Method for determining the accelerator content of vulcanized rubber residues from tires by high performance liquid chromatography

Abstract

The application discloses a kind of high-efficiency liquid chromatography determination methods of tire vulcanized rubber residual accelerator content, it is related to rubber product residual detection technical field, the specific steps of the method are as follows: tire vulcanized rubber sample is cut and weighed, mixed extraction solvent containing mild reducing agent is added, internal combined state vulcanization accelerator is released by constant-temperature ultrasonic extraction, and the solution to be measured is prepared after centrifugal filtration;Preparation matrix matching standard working solution, using high performance liquid chromatography separation detection, the residual accelerator content is obtained by calibration curve quantification;The application uses the extraction system containing mild reducing agent, breaks the crosslinking disulfide bond of rubber to release combined state accelerator, combines constant-temperature ultrasonic to improve extraction efficiency, avoids target degradation, and guarantees that detection result is true and accurate;While using matrix matching calibration curve offsets matrix interference, optimizes chromatographic condition to realize the synchronous detection of multiple components, standardized process guarantees method precision and repeatability, provides technical support for tire quality control.

Description

Technical Field

[0001] This invention relates to the field of rubber product residue detection technology, specifically a high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber. Background Technology

[0002] Vulcanization accelerators are core additives in the vulcanization process of tire rubber, shortening the vulcanization cycle, lowering the vulcanization temperature, and optimizing the physical and mechanical properties of the vulcanized rubber. Their residual content in vulcanized rubber directly affects the tire's aging resistance, safety, and environmental compatibility. With the tire industry's continuously increasing demands for product quality control and environmental compliance, accurately determining the total content of residual accelerators in vulcanized rubber has become a crucial step in rubber formulation optimization, finished product quality inspection, and aging performance evaluation. High-performance liquid chromatography (HPLC) is currently the mainstream technique for detecting residual rubber additives due to its strong separation capabilities and high detection sensitivity. However, the encapsulation effect of the three-dimensional cross-linked network in vulcanized rubber remains a core technical challenge limiting the extraction efficiency and detection accuracy of accelerators.

[0003] Existing extraction and detection technologies for vulcanization accelerators have several shortcomings: conventional solvent-based ultrasonic and Soxhlet extraction methods can only extract free accelerators from the rubber matrix surface, failing to break through the three-dimensional network structure formed by vulcanization crosslinking. A large amount of bound accelerators remain encapsulated within the network, resulting in final detection results significantly lower than the actual residual amount, leading to significant quantitative distortion. Some extraction methods employing reduction methods require harsh reaction conditions with reducing agents such as dithiothreitol, necessitating high temperatures and strong alkalinity, which easily induces degradation and structural damage to the target accelerator. Furthermore, these methods readily introduce numerous impurities that interfere with chromatographic separation, further reducing detection reliability. Existing detection methods often use pure solvents to prepare standard curves, neglecting the matrix effect interference from the rubber matrix, resulting in significant quantitative deviations. Moreover, the sample particle size and extraction parameters lack standardized control before extraction, leading to poor repeatability of results across different batches, making it difficult to meet the actual needs of accurate tire product testing.

[0004] In summary, existing technologies for detecting residual accelerators in tire vulcanized rubber have consistently failed to achieve efficient release and accurate quantification of bound accelerators under mild conditions. Problems such as low extraction efficiency, easy degradation of target substances, strong matrix interference, and poor method repeatability are compounded, hindering the implementation of tire vulcanization quality control and additive residue assessment. Therefore, there is an urgent need to develop a high-performance liquid chromatography (HPLC) method that can gently break the cross-linked disulfide bonds in rubber, fully release total residual accelerators, effectively counteract matrix effects, and provide stable and reliable detection results. This would fill the current technological gap and provide precise technical support for tire vulcanization process optimization and product quality control. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-performance liquid chromatography (HPLC) method for determining the content of residual accelerators in tire vulcanized rubber. The method involves cutting the vulcanized rubber sample into small pieces and then performing isothermal ultrasonic extraction using a mixed extraction solvent containing a mild reducing agent. This reduces the disulfide bonds in the broken rubber crosslinking network, releasing the bound vulcanization accelerators. The solution to be tested is prepared by centrifugation and filtration. Simultaneously, a matrix-matched standard working solution is prepared using a blank matrix extract. Separation is achieved using gradient elution on a reversed-phase C18 column, combined with ultraviolet detection. Quantification is achieved by establishing a calibration curve using the external standard method.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber, the method comprising:

[0007] S100. Take the test part of the tire vulcanized rubber, remove surface contaminants, cut it into the set particle size, mix it well, weigh the set mass of the test sample and place it in a sealed extraction container.

[0008] S200. Add a mixed extraction solvent containing a mild reducing agent to the extraction container, vortex mix, and then perform constant temperature ultrasonic extraction. The mild reducing agent reacts with the disulfide bonds in the rubber crosslinking network to break the disulfide bond crosslinking points, loosen the three-dimensional network structure to release the bound vulcanization accelerator encapsulated inside, and obtain the crude extract.

[0009] S300. After cooling the crude extract to room temperature, centrifuge and let it settle. Take the supernatant and filter it through an organic phase filter membrane. Discard the initial filtrate and collect the subsequent filtrate as the test solution.

[0010] S400. Weigh out various vulcanization accelerator standards, dissolve and dilute them with methanol to prepare single-component standard stock solutions, transfer each single-component standard stock solution to mix, and then dilute with blank matrix extract to prepare matrix-matched standard working solutions of a series of concentrations.

[0011] S500. Inject the standard working solution and the test solution into the high performance liquid chromatograph, separate them using a reversed-phase C18 column, collect the signal using an ultraviolet detector, establish a calibration curve based on the concentration and peak area of ​​the standard working solution, and obtain the content of residual accelerator in the rubber sample.

