Method for determining migration volume of alkyl gallate in food contact material by using solid food simulant

Abstract

The invention discloses a method for determining the migration amount of alkyl gallate in a food contact material by using a solid food simulant, which adopts thermal desorption cold injection-gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry to simultaneously determine octyl gallate and lauryl gallate in modified polyphenyl ether. Wherein solvent-free extraction and enrichment of alkyl gallate in a modified polyphenyl ether standard sample and a modified polyphenyl ether sample to be detected are realized through thermal desorption and cold sample injection, and accurate determination of octyl gallate and lauryl gallate is realized through gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry. The method has the advantages of high selectivity, high accuracy, high sensitivity, good recovery rate and good precision. According to the method, a toxic solvent is not used, complicated solvent extraction and concentration operation is omitted, the working efficiency of daily detection in a laboratory is improved, the body health of testers is effectively guaranteed, the practicability and usability are higher, and the method is more beneficial to testing of large-batch samples.

Description

Technical Field:

[0001] The present invention relates to the technical field of detection of food contact materials, and specifically relates to a method for determining the migration amount of alkyl gallates in food contact materials by using solid food simulants. Background Art:

[0002] In 2023, the newly revised national food safety standard GB 31604.1-2023 "General Rules for Migration Tests of Food Contact Materials and Articles" added a dry food category, but its corresponding food simulant is still a liquid food simulant, which cannot truly reflect the mass transfer of food contact materials to dry foods. Dry foods packaged in food contact materials are very common in daily life, such as powdered dairy products, powdered egg products, dry cereal products, fragmented bean products, dried and dehydrated fruits and vegetables, nuts, solid sugar, powdered seasonings, etc. Therefore, it is very necessary to select a suitable food simulant to as realistically as possible reflect the mass transfer of chemical substances in the food contact materials with which it comes into contact.

[0003] Modified polyphenylene ether is a loose and porous amorphous granular or powdery adsorbent material, mainly composed of a mixture of polyphenylene ether and polystyrene, and has the characteristics of high thermal stability, high chemical inertness, and low water absorption. Existing research has shown that modified polyphenylene ether has good adsorption capacity for polar volatile, weakly polar volatile, non-polar volatile, and non-polar weakly volatile compounds within a wide temperature range. Therefore, it can better adsorb the chemical substances diffused from food contact materials and more realistically reflect the mass transfer of the above chemical substances to dry foods. Alkyl gallates are synthetic antioxidants obtained by esterifying gallic acid with straight-chain alkyl alcohols and are currently widely added to foods and food contact materials. Although alkyl gallates are generally considered safe, their excessive addition may cause allergic reactions. Therefore, it is necessary to limit their migration amount. The 21 CFR 178.2010 promulgated by the US Food and Drug Administration stipulates that the content of octyl gallate and lauryl gallate shall not be higher than 0.02% of the total mass of polymer food contact materials. The EU food contact materials regulation (EC) No 10 / 2011 has limited the specific migration amounts of octyl gallate and lauryl gallate, that is, not higher than 3 mg / kg and 1.2 mg / kg. For dry foods, using modified polyphenylene ether as a solid food simulant can more realistically reflect the mass transfer of alkyl gallates to them, that is, the migration amount to dry foods can be calculated by measuring the content of alkyl gallates in modified polyphenylene ether. However, there is currently no corresponding determination method reported.

