A method for determining the content of disperse red 9 in PET colored products by high performance liquid chromatography

Abstract

The application discloses a method for determining the content of disperse red 9 in PET colored products by using high performance liquid chromatography. The application uses accelerated solvent extraction as a pretreatment technology, adds neutral alumina as a dispersion layer and an adsorbent (mixed with the sample) in batches, strengthens solvent penetration, uses a methanol-acetone binary mixed solvent as an extraction solvent system, and realizes efficient and controllable extraction of the target object under specific conditions. The ASE extraction liquid is purified by using an HLB solid phase extraction column, the interference in the matrix is effectively removed, the specificity of the method is improved, and the signal-to-noise ratio of the chromatographic peak is improved. The method has high pretreatment efficiency, good repeatability and low solvent consumption, can realize trace detection at the level of 0.1 mg / kg, can fully meet the compliance detection requirements of disperse red 9 in PET colored products for food contact, and is suitable for popularization and use in various food safety detection institutions and enterprise quality control laboratories.

Description

Technical Field

[0001] This invention belongs to the field of chemical analysis technology, and more specifically, it relates to a method for determining the content of Disperse Red 9 in PET colored products using high performance liquid chromatography. Background Technology

[0002] Disperse Red 9, chemically named 1-(Methylamino)anthraquinone (CI Solvent Red 111, CAS No. 82-38-2, CI 60505), also known as Smoky Red, Transparent Red GS, Solvent Red GS, etc., is a basic anthraquinone organic small molecule dye with the molecular formula C15H11NO2 and a relative molecular mass of 237.25. This dye is a deep red powder with a melting point of approximately 170–173 °C. It has good solubility in organic solvents (such as acetone, ethyl acetate, DMF, etc.) but is almost insoluble in water. Its bright color, excellent heat resistance, and strong tinting strength have led to its widespread application in the dye chemical industry, including dyeing polyester, nylon, acrylic, acetate fiber, blended fabrics, triacetate fiber, sheepskin, and plastics. In plastics processing, it is typically first dispersed in a high concentration in a carrier resin to form a masterbatch, which is then blended with the substrate in a specific ratio.

[0003] According to my country's National Food Safety Standard for the Use of Additives in Food Contact Materials and Articles (GB9685-2016), Disperse Red 9 has been included in the list of permitted colorants for plastic food contact materials (such as PET, PS, AS, ABS, PA, PC, etc.), specifying the maximum usage and purity requirements. However, this standard lacks a dedicated testing method for Disperse Red 9 and corresponding quantitative detection technology.

[0004] From the perspective of the current status of detection technology, after searching domestic and foreign standards and literature, there are currently no reports on specific detection standards or methods for Disperse Red 9 in PET plastic matrix. Existing literature on the detection technology of anthraquinone dyes and active substances can be summarized into the following two categories: (I) Ultraviolet-visible spectrophotometry. Anthraquinone dye molecules contain conjugated double bond systems (such as the carbonyl group and benzene ring of the anthraquinone core), which can produce characteristic absorption of ultraviolet-visible light. Characteristic peaks usually appear at 240–260 nm (strong absorption, B band) and 400–500 nm (weaker visible light absorption, corresponding color). The absorbance and concentration conform to the Lambert-Beer law and can be used for quantification. However, this method has the following limitations: (1) The ultraviolet spectrophotometry has poor selectivity and serious interference in complex PET plastic matrix; (2) Limited sensitivity, low detection limit, and difficulty in trace analysis; (3) It is greatly affected by solution environment and physical factors. (II) Liquid chromatography. Compared with ultraviolet-visible spectrophotometry, liquid chromatography has higher precision and selectivity, but it also faces the following problems: (1) Some liquid chromatography methods use highly toxic solvents such as benzene and toluene for extraction, which poses environmental and operational safety risks; (2) Existing pretreatment methods have unstable extraction efficiency, and the target substance in the PET plastic matrix is ​​tightly bound to the resin, making it difficult to achieve complete extraction; (3) Ordinary ultrasonic extraction methods are greatly affected by operating conditions, and the batch-to-batch repeatability is poor.

