High-sensitivity extraction and detection method for unknown VOC and SVOC in food contact paper

Abstract

The invention discloses a high-sensitivity extraction and detection method for unknown VOC and SVOC in food contact paper. The method comprises the following steps: (1) pretreatment of a sample; (2) placing the sample in a headspace bottle, releasing potentially unknown VOC and SVOC substances in the sample into the headspace bottle, and performing efficient extraction on the substances by an optimized solid phase microextraction SPME method; (3) respectively acquiring data in an electron ionization mode and a positive chemical ionization mode, performing non-targeted analysis by using gas chromatography-quadrupole rod-flight time high-resolution mass spectrometry, and accurately identifying and identifying the released unknown substance; and (4) contrastively analyzing the conditions of substances detected in the contact paper for foods with different materials and different purposes. The invention provides a technical method for broad-spectrum screening, efficient extraction and high-sensitivity accurate detection of unknown VOC and SVOC in various types of food contact paper, and can be applied to exploring more unknown fields in the future.

Description

Technical Field

[0001] The present invention relates to the fields of food and analytical chemistry, and particularly to a method for highly sensitive extraction and detection of unknown VOCs and SVOCs in food contact paper. Background Art

[0002] With the improvement of people's living standards, food safety issues have received increasing attention. As the direct contact surface of food, the safety of food packaging materials is of crucial importance. Among various food packaging materials, paper-based packaging materials are widely used due to their excellent printing suitability, environmental protection and degradability, and low price. China and countries around the world have formulated strict regulations and standards for food contact paper, such as "National Food Safety Standard - Food Contact Paper and Board Materials and Articles" (GB 4806.8-2022), "General Safety Requirements for Food Contact Materials and Articles" (GB 4806.1-2016), "Standard for the Use of Additives in Food Contact Materials and Articles" (GB 9685-2016), EU Regulation (EC) No 1935 / 2004, US FDA 21 CFR Part 176, Japanese "Food Safety Law", etc. However, the safety issues of food contact paper have still been prominent in recent years. According to our statistics, from 2022 to 2024, the EU Rapid Alert System for Food and Feed (RASFF) notified 594 non-compliance cases related to food contact materials, among which 59 cases involved food contact paper. The main problems include excessive content of substances such as heavy metal lead, phthalate plasticizers, photoinitiators, bisphenol A, chloropropanol, formaldehyde, perfluorinated compounds, as well as phenomena such as product odor and color migration.

[0003] In fact, in addition to the chemical substances restricted by the above regulations, food contact paper may generate or adsorb various volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) during the production, processing, storage, and transportation processes. Many of these substances have not been discovered and are not restricted by regulations. Some VOCs and SVOCs have potential toxicity and can enter food through migration, posing a hidden danger to food safety. Due to the large variety of food contact paper, it can be classified into tableware, paper cups, paper bags, steaming paper, paper trays, paper boxes, pizza packaging, etc. according to use, and kraft paper, pulp paper, laminated paper, silicone paper, white cardboard, corrugated paper, etc. according to material. Problems such as a large number of unknown VOCs and SVOCs in products, difficult qualitative analysis, and low substance content still lack a detection method that can be used for broad-spectrum screening, high sensitivity, and accurate detection of unknown VOCs and SVOCs in various types of food contact paper. As the world's largest producer and consumer of food contact materials, developing corresponding detection methods is of great significance for improving the quality and safety of "Made in China" products and ensuring consumer health. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper. The present invention provides a technical method for broad-spectrum screening, efficient extraction, and highly sensitive and accurate detection of unknown VOCs and SVOCs in various types of food-contact paper, and is also used to monitor unknown VOCs and SVOC chemical substances in food-contact paper and further evaluate the potential risks to consumers. In the future, it can be applied to explore more unknown fields.

[0005] The highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper of the present invention includes the following steps:

[0006] (1) Pretreatment of the sample;

[0007] (2) Place the sample in a headspace vial, and the potential unknown VOCs and SVOCs in the sample are released into the headspace vial. The substances are efficiently extracted by an optimized solid-phase microextraction (SPME) method.

