A method for accurately measuring the content of azobisisobutyronitrile in dimethyl sulfoxide solution

Abstract

This invention discloses a method for accurately measuring the content of azobisisobutyronitrile (AIBN) in dimethyl sulfoxide (DMSO) solution. The method includes the following steps: First, using DMSO as the solvent, prepare a series of standard solutions with AIBN mass concentrations ranging from 0 to 1.0%. Using the pure solvent as a blank reference, measure the absorbance of each standard solution at a characteristic wavelength of 350 nm using a UV-Vis spectrophotometer, ensuring the absorbance value is within the range of 0 to 1. Plot a standard curve with absorbance as the abscissa and concentration as the ordinate, and calculate the linear regression formula. When testing the test solution, use the same solvent as a blank reference and measure the absorbance at the same wavelength. If the absorbance is between 0 and 1, directly substitute it into the formula for calculation; if the absorbance is greater than 1, dilute with the solvent until the absorbance drops to the range of 0 to 1, multiply by the dilution factor, and calculate the original solution concentration. This invention is simple to operate, highly accurate, and repeatable, and is particularly suitable for the rapid detection of AIBN content in industrial production.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile dope polymerization technology, and in particular to a method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution, specifically used for detecting the amount of azobisisobutyronitrile initiator added to the polymerization solution when preparing polyacrylonitrile-based carbon fiber precursor. Background Technology

[0002] Azobisisobutyronitrile (AIBN) is a key initiator in the preparation of polyacrylonitrile (PAN)-based carbon fiber precursors. Its dosage directly affects the molecular weight and distribution of the polymer, thus determining the spinning performance of the precursor and the final mechanical strength of the carbon fiber. Insufficient initiator dosage leads to a slow reaction rate and excessively high molecular weight, potentially causing difficulties in precursor spinning; excessive dosage results in excessively low molecular weight, reducing precursor strength. Therefore, accurately detecting the AIBN content involved in the polymerization reaction is crucial for guiding production and controlling product quality.

[0003] Currently, there is a lack of a rapid and accurate method specifically for detecting AIBN content in dimethyl sulfoxide (DMSO) solvent systems. Existing technologies mostly employ gravimetric or chromatographic methods, which are cumbersome and time-consuming, making them unsuitable for the rapid detection needs of industrial production. While ultraviolet spectrophotometry has applications, a systematic, accurate, and applicable detection scheme for high-concentration samples in the DMSO-AIBN specific system has not yet been developed. Summary of the Invention

[0004] The present invention aims to provide an accurate, rapid, and easy-to-operate method for measuring the content of azobisisobutyronitrile in dimethyl sulfoxide solution, in order to overcome the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution includes the following steps:

[0007] 1. Establish a standard UV curve: Prepare a series of azobisisobutyronitrile (AIB) standard solutions of different known concentrations using dimethyl sulfoxide (DMSO) as the solvent; using the pure solvent as a blank reference, measure the absorbance of each standard solution at a characteristic wavelength of 350 nm using a UV-Vis spectrophotometer. Plot a standard curve with absorbance on the x-axis and concentration on the y-axis to obtain the standard linear formula.

[0008] 2. Concentration test of the test solution: Using the same solvent as the test solution as a blank reference, measure its absorbance at a characteristic wavelength of 350 nm. If the absorbance is within the instrument's optimal linear range (0~1), directly substitute it into the standard linear formula to calculate the concentration; if the absorbance is greater than 1, dilute it by volume with solvent so that the AIBN concentration of the diluted solution falls within the range of the standard curve, measure the absorbance of the diluted solution, substitute it into the standard linear formula, and then multiply it by the dilution factor to calculate the concentration of the original test solution.

[0009] Preferably, the mass concentration of azobisisobutyronitrile in the standard solution is in the range of 0~1.0%, within which the absorbance and concentration have a good linear relationship (R0). 2 ≥0.999).

[0010] Preferably, the characteristic wavelength of 350 nm is determined based on the following: after ultraviolet spectroscopy scanning, AIBN has a stable characteristic absorption peak at 350 nm in DMSO, and the solvent DMSO has no absorption interference at this wavelength, which conforms to the Lambert-Beer law.

[0011] Preferably, the formula for calculating the volume dilution factor is:

[0012] Stock solution concentration (%) = Dilution factor × Concentration of diluted solution (%)

[0013] Wherein, the dilution factor n = (V0 + V) / V0, where V0 is the sample volume of the solution to be tested, and V is the volume of the solvent used for dilution.

