Method for detecting liquid phase content of BHT and EMQ in solid antioxidant

Abstract

The invention discloses a method for detecting the liquid phase content of BHT and EMQ in a solid antioxidant, belongs to the technical field of chemical analysis methods, and adopts a liquid chromatograph to detect BHT and EMQ by a single-point method; the method comprises the following steps: extracting a to-be-detected sample with methanol to obtain a primary extracting solution, then adding methanol and aminated carbon nanotubes into sample residues, carrying out vortex centrifugal treatment, ultrasonic treatment and filtration to obtain a secondary extracting solution, and combining the primary extracting solution and the secondary extracting solution for liquid chromatographic analysis; the aminated carbon nanotube contains a pyridine group and / or a thiophene group. The method is simple to operate, the detection time is saved, the modified CNTs-NH2 is adopted to treat sample residues obtained after methanol extraction, and the detection result of the content of BHT and EMQ can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis methods, and particularly relates to a method for detecting the liquid phase content of BHT and EMQ in a solid antioxidant. Background Art

[0002] 2,6-Di-tert-Butyl-p-cresol (BHT) is an organic compound and the largest phenolic antioxidant (called antioxidant in the rubber industry). It is a white crystalline powder that turns yellow and gradually darkens when exposed to light. 2,6-Di-tert-Butyl-p-cresol is widely used in organic synthesis and as an antioxidant for rubber and plastics, gasoline, transformer oil, turbine oil, animal and vegetable oils, and food.

[0003] Ethoxyquin (EMQ), also known as ethoxyquin, has a chemical name of 6-ethoxy 1,2-dihydro-2,2,4-trimethylquinoline. It is one of the excellent feed antioxidants and the most economical antioxidant. It is suitable for premixes, fish meal and fat-added products. It can prevent the deterioration of vitamins A, D, E and fat oxygen and the oxidation and discoloration of natural pigments. It also has certain anti-mildew and preservation effects. It can also be used as a food antioxidant, fruit preservative and rubber antioxidant.

[0004] When BHT and EMQ are mixed in feed, their antioxidant effect is stronger, and BHT can be dissolved in EMQ, which helps to improve the quality of feed. However, in order to ensure the safety of feed, the amount of antioxidant added should not be too much, and the feed may produce process by-products and degradation products during processing and storage, or related substances or impurities may change, thus affecting the quality of the feed. Therefore, it is necessary to conduct a limit check on antioxidants in feed. However, when using high performance liquid chromatography to determine BHT and EMQ, the quantitative method also uses external standard method and internal standard method, but due to insufficient sample processing and extraction, it often leads to inaccurate detection. Summary of the invention

[0005] The object of the present invention is to provide a method for detecting the liquid phase content of BHT and EMQ in a solid antioxidant, which can simplify the operation steps and improve the accuracy of the detection results.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: Detection method of BHT and EMQ liquid content in solid antioxidants, Liquid chromatography was used to detect BHT and EMQ using a single-point method under certain chromatographic operating conditions; The sample is extracted with methanol to obtain a primary extract, and methanol and amino carbon nanotubes (CNTs-NH2) are added to the remaining residue, followed by vortex centrifugation, and then ultrasonic treatment, filtration to obtain a secondary extract, and the primary extract and the secondary extract are combined for liquid chromatography analysis. The amino carbon nanotubes are obtained by modifying carbon nanotubes, and have pyridine groups and / or thiophene groups.

[0007] Preferably, the chromatographic operating conditions are: Chromatographic column: C 18 Column, length 150mm, inner diameter 4.6mm, particle size 5μm, or equivalent; mobile phase: acetonitrile and 2% acetic acid solution (V:V=65:35); flow rate: 1.0mL / min; column temperature: 20-30℃; injection volume: 20 μL; detection wavelength: 280 nm.

[0008] Preferably, methanol is used to extract the sample to be tested, and during the two extraction processes, the mass volume ratio of the sample to be tested to methanol is 0.3-5g:25-100mL.