[0012] Furthermore, the tested area is selected from the vulcanized rubber layer of the tire tread. After removing the dust and release agent adhering to the surface, it is sheared and crushed. The maximum particle size of the rubber particles does not exceed 2 mm. The crushed sample is placed in a brown sample bottle and mixed evenly. The sample weight is controlled within the range of 0.4 g to 0.6 g. The extraction container is a polypropylene centrifuge tube with a sealed cap and a volume of 50 mL. The sample to be tested is placed at the bottom of the centrifuge tube before the extraction solvent is added. The crushing operation is carried out at room temperature. The crushed particle size of the same batch of samples is kept consistent. After weighing, the centrifuge tube is immediately sealed.

[0013] Furthermore, the basic component of the mixed extraction solvent is a mixed solution of methanol and acetonitrile, with a volume ratio of methanol to acetonitrile of 1:1 to 3:1; the mild reducing agent is tris-2-carboxyethylphosphine, with a mass-volume concentration of 0.3% to 2.0% in the mixed extraction solvent, and the added volume of the mixed extraction solvent is 20 mL, corresponding to a liquid-to-solid ratio of 40 mL / g for every 0.5 g of sample to be tested; the mild reducing agent is pre-dissolved in the methanol phase by thorough stirring, and then mixed evenly with acetonitrile according to the set ratio. The prepared extraction solvent containing the reducing agent is put into use within 2 hours, and both the preparation and extraction processes are conducted away from direct sunlight; after controlled dissociation extraction, a crude extract is obtained.

[0014] Furthermore, the temperature of the isothermal ultrasonic extraction is controlled within the range of 35℃ to 55℃, the output power of the ultrasonic equipment is 200W to 400W, and the extraction time for a single extraction is set to 15min to 40min. Before ultrasonic extraction begins, the centrifuge tube is vortexed for 1min at a rotation speed of 2000r / min. During ultrasonic extraction, the centrifuge tube is removed every 5min and vortexed for 30s before being returned to the ultrasonic equipment to continue extraction. The water bath level of the ultrasonic equipment is higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer.

[0015] Furthermore, a phosphate buffer component, prepared from sodium dihydrogen phosphate and disodium hydrogen phosphate, is added to the mixed extraction solvent, and the final concentration in the mixed extraction solvent is 10 mmol / L. The buffer component is pre-dissolved in ultrapure water to prepare a stock solution, which is then added to the mixed extraction solvent. After thorough mixing, the pH value of the mixed extraction solvent is adjusted to the range of 6.5 to 7.5, and then a reducing agent is added and stirred to dissolve.

[0016] Furthermore, after the crude extract is cooled to room temperature of 25°C, it is centrifuged in a high-speed centrifuge at a speed of 8000 r / min for 5 min. After centrifugation, the centrifuge tube is removed, and the supernatant is aspirated with a pipette at a depth of 1 cm below the liquid surface to avoid aspirating the bottom solid precipitate. The organic phase filter membrane is made of nylon with a pore size of 0.22 μm. The first 1 mL of initial filtrate is discarded during filtration, and the subsequent filtrate is collected and placed in a brown sample vial. The vial is then tightly capped and ready for instrumental analysis.

[0017] Furthermore, the vulcanization accelerator standards include 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide; the single-component standard stock solution has a mass concentration of 1000 mg / L, dissolved in chromatographically pure methanol and diluted to the mark of the volumetric flask; the blank matrix extract is obtained by processing the same type of vulcanized rubber sample without the target vulcanization accelerator according to steps S100 to S300; the standard working solution is set with six concentration gradients, namely 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L; the standard stock solution is stored in a light-protected environment at -20°C.

[0018] Furthermore, the reversed-phase C18 column has a length of 250 mm, an inner diameter of 4.6 mm, and a packing particle size of 5 μm. The mobile phase consists of an organic phase and an aqueous phase, with the organic phase being acetonitrile and the aqueous phase being a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode is used, with the elution program set as follows: from 0 min to 5 min, the organic phase volume percentage increases from 20% to 40%; from 5 min to 12 min, the organic phase volume percentage increases from 40% to 60%; from 12 min to 18 min, the organic phase volume percentage increases from 60% to 80%; from 18 min to 20 min, the organic phase volume percentage remains at 80%; from 20 min to 22 min, the organic phase volume percentage decreases to 20%, and then remains at this level for 3 min for system equilibration.

[0019] Furthermore, the elution flow rate of the mobile phase was set to 1.0 mL / min, the column temperature was controlled at 30℃, the detection wavelength of the UV detector was set to 254 nm, the injection volume for a single injection was 20 μL, and the chromatographic system was equilibrated with the initial ratio of the mobile phase for at least 30 min before injection. After the baseline stabilized, samples were injected sequentially for detection. After every 10 samples were detected, a standard working solution of intermediate concentration was inserted for verification to confirm the response stability of the chromatographic system.

[0020] Furthermore, the calibration relationship is established using the external standard method. The concentration of the target analyte in each standard working solution is used as the abscissa, and the peak area of ​​the corresponding chromatographic peak is used as the ordinate. A linear fit is performed to obtain the calibration curve. The test solution is injected and measured under the same chromatographic conditions as the standard working solution. The obtained peak area of ​​the target analyte is substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The same sample is measured twice in parallel. When the relative deviation between the two measurements does not exceed 5%, the arithmetic mean is taken as the final result.

[0021] Compared with existing technologies, this high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber has the following advantages:

[0022] I. This invention employs a mixed extraction system containing a mild reducing agent, which specifically targets the disulfide bonds in the rubber crosslinking network. Under mild conditions, it loosens the three-dimensional crosslinking structure, fully releasing the bound vulcanization accelerators encapsulated within the network. This overcomes the limitation of traditional extraction methods that can only obtain surface free components, significantly improving the extraction and recovery rate of the total residual vulcanization accelerators. Simultaneously, it combines a constant-temperature ultrasonic extraction method to enhance the penetration of the solvent into the rubber matrix, further accelerating the dissolution rate of the target analyte. Moreover, the entire extraction process is conducted under mild reaction conditions, preventing structural degradation and component loss of the target accelerator, effectively ensuring the authenticity and accuracy of subsequent test results, and accurately reflecting the actual residual level of accelerators inside the vulcanized rubber.

