Determination of hydroquinone content in polystyrene plastics

Abstract

The present invention discloses a method for determining the content of hydroquinone in polystyrene plastic. The method comprises the following steps: firstly dissolving the polystyrene plastic with dichloromethane so that the hydroquinone and polystyrene are completely extracted into the solvent; then, dropping an excess of methanol as a main precipitant to precipitate the polymer molecules of the polystyrene; then adding ether as an auxiliary precipitant to perform secondary precipitation so that the small polymer molecules in the supernatant are more thoroughly precipitated; and finally, detecting the content of the hydroquinone in the polystyrene by using a GC-MS method. The method solves the problem that the solvent extraction method in the prior art cannot extract the hydroquinone substance inside the plastic, resulting in an inability to accurately measure the hydroquinone in the polystyrene plastic. The method also solves the problem that the solution extracted by the solvent extraction method in the prior art will subsequently have polymer molecules precipitated out and require multiple purification treatments, resulting in a long processing time and low efficiency, and the problem that the residual polymer molecules during detection are likely to contaminate the chromatography-mass spectrometry system.

Description

Technical field:

[0001] The present invention relates to the field of plastic product detection, and in particular to a method for determining the content of hydroquinone in polystyrene plastic. Background technology:

[0002] Hydroquinone, also known as hydroquinone, is a commonly used antioxidant, stabilizer, and polymerization inhibitor used in a variety of rubber and plastic resins. It is also a hazardous chemical harmful to the human body and is classified as a Class 3 carcinogen by the World Health Organization's International Agency for Research on Cancer. Polystyrene plastic is a colorless, transparent thermoplastic commonly used to make various disposable food containers and is widely used. Therefore, detecting the hydroquinone content in polystyrene plastic is of great significance for human health risk assessment. Prior art literature and relevant standards all use solvent extraction to extract hydroquinone from plastics, followed by GC-MS analysis after appropriate purification methods. However, these methods are unable to extract the hydroquinone content within the plastic, meaning they cannot meet the requirements for accurate quantification of hydroquinone in polystyrene plastics. Furthermore, the solution extracted using solvent extraction will subsequently precipitate polymer molecules, necessitating multiple purification treatments. This has the disadvantages of long processing times, low efficiency, and the potential for contamination of the chromatography-mass spectrometry system during detection.

[0003] There is an urgent need for a method that can efficiently, quickly and accurately detect hydroquinone in polystyrene plastics. Summary of the invention:

[0004] The present invention provides a method for determining the content of hydroquinone in polystyrene plastic. Based on a "dissolution-precipitation" method, a "dissolution-primary precipitation-auxiliary precipitation" method is established. First, dichloromethane is added to dissolve the polystyrene plastic. Then, an excess of methanol (primary precipitant) is added dropwise to precipitate polymer polystyrene molecules. Then, an auxiliary precipitant (ethyl ether) is used to completely remove the polymer polystyrene molecules. Finally, a GC-MS method is used to detect the content of hydroquinone in the polystyrene. The method solves the problem that the prior art using a solvent extraction method to extract hydroquinone from plastic for detection cannot accurately measure the hydroquinone in the polystyrene plastic. The method also solves the problem that the solution extracted by the solvent extraction method in the prior art will subsequently have polymer molecules precipitated and require multiple purification treatments, resulting in long processing time, low efficiency, and residual polymer molecules easily contaminating the chromatography-mass spectrometry system during detection.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for determining the content of hydroquinone in polystyrene plastic is characterized by comprising the following steps: respectively taking a sample to be tested and a standard working solution for GC-MS analysis to determine the content of hydroquinone, wherein the preparation method of the sample to be tested is as follows: crushing the polystyrene plastic, adding dichloromethane and shaking evenly until the polystyrene plastic is completely dissolved, adding methanol dropwise while shaking until no polymer continues to precipitate, adding ether dropwise to a bottle until precipitation is complete, and making up the volume to the calibration mark with ether, shaking the solution in the bottle thoroughly and letting it stand, taking the supernatant, concentrating it with nitrogen, and filtering it with an organic filter membrane; the GC-MS conditions are as follows: chromatographic column: HP-INNOWAX capillary column; heating program: initial temperature 80-120 ℃ and hold for 1 min, then increase the temperature at a rate of 5-25℃ / min to 200-260℃ and hold for 5-20 min; inlet temperature: 220-250℃; column flow rate: 0.8-1.5mL / min; injection volume: 0.5-2μL; injection mode: split injection, split ratio 10:1; ion source: electron impact ion source (EI); ion source temperature: 230℃; quadrupole mass analyzer temperature: 150℃; transfer line temperature: 250℃; ionization energy: 70eV; solvent delay: 4min; detection mode: selected ion; run time: 21min. Under full scan and selected ion conditions, the quantitative ion of hydroquinone was determined to be 110, and the qualitative ions were 83 and 53.