[0005] The matrix of PET colored products is extremely complex, posing two major technical challenges to the accurate detection of Disperse Red 9: (1) Physical embedding effect: During high-temperature melt blending, Disperse Red 9 molecules are tightly embedded in the high molecular weight PET polymer chain network, making them difficult to extract before the material undergoes a phase change, requiring optimization of the appropriate temperature selection. (2) Severe matrix interference: During the extraction process, the PET matrix releases a large amount of interfering substances such as oligomers, ester additives, and unreacted monomers. These interfering substances have similar polarity to Disperse Red 9 and are prone to co-elution in chromatographic analysis, severely interfering with the qualitative and quantitative analysis of the target analyte and leading to a high risk of false positives.

[0006] Therefore, there is an urgent need in this field for a proprietary method that can simultaneously achieve efficient cell wall disruption extraction, highly selective purification, and rapid and accurate detection to solve the problem of accurate quantification of Disperse Red 9 in PET colored products. Summary of the Invention

[0007] This invention provides a method for determining the content of Disperse Red 9 in colored PET products using high-performance liquid chromatography (HPLC). Accelerated Solvent Extraction (ASE) is employed as the core pretreatment technology. Neutral alumina is added in stages as a dispersion layer and adsorbent (mixed with the sample). Under specific conditions (100 °C; 10.3 MPa; 5 min, 2 cycles), efficient and controllable extraction of the target analyte is achieved. Precise quantification is then accomplished using a C8 reversed-phase HPLC column and a UV-Vis detector (UV-VIS, 245 nm). This method offers high pretreatment efficiency, good repeatability, and low solvent consumption, enabling trace detection at the 0.1 mg / kg level, fully meeting the compliance testing requirements for Disperse Red 9 in colored PET products intended for food contact.

[0008] This invention is achieved through the following technical solutions:

[0009] A method for determining the content of Disperse Red 9 in colored PET products using high performance liquid chromatography includes the following steps:

[0010] 1) Neutral alumina is packed at the bottom of the extraction cell of the accelerated solvent extraction device as a dispersion layer. The shredded PET colored product sample is mixed evenly with the neutral alumina and packed on the dispersion layer. A mixed solution of methanol and acetone is used as the extraction solvent. Static extraction is carried out at a temperature of 60~120 ℃ and a pressure of 8.3~13.8 MPa for 3~10 min, and the extract is collected.

[0011] 2) The extract was purified by solid-phase extraction column, and the eluent was collected as the test solution. The solution was then detected by high performance liquid chromatography (HPLC) to obtain the chromatographic response value of Disperse Red 9. The HPLC conditions were as follows: reversed-phase HPLC column was used, and isocratic elution was performed using a mixture of methanol and water as the mobile phase.

[0012] 3) The external standard method was used to quantify the chromatographic response value and determine the content of Disperse Red 9 in PET colored products.

[0013] Preferably, in step 1), the size of the PET colored product sample is 2~5 mm.

[0014] Preferably, in step 1), the PET colored product sample is mixed with neutral alumina at a mass ratio of 1:2.

[0015] Preferably, in step 1), glass fiber filter paper is provided at both the bottom and top of the extraction tank.

[0016] Preferably, in step 1), the volume ratio of methanol to acetone in the extraction solvent is (0.5~1):(1~2).

[0017] Preferably, in step 1), the number of extraction cycles is 2 to 5, the rinsing volume is 50 to 80% of the extraction tank volume, and the nitrogen purging time is 60 to 120 s.

[0018] Preferably, in step 2), the solid phase extraction column purification treatment is HLB solid phase extraction column purification treatment.

[0019] Further preferably, the purification process of the HLB solid-phase extraction column is as follows: the solid-phase extraction column is activated with methanol, equilibrated with water, the extract is loaded onto the column, and then rinsed with a 30% (v / v) methanol aqueous solution to remove impurities; the column is eluted with methanol and the eluent is collected.

