Detection method of monomer content in Tritan plastic

Abstract

The present invention discloses a method for detecting the content of monomer substances in Tritan plastic. The method comprises: preparing a standard working solution with a series of concentrations, preparing a sample test solution, and detecting the monomer substance content of the sample solution by gas chromatography-tandem mass spectrometry; the sample pretreatment and sample test solution preparation comprising: dissolving the sample with a dissolving solvent, first precipitating it with a main precipitant, taking the supernatant and then precipitating it with an auxiliary precipitant, filtering, drying, and re-dissolving. The present invention utilizes a dissolution-precipitation-precipitation method as a sample pretreatment operation, which can achieve excellent results. Hexafluoroisopropanol is used to dissolve Tritan plastic, and any residual monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol is completely extracted. After precipitation with methanol as the main precipitant, acetonitrile is used as an auxiliary precipitant to almost completely remove high-molecular-weight polymers, protecting the chromatography-mass spectrometry system from contamination.

Description

Technical Field

[0001] The present invention relates to the field of plastic detection, and in particular to a method for detecting the content of monomer substances in Tritan plastic. Background Art

[0002] Tritan, short for Tritan Copolyester, is a new generation of heat-resistant copolyester developed by Eastman Chemical. Eastman Chemical Company launched this new copolyester in 2008. Tritan is an alcohol-modified poly(ethylene terephthalate-co-1,4-cyclohexylene dimethylene terephthalate) (modified PCT), but it differs structurally from standard PCTG, with a more unique unit structure. While Tritan is approved by the US FDA as a food contact material, its synthetic monomer, 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), differs from the monomer specified in US 21CFR 177.2420, and therefore does not comply with this sanitation standard. my country's October 2011 announcement, "Announcement on the List of 107 Resins Including Polybutylene Adipamide for Use in Food Packaging Materials (Ministry of Health Announcement No. 23 of 2011)," permitted the use of modified PCT in food packaging materials and stipulated a specific migration limit of 2,2,4,4-tetramethyl-1,3-cyclobutanediol of no more than 5 mg / kg. The 2017 new national standard, GB 4806.6-2016, "National Food Safety Standard for Plastic Resins for Food Contact," also allows the use of modified PCT in food contact materials, but stipulates a specific migration limit of no more than 5 mg / kg and a temperature limit of no more than 100°C.

[0003] Currently, detection methods for 2,2,4,4-tetramethyl-1,3-cyclobutanediol (2,2,4,4-tetramethyl-1,3-cyclobutanediol) are significantly lagging behind, and there are gaps in the testing and regulation of the hygienic safety performance of products made from this material. Literature reports have examined the migration of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic using GC-FID, GC-MS, or LC-MS / MS, but research on residual amounts is limited. Furthermore, Tritan plastic contains numerous impurities, particularly large polymers, which interfere with the detection of 2,2,4,4-tetramethyl-1,3-cyclobutanediol residues and damage the chromatography-mass spectrometry system and instrumentation. Therefore, establishing a method for determining 2,2,4,4-tetramethyl-1,3-cyclobutanediol residues in Tritan plastic and applying this method to scientifically and effectively test the toxicity of products such as baby bottles and drinking cups made from modified PCT is urgently needed for safety testing of modified PCT products. Summary of the Invention

[0004] The present invention provides a method for detecting the content of monomer substances in Tritan plastic, which comprises the following steps: preparing a standard working solution with a series of concentrations, preparing a sample test solution, and detecting the monomer substance content of the sample solution by gas chromatography-tandem mass spectrometry;

[0005] The monomer substance is 2,2,4,4-tetramethyl-1,3-cyclobutanediol;

[0006] The preparation of the sample test solution comprises: accurately weighing a shredded Tritan plastic sample, adding hexafluoroisopropanol to dissolve the sample, adding methanol dropwise after the sample is completely dissolved, shaking while adding, and diluting the volume to the calibration mark with methanol after the polymer is completely precipitated; thoroughly shaking the solution in the bottle and letting it stand, filtering the supernatant, and then adding acetonitrile dropwise, diluting the volume to the calibration mark with acetonitrile after precipitation is complete, filtering, concentrating to dryness, and re-dissolving with acetonitrile for testing;