[0009] According to the above scheme, during the sample treatment process, CNTs-NH2 is used to treat the residue obtained after obtaining the primary extract. During the vortex centrifugation process, the contact probability between BHT and EMQ in the sample residue and CNTs-NH2 can be increased. Since CNTs-NH2 has a hollow structure, BHT and EMQ can be enriched. In the subsequent methanol ultrasonic extraction process, the extraction effect of BHT and EMQ is improved, thereby ensuring the accuracy of the content of BHT and EMQ. In addition, due to the presence of amino groups in CNTs-NH2, the surface of the carbon nanotubes is activated, and its microstructure is changed, providing sufficient space structure for the enrichment of BHT and EMQ. In addition, the presence of amino groups makes it more likely that BHT and EMQ are attached to the inside or surface of CNTs-NH2 molecules during the contact process with CNTs-NH2 molecules, thereby ensuring the extraction rate of BHT and EMQ in the sample to be tested, and then ensuring the accuracy of the test results.

[0010] Preferably, the mass ratio of the amino-modified carbon nanotubes to the sample to be tested is 1:4-8.

[0011] According to one aspect of the present invention, there is provided a method for preparing amino carbon nanotubes, comprising the following steps: S1. Preparation of Acidified Carbon Nanotubes The carbon nanotubes are dispersed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid, and after ultrasonic treatment, the mixture is heated to reflux, and the obtained product is washed with water until it is neutral, filtered and dried to obtain acidified carbon nanotubes; S2. Preparation of carboxylated carbon nanotubes The acidified carbon nanotubes obtained in step S1 are placed in a DMF solvent, and after ultrasonic treatment, a suspension of the acidified carbon nanotubes is obtained, DCC, DMAP and PAA are added thereto, and the suspension is heated to react under an inert atmosphere, and the obtained product is washed with water, filtered and dried to obtain carboxylated carbon nanotubes; S3. Preparation of amino-modified carbon nanotubes The carboxylated carbon nanotubes obtained in step S2 are placed in a DMF solvent, and after ultrasonic treatment, 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine are added to react at room temperature under an inert atmosphere. The obtained product is washed with water, filtered and dried to obtain amino carbon nanotubes.

[0012] Preferably, in step S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1-2; and the mass volume ratio of the carbon nanotubes to the mixed solution of concentrated sulfuric acid and concentrated nitric acid is 1 g:30-50 mL.

[0013] Preferably, in step S1, the ultrasonic treatment is performed for 20-40 min, and the heating reflux temperature is 120-150° C. and the time is 45-80 min.

[0014] Preferably, in step S2, the mass volume ratio of the acidified carbon nanotubes to DMF is 50 mg:30-60 mL; the mass ratio of the acidified carbon nanotubes to DCC, DMAP and PAA is 10:30-50:2-5:80-120.

[0015] Preferably, in step S2, the ultrasonic treatment is performed for 20-40 min, and the heating reaction temperature is 70-90° C. for 20-30 h.

[0016] Preferably, in step S3, the mass volume ratio of carbonylated carbon nanotubes to DMF is 200 mg:30-60 mL; the mass ratio of carbonylated carbon nanotubes to 3-(4-pyridyl)propylamine to 2-(5-methyl-2-thienyl)ethylamine is 5-10:1-2:1-2.

[0017] Preferably, in step S3, the ultrasonic treatment is performed for 20-40 min, and the reaction time at room temperature is 20-30 h.

[0018] The use of 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine further modifies CNTs to obtain CNTs-NH2, which increases the content of non-carbon atoms in the modified carbon nanotubes, grafts amino groups on the molecular surface, and further changes the microstructure due to the presence of pyridine and thiophene groups. The diameter of the carbon nanotubes also increases, and the hollow structure tends to be blurred, with polymerized layers, varying degrees of bending, and rough outer edges, and even sheet or branch structures on the surface. The modified CNTs-NH2 provides more chimeric sites for the target molecules BHT and EMQ, especially the presence of pyridine and thiophene groups increases the chimeric sites on the surface of the modified CNTs, which also helps to improve the adsorption capacity of BHT and EMQ molecules.

