A method for determining 2,6-diisopropyl aniline in biodegradable films

Abstract

The present invention discloses a method for determining 2,6-diisopropylaniline in a biodegradable film, comprising the following steps: S1, adding a sample of biodegradable mulch film fragments to a headspace bottle, adding a recovery correction internal standard solution, adding an acidic solution and placing it in a constant temperature metal bath for heating extraction, and filtering after cooling to room temperature to obtain an extraction filtrate; S2, placing the extraction filtrate in a centrifuge tube, adding ultrapure water, adding a hydrophilic extractant and vortex mixing to obtain a homogeneous system, ice bathing, adding an alkaline solution to adjust the pH, so that the hydrophilic extractant is converted into a hydrophobic extractant in an alkaline environment, achieving two-phase separation, centrifugation, taking the upper liquid in another centrifuge tube, and centrifuging; S3, taking the upper organic solution in a microinjection bottle, adding an internal standard solution calibrated by the instrument, vortex mixing and performing GC-MS analysis. The present invention has the advantages of being fast, sensitive, and saving solvents, and has higher sensitivity than traditional methods, and can determine the total amount of 2,6-DIPA in PBAT biodegradable film.

Description

Technical Field

[0001] The invention relates to a method for determining 2,6-diisopropylaniline in a biodegradable film, belonging to the technical field of biodegradable film additive measurement. Background Art

[0002] Polybutylene adipate / terephthalate (PBAT) is a biodegradable aliphatic-aromatic polyester and a petrochemical-based biodegradable plastic. It exhibits excellent ductility and elongation at break, high toughness, high-temperature resistance, and excellent biodegradability, making it a fully biodegradable plastic. PBAT is currently considered the most promising new organic material to replace traditional mulch materials in the production of biodegradable mulch. It is considered one of the sustainable materials produced by modern "green materials" and is now widely used in the production of agricultural biodegradable mulch. During processing, PBAT biodegradable films are added with various organic additives, such as anti-slip agents, lubricants, antioxidants, stabilizers, plasticizers, flame retardants, fillers, and rubber additives. The ecotoxicological effects of phthalate esters (PAEs), plasticizers in conventional plastics, have been widely reported. Certain additives in PBAT possess significant toxic units and may be potential emerging environmental pollutants, potentially affecting plant growth and development, soil microbial communities, and function. Previous studies have indicated that the ecological impacts of additives must be considered in the evaluation of biodegradable materials.

[0003] The 2,6-DIPA in PBAT biodegradable film mainly comes from the degradation of the anti-hydrolysis additive N,N′-bis(2,6-diisopropylphenyl)carbodiimide (BDICDI), such as Figure 1 As shown, BDICDI first slowly degrades into the corresponding 2,6-DIPI and ultimately into the chemically stable and quantifiable 2,6-DIPA. Therefore, as a degradation byproduct, 2,6-DIPA and 2,6-DIPI play an important role in evaluating the production process, formulation quality, and performance changes of biodegradable membranes. 2,6-DIPA shares structural similarities with environmental pollutants such as aniline and may have certain impacts on the environment and human health. Therefore, analytical methods for 2,6-DIPA and 2,6-DIPI have been established for production process monitoring or safety evaluation of related products.

[0004] However, due to the high reactivity of the isocyanate group in 2,6-DIPI, protonated solvents can convert isocyanate into corresponding by-products, resulting in the inability to accurately quantify the total amount of 2,6-DIPA (2,6-DIPA and 2,6-DIPI) in PBAT biodegradable mulch films, for example, the literature: Cui, H, Gao, W, Lin, Y, et al. Development of microwave-assisted extraction and dispersive liquid–liquid microextraction followed by gaschromatography-mass spectrometry for the determination of organic additives in biodegradable mulch films[J]. Microchemical Journal, 2021, 160; 105722. Summary of the Invention

[0005] Based on the above, the present invention provides a method for determining 2,6-diisopropylaniline in biodegradable films, which can accurately quantify the total amount of 2,6-DIPA (2,6-DIPA and 2,6-DIPI) in PBAT biodegradable films to overcome the shortcomings of the existing technology.