[0007] Chromatographic conditions: 6% cyanopropyl / phenyl 94% dimethylpolysiloxane capillary column; injection port temperature 250°C; nitrogen carrier gas, flow rate 1.0-1.5 mL / min; splitless injection; injection volume 0.5-2 μL; temperature program: 90°C for 0 min, then increase to 240-260°C at 10-15°C / min, and hold for 1-2 min.

[0008] Mass spectrometry conditions: EI source; ion source temperature; quadrupole temperature; selected ion monitoring (SIM); quantitative ion; qualifier ions; 57 and 43.

[0009] Preferably, the filtration is performed using a 0.22 μm filter membrane.

[0010] Preferably, the shredded Tritan plastic sample is a Tritan plastic sample cut into 4-6 mm×4-6 mm.

[0011] Preferably, the specification of the 6% cyanopropyl / phenyl 94% dimethylpolysiloxane capillary chromatographic column is 30m×0.25mm×1.4μm.

[0012] Preferably, the sample test solution is prepared as follows: 1.0 g of a Tritan plastic sample cut into 5 mm × 5 mm is weighed and placed in a clean 25 mL volumetric flask, 10 mL of hexafluoroisopropanol is added, and the sample is placed in a vortex shaker for shaking and dissolving; after the sample is completely dissolved, methanol is added dropwise to the volumetric flask, while shaking the volumetric flask while adding, and after the polymer is completely precipitated, the volume is adjusted to the calibration mark with methanol; the solution in the bottle is fully shaken and allowed to stand, 10 mL of the supernatant is taken and filtered through a 0.22 μm filter membrane in a 20 mL colorimetric tube to obtain 10 mL of sample solution, and then acetonitrile is added dropwise. After precipitation is complete, the volume is adjusted to the mark with acetonitrile, filtered through a 0.22 μm filter membrane into a test tube, concentrated to dryness in a nitrogen blower, and then re-dissolved with 1 mL of acetonitrile for GC-MS testing.

[0013] Preferably, the concentrations of the standard working solutions are 0.020 mg / L, 0.040 mg / L, 0.080 mg / L, 0.10 mg / L and 0.20 mg / L, respectively.

[0014] Preferably, the solvent of the standard working solution is a mixture of hexafluoroisopropanol and methanol.

[0015] Advantages of the present invention:

[0016] 1. The present invention utilizes a dissolution-precipitation-precipitation method as a sample pretreatment operation, which can achieve excellent results. Not only can hexafluoroisopropanol be used to dissolve Tritan plastic and completely extract the possible residual monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol, but also high molecular weight polymers can be almost completely removed by precipitation, thus protecting the chromatography-mass spectrometry system from contamination.

[0017] 2. In addition to using methanol as the main precipitant for precipitation, the present invention filters the solution using a 0.22 μm filter membrane and then uses acetonitrile as an auxiliary precipitant to precipitate again, so as to fully precipitate the macromolecular polymer and better protect the chromatography-mass spectrometry system.

[0018] 3. The present invention reduces the noise impact of the detection system, further lowering the detection limit by 1 to 2 orders of magnitude, achieving higher accuracy and sensitivity. GC-MS was used to separate the components of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic using a DB-624 (30m×0.25mm×1.4μm) capillary column, with scanning performed in selected ion monitoring (SIM) mode. The results showed that 2,2,4,4-tetramethyl-1,3-cyclobutanediol was well separated under the selected chromatographic conditions, with good linearity within the concentration range of 0.020 to 0.20 mg / L. The limit of detection was 0.01 mg / L, the limit of quantification was 0.020 mg / L, the spiked recoveries ranged from 91.5% to 109.7%, and the relative standard deviations were all below 8.3%, indicating that the present method has good recovery and precision. The established gas chromatography-tandem mass spectrometry (GC-MS) method not only has the advantages of good separation effect, high sensitivity and good selectivity, but also has the advantages of rapidity and low detection limit, and has a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the total ion current chromatogram of 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0020] Figure 2 This is the standard curve of 2,2,4,4-tetramethyl-1,3-cyclobutanediol. DETAILED DESCRIPTION

[0021] The following examples are provided to further illustrate the present invention, but are not intended to limit the present invention.