[0020] Preferably, in step 2), the conditions for high performance liquid chromatography are as follows: using an Eclipse XDB-C8 column, using a solution of methanol and water mixed at a volume ratio of 80:20 to 70:30 as the mobile phase for isocratic elution, with a flow rate of 0.8 to 1.2 mL / min; a column temperature of 40 ℃, and a detection wavelength of 245 nm.

[0021] Further preferably, the Eclipse XDB-C8 column has the following specifications: 4.6 × 250 mm, 5 μm.

[0022] Beneficial effects:

[0023] 1. Filling a technological gap: This invention establishes for the first time a dedicated high-performance liquid chromatography quantitative detection method for Disperse Red 9 (CAS 82-38-2) in colored PET products, filling the industry gap of no dedicated detection standard for this target substance and providing key technical support for the compliance management of this colorant in food contact materials.

[0024] 2. Innovative Pretreatment Method, High Efficiency and Excellent Reproducibility: This invention employs an accelerated solvent extraction (ASE) pretreatment method specifically optimized for plastic samples. It eliminates the need for complex low-temperature pulverization procedures, reducing sample preparation time from approximately 1.5 hours to approximately 20 minutes per sample. Specific conditions, such as high temperature and pressure and an alumina dispersion layer, prevent sample thermal adhesion, achieving a high extraction rate with batch-to-batch RSD < 5%, significantly improving analytical throughput and data reliability.

[0025] 3. High reagent safety: This invention uses a methanol-acetone binary system to replace the highly toxic / high-cost solvents such as benzene, toluene, and hexafluoroisopropanol used in traditional detection. Moreover, the ASE system is a closed extraction system, which greatly reduces the operator's risk of solvent exposure, in line with the concept of green analytical chemistry.

[0026] 4. Low matrix interference and high specificity: This invention uses HLB solid-phase extraction purification combined with reversed-phase C8 column separation. The target analyte has sharp and symmetrical peaks, good separation from matrix interferences, and excellent method specificity, which can effectively avoid false positive results.

[0027] 5. High detection sensitivity: The detection method established in this invention has a detection limit of 0.1 mg / kg and a quantitation limit of 0.3 mg / kg, which can meet the trace detection requirements of Disperse Red 9 in PET colored products and the requirements of food safety risk assessment.

[0028] 6. Wide applicability: The method of this invention has a standardized operation process and clear conditions and parameters, making it suitable for promotion and use in various food safety testing institutions and enterprise quality control laboratories. Attached Figure Description

[0029] Figure 1 High performance liquid chromatogram of Disperse Red 9 standard solution (0.1 mg / L). Detailed Implementation

[0030] To ensure that the objectives, technical solutions, and advantages of this invention are clearer and more complete, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. Specific embodiments are further illustrations of this invention and are not intended to limit it. Based on the embodiments of this invention, embodiments obtained by those skilled in the art without inventive technological improvements will be considered to fall within the scope of protection of this invention. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following embodiments are all commercially available.

[0031] To investigate the safety and potential risks of Disperse Red 9 in colored PET food contact materials, a systematic study was conducted on the detection method of Disperse Red 9 content in colored PET products based on HPLC-UV technology. An accurate and efficient qualitative and quantitative detection technology was established to achieve rapid identification and accurate detection of this target substance.

[0032] Example 1: Method Establishment and Optimization

[0033] 1. Reagents and Materials

[0034] 1.1 Reagents

[0035] Methanol, acetonitrile, acetone, and ethyl acetate were all of chromatographic purity; water was ultrapure water (resistivity ≥18.2 MΩ·cm).

[0036] 1.2 Standard Products

[0037] Disperse Red 9 (1-methylaminoanthraquinone, CI Solvent Red 111), CAS No.: 82-38-2, purity ≥98%, or a certified reference material that has been certified by the state and granted a reference material certificate.