[0004] At present, the content of some chemical substances adsorbed in modified polyphenylene ether other than alkyl gallates is usually determined by solvent extraction (Food Additives and Contaminants: Part A, 2020, 37(12), 2165-2183). Although this extraction method is widely used, its drawbacks are also very obvious: first, a large amount of solvent is required, and in order to improve the extraction efficiency, dichloromethane with relatively high toxicity is usually used as the extraction solvent; second, the extraction process is time-consuming and laborious, with low efficiency, which is not conducive to the testing of a large number of samples. On the other hand, alkyl gallates are usually determined by gas chromatography-mass spectrometry (Chap. 14 in Flow Injection Analysis of Food Additives, 1 st Ed., 2015, CRC Press, ISBN: 9780429170300). However, due to the low molecular ion response and extremely similar fragment ions of alkyl gallates in the electron impact ionization (70 eV) mode (NIST Mass Spectral Library 2023), and the relatively low selectivity of the selected ion monitoring mode of gas chromatography-mass spectrometry, it is impossible to accurately distinguish octyl gallate and lauryl gallate restricted by regulations from various alkyl gallates. Therefore, although the content of octyl gallate and lauryl gallate adsorbed in modified polyphenylene ether can be determined by the above solvent extraction and gas chromatography-mass spectrometry, the many drawbacks of this method not only pose severe challenges to its accurate qualitative and quantitative analysis, but also reduce the efficiency of laboratory testing work and have a negative impact on the health of testers. Therefore, there is an urgent need to develop a method for determining the content of octyl gallate and lauryl gallate adsorbed in modified polyphenylene ether with high selectivity, high accuracy, high sensitivity, high automation and without using toxic solvents. Summary of the Invention:

[0005] The purpose of the present invention is to provide a method for determining the migration amount of alkyl gallates in food contact materials using solid food simulants.

[0006] The present invention is realized through the following technical solutions:

[0007] Method for determining migration amount of alkyl gallates in food contact materials using solid food simulants. The solid food simulant is modified polyphenylene ether, and the alkyl gallates are octyl gallate and lauryl gallate. The method comprises the following steps: performing a migration test using modified polyphenylene ether as the solid food simulant, so that the alkyl gallates in the food contact materials migrate to the modified polyphenylene ether to obtain a modified polyphenylene ether test sample adsorbed with alkyl gallates. Taking a modified polyphenylene ether standard sample adsorbed with alkyl gallates and a modified polyphenylene ether test sample adsorbed with alkyl gallates, filling them in a glass thermal desorption tube, and accurately determining octyl gallate and lauryl gallate therein by thermal desorption cold injection-gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry. The thermal desorption conditions are as follows: the initial desorption temperature is 30 °C, after maintaining for 1 min, the temperature is raised to 300 °C at a rate of 60-100 °C / min, preferably 70-90 °C / min, and most preferably 80 °C / min, and maintained for 5 min; the transfer line temperature: 300 °C; the cold injection conditions are as follows: cooled by liquid nitrogen, the initial temperature of the cold trap: -90 °C - 0 °C, preferably -30 °C; the equilibration time: 2 min; the hold time: 10 min; the heating rate of the cold trap: 80 °C / s; the final temperature of the cold trap: 320 °C; the split ratio: 10:1; the liner material of the cold trap injection port: Tenax TA, Carbotrap B / C, glass beads or quartz wool; preferably Tenax TA, Carbotrap B / C, and most preferably Tenax TA; the gas chromatography conditions are as follows: the chromatographic column: diphenyl dimethyl polysiloxane or dimethyl polysiloxane; the carrier gas: helium; the carrier gas flow rate: 1.2 mL / min; the column temperature program: the initial temperature is 100 °C, and the temperature is raised to 300 °C at a rate of 20 °C / min and maintained for 5 min; the tandem mass spectrometry conditions are as follows: APCI positive ion mode; the ion source: atmospheric pressure chemical ionization source APCI; the ion source temperature: 400 °C - 600 °C, preferably 550 °C; the ionization mode: positive ion mode; the corona discharge current: 2.0 - 5.0 μA, preferably 3.5 μA; the cone voltage: 10 - 50 V, preferably 25 V; the cone nitrogen flow rate: 3 SLM; the auxiliary gas flow rate: 6 SLM; the compensation gas flow rate: 2 SLM; the detection mode: selected reaction monitoring SRM; the running time: 15 min, and the post-run time: 5 min.

[0008] The chromatographic column is DB-1 (30 m × 0.25 mm × 0.25 μm), HP-1 (30 m × 0.25 mm × 0.25 μm), DB-5 (30 m × 0.25 mm × 0.25 μm) or HP-5 (30 m × 0.25 mm × 0.25 μm).