[0007] Preferably, the polystyrene plastic is crushed into small pieces of (4-6) mm x (4-6) mm.

[0008] Preferably, the organic filter membrane is 0.2 μm.

[0009] Preferably, the capillary column has a specification of 30 m×0.25 mm and a diameter of 0.25 μm.

[0010] The preparation of the standard working solution includes the following steps: using dichloromethane as the solvent, weighing 0.1 g of hydroquinone into a 10 mL volumetric flask, dissolving and diluting to the scale to prepare a standard stock solution, and then diluting the standard stock solution with a mixed solution of dichloromethane and methanol with a volume ratio of 1:1 to prepare standard working solutions with concentrations of 4.0, 2.0, 1.0, 0.5, and 0.2 mg / L, respectively.

[0011] The present invention adopts a "dissolution-precipitation method" in which dichloromethane is first added to dissolve the polystyrene plastic so that hydroquinone and polystyrene are extracted into the dichloromethane solvent. Then, the polystyrene polymer molecules are removed by precipitation by dropwise adding excess methanol (main precipitant) to obtain a supernatant.

[0012] However, the inventors found that tiny polymer molecules invisible to the naked eye still existed in the supernatant, forming a larger sample matrix solution background, which weakened the response of the target on the chromatography. At the same time, long-term sampling and analysis led to the accumulation of polymer molecules, which may also burden the chromatography system.

[0013] Therefore, the present invention further selects ether, water and heptane as co-precipitants for testing, and performs deep purification through secondary precipitation to more thoroughly precipitate the polymer small molecules in the supernatant, further reducing the interference of the polystyrene plastic matrix on the detection of the target object, while improving the chromatographic response of the target object, thereby establishing a "dissolution-primary precipitation-auxiliary precipitation" method based on the "dissolution-precipitation method".

[0014] The beneficial effects of the present invention are as follows:

[0015] 1) The present invention utilizes a "dissolution-primary precipitation-auxiliary precipitation" method. The polystyrene plastic is first dissolved in dichloromethane to completely extract hydroquinone and polystyrene into the solvent. Excess methanol (primary precipitant) is then dropwise added to precipitate the polymer molecules polystyrene. Ether (auxiliary precipitant) is then added for secondary precipitation to more thoroughly precipitate the small polymer molecules in the supernatant. Compared to conventional dissolution-precipitation methods, this method can more effectively extract hydroquinone from the polystyrene plastic, improve recovery, avoid subsequent precipitation of polymer molecules, and protect the chromatography-mass spectrometry system from contamination.

[0016] 2) This method is solvent-saving, accurate, has minimal interference, high sensitivity, and high analytical efficiency, meeting higher detection requirements. The detection limit of hydroquinone can reach 0.5 mg / kg, and the limit of quantification can reach 1 mg / kg. It also has good recovery and precision. The spiked recovery of hydroquinone in polystyrene ranges from 98.3% to 107%, with relative standard deviations below 5.1%. Description of the drawings:

[0017] Figure 1 This is the gas chromatogram of hydroquinone (0.2 mg / L). Specific implementation method:

[0018] In order to make the purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are only for the purpose of explaining the present invention and are not intended to limit the present invention. The parameters, proportions, etc. of the embodiments can be selected according to local conditions without substantial impact on the results.

