[0004] The purpose of the present invention is to provide a back titration detection method for chloride ion content in antifreeze solution in view of the deficiencies in the prior art. The detection method is simple to operate, has accurate measurement results, does not require specific detection equipment, and has low cost.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] The back titration detection method of chloride ion content in antifreeze liquid comprises the following steps:

[0007] 1) Pre-treatment

[0008] Take a certain amount of antifreeze, add nitric acid solution to adjust the pH value to 2-5, add hydrogen peroxide solution, heat to boiling, and obtain the solution to be tested;

[0009] The volume ratio of hydrogen peroxide to antifreeze is 1:13-17, and the mass percentage concentration of hydrogen peroxide is 30%;

[0010] 2) Back titration

[0011] In step 1), AgNO3 solution is added to the solution to be tested, the volume ratio of AgNO3 solution to antifreeze solution is 1:4-6, the concentration of AgNO3 solution is 0.09-0.5 mol / L, ammonium ferric alum solution is added as an indicator, and the AgNO3 solution is back-titrated with potassium thiocyanate solution, the concentration of potassium thiocyanate solution is 0.09-0.5 mol / L;

[0012] 3) Calculation

[0013] According to the mass of antifreeze used in step 1) and the amount of AgNO3 and potassium thiocyanate used in step 2), calculate the chloride ion content in the antifreeze:

[0014]

[0015] In the formula,

[0016] Cl - ——Chloride ion content in antifreeze, in milligrams per kilogram (mg / Kg);

[0017] C (AgNO3) ——The concentration of AgNO3 solution, in moles per liter (mol / L);

[0018] C (KSCN) ——The concentration of KSCN solution, in moles per liter (mol / L);

[0019] V (AgNO3) ——The volume of AgNO3 solution, in milliliters (mL);

[0020] V (KSCN) ——The volume of KSCN solution, in milliliters (mL);

[0021] m——the mass of antifreeze, in grams (g);

[0022] 35.453——Chloride ion (Cl - ) is the molar mass of a substance in grams per mole (g / mol).

[0023] Preferably, the boiling time of step 1) is 2 to 3 minutes.

[0024] Preferably, the concentration of the AgNO3 solution in step 2) is 0.095-0.105 mol / L.

[0025] Preferably, the concentration of the potassium thiocyanate solution in step 2) is 0.09 to 0.115 mol / L 。

[0026] Preferably, the adding of the ammonium ferric alum solution is 1 to 2 drops.

[0027] The present invention has the following advantages over the prior art:

[0028] The detection method of the present invention adopts manual titration to measure the chloride ion content in the antifreeze solution, does not require special detection equipment, and thus has low cost;

[0029] The detection method of the present invention only needs to weigh the mass of the antifreeze solution and the volume of each solution to measure the chloride ion content in the antifreeze solution, so the operation is simple;

[0030] The detection method of the present invention adds an excess of hydrogen peroxide solution in the pretreatment to oxidize the mercaptobenzothiazolidine in the antifreeze solution to generate sulfonate, thereby reducing interference factors in the antifreeze solution and making the titration result more accurate.

[0031] Applicant's experimental verification:

[0032] Generally, the relative standard deviation is no more than 2%, which indicates that the measurement result is accurate and reliable. The detection method of the present invention has been verified by experiments, and the relative standard deviation analysis result is 0.28% to 0.81%, which indicates that the measurement result of the detection method of the present invention is accurate and reliable. DETAILED DESCRIPTION

[0033] The present invention is further described below, but the present invention is not limited to the described embodiments.

[0034] Embodiment 1:

[0035] The back titration detection method of chloride ion content in antifreeze solution comprises the following steps:

[0036] 1) Pretreatment: 80.0072g of antifreeze solution was weighed with an electronic balance and added to a 250mL conical flask. 5mL of 6mol / L nitric acid solution was measured with a measuring cylinder and added to the conical flask. The mixture was shaken and the pH value of the solution was 3.9 measured with an acidometer. Under acidic conditions, silver ions and thiocyanate ions combine to form insoluble silver thiocyanate (AgSCN) precipitation. 5mL of 30% hydrogen peroxide solution was measured with a measuring cylinder and added to a conical flask to oxidize the mercaptobenzothiocyanate in the antifreeze solution to form sulfonate. The mixture was shaken and heated until the solution boiled for 3 minutes to remove excess hydrogen peroxide. The mixture was removed and cooled to obtain a test solution.

[0037] 2) Back titration: Use a pipette to transfer 15.00mL of 0.1005mol / L AgNO3 solution to the test solution, add 1-2 drops of saturated ammonium ferric alum solution, shake well, and then titrate the test solution with 0.1130mol / L potassium thiocyanate solution. When the solution turns brick red, stop titration and read the volume of potassium thiocyanate solution consumed, which is 12.44mL.

[0038] 3) Calculation:

[0039]

[0040] In the formula,

[0041] Cl - ——Chloride ion content in antifreeze, in milligrams per kilogram (mg / Kg);

[0042] C (AgNO3) ——The concentration of AgNO3 solution, in moles per liter (mol / L);

[0043] C (KSCN) ——The concentration of KSCN solution, in moles per liter (mol / L);

[0044] V (AgNO3) ——The volume of AgNO3 solution, in milliliters (mL);

[0045] V (KSCN) ——The volume of KSCN solution, in milliliters (mL);

[0046] m——the mass of antifreeze, in grams (g);

[0047] 35.453——Chloride ion (Cl - ) is the molar mass of a substance in grams per mole (g / mol).