[0014] This invention achieves high-precision and high-repeatability detection of AIBN content in DMSO through a combination of technologies including "solvent blank reference + characteristic wavelength selection + linear range control + volume dilution correction", which is especially suitable for rapid analysis of high-concentration samples in industrial production.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] High accuracy: By strictly defining the characteristic wavelength (350nm) and linear range (0~1% concentration, absorbance 0~1), the measurement is ensured to strictly follow the Lambert-Beer law, the correlation coefficient of the standard curve can reach above 0.999, and the systematic error is small.

[0017] Excellent repeatability: The "dilution measurement" strategy for high-concentration samples eliminates the nonlinear response error of the instrument in the high absorbance range, resulting in excellent repeatability.

[0018] Quick, easy, and low-cost: No sample pretreatment or expensive instruments are required; a regular UV spectrophotometer can complete the test. The testing time for a single sample is usually within 5 minutes, making it ideal for the rapid quality control needs of industrial production lines.

[0019] Highly targeted: Specifically designed for the DMSO-AIBN system in PAN precursor production, it fills the technological gap for rapid and accurate detection of AIBN in this specific scenario. Attached Figure Description

[0020] Figure 1 This is a standard concentration-absorbance curve of dimethyl sulfoxide solutions of azobisisobutyronitrile at different concentrations at a wavelength of 350 nm, as shown in the embodiments of the present invention. The linear regression equation is y = 1.1348x, and the correlation coefficient R is [missing value]. 2 =0.9998. Detailed Implementation

[0021] The following is in conjunction with the appendix Figure 1 The specific implementation of the method for accurately measuring the content of azobisisobutyronitrile in dimethyl sulfoxide solution according to the present invention will be further described in detail.

[0022] Example 1: Establishment and Verification of Standard Curve

[0023] (1) Preparation of standard solutions

[0024] Accurately weigh 0g, 0.2g, 0.3g, 0.4g, 0.5g, 0.6g, 0.7g, 0.8g, and 1.0g of azobisisobutyronitrile (AIBN), and dissolve them in 100g, 99.8g, 99.7g, 99.6g, 99.5g, 99.4g, 99.3g, 99.2g, and 99g of dimethyl sulfoxide (DMSO), respectively, to obtain AIBN standard solutions with mass fractions of 0%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, and 1.0%. Shake well and set aside for use. Prepare and use immediately, and store at a temperature between 20℃ and 30℃ after preparation (preferably 25℃ in this example).

[0025] (2) Establish a standard UV curve

[0026] Using the reagents for preparing the standard solutions as blank references, an ultraviolet spectrophotometer (Shanghai Xipu, model UV-1800) was used with 10mm adaptive cuvettes to measure the absorbance of standard solutions of various concentrations at the characteristic wavelength of 350nm. A standard curve of mass fraction (y) versus absorbance (x) of azobisisobutyronitrile solution at the characteristic wavelength of 350nm was obtained by plotting the mass fraction of the standard solutions at different concentrations on the ordinate and the measured absorbance at the corresponding concentrations on the abscissa. (See figure). Figure 1 .

[0027] from Figure 1 As can be seen, the curve exhibits a linear pattern, and the fitted formula is: y = 1.1348x, with a correlation coefficient R0. 2 =0.9998, indicating excellent linearity in the concentration range of 0~1.0%.

[0028] Example 2: Testing of actual production samples (high concentration)

[0029] This embodiment provides a method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution. The test solution is an actual industrial sample taken from the preparation area of ​​a manufacturing plant (the estimated mass concentration of azobisisobutyronitrile is approximately 1.5%).

[0030] 2.1 Dilution Scheme Design

[0031] Since the estimated concentration of the test solution (approximately 1.5%) exceeds the linear range of the standard curve (0–1.0%), volumetric dilution is required to bring the concentration of azobisisobutyronitrile in the diluted solution into the range of 0–1.0%. To this end, three parallel schemes with different dilution factors were designed to verify the accuracy and repeatability of the method.

[0032]

[0033] 2.2 Sample Preparation

[0034] 1. Procedure A: Accurately transfer 4 mL of the test solution into a 20 mL volumetric flask, dilute to volume with dimethyl sulfoxide solution used in the on-site preparation area, and shake well before testing. Simultaneously perform this procedure and prepare 3 samples to obtain 2 parallel test samples, numbered 1# and 2#.

[0035] 2. Scheme B: Accurately transfer 5 mL of the test solution to a 20 mL volumetric flask, dilute to volume with dimethyl sulfoxide solution used in the on-site preparation area, and shake well before testing. Simultaneously prepare two samples to obtain two parallel test samples, numbered 3# and 4#.