[0023] II. This invention establishes a calibration curve using a matrix-matched standard working solution, effectively offsetting the interference effect of rubber matrix components on the chromatographic response, reducing quantitative deviation, and improving the accuracy of detection results. Simultaneously, it optimizes reversed-phase chromatographic separation and gradient elution conditions, enabling the simultaneous separation and quantitative detection of various types of vulcanization accelerators. The target analytes exhibit symmetrical peak shapes and good separation, effectively avoiding interference from matrix impurity peaks. Combined with a standardized pretreatment process and system stability verification mechanism, it effectively controls detection errors between different batches of samples, ensuring the precision and repeatability of the method. The entire detection process is standardized and controllable, meeting the actual needs of batch testing of tire vulcanized rubber samples and providing a reliable technical basis for tire vulcanization process control and product quality assessment.

[0024] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0026] Figure 1 A flowchart illustrating the steps of a high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber;

[0027] Figure 2 A flowchart illustrating the extraction solvent preparation and ultrasonic extraction process for a high-performance liquid chromatography method of determining the content of residual accelerators in tire vulcanized rubber.

[0028] Figure 3 This is a flowchart of the standard solution preparation process for a high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber. Detailed Implementation

[0029] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0030] Example 1:

[0031] S100. Select the vulcanized rubber layer of the tire tread as the test area. Wipe the rubber surface with anhydrous ethanol to remove dust and release agent, and place it in a ventilated area to air dry naturally. Specifically, after drying, the rubber sample is cut and crushed with rubber scissors, and then passed through a 2mm standard sieve to ensure that the maximum particle size of the rubber particles does not exceed 2mm. Transfer all the crushed rubber particles to a brown sample bottle and shake it manually to mix the sample evenly. Weigh 0.5g of the mixed sample and place it at the bottom of a 50mL polypropylene centrifuge tube with a sealed cap. Immediately after weighing, tighten the cap of the centrifuge tube. The crushing operation is carried out at room temperature. The particle size of the crushed samples in the same batch is kept consistent to avoid affecting the parallelism of extraction efficiency due to particle size differences.

[0032] S200. Prepare a mixed extraction solvent containing a mild reducing agent. The base solvent is a mixed solution of methanol and acetonitrile, with a volume ratio of methanol to acetonitrile of 2:1. The mild reducing agent is tris(2-carboxyethylphosphine), and its mass-volume concentration in the mixed extraction solvent is 1.0%. During preparation, tris(2-carboxyethylphosphine) is first added to the methanol phase and magnetically stirred for 10 minutes until completely dissolved. Then, it is mixed evenly with acetonitrile according to the set volume ratio. The prepared extraction solvent containing the reducing agent should be used within 1 hour. The preparation and subsequent extraction processes should avoid direct sunlight to prevent the reducing agent from becoming ineffective and the target promoter from degrading. Add 20 mL of the above-mentioned mixed extraction solvent to a centrifuge tube containing the sample to be tested, corresponding to a liquid-to-solid ratio of 40 mL / g for every 0.5 g of sample. After tightening the cap of the centrifuge tube, place it on a vortex mixer and vortex at 2000 r / min for 1 min to ensure full contact between the sample and the extraction solvent. Then, place the centrifuge tube in a constant-temperature ultrasonic device for extraction. Set the output power of the ultrasonic device to 300 W, the extraction temperature to 45℃, and the total extraction time for a single extraction to 30 min. During the ultrasonic extraction process, remove the centrifuge tube every 5 min, vortex at 2000 r / min for 30 s, and then place it back into the ultrasonic device to continue extraction. The water level in the ultrasonic device should be higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer. After rubber vulcanization, a three-dimensional cross-linked network is formed, and some accelerator molecules are wrapped inside the network. It is difficult to completely release them by conventional solvent extraction alone. In this step, tris(2-carboxyethylphosphine) can undergo a reduction reaction with the disulfide bonds in the rubber cross-linked network, selectively breaking the disulfide bond cross-linking points, loosening the three-dimensional network structure, and releasing the bound vulcanization accelerator wrapped inside. At the same time, it does not destroy the molecular structure of the accelerator itself, ensuring the accuracy of detection. After extraction, a crude extract is obtained.

[0033] S300. Remove the crude extract from the ultrasonic device and cool it to 25°C at room temperature. Then, centrifuge it in a high-speed centrifuge at 8000 r / min for 5 min. After centrifugation, remove the centrifuge tube gently to avoid disturbing the solid precipitate at the bottom. Use a pipette to aspirate the supernatant 1 cm below the liquid surface to avoid aspirating the solid precipitate and affecting subsequent chromatographic detection. Filter the supernatant through a nylon organic phase filter membrane with a pore size of 0.22 μm. Discard the first 1 mL of filtrate and collect the subsequent filtrate in a brown sample vial. Tightly cap the vial and prepare it for analysis.

[0034] S400. Four commonly used vulcanization accelerators for tire rubber were selected as the detection targets: 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide. Appropriate amounts of each standard were accurately weighed, dissolved in chromatographically pure methanol, and diluted to the mark of the volumetric flask to prepare a single-component standard stock solution with a mass concentration of 1000 mg / L. Transfer appropriate amounts of each single-component standard stock solution to the same volumetric flask, mix thoroughly, and then dilute stepwise with blank matrix extract to prepare matrix-matched standard working solutions with six concentration gradients: 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L, respectively. The blank matrix extract is obtained from the same type of vulcanized rubber sample without the target vulcanization accelerator, processed according to steps S100 to S300 above, and is used to counteract the interference of matrix effect on quantitative results. The single-component standard stock solutions are sealed and stored in a light-protected environment at -20°C.

