Method for detecting content of vinyl acetate by headspace-gas chromatography

Abstract

The invention relates to the field of chemical analysis, in particular to a method for detecting the content of vinyl acetate by headspace-gas chromatography. The invention relates to a method for detecting the content of vinyl acetate by headspace-gas chromatography, which comprises the following steps: 1) solution preparation: accurately weighing an internal standard substance, diluting with a solvent to obtain an internal standard stock solution, taking a plurality of headspace bottles, respectively adding vinyl acetate standard stock solutions with different volumes to prepare a standard series solution, weighing samples in the headspace bottles, and measuring the content of the internal standard substance in the headspace bottles; adding a solvent and an internal standard solution, and adding anhydrous sodium sulfate; 2, headspace sample injection analysis: sealing the headspace bottle, putting the headspace bottle into a sample disc of a headspace automatic sampler, setting headspace and gas chromatography parameters, and operating the headspace and gas chromatography parameters. The method integrates automatic headspace sampling, internal standard quantification, matrix effect elimination, chromatographic analysis optimization and other technologies, has extremely high accuracy and reliability, and also has excellent sensitivity and wide detection range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical analysis, and particularly to a method for detecting the content of vinyl acetate by headspace-gas chromatography. BACKGROUND

[0002] Headspace-gas chromatography is an instrumental analysis method that combines headspace sampling technology with gas chromatography analysis. It is widely used in fields that require detection of volatile organic compounds, such as environmental analysis, food and flavor research, pharmaceutical quality control, and chemical and material analysis.

[0003] When applied to the measurement of vinyl acetate content, there are several key technical challenges: (1) Poor headspace equilibrium efficiency and reproducibility. The headspace gas phase equilibrium of vinyl acetate is greatly affected by temperature, time, and sample matrix. If temperature or time control is not proper, it may lead to insufficient or excessive equilibrium, making the gas phase concentration in the headspace bottle unable to stably and truly reflect the original concentration in the sample, resulting in poor reproducibility and low accuracy of the analysis results. (2) Serious matrix effect interference. When the sample is not pure water or a simple solvent, other components in the sample may interact with vinyl acetate or change its activity coefficient, significantly affecting its volatilization degree into the headspace gas phase. (3) Insufficient sensitivity, making it difficult to meet the detection requirements of low content. For detection scenarios such as food packaging material migration, trace vinyl acetate monomer residues in the air of the workplace, and impurities in pharmaceuticals, conventional headspace parameters and ordinary gas chromatography detectors may not meet the required sensitivity. (4) Poor chromatographic separation effect. There may be other volatile impurities in the sample matrix, whose peak time may be close to or overlap with that of vinyl acetate, making it impossible to accurately quantify.

[0004] Other methods for detecting the content of vinyl acetate include direct injection gas chromatography, solvent extraction-gas chromatography, and early headspace technology. These methods either have complex operations and low efficiency or have obvious shortcomings in accuracy, reproducibility, and sensitivity. Therefore, developing more advanced and automated headspace-gas chromatography technology and optimizing its method parameters has become an inevitable direction to solve the above problems. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a method for detecting the content of vinyl acetate by headspace-gas chromatography. This method integrates automatic headspace sampling, internal standard quantification, matrix effect elimination, and optimized chromatographic analysis, and has high accuracy and reliability, as well as excellent sensitivity and a wide detection range.

[0006] To address the problems in the prior art, this invention discloses a method for detecting vinyl acetate content using headspace-gas chromatography, comprising the following steps: Step 1: Solution preparation: Accurately weigh the internal standard, dilute it with solvent to prepare an internal standard stock solution, take multiple headspace vials, and add equal volumes of internal standard solutions with the same internal standard concentration. Add different volumes of vinyl acetate standard stock solutions to prepare a standard series solution. Weigh 0.5g of sample into a headspace vial, add the same volume of solvent and internal standard solution as the standard series solution, and add 1-2g of anhydrous sodium sulfate.