[0022] Example 1:

[0023] In order to better determine the content of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic, the dissolution-precipitation (main precipitant)-precipitation (auxiliary precipitant) method was used to pre-treat the Tritan plastic samples. Based on GC-MS technology, a detection method for the content of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic was established, which will provide a certain research basis for the safety and potential risks of Tritan plastic in the future.

[0024] 1 Reagents and materials

[0025] 1.1 Reagents

[0026] Hexafluoroisopropanol, methanol, and acetonitrile were all chromatographically pure.

[0027] 1.2 Standards

[0028] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol, purity ≥98%, or standard substances certified by the state and awarded with standard substance certificates.

[0029] 1.3 Preparation of standard solution

[0030] (1) 2,2,4,4-Tetramethyl-1,3-cyclobutanediol standard stock solution (1000 mg / L): Accurately weigh 10 mg (accurate to 0.1 mg) of 2,2,4,4-tetramethyl-1,3-cyclobutanediol standard into a 10 mL brown volumetric flask, dilute to the mark with methanol, and store in a sealed container at 4°C in the dark. The shelf life is 6 months.

[0031] (2) 2,2,4,4-Tetramethyl-1,3-cyclobutanediol standard intermediate solution (10 mg / L): Accurately pipette 0.1 mL of the 2,2,4,4-tetramethyl-1,3-cyclobutanediol standard stock solution prepared in step (1) above into a 10 mL brown volumetric flask, dilute to the mark with a mixed solution of hexafluoroisopropanol and methanol (1:1, v:v), and store in a sealed container at 4°C in the dark. The shelf life is 3 months.

[0032] (3) Preparation of standard working solution.

[0033] Before use, the standard intermediate solution was diluted stepwise with a mixed solution of hexafluoroisopropanol + methanol (1:1, v:v) to prepare standard working solutions with concentrations of 0.020 mg / L, 0.040 mg / L, 0.080 mg / L, 0.10 mg / L, and 0.20 mg / L.

[0034] 2. Sample pretreatment

[0035] 2.1 Sample pretreatment

[0036] Weigh approximately 2.00 to 4.00 g of a Tritan plastic sample, cut the sample into 5 mm x 5 mm pieces with scissors, and mix thoroughly.

[0037] 2.2 Preparation of sample solution

[0038] Weigh 1.0 g (accurate to 0.1 mg) of the shredded Tritan plastic sample obtained in 2.1 and place it in a clean 25 mL volumetric flask. Add 10 mL of hexafluoroisopropanol and place it in a vortex shaker to dissolve. After the sample is completely dissolved, add methanol dropwise to the volumetric flask, shaking the volumetric flask while adding. After the polymer is completely precipitated, dilute to the mark with methanol (primary precipitant). After shaking the solution in the bottle thoroughly and letting 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 (precipitant) dropwise. After precipitation is complete, dilute to the mark with acetonitrile, and filter all the obtained solutions with a 0.22 μm filter membrane into a test tube. Concentrate to dryness in a nitrogen blower, then reconstitute with 1 mL of acetonitrile and test by GC-MS.

[0039] 3. Preparation of blank sample solution

[0040] Prepare a method blank solution as described in step 2.2 above, except that the Tritan plastic is omitted.