[0038] 1.3 Preparation of standard solutions

[0039] 1.3.1 Disperse Red 9 Standard Stock Solution (1000 mg / L)

[0040] Accurately weigh 10 mg (accurate to 0.1 mg) of Dispersible Red 9 standard, dissolve it in an appropriate amount of acetone, transfer it to a 10 mL brown volumetric flask, and dilute to the mark with acetone. Shake well. Store in a sealed container at 4 ℃, protected from light, for up to 6 months.

[0041] 1.3.2 Disperse Red 9 Standard Intermediate Solution (100 mg / L)

[0042] Accurately pipette 1.0 mL of Disperse Red 9 standard stock solution (1.3.1) into a 10 mL brown volumetric flask, dilute to the mark with methanol, and mix well. Store in a sealed container at 4 ℃, protected from light, for up to 3 months.

[0043] 1.3.3 Preparation of Standard Working Solutions

[0044] Before use, dilute the intermediate standard solution stepwise with methanol to prepare standard working solutions with mass concentrations of 0.050 mg / L, 0.10 mg / L, 0.25 mg / L, 0.50 mg / L, 1.0 mg / L, and 2.0 mg / L. Prepare and use immediately.

[0045] 2. Optimization of experimental conditions

[0046] PET colored product samples were treated with different pretreatments or purification methods to obtain test solutions, which were then detected by high-performance liquid chromatography (HPLC). Optimal conditions were selected based on the detection results. All optimization experiments were conducted under uniform chromatographic detection conditions: an Eclipse XDB-C8 column (4.6 × 250 mm, 5 μm) was used as the analytical column; the mobile phase was methanol-water (80:20, v / v) with isocratic elution; the flow rate was 1.0 mL / min; the column temperature was 40 ℃; and the injection volume was 20 μL.

[0047] 2.1 Optimization of Sample Pretreatment Method

[0048] PET colored products are concentrated blends of dyes and resins at a fixed concentration. The target analyte is tightly bound within the resin matrix, and traditional pretreatment methods have significant limitations. This experiment systematically compared the extraction effects of four pretreatment methods: the method with the largest peak area was used as the baseline (100%), and the extraction efficiency of other methods was expressed as relative peak area. The results are shown in Table 1.

[0049] Table 1 Comparison of the effects of different sample pretreatment methods

[0050] The results showed that the optimized accelerated solvent extraction (ASE) method significantly enhanced the solvent's penetration into the matrix under high temperature and high pressure conditions, effectively disrupting the physical bond between the target analyte and PET resin, thus achieving more complete extraction. The pre-filled alumina dispersion layer acted as an "online stationary phase" during the extraction process. Utilizing its surface active sites, it preferentially adsorbed the more polar PET oligomers and degradation products flowing out with the extractant under high temperature and pressure, while retaining the relatively less polar target analyte, Disperse Red 9, weakly, thus achieving simultaneous extraction and preliminary purification. Compared to liquid nitrogen cryogenic pulverization, ASE eliminates the need for complex pulverization procedures, significantly shortening pretreatment time, and offering higher automation and better batch-to-batch repeatability. However, the unoptimized ASE method may experience sample adhesion, leading to impaired extraction rates. Therefore, the optimized accelerated solvent extraction method was selected as the sample pretreatment method.

[0051] 2.2 Optimization of the extraction solvent system

[0052] Disperse Red 9 (1-methylaminoanthraquinone) is an anthraquinone solvent dye. Its molecule contains an anthraquinone core and an N-methylamino group, which has a large conjugated system and strong hydrophobicity. It has low solubility in common polar solvents (water, ethanol) but good solubility in moderately polar organic solvents such as acetone, methanol, and ethyl acetate.

[0053] Based on the determination to use the optimized accelerated solvent extraction method as the sample pretreatment method, the ASE extraction solvents were screened. Systems such as methanol, acetonitrile, acetone, methanol-acetone (1:1, v / v), and acetonitrile-acetone (1:1, v / v) were investigated. The same positive sample was extracted under the same ASE extraction conditions (100 ℃, 10.3 MPa, 5 min, 2 cycles). The area of ​​the dispersed red 9 peak in the extract was used as the evaluation index. The results are shown in Table 2.