[0035] S500. Inject the standard working solution and the test solution separately into the high-performance liquid chromatograph (HPLC) for detection. Separation is performed using a reversed-phase C18 column with a length of 250 mm, an inner diameter of 4.6 mm, and a packing particle size of 5 μm. The mobile phase consists of an organic phase and an aqueous phase. The organic phase is acetonitrile, and the aqueous phase is a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode is used, with the elution program set as follows: from 0 min to 5 min, the organic phase volume percentage increases from 20% to 40%; from 5 min to 12 min, the organic phase volume percentage increases from 40% to 60%; from 12 min to 18 min, the organic phase volume percentage increases from 60% to 80%; from 18 min to 20 min, the organic phase volume percentage remains at 80%; from 20 min to 22 min, the organic phase volume percentage decreases to 20%, and then the system is held for 3 min to equilibrate. The elution flow rate of the mobile phase was set to 1.0 mL / min, the column temperature was controlled at 30℃, the detection wavelength of the UV detector was set to 254 nm, and the injection volume for a single injection was 20 μL. Before injection, the chromatographic system was equilibrated for at least 30 minutes using the initial mobile phase ratio, and injections were performed sequentially after the baseline stabilized. After every 10 samples, a standard working solution of intermediate concentration was inserted for verification to confirm the response stability of the chromatographic system and ensure the accuracy of the quantitative results for batch samples. The calibration relationship was established using the external standard method, with the concentration of the target analyte in each concentration of the standard working solution as the x-axis and the peak area of ​​the corresponding chromatographic peak as the y-axis, and a linear fit was performed to obtain the calibration curve. The test solution was injected and measured under the same chromatographic conditions as the standard working solution. The obtained peak area of ​​the target analyte was substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The content of residual accelerator in the rubber sample was then calculated by combining the sample weight and extraction volume. The same sample was measured twice in parallel, and the arithmetic mean of the two results was taken as the final result when the relative deviation of the two measurements did not exceed 5%. Figure 1 As shown.

[0036] Example 2:

[0037] S100. Select the vulcanized rubber layer of the tire tread as the test area. Wipe the rubber surface with anhydrous ethanol to remove dust and release agent, and let it air dry in a ventilated place. Specifically, after drying, the rubber sample is cut and crushed with rubber scissors. After crushing, it is passed through a 2mm standard sieve to ensure that the maximum particle size of the rubber particles does not exceed 2mm. All the crushed rubber particles are transferred to a brown sample bottle and shaken by hand to mix the sample evenly. Weigh 0.6g of the mixed sample and place it at the bottom of a 50mL polypropylene centrifuge tube with a sealed cap. Immediately after weighing, tighten the cap of the centrifuge tube. The crushing operation is carried out at room temperature. The particle size of the crushed samples in the same batch is kept consistent to avoid affecting the parallelism of extraction efficiency due to particle size differences.

[0038] S200. Prepare a mixed extraction solvent containing a mild reducing agent. The base solvent is a mixture of methanol and acetonitrile in a volume ratio of 1:1. Add a phosphate buffer component to the mixed extraction solvent. The buffer component is prepared from sodium dihydrogen phosphate and disodium hydrogen phosphate. Dissolve sodium dihydrogen phosphate and disodium hydrogen phosphate in ultrapure water to prepare a high-concentration stock solution. Add an appropriate amount of the stock solution to the mixed extraction solvent to make the final concentration of the buffer component in the mixed extraction solvent 10 mmol / L. After thorough mixing, adjust the pH of the mixed extraction solvent to 7.0. Then add tris(2-carboxyethylphosphine) and stir until completely dissolved. The mass-volume concentration of tris(2-carboxyethylphosphine) in the mixed extraction solvent is 2.0%. The prepared extraction solvent containing the reducing agent should be used within 1.5 hours. The preparation and subsequent extraction processes should be carried out in a cool, dry environment to prevent the reducing agent from becoming ineffective and the target promoter from degrading. Add 20 mL of the above-mentioned mixed extraction solvent to the centrifuge tube containing the sample to be tested, matching the current sample weight with the liquid-to-solid ratio. After tightening the centrifuge tube's sealing cap, place it on a vortex mixer and vortex at 2000 r / min for 1 min to ensure sufficient contact between the sample and the extraction solvent. Then, place the centrifuge tube in a constant-temperature ultrasonic device for extraction. Set the output power of the ultrasonic device to 400 W, the extraction temperature to 55℃, and the total extraction time for a single extraction to 40 min. During the ultrasonic extraction process, remove the centrifuge tube every 5 min, vortex at 2000 r / min for 30 s, and then return it to the ultrasonic device to continue extraction. The water bath level of the ultrasonic device should be higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer. After rubber vulcanization, a three-dimensional cross-linked network is formed, with some accelerator molecules encapsulated within it. Conventional solvent extraction alone is insufficient for complete release. In this step, tris(2-carboxyethylphosphine) can undergo a reduction reaction with the disulfide bonds in the rubber cross-linked network, selectively breaking the disulfide bond cross-linking points, loosening the three-dimensional network structure, and releasing the bound vulcanization accelerators encapsulated within. The phosphate buffer component maintains pH stability in the extraction system, reducing the impact of pH fluctuations on the activity of the reducing agent and the stability of the target compound, further improving the stability of the extraction process. After extraction, a crude extract is obtained, such as... Figure 2 As shown.

[0039] S300. Remove the crude extract from the ultrasonic device and cool it to 25°C at room temperature. Then, centrifuge it in a high-speed centrifuge at 8000 r / min for 5 min. After centrifugation, remove the centrifuge tube gently to avoid disturbing the solid precipitate at the bottom. Use a pipette to aspirate the supernatant 1 cm below the liquid surface to avoid aspirating the solid precipitate and affecting subsequent chromatographic detection. Filter the supernatant through a nylon organic phase filter membrane with a pore size of 0.22 μm. Discard the first 1 mL of filtrate and collect the subsequent filtrate in a brown sample vial. Tightly cap the vial and prepare it for analysis.