[0019] Preferably, in step S3, during the preparation of CNTs-NH2, tyramine is added after carbonylating the carbon nanotubes with 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine.

[0020] Preferably, the mass ratio of 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine is 1-2:1-2:1-3.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The single-point method is used to detect the liquid content of BHT and EMQ in solid antioxidants. Compared with the traditional method, it is simple to operate and saves detection time.

[0022] 2. Using the modified CNTs-NH2 to treat the sample residue after methanol extraction can significantly improve the detection results of BHT and EMQ content; this may be because the surface of the modified CNTs-NH2 is grafted with amino groups, which can increase its affinity for BHT, thereby greatly improving the enrichment of BHT and EMQ molecules in the sample.

[0023] 3. Compared with CNTs, the microstructure of CNTs-NH2 has changed. Its rough outer edge and the lamellar or branched structures on the surface provide more embedding sites for BHT and EMQ molecules. In particular, the surface of the modified CNTs-NH2 contains pyridine, thiophene and other groups, which increases the embedding sites on the surface of the modified CNTs and also helps to improve the adsorption capacity of BHT and EMQ molecules.

[0024] 4. In the process of preparing CNTs-NH2, adding an appropriate amount of tyramine can further improve the detection results of BHT and EMQ in antioxidants. This may be because the presence of amino and hydroxyl groups in tyramine promotes the reaction of 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine with carboxylated carbon nanotubes, thereby increasing the grafting rate of the obtained CNTs-NH2; it may also be because tyramine interacts with pyridine, thiophene and other groups in 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine, which further increases the chimeric sites on the surface of the modified CNTs, thereby improving the adsorption capacity of BHT and EMQ molecules.

[0025] 5. The use of modified CNTs-NH2 to treat the sample residue after methanol extraction can improve the accuracy and reproducibility of the test plan, and the results of the spike recovery test are good. This may be because the modified CNTs-NH2 can improve the extraction rate of BHT and EMQ in the sample after treating the sample, and can also avoid the influence of other impurities in the sample on BHT and EMQ, that is, reduce the loss rate of BHT and EMQ in the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the HPLC chromatogram of the BHT reference substance obtained in Example 1 of the present invention; Figure 2 The HPLC chromatogram of the EMQ reference substance obtained in Example 1 of the present invention; Figure 3 The HPLC chromatogram of the sample to be tested obtained in Example 1 of the present invention; Figure 4 TEM image of CNTs in Example 2 of the present invention; Figure 5 This is the TEM image of CNTs-NH2 in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The following is a further detailed description of the technical solution of the method for detecting the liquid content of BHT and EMQ in the solid antioxidant of the present invention in combination with the specific implementation manner and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Example 1 Sample to be tested: Danxianbao II-K20240308, purchased from Zhejiang Nuobida Biopharmaceutical Co., Ltd. Instrument: High performance liquid chromatograph, Shimadzu LC-2030plus UV detector Reagent: BHT reference substance (source: Aladdin, batch number B2316445, content 99.378%) EMQ reference substance (source: Aladdin, batch number A1712028, content 93.19%) Acetic acid (analytical grade, Sinopharm Chemical Reagent Co., Ltd.) Acetonitrile (chromatographic grade, Honeywell) Deionized water (self-made from a pure water machine) Chromatographic conditions Mobile phase: acetonitrile and 2% acetic acid solution (V:V=65:35) Chromatographic column: Shimadzu ShimNex CS C18, 150 mm*4.6 mm*5 um Flow rate: 1.0 mL / min Column temperature: 30 °C Detection wavelength: 280 nm Injection volume: 20 μL Analysis time: 25 min Sample processing Weigh the sample to be tested, add methanol to the sample at a mass volume ratio of 5g:25mL, shake well, and perform ultrasonic extraction for 40min at an ultrasonic temperature of 30°C and an ultrasonic power of 40%, shake 3 times during the period, shake well and let stand at room temperature, collect the supernatant to obtain the primary extract. Add methanol to the remaining residue, the volume ratio of the two amounts of methanol before and after is 1:1, collect the supernatant after the same steps to obtain the secondary extract, and combine the primary extract and the secondary extract. Pipette 1mL of the combined supernatant to 50mL, shake well, and obtain the sample extract to be tested for standby use.