[0006] The technical solution of the present invention is: a method for determining 2,6-diisopropylaniline in a biodegradable film, comprising the following steps:

[0007] S1, adding a sample of biodegradable mulch film fragments to a headspace bottle, adding an internal standard solution for recovery correction, adding an acidic solution, and heating in a constant temperature metal bath to simultaneously extract 2,6-DIPA and hydrolyze 2,6-DIPI. After cooling to room temperature, the sample is filtered to obtain an extraction filtrate;

[0008] S2: Place the extracted filtrate in a centrifuge tube, add ultrapure water, add a hydrophilic extractant, and vortex mix to obtain a homogeneous system. Place in an ice bath, add an alkaline solution to adjust the pH so that the hydrophilic extractant is converted into a hydrophobic extractant in an alkaline environment to achieve two-phase separation, centrifuge, and collect the upper liquid into another centrifuge tube;

[0009] S3, the upper liquid obtained from S2 was centrifuged again, the upper organic solution was taken into a microinjection bottle, the internal standard solution for instrument calibration was added, and the mixture was vortexed for GC-MS analysis.

[0010] Preferably, in step S1, the internal standard solution for recovery correction is 2,6-diethylaniline, the acidic solution is H2SO4, the concentration is 3 mol / L, the heating temperature is 90°C, and the time is 3 h.

[0011] Preferably, in step S2, the hydrophilic extractant is n-dipropylamine, the amount used is 100 μL, the alkaline solution is NaOH, the pH is adjusted to 14, and the extraction time is 1 min.

[0012] Preferably, in step S3, the internal standard solution for instrument calibration is 2,4,6-tri-tert-butylaniline.

[0013] Preferably, in step S3, the conditions for GC-MS analysis are: chromatographic column type: DB-5 capillary column, carrier gas: helium, programmed temperature conditions: initial temperature 40°C, hold for 1 min; then 10°C min -1 Raise to 230℃, hold for 1min; -1 Heat to 280°C, hold for 0 min, injection port temperature: 280°C, injection volume: 1.0 μL, split injection, split ratio: 20:1, constant flow rate: 1.0 mL min -1 , the total running time was 24.333 min; ion source temperature: 230°C, quadrupole temperature: 150°C; mass spectrometer transfer line temperature: 280°C, solvent delay time: 12 min, ionization mode was electron impact ionization 70 eV, and the full scan and selected ion scan (SIM) modes were adopted, with the Full Scan range of m / z = 45 to 500.

[0014] Preferably, the biodegradable film is a polybutylene adipate / terephthalate biodegradable film.

[0015] The beneficial effects of the present invention are as follows: the present invention adopts heating simultaneous hydrolysis-extraction and switchable hydrophilic solvent homogeneous liquid-liquid microextraction combined with GC-MS chromatography analysis technology to establish and verify the qualitative and quantitative methods of 2,6-DIPA in biodegradable films. DPA is a switchable hydrophilic reagent, and the conversion of DPA from hydrophilicity to hydrophobicity is achieved by adjusting the pH value to complete the extraction process. The present invention has the advantages of being fast, sensitive, and saving solvents, and has higher sensitivity than traditional methods, and can simultaneously determine the total amount of 2,6-DIPA in PBAT biodegradable films. The present invention can be used to monitor the content of the additive 2,6-DIPA in biodegradable mulch films, thereby conducting production process monitoring or safety evaluation of related products, and providing a basic theoretical reference for subsequent applications of biodegradable mulch films.

[0016] Compared with the existing technology, the present invention has the following advantages: 1. It reports for the first time a qualitative and quantitative analysis method for the total amount of 2,6-DIPA (2,6-DIPA and 2,6-DIPI) in PBAT biodegradable films; 2. It uses a switchable hydrophilic solvent DPA homogeneous liquid-liquid microextraction to purify and enrich 6-DIPA in PBAT biodegradable films; 3. Microextraction reduces the amount of organic solvent used, and has a fast extraction time, high efficiency, and a high enrichment coefficient, which is between 73.2 and 83.4; 4. The method has high sensitivity, accuracy, and precision.

