A carbon dot modified molecular sieve, a preparation method thereof, a food sample pretreatment extract and a preparation method and application thereof

Abstract

The application provides a carbon dot modified molecular sieve and a preparation method thereof, a food sample pretreatment extract and a preparation method and application thereof, and belongs to the technical field of food sample pretreatment. The ZSM-5 molecular sieve and the ferroferric oxide powder are dispersed in water to obtain a mixed dispersion liquid; the mixed dispersion liquid and a paramecium culture solution are mixed, and then static treatment and centrifugal separation are sequentially performed to obtain supernatant and a precipitate; finally, the precipitate is sequentially subjected to carbonization treatment, freeze-drying and magnetic separation to obtain the carbon dot modified molecular sieve. The carbon dot modified molecular sieve is mixed with a salt solution to obtain the food sample pretreatment extract. The food sample pretreatment extract of the application can adsorb biological macromolecules such as proteins and fats through the micropores of the molecular sieve, and the polypeptides in the carbon dots can form small cavities on the surface of the molecular sieve by winding each other, so that the small cavities can adsorb additives such as pigments and essences.

Description

Technical Field

[0001] This invention relates to the field of food sample pretreatment technology, and in particular to a carbon dot modified molecular sieve and its preparation method, a food sample pretreatment extract and its preparation method and application. Background Technology

[0002] With a wide variety of food types and processing methods, various food additives are needed to improve product quality. Food additives mainly include preservatives, antioxidants, quality improvers, colorants, pigments, humectants, flavor enhancers, fragrances, and enzymes. Many unscrupulous merchants illegally add excessive amounts of food additives for profit, leading to a series of food safety incidents. To promote the improvement of the food safety testing system and meet the needs of food testing, the construction of rapid testing laboratories in farmers' markets and seafood markets is rapidly underway. However, food samples are subject to interference from a large number of biomolecules such as fats and proteins, as well as food additives such as pigments and fragrances, during the pretreatment stage. Therefore, pretreatment of food samples using extraction solutions before food safety testing is particularly important.

[0003] Food sample pretreatment extracts are used to remove impurities, bacteria, pathogens and other contaminants from food samples, playing a crucial role in food analysis and detection. The traditional QuEChERS reagent is widely used in the sample purification process for food safety testing, but it has the following problems: (1) Limited extraction efficiency: The QuEChERS method cannot completely extract all target analytes, especially for highly polar or non-polar compounds. The recovery rate of some analytes with challenging chemical properties may be low, leading to underestimation or false negatives in the analysis. (2) Matrix effects: Food matrices may contain various interfering compounds, such as pigments, sugars and lipids, which may affect the accuracy and precision of the analysis. Although QuEChERS performs a cleaning step, some matrix effects still exist, leading to reduced sensitivity, ion suppression or enhancement, and impaired analytical performance. (3) Lack of selectivity: The QuEChERS method typically relies on non-selective extraction and cleaning methods, resulting in the co-extraction of unwanted compounds and interfering with the analysis of target analytes. Additional chromatographic separation techniques may be needed to enhance selectivity. (4) Variability: Due to variations in sample preparation techniques, differences in adsorbents, and different analytical techniques, the QuEChERS method may exhibit variability. This variability leads to inconsistent results between laboratories and poses challenges in establishing standardized procedures. (5) Matrix complexity: While QuEChERS is effective for many food matrix solutions, for highly complex matrices, additional extraction and cleaning are required in addition to the QuEChERS method. (6) Lack of quantitative accuracy: Achieving high quantitative accuracy is challenging due to the multi-step nature of the QuEChERS method and potential matrix effects. The presence of interfering compounds and variations in extraction and cleaning efficiency can lead to deviations from the true analyte concentration. (7) Difficulty in elution: QuEChERS can remove various organic acids, pigments, and some sugars and fatty acids. However, due to the strong adsorption properties of QuEChERS, some pesticides are difficult to remove.

[0004] The food testing industry has broad prospects, but existing food sample pretreatment extracts suffer from poor selectivity, susceptibility to matrix effects, limited extraction efficiency, lack of quantitative accuracy, and difficulty in elution. Therefore, researching a carbon-dot-modified molecular sieve and its preparation method to formulate it into a food sample pretreatment extract is of great significance for improving the selectivity of food sample pretreatment. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon dot modified molecular sieve and its preparation method, a food sample pretreatment extract and its preparation method and application, so as to solve the problems of low selectivity and low extraction efficiency of food sample pretreatment extracts in the prior art.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing carbon dot-modified molecular sieves, comprising the following steps:

[0008] (1) Disperse ZSM-5 molecular sieve and iron oxide powder in water to obtain a mixed dispersion;

[0009] (2) After mixing the mixed dispersion and Paramecium culture medium, the mixture was allowed to stand and then centrifuged in sequence to obtain the supernatant and precipitate.

[0010] (3) The precipitate is subjected to carbonization, freeze drying and magnetic separation in sequence to obtain carbon dot modified molecular sieve.