[0040] S400. Four commonly used vulcanization accelerators for tire rubber were selected as detection targets: 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide. Appropriate amounts of each standard were accurately weighed, dissolved in chromatographically pure methanol, and diluted to the mark on a volumetric flask to prepare a single-component standard stock solution with a mass concentration of 1000 mg / L. Appropriate amounts of each single-component standard stock solution were transferred to the same volumetric flask, mixed thoroughly, and then tested with a blank matrix. The extract was serially diluted to prepare matrix-matched standard working solutions with six concentration gradients: 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. The blank matrix extract was prepared from the same type of vulcanized rubber sample without the target vulcanization accelerator, processed according to steps S100 to S300 above, and was used to counteract the interference of matrix effect on the quantitative results. The single-component standard stock solution was sealed and stored in a light-protected environment at -20°C.

[0041] S500. The standard working solution and the test solution were injected separately into the high-performance liquid chromatograph for detection. A reversed-phase C18 column was used for separation. The column length was 250 mm, the inner diameter was 4.6 mm, and the packing particle size was 5 μm. The mobile phase consisted of an organic phase and an aqueous phase. The organic phase was acetonitrile, and the aqueous phase was a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode was used. The elution program was set as follows: from 0 min to 5 min, the volume percentage of the organic phase increased from 20% to 40%; from 5 min to 12 min, the volume percentage of the organic phase increased from 40% to 60%; from 12 min to 18 min, the volume percentage of the organic phase increased from 60% to 80%; from 18 min to 20 min, the volume percentage of the organic phase remained at 80%; from 20 min to 22 min, the volume percentage of the organic phase decreased to 20%, and then the system was equilibrated for 3 min. The elution flow rate of the mobile phase was set to 1.0 mL / min, the column temperature was controlled at 30℃, the detection wavelength of the UV detector was set to 254 nm, and the injection volume for a single injection was 20 μL. Before injection, the chromatographic system was equilibrated for at least 30 min using the initial ratio of the mobile phase, and injections were performed sequentially after the baseline stabilized. After every 10 samples were tested, a standard working solution of intermediate concentration was inserted for verification to confirm the response stability of the chromatographic system and ensure the accuracy of the quantitative results for batch samples. The calibration relationship was established using the external standard method, with the concentration of the target analyte in each concentration of the standard working solution as the x-axis and the peak area of ​​the corresponding chromatographic peak as the y-axis, and a linear fit was performed to obtain the calibration curve. The test solution was injected and measured under the same chromatographic conditions as the standard working solution, and the obtained peak area of ​​the target analyte was substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The content of residual accelerator in the rubber sample was then calculated by combining the sample weight and extraction volume. The same sample was measured twice in parallel, and the arithmetic mean of the two results was taken as the final result when the relative deviation of the two results did not exceed 5%.

[0042] Example 3:

[0043] S100. Select the vulcanized rubber layer of the tire tread as the test area. Wipe the rubber surface with anhydrous ethanol to remove dust and release agent, and place it in a ventilated area to air dry naturally. Specifically, after drying, the rubber sample is cut and crushed with rubber scissors. After crushing, it is passed through a 2mm standard sieve to ensure that the maximum particle size of the rubber particles does not exceed 2mm. All the crushed rubber particles are transferred to a brown sample bottle and manually shaken to mix the sample evenly. Weigh 0.4g of the mixed sample and place it at the bottom of a 50mL polypropylene centrifuge tube with a sealed cap. Immediately after weighing, tighten the cap of the centrifuge tube. The crushing operation is carried out at room temperature. The particle size of the crushed samples in the same batch is kept consistent to avoid affecting the parallelism of extraction efficiency due to particle size differences.

[0044] S200: Prepare a mixed extraction solvent containing a mild reducing agent. The base solvent is a mixture of methanol and acetonitrile, with a volume ratio of methanol to acetonitrile of 3:1. Add a phosphate buffer component to the mixed extraction solvent. The buffer component is prepared by dissolving sodium dihydrogen phosphate and disodium hydrogen phosphate in ultrapure water to prepare a stock solution. Take an appropriate amount of the stock solution and add it to the mixed extraction solvent to make the final concentration of the buffer component in the mixed extraction solvent 10 mmol / L. After thorough mixing, adjust the pH of the mixed extraction solvent to 6.5, and then add tris(2-carboxyethylphosphine) and stir until completely dissolved. The mass-volume concentration of tris(2-carboxyethylphosphine) in the mixed extraction solvent is 0.3%. The prepared extraction solvent containing the reducing agent should be used within 2 hours. The preparation and subsequent extraction processes should be carried out in a cool, dark environment to prevent the reducing agent from becoming ineffective and the target promoter from degrading. Add 20 mL of the above-mentioned mixed extraction solvent to the centrifuge tube containing the sample to be tested, matching the current sample weight with the liquid-to-solid ratio. After tightening the centrifuge tube's sealing cap, place it on a vortex mixer and vortex at 2000 r / min for 1 min to ensure full contact between the sample and the extraction solvent. Then, place the centrifuge tube in a constant-temperature ultrasonic device for extraction. Set the output power of the ultrasonic device to 200 W, the extraction temperature to 35℃, and the total extraction time for a single extraction to 15 min. During the ultrasonic extraction process, remove the centrifuge tube every 5 min, vortex at 2000 r / min for 30 s, and then return it to the ultrasonic device to continue extraction. The water bath level of the ultrasonic device should be higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer. After rubber vulcanization, a three-dimensional cross-linked network is formed, and some accelerator molecules are encapsulated inside the network. It is difficult to completely release them by conventional solvent extraction alone. In this step, tris(2-carboxyethylphosphine) can undergo a reduction reaction with the disulfide bonds in the rubber cross-linked network, selectively breaking the disulfide bond cross-linking points, loosening the three-dimensional network structure, and releasing the bound vulcanization accelerators encapsulated inside. The phosphate buffer component can maintain the pH stability of the extraction system and reduce the impact of pH fluctuations on the activity of the reducing agent and the stability of the target substance. After extraction, a crude extract is obtained.