[0054] Table 2. Effect of different ASE extraction solvents on the extraction efficiency of Dispersible Red 9

[0055] The results showed that the methanol-acetone (1:1, v / v) binary mixed solvent had the highest extraction efficiency for Disperse Red 9 under ASE conditions (relative peak area set at 100%), and the extract was clear, which facilitated direct concentration, reconstitution, and injection. Therefore, methanol-acetone (volume ratio 1:1) was determined to be the ASE extraction solvent.

[0056] 2.3 Optimization of ASE extraction temperature and pressure

[0057] Based on the determined extraction solvent, the ASE extraction temperature (60 ℃, 80 ℃, 100 ℃, 120 ℃), extraction pressure (8.3 MPa, 10.3 MPa, 12.0 MPa, 13.8 MPa), and static extraction time (3 min, 5 min, 10 min) were optimized. The results showed that the extraction yield of Disperse Red 9 reached a plateau at 100 ℃, 10.3 MPa, and 5 min. While further increasing the temperature to 120 ℃ slightly increased the extraction yield, it also significantly increased chromatographic background impurities and worsened baseline interference in the chromatogram. Increasing the extraction pressure to 12.0 MPa and 13.8 MPa had little effect on improving the extraction efficiency of Disperse Red 9, and increasing the extraction pressure also posed a risk of increased equipment wear. Considering both extraction efficiency and matrix interference, the optimal ASE extraction conditions were selected: extraction temperature 100 ℃, extraction pressure 10.3 MPa, static extraction time 5 min, and two cycles. Under these conditions, the extraction efficiency reached over 96%.

[0058] 2.4 Optimization of Purification Methods

[0059] The ASE extract of colored PET products contains a certain amount of oligomers, auxiliaries, and pigment co-extracts, which interfere with liquid chromatography analysis. This experiment compared two purification schemes: ① direct concentration and membrane injection; ② HLB solid-phase extraction column purification. The evaluation indicators were baseline stability, peak shape symmetry of the target analyte, and signal-to-noise ratio (S / N). The results showed that direct injection resulted in larger baseline fluctuations and some tailing of the target analyte peaks; after purification with the HLB solid-phase extraction column, the baseline was stable, the target analyte peaks were sharp and symmetrical, and the S / N was significantly improved (by about 3 times). HLB packing material has good retention ability for Disperse Red 9, and the methanol elution recovery rate is over 92%, therefore, the HLB solid-phase extraction column was selected as the purification method.

[0060] 2.5 Optimization of Instrument Conditions

[0061] 2.5.1 Detection Wavelength

[0062] Based on the UV-Vis absorption characteristics of Disperse Red 9 (1-methylaminoanthraquinone), a full scan of the standard solution was performed across the entire wavelength range. The target analyte was found to have a maximum absorption peak at 245 nm, with a secondary absorption peak near 430 nm. 245 nm was selected as the quantitative detection wavelength for the highest sensitivity.

[0063] 2.5.2 Chromatographic column

[0064] Regarding column selection, a C18 column (Eclipse Plus C18, 4.6 × 250 mm, 5 μm) and a C8 column (Eclipse XDB-C8, 4.6 × 250 mm, 5 μm) were compared. The results showed that Disperse Red 9 had a longer retention time on the C18 column (greater than 15 min), requiring an organic phase concentration of over 95% in the mobile phase for elution. On the C8 column, using isocratic elution with 80% methanol and 20% water, the target analyte retention time was approximately 5.4 min, with symmetrical peak shape and good separation from adjacent impurity peaks (R > 1.5), resulting in higher analytical efficiency. Therefore, the Eclipse XDB-C8 column (4.6 × 250 mm, 5 μm) was selected as the analytical column, with isocratic elution of methanol-water (80:20, v / v), a flow rate of 1.0 mL / min, a column temperature of 40 ℃, and an injection volume of 20 μL.