[0009] Preferably, the relative humidity for the operation in the APCI positive ion mode is 80% - 100%, more preferably 80% - 85%, and most preferably 85%.

[0010] Preferably, the collision energy used in the selected reaction monitoring SRM is 10-40 eV, more preferably 20-25 eV.

[0011] The preparation method of the modified polyphenylene ether standard sample adsorbed with gallic acid alkyl ester is as follows: octyl gallate and lauryl gallate are dissolved in ethanol to obtain a standard stock solution with a concentration of 1000 mg / L for octyl gallate and lauryl gallate, and then the above standard stock solution is diluted with ethanol to obtain standard working solutions with a concentration of 1, 2, 5, 10 and 20 mg / L for octyl gallate and lauryl gallate; 10 μL of the above standard working solution is respectively transferred to 5 groups of modified polyphenylene ethers pre-filled into glass thermal desorption tubes, and the filling amount of the modified polyphenylene ether is 1.5 g, and the modified polyphenylene ether is pre-aged at 320° C. for 2 hours.

[0012] The preparation of the modified polyphenylene ether sample adsorbed with alkyl gallate is as follows: the modified polyphenylene ether is used as a solid food simulant for migration test, the alkyl gallate in the food contact material migrates to the modified polyphenylene ether to obtain the modified polyphenylene ether sample adsorbed with alkyl gallate, which is filled in a glass thermal desorption tube, and the tube mouth is sealed with a polytetrafluoroethylene stopper for testing; the conditions of the migration test refer to relevant regulations or standards, and the ratio of the surface area of ​​the food contact material to be tested that is expected to contact the food to the mass of the modified polyphenylene ether is 250dm 2 / kg, the migration time is 10d, the migration test temperature is 60℃, or according to actual situation.

[0013] The beneficial effects of the present invention are as follows: The present invention adopts thermal desorption cold injection-gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry to establish a method for simultaneously determining octyl gallate and lauryl gallate in modified polyphenylene ether, wherein thermal desorption cold injection realizes solvent-free extraction and enrichment of gallic acid alkyl esters in modified polyphenylene ether standard samples and modified polyphenylene ether test samples, and gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry realizes accurate determination of octyl gallate and lauryl gallate, and the method has high selectivity, high accuracy and high sensitivity, and also has good recovery rate and precision. The method avoids the use of toxic solvents, eliminates complex and tedious solvent extraction and concentration operations, improves the work efficiency of daily laboratory testing, and effectively protects the health of test personnel. It is more practical and easy to use, more conducive to the testing of large batches of samples, and is conducive to the supervision of octyl gallate and lauryl gallate in food contact materials. Description of the drawings:

[0014] Figure 1 is the total ion current chromatogram of octyl gallate and lauryl gallate;

[0015] Figure 2 is the secondary mass spectrum of octyl gallate (APCI positive ion mode, collision energy is 20 eV);

[0016] Figure 3 is the secondary mass spectrum of lauryl gallate (APCI positive ion mode, collision energy is 25 eV);

[0017] Figure 4 is the EI mass spectrum of octyl gallate (ionization energy is 70 eV);

[0018] Figure 5 is the EI mass spectrum of lauryl gallate (ionization energy is 70 eV). Specific implementation manners:

[0019] The following is a further description of the present invention, rather than a limitation to the present invention.

[0020] Example 1: Analysis by gas chromatography - atmospheric pressure chemical ionization - tandem mass spectrometry and confirmation of positive results

[0021] A method for determining the migration amount of alkyl gallates in food contact materials using a solid food simulant, wherein the solid food simulant is modified polyphenylene ether, and the alkyl gallates are octyl gallate and lauryl gallate, comprising the following steps:

[0022] (1) Preparation of a modified polyphenylene ether standard sample adsorbed with alkyl gallates:

[0023] a. Take a number of glass thermal desorption tubes with an inner diameter of 4 mm and a length of 15 mm, and bake them in an air atmosphere at 480 °C for 2 h for later use.