[0017] Analysis showed that under optimal experimental conditions, the method exhibited good linearity for 2,6-DIPA in the range of 0.0144 to 7.200 μg / mL (correlation coefficient r ≥ 0.9986), a detection limit of 0.0033 μg / g, a limit of quantification of 0.0103 μg / g, a recovery rate of 91.4% to 104.3%, and a precision range of 2.54% to 4.58%. This method exhibits excellent linearity, detection limit, recovery rate, and precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The conversion of BDICDI to 2,6-DIPI and 2,6-DIPA in biodegradable mulch

[0019] Figure 2 Full scan mass spectrum of the target compound 2,6-DIPA;

[0020] Figure 3 Standard curve for determination of 2,6-DIPA by gas chromatography-mass spectrometry;

[0021] Figure 4 The hydrolysis rates of 2,6-DIPI and BDICDI by different hydrolysis solvents;

[0022] Figure 5 The hydrolysis rate of 2,6-DIPI at different H2SO4 concentrations;

[0023] Figure 6 The hydrolysis rate of 2,6-DIPI at different temperatures;

[0024] Figure 7 The hydrolysis rate of 2,6-DIPI at different heating times;

[0025] Figure 8 Optimization of the types of organic extraction reagents for homogeneous liquid-liquid microextraction with switchable hydrophilic solvents;

[0026] Figure 9 Optimization of extraction reagent volume for homogeneous liquid-liquid microextraction with switchable hydrophilic solvents;

[0027] Figure 10 Effects of different pH systems on homogeneous liquid-liquid microextraction with switchable hydrophilic solvents;

[0028] Figure 11 Effects of different extraction times on homogeneous liquid-liquid microextraction with switchable hydrophilicity solvents. DETAILED DESCRIPTION

[0029] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] 1. Test materials:

[0031] 1. Materials and Reagents

[0032] PBAT biodegradable mulch film is commercially available and cut into pieces of approximately 2 mm × 2 mm.

[0033] Acetone, methanol, 2,6-DIPI, BDICDI, 2,6-DIPA, triethylamine (TEA), sodium hydroxide (NaOH), hydrochloric acid (HCl), sulfuric acid (H2SO4), 2,6-diethylaniline (DEA), 2,4,6-tri-tert-butylaniline (TBA), 2,4,6-trimethylaniline (TMA), N,N-dimethylbenzylamine (BDMA), dipropylamine (DPA), N,N-dimethylcyclohexylamine (DMCHA), and methanesulfonic acid (MSA) were purchased from Aladdin Reagent Co. 2,6-DIPA and BDICDI standard solutions were prepared in acetone to 10.800 mg / mL and 10.300 mg / mL stock solutions, respectively, and diluted for use. Internal standard TBA and DEA standard solutions were prepared in acetonitrile to 2.808 and 1.080 mg / mL solutions, respectively, and stored at 5°C until use.

[0034] 2. Instruments and equipment

[0035] Agilent 7890A-5975C gas chromatograph-mass spectrometer (Agilent Technologies Co., Ltd.), constant temperature metal bath (Hangzhou Ruicheng Instrument Co., Ltd.), Vortex-1 vortexer (Hangzhou Miou Instrument Co., Ltd.), HH-2 constant temperature water bath (Shanghai Meixiang Instrument Co., Ltd.), TDL-80-2B low-speed centrifuge (Shanghai Anting Scientific Instrument Factory), Milli-Q ultrapure water preparation device (Millipore Corporation, USA), Eppendorf mini centrifuge (Eppendorf AG, Germany), AL204-IC electronic balance (Mettler-Toledo Instrument Shanghai Co., Ltd.).