[0045] S300. Remove the crude extract from the ultrasonic device and cool it to 25°C at room temperature. Then, centrifuge it in a high-speed centrifuge at 8000 r / min for 5 min. After centrifugation, remove the centrifuge tube gently to avoid disturbing the solid precipitate at the bottom. Use a pipette to aspirate the supernatant 1 cm below the liquid surface to avoid aspirating the solid precipitate and affecting subsequent chromatographic detection. Filter the supernatant through a nylon organic phase filter membrane with a pore size of 0.22 μm. Discard the first 1 mL of filtrate and collect the subsequent filtrate in a brown sample vial. Tightly cap the vial and prepare it for analysis.

[0046] S400. Four commonly used vulcanization accelerators for tire rubber were selected as the test targets: 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide. Accurately weigh appropriate amounts of each standard, dissolve them in chromatographically pure methanol, and dilute to the mark on a volumetric flask to prepare a single-component standard stock solution with a mass concentration of 1000 mg / L. Transfer appropriate amounts of each single-component standard stock solution to the same volumetric flask, mix thoroughly, and then serially dilute with blank matrix extract to prepare matrix-matched standard working solutions with six concentration gradients: 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. The blank matrix extract is obtained from a vulcanized rubber sample of the same type without the target vulcanization accelerator, processed according to steps S100 to S300 above, and is used to counteract the interference of matrix effects on the quantitative results. After sealing, the single-component standard stock solutions are stored in a light-protected environment at -20°C. Figure 3 As shown.

[0047] S500. Inject the standard working solution and the test solution separately into the high-performance liquid chromatograph (HPLC) for detection. A reversed-phase C18 column was used for separation. The column length was 250 mm, the inner diameter was 4.6 mm, and the packing particle size was 5 μm. The mobile phase consisted of an organic phase and an aqueous phase. The organic phase was acetonitrile, and the aqueous phase was a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode was used. The elution program was set as follows: from 0 min to 5 min, the organic phase volume percentage increased from 20% to 40%; from 5 min to 12 min, the organic phase volume percentage increased from 40% to 60%; from 12 min to 18 min, the organic phase volume percentage increased from 60% to 80%; from 18 min to 20 min, the organic phase volume percentage remained at 80%; from 20 min to 22 min, the organic phase volume percentage decreased to 20%, and then the system was held for 3 min to equilibrate. The elution flow rate of the mobile phase was set to 1.0 mL / min, the column temperature was controlled at 30℃, the detection wavelength of the UV detector was set to 254 nm, and the injection volume for a single injection was 20 μL. Before injection, the chromatographic system was equilibrated with the initial mobile phase ratio for at least 30 min. After the baseline stabilized, samples were injected sequentially for detection. After every 10 samples, a standard working solution of intermediate concentration was inserted for verification to confirm the response stability of the chromatographic system and ensure the accuracy of the quantitative results for batch samples. The calibration relationship was established using the external standard method. The concentration of the target analyte in each concentration of the standard working solution was used as the x-axis, and the peak area of ​​the corresponding chromatographic peak was used as the y-axis. A linear fit was performed to obtain the calibration curve. The test solution was injected and measured under the same chromatographic conditions as the standard working solution. The peak area of ​​the target analyte was substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The content of residual accelerator in the rubber sample was then calculated by combining the sample weight and extraction volume. The same sample was measured twice in parallel. When the relative deviation between the two measurements did not exceed 5%, the arithmetic mean was taken as the final result.

[0048] Comparative example:

[0049] This comparative example uses conventional solvent extraction for pretreatment, and the specific implementation process is as follows:

[0050] S100. Select the vulcanized rubber layer of the tire tread as the test area. Wipe the rubber surface with anhydrous ethanol to remove dust and release agent, and place it in a ventilated area to air dry naturally. Specifically, after drying, the rubber sample is cut and crushed with rubber scissors, and then passed through a 2mm standard sieve to ensure that the maximum particle size of the rubber particles does not exceed 2mm. Transfer all the crushed rubber particles to a brown sample bottle and shake it manually to mix the sample evenly. Weigh 0.5g of the mixed sample and place it at the bottom of a 50mL polypropylene centrifuge tube with a sealed cap. Immediately after weighing, tighten the cap of the centrifuge tube. The crushing operation is carried out at room temperature. The particle size of the crushed samples in the same batch is kept consistent to avoid affecting the parallelism of extraction efficiency due to particle size differences.

[0051] S200, prepare a mixed extraction solvent. The base solvent is a mixed solution of methanol and acetonitrile with a volume ratio of 2:1. No reducing agent components are added. The prepared extraction solvent was used within 2 hours. Both the preparation and subsequent extraction processes were conducted away from direct sunlight to prevent degradation of the target promoter. 20 mL of the above-mentioned mixed extraction solvent was added to a centrifuge tube containing the sample to be tested, corresponding to a liquid-to-solid ratio of 40 mL / g for every 0.5 g of sample. After tightly sealing the centrifuge tube, it was placed on a vortex mixer and vortexed at 2000 rpm for 1 min to ensure sufficient contact between the sample and the extraction solvent. The centrifuge tube was then placed in a constant-temperature ultrasonic device for extraction. The output power of the ultrasonic device was set to 300 W, the extraction temperature was controlled at 45℃, and the total extraction time for a single extraction was set to 30 min. During ultrasonic extraction, the centrifuge tube was removed every 5 min, vortexed at 2000 rpm for 30 s, and then returned to the ultrasonic device for further extraction. The water level in the ultrasonic device was higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer. A crude extract was obtained after extraction.