[0007] Step 2 Headspace Sampling Analysis: After sealing the headspace vial, place it in the sample tray of the headspace autosampler, set the headspace and gas chromatography parameters, and run the program.

[0008] Preferably, the internal standard in step 1 is tert-butanol, and the diluent is ultrapure water or N,N-dimethylformamide.

[0009] Preferably, the standard series solutions in step 1 are standard solutions of different concentrations.

[0010] Preferably, the parameters of the headspace sampler in step 2 are: equilibrium temperature 70-90℃, equilibrium time 20-40min, quantitative loop temperature 100-110℃, transfer line temperature 110-120℃, pressurization pressure 10-20psi, pressurization time 0.5-1.0min, quantitative loop volume 1mL, and injection time 0.5-1.0min.

[0011] Preferably, the gas chromatography parameters are as follows: column: HP-INNOWax.30m*0.32mm*0.5μm polar column; carrier gas: high-purity nitrogen or helium; carrier gas flow rate: 1.0-2.0mL / min; injection port temperature: 200℃; split ratio: 10:1; FID temperature: 250℃; and make-up gas flow rate: 30mL / min.

[0012] Preferably, the programmed temperature rise is set as follows: initial 40°C, hold for 3 min, rise to 90°C at 10°C / min, then rise to 200°C at 25°C / min, and hold for 2 min.

[0013] The beneficial effects of this invention are as follows: It exhibits extremely high accuracy and reliability. Using tert-butanol as an internal standard, it can effectively correct for random errors such as slight fluctuations in injection volume and differences in headspace equilibrium efficiency during sample processing and instrument analysis. The selection of a polar chromatographic column and optimization of the programmed temperature conditions ensure that vinyl acetate and the internal standard, as well as any volatile impurities that may coexist, achieve baseline separation, guaranteeing the purity of the quantitative peak and avoiding erroneous quantification due to co-elution.

[0014] It exhibits excellent sensitivity and a broad detection range. Through the combined use of headspace enrichment, salting-out effect (with the addition of anhydrous sodium sulfate), and a high-sensitivity detector, the limits of detection and quantitation for vinyl acetate are extremely low, fully meeting the stringent requirements for trace analysis of residual monomers and migration amounts. By systematically optimizing headspace and gas chromatography parameters, the established standard curve maintains good linearity across several orders of magnitude of concentration, enabling the detection of both high-content raw materials and extremely low-content final products.

[0015] It is easy to operate and more efficient. Headspace technology eliminates the need for complex solvent extraction, concentration, and purification steps. Simply weigh the sample into the headspace vial, add the internal standard and salt, and seal it. This greatly simplifies the process, saves time, and reduces sample loss and human error caused by cumbersome steps. Detailed Implementation

[0016] The present invention will now be further described. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0017] A method for determining vinyl acetate content using headspace-gas chromatography, comprising the following instruments and reagents: a gas chromatograph equipped with a flame ionization detector or mass spectrometer, an automated headspace sampler, a chromatographic column (polar or medium polarity), an analytical balance (0.01 g), a microsyringe; vinyl acetate standards, an internal standard (tert-butanol), a solvent of ultrapure water or N,N-dimethylformamide, and a salt (anhydrous sodium sulfate).

[0018] A method for detecting vinyl acetate content using headspace gas chromatography includes the following steps: Step 1: Solution preparation: Accurately weigh the internal standard, dilute it with solvent to prepare an internal standard stock solution, take multiple headspace vials, and add equal volumes of internal standard solutions with the same internal standard concentration. Add different volumes of vinyl acetate standard stock solutions to prepare a standard series solution. Weigh 0.5g of sample into a headspace vial, add the same volume of solvent and internal standard solution as the standard series solution, and add 1-2g of anhydrous sodium sulfate.

[0019] In this step, the internal standard used is tert-butanol, and the diluent is ultrapure water or N,N-dimethylformamide. The standard series solutions are standard solutions of different concentrations. In this step, the added anhydrous sodium sulfate can utilize the salting-out effect to increase the volatility of vinyl acetate.