[0024] b. Take a certain amount of modified polyphenylene ether and fill it into the above-mentioned glass thermal desorption tubes. The filling amount of each glass thermal desorption tube is 1.5 g, and then load silanized quartz wool. Connect the glass thermal desorption tubes filled with modified polyphenylene ether to the nitrogen gas circuit, set the total nitrogen gas flow rate to 0.5 SLM, and age the modified polyphenylene ether at 320 °C for 2 h.

[0025] c. Take the target mass of octyl gallate and lauryl gallate and dissolve them in ethanol to obtain a standard stock solution with the concentrations of both octyl gallate and lauryl gallate being 1000 mg / L. Then, dilute the above standard stock solution with ethanol to obtain standard working solutions with the concentrations of octyl gallate and lauryl gallate being 1, 2, 5, 10, and 20 mg / L. Furthermore, respectively pipette 10 μL of the above standard working solutions into 5 tubes of modified polyphenylene ether pre-filled in glass thermal desorption tubes for testing.

[0026] (2) Preparation of the modified polyphenylene ether test sample adsorbed with alkyl gallate: Using the modified polyphenylene ether as a solid food simulant for migration tests, the alkyl gallate in the food contact material migrates to the modified polyphenylene ether to obtain the modified polyphenylene ether test sample adsorbed with alkyl gallate, which is filled in a glass thermal desorption tube and sealed with a polytetrafluoroethylene plug at the tube mouth for testing; Conditions of the migration test: The ratio of the surface area of the food contact material expected to contact food to the mass of the modified polyphenylene ether is 250 dm 2 / kg, the migration time is 10 d, and the migration test temperature is 60 °C.

[0027] (3) Qualitative and quantitative analysis is carried out on the modified polyphenylene ether standard sample adsorbed with alkyl gallate obtained in step (1) and the modified polyphenylene ether test sample adsorbed with alkyl gallate obtained in step (2) by thermal desorption cold injection - gas chromatography - atmospheric pressure chemical ionization - tandem mass spectrometry.

[0028] a. Thermal desorption conditions: The initial desorption temperature is 30 °C, hold for 1 min and then increase the temperature to 300 °C at a rate of 80 °C / min and hold for 5 min; Transfer line temperature: 300 °C.

[0029] b. Cold injection conditions: Liquid nitrogen refrigeration, cold trap initial temperature: -30 °C; Equilibration time: 2 min; Hold time: 10 min; Cold trap heating rate: 80 °C / s; Cold trap final temperature: 320 °C; Split ratio: 10:1; Liner material of the cold trap injection port: Tenax TA.

[0030] c. Gas chromatography conditions: Chromatographic column: DB-5 or HP-5 (30 m × 0.25 mm × 0.25 μm); Carrier gas: Helium; Carrier gas flow rate: 1.2 mL / min; Column temperature program: The initial temperature is 100 °C, increase the temperature to 300 °C at a rate of 20 °C / min and hold for 5 min. d. Tandem mass spectrometry conditions: APCI positive ion mode; Ion source: Atmospheric pressure chemical ionization source APCI; Ion source temperature: 550 °C; Ionization mode: Positive ion mode; Corona discharge current: 3.5 μA; Cone voltage: 25 V; Cone hole nitrogen flow rate: 3 SLM; Auxiliary gas flow rate: 6 SLM; Compensation gas flow rate: 2 SLM; Detection method: Selected reaction monitoring SRM; Running time: 15 min, post-run 5 min.

[0031] e. APCI positive ion mode conditions: Relative humidity is 80%.

[0032] f. Selected reaction monitoring conditions: Collision energy is 20 - 25 eV.

[0033] If the retention time of the chromatographic peak in the sample is consistent with that of octyl gallate or lauryl gallate, and all ion pairs monitored by selected ion monitoring should appear, then positive confirmation is carried out according to the relative abundance ratio of the qualitative ion pairs. During qualitative analysis, if the allowable deviation of its relative abundance does not exceed the range specified in Table 1, it can be determined that the corresponding analyte exists in the sample.