[0041] 4 Instrument conditions

[0042] 4.1 Chromatographic conditions

[0043] Chromatographic column: 6% cyanopropyl / phenyl 94% dimethylpolysiloxane capillary column, 30m×0.25mm×1.4μm; inlet temperature: 250℃; carrier gas: nitrogen, flow rate: 1.5mL / min; injection mode: splitless; injection volume: 1μL; heating program: 90℃ for 0min, increase to 250℃ at 15℃ / min, and hold for 1min.

[0044] 4.2 Mass spectrometry conditions

[0045] Ion source: EI source; ion source temperature: 230°C; quadrupole temperature: 150°C; mass spectrometry scanning mode: selected ion monitoring mode (SIM); quantitative ions: 72; qualitative ions: 57, 43.

[0046] 5 Qualitative determination

[0047] According to the above instrument reference conditions, the sample solution and the standard working solution are measured respectively. If the retention time deviation of the corresponding chromatographic peaks in the sample solution and the standard solution is within the range of ±0.5%, and the selected ions all appear in the mass spectrum of the sample solution after subtracting the background, and the signal-to-noise ratio is not less than 3, the relative abundance of the qualifier ions in the mass spectrum of the sample solution is compared with the relative abundance of the qualifier ions corresponding to the spectrum of the standard solution with similar concentration, and the deviation does not exceed the range specified in Table 1, then it can be judged that the corresponding target substance to be measured exists in the sample solution. The total ion current chromatogram of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is as follows Figure 1 shown.

[0048] Table 1 Maximum allowable deviation of ion relative abundance ratio

[0049]

[0050] 6 Quantitative determination

[0051] According to the instrument reference conditions listed above, the sample solution and the blank sample solution were respectively injected into the gas chromatography-mass spectrometer to obtain the chromatographic peak area of ​​each target substance to be measured, and the concentration of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in the sample solution and the blank sample solution was calculated according to the standard working curve.

[0052] 7. Linear relationship of standard working curve, detection limit, quantification limit and recovery rate

[0053] According to the optimized determination conditions, the standard working solution (0.020mg / L~0.20mg / L) was tested, with the concentration of 2,2,4,4-tetramethyl-1,3-cyclobutanediol in the Tritan plastic sample as the horizontal axis, expressed in mg / L, and the corresponding peak area average as the vertical axis. The standard working curve was drawn to obtain the linear equation and correlation coefficient. The test results showed that there was a good linear relationship between its concentration and the response value (see Figure 2 ) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol, all exhibited linearity exceeding 0.995, with limits of detection of 0.01 mg / L and limits of quantification of 0.020 mg / L, effectively meeting the testing requirements. Blank samples, devoid of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, were pretreated to prepare target concentrations of 0.020 mg / L, 0.10 mg / L, and 0.15 mg / L. Recovery and precision tests were conducted for each concentration, with six replicates performed. The results indicate that the spiked recoveries for 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic samples ranged from 91.5% to 109.7%, with relative standard deviations below 8.3%, demonstrating excellent recovery and precision.

[0054] Example 2: Selection of sample dissolving solvent

[0055] The specific steps were the same as in Example 1, except that the hexafluoroisopropanol in step 2.2 was replaced with dichloromethane, chloroform, toluene, or benzene. The solubility of hexafluoroisopropanol, dichloromethane, chloroform, toluene, and benzene in Tritan plastic was investigated. Comparative testing revealed that only hexafluoroisopropanol completely dissolved the target material, making it the optimal solvent for dissolving Tritan plastic.

[0056] Example 3: Selection of the best precipitant

[0057] The specific steps are as in Example 1, except that the main precipitant in step 2.2 is replaced with methanol, dichloromethane, n-hexane, tetrahydrofuran, ethyl acetate, acetone, methyl tert-butyl ether, ethanol, acetonitrile, or butanone, and no auxiliary precipitant is added. The precipitation performance of methanol, dichloromethane, n-hexane, tetrahydrofuran, ethyl acetate, acetone, methyl tert-butyl ether, ethanol, acetonitrile, and butanone after Tritan material is dissolved in hexafluoroisopropanol was systematically investigated. After experimentation, it was found that dichloromethane and n-hexane had no precipitation effect, while methanol and acetonitrile had the best precipitation effect. Therefore, methanol was selected as the main precipitating agent and acetonitrile as the auxiliary precipitating agent.

