Method for determining content of methyl oleate plasticizer in recycled polyvinyl chloride plastic

Abstract

The application discloses a method for determining the content of methyl oleate plasticizer in regenerated polyvinyl chloride plastic, and utilizes a dissolution-precipitation (main precipitant)-precipitation (auxiliary precipitant) method to pretreat a regenerated polyvinyl chloride sample, and combines a GC-MS technology to detect the content of methyl oleate in the regenerated polyvinyl chloride, so that the problem that the solvent extraction method in the prior art cannot accurately measure the methyl oleate in the regenerated polyvinyl chloride plastic is solved, and the problem that the solution extracted by the solvent extraction method in the prior art will have polymer molecules precipitated and separated out subsequently, needs multiple purification treatments, leads to long processing time, low efficiency, and the problem that the residual polymer molecules are easy to pollute a chromatography-mass spectrometry system during detection is solved.

Description

Technical fields:

[0001] This invention relates to a method for determining the methyl oleate plasticizer content in recycled polyvinyl chloride plastics. Background technology:

[0002] Methyl oleate, also known as cis-9-octadecenoic acid methyl ester or 9-octadecenoic acid methyl ester, is a colorless to pale yellow oily liquid, insoluble in water but miscible with organic solvents such as ethanol and ether. It is an unsaturated higher fatty acid ester, commonly used as a plasticizer, resin toughening agent, rubber softener, water-resistant agent, and basic raw material for surfactants. With the rapid development of the plastics industry, plastics have replaced more and more other materials in people's lives. Polyvinyl chloride (PVC) is the world's largest-produced plastic, and plasticizers are the world's largest-produced and consumed plastic additives, used to improve the plasticity and processability of PVC. However, methyl oleate residues in PVC pose certain potential health hazards, such as causing endocrine disorders, and having some carcinogenic and teratogenic effects. Therefore, corresponding detection methods urgently need to be developed. Summary of the Invention:

[0003] The purpose of this invention is to provide a method for determining the methyl oleate plasticizer content in recycled polyvinyl chloride (PVC) plastics. The method utilizes a dissolution-precipitation (main precipitant)-precipitation (co-precipitant) method for pretreatment of recycled PVC samples, combined with GC-MS technology to detect the methyl oleate content in the recycled PVC. This method solves the problem that existing solvent extraction methods cannot accurately measure the methyl oleate content within recycled PVC plastics. It also addresses the issues of polymer molecule precipitation requiring multiple purification processes in existing solvent extraction methods, leading to long processing times, low efficiency, and contamination of the chromatographic-mass spectrometry system by residual polymer molecules during detection.

[0004] This invention is achieved through the following technical solutions:

[0005] A method for determining the methyl oleate plasticizer content in recycled polyvinyl chloride (PVC) plastic includes the following steps: GC-MS analysis is performed on the sample to be tested and a standard working solution to determine the methyl oleate content. The sample to be tested is prepared as follows: The recycled PVC plastic is pulverized, tetrahydrofuran is added and shaken until the recycled PVC plastic is completely dissolved, methanol is added dropwise while shaking until the polymer is completely precipitated, and the volume is adjusted to the calibration mark with methanol. The solution in the bottle is thoroughly shaken and allowed to stand. The supernatant is filtered through a 0.22 μm filter membrane, and acetonitrile is added dropwise to the filtrate until… After complete precipitation, dilute to the mark with acetonitrile, shake the solution in the bottle thoroughly, let it stand, take the supernatant and filter it through a 0.22 μm filter membrane, concentrate by nitrogen blowing, redissolve with acetonitrile, and then analyze; Chromatographic conditions: Column: DB-5MS capillary column; Temperature program: 100℃ for 1 min, then increase to 260-280℃ at a rate of 10-15℃ / min and hold for 1-2 min; Injector temperature: 280℃; Carrier gas: Nitrogen, flow rate: 1.0-1.5 mL / min; Injection volume: 0.5-2 μL; Injection method: Split injection, split ratio 2:1;

[0006] Mass spectrometry conditions: Ion source: Electron impact ion source (EI); Ion source temperature: 230℃; Quadrupole mass analyzer temperature: 150℃; Mass spectrometry scan mode: Selected ion monitoring mode (SIM); Quantitative ions: 264; Qualitative ions: 296, 97.

[0007] Recycled polyvinyl chloride plastic is crushed into small pieces of (4-6)mm × (4-6)mm.

[0008] A vortex oscillator was used to perform the oscillation and shaking.

[0009] The capillary column has dimensions of 30m × 0.25mm × 0.25μm.