[0065] 2.6 Chromatographic characteristics of standard working solutions

[0066] A standard working solution (0.1 mg / L) was injected under chromatographic conditions. The chromatogram showed that Disperse Red 9 eluted at 5.387 min, with a sharp and symmetrical peak, completely separated from other components in the baseline, verifying the specificity of this method. Figure 1 ).

[0067] Example 2

[0068] Based on the conditions obtained in Example 1, the content of Disperse Red 9 was determined in three actual PET colored product samples (numbered S1, S2, and S3, with colors of bright red, light red, and dark red, respectively).

[0069] 1. Optimized Accelerated Solvent Extraction (ASE) Pretreatment of Samples

[0070] Optimized Accelerated Solvent Extraction (ASE): Actual PET colored product samples are shredded using clean metal scissors (approximately 3mm × 3mm pieces), without liquid nitrogen cryogenic pulverization. Glass fiber filter paper is placed at the bottom of an 11 mL stainless steel extraction cell to prevent particle blockage. Then, 2.0 g of neutral alumina is uniformly added as a dispersion layer. Next, 0.5 g (accurate to 0.1 mg) of the shredded sample is accurately weighed and mixed thoroughly with 1.0 g of neutral alumina, then loaded onto the dispersion layer. Finally, another piece of glass fiber filter paper is placed on top. The neutral alumina dispersion layer mechanically prevents the PET from thermally bonding in its highly elastic state, ensuring uniform penetration of the matrix by the closed, high-pressure fluid.

[0071] The ASE extraction conditions were set as follows: the extraction solvent was methanol-acetone (volume ratio 1:1), the extraction temperature was 100 ℃, the extraction pressure was 10.3 MPa (1500 psi), the static extraction time was 5 min, the number of cycles was 2, the washing volume was 60%, the nitrogen purging time was 60 s, and the collected liquid was the entire extract.

[0072] 2. Purification and volume adjustment of the extract

[0073] The ASE collection solution was concentrated to approximately 1 mL by purging with nitrogen at 40 °C. The HLB solid-phase extraction column (60 mg / 3 mL) was activated with 10 mL of methanol, equilibrated with 5 mL of water, and the concentrate was loaded onto the column (flow rate approximately 1 mL / min). Impurities were removed by rinsing with 5 mL of 30% methanol aqueous solution, and the target analyte was eluted with 5 mL of methanol. All eluent was collected and evaporated to near dryness under nitrogen at 40 °C. The solution was then precisely diluted to 1.0 mL with methanol (80% methanol aqueous solution), filtered through a 0.22 μm organic phase filter membrane, and transferred to a liquid chromatography vial for analysis.

[0074] 3. Liquid Chromatography Instrument Conditions

[0075] a) Column: Eclipse XDB-C8 column, 4.6 × 250 mm, 5 μm;

[0076] b) Mobile phase: methanol-water (volume ratio 80:20), isocratic elution;

[0077] c) Flow rate: 1.0 mL / min;

[0078] d) Column temperature: 40 ℃;

[0079] e) Detection wavelength: 245 nm (UV-VIS detector);

[0080] f) Injection volume: 20 μL.

[0081] 4. Qualitative judgment

[0082] The sample solution and the standard working solution (prepared as in Example 1) were measured separately. If a chromatographic peak appeared in the sample solution and the retention time of the peak of Disperse Red 9 in the standard working solution deviated from that in ±2.5%, it could be preliminarily determined that Disperse Red 9 was present in the sample. The reference retention time of the Disperse Red 9 standard was approximately 5.4 min (under the chromatographic conditions described above). If the concentration of Disperse Red 9 in the sample solution was too high, it was diluted to an appropriate factor.

[0083] 5. Quantitative determination

[0084] Following steps 1-2 above, prepare a method blank sample using blank PET particles (without Disperse Red 9) as a control. Inject the blank sample solution and the sample solution sequentially, and obtain the peak area of ​​the target analyte after subtracting the blank background. Ensure consistent instrument operating conditions throughout the determination process for both the sample and the standard working solution. Quantify using the external standard method. Plot a standard working curve with the concentration of the standard working solution as the x-axis (mg / L) and the corresponding peak area as the y-axis. Calculate the content of Disperse Red 9 in the sample using the regression equation, expressed in mg / kg.