[0034] Table 1 Maximum allowable deviation of relative abundance ratio of ion pairs during positive result confirmation

[0035]

[0036] Example 2: Selection of thermal desorption heating rate

[0037] The alkyl gallates adsorbed in the modified polyphenylene ether need to be fully desorbed to truly reflect the mass transfer of alkyl gallates in food contact materials to solid foods. Therefore, appropriate thermal desorption conditions need to be selected. For the modified polyphenylene ether, generally, heating to 300 °C and maintaining for a sufficient long time can achieve the desorption of the vast majority of adsorbed substances. However, to reduce the thermal desorption time and improve the detection efficiency, the heating rate during thermal desorption still needs to be optimized. The influence of the thermal desorption heating rate on the instrument response was investigated using modified polyphenylene ether with both octyl gallate and lauryl gallate contents of 100 ng. As shown in Table 2, when the heating rate increased from 60 °C / min to 80 °C / min, the instrument responses of both octyl gallate and lauryl gallate increased significantly. When further increasing to 100 °C / min, there was no obvious change in their peak areas. Considering the instrument response, heating energy consumption, and the service life of the modified polyphenylene ether and the glass thermal desorption tube comprehensively, 70 - 90 °C / min was selected as the preferred thermal desorption heating rate, and 80 °C / min was selected as the most preferred thermal desorption heating rate.

[0038] Table 2 Selection of thermal desorption conditions

[0039]

[0040] Example 3: Selection of cold injection conditions

[0041] The purpose of cold injection is to enrich octyl gallate and lauryl gallate released by thermal desorption of modified polyphenylene ether, so as to improve the chromatographic peak shape and enhance the detection sensitivity. There are two key parameters for cold injection. One is the cold trap temperature, and the other is the liner material of the injection port. Both the cold trap temperature and the liner material directly determine whether the analytes can be fully enriched in the cold trap. Modified polyphenylene ether with both octyl gallate and lauryl gallate content of 100 ng was used to investigate the influence of thermal cold trap temperature and liner material on its instrument response. As shown in Table 3, when the liner material is Tenax TA, as the cold trap temperature rises from -90 °C to -30 °C, the peak areas of octyl gallate and lauryl gallate change little, while when further increased to 0 °C, the peak areas of the two show an obvious decrease. The enrichment ability of other liner materials for octyl gallate and lauryl gallate is significantly weaker than that of Tenax TA. Considering the instrument response and refrigeration energy consumption comprehensively, -30 - -60 °C is selected as the preferred cold trap temperature, -30 °C is selected as the optimal cold trap temperature, Tenax TA and Carbotrap B / C are selected as the preferred liner materials, and Tenax TA is selected as the optimal liner material.

[0042] Table 3 Selection of Cold Injection Conditions

[0043]

[0044] Example 4: Selection of Chromatographic Column

[0045] Based on the above detection conditions, considering that both octyl gallate and lauryl gallate are high-boiling compounds, a non-polar or weakly polar fused silica capillary chromatographic column with dimethylpolysiloxane or dimethyldiphenylpolysiloxane as the stationary phase can be selected for their analysis. Common chromatographic column models include but are not limited to: DB-1, HP-1, DB-5, and HP-5. The above models of chromatographic columns with specifications of 30 m × 0.25 mm × 0.25 μm were respectively used to separate octyl gallate and lauryl gallate. As shown in Table 4, when using DB-5 or HP-5 chromatographic columns, the peak emergence times of octyl gallate and lauryl gallate are shorter and the resolution is slightly higher. Considering factors such as instrument response, analysis time, and resolution comprehensively, DB-5 or HP-5 is selected for the separation of octyl gallate and lauryl gallate.