[0008] (3) Collect data separately under electron ionization mode and positive chemical ionization mode, and perform non-targeted analysis using gas chromatography-quadrupole-time-of-flight high-resolution mass spectrometry to accurately identify and authenticate the released unknowns.

[0009] (4) Conduct comparative analysis on the detected substances in samples of different materials and uses.

[0010] In the highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper of the present invention, step (1) includes the following steps: Cut food-contact paper samples of various types into pieces smaller than 5 mm × 5 mm. After each operation, wipe the scissors with anhydrous ethanol to avoid cross-contamination between samples.

[0011] In the highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper of the present invention, step (2) includes the following steps: Add 1 g of the sample to a 20 mL headspace sample vial, immediately seal the sample vial with a metal screw cap equipped with a polytetrafluoroethylene / silicone resin septum, then incubate the sample at a headspace temperature of 100 °C for 30 minutes, extract with an 80 μm DVB / Carbon WR / PDMS solid-phase microextraction fiber for 15 minutes, and then inject into the gas chromatography injection port for 5 minutes. Before and after injection, the SPME fiber is aged at 270 °C for 5 minutes and 20 minutes respectively to eliminate residual substances.

[0012] In the highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper of the present invention, the detection conditions in step (3) are as follows:

[0013] Analysis was performed using a 7250GC-Q-TOF system equipped with a TriPlus RSH autosampler. The inlet temperature was 270 °C, and the split injection mode was adopted with a split ratio set at 10:1. The carrier gas was helium with a purity of 99.999%, and the flow rate was 1 mL / min.

[0014] Separation was carried out using a DB-5MS UI chromatographic column (30 m × 0.25 mm × 0.25 μm). The programmed temperature conditions were as follows: the initial temperature was 40 °C, held for 1 minute, then increased to 280 °C at a rate of 6 °C / minute and held for 2 minutes. The full-scan mass spectrometry acquisition range was 40 to 500 m / z, the ion source temperature was 230 °C, and each sample was analyzed in both electron ionization (EI) and positive chemical ionization (PCI) modes. In the EI mode, the electron energy was set at 70 eV. In the PCI mode, methane was used as the reaction gas with a flow rate of 1.5 mL / min. The mass spectrometry transfer line temperature was set at 280 °C, the quadrupole temperature was set at 150 °C, the ion source temperature was set at 200 °C, and the ion source emission current was set at 0.5 μA.

[0015] The highly sensitive extraction and detection method for unknown VOCs and SVOCs in the food-contact paper described in the present invention, wherein the analysis method in step (4) includes the following steps:

[0016] Qualitative analysis of unknown VOC / SVOC substances:

[0017] Data collection and analysis were performed using Agilent MassHunter Unknowns Analysis 12.0 and Agilent MassHunter Qualitative Analysis 10.0 software. The high-resolution spectra of unknown substances were deconvoluted into relatively pure spectra using the Suremass plug-in and compared with the standard spectra in the NIST 2020 spectral library. After subtracting the impurity peaks in the blank sample, substances with a matching factor ≥ 80, a base peak ion mass deviation ≤ 5 ppm, a peak area ≥ 500000, and a chromatographic retention index deviation ΔRI < 50 were identified using the NIST spectral library. The smaller the ΔRI value, the more reliable the result. Subsequently, the molecular ion peak and molecular formula were confirmed through the data detected in the PCI mode to distinguish interfering substances with similar scores or lacking chromatographic retention index data. For individual substances such as difficult-to-distinguish isomers, chemical standards were used for final confirmation.

[0018] The highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper according to the present invention further comprises the following steps: using a headspace vial without a sample as a blank control; inserting a blank sample after analyzing five samples in the sample sequence, and then performing instrument calibration to ensure that the mass accuracy is maintained below 1 ppm and the minimum mass resolution reaches 20,000 FWHM; comprehensively maintaining the instrument before analyzing the sample to reduce background interference, including cleaning the ion source, using a new chromatographic column and SPME extraction fiber, inlet liner, and septum.