[0020] By correcting process errors using the "internal standard method," the matrix effect is eliminated, thus achieving comprehensive quality assurance in sample preparation.

[0021] Step 2: Headspace Sampling Analysis: After sealing the headspace vial, place it in the sample tray of the automatic headspace sampler, set the headspace and gas chromatography parameters, and run the program. Using a fully automated headspace sampler replaces manual headspace sampling, with the instrument precisely controlling the entire process of heating, pressurization, quantification, and injection.

[0022] The parameters for the headspace sampler in this step are as follows: equilibrium temperature 70-90℃, equilibrium time 20-40min, quantitative loop temperature 100-110℃, transfer line temperature 110-120℃, pressurization pressure 10-20psi, pressurization time 0.5-1.0min, quantitative loop volume 1mL, and injection time 0.5-1.0min.

[0023] The gas chromatography parameters for this step are as follows: column: HP-INNOWax.30m*0.32mm*0.5μm polar column; carrier gas: high-purity nitrogen or helium; carrier gas flow rate: 1.0-2.0mL / min; injection port temperature: 200℃; split ratio: 10:1; FID temperature: 250℃; and make-up gas flow rate: 30mL / min.

[0024] In this step, the temperature program is set as follows: initial temperature 40℃, hold for 3 minutes, increase to 90℃ at 10℃ / min, then increase to 200℃ at 25℃ / min, and hold for 2 minutes.

[0025] By optimizing chromatographic separation, interference is effectively avoided and the accuracy of data generation is improved. This application is not only applicable to simple solution samples, but also improves the adaptability to complex matrix samples such as polymers, coatings, and adhesives through strategies such as standard addition methods.

[0026] Example 1: When this invention is applied to the measurement of residual vinyl acetate monomer in polymer emulsions, first weigh 25 mg of tert-butanol into a 25 mL volumetric flask, dilute to the mark with ultrapure water, and shake well; weigh 0.5 g of homogeneous polymer emulsion sample into a 20 mL headspace vial, add 50 μL of internal standard stock solution using a pipette, so that each vial contains 5 μg of tert-butanol; then add 10 mL of ultrapure water, gently shake to disperse the sample, quickly add 1.5 g of anhydrous sodium sulfate, and immediately seal.

[0027] Weigh 0.5 g of blank emulsion without vinyl acetate into a series of headspace vials, add 50 μL of internal standard stock solution to each, and then add vinyl acetate standard solution to each, so that the concentrations in the emulsion are 2, 5, 10, 20, and 40 μg / g, respectively; similarly, add 10 mL and 1.5 g of anhydrous sodium sulfate, and seal.

[0028] The headspace conditions were set as follows: equilibrium temperature 80℃, equilibrium time 30 min, quantitative loop temperature 105℃, quantitative loop volume 1 mL, and injection time 0.75 min.

[0029] GC conditions were set as follows: carrier gas: nitrogen, constant flow rate 1.5 mL / min, inlet temperature: 200℃, split ratio 10:1, FID temperature: 250℃.

[0030] The temperature program is set as follows: initial temperature 40℃, hold for 3 minutes, increase to 90℃ at 10℃ / min, then increase to 200℃ at 25℃ / min, hold for 2 minutes, with a total running time of approximately 13 minutes.

[0031] A linear regression was performed with vinyl acetate concentration on the x-axis and the ratio of vinyl acetate peak area to tert-butanol peak area on the y-axis. The peak area ratio of the sample was substituted into the standard curve equation to calculate the vinyl acetate content in the sample.

[0032] Example 2: When this invention is applied to detect the migration amount of vinyl acetate in pharmaceutical packaging materials, the packaging material to be tested is first cut into small pieces and mixed. Then, 2.0g of the material is accurately weighed into a glass-stoppered conical flask, and a certain volume of simulated solvent is added. Here, a 50% ethanol aqueous solution is used, and the flask is sealed. A migration test is then conducted under specified time and temperature conditions. After the migration is completed, the leachate is taken and filtered through a 0.45μm filter membrane.