[0010] The preparation of the standard working solution includes the following steps:

[0011] 1) Preparation of 1000 mg / L methyl oleate stock solution: Accurately weigh 10 mg of each methyl oleate standard (accurate to 0.1 mg) into a 10 mL volumetric flask, and dilute to the mark with methanol to obtain a methyl oleate stock solution with a concentration of 1000 mg / L.

[0012] 2) Preparation of 10 mg / L methyl oleate standard intermediate solution: Pipette 0.1 mL of methyl oleate stock solution into a 10 mL volumetric flask, and dilute to the mark with a 1:1 mixture of tetrahydrofuran and methanol to obtain a 10 mg / L methyl oleate standard intermediate solution.

[0013] 3) Preparation of standard working solutions: Accurately transfer 10 mg / L of methyl oleate standard intermediate solution and dilute it stepwise to prepare standard working solutions with concentrations of 0.050 mg / L, 0.080 mg / L, 0.10 mg / L, 0.20 mg / L and 0.50 mg / L.

[0014] This invention employs a "dissolution-precipitation method." First, tetrahydrofuran is added to dissolve the recycled polyvinyl chloride plastic, allowing polyvinyl chloride and methyl oleate to be extracted into the solvent. Then, the polyvinyl chloride polymer molecules are removed by the precipitation effect of adding excess methanol (the main precipitant) dropwise, resulting in a visible supernatant.

[0015] However, the inventors discovered that there are still tiny polymer molecules invisible to the naked eye in the supernatant, which interfere with the chromatographic response of methyl oleate during detection. At the same time, these polymer molecules gradually accumulate after long-term sample injection and analysis, and may also contaminate the chromatographic system.

[0016] Therefore, based on the "dissolution-precipitation method", a "dissolution-main precipitation-co-precipitation" method was established. Acetonitrile was selected as the co-precipitant, and deep purification was carried out through secondary precipitation to more thoroughly precipitate the small polymer molecules in the supernatant. The polymer molecules were then removed by filtration using a 0.22μm organic filter membrane, which further reduced the interference of the recycled polyvinyl chloride plastic matrix on the detection of methyl oleate, improved the chromatographic response of the target analyte, and protected the chromatographic system.

[0017] The beneficial effects of this invention are as follows:

[0018] 1) This invention utilizes a "dissolution-primary precipitation-auxiliary precipitation" method. First, tetrahydrofuran is added to dissolve the recycled polyvinyl chloride (PVC) plastic, allowing PVC and methyl oleate to be extracted into the solvent. Then, excess methanol (primary precipitant) is added dropwise to remove PVC polymer molecules. Acetonitrile (auxiliary precipitant) is then added for secondary precipitation, further precipitating the small polymer molecules in the supernatant. This method can more effectively extract methyl oleate from polynylon plastic. Furthermore, a 0.22 μm organic filter membrane is used to remove polymer molecules, further reducing the interference of the nylon plastic matrix on the detection of methyl oleate, improving the chromatographic response of the target analyte, and protecting the chromatographic system.

[0019] 2) This method is accurate, has little interference, reduces noise in the mass spectrometry detection system, further reduces the detection limit by 1-2 orders of magnitude, has higher accuracy and sensitivity, high analysis efficiency, and can meet higher detection requirements.

[0020] 3) This invention utilizes GC-MS to detect methyl oleate in recycled polyvinyl chloride plastics. Under the selected chromatographic conditions, the separation effect is good, and the linear relationship is good in the concentration range of 0.050-0.50 mg / L. The limit of detection is 0.02 mg / L, the limit of quantitation is 0.050 mg / L, and the spiked recovery rate is between 90.5% and 105%. The relative standard deviation is less than 7.7%, indicating that this method has good recovery rate and precision and has broad application prospects. Attached image description:

[0021] Figure 1 This is a chromatogram of methyl oleate in a specific embodiment, where the horizontal axis represents retention time and the vertical axis represents peak intensity. Detailed implementation method:

[0022] The following is a further description of the invention, but not a limitation thereof.

[0023] 1. Reagents and materials

[0024] 1.1 Reagents: Tetrahydrofuran, acetonitrile, and methanol, all of chromatographic grade.

[0025] 1.2 Standard Products

[0026] Methyl oleate, with a purity of ≥98%, or a standard substance that has been certified by the state and granted a standard substance certificate.

[0027] 1.3 Preparation of standard solutions:

[0028] 1.3.1 Methyl oleate standard stock solution (1000 mg / L): Accurately weigh 10 mg of each methyl oleate standard (accurate to 0.1 mg) into a 10 mL brown volumetric flask, dilute to the mark with methanol, and store in a sealed container protected from light at 4 °C for 6 months.