[0058] Example 4: Optimization of injection port temperature

[0059] The specific steps are the same as those in Example 1, except that the injection port temperature in step 4.1 is changed to five different injection port temperatures of 200°C, 230°C, 250°C, 280°C, and 300°C.

[0060] The boiling point of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is 220.3℃. The effects of five different injection port temperatures on the peak area response of the target compound were investigated. The optimization results of the injection port temperature are as follows: the peak area of ​​the target compound increases with the increase of the injection port temperature. When the injection port temperature reaches 250℃, the response reaches the maximum value. Thereafter, the peak area response increases little with the increase of the injection port temperature. Considering comprehensive factors such as instrument energy consumption, the injection port temperature is finally set to 250℃.

[0061] Example 5: Selection of injection mode

[0062] The specific steps are the same as those in Example 1, except that the injection mode in step 4.1 is changed to splitless injection or split injection (split ratio 1:1, 2:1, 5:1, 10:1 or 20:1).

[0063] The peak elution and response of chromatographic samples were investigated for the same concentration using splitless and split injection modes (split ratios of 1:1, 2:1, 5:1, 10:1, and 20:1). On-line measurements revealed that the peak response of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was the best when using splitless injection. In split mode, increasing the split ratio (split flow rate)—equivalent to an increase in total flow rate—shortens the time between sample injection and column entry, reducing peak broadening during transport and narrowing the initial band width on the column. However, increasing the split ratio decreases the amount of sample entering the column, resulting in a corresponding decrease in the peak area response of the target. After comprehensive analysis and comparison of the on-line results, the splitless injection mode was selected with an injection volume of 1 μL to ensure optimal response at low target concentrations.

[0064] Example 6: Selection of chromatographic column

[0065] The specific steps are the same as those in Example 1, except that the chromatographic column in step 4.1 is replaced with a relatively weakly polar DB-5MS (30m×0.25mm×0.25μm) or a highly polar HP-INNOWax (30m×0.25mm×0.25μm) capillary chromatographic column.

[0066] When selecting a chromatographic column, our primary considerations were: a) good peak shape for accurate quantification; and b) minimal interference from the sample matrix. In this method, 2,2,4,4-tetramethyl-1,3-cyclobutanediol is the sole target, and simultaneous detection of multiple targets is not necessary. Therefore, theoretically, polar, nonpolar, and moderately polar columns can all be used. A comparison of the weakly polar DB-5MS, moderately polar DB-624, and highly polar HP-INNOWax capillary columns revealed that the DB-624 (30 m × 0.25 mm × 1.4 μm) column provided the best separation.

[0067] Example 7: Selection of chromatographic column flow rate

[0068] The specific steps are the same as those in Example 1, except that the flow rate in step 4.1 is changed to 0.5 mL / min, 1.0 mL / min, 1.5 mL / min, 2.0 mL / min, 3.0 mL / min or 4.0 mL / min.

[0069] According to the rate theory equation, the molecular longitudinal diffusion term is inversely proportional to the carrier gas flow rate, while the mass transfer resistance term is directly proportional to the carrier gas flow rate. Therefore, there must be an optimal flow rate that minimizes plate height and maximizes column efficiency. After fixing the column (DB-624 capillary column) and column temperature, and maintaining other experimental conditions, the carrier gas flow rate was varied (0.5 mL / min, 1.0 mL / min, 1.5 mL / min, 2.0 mL / min, 3.0 mL / min, and 4.0 mL / min). It was found that lower column flow rates resulted in a later peak elution time, while higher flow rates resulted in an earlier peak elution time, resulting in a lack of baseline separation between the two isomers of 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Column flow rates that are too high or too low can affect column efficiency, with a flow rate of 1.5 mL / min being the optimal value.