[0052] S300. Remove the crude extract from the ultrasonic device and cool it to 25°C at room temperature. Then, centrifuge it in a high-speed centrifuge at 8000 rpm for 5 minutes. After centrifugation, gently remove the centrifuge tube, avoiding disturbing the bottom solid precipitate. Use a pipette to aspirate the supernatant, placing the aspirate 1 cm below the liquid surface to avoid aspirating the bottom solid precipitate and affecting subsequent chromatographic detection. Filter the obtained supernatant through a nylon organic phase filter membrane with a pore size of 0.22 μm. Discard the first 1 mL of filtrate during filtration, and collect the subsequent filtrate in a brown sample vial. Tightly cap the vial and prepare it for analysis.

[0053] S400. Four commonly used vulcanization accelerators for tire rubber were selected as detection targets: 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide. Appropriate amounts of each standard were accurately weighed, dissolved in chromatographically pure methanol, and diluted to the mark on a volumetric flask to prepare a single-component standard stock solution with a mass concentration of 1000 mg / L. Appropriate amounts of each single-component standard stock solution were transferred to the same volumetric flask, mixed thoroughly, and then serially diluted with blank matrix extract to prepare matrix-matched standard working solutions with six concentration gradients: 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. Blank matrix extract is obtained by processing a vulcanized rubber sample of the same type without the target vulcanization accelerator according to the steps S100 to S300 above, and is used to counteract the interference of matrix effect on quantitative results; the single-component standard stock solution is sealed and stored in a light-protected environment at -20°C.

[0054] S500. Inject the standard working solution and the test solution separately into the high-performance liquid chromatograph (HPLC) for detection. A reversed-phase C18 column was used for separation. The column length was 250 mm, the inner diameter was 4.6 mm, and the packing particle size was 5 μm. The mobile phase consisted of an organic phase and an aqueous phase. The organic phase was acetonitrile, and the aqueous phase was a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode was used. The elution program was set as follows: from 0 min to 5 min, the organic phase volume percentage increased from 20% to 40%; from 5 min to 12 min, the organic phase volume percentage increased from 40% to 60%; from 12 min to 18 min, the organic phase volume percentage increased from 60% to 80%; from 18 min to 20 min, the organic phase volume percentage remained at 80%; from 20 min to 22 min, the organic phase volume percentage decreased to 20%, and then the system was held for 3 min to equilibrate. The elution flow rate of the mobile phase was set to 1.0 mL / min, the column temperature was controlled at 30℃, the detection wavelength of the UV detector was set to 254 nm, and the injection volume for a single injection was 20 μL. Before injection, the chromatographic system was equilibrated for at least 30 min using the initial mobile phase ratio, and injections were performed sequentially after the baseline stabilized. After every 10 samples were analyzed, a standard working solution of intermediate concentration was inserted for verification to confirm the response stability of the chromatographic system and ensure the accuracy of the quantitative results for batch samples. The calibration relationship was established using the external standard method, with the concentration of the target analyte in each concentration of the standard working solution as the x-axis and the peak area of ​​the corresponding chromatographic peak as the y-axis, and a linear fit was performed to obtain the calibration curve. The test solution was injected and measured under the same chromatographic conditions as the standard working solution. The obtained peak area of ​​the target analyte was substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The content of residual accelerator in the rubber sample was then calculated by combining the sample weight and extraction volume. The same sample was measured twice in parallel, and the arithmetic mean of the two results was taken as the final result when the relative deviation of the two results did not exceed 5%.

[0055] To clearly compare the differences in core parameters and actual detection results between the various embodiments and comparative examples, the average spiked recoveries of the core process parameters and the four target accelerators for each group are summarized in the following table:

[0056] project Example 1 Example 2 Example 3 Comparative Example methanol-acetonitrile volume ratio 2:1 1:1 3:1 2:1 2-Carboxyethylphosphine mass volume concentration 1.0% 2.0% 0.3% 0 Phosphate buffer system none Yes, pH 7.0 Yes, pH 6.5 none Extraction temperature 45℃ 55℃ 35℃ 45℃ Ultrasonic power 300W 400W 200W 300W Extraction time 30min 40min 15min 30min Average spiked recovery of four accelerators 90.7% 93.2% 87.4% 58.3%

[0057] In summary, the determination methods corresponding to the three embodiments all have good extraction efficiency and detection accuracy. Compared with the comparative example, the extraction system containing a mild reducing agent can effectively improve the release efficiency of bound accelerators in vulcanized rubber. The methods can operate stably under different parameter combinations, indicating that the technical solution has a wide range of applicable parameters and good operational tolerance.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-performance liquid chromatography method for determining the content of residual accelerators in tire vulcanized rubber, characterized in that, The method includes: S100. Take the test part of the tire vulcanized rubber, remove surface contaminants, cut it into the set particle size, mix it well, weigh the set mass of the test sample and place it in a sealed extraction container. S200. Add a mixed extraction solvent containing a mild reducing agent to the extraction container, vortex mix, and then perform constant temperature ultrasonic extraction. The mild reducing agent reacts with the disulfide bonds in the rubber crosslinking network to break the disulfide bond crosslinking points, loosen the three-dimensional network structure to release the bound vulcanization accelerator encapsulated inside, and obtain the crude extract. S300. After cooling the crude extract to room temperature, centrifuge and let it settle. Take the supernatant and filter it through an organic phase filter membrane. Discard the initial filtrate and collect the subsequent filtrate as the test solution. S400. Weigh out various vulcanization accelerator standards, dissolve and dilute them with methanol to prepare single-component standard stock solutions, transfer each single-component standard stock solution to mix, and then dilute with blank matrix extract to prepare matrix-matched standard working solutions of a series of concentrations. S500. Inject the standard working solution and the test solution into the high performance liquid chromatograph, separate them using a reversed-phase C18 column, collect the signal using an ultraviolet detector, establish a calibration curve based on the concentration and peak area of ​​the standard working solution, and obtain the content of residual accelerator in the rubber sample.

2. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S100, the test area is selected as the vulcanized rubber layer of the tire tread. After removing the dust and release agent attached to the surface, it is sheared and crushed. The maximum particle size of the rubber particles does not exceed 2 mm. The crushed sample is placed in a brown sample bottle and mixed evenly. The sample weight is controlled within the range of 0.4 g to 0.6 g. The extraction container is a polypropylene centrifuge tube with a sealed cap and a volume of 50 mL. The sample to be tested is placed at the bottom of the centrifuge tube before the extraction solvent is added. The crushing operation is carried out at room temperature. The crushed particle size of the same batch of test samples is kept consistent. After weighing, the centrifuge tube is immediately sealed.

3. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S200, the basic component of the mixed extraction solvent is a mixed solution of methanol and acetonitrile, with a volume ratio of methanol to acetonitrile of 1:1 to 3:1; the mild reducing agent is tris-2-carboxyethylphosphine, with a mass-volume concentration of 0.3% to 2.0% in the mixed extraction solvent, and the added volume of the mixed extraction solvent is 20 mL, corresponding to a liquid-to-solid ratio of 40 mL / g for every 0.5 g of sample to be tested; the mild reducing agent is pre-added to the methanol phase and thoroughly stirred to dissolve, and then mixed evenly with acetonitrile according to the set ratio. The prepared extraction solvent containing the reducing agent is put into use within 2 hours, and both the preparation and extraction processes are conducted away from direct sunlight; after controlled dissociation extraction, a crude extract is obtained.

4. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S200, the temperature of the isothermal ultrasonic extraction is controlled within the range of 35°C to 55°C, the output power of the ultrasonic device is 200W to 400W, and the extraction time for a single extraction is set to 15min to 40min. Before the ultrasonic extraction begins, the centrifuge tube is vortexed for 1min at a rotation speed of 2000r / min. During the ultrasonic extraction process, the centrifuge tube is removed every 5min and vortexed for 30s before being returned to the ultrasonic device to continue extraction. The water bath level of the ultrasonic device is higher than the extraction solvent level in the centrifuge tube to ensure uniform heat transfer.

5. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S200, a phosphate buffer component, prepared from sodium dihydrogen phosphate and disodium hydrogen phosphate, is added to the mixed extraction solvent, and the final concentration in the mixed extraction solvent is 10 mmol / L. The buffer component is pre-dissolved in ultrapure water to prepare a stock solution, which is then added to the mixed extraction solvent. After thorough mixing, the pH value of the mixed extraction solvent is adjusted to the range of 6.5 to 7.5, and then a reducing agent is added and stirred to dissolve.

6. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S300, the crude extract is cooled to room temperature of 25°C and then centrifuged in a high-speed centrifuge at a speed of 8000 r / min for 5 min. After centrifugation, the centrifuge tube is removed and the supernatant is aspirated with a pipette at a depth of 1 cm below the liquid surface to avoid aspirating the bottom solid precipitate. The organic phase filter membrane is made of nylon with a pore size of 0.22 μm. The first 1 mL of initial filtrate is discarded during filtration, and the subsequent filtrate is collected and placed in a brown sample vial. The vial is then tightly capped and ready for instrumental analysis.

7. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S400, the vulcanization accelerator standard includes 2-mercaptobenzothiazole, dibenzothiazole disulfide, tetramethylthiuram disulfide, and N-cyclohexyl-2-benzothiazole sulfenamide; the single-component standard stock solution has a mass concentration of 1000 mg / L, is dissolved in chromatographically pure methanol and diluted to the mark of a volumetric flask; the blank matrix extract is obtained by processing the same type of vulcanized rubber sample without the target vulcanization accelerator according to steps S100 to S300; The standard working solution is set with six concentration gradients: 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. The standard stock solution is stored in a light-protected environment at -20°C.

8. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S500, the reversed-phase C18 column has a length of 250 mm, an inner diameter of 4.6 mm, and a packing particle size of 5 μm. The mobile phase consists of an organic phase and an aqueous phase. The organic phase is acetonitrile, and the aqueous phase is a 0.1% (v / v) aqueous solution of acetic acid. A gradient elution mode is used, and the elution program is set as follows: from 0 min to 5 min, the volume percentage of the organic phase increases from 20% to 40%; from 5 min to 12 min, the volume percentage of the organic phase increases from 40% to 60%; from 12 min to 18 min, the volume percentage of the organic phase increases from 60% to 80%; from 18 min to 20 min, the volume percentage of the organic phase remains at 80%; from 20 min to 22 min, the volume percentage of the organic phase decreases to 20%, and then the system is held for 3 min to equilibrate.

9. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S500, the elution flow rate of the mobile phase is set to 1.0 mL / min, the column temperature of the chromatographic column is controlled at 30℃, the detection wavelength of the ultraviolet detector is set to 254 nm, the injection volume of a single injection is 20 μL, and the chromatographic system is equilibrated for at least 30 min using the initial ratio of the mobile phase before injection. After the baseline is stable, samples are injected sequentially for detection. After every 10 samples are detected, a standard working solution of intermediate concentration is inserted for verification to confirm the response stability of the chromatographic system.

10. The high-performance liquid chromatography method for determining the content of residual accelerator in tire vulcanized rubber according to claim 1, characterized in that, In step S500, the calibration relationship is established using the external standard method. The concentration of the target analyte in each concentration standard working solution is used as the abscissa, and the peak area of ​​the corresponding chromatographic peak is used as the ordinate. A linear fit is performed to obtain the calibration curve. The test solution is injected and measured under the same chromatographic conditions as the standard working solution. The obtained peak area of ​​the target analyte is substituted into the calibration curve to obtain the concentration of the target analyte in the test solution. The same sample is measured twice in parallel. When the relative deviation between the two measurements does not exceed 5%, the arithmetic mean is taken as the final result.

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