[0019] The difference between the highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper according to the present invention and the prior art lies in:

[0020] (1) It is applicable to the detection of food-contact paper samples for various purposes (tableware, paper cups, paper bags, steamer paper, paper trays, paper boxes, pizza packaging) and various materials (kraft paper, pulp paper, laminated paper, silicone paper, white cardboard, corrugated paper), different from the previous methods that are only applicable to individual types of food-contact paper samples;

[0021] (2) By using three representative types of samples, various conditions such as the injection method, SPME extraction fiber, sample injection volume, headspace incubation temperature, headspace SPME extraction time, split conditions, etc. are optimized and investigated, so that the sample extraction method can adapt to the extraction of various types of food-contact paper samples and has high sensitivity, and can extract as many unknown VOCs and SVOCs in the sample as possible. The results show that up to 277 substances are extracted.

[0022] (3) The method of non-target screening by gas chromatography - quadrupole - time-of-flight high-resolution mass spectrometry (GC-Q-TOF) is used to identify each unknown substance, and spectral library matching, high-resolution mass spectrometry information filtering, chromatographic retention time deviation, chemical ionization to obtain the molecular ion peak [M] + and the hydrogenation peak [M + H] + etc. are comprehensively used, so that the identification of unknown substances has high accuracy. In summary, the present invention is the first method for broad-spectrum screening, high sensitivity, and accurate detection of unknown VOCs and SVOCs in various types of food-contact paper.

[0023] The following further illustrates the highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper according to the present invention with reference to the accompanying drawings. Description of the Drawings

[0024] Figure 1 It is the optimized result diagram of the chromatographic injection method in the present invention;

[0025] Figure 2 It is the optimized result diagram of the sample injection volume in the present invention;

[0026] Figure 3 It is the optimized result diagram of the headspace incubation temperature of Sample 1 in the present invention;

[0027] Figure 4 It is the optimized result diagram of the headspace incubation temperature of Sample 2 in the present invention;

[0028] Figure 5 It is the optimized result diagram of the headspace incubation temperature of Sample 3 in the present invention;

[0029] Figure 6 It is the optimized result diagram of the headspace SPME extraction time of Sample 1 in the present invention;

[0030] Figure 7 It is the optimized result diagram of the headspace SPME extraction time of Sample 2 in the present invention;

[0031] Figure 8 It is the optimized result diagram of the headspace SPME extraction time of Sample 3 in the present invention;

[0032] Figure 9 It is the optimized result diagram of the chromatographic split flow conditions in Sample 1 of the present invention;

[0033] Figure 10 It is the optimized result diagram of the chromatographic split flow conditions in Sample 2 of the present invention;

[0034] Figure 11 It is the optimized result diagram of the chromatographic split flow conditions in Sample 3 of the present invention;

[0035] Figure 12 It is the result diagram of the investigation on the experimental repeatability in the present invention;

[0036] Figure 13 It is the pie chart of the compounds detected in the food contact paper of the present invention;

[0037] Figure 14 They are the compounds detected in the food contact papers for different uses of the present invention;

[0038] Figure 15 They are the compounds detected in the food contact papers made of different materials of the present invention;

[0039] Note: Figures 1 to 11 Among them: Sample 1, a paper tray made of silicone paper; Sample 2, a paper cup made of kraft paper; Sample 3, a tableware made of pulp. Detailed implementation mode

[0040] I. Experimental part

[0041] 1. Instruments and reagents

[0042] GC-Q-TOF gas chromatography, quadrupole, time-of-flight high-resolution mass spectrometry, equipped with TriPlus RSH autosampler (Agilent, USA), Milli-Q Integral 5 water purification system (Millipore, USA).

[0043] C7-C40 normal alkane standard mixture (1000 μg / mL n-hexane) was purchased from Sigma-Aldrich, USA. Pesticide-grade n-hexane was purchased from Beijing Bailingwei Technology Co., Ltd. Chromatographic-grade methanol was provided by Shanghai Anpu Experimental Technology Co., Ltd. Dipentyl phthalate, dibutyl phthalate, 4-vinylphenol, 2,7-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,5-dimethylnaphthalene, 2,5-dichlorotoluene, 2,3-dichlorotoluene, the purity of these substances is ≥95%, and they are used for the final verification of some unknown volatiles.