[0029] Methanol was added to the BHT reference substance and the EMQ reference substance at a mass volume ratio of 5 g:50 mL to obtain BHT reference solution and EMQ reference solution for later use.

[0030] Chromatographic analysis Take 10 mL of the above-mentioned sample extract, BHT control solution, and EMQ control solution, adjust the pH value to 10.0 with a 20% NaOH solution, pass through a 0.22 μm filter membrane, inject the sample into the machine, and use the single-point method to detect and analyze using a high performance liquid chromatography.

[0031] The spectrum obtained by BHT reference substance is shown in Figure 1 , the spectrum obtained by EMQ reference substance is shown in Figure 2 , the spectrum of the sample to be tested can be found in Figure 3 .

[0032] Example 2 Compared with Example 1, this embodiment is different in that: During the sample processing, in the preparation of the sample extract to be tested, after obtaining the primary extract, methanol is added to the remaining residue, the volume ratio of the two amounts of methanol is 1:1, and amino carbon nanotubes (CNTs-NH2) are added, the mass ratio of CNTs-NH2 to the sample is 1:20, and then vortexed for 5 minutes, centrifuged at 8000r / min for 20 minutes. Then the above system is ultrasonically treated for 10 minutes under the conditions of ultrasonic temperature of 45°C and ultrasonic power of 40%, shaken 3 times during the period, shaken and allowed to stand at room temperature, filtered and collected supernatant, and a secondary extract is obtained. Combine the primary extract and the secondary extract. Take 1mL of the combined supernatant and make it up to 50mL, shake well, and obtain the sample extract to be tested for standby use.

[0033] Other conditions and steps are the same.

[0034] The preparation method of CNTs-NH2 is as follows: 1. Preparation of acidified carbon nanotubes (CNTs-OH) Carbon nanotubes (CNTs) were dispersed in a mixture of concentrated sulfuric acid and concentrated nitric acid at a mass volume ratio of 1 g: 20 mL: 20 mL, ultrasonically dispersed for 30 min (100 Hz), and then refluxed at 140 ° C for 60 min. The product was washed with distilled water for 3 times, filtered, and dried to obtain CNTs-OH.

[0035] 2. Preparation of carboxylated carbon nanotubes (CNTs-COOH) The CNTs-OH was placed in a DMF solvent at a mass volume ratio of 50 mg: 40 mL, and ultrasonically dispersed at 100 Hz for 30 min to obtain a CNTs-OH suspension. Then, DCC, DMAP, and PAA were dissolved in DMF at a mass volume ratio of 200 mg: 150 mg: 1000 mg: 40 mL, and then poured into the CNTs-OH suspension, protected by an argon atmosphere, and reacted at 85 ° C for 24 h. Then, the product was washed 3 times with distilled water, filtered, and dried to obtain CNTs-COOH.

[0036] 3. Preparation of amino-modified carbon nanotubes (CNTs-NH2) According to the mass volume ratio of 200mg:50mL, the above CNTs-COOH was placed in DMF solvent, ultrasonically dispersed (100Hz) for 30min, and then 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine were added, wherein the mass ratio of 3-(4-pyridyl)propylamine to 2-(5-methyl-2-thienyl)ethylamine was 1:1, and the mass ratio of CNTs-COOH to 3-(4-pyridyl)propylamine to 2-(5-methyl-2-thienyl)ethylamine was 5:1:1; the reaction was carried out at room temperature for 24h under argon atmosphere protection. Then, the product was washed with distilled water 3 times, filtered, and dried to obtain CNTs-NH2.