[0036] 2. Method for determining 2,6-diisopropylaniline in biodegradable films

[0037] This embodiment provides a method for determining 2,6-diisopropylaniline in a biodegradable film, comprising the following steps:

[0038] S1. Accurately weigh 50 mg of PBAT biodegradable mulch film sample into a 20 mL headspace vial, add 10 μL of 1.080 mg / mL LDEA internal standard solution, add 3 mL of 3 mol / L H2SO4 solution, and heat in a constant temperature metal bath at 90°C for 3 h to extract 2,6-DIPA and hydrolyze 2,6-DIPI. After cooling to room temperature, filter through a 0.22 μm organic filter membrane and transfer the resulting extract filtrate to a 10 mL glass centrifuge tube for later use.

[0039] S2, take 2mL of sample solution in a 10mL centrifuge tube, add 2mL of ultrapure water, add 100μL of n-dipropylamine and vortex mix to observe a homogeneous system; ice bath for 2min, add 12mol / LNaOH to adjust pH = 14 and vortex thoroughly for 60s to achieve two-phase separation and complete the extraction process. Centrifuge at 3000rpm for 5min, use a 100μL pipette to remove the upper layer (containing a small amount of impurities and water) into a 1.5mL centrifuge tube, centrifuge at 3000rpm for 3min, use a 50μL manual injection valve syringe to take the upper organic solution into a microinjection bottle (the final upper organic solution is about 60μL), add 2μL of 2.808mg / mL TBA instrument calibration internal standard solution and vortex mix for GC-MS analysis.

[0040] The GC-MS analysis conditions were as follows: column type: DB-5 capillary column, carrier gas: helium, programmed temperature conditions: initial temperature 40°C, hold for 1 min; then 10°C min -1 Raise to 230℃, hold for 1min; -1 Heat to 280℃, hold for 0min, injection port temperature: 280℃, injection volume: 1.0μL, split injection, split ratio: 20:1, constant flow rate: 1.0mLmin -1The total running time was 24.333 min; the ion source temperature was 230°C, the quadrupole temperature was 150°C; the mass spectrometer transfer line temperature was 280°C, the solvent delay time was 12 min, the ionization mode was electron impact ionization at 70 eV, and the full scan and selected ion scan (SIM) modes were adopted with a Full Scan range of m / z = 45 to 500. The SIM quantitative ions of 2,6-DIPA, DEA and TBA were m / z 162, 134 and 226, respectively, and the qualitative ions were m / z 177, 120, 149, 119 and 261, 230, respectively. Figure 2 This is the full scan mass spectrum of the target compound 2,6-DIPA.

[0041] 3. Method Validation

[0042] 1. Linear regression equation and detection limit

[0043] Under the conditions of the above embodiment, 4 μL, 8 μL, 10 μL, 50 μL, and 100 μL of 2,6-DIPA at a concentration of 0.0108 mg / mL were taken, and 5 μL, 10 μL, and 20 μL of the mother liquor at 1.080 mg / mL were used to prepare a standard curve, where x was the 2,6-DIPA concentration and y was the ratio of the 2,6-DIPA peak area to the TBA peak area. A standard curve was plotted between the 2,6-DIPA concentration (x) and the 2,6-DIPA to TBA peak area ratio (y). The linear equation was y = 0.2377x - 0.0049, and a good linear relationship was observed in the range of 0.0144 to 7.200 μg / mL (correlation coefficient r ≥ 0.9986). The detection limit was 0.0033 μg / g, and the quantification limit was 0.0103 μg / g, calculated based on S / N = 3 and the sample weight, dilution ratio, and recovery rate. The standard curves of 2,6-DIPA at 8 concentrations are as follows Figure 3 From the results, we can see that the standard curve has a wide range and a good linear correlation coefficient.