[0036] 3. Procedure C: Accurately transfer 20 mL of the test solution into a 50 mL volumetric flask, dilute to volume with dimethyl sulfoxide solution used in the on-site preparation area, and shake well before testing. Simultaneously prepare two samples to obtain two parallel test samples, numbered 5# and 6#.

[0037] 2.3 Absorbance Measurement

[0038] Six diluted solutions (1#, 2#, 3#, 4#, 5#, and 6#) were tested. Using the dimethyl sulfoxide solution prepared on-site as a blank reference, the absorbance was measured at the characteristic wavelength of 350 nm using a UV-Vis spectrophotometer (Shanghai Xipu, model UV-1800). The test results are shown in the table.

[0039] 2.4 Concentration Calculation

[0040] Based on the standard curve formula y = 1.1348x established in Example 1 (where y is the mass percentage concentration %, and x is the absorbance), the concentration of the stock solution is calculated according to the following steps:

[0041] Step 1: Substitute the measured absorbance x into the formula to calculate the concentration of the diluted solution, y = 1.1348x.

[0042] Step 2: Calculate the stock solution concentration ω = n × y × 100% based on the dilution factor n. The calculation results are shown in the table below.

[0043] 2.5 Test Results

[0044]

[0045] 2.6 Results Analysis

[0046] (1) Verification of absorbance range

[0047] The absorbance of all diluted solutions was in the range of 0.265 to 0.533, which is within the optimal response range (0.2 to 0.8) of the UV spectrophotometer, and all were below 1.0, indicating that the dilution scheme was reasonably designed and all measurements were performed within the linear range of the standard curve.

[0048] (2) Consistency of different dilution schemes

[0049] The calculated stock solution concentrations at three different dilution ratios (5x, 4x, and 2.5x) were highly consistent.

[0050] Option A (5-fold dilution): 1.503%~1.509%;

[0051] Option B (4-fold dilution): 1.502%~1.511%;

[0052] Option C (2.5-fold dilution): 1.509%~1.512%;

[0053] The concentration range was 1.502% to 1.512%, with a maximum deviation of only 0.010% (absolute deviation) and a relative deviation of about 0.67%, indicating that the method has good robustness to different dilution factors.

[0054] (3) Repeatability assessment

[0055] Statistical analysis was performed on the stock solution concentrations of the six samples:

[0056] average value: ;

[0057] Standard deviation (SD): According to the formula Substituting the data, SD≈0.004;

[0058] Relative Standard Deviation (RSD): According to the formula Substituting the data, RSD≈0.27%.

[0059] The standard deviation (SD) was only 0.004, and the relative standard deviation (RSD) was 0.27%, which is far below the precision standard usually required in the field of analytical chemistry (generally requiring RSD ≤ 2%), proving that this method has extremely high repeatability.

[0060] This embodiment demonstrates that the method can be directly used for the detection of actual production samples without special pretreatment;

[0061] Consistent results can be obtained at different dilution ratios, and operators can flexibly choose the dilution ratio according to the sample concentration.

[0062] RSD=0.27%, which meets the quality control requirements for industrial production;

[0063] The calculation results from the three independent dilution schemes were consistent, verifying the formula for calculating the dilution factor. The correctness of the statement.

[0064] Example 3: Self-prepared 1.5% sample (diluted required)

[0065] This embodiment provides a method for accurately measuring the content of azobisisobutyronitrile (AIOBR) in a dimethyl sulfoxide (DMSO) solution; wherein the solution is a DMSO solution with an AIOBR concentration of 1.5% by mass.

[0066] 1) Take 1.5g of azobisisobutyronitrile and dissolve it in 98.5g of dimethyl sulfoxide to obtain a 1.5% azobisisobutyronitrile solution. Shake well and set aside for later use.

[0067] 2) Accurately transfer 10 mL of the prepared solution into a 50 mL volumetric flask, dilute to volume with the prepared dimethyl sulfoxide solution, and shake well before testing. Simultaneously perform this operation and prepare 3 samples to obtain 3 parallel test samples.

[0068] 3) Using the prepared dimethyl sulfoxide solution as a blank reference, the absorbance of three parallel samples was measured at the characteristic wavelength of 350 nm using a UV-Vis spectrophotometer (Shanghai Xipu, model UV-1800). The measured absorbances were 0.265, 0.265, and 0.266, respectively.

[0069] 4) The concentrations of azobisisobutyronitrile in the self-prepared solution were calculated based on the linear formula and dilution factor as follows: 1.503%, 1.502%, and 1.509%, with an average value of 1.505% and a standard deviation (SD) of 0.0035.