[0029] 1.3.2 Methyl oleate standard intermediate solution (10 mg / L): Accurately pipette 0.1 mL of methyl oleate standard stock solution (1.3.1) into a 10 mL brown volumetric flask, dilute to the mark with a mixture of tetrahydrofuran and methanol (1:1, v:v), and store in a sealed container at 4 °C protected from light for 3 months.

[0030] 1.3.3 Preparation of standard working solutions.

[0031] Before use, the standard intermediate solution was serially diluted with a mixture of tetrahydrofuran and methanol (1:1, v:v) to prepare standard working solutions with concentrations of 0.050 mg / L, 0.080 mg / L, 0.10 mg / L, 0.20 mg / L, and 0.50 mg / L.

[0032] 2 Sample Pretreatment

[0033] 2.1 Sample Pretreatment

[0034] Weigh 4.00g of recycled polyvinyl chloride sample, cut the sample into 5mm×5mm pieces with scissors, and mix well.

[0035] 2.2 Preparation of test solution

[0036] Weigh 1.0 g (accurate to 0.1 mg) of the shredded recycled polyvinyl chloride sample obtained in step 2.1 into a clean 25 mL volumetric flask, add 10 mL of tetrahydrofuran, and vortex to dissolve. After the sample is completely dissolved, add methanol dropwise to the volumetric flask while shaking. After the polymer is completely precipitated, dilute to the mark with methanol (the main precipitant). Shake the solution in the flask thoroughly and let it stand. Take 10 mL of the supernatant and filter it through a 0.22 μm filter membrane into a 20 mL colorimetric tube to obtain 10 mL of sample solution. Then add acetonitrile (a co-precipitant) dropwise. After precipitation is complete, dilute to the mark with acetonitrile and filter through a 0.22 μm filter membrane into a test tube. Concentrate to dryness using a nitrogen blower, then redissolve with 1 mL of acetonitrile. Analyze by GC-MS.

[0037] 3. Preparation of blank samples

[0038] Prepare a method blank sample according to the above procedure.

[0039] 4. Instrument conditions

[0040] 4.1 Chromatographic conditions

[0041] Chromatographic column: DB-5MS capillary column; temperature program: 100℃ held for 1 min, then increased to 260-280℃ at a rate of 10-15℃ / min and held for 1-2 min; injection port temperature: 280℃; carrier gas: nitrogen, flow rate: 1.0-1.5 mL / min; injection volume: 0.5-2 μL; injection method: split injection, split ratio 2:1;

[0042] 4.2 Mass Spectrometry Conditions

[0043] Ion source: EI source; Ion source temperature: 230℃; Quadrupole temperature: 150℃; Mass spectrometry scanning mode: Selected Ion Monitoring Mode (SIM); Quantitative ions: 264; Qualitative ions: 296, 97.

[0044] 5. Qualitative determination

[0045] According to the instrument reference conditions described above, the sample solution and the standard working solution were measured separately. If the retention time deviation of the corresponding chromatographic peaks in the sample solution and the standard solution is within ±0.5%, and in the mass spectrum of the sample solution after background subtraction, all selected ions appear and the signal-to-noise ratio is not less than 3, and the relative abundance of qualitative ions in the mass spectrum of the sample solution is compared with the relative abundance of qualitative ions in the mass spectrum of the standard solution with similar concentrations, and the deviation does not exceed the range specified in Table 1, then it can be determined that the corresponding target analyte exists in the sample solution.

[0046] Table 1 Maximum permissible deviation of relative ion abundance ratio

[0047] Maximum allowable deviation / % ±10 ±15 ±20 ±50

[0048] 6. Quantitative determination

[0049] According to the instrument reference conditions listed above, the sample solution and blank sample solution were injected into the gas chromatograph-mass spectrometer respectively to obtain the peak area of ​​each target analyte. The concentration of methyl oleate in the sample solution and blank sample solution was calculated based on the standard working curve.

[0050] Example 1: Selection of Pretreatment Experimental Conditions

[0051] 1. Selection of sample solvent

[0052] Weigh 1.0 g (accurate to 0.1 mg) of the shredded recycled PVC sample obtained in section 2.1 and place it in a clean 25 mL volumetric flask. Add 10 mL of tetrahydrofuran, methyl ketone, and cyclohexanone respectively to dissolve the PVC. It was found that only tetrahydrofuran had a good dissolving effect on the recycled PVC.

[0053] 2. Selection of precipitation solvent

[0054] After dissolving the above-mentioned recycled polyvinyl chloride sample in tetrahydrofuran, methanol, ethanol, butanone, acetone, and ethyl acetate were investigated as precipitants. It was found that methanol, ethanol, and acetonitrile had better precipitation effects, with methanol being the optimal one.