[0044] 70 batches of food contact paper samples were randomly purchased from shopping malls or e-commerce platforms in Beijing. These samples can be divided into seven categories according to their use and six categories according to their materials. See Table 1 for details.

[0045] Table 1 Types of food contact paper involved in the present invention

[0046]

[0047] 2. Sample preparation and substance extraction

[0048] Various types of food contact paper samples were cut into pieces less than 5 mm × 5 mm. After each operation, the scissors were wiped with anhydrous ethanol to avoid cross contamination between samples. One gram of sample was added to a 20 mL headspace vial and the vial was immediately sealed with a metal screw cap equipped with a polytetrafluoroethylene / silicone septum. The sample was then incubated at 100 °C headspace temperature for 30 min, extracted with an 80 μm DVB / Carbon WR / PDMS solid phase microextraction (SPME) fiber for 15 min, and then injected into the gas chromatograph injection port for 5 min. Before and after injection, the SPME fiber was aged at 270 °C for 5 min and 20 min, respectively, to eliminate residual substances.

[0049] 3. Test conditions

[0050] The analysis was performed using a 7250GC-Q-TOF system equipped with a TriPlus RSH autosampler (Agilent Technologies, USA). The inlet temperature was 270 °C, and the split injection mode was adopted with a split ratio of 10:1. The carrier gas was helium (purity 99.999%), and the flow rate was 1 mL / min. A DB-5MS UI chromatographic column (30 m × 0.25 mm × 0.25 μm) was used for separation, and the programmed temperature conditions were as follows: the initial temperature was 40 °C, held for 1 minute, then increased to 280 °C at a rate of 6 °C / min and held for 2 minutes. The full-scan mass spectrometry acquisition range was 40 to 500 m / z, the ion source temperature was 230 °C, and each sample was analyzed in both electron ionization (EI) and positive chemical ionization (PCI) modes. In the EI mode, the electron energy was set to 70 eV; in the PCI mode, methane was used as the reaction gas with a flow rate of 1.5 mL / min. The mass spectrometry transfer line temperature was set to 280 °C, the quadrupole temperature was set to 150 °C, the ion source temperature was set to 200 °C, and the ion source emission current was set to 0.5 μA.

[0051] In this study, a headspace vial without sample was used as a blank control. In the sample sequence, after analyzing five samples, a blank sample was inserted, and then the instrument was calibrated to ensure that the mass accuracy was maintained below 1 ppm and the minimum mass resolution was 20000 FWHM. Before analyzing the samples, the instrument needed to be comprehensively maintained to reduce background interference, including cleaning the ion source, using new chromatographic columns and SPME extraction fibers, inlet liners, and septa.

[0052] 4. Qualitative Analysis of Unknown VOC / SVOC Substances

[0053] Agilent MassHunter Unknowns Analysis 12.0 and Agilent MassHunter Qualitative Analysis 10.0 software were used for data collection and analysis. The high-resolution spectra of unknown substances were deconvoluted into relatively pure spectra using the Suremass plug-in and compared with the standard spectra in the NIST 2020 spectral library. After subtracting the impurity peaks in the blank sample, substances with a matching factor ≥ 80, a base peak ion mass deviation ≤ 5 ppm, a peak area ≥ 500000, and a chromatographic retention index deviation (ΔRI) ≤ 50 were identified using the NIST spectral library. The smaller the ΔRI value, the more reliable the result. Subsequently, the molecular ion peak and molecular formula were confirmed through the data detected in the PCI mode to distinguish interfering substances with similar scores or lacking chromatographic retention index data. For individual substances such as difficult-to-distinguish isomers, chemical standards were used for final confirmation.