[0019] Unless otherwise specified, the test materials used in the following examples can be purchased through conventional commercial channels.

[0020] 1. Sample pretreatment

[0021] Weigh 4.00 g of a polystyrene plastic sample and cut the sample into small pieces of 5 mm × 5 mm using scissors.

[0022] 2. Sample Extraction

[0023] Weigh 1.0 g (accurate to 0.1 mg) of the polystyrene plastic crushed sample obtained in step 1 into a clean 25 mL volumetric flask. Add 10 mL of dichloromethane to dissolve the mixture. Shake the flask until the polystyrene plastic crushed sample is completely dissolved. Add methanol dropwise to the flask, shaking the flask while adding until no polymer continues to precipitate. Add ether dropwise to the flask until precipitation is complete, and dilute to the mark with ether. Shake the solution in the flask thoroughly and let it stand. Take 5 mL of the supernatant, concentrate it to 1 mL with nitrogen, filter it with an organic filter membrane, and set aside.

[0024] 3. Preparation of blank samples and standard working solutions

[0025] Refer to the above operating procedures to prepare the method blank sample.

[0026] The preparation of the standard working solution includes the following steps: using dichloromethane as the solvent, weighing 0.1 g of hydroquinone into a 10 mL volumetric flask, dissolving and diluting to the scale to prepare a standard stock solution, and then diluting the standard stock solution with a mixed solution of dichloromethane and methanol with a volume ratio of 1:1 to prepare standard working solutions with concentrations of 4.0, 2.0, 1.0, 0.5, and 0.2 mg / L, respectively.

[0027] 4. Gas chromatography-tandem mass spectrometry analysis and confirmation of positive results

[0028] Analyze the sample and standard working solution using GC-MS conditions. If the sample's mass chromatographic peak retention time matches that of the standard and both target selected ion pairs are present, confirm the presence of the selected ion pairs based on their relative abundance ratios. For qualitative analysis, if the relative abundance tolerances do not exceed the ranges specified in Table 1, the presence of the target substance in the sample is confirmed.

[0029] Table 1 Maximum allowable deviation of relative ion abundance ratios for confirmation of positive results

[0030] Relative ion abundance ratio >50％ >20％～50％ >10％～20％ ≤10％ Allowable relative deviation ±10％ ±15％ ±20％ ±50％

[0031] Inject the blank sample and method blank sample sequentially. After subtracting the blank background, calculate the chromatographic peak area of ​​hydroquinone. Inject each solution twice in parallel, and calculate the average peak area. Ensure consistent operating conditions throughout the measurement of the sample and standard working solution. Quantification is performed using the external standard method.

[0032] GC-MS conditions were as follows: chromatographic column: HP-INNOWAX capillary column (30 m × 0.25 mm, 0.25 μm); temperature program: initial temperature 120°C (hold for 1 min), then 10°C / min to 220°C and hold for 10 min; injection port temperature: 220°C; column flow rate: 1.0 mL / min; injection volume: 1 μL; injection mode: split injection, split ratio 10:1; ion source: electron impact ionization (EI); ion source temperature: 230°C; quadrupole mass analyzer temperature: 150°C; transfer line temperature: 250°C; ionization energy: 70 eV; solvent delay: 4 min; detection mode: selected ionization; run time: 21 min. The quantification ion of hydroquinone was 110, and the qualifier ions were 83 and 53 under full scan and selected ionization conditions.

[0033] 5. Standard working curve

[0034] The standard working solutions (0.20 mg / L to 4.0 mg / L) were measured under the optimized conditions. A standard working curve was plotted, with the concentration of each standard expressed in mg / L as the abscissa and the average of the corresponding peak areas as the ordinate. A linear equation and correlation coefficient were obtained (Table 2). The results showed a good linear relationship between concentration and response. For hydroquinone, the linear correlation coefficient was greater than 0.995 within the linear range of 0.20 mg / L to 4.0 mg / L, effectively meeting the testing requirements.