[0044] 2. Accuracy and precision

[0045] Thirty 50 mg sample QC aliquots were weighed. Fifteen aliquots were spiked at low concentrations, with 10 serving as low-level spikes and the remaining five serving as blanks, spiked with 3 μL and 6 μL of a 1.080 mg / mL 2,6-DIPA standard solution, respectively. Fifteen aliquots were spiked at high concentrations, with 5 serving as blanks and the remaining ten serving as spikes with 7 μL and 14 μL of a 10.800 mg / mL 2,6-DIPA standard solution. Following the optimized method, microextraction was performed after heating and hydrolysis, and analysis was performed by GC-MS. Recovery was calculated as the 2,6-DIPA content in the spiked sample minus the blank 2,6-DIPA content, divided by the spiked 2,6-DIPA content, and multiplied by 100%. Precision was evaluated using the assay deviations of both unspiked and spiked samples. As shown in Table 1, the recovery rate of 2,6-DIPA is between 91.4% and 104.3%, and the precision range is 2.54% to 4.58%, indicating that this method has good accuracy, repeatability and stability, and is suitable for the qualitative and quantitative analysis of 2,6-DIPA in PBAT biodegradable films.

[0046] Table 1 Recovery and precision of spiked low / high content samples

[0047]

[0048] IV. Application Cases

[0049] Ten PBAT biodegradable film samples from different sources (PBAT-1, PBAT-2, PBAT-3, PBAT-4, PBAT-5, PBAT-6, PBAT-7, PBAT-8, PBAT-9, and PBAT-10) were collected and analyzed for total 2,6-DIPA using an established method. The results are shown in Table 2 below. All ten samples contained 2,6-DIPA at levels exceeding 85.1 μg / g. 2,6-DIPA primarily originates from the degradation of the anti-hydrolysis agent BDICDI, which is first converted to 2,6-DIPI and then degraded to 2,6-DIPA. This suggests that the anti-hydrolysis agent BDICDI is added during the production of most PBAT biodegradable films. The high 2,6-DIPA content (mg / g level) also suggests that the production process needs to be adjusted to reduce BDICDI degradation during production.

[0050] Table 2 Analysis of 2,6-DIPA content in PBAT biodegradable film samples from 10 different sources

[0051]

[0052] The following details the selection of internal standard reagents, optimization of simultaneous heating and hydrolysis-extraction, and optimization of SHS-HLLME extraction conditions during the research process of the present invention:

[0053] 1. Selection of internal standard reagent

[0054] The internal standard in chromatographic analysis is used to correct the recovery rate of the target compound and the injection and response errors of the instrument. A suitable internal standard can make the results more accurate. Internal standards are generally selected from substances with physical and chemical properties similar to those of the target compound (such as homologs). DEA, TBA, and TMA were selected as internal standards for screening. The pK values of the three substances were a The pK values of 2,6-DIPA are 4.13, 3.30, and 5.38, respectively. a The pK value of DEA is 4.25. TMA is too alkaline, which easily forms tailing and produces a high matrix effect at the injection port. a The value is close to that of 2,6-DIPA, so DEA is added as the internal standard for recovery correction during the hydrolysis-extraction of samples. TBA has a weak alkalinity and is easily lost by high-temperature heating. Therefore, TBA is added after sample enrichment and purification as the internal standard for instrument calibration.

[0055] 2. Heating and hydrolysis-extraction optimization

[0056] 2.1 Types of extraction and hydrolysis solvents

[0057] PBAT biodegradable films contain both free 2,6-DIPA and 2,6-DIPI. Therefore, this experiment used an acidic aqueous solution for simultaneous extraction and hydrolysis of 2,6-DIPA and 2,6-DIPI in the PBAT biodegradable films. Compared to other pretreatment methods (ultrasonic-assisted extraction, Soxhlet extraction, microwave-assisted extraction, accelerated solvent extraction, and heating extraction), heating extraction is simpler, safer, and requires no expensive laboratory equipment. These other extraction methods require large amounts of sample and organic solvent, are subject to numerous impurity interferences, and are associated with resource waste, environmental pollution, and potential impacts on analytical results. Furthermore, the combination of acidic aqueous solution and heating extraction promotes the hydrolysis of 2,6-DIPI, enabling the simultaneous determination of the total amount of 2,6-DIPA.