[0070] Results analysis:

[0071] In this embodiment, the theoretical concentration of the self-prepared solution was 1.500%, the measured average value was 1.505%, the relative error was only 0.33% (= |1.505%-1.500%| / 1.500%×100%), and the recovery rate was 100.33% (=1.505% / 1.500%×100%), indicating that the measurement results of this method are in high agreement with the theoretical value and have excellent accuracy.

[0072] The standard deviation (SD) of the three parallel samples was 0.0035, and the relative standard deviation (RSD) was (0.0035 / 1.505)×100% = 0.23%, which is far below the precision standard (RSD≤2%) usually required in the field of analytical chemistry, proving that the method has excellent repeatability.

[0073] Conclusion of this embodiment: For high-concentration samples (1.5%) that exceed the linear range of the standard curve, this method can still obtain accurate and reliable detection results after dilution, with a relative error of only 0.33% and an RSD of only 0.23%.

[0074] Example 4: Self-prepared 0.5% sample (direct measurement)

[0075] This embodiment provides a method for accurately measuring the content of azobisisobutyronitrile (AIOBR) in a dimethyl sulfoxide (DMSO) solution; wherein the solution is a DMSO solution with an AIOBR concentration of 0.5% by mass.

[0076] 1) Take 0.5g of azobisisobutyronitrile and dissolve it in 99.5g of dimethyl sulfoxide to obtain a 0.5% azobisisobutyronitrile solution. Shake well and set aside for later use.

[0077] 2) Using the prepared dimethyl sulfoxide solution as a blank reference, a UV-Vis spectrophotometer (Shanghai Xipu, model UV-1800) was used to measure three absorbance data at the characteristic wavelength of 350 nm. The measured absorbances were 0.440, 0.442 and 0.438, respectively.

[0078] 3) The concentrations of azobisisobutyronitrile in the self-prepared solution were calculated based on the linear formula and dilution factor as follows: 0.499%, 0.502%, and 0.497%, with an average value of 0.499%. The standard deviation (SD) of the results was 0.0025, and the relative standard deviation (RSD) was (0.0025 / 0.499)×100% = 0.50%.

[0079] Results analysis:

[0080] In this embodiment, the theoretical concentration of the self-prepared solution was 0.500%, the measured average value was 0.499%, the relative error was only 0.20% (=|0.499%-0.500%| / 0.500%×100%), and the recovery rate was 99.8% (=0.499% / 0.500%×100%), indicating that this method has excellent accuracy for direct measurement of samples within the linear range of the standard curve.

[0081] The standard deviation (SD) of the three parallel samples was 0.0025, and the relative standard deviation (RSD) was 0.50%, indicating good precision.

[0082] Conclusion of this embodiment: For low-concentration samples (0.5%) within the linear range of the standard curve, accurate and reliable detection results can be obtained by direct measurement without dilution, with a relative error of only 0.20% and an RSD of only 0.50%.

[0083] Examples 3 and 4 together demonstrate that regardless of whether the sample concentration is within the linear range of the standard curve (0.5%) or outside the linear range (1.5%), this method can achieve high accuracy and high precision detection, and has good concentration adaptability and wide industrial application value.

[0084] Comparative example: Direct measurement of high-concentration samples without dilution

[0085] To verify the necessity of dilution measurement, this comparative example uses a self-prepared dimethyl sulfoxide solution with a mass fraction of 3.0% azobisisobutyronitrile for comparative experiments.

[0086] 1. Preparation of the test solution

[0087] Take 3.0 g of azobisisobutyronitrile and dissolve it in 97.0 g of dimethyl sulfoxide to obtain a 3.0% azobisisobutyronitrile solution.

[0088] 2. Direct measurement without dilution (comparative example)

[0089] Without dilution, the absorbance was measured directly at 350 nm using a spectrophotometer. Due to the excessively high sample concentration, the absorption of ultraviolet light by the solution exceeded the linear response range of the instrument. The absorbances of the three parallel samples were 2.494, 2.491, and 2.497, respectively, with an average of 2.494. The actual instrument deviated from the Lambert-Beer law when the absorbance was >1, indicating a significant nonlinear response.

[0090] 3) Substitute the measured absorbance of 2.494 directly into the standard curve equation y = 1.1348x to calculate the "apparent concentration" as 1.1348 × 2.494 ≈ 2.830%.

[0091] Result comparison:

[0092] True concentration of sample: 3.0%; Apparent concentration measured directly without dilution: 2.830%;

[0093] The relative error is (3.0%-2.830%) / 3%×100%)=5.7%, which is relatively large.