[0046] Table 4 Selection of Chromatographic Column

[0047]

[0048] Example 5: Selection of Ionization Mode and Optimization of Ion Source Parameters

[0049] Selection of ionization mode: As Figure 4 and Figure 5As shown, the inventors found that the EI mass spectra of octyl gallate and lauryl gallate obtained at an ionization energy of 70 eV are very similar, that is, both have m / z = 153 and m / z = 170 as the two examples with the strongest responses, and the distributions of other ions with lower responses are also basically the same. In particular, the molecular ion [M] + which is the basis for distinguishing the two Figure 2 and Figure 3 have very low responses, only about 5% of the ions with the strongest responses. Therefore, it is difficult to accurately identify the two. Moreover, when other alkyl gallates are present in the sample, the qualitative analysis will be even more difficult. Therefore, this invention adopts the APCI source, a soft ionization method, whose advantage is that it can obtain a molecular ion peak with a relatively high response. As + and + shown, in the second-level mass spectra of octyl gallate and lauryl gallate, the responses of the molecular ion [M+H]

[0050] are 20% - 30% of the strongest ions respectively, far higher than the relative abundances of the [M]

[0051] ions in the above EI mass spectra. Therefore, accurate identification of the two can be achieved, and even when there are multiple alkyl gallates in the sample, accurate identification of the two can still be realized. Therefore, this invention selects APCI as the ionization method.

[0052] On the other hand, the ion source parameters are related to the ionization efficiency of octyl gallate and lauryl gallate, especially the three parameters of corona discharge current, cone voltage, and ion source temperature. Atmospheric pressure chemical ionization can overcome the problem of weak response of the molecular ion peak caused by traditional electron impact ionization, and atmospheric pressure chemical ionization is less interfered, which is beneficial to improving the selectivity of the determination method. Both of the above two alkyl gallates have an ester group structure and are easy to form positive ions, so the ionization mode is selected as the positive ion mode. On the basis of the above detection conditions, the corona discharge current (2.0 - 5.0 μA), cone voltage (10 - 50 V), and ion source temperature (400 °C - 600 °C) are optimized one by one, and their change gradients are 0.5 μA, 5 V, and 50 °C respectively. The effects of these parameters on the instrument responses of octyl gallate and lauryl gallate are investigated. The results show that when the corona discharge current is set to 3.5 μA, the cone voltage is set to 35 V, and the ion source temperature is set to 550 °C, the instrument responses of octyl gallate and lauryl gallate are the highest. + ions, but too high humidity may lead to ionization suppression and thus reduce the [M+H] +The response of ions was thus investigated, and the influence of relative humidity (80%-100%) on the instrument response of octyl gallate and lauryl gallate in the positive ion mode of atmospheric pressure chemical ionization was examined. As shown in Table 5, after the relative humidity increased to 85%, the instrument responses of octyl gallate and lauryl gallate both began to decline. Therefore, 80%-85% was selected as the preferred relative humidity in the positive ion mode of atmospheric pressure chemical ionization, and 85% was selected as the optimal relative humidity in the positive ion mode of atmospheric pressure chemical ionization.

[0053] Table 5 Selection of Relative Humidity

[0054]

[0055] Example 7: Selection of Selected Reaction Monitoring (SRM) Conditions

[0056] Both octyl gallate and lauryl gallate are prone to form [M+H] + peaks, so 283 and 339 were selected as the precursor ions for both. The product ions of both were scanned fully at collision energies of 10 - 40 eV, and it was found that the two product ions with stronger responses for octyl gallate and lauryl gallate were both 153 and 171. The instrument responses of the two product ions 153 and 171 were optimized with a step size of 5 eV. It was found that when the collision energy was 20 eV, the response of the product ion 153 of octyl gallate was the largest; when the collision energy was 25 eV, the response of the product ion 153 of lauryl gallate was the largest. Therefore, 20 eV and 25 eV were respectively selected as the collision energies for selected ion monitoring of octyl gallate and lauryl gallate, and the product ions (153) with the highest responses at this time were selected to establish ion pairs (283→153 and 339→153) for quantification, and the ion pairs with the second highest responses (283→171 and 339→171) were used for auxiliary qualitative analysis. The optimized parameters are shown in Table 6.