[0058] In the experiment, 2,6-DIPI was hydrolyzed and extracted with 3 mol / L H2SO4, 6 mol / L HCl, and 6 mol / L MSA to evaluate its hydrolysis rate of BDICDI. 100 μL of high concentration BDICDI standard solution (10.300 mg / mL) was heated at 90 °C for 3 h for hydrolysis. Figure 4The results showed no significant difference in the hydrolysis efficiency of 2,6-DIPI among the three acids, with H₂SO₄ showing the lowest hydrolysis efficiency for BDICDI, at only 0.65%. Both HCl and MSA showed significantly higher hydrolysis rates for BDICDI than H₂SO₄. Therefore, H₂SO₄ was selected for the simultaneous extraction and hydrolysis of 2,6-DIPA and 2,6-DIPI from the PBAT biodegradable membrane. The higher hydrolysis rate of BDICDI under HCl and MSA conditions resulted in a higher 2,6-DIPA analysis result.

[0059] 2.2 Selection of H2SO4 concentration

[0060] According to step S1, the effect of H2SO4 concentration (0.5mol / L, 1mol / L, 2mol / L, 3mol / L, 4mol / L, 6mol / L) on the hydrolysis of 2,6-DIPI was investigated. Figure 5 The results showed that the hydrolysis rate of 2,6-DIPI increased with increasing H2SO4 concentration. At 3 mol / L, the hydrolysis rate reached 91%. As the concentration continued to rise, the 2,6-DIPI hydrolysis rate remained essentially stable. Therefore, 3 mol / L H2SO4 was selected to optimize subsequent conditions; further increasing the sulfuric acid concentration would increase the risk of BDICDI hydrolysis.

[0061] 2.3 Heating temperature

[0062] Refer to step S1 and, under the condition that other conditions remain unchanged, set the heating temperatures to 50°C, 70°C, 90°C, and 110°C respectively to determine the optimal heating temperature. Figure 6 The results showed that the hydrolysis rate of 2,6-DIPI was 39% when heated at 50°C, 64% at 70°C, 92% at 90°C, and 93% at 110°C. The increase in heating temperature also increased the hydrolysis rate. When the temperature was 90°C, the isocyanate in the sample was completely hydrolyzed. As the temperature continued to rise, the hydrolysis rate remained basically stable. 90°C was selected as the optimal hydrolysis temperature. Increasing the heating temperature would increase the risk of BDICDI hydrolysis.

[0063] 2.4 Heating time

[0064] In order to obtain the optimal hydrolysis-extraction time, keep other conditions unchanged and follow step S1 to change the heating time (1h, 2h, 3h, 6h, 12h). Figure 7 The results showed that the hydrolysis rate product of H2SO4 on the mulch film sample gradually increased with increasing heating time within the range of 1 to 3 hours. The hydrolysis rate reached 95% at 3 hours and remained essentially stable thereafter. This indicates that the hydrolysis rate was high within 3 hours and remained unchanged, indicating that the isocyanate was essentially completely hydrolyzed and extracted. 3 hours was selected as the optimal hydrolysis-extraction time.

[0065] 3. Optimization of SHS-HLLME extraction conditions

[0066] Sample cleanup is an essential step in the analysis and detection of target compounds. Common cleanup methods include dispersive liquid-liquid microextraction (DLLME), solid-phase extraction (SPE), solid-phase microextraction (SPME), and homogeneous liquid-liquid microextraction with switchable hydrophilicity solvents (SHS-HLLME). SHS-HLLME is a green and efficient extraction technique proposed by Jessop et al. in 2010. It uses a switchable hydrophilicity solvent (SHS) as the extraction phase. SHSs are solvents that can reversibly switch between a homogeneous miscible phase and a two-phase mixture. These solvents primarily include dipropylamine (DPA), triethylamine (TEA), N,N-diethylbutylamine (DEBA), and N,N-dimethylcyclohexylamine (DMCHA). The hydrophilicity and hydrophobicity of switchable hydrophilicity solvents can be altered by adjusting the pH value, forming an emulsion of numerous small organic droplets in a short period of time, maximizing the contact area between the two phases and improving extraction efficiency. Compared to the other three pretreatment techniques, SHS-HLLME has advantages such as fast extraction time, high extraction efficiency, and a high enrichment factor. Furthermore, SHS-HLLME reduces the amount of organic solvent used, is low-cost, and poses minimal environmental pollution. It is a green and efficient extraction technology, and therefore was selected as the purification method of the present invention.