[0070] This method uses hexafluoroisopropanol, dichloromethane, chloroform, toluene, and benzene on Tritan plastic samples. It was found that only hexafluoroisopropanol has a good dissolution effect on Tritan plastic. At the same time, methanol, dichloromethane, n-hexane, tetrahydrofuran, ethyl acetate, acetone, methyl tert-butyl ether, ethanol, acetonitrile, and butanone are used as precipitants. It was found that methanol, ethanol, and acetonitrile have better precipitation effects. When methanol is used as the main precipitant and acetonitrile is used as the auxiliary precipitant, the precipitation effect is more obvious and more uniform.

[0071] 2,2,4,4-tetramethyl-1,3-cyclobutanediol in Tritan plastic was separated by GC-MS using a DB-624 (30m×0.25mm×1.4μm) capillary column in selected ion monitoring (SIM) mode. The results showed that 2,2,4,4-tetramethyl-1,3-cyclobutanediol was separated well under the selected chromatographic conditions, with good linearity over the concentration range of 0.020 to 0.20 mg / L. The limits of detection were 0.01 mg / L and the limits of quantification were 0.020 mg / L. Spiked recoveries ranged from 91.5% to 109.7%, with relative standard deviations (RSDs) below 8.3%, demonstrating the method's excellent recovery and precision.

Claims

1. A method for detecting the content of monomeric substances in Tritan plastic, characterized in that: The following steps are involved: Prepare standard working solutions with a series of concentrations, prepare sample test solutions, and use gas chromatography-tandem mass spectrometry to detect the monomer content of the sample solutions; The monomer substance is 2,2,4,4-tetramethyl-1,3-cyclobutanediol; The sample test solution is prepared as follows: 1.0 g of a Tritan plastic sample cut into 5 mm × 5 mm is weighed and placed in a clean 25 mL volumetric flask, 10 mL of hexafluoroisopropanol is added, and the sample is placed in a vortex shaker for shaking and dissolving; after the sample is completely dissolved, methanol is added dropwise to the volumetric flask while shaking the volumetric flask while adding, and after the polymer is completely precipitated, the volume is adjusted to the calibration mark with methanol; the solution in the flask is fully shaken and allowed to stand, 10 mL of the supernatant is taken and filtered through a 0.22 μm filter membrane in a 20 mL colorimetric tube to obtain 10 mL of sample solution, and acetonitrile is then added dropwise. After precipitation is complete, the volume is adjusted to the scale with acetonitrile, filtered through a 0.22 μm filter membrane into a test tube, concentrated to dryness in a nitrogen blower, and then re-dissolved with 1 mL of acetonitrile for GC-MS testing.

2. The detection method according to claim 1, wherein The gas chromatography-tandem mass spectrometry method detects: Chromatographic conditions: the chromatographic column is a 6% cyanopropyl / phenyl 94% dimethylpolysiloxane capillary column; the injection port temperature is 250°C; the carrier gas is nitrogen, with a flow rate of 1.0-1.5 mL / min; the injection mode is splitless; the injection volume is 0.5-2 μL; the temperature program is 90°C for 0 min, then rises to 240-260°C at 10-15°C / min, and holds for 1-2 min; mass spectrometry conditions: the ion source is an EI source; the ion source temperature is 230°C; the quadrupole temperature is 150°C; the mass spectrometry scanning mode is selected ion monitoring mode (SIM); the quantitative ion is 72; the qualitative ions are 57 and 43.

3. The detection method according to claim 2, characterized in that The specification of the 6% cyanopropyl / phenyl 94% dimethylpolysiloxane capillary chromatographic column is 30m×0.25mm×1.4μm.

4. The detection method according to claim 1, wherein The concentrations of the standard working solutions are 0.020 mg / L, 0.040 mg / L, 0.080 mg / L, 0.10 mg / L and 0.20 mg / L, respectively.

5. The detection method according to claim 1 or 4, characterized in that The solvent of the standard working solution is a mixture of hexafluoroisopropanol and methanol.

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