[0054] II. Results and Analysis

[0055] 1. Parameter Optimization

[0056] 1.1. Optimization of Sampling Method

[0057] Three representative food-contact paper samples were selected (Sample 1, a paper tray made of siliconized paper; Sample 2, a paper cup made of kraft paper; Sample 3, tableware made of pulp paper), and the detection effects of headspace solid-phase microextraction (SPME) and direct headspace sampling method (HS) were compared. Under the same other conditions, different sampling methods were controlled. Among them, 1 g of the sample was incubated in the headspace at 80 °C for 30 minutes, extracted for 20 minutes, and injected into the injection port in splitless mode for 5 minutes.

[0058] It can be seen from Figure 1 that for the three samples, both the number of chromatographic peaks and the peak response of the HS method are significantly lower than those of the SPME method. By comparing different extraction fiber heads of SPME, it was found that the peak response of the 80-μm DVB / Carbon WR / PDMS extraction head in the 25-30 minute time period of Sample 1 and in the 20-25 minute time period of Sample 2 is stronger than that of the 65-μm PDMS / DVB extraction head. In the 20-30 minute time period of Sample 3, obvious bulging occurred with the 65-μm PDMS / DVB, which may be due to the weak adsorption ability of its coating to the target substances, resulting in excessive or incomplete separation of the sample during injection. In contrast, the multi-coated structure of the 80-μm DVB / Carbon WR / PDMS provides better adsorption and separation performance, reduces peak broadening and overlap, and thus avoids the bulging phenomenon. The 80-μm DVB / Carbon WR / PDMS extraction head has broad-spectrum applicability, thermal stability and durability, can effectively cover polar and non-polar compounds in food, and can tolerate high temperatures and repeated use. Therefore, in the analysis of food-contact paper, the extraction method of SPME and the 80-μm DVB / Carbon WR / PDMS extraction head were selected to obtain better extraction effects.

[0059] 1.2. Optimization of Sample Injection Volume

[0060] Next, the sample injection volume was investigated, and chromatograms of 0.5 g, 1 g, and 1.5 g of the injected sample were obtained. Under the same other conditions, different sample amounts were controlled. Among them, it was incubated in the headspace at 80 °C for 30 minutes, extracted with an 80-μm DVB / Carbon WR / PDMS SPME extraction fiber for 20 minutes, and injected into the injection port in splitless mode for 5 minutes.

[0061] In Figure 2Among them, the number and response intensity of the chromatographic peaks of the 0.5 g and 1.5 g samples are overall weaker than those of the 1 g sample. In particular, it is clearly visible for all three contact paper samples that the chromatographic peak intensity of the 1 g sample is significantly higher than that of the 0.5 g and 1.5 g samples within 10 - 20 min, indicating that the injection volume of the 1 g sample can more effectively release VOC and SVOC compounds. This may be because the injection volume of 0.5 g is too small to provide sufficient quantity of substances and response intensity, while the sample volume of 1.5 g is too large, resulting in the tight packing of the paper sample in the headspace vial and hindering the effective release of substances. The 1 g sample volume can provide a moderate quantity and concentration of compounds, thus ensuring a rich and clear chromatogram peak shape, facilitating analysis, and improving the detection sensitivity.

[0062] 1.3. Optimization of Headspace Incubation Temperature

[0063] The chromatograms at incubation temperatures of 60°C, 80°C, 100°C, 120°C, and 140°C were investigated. Under the same other conditions, different incubation temperatures were controlled. Among them, the 1 g sample was equilibrated for 30 minutes at the incubation temperature, extracted with an 80 μm DVB / CarbonWR / PDMS SPME fiber for 20 minutes, and injected in a splitless mode at the injection port for 5 minutes.

[0064] In Figures 3 to 5 Among them, obvious bulging phenomena occurred in Sample 1 and Sample 3 above 120°C, which may be due to the volatilization or degradation of certain components in the sample at high temperatures, thus affecting the stability and accuracy of the analysis. And Sample 2 also showed similar phenomena above 120°C, indicating that too high temperatures may not be suitable for the analysis of food contact paper. Further analysis found that for the 3 samples, there were fewer peaks in the second half at 60°C and 80°C, which should be because it is not conducive to the release of high-boiling substances at low temperatures, and the number and response of the peaks at 100°C were significantly higher than those at 60°C and 80°C. This indicates that the incubation temperature of 100°C can better promote the release and extraction of compounds, while avoiding side reactions that may be caused by high temperatures. In addition, considering that food contact paper may be exposed to temperatures above 100°C during actual use (such as during baking), and even reach above 200°C in some extreme cases (such as baking paper used in air fryers). Therefore, in the analysis of food contact paper, an incubation temperature of 100°C was selected for analysis, which can not only avoid the bulging phenomenon and compound decomposition problems that may occur at high temperatures, but also obtain better extraction effects and analysis results under conditions close to the actual use temperature.