[0067] In the SHS-HLLME microextraction process, the main factors affecting the extraction efficiency are the type and dosage of SHS, the pH value of SHS homogeneous phase and phase separation, and the extraction time. In order to obtain the optimal microextraction efficiency of 2,6-DIPA, the peak area of extracted 2,6-DIPA (R) multiplied by the final extraction hydrophilic reagent volume (V org ) to TBA peak area ratio (R IS ) to evaluate the extraction efficiency.

[0068] 3.1 Types of SHS

[0069] Hydrophilic reagents must meet the following two conditions to have switchable properties: First, the n-octanol / water partition coefficient (logK ow ) must be between 1.2 and 2.5 with a lower logarithmic K ow The reagent is too hydrophilic and forms a single-phase mixture with water in its neutral form, with a high logarithmic K ow If the reagent is too hydrophobic, it will form a two-phase mixture with water; second, the conjugate acid strength coefficient pK a If the reagent is not alkaline enough, the reaction with carbonated water will not be sufficient to switch from a two-phase mixture to a single-phase mixture.ow =1.64, pK a =11.05; log K of triethylamine (TEA) ow =1.47, pK a =10.68; log K of N,N-dimethylcyclohexylamine (DMCHA) ow =2.04, pK a =10.48; log K of N,N-dimethylbenzylamine (BDMA) ow =1.86, pK a =9.03, and all four selected reagents have switchable properties

[20] .

[0070] According to the single variable investigation mode, when other conditions remain unchanged, 200 μL of hydrophilic reagents, such as DPA, TEA, DMCHA, and BDMA, were added to the test tube respectively. The switchable hydrophilic solvent homogeneous liquid-liquid microextraction was performed according to step S2. The results showed that all four solvents could achieve phase separation, and Figure 8 The results showed that TEA had the smallest extraction volume and lower efficiency, indicating that it was more water-soluble, while BDMA showed more interference peaks. Comparing the extraction effects of DPA and DMCHA, the extraction efficiencies of the two were similar, while the extraction efficiency error of DMCHA was larger. DPA was selected as the best hydrophilic extractant.

[0071] 3.2 DPA dosage for SHS

[0072] In the SHS-HLLME extraction process, the amount of homogeneous DPA directly affects the extraction efficiency and enrichment multiple. In order to obtain the optimal amount of homogeneous DPA, under the same conditions as step S2, the amount of 50, 80, 100, 150, 200, and 250 μL was investigated. The experimental results are shown in Figure 9 50μL DPA was unable to form an effective organic layer. With the increase in the amount of homogeneous DPA from 80 to 250μL, the extraction efficiency also increased. When the amount reached 100μL, the extraction efficiency remained basically unchanged, and the enrichment multiple reached the maximum. Therefore, the optimal amount of homogeneous DPA selected in this experiment was 100μL.

[0073] 3.3 pH value of SHS homogeneity and phase separation

[0074] Literature reports that homogeneous hydrophilic reagents can be obtained by using acid solutions instead of dry ice CO2. In this experiment, the solution for sample hydrolysis-extraction was H2SO4 solution. 3M H2SO4 solution was sufficient for DPA to form a homogeneous solution with a large number of droplets. In order to reduce the number of experimental steps, the pH of the homogeneous phase was not adjusted. After the homogeneous phase is formed, the pH needs to be adjusted to convert the hydrophilic DPA into hydrophobic DPA in an alkaline environment, achieve two-phase separation, and complete the extraction process. The pH value of the system directly affects the extraction efficiency. 12mol / LNaOH was used to adjust the pH of the entire system. After adding DPA, the pH was adjusted to 8, 10, 12, and 14 respectively. Figure 10 The results showed that no organic phase separation occurred at a pH of 8. The volume of DPA extracted gradually increased with increasing pH. The extraction efficiency of 2,6-DIPA reached its maximum at pH 14, indicating that pH 14 was the optimal phase separation condition.