[0037] TEM images of CNTs and CNTs-NH2 are shown in Figure 4 and Figure 5 , CNTs have an obvious hollow structure and the edge morphology is relatively clear and complete; while the microstructure of CNTs-NH2 obtained after multiple modification treatments is rough on the outer edge and has an increased diameter compared to CNTs. In addition, the hollow structure of CNTs-NH2 is relatively fuzzy, with a polymerization layer and varying degrees of bending, which indicates that the CNTs modification treatment successfully grafted the amino compounds on the surface of CNTs.

[0038] Example 3 Compared with Example 2, this embodiment is different in that: During the sample processing, the mass ratio of CNTs-NH2 to sample was 1:15. Other conditions and steps were the same.

[0039] Example 4 Compared with Example 2, this embodiment is different in that: During the sample processing, the mass ratio of CNTs-NH2 to sample was 1:10. Other conditions and steps were the same.

[0040] Example 5 Compared with Example 2, this embodiment is different in that: In the preparation process of CNTs-NH2, tyramine is added after CNTs-COOH, 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine; the mass ratio of 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine is 1:1:1. Then, under the protection of argon atmosphere, the reaction is carried out at room temperature for 24 hours, and the product is washed with distilled water three times, filtered, and dried to obtain CNTs-NH2.

[0041] Other conditions and steps are the same.

[0042] Example 6 Compared with Example 2, this embodiment is different in that: In the preparation process of CNTs-NH2, tyramine is added after CNTs-COOH, 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine; the mass ratio of 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine is 1:1:2. Then, under the protection of argon atmosphere, the reaction is carried out at room temperature for 24 hours, the product is washed with distilled water three times, filtered, and dried to obtain CNTs-NH2.

[0043] Other conditions and steps are the same.

[0044] Comparative Example 1 Compared with Example 2, this comparative example is different in that: During the sample processing, CNTs-NH2 was replaced by CNTs of equal mass. Other conditions and steps were the same.

[0045] Comparative Example 2 Compared with Example 2, this comparative example is different in that: During the sample processing, CNTs-OH was used to replace CNTs-NH2 with equal mass. Other conditions and steps were the same.

[0046] Comparative Example 3 Compared with Example 2, this comparative example is different in that: During the preparation of CNTs-NH2, 2-(5-methyl-2-thienyl)ethylamine was replaced with 3-(4-pyridyl)propylamine. Other conditions and steps were the same.

[0047] Comparative Example 4 Compared with Example 2, this comparative example is different in that: During the preparation of CNTs-NH2, 3-(4-pyridyl)propylamine was replaced with 2-(5-methyl-2-thienyl)ethylamine. Other conditions and steps were the same.

[0048] The liquid phase contents of BHT and EMQ in the samples obtained by testing in Examples 1-6 and Comparative Examples 1-4 are shown in Tables 1 and 2.

[0049] Table 1 BHT liquid content in the samples tested in various embodiments and comparative examples

[0050] Referring to the data in Table 1, compared with Example 1, the BHT contents detected in Examples 2-4 were significantly increased, with increases of 7.69%, 10.00%, and 11.11%, respectively; it can be seen that using CNTs-NH2 to treat the sample residue after methanol extraction during the sample processing process can significantly improve the detection value of the BHT content, and as the amount of CNTs-NH2 used increases, the detection results are better.

[0051] The BHT contents obtained by detecting Comparative Examples 1 and 2 are lower than those of Example 2, but are both higher than those of Example 1. It can be seen that the use of CNTs and CNTs-OH to treat the sample residue after methanol extraction can indeed increase the detection value of the BHT content, but the effect is slightly worse than that of the CNTs-NH2 obtained by modifying with 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine.