[0065] 1.4. Optimization of Headspace SPME Extraction Time

[0066] Next, chromatograms with headspace SPME extraction times of 5 minutes, 10 minutes, 15 minutes, and 20 minutes were examined. Under the same other conditions, different SPME extraction times were controlled. Among them, 1 g of the sample was incubated at 100 °C for 30 minutes, extracted with an 80-μm DVB / Carbon WR / PDMS SPME fiber, and injected into the injection port in splitless mode for 5 minutes.

[0067] Among Figures 6 to 8 them, the three samples had the worst effect at an extraction time of 5 minutes, indicating that a shorter extraction time could not fully extract the target compounds, resulting in fewer chromatographic peaks and weaker responses. For Sample 1, when the extraction time was 15 minutes, the chromatographic peaks within 30 - 40 minutes were relatively dense, with clear peak shapes and higher response values, which were significantly better than the chromatogram at 20 minutes, indicating that an extraction time of 15 minutes could more effectively extract the target compounds. For Sample 2, the chromatographic peaks within 20 - 40 minutes also showed a relatively high density, and the difference between the chromatograms at 15 minutes and 20 minutes was small, but both were significantly better than the results at 5 minutes and 10 minutes, further demonstrating that an extraction time of 15 minutes could achieve a better extraction effect. For Sample 3, the peak intensity at 15 minutes was also significantly better than that at 10 minutes, indicating that a longer extraction time was helpful for improving the release and adsorption efficiency of the target compounds. Considering the experimental results of the three samples, an extraction time of 15 minutes could ensure efficient extraction while obtaining a chromatogram with clear peak shapes and higher response values, and at the same time avoid problems such as decreased efficiency or overloading of the extraction fiber caused by too long extraction times. Therefore, 15 minutes was selected as the optimized extraction time.

[0068] 1.5. Optimization of split conditions

[0069] The split ratio is one of the key parameters in chromatographic injection. We examined the chromatograms of splitless injection, split injection at 5:1, split injection at 10:1, and split injection at 20:1. Under the same other conditions, different injection modes were controlled, including incubating 1 g of the sample at 100 °C for 30 minutes, extracting with an 80-μm DVB / Carbon WR / PDMS SPME fiber for 15 minutes, and injecting into the injection port for 5 minutes.

[0070] Among Figures 9 to 11In the analysis results, it can be observed that when using the non-split condition, although the number of chromatographic peaks is the largest, the peak shape is poor. For sample 3, there is even an obvious bulging phenomenon, which may be due to overloading during injection, resulting in a decrease in the separation efficiency of the chromatographic column and thus affecting the peak shape quality. Under the split condition of 20:1, the number of chromatographic peaks is the least, and the peak responses of the three samples within the first 25 minutes are not obvious, indicating that this condition is not conducive to the effective detection of compounds. Therefore, both of these conditions are excluded. For sample 2 and sample 3, under the split conditions of 10:1 and 5:1, the chromatograms and the shapes of the chromatographic peaks are similar, indicating that these two split ratios have little effect on these two samples. Although in sample 1, the number of chromatographic peaks under the 5:1 condition is slightly more than that under the 10:1 condition, when analyzing the main compounds in food contact paper, we are more concerned about significant and meaningful peaks, and overly small peaks may not have a substantial impact on the analysis results. Therefore, they are decided not to be considered. Therefore, we selected a split ratio of 10:1, which can not only provide a sufficient number of chromatographic peaks but also ensure good peak shape and peak resolution, thus providing suitable experimental conditions for the accurate analysis of compounds in food contact paper.