[0075] 3.4 Extraction time

[0076] During the SHS-HLLME extraction process, the extraction time is defined as the time from the addition of NaOH to separate the two phases to the time before the phases are transferred to the centrifuge. Under the condition that other conditions remain unchanged, the effects of different extraction times (0.5min, 1min, 2min, 3min, 4min, 5min) on the extraction efficiency were investigated. Figure 11 The results showed that the SHS-HLLME extraction process was completed quickly, maintaining a nearly equilibrium state at different extraction times. This is because the homogeneous DPA is miscible with the sample. When NaOH is added, the H2SO4 in the sample solution is rapidly neutralized, rapidly converting the hydrophilic DPA to the hydrophobic DPA, forming countless small organic droplets and transforming the entire sample solution into an emulsion. This allows for full contact between the organic and aqueous phases, allowing 2,6-DIPA to quickly transfer from the sample to the DPA, leading to rapid extraction. The optimal extraction time was 1 minute.

[0077] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for determining 2,6-diisopropylaniline in a biodegradable film, characterized in that: The following steps are involved: S1: Add the biodegradable mulch fragment sample to the headspace bottle, add the recovery correction internal standard solution, add the acidic solution, place it in a constant temperature metal bath and heat it, while extracting 2, 6-DIPA and hydrolyzing 2, 6-DIPI. After cooling to room temperature, filter and obtain the extraction filtrate. The recovery correction internal standard solution is 2, 6-diethylaniline, the acidic solution is H2SO4, the concentration is 3 mol / L, the heating temperature is 90°C, and the time is 3 hours; S2: Place the extracted filtrate in a centrifuge tube, add ultrapure water, add a hydrophilic extractant, and vortex mix to obtain a homogeneous system. Place in an ice bath, add an alkaline solution to adjust the pH so that the hydrophilic extractant is converted into a hydrophobic extractant in an alkaline environment to achieve two-phase separation, centrifuge, and collect the upper liquid into another centrifuge tube. The hydrophilic extractant is n-dipropylamine, the amount used is 100 μL, the alkaline solution is NaOH, the pH is adjusted to 14, and the extraction time is 1 min. S3, the upper liquid obtained from S2 was centrifuged again, the upper organic solution was taken into a micro-injection bottle, the internal standard solution for instrument calibration was added, vortexed and mixed for GC-MS analysis. The conditions for GC-MS analysis were: chromatographic column type: DB-5 capillary column, carrier gas: helium, programmed temperature condition: initial temperature 40℃, hold for 1 min; then 10℃ min -1 Raise to 230℃, hold for 1min; -1 Heat to 280°C, hold for 0 min, injection port temperature: 280°C, injection volume: 1.0 µL, split injection, split ratio: 20:1, constant flow rate: 1.0 mL min -1 , the total running time was 24.333 min; ion source temperature: 230°C, quadrupole temperature: 150°C; mass spectrometer transfer line temperature: 280°C, solvent delay time: 12 min, ionization mode was electron impact ionization 70 eV, by using full scan and selected ion scan (SIM) mode, the Full Scan range was m / z =45~500.

2. The method for measuring 2,6-diisopropylaniline in a biodegradable film according to claim 1, wherein In step S3, the internal standard solution for instrument calibration is 2,4,6-tri-tert-butylaniline.

3. The method for measuring 2,6-diisopropylaniline in a biodegradable film according to claim 1, wherein The biodegradable film is a poly(butylene adipate) / terephthalate biodegradable film.

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