[0094] 3. Measurement after dilution using the method of this invention.

[0095] According to the method of the present invention, the above-mentioned 3.0% sample is diluted by volume:

[0096] Accurately transfer 10 mL of the test solution into a 50 mL volumetric flask, and dilute to the mark with dimethyl sulfoxide solvent. The dilution factor is 5 times.

[0097] The absorbance of the diluted solution was measured, and the values ​​for the three parallel samples were 0.526, 0.529, and 0.528, respectively. The diluted concentrations were calculated by substituting them into the standard curve equation, and then multiplied by the dilution factor of 5 to calculate the original concentration. The original concentrations calculated for the three parallel samples were 2.985%, 3.001%, and 2.996%, respectively, with an average of 2.994%, a standard deviation (SD) of 0.007, and a relative error of 0.2%.

[0098] This comparative example demonstrates that for high-concentration samples, if measured directly without dilution, the absorbance will deviate from the linear range of the Lambert-Beer law, leading to a significant discrepancy between the calculated results and the true values. In contrast, if the sample is appropriately diluted (e.g., 5 times) to the linear range according to the method of this invention before measurement, the measurement results closely match the true values. Therefore, the "volume dilution when absorbance is greater than 1" proposed in this invention is a key technical feature ensuring the accuracy of high-concentration sample detection.

[0099] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution, characterized in that, Includes the following steps: (1) Establishing a standard curve: Using dimethyl sulfoxide as solvent, a series of standard solutions with a mass concentration of azobisisobutyronitrile in the range of 0~1.0% were prepared; using pure dimethyl sulfoxide as blank reference, the absorbance of each standard solution was measured at the characteristic wavelength of 350nm using a UV-Vis spectrophotometer to ensure that the measured absorbance value was in the range of 0~1; the standard curve was plotted with the measured absorbance as the abscissa and the corresponding standard solution concentration as the ordinate, and the linear regression formula was calculated. (2) Test of the test solution: Using the same dimethyl sulfoxide solvent as the test solution as a blank reference, the absorbance was measured at a characteristic wavelength of 350 nm. If the absorbance is between 0 and 1, directly substitute the absorbance value into the linear regression formula in step (1) to calculate the concentration of azobisisobutyronitrile in the test solution. If the absorbance is greater than 1, the test solution is diluted by volume with dimethyl sulfoxide until the absorbance of the diluted solution drops to the range of 0 to 1. The dilution factor is recorded, and the absorbance of the diluted solution is substituted into the linear regression formula to obtain the concentration after dilution. Then, the concentration of azobisisobutyronitrile in the original test solution is calculated by multiplying by the dilution factor.

2. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In the step (1), the linear regression formula of the standard curve is specifically y = k x, wherein y is the mass percentage concentration (%) of azobisdimethylvaleronitrile, x is the absorbance, k is a constant obtained by fitting the standard curve, and the linear correlation coefficient R 2 ≥ 0.999 in the concentration range of 0-1.0%.

3. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In step (2), the formula for calculating the volume dilution factor is: dilution factor n = (V0 + V) / V0, where V0 is the volume of the test solution taken during dilution, and V is the volume of dimethyl sulfoxide solvent added during dilution, both in mL; original test solution concentration = n × dilute solution concentration.

4. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In steps (1) and (2), the detection wavelength of the UV-Vis spectrophotometer used is 350 nm, and the optical path of the cuvette used is 10 mm.

5. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In step (1), the prepared series of standard solutions includes at least 5 different concentration points, and the concentration points are evenly distributed in the range of 0~1.0%.

6. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In step (2), when the absorbance of the solution to be tested is greater than 1, a single dilution or stepwise dilution method is used until the absorbance of the diluted solution drops to the range of 0.2 to 0.

8.

7. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: Both the standard solutions and the test solutions were stored at 20℃~30℃ before testing.

8. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In step (2), when performing volume dilution, the tool used to transfer the solution to be tested and the solvent is a pipette or pipette gun, and the volumetric container is a volumetric flask.

9. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: In step (1), when preparing a series of standard solutions, the weighing accuracy of azobisisobutyronitrile and dimethyl sulfoxide is not less than 0.001g.

10. The method for accurately measuring the content of azobisisobutyronitrile in a dimethyl sulfoxide solution according to claim 1, characterized in that: The method is used for quality control and detection of the azobisisobutyronitrile initiator content in the dimethyl sulfoxide solution during the polymerization solution preparation stage in the production of polyacrylonitrile-based carbon fiber precursor.

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