[0057] Table 6 Parameters Related to Selected Ion Monitoring of Octyl Gallate and Lauryl Gallate (* for Quantification Ions)

[0058]

[0059] Example 8: Linear Range, Detection Limit and Quantification Limit

[0060] 1. Under the determination conditions in the optimized Example 1, the modified polyphenylene ether added with the alkyl gallate standard working solution was detected. Taking the mass of octyl gallate and lauryl gallate in the modified polyphenylene ether as the abscissa, with the unit in ng, and the corresponding peak area as the ordinate, a standard working curve was plotted to obtain the linear equation and correlation coefficient. The test results show that there is a good linear relationship between its concentration and the response value. The linear equation and correlation coefficient are shown in Table 7. It can be seen that octyl gallate and lauryl gallate have a wide linear range, and the linear correlation coefficients are both greater than 0.9990, which can well meet the needs of the test work.

[0061] Table 7 Linear equations, detection limits and quantification limits of octyl gallate and lauryl gallate

[0062]

[0063] 2. Detection limit and quantification limit

[0064] The detection limit and determination low limit of this method are determined according to the sensitivity of octyl gallate and lauryl gallate detected by the thermal desorption cold injection - gas chromatography - atmospheric pressure chemical ionization - tandem mass spectrometry method described. The modified polyphenylene ether added with the above analytes was tested under the determination conditions in the optimized Example 1. Taking 3 times the signal-to-noise ratio (S / N) as the lowest detection limit, and using the standard deviation σ of 7 repeated tests and the coefficient T (n-1，1-α＝0.99) of the obtained detection limit concentration to verify the effectiveness of the detection limit. When the number of repetitions n = 7 and the confidence level is 99%, T is 3.143, and the product value is calculated according to the above formula. If this value is not higher than the signal-to-noise ratio, the obtained detection limit is effective. Taking 10 times the signal-to-noise ratio (S / N) as the quantification limit, the detection limits and quantification limits of octyl gallate and lauryl gallate are shown in Table 7.

[0065] 3. Recovery rate and precision of the method

[0066] The recovery tests of octyl gallate and lauryl gallate were carried out by the method of adding standard to the modified polyphenylene ether. The spiked modified polyphenylene ether containing 10 ng, 50 ng and 200 ng of octyl gallate and lauryl gallate were prepared respectively, and each spiked level was measured separately 3 times for the recovery rate and precision tests. As shown in Table 8, the spiked recovery rates of octyl gallate and lauryl gallate in the modified polyphenylene ether are between 91.9% - 95.0%, and the relative standard deviations are both between 4.1% - 9.4%, indicating that this method has good recovery rate and precision.

[0067] Table 8 Spiked recovery rates and precisions of octyl gallate and lauryl gallate

[0068]

[0069] Example 9: Determination of Migration Amounts of Octyl Gallate and Lauryl Gallate in Paper-Based Composite Packaging Boxes

[0070] According to the determination conditions in Example 1 after optimization, the migration amounts of octyl gallate and lauryl gallate in a paper-based composite packaging box were determined. An equal volume of modified polyphenylene ether was added according to the stacking method of the dry food expected to be packaged in this paper-based composite packaging box, and then adsorbed at the temperature expected to contact the food for 24 h. Subsequently, the above-mentioned modified polyphenylene ether was filled into a glass thermal desorption tube, with a filling amount of 1.5 g, and according to the conditions of Example 1 after optimization, the contents of octyl gallate and lauryl gallate in it were determined by thermal desorption cold injection-gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry. The obtained chromatogram is as shown in Figure 1 shown. The results show that the contents of octyl gallate and lauryl gallate in the filled 1.5 g of modified polyphenylene ether are 170 ng and 195 ng respectively, and the corresponding migration amounts for this paper-based composite packaging box are 0.09 mg / dm 2 and 1.03 mg / dm 2 .