[0071] 1.6. Sample repeatability experiment

[0072] Based on the above optimization results, finally, 1 g of the sample was incubated in the headspace at 100 °C for 30 minutes, extracted with an 80 μm DVB / Carbon WR / PDMS SPME fiber for 15 minutes, and injected into the chromatographic injector in a split mode of 10:1 for 5 minutes. The ion source temperature was 230 °C, the quadrupole temperature was 150 °C, and the emission current was 5 μA.

[0073] Figure 12 The chromatograms of three repeated experiments of three food contact paper samples under the same experimental conditions are shown. The results indicate that each sample shows highly consistent chromatographic peak shapes, retention times, and response intensities in multiple repeated analyses, fully demonstrating the stability and reliability of the experimental method. This good repeatability not only reflects the strict control of experimental conditions, such as the optimization of incubation temperature, extraction time, and split ratio, but also indicates that the SPME method adopted can stably and efficiently extract target compounds, while avoiding the influence of matrix interference and operation errors on the results. In addition, the consistency of the repeated experiments also provides a reliable data basis for subsequent qualitative and quantitative analyses, ensuring the accuracy and repeatability of the analysis results. Therefore, Figure 6 it not only verifies the stability of the experimental method but also further supports the rationality of the optimized conditions such as a 10:1 split ratio, a 100 °C incubation temperature, and a 15-minute extraction time, providing a solid technical guarantee for the safety assessment of food contact paper.

[0074] 2. Detection of actual samples

[0075] Based on the above optimized extraction and injection conditions, a sample treatment method and an injection method for various VOCs and SVOCs in multiple food-contact papers were developed. Detection was carried out using GC-Q-TOF high-resolution mass spectrometry. For the non-target screening of 70 food-contact papers, a total of 277 VOC / SVOC substances were identified. The detailed qualitative parameters are listed in Table 2. Among these substances, 43 substances generated [M+H] through PCI chemical ionization. + ions. The base peak ions [M] + and [M+H] + of all substances had a mass deviation of less than 10 ppm. In addition, the chromatographic retention time deviation ΔRI values of all substances were less than 50, and the ΔRI values of 205 substances were less than 10. To ensure the accuracy of the identification, chemical reference substances were used to verify the candidate substances with similar ΔRI values and extremely close unknowns.

[0076] According to the classification of the detected substances using SciFinder and ChemicalBook, Figure 13 The pie chart in shows the distribution of 11 types of substances. Among them, the alcohols and phenols (18.1%) accounted for the largest proportion, followed by acids and esters (17.3%), aldehydes and ketones (15.2%), while the chloroalkanes and amines had the lowest proportions (1.8% and 2.2% respectively). Figure 8 and Figure 9 reveal the distribution of chemical substances in food-contact papers for different uses and materials. The largest number of substances (181) was detected in the paper boxes, while the smallest number (68) was detected in the bamboo steamer papers. In terms of materials, the largest number of substances (219) was detected in the coated papers, while the smallest number (94) was detected in the silicone oil papers.

[0077] The study found that the content of carbonyl compounds was relatively high in recycled papers. Figure 14 and Figure 15 The data in show a trend that fewer carbonyl compounds were detected in the bamboo steamer liner papers and silicone oil papers than in other types of samples. In addition, the types of compounds in recycled papers were more than those in virgin papers. The chromatogram of virgin papers was clearer and had basically no bulges. Based on the superposition of the chromatograms of each type of sample and the aforementioned information, it was speculated that the bamboo steamer liner and silicone oil papers might be mainly made of virgin papers, while other types of food-contact papers might be partially sourced from recycled papers and partially from virgin papers.

[0078] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

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Claims

1. A highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper, characterized in that: It includes the following steps: (1) Pretreatment of the sample; (2) Place the sample in a headspace vial. The potentially unknown VOC and SVOC substances in the sample are released into the headspace vial, and the substances are efficiently extracted by an optimized solid-phase microextraction (SPME) method; (3) Collect data separately in the electron ionization mode and the positive chemical ionization mode, and perform non-targeted analysis using gas chromatography - quadrupole - time-of-flight high-resolution mass spectrometry to accurately identify and authenticate the released unknown substances; (4) Conduct a comparative analysis of the detected substances in samples of different materials and uses.