[0035] Table 2

[0036]

[0037] Example 1, detection limit and quantification limit experiment

[0038] The detection limit and quantification limit of this method are determined by the sensitivity of hydroquinone in GC-MS detection. A sample with a blank sample matrix is ​​tested according to the GC-MS measurement conditions optimized in step 4 above to obtain an extract. The extract with the blank sample matrix is ​​used to prepare a series of standard solutions with concentrations ranging from 0.20 mg / L to 4.0 mg / L for testing. A signal-to-noise ratio (S / N) of 3 times is used as the minimum detection limit, and the detection limit concentration obtained is calculated by the standard deviation S of 7 repeated tests. MDL × coefficient T (n-1，1-α＝0.99) The validity of the detection limit was verified when T was 3.143 with 7 replicates and a 99% confidence level. This was established when the calculated value was ≤ the detection limit derived from the signal-to-noise ratio. Using a 10x signal-to-noise ratio (S / N) as the quantification limit, the detection limit for hydroquinone was 0.5 mg / kg, and the quantification limit was 1 mg / kg.

[0039] Example 2, recovery and precision experiment of the method

[0040] Hydroquinone recovery tests were conducted using a blank sample spiked method. Hydroquinone was extracted from blank samples containing no target compound using the method described in Step 2, Sample Extraction, in Example 1. Standard sample solutions were then added to prepare three concentration levels: 0.2 mg / L, 1 mg / L, and 3 mg / L. GC-MS analysis was performed using the same conditions as in Step 4 of Example 1. Six separate measurements were performed at each concentration level to test recovery and precision. The results are detailed in Table 3.

[0041] Table 3

[0042]

[0043] The test results show that the recovery rate of hydroquinone in polystyrene determined by this method is between 98.3% and 107%, and the relative standard deviation is less than 5.1%, indicating that this method has good recovery and precision.

[0044] Example 3 Dissolution solvent selection experiment

[0045] Weigh 4.00g of polystyrene sample and cut it into 5mm x 5mm pieces with scissors. Weigh 1.0g of each of three polystyrene crushed samples (accurate to 0.1mg) and place them into a clean 25mL volumetric flask. Add 10mL of benzene, carbon disulfide, and dichloromethane, respectively, to perform a dissolution experiment.

[0046] The results showed that carbon disulfide dissolves styrene more slowly, while benzene and dichloromethane are equally effective. However, benzene requires evaporation and concentration, and dichloromethane, with its lower boiling point, evaporates more quickly, thus eliminating the need for subsequent evaporation and concentration. Therefore, considering all factors, dichloromethane was preferred as the dissolution solvent due to its lower toxicity, the lack of need for subsequent evaporation and concentration, and the resulting reduction in experimental time.

[0047] Example 4 Main precipitant selection experiment

[0048] Weigh 4.00 g of polystyrene sample and cut it into 5 mm x 5 mm pieces with scissors. Weigh 1.0 g of each of three polystyrene pulverizers (accurate to 0.1 mg) into a clean 25 mL volumetric flask and dissolve in 10 mL of dichloromethane, shaking the flask until completely dissolved. Then, add methanol, n-hexane, and petroleum ether dropwise to the flask while shaking to perform polymer precipitation experiments. The results are shown in Table 4.

[0049] Table 4

[0050]

[0051] As can be seen from Table 4, methanol has the best precipitation effect and petroleum ether has the worst precipitation effect. Therefore, methanol is selected as the main precipitant.

[0052] Example 5, precipitation aid selection experiment

[0053] Although methanol was used as a precipitant to produce a visible supernatant, tiny polymer molecules invisible to the naked eye still remained in the supernatant, forming a large sample matrix solution background, which weakened the chromatographic response of the target compound. Furthermore, prolonged injection and analysis led to the accumulation of small polymer molecules, which could also burden the chromatographic system. Therefore, ether, water, and heptane were selected as co-precipitants for the experiment.