[0085] 6. Measurement Results

[0086] Each sample was measured in triplicate, and the average value was taken to calculate the relative standard deviation (RSD). The measurement results are shown in Table 3.

[0087] Table 3. Results of Disperse Red 9 Content Determination in Actual Samples of Colored PET Products

[0088] Table 3 shows that the content of Disperse Red 9 in the three actual samples ranged from 156.4 to 892.0 mg / kg, with RSD values ​​all less than 2.0% (the RSD of sample S3 was only 0.7%), indicating that the method has good repeatability. The darker the sample color, the higher the corresponding content level of Disperse Red 9, which is consistent with the constant. These results demonstrate that the established ASE-HPLC method can accurately determine the content levels of Disperse Red 9 in PET masterbatches, meeting the actual needs of compliance testing for food contact materials.

[0089] Example 3 Methodological Validation

[0090] 1. Standard working curve

[0091] Under the optimized measurement conditions, the standard working solutions (0.050 mg / L to 2.0 mg / L) were tested. A standard working curve was plotted with the standard concentration as the abscissa (mg / L) and the average peak area as the ordinate, yielding the linear equation and correlation coefficient. The results showed that Disperse Red 9 exhibited a good linear relationship with the response value within the concentration range of 0.050 mg / L to 2.0 mg / L, with linear correlation coefficients R² all greater than 0.999, which well met the requirements of the testing work. The linear equation and correlation coefficient are shown in Table 4.

[0092] Table 4. Linear equation and detection limit of the Disperse Red 9 standard working curve

[0093] 2. Limit of detection and limit of quantitation

[0094] The limits of detection (LOD) and quantitation (LOQ) of this method were determined using a blank sample spiked method. Spiking experiments were conducted using blank PET particles to prepare a series of low-concentration standard solutions ranging from 0.025 mg / L to 0.20 mg / L. The lowest detection concentration was set at 3 times the signal-to-noise ratio (S / N=3), and the quantitation limit was set at 3 times the LOD (LOQ=3×LOD). Following the provisions of GB 31604.59-2023 "National Food Safety Standard - General Rules for Validation of Chemical Analysis Methods for Food Contact Materials and Products", the estimated LOD concentration was determined through 20 repeated tests to determine the detection rate, and the quantitation limit was verified for accuracy and precision through 6 repeatability tests. The results showed that the method detection limit for Disperse Red 9 in the PET colored product matrix was 0.1 mg / kg, and the quantitation limit was 0.3 mg / kg (i.e., 3 times the LOD).

[0095] 3. Recovery and precision of the method

[0096] Recovery tests were conducted using a blank PET particle spiked method. Three spiking levels were set up (0.5 mg / kg, 2.0 mg / kg (medium concentration), and 5.0 mg / kg (high concentration)). Each level was measured in parallel six times. Recovery and precision tests were performed, and the results are detailed in Table 5. The test results show that the spiked recoveries of the target analyte in this method ranged from 88.0% to 112%, and the relative standard deviations (RSDs) were all below 8.0%, indicating that this method has good recovery and precision, meeting the validation requirements of GB 31604.59-2023.

[0097] Table 5. Recovery and precision of Disperse Red 9

[0098] in conclusion:

[0099] 1. This invention replaces the liquid nitrogen cryogenic pulverization + ultrasonic extraction method with an optimized accelerated solvent extraction method for the extraction of Disperse Red 9 from colored PET products. By using specific optimized conditions (high temperature 100 °C, high pressure 10.3 MPa), neutral alumina is added as a dispersion layer to enhance solvent penetration, effectively overcoming the physical binding of the PET resin to the target analyte and avoiding the decrease in extraction rate caused by the adhesion of the plastic sample. This method achieves automated, highly efficient, and highly repeatable pretreatment, with a batch-to-batch RSD of <5%, significantly superior to other pretreatment methods.