[0048] According to the mass of the antifreeze solution used in step 1) and the volume and concentration of AgNO3 and potassium thiocyanate used in step 2), the chloride ion content is calculated to be 45.10 mg / Kg using Formula 1.

[0049] Embodiment 2:

[0050] Relative standard deviation test:

[0051] Weigh 0.0609g, 0.1044g, 0.1533g, 0.2548g, and 0.3855g of NaCl (standard reagent) and dissolve them in 5 1000mL volumetric flasks, dilute to 1000mL with water, and shake well. Calculate the Cl content in the solution according to formula 2 - Actual content (as Cl - mg / Kg) were: 36.95, 63.33, 93.00, 154.58, 233.87, 80±0.5g of each of the above 5 solutions were respectively transferred into 250mL conical flasks and numbered as 6#, 7#, 8#, 9#, 10# test solution;

[0052] Cl in solution - Actual content:

[0053] Cl- =35.453×m×1000 / 58.44 (Formula 2);

[0054] Cl - ——The content of chloride ions in the solution after dilution with NaCl reagent, in milligrams per kilogram (mg / Kg); 35.453——Chloride ions (Cl - ) is the molar mass of a substance in grams per mole (g / mol);

[0055] 58.44 – the molar mass of NaCl in grams per mole (g / mol);

[0056] m – the mass of NaCl weighed, in grams (g).

[0057] The five test solutions were tested according to the steps in Example 1, and calculated according to the calculation formula 1 in Example 1. Five parallel samples were measured for each test solution to obtain the Cl in Table 1. - The arithmetic mean, sample standard deviation and relative standard deviation of the measurement results are calculated according to Formula 3, Formula 4 and Formula 5;

[0058] Arithmetic mean:

[0059]

[0060] In the formula,

[0061] ——The average value of the five parallel samples of the same number, in milligrams per kilogram (mg / Kg);

[0062] n——the number of parallel samples of this number;

[0063] x i ——The ith data of the parallel sample with the same number;

[0064] Sample standard deviation:

[0065]

[0066] In the formula,

[0067] s——standard deviation of the sample of this number, in milligrams per kilogram (mg / Kg);

[0068] n——the number of parallel samples of this number;

[0069] x i ——The ith data of the parallel sample with the same number;

[0070] ——The average value of 5 parallel samples of the same number;

[0071] Relative standard deviation:

[0072]

[0073] In the formula,

[0074] RSD——Relative standard deviation of the number, in %;

[0075] ——The average value of the five parallel samples of the same number, in milligrams per kilogram (mg / Kg);

[0076] s——Standard deviation of the sample of this number, in milligrams per kilogram (mg / Kg).

[0077] The arithmetic mean, sample standard deviation and relative standard deviation of each sample in Table 1 were obtained. The results are shown in Table 1;

[0078] Table 1 Relative standard deviation analysis results

[0079]

[0080] It can be seen from Table 1 that the relative standard deviation analysis result of the back titration detection method for chloride ion content in the antifreeze solution of the present invention is 0.28% to 0.81%, and the relative standard deviation is not greater than 2%, indicating that the determination result of the detection method of the present invention is accurate and reliable.

Claims

1. A back titration detection method for chloride ion content in antifreeze solution, characterized in that: The detection method comprises the following steps: 1) Pre-treatment Take a certain amount of antifreeze, add nitric acid solution to adjust the pH value to 2-5, add hydrogen peroxide solution, heat to boiling, and obtain the solution to be tested; The volume ratio of hydrogen peroxide to antifreeze is 1:13-17, and the mass percentage concentration of hydrogen peroxide is 30%; 2) Back titration In step 1), AgNO3 solution is added to the solution to be tested, the volume ratio of AgNO3 solution to antifreeze solution is 1:4-6, the concentration of AgNO3 solution is 0.09-0.5 mol / L, ammonium ferric alum solution is added as an indicator, and the AgNO3 solution is back-titrated with potassium thiocyanate solution, the concentration of potassium thiocyanate solution is 0.09-0.5 mol / L; 3) Calculation According to the mass of antifreeze used in step 1) and the amount of AgNO3 and potassium thiocyanate used in step 2), calculate the chloride ion content in the antifreeze: In the formula, Cl - ——Chloride ion content in antifreeze, in milligrams per kilogram (mg / Kg); C (AgNO3) ——The concentration of AgNO3 solution, in moles per liter (mol / L); C (KSCN) ——The concentration of KSCN solution, in moles per liter (mol / L); V (AgNO3) ——The volume of AgNO3 solution, in milliliters (mL); V (KSCN) ——The volume of KSCN solution, in milliliters (mL); m——the mass of antifreeze, in grams (g); 35.453——Chloride ion (Cl - ) is the molar mass of a substance in grams per mole (g / mol).

2. The detection method according to claim 1, characterized in that: The boiling time of step 1) is 2 to 3 minutes.

3. The detection method according to claim 1, characterized in that: Step 2) The concentration of the AgNO3 solution is 0.095-0.105 mol / L.

4. The detection method according to claim 1, characterized in that: Step 2) The concentration of the potassium thiocyanate solution is 0.09 to 0.115 mol / L.

5. The detection method according to claim 1, characterized in that: In step 2), the adding of ammonium ferric alum solution is 1 to 2 drops.

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