[0054] Experimental method: A 1000 mg / L hydroquinone standard solution was prepared using dichloromethane as the solvent. 1.0 g of each of 12 samples known to contain no hydroquinone was weighed into a volumetric flask. 0.005, 0.025, and 0.075 mL of a 1000 mg / L hydroquinone standard solution (the solvent used for this mixed standard solution was dichloromethane) were added, respectively. Dichloromethane was added to the volume to 10 mL, and the flask was shaken until completely dissolved. Methanol was added dropwise to the flask, shaking the bottle while adding until no polymer continued to precipitate. Ether, water, and heptane were selected as precipitants, and equal volumes of the three solutions were added dropwise. Two replicates were prepared for each solution, and the volumetric flask was gently shaken during the process. After standing for 10 minutes, 5 mL of the supernatant was taken, concentrated to 1 mL under nitrogen purge, and filtered through an organic filter membrane for gas chromatography-mass spectrometry analysis. The GC-MS test conditions were the same as in Example 1. No precipitant was added as a control. The solutions were tested after treatment, and the response results of the targets obtained are shown in Table 5.

[0055] Table 5

[0056]

[0057] As shown in Table 5, when the sample solutions were treated with different precipitants, it can be seen that at the same concentration, the solution treated with water had the lowest response, followed by heptane. The response obtained without the addition of a precipitant was comparable to that obtained with heptane, while the solution treated with diethyl ether had the highest response and the recovery rate was closest to 100%. Therefore, diethyl ether was selected as the precipitant.

Claims

1. A method for determining the content of hydroquinone in polystyrene plastic, characterized in that: The method comprises the following steps: respectively taking a sample to be tested and a standard working solution for GC-MS analysis to determine the content of hydroquinone, wherein the preparation method of the sample to be tested is as follows: weighing 4.00 g of a polystyrene plastic sample, cutting the sample into small pieces of 5 mm×5 mm; weighing 1.0 g of the sample into a clean 25 mL volumetric flask, adding 10 mL of dichloromethane to dissolve the sample, shaking the bottle until the crushed polystyrene plastic sample is completely dissolved, adding methanol dropwise into the bottle while shaking the bottle until no polymer continues to precipitate, adding ether dropwise into the bottle until precipitation is complete, diluting the volume to the calibration mark with ether, shaking the solution in the bottle thoroughly and then letting it stand, taking 5 mL of the supernatant, concentrating the solution to 1 mL with nitrogen, filtering the solution with an organic filter membrane, and setting aside.

2. The method according to claim 1, characterized in that GC-MS conditions were as follows: chromatographic column: HP-INNOWAX capillary column; heating program: initial temperature 80-120°C, hold for 1 min, then increase the temperature to 200-260°C at a rate of 5-25°C / min and hold for 5-20 min; injection port temperature: 220-250°C; column flow rate: 0.8-1.5 mL / min; injection volume: 0.5-2 μL; injection mode: split injection, split ratio 10:1; Ion source: electron bombardment ion source; ion source temperature: 230°C; quadrupole mass analyzer temperature: 150°C; transfer line temperature: 250°C; ionization energy: 70 eV; solvent delay: 4 min; detection mode: selected ion; run time: 21 min; under full scan and selected ion conditions, the quantitative ion of hydroquinone was determined to be 110, and the qualitative ions were 83 and 53.

3. The method according to claim 1, characterized in that The organic filter membrane is 0.2μm.

4. The method according to claim 2, characterized in that The capillary column specifications are 30m×0.25mm, 0.25μm.

5. The method according to claim 1, wherein The preparation of standard working solution includes the following steps: Using dichloromethane as the solvent, weigh 0.1 g of hydroquinone into a 10 mL volumetric flask, dissolve it, and dilute it to the mark to prepare a standard stock solution. Then, the standard stock solution was diluted with a mixed solution of dichloromethane and methanol with a volume ratio of 1:1 to prepare standard working solutions with concentrations of 4.0, 2.0, 1.0, 0.5, and 0.2 mg / L, respectively.

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