[0052] First, most of the BHT in the sample is extracted with methanol, and then the modified CNTs-NH2 is used to treat the sample residue after methanol extraction. Compared with the extraction with methanol alone, the extraction effect of BHT in the residue can be greatly improved. This may be because the surface of CNTs-NH2 is grafted with amino groups, which can improve its affinity for BHT, thereby greatly improving the enrichment of BHT molecules in the sample residue. In addition, the changes in the microstructure of CNTs-NH2, its rough outer edge, and the lamellar or branched structures on the surface provide more chimeric sites for BHT molecules. In addition, the presence of pyridine and thiophene groups on the surface of CNTs-NH2 may also improve the adsorption capacity of BHT molecules.

[0053] Compared with Example 2, the BHT contents detected in Example 5 and Example 6 also increased, with increases of 7.14% and 10.00%, respectively; it can be seen that the sample residue after methanol extraction is treated with CNTs-NH2 modified with 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine, which can further improve the detection value of BHT content compared with CNTs-NH2 modified with only 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine.

[0054] This may be because the microstructure of CNTs-NH2 obtained by combining tyramine with 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine is further changed due to the presence of tyramine, thereby further enhancing its adsorption capacity for BHT molecules. This may be because the addition of tyramine further changes the surface grafting structure of CNTs-NH2, thereby further improving the adsorption capacity for BHT molecules in the residue. It may also be because the presence of tyramine increases the grafting rate of 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine on the surface of CNTs-COOH.

[0055] The BHT contents obtained in Comparative Examples 3 and 4 are lower than those in Example 2, but are both higher than those in Example 1. It can be seen that the sample residue after methanol extraction is treated with CNTs-NH2 modified with 3-(4-pyridyl)propylamine and a functional agent, which can indeed improve the detection value of BHT content compared with CNTs-NH2 modified with 3-(4-pyridyl)propylamine alone or 2-(5-methyl-2-thienyl)ethylamine alone.

[0056] Table 2 EMQ liquid content in the samples tested in each embodiment and comparative example

[0057] Referring to the data in Table 2, compared with Example 1, the EMQ contents detected in Examples 2-4 were significantly increased, with increases of 8%, 10%, and 14%, respectively. It can be seen that the use of CNTs-NH2 to treat the sample residue after methanol extraction during the sample treatment process can significantly improve the detection value of the EMQ content, and as the amount of CNTs-NH2 increases, the detection results are better.

[0058] The EMQ contents obtained by detection in Comparative Examples 1 and 2 are lower than those in Example 2, but are both higher than those in Example 1. It can be seen that the use of CNTs and CNTs-OH to treat the sample residue after methanol extraction can indeed improve the detection value of the EMQ content, but the effect is slightly worse than that of CNTs-NH2 obtained by modification with 3-(4-pyridyl)propylamine and a functional agent.

[0059] First, most of the EMQ in the sample was extracted with methanol, and then the modified CNTs-NH2 was used to treat the sample residue after methanol extraction. Compared with the re-extraction with methanol alone, the extraction effect of EMQ in the residue can be greatly improved. This may be because the modified CNTs-NH2 was used to treat the sample residue after methanol extraction. Because the surface of CNTs-NH2 was grafted with amino groups, it can improve its affinity for EMQ, thereby greatly improving the enrichment of EMQ molecules in the sample residue. In addition, the changes in the microstructure of CNTs-NH2, its rough outer edge, and the lamellar or branched structures on the surface all provide more chimeric sites for EMQ molecules. In addition, the presence of pyridine and thiophene groups on the surface of CNTs-NH2 may also improve the adsorption capacity of EMQ molecules.

[0060] Compared with Example 2, the BHT contents detected in Examples 5 and 6 also increased, with increases of 7.41% and 11.12%, respectively; it can be seen that the sample residue after methanol extraction is treated with CNTs-NH2 modified with 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine, which can further improve the detection value of EMQ content compared with CNTs-NH2 modified with only 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine.