[0055] However, the inventors discovered that there are still tiny polymer molecules invisible to the naked eye in the supernatant, which interfere with the chromatographic response of methyl oleate during detection. At the same time, these polymer molecules gradually accumulate after long-term sample injection and analysis, and may also contaminate the chromatographic system.

[0056] Therefore, when methanol is used as the primary precipitant and acetonitrile as the co-precipitant, the precipitation effect is more obvious and uniform. Further purification allows for more thorough precipitation of small polymer molecules in the supernatant, and filtration using a 0.22μm organic filter membrane removes these polymer molecules, further reducing the interference of the recycled PVC plastic matrix on the detection of methyl oleate, improving the chromatographic response of the target analyte, and protecting the chromatographic system.

[0057] Example 2: Linearity of standard working curves, limit of detection, limit of quantitation, and recovery rate

[0058] Under optimized testing conditions, standard working solutions (0.050 mg / L to 0.50 mg / L) were analyzed. A standard working curve was plotted with the concentration of methyl oleate in the standard working solutions as the abscissa (in mg / L) and the average peak area as the ordinate, yielding the linear equation and correlation coefficient. The experimental results showed a good linear relationship between concentration and response value. The linearity of methyl oleate was consistently higher than 0.995, with a detection limit of 0.02 mg / L and a quantitation limit of 0.050 mg / L, which well met the requirements of the testing. Blank samples without methyl oleate in the background were pretreated to prepare three concentration levels of the target analyte: 0.050 mg / L, 0.20 mg / L, and 0.40 mg / L. Each level was measured six times individually, and recovery and precision tests were performed. The test results (see Table 2) show that the spiked recovery rate of methyl oleate in recycled polyvinyl chloride samples determined by this method is between 98.7% and 109%, and the relative standard deviation is less than 7.7%, indicating that this method has good recovery rate and precision.

[0059] Table 2 Precision and Recovery Rate

[0060]

Claims

1. A method for determining the methyl oleate plasticizer content in recycled polyvinyl chloride plastic, characterized in that, The steps include: GC-MS analysis of the sample to be tested and the standard working solution to determine the content of methyl oleate. The preparation method of the sample to be tested is as follows: crush the recycled polyvinyl chloride plastic into small pieces of (4~6) mm × (4~6) mm, add tetrahydrofuran and shake until the recycled polyvinyl chloride plastic is completely dissolved, add methanol dropwise while shaking until the polymer is completely precipitated, dilute to the mark with methanol, shake the solution in the bottle thoroughly and let it stand, take the supernatant and filter it through a 0.22 μm filter membrane, add acetonitrile dropwise to the filtrate until precipitation is complete, dilute to the mark with acetonitrile, shake the solution in the bottle thoroughly and let it stand, take the supernatant and filter it through a 0.22 μm filter membrane, concentrate by nitrogen blowing, redissolve with acetonitrile, and then test. Chromatographic conditions: Column: DB-5MS capillary column; Temperature program: 100℃ for 1 min, then increase to 260-280℃ at a rate of 10-15℃ / min and hold for 1-2 min; Injector temperature: 280℃; Carrier gas: Nitrogen, flow rate: 1.0-1.5 mL / min; Injection volume: 0.5-2 mL; Injection method: Split injection, split ratio 2:

1. Mass spectrometry conditions: Electron impact ion source, ion source temperature: 230℃; Quadrupole mass analyzer temperature: 150℃; Mass spectrometry scan mode: Ion monitoring mode selected; Quantitative ions: 264; Qualitative ions: 296, 97.

2. The method according to claim 1, characterized in that, A vortex oscillator was used to perform the oscillation and shaking.

3. The method according to claim 1, characterized in that, The capillary column has dimensions of 30 m × 0.25 mm × 0.25 μm.

4. The method according to claim 1, characterized in that, The preparation of the standard working solution includes the following steps: 1) Preparation of 1000 mg / L methyl oleate stock solution: Accurately weigh 10 mg of each methyl oleate standard into a 10 mL volumetric flask, and dilute to the mark with methanol to obtain a methyl oleate stock solution with a concentration of 1000 mg / L. 2) Preparation of 10 mg / L methyl oleate standard intermediate solution: Pipette 0.1 mL of methyl oleate stock solution into a 10 mL volumetric flask, and dilute to the mark with a 1:1 mixture of tetrahydrofuran and methanol to obtain a 10 mg / L methyl oleate standard intermediate solution. 3) Preparation of standard working solutions: Accurately transfer 10 mg / L of methyl oleate standard intermediate solution and dilute it stepwise to prepare standard working solutions with concentrations of 0.050 mg / L, 0.080 mg / L, 0.10 mg / L, 0.20 mg / L and 0.50 mg / L.

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