2. The highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper according to claim 1, characterized in that: Step (1) includes the following steps: Cut various types of food contact paper samples into pieces smaller than 5 mm × 5 mm. After each operation, wipe the scissors with anhydrous ethanol to avoid cross-contamination between samples.

3. The highly sensitive extraction and detection method for unknown VOCs and SVOCs in food-contact paper according to claim 1, characterized in that: Step (2) includes the following steps: Add 1 g of the sample to a 20-mL headspace sample vial, immediately seal the sample vial with a metal screw cap equipped with a polytetrafluoroethylene / silicone resin septum, then incubate the sample at a headspace temperature of 100 °C for 30 minutes, extract with an 80-μm DVB / Carbon WR / PDMS solid-phase microextraction fiber for 15 minutes, and then inject into the gas chromatography injection port for 5 minutes. Before and after injection, the SPME fiber is aged at 270 °C for 5 minutes and 20 minutes respectively to eliminate residual substances.

4. The highly sensitive extraction and detection method for unknown VOCs and SVOCs in food contact paper according to claim 1, characterized in that: The detection conditions in step (3) are as follows: The analysis is carried out using a 7250GC-Q-TOF system equipped with a TriPlus RSH autosampler. The injection port temperature is 270 °C, and the split injection mode is adopted. The split ratio is set to 10:1; the carrier gas is helium with a purity of 99.999%, and the flow rate is 1 mL / min; Separation is carried out using a DB-5MS UI chromatographic column, 30 m × 0.25 mm × 0.25 μm. The programmed temperature conditions are as follows: The initial temperature is 40 °C, held for 1 minute, then raised to 280 °C at a rate of 6 °C / minute and held for 2 minutes; the full-scan mass spectrometry acquisition range is 40 to 500 m / z, the ion source temperature is 230 °C, and each sample is analyzed in both the electron ionization (EI) and positive chemical ionization (PCI) modes. In the EI mode, the electron energy is set to 70 eV; in the PCI mode, methane is used as the reaction gas with a flow rate of 1.5 mL / min; the mass spectrometry transfer line temperature is set to 280 °C, the quadrupole temperature is set to 150 °C, the ion source temperature is set to 200 °C, and the ion source emission current is set to 0.5 μA.

5. The method for highly sensitive extraction and detection of unknown VOCs and SVOCs in food contact paper according to claim 1, wherein: The analysis method in step (4) includes the following steps: Qualitative analysis of unknown VOC / SVOC substances: Data collection and analysis were performed using Agilent MassHunter Unknowns Analysis 12.0 and Agilent MassHunter Qualitative Analysis 10.0 software; the high-resolution spectra of unknown substances were deconvolved into relatively pure spectra using the Suremass plug-in and compared with the standard spectra in the NIST 2020 spectral library; after subtracting the impurity peaks in the blank sample, substances with a matching factor ≥80, a base peak ion mass deviation ≤5 ppm, a peak area ≥500000, and a chromatographic retention index deviation ΔRI ≤50 were identified using the NIST spectral library, where the smaller the ΔRI value, the more reliable the result; subsequently, the molecular ion peak and molecular formula were confirmed through the data detected in the PCI mode to distinguish interfering substances with similar scores or lacking chromatographic retention index data; for individual substances such as difficult-to-distinguish isomers, chemical reference standards were used for final confirmation.

6. The method for highly sensitive extraction and detection of unknown VOCs and SVOCs in food-contact paper according to claim 1, wherein: The method further includes the following steps: using a headspace vial without sample as a blank control; in the sample sequence, after analyzing five samples, inserting a blank sample and then performing instrument calibration to ensure that the mass accuracy remains below 1 ppm and the minimum mass resolution reaches 20000 FWHM; before analyzing the sample, comprehensively maintaining the instrument to reduce background interference, including cleaning the ion source, using a new chromatographic column and SPME extraction fiber, inlet liner, and septum.

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