[0100] 2. This invention uses a methanol-acetone (volume ratio 1:1) binary mixed solvent as the extraction solvent system. This system balances high solubility for anthraquinone dyes and compatibility with the HPLC mobile phase, effectively avoiding the use of highly toxic solvents such as benzene and toluene.

[0101] 3. This invention uses an HLB (hydrophilic-lipophilic balanced) solid-phase extraction column to purify the ASE extract, effectively removing co-extraction interferences such as oligomers and plasticizers in the PET matrix, significantly improving the specificity of the method and the signal-to-noise ratio of chromatographic peaks.

[0102] 4. The HPLC-UV detection conditions used in this invention achieve peak elution and complete separation of Disperse Red 9 within 5 min, resulting in highly efficient analysis. This invention establishes a complete set of methodological validation indicators, including linear range (0.050–2.0 mg / L), limit of detection (0.1 mg / kg), limit of quantitation (0.3 mg / kg), recovery rate (88%–112%), and precision (RSD < 8%), meeting the requirements of GB31604.59-2023.

Claims

1. A method for determining the content of Disperse Red 9 in colored PET products using high performance liquid chromatography, characterized in that, Includes the following steps: 1) Neutral alumina is packed at the bottom of the extraction cell of the accelerated solvent extraction device as a dispersion layer. The shredded PET colored product sample is mixed evenly with the neutral alumina and packed on the dispersion layer. A mixed solution of methanol and acetone is used as the extraction solvent. Static extraction is carried out at a temperature of 60~120 ℃ and a pressure of 8.3~13.8 MPa for 3~10 min, and the extract is collected. 2) The extract was purified by solid-phase extraction column, and the eluent was collected as the test solution. The solution was then detected by high performance liquid chromatography (HPLC) to obtain the chromatographic response value of Disperse Red 9. The HPLC conditions were as follows: reversed-phase HPLC column was used, and isocratic elution was performed using a mixture of methanol and water as the mobile phase. 3) The external standard method was used to quantify the chromatographic response value and determine the content of Disperse Red 9 in PET colored products.

2. The method according to claim 1, characterized in that, In step 1), the size of the PET colored product sample is 2~5 mm.

3. The method according to claim 1, characterized in that, In step 1), the PET colored product sample is mixed with neutral alumina at a mass ratio of 1:

2.

4. The method according to claim 1, characterized in that, In step 1), glass fiber filter paper is provided at both the bottom and top of the extraction tank.

5. The method according to claim 1, characterized in that, In step 1), the volume ratio of methanol to acetone in the extraction solvent is (0.5~1):(1~2).

6. The method according to claim 1, characterized in that, In step 1), the number of extraction cycles is 2 to 5, the rinsing volume is 50 to 80% of the extraction tank volume, and the nitrogen purging time is 60 to 120 seconds.

7. The method according to claim 1, characterized in that, In step 2), the solid phase extraction column purification treatment is HLB solid phase extraction column purification treatment.

8. The method according to claim 7, characterized in that, The purification process of the HLB solid-phase extraction column is as follows: the solid-phase extraction column is activated with methanol, equilibrated with water, the extract is loaded onto the column, and then rinsed with a 30% (v / v) methanol aqueous solution to remove impurities. The column is then eluted with methanol and the eluent is collected.

9. The method according to claim 1, characterized in that, In step 2), the conditions for high performance liquid chromatography are as follows: using an Eclipse XDB-C8 column, isocratic elution is performed using a solution obtained by mixing methanol and water at a volume ratio of 80:20 to 70:30 as the mobile phase, the flow rate is 0.8 to 1.2 mL / min, the column temperature is 40 ℃, and the detection wavelength is 245 nm.

10. The method according to claim 9, characterized in that, The Eclipse XDB-C8 column has the following specifications: 4.6 × 250 mm, 5 μm.

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