[0033] Take another 5 mL of the filtered leachate into a 20 mL headspace vial, add 25 μL of internal standard stock solution, add 1.0 g of anhydrous sodium sulfate, and seal immediately.

[0034] Prepare standard solutions of vinyl acetate with concentrations of 0.1, 0.5, 1.0, 2.0, and 5.0 μg / mL using 50% ethanol aqueous solution as solvent. Similarly, measure 5.0 mL of each of the above standard solutions into a headspace vial, add an equal volume of internal standard, add salt, and seal.

[0035] The headspace conditions were set as follows: equilibrium temperature 70℃, equilibrium time 40 min, quantitative loop temperature 105℃, quantitative loop volume 1 mL, and injection time 0.75 min. In this embodiment, the equilibrium temperature was set lower to prevent excessive ethanol vapor pressure due to excessive temperature, and the longer equilibrium time ensured that trace components were fully equilibrated.

[0036] The GC conditions were set as follows: carrier gas: nitrogen, constant flow rate 1.5 mL / min, injection port temperature: 200 °C, split valve opened after 0.75 min, FID temperature: 250 °C. In this embodiment, a splitless injection mode was used to improve sensitivity, and the split valve opened after a period of time during injection.

[0037] The temperature program is set as follows: initial temperature 40℃, hold for 3 minutes, increase to 90℃ at 10℃ / min, then increase to 200℃ at 25℃ / min, hold for 2 minutes, with a total running time of approximately 13 minutes.

[0038] A linear regression was performed with vinyl acetate concentration on the x-axis and the ratio of vinyl acetate peak area to tert-butanol peak area on the y-axis. The peak area ratio of the sample was substituted into the standard curve equation to calculate the vinyl acetate content in the sample.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining vinyl acetate content using headspace-gas chromatography, characterized in that: Includes the following steps: Step 1 Solution preparation: Accurately weigh the internal standard and dilute it with a solvent to prepare an internal standard stock solution. Take multiple headspace vials and add equal volumes of internal standard solution with the same internal standard concentration. Then, add different volumes of vinyl acetate standard stock solution to each vial to prepare a standard series of solutions. Weigh 0.5g of sample into a headspace vial, add the same volume of solvent and internal standard solution as the standard series solutions, and add 1-2g of anhydrous sodium sulfate. Step 2 Headspace Sampling Analysis: After sealing the headspace vial, place it in the sample tray of the headspace autosampler, set the headspace and gas chromatography parameters, and run the program.

2. The method for determining vinyl acetate content using headspace gas chromatography according to claim 1, characterized in that: The internal standard in step 1 is tert-butanol, and the diluent is ultrapure water or N,N-dimethylformamide.

3. The method for determining vinyl acetate content using headspace gas chromatography according to claim 1, characterized in that: The standard series solutions in step 1 are standard solutions of different concentrations.

4. The method for determining vinyl acetate content using headspace gas chromatography according to claim 1, characterized in that: The parameters of the headspace sampler in step 2 are as follows: equilibrium temperature 70-90℃, equilibrium time 20-40min, quantitative loop temperature 100-110℃, transfer line temperature 110-120℃, pressurization pressure 10-20psi, pressurization time 0.5-1.0min, quantitative loop volume 1mL, and injection time 0.5-1.0min.

5. The method for determining vinyl acetate content using headspace gas chromatography according to claim 1, characterized in that: The gas chromatography parameters are as follows: column: HP-INNOWax.30m*0.32mm*0.5μm polar column; carrier gas: high-purity nitrogen or helium; carrier gas flow rate: 1.0-2.0mL / min; injection port temperature: 200℃; split ratio: 10:1; FID temperature: 250℃; and make-up gas flow rate: 30 mL / min.

6. The method for determining vinyl acetate content using headspace gas chromatography according to claim 1, characterized in that: The temperature program is set as follows: initial temperature 40℃, hold for 3 minutes, increase to 90℃ at 10℃ / min, then increase to 200℃ at 25℃ / min, and hold for 2 minutes.