[0061] This may be because the microstructure of CNTs-NH2 obtained by combining tyramine with 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine further changes due to the presence of tyramine, thereby further enhancing its adsorption capacity for EMQ molecules. This may be because the addition of tyramine further changes the surface grafting structure of CNTs-NH2, thereby further improving the adsorption capacity for EMQ molecules in the residue. It may also be because the presence of tyramine increases the grafting rate of 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine on the surface of CNTs-COOH.

[0062] The EMQ contents obtained in Comparative Examples 3 and 4 were lower than those in Example 2, but both were higher than those in Example 1. It can be seen that the sample residue after methanol extraction was treated with CNTs-NH2 modified with 3-(4-pyridyl)propylamine and a functional agent, which can improve the detection value of the EMQ content compared with CNTs-NH2 modified with 3-(4-pyridyl)propylamine alone or 2-(5-methyl-2-thienyl)ethylamine alone.

[0063] Test example Spike recovery test A breeding feed for mice and rats that was negative for both BHT and EMQ (purchased from Beijing Keao Xieli Feed Co., Ltd.) was selected and divided into three groups. BHT and EMQ reference standard solutions were added thereto respectively, so that the concentrations of BHT and EMQ reference solutions after addition were both 20 mg / kg.

[0064] Then, the samples were processed in the manner described in Examples 1-6 and Comparative Examples 1-4, and the liquid phase contents of BHT and EMQ were determined according to the chromatographic conditions in Example 1. Six parallel tests were performed to measure the recovery rates. The recovery rates of BHT are shown in Table 3, and the recovery rates of EMQ are shown in Table 4.

[0065] Table 3 Average recovery rate of BHT (%)

[0066] Referring to the data in Table 3, the recovery rate of the sample treated according to the technical solution of Example 1 is low, while the recovery rate of the sample treated according to the technical solution of Examples 2-6 and Comparative Examples 1-4 is greatly increased; it can be seen that the use of CNTs or modified carbon nanotubes, such as CNTs-NH2, CNTs-OH, etc., to treat the sample residue during the sample treatment process can significantly improve the recovery rate. Among them, the recovery rate of Examples 2-4 is increased by an average of 22.2% relative to Example 1; the recovery rate of Examples 5-6 is increased by an average of 23.3% relative to Example 1, and the recovery rate of Comparative Examples 3-4 is increased by an average of 19.5% relative to Example 1. It can be seen that the method of using CNTs-NH2 to treat the sample residue during the sample treatment process has high accuracy and good reproducibility. In particular, the recovery rate of BHT is above 94% when the sample residue is treated with CNTs-NH2.

[0067] Table 4 Average recovery rate of EMQ (%)

[0068] Referring to the data in Table 4, the recovery rate of the sample treated according to the technical solution of Example 1 is low, while the recovery rate of the sample treated according to the technical solution of Examples 2-6 and Comparative Examples 1-4 is greatly increased; it can be seen that the use of CNTs or modified carbon nanotubes, such as CNTs-NH2, CNTs-OH, etc., to treat the sample residue during the sample treatment process can significantly improve the recovery rate. Among them, the recovery rate of Examples 2-4 is increased by an average of 8.8% relative to Example 1; the recovery rate of Examples 5-6 is increased by an average of 10.4% relative to Example 1, and the recovery rate of Comparative Examples 3-4 is increased by an average of 7.1% relative to Example 1. It can be seen that the method of using CNTs-NH2 to treat the sample residue during the sample treatment process has high accuracy and good reproducibility. In particular, the recovery rate of EMQ is above 93% when the sample residue is treated with CNTs-NH2.

[0069] The conventional operations in the operating steps of the present invention are well known to those skilled in the art and will not be described in detail here.

[0070] The above-described embodiments provide a detailed description of the technical solution of the present invention. It should be understood that the above-described embodiments are only specific embodiments of the present invention and are not intended to limit the present invention. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The liquid phase content detection method of BHT and EMQ in solid antioxidants is to detect BHT and EMQ by liquid chromatography using a single-point method; The sample to be tested is extracted with methanol to obtain a primary extract, and then methanol and amino carbon nanotubes are added to the remaining residue, vortex centrifuged, ultrasonically treated, and filtered to obtain a secondary extract, and the primary extract and the secondary extract are combined for liquid chromatography analysis; The amino-modified carbon nanotubes are obtained by modifying carbon nanotubes, and contain pyridine groups and / or thiophene groups.

2. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 1, characterized in that: The chromatographic operating conditions of the liquid chromatograph are: Chromatographic column: C 18 Column, length 150mm, inner diameter 4.6mm, particle size 5μm, or equivalent; mobile phase: acetonitrile and 2% acetic acid solution; flow rate: 1.0mL / min; Column temperature: 20-30℃; injection volume: 20 μL; detection wavelength: 280 nm.

3. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 1, characterized in that: Methanol was used to extract the sample to be tested. During the two extraction processes, the mass volume ratio of the sample to be tested to methanol was 0.3-5g:25-100mL.

4. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 1, characterized in that: The mass ratio of the amino-modified carbon nanotubes to the sample to be tested is 1:5-25.

5. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 1, characterized in that: The preparation method of the amino carbon nanotubes comprises the following steps: S1. Preparation of acidified carbon nanotubes: dispersing carbon nanotubes in a mixture of concentrated sulfuric acid and concentrated nitric acid, ultrasonically treating, heating under reflux, washing the obtained product with water until neutral, filtering and drying to obtain acidified carbon nanotubes; S2. Preparation of carboxylated carbon nanotubes: The acidified carbon nanotubes obtained in step S1 are placed in a DMF solvent, and after ultrasonic treatment, a suspension of acidified carbon nanotubes is obtained, DCC, DMAP and PAA are added thereto, and the reaction is heated under an inert atmosphere, and the obtained product is washed with water, filtered and dried to obtain carboxylated carbon nanotubes; S3. Preparation of amino carbon nanotubes: The carboxylated carbon nanotubes obtained in step S2 are placed in a DMF solvent, and after ultrasonic treatment, 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine are added to react at room temperature under an inert atmosphere. The obtained product is washed with water, filtered and dried to obtain amino carbon nanotubes.

6. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 5, characterized in that: In step S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:1-2; the mass volume ratio of the carbon nanotubes to the mixed solution of concentrated sulfuric acid and concentrated nitric acid is 1g:30-50mL; In step S1, the ultrasonic treatment is performed for 20-40 minutes, and the heating reflux temperature is 120-150° C. and the time is 45-80 minutes.

7. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 5, characterized in that: In step S2, the mass volume ratio of the acidified carbon nanotubes to DMF is 50 mg:30-60 mL; the mass ratio of the acidified carbon nanotubes to DCC, DMAP and PAA is 10:30-50:2-5:80-120; In step S2, the ultrasonic treatment is performed for 20-40 minutes, and the heating reaction temperature is 70-90° C. and the time is 20-30 hours.

8. The method for detecting the liquid phase content of BHT and EMQ in a solid antioxidant according to claim 5, characterized in that: In step S3, the mass volume ratio of carbonyl carbon nanotubes to DMF is 200 mg: 30-60 mL; the mass ratio of carbonyl carbon nanotubes to 3-(4-pyridyl)propylamine to 2-(5-methyl-2-thienyl)ethylamine is 5-10: 1-2: 1-2; In step S3, the ultrasonic treatment is carried out for 20-40 minutes, and the reaction time at room temperature is 20-30 hours.

9. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 5, characterized in that: In step S3, during the preparation of CNTs-NH2, tyramine is added after carbonylating carbon nanotubes, 3-(4-pyridyl)propylamine and 2-(5-methyl-2-thienyl)ethylamine.

10. The method for detecting the liquid content of BHT and EMQ in a solid antioxidant according to claim 9, characterized in that: The mass ratio of 3-(4-pyridyl)propylamine, 2-(5-methyl-2-thienyl)ethylamine and tyramine is 1-2:1-2:1-3.

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