Claims

1. Method for determining the migration amount of alkyl gallate in food contact materials using a solid food simulant, wherein the solid food simulant is modified polyphenylene ether, characterized in that, The alkyl gallates are octyl gallate and lauryl gallate. The method includes the following steps: Using modified polyphenylene ether as a solid food simulant for migration testing, the alkyl gallates in the food contact material migrate to the modified polyphenylene ether to obtain a modified polyphenylene ether test sample adsorbed with alkyl gallates. Take the modified polyphenylene ether standard sample adsorbed with alkyl gallates and the modified polyphenylene ether test sample adsorbed with alkyl gallates, fill them in a glass thermal desorption tube, and accurately determine the octyl gallate and lauryl gallate in them by thermal desorption cold injection-gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry. The thermal desorption conditions are as follows: starting desorption temperature 30°C, holding for 1 min and then heating to 300°C at a rate of 60-100°C / min and holding for 5 min; transfer line temperature: 300°C; cold injection conditions are: liquid nitrogen refrigeration, cold trap initial temperature: -90°C - 0°C; equilibration time: 2 min; holding time: 10 min; cold trap heating rate: 80°C / s; cold trap final temperature: 320°C; split ratio: 10:1; liner material of the cold trap injection port: Tenax TA, Carbotrap B / C, glass beads or quartz wool; gas chromatography conditions are: chromatographic column: diphenyl dimethyl polysiloxane or dimethyl polysiloxane; carrier gas: helium; carrier gas flow rate: 1.2 mL / min; column temperature program: starting temperature 100°C, heating to 300°C at a rate of 20°C / min and holding for 5 min; tandem mass spectrometry conditions are: APCI positive ion mode; ion source: atmospheric pressure chemical ionization source APCI; ion source temperature: 400°C - 600°C; ionization mode: positive ion mode; corona discharge current: 2.0 - 5.0 μA; cone voltage: 10 - 50 V; cone nitrogen flow rate: 3 SLM; auxiliary gas flow rate: 6 SLM; compensation gas flow rate: 2 SLM; detection mode: selected reaction monitoring SRM; Run time: 15 min, post-run 5 min.

2. The method according to claim 1, wherein The thermal desorption conditions are as follows: starting desorption temperature 30°C, holding for 1 min and then heating to 300°C at a rate of 70 - 90°C / min.

3. The method according to claim 1, wherein Cold injection conditions are: liquid nitrogen refrigeration, cold trap initial temperature: -30°C.

4. The method according to claim 1, characterized in that, Ion source temperature is 550°C; corona discharge current is 3.5 μA; Cone voltage is 25 V.

5. The method according to claim 1, wherein The chromatographic columns are DB-1, HP-1, DB-5 or HP-5. The specifications of DB-1 are 30 m × 0.25 mm × 0.25 μm, the specifications of HP-1 are 30 m × 0.25 mm × 0.25 μm, the specifications of DB-5 are 30 m × 0.25 mm × 0.25 μm, and the specifications of HP-5 are 30 m × 0.25 mm × 0.25 μm.

6. The method according to claim 1, characterized in that, The operating relative humidity of the APCI positive ion mode is 80% - 100%; the collision energy used in the selected reaction monitoring SRM is 10 - 40 eV.

7. The method according to claim 6, characterized in that, The operating relative humidity of the APCI positive ion mode is 80% - 85%; the collision energy used in the selected reaction monitoring SRM is 20 - 25 eV.

8. The method according to claim 1, wherein The preparation method of the modified polyphenylene ether standard sample adsorbed with alkyl gallate is as follows: Take octyl gallate and lauryl gallate and dissolve them in ethanol to obtain a standard stock solution with the concentrations of both octyl gallate and lauryl gallate being 1000 mg / L. Then dilute the above standard stock solution with ethanol to obtain standard working solutions with the concentrations of octyl gallate and lauryl gallate being 1, 2, 5, 10, and 20 mg / L. Respectively pipette 10 μL of the above standard working solutions into 5 groups of modified polyphenylene ethers pre-filled in glass thermal desorption tubes. The filling amount of the modified polyphenylene ether is 1.5 g, and the said modified polyphenylene ether is pre-aged at 320 °C for 2 h.

9. The method according to claim 1, wherein The preparation of the modified polyphenylene ether test sample adsorbed with alkyl gallate is as follows: Use the modified polyphenylene ether as a solid food simulant for migration tests. The alkyl gallate in the food contact material migrates to the modified polyphenylene ether to obtain the modified polyphenylene ether test sample adsorbed with alkyl gallate, which is filled in a glass thermal desorption tube and sealed with a polytetrafluoroethylene plug at the tube opening for testing.

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