[0011] Preferably, in step (1), the mass ratio of ZSM-5 molecular sieve, iron oxide powder and water is 1.5-2.5:0.5-1.5:10-20.

[0012] Preferably, in step (2), the volume ratio of the mixed dispersion to the Paramecium culture medium is 0.5-1.5:2.5-4.5; and the OD580-660 value of the Paramecium culture medium is 10-150.

[0013] Preferably, in step (2), the settling time is 8 to 12 hours; the centrifugation speed is 6000 to 10000 rpm; and the centrifugation time is 10 to 20 minutes.

[0014] Preferably, in step (3), the carbonization temperature is 200-240°C and the carbonization time is 6-10 hours; the freeze-drying temperature is -20--10°C and the freeze-drying time is 8-16 hours.

[0015] This invention provides a method for preparing carbon dot-modified molecular sieves as described above, resulting in carbon dot-modified molecular sieves.

[0016] This invention also provides a method for preparing a food sample pretreatment extract, comprising the following steps:

[0017] By mixing the carbon dot-modified molecular sieve described above or the carbon dot-modified molecular sieve prepared by the above method with a salt solution, a food sample pretreatment extract can be obtained.

[0018] The salt solution consists of sodium chloride, magnesium salt, and water.

[0019] Preferably, the magnesium salt comprises magnesium chloride and / or magnesium sulfate; the mass ratio of sodium chloride, magnesium salt and water is 3-5:1-3:30-70; and the mass-volume ratio of the carbon dot-modified molecular sieve to the salt solution is 10-50 mg:500-1500 mL.

[0020] The present invention also provides a food sample pretreatment extract prepared by the above-mentioned method.

[0021] The present invention also provides an application of the above-mentioned food sample pretreatment extract in food sample pretreatment, wherein the food sample pretreatment extract and the food sample are mixed and centrifuged to obtain the food sample eluent.

[0022] The mass-to-volume ratio of the food sample and the food sample pretreatment extract is 1g:2-20mL.

[0023] The beneficial effects of this invention are:

[0024] (1) The present invention uses a biological internal modification method with porous ZSM-5 molecular sieve, iron(III) oxide (Fe3O4) and Paramecium fasciatus as raw materials. The porous ZSM-5 molecular sieve has many tiny pores on its surface, which can adsorb iron(III) oxide into the pores. When Paramecium fasciatus engulfs Klebsiella pneumoniae in Paramecium culture medium, it ingests ZSM-5 molecular sieve and iron(III) oxide into its body. Paramecium fasciatus has a variety of polypeptide chains in its body. The carbon dots formed by carbonization treatment are adsorbed on the tiny pores of ZSM-5 molecular sieve to obtain carbon dot modified ZSM-5 molecular sieve.

[0025] (2) The carbon dot modified molecular sieve prepared by the present invention is mixed with salt solution to prepare food sample pretreatment extract. When pretreating food samples, the micropores of ZSM-5 molecular sieve adsorb biological macromolecules such as proteins and fats in food samples. The polypeptide chains in carbon dots are intertwined on the surface of ZSM-5 molecular sieve to form nano-sized micro-cavities, which can adsorb pigments, flavorings and other additives in food samples.

[0026] (3) The food sample pretreatment extract prepared by this invention has the characteristics of high efficiency and large adsorption volume, which can shorten the food sample pretreatment time to within 10 minutes. Moreover, the materials used in the preparation are simple and easy to obtain, the manufacturing cost is low, the reaction is mild, and the safety factor is high. Attached Figure Description

[0027] Figure 1SEM images of ZSM-5 molecular sieve and the carbon dot-modified molecular sieve prepared in Example 1 are shown, where a is a 10,000x magnified SEM image of ZSM-5 molecular sieve, b is a 21,000x magnified SEM image of ZSM-5 molecular sieve, c is a 10,000x magnified SEM image of carbon dot-modified molecular sieve, and d is a 21,000x magnified SEM image of carbon dot-modified molecular sieve.

[0028] Figure 2 The mass spectra of the three food additives detected by GC-MS in Application Example 1 are shown. Detailed Implementation

[0029] This invention provides a method for preparing carbon dot-modified molecular sieves, comprising the following steps:

[0030] (1) Disperse ZSM-5 molecular sieve and iron oxide powder in water to obtain a mixed dispersion;

[0031] (2) After mixing the mixed dispersion and Paramecium culture medium, the mixture was allowed to stand and then centrifuged in sequence to obtain the supernatant and precipitate.

[0032] (3) The precipitate is subjected to carbonization, freeze drying and magnetic separation in sequence to obtain carbon dot modified molecular sieve.

[0033] In this invention, it is preferable to grind ZSM-5 molecular sieve into powder and then mix it with iron oxide powder and water.

[0034] In this invention, in step (1), the mass ratio of ZSM-5 molecular sieve, iron oxide powder and water is 1.5-2.5:0.5-1.5:10-20, preferably 1.7-2.3:0.7-1.3:12-18, and more preferably 1.9-2.1:0.9-1.1:14-16.

[0035] In this invention, ZSM-5 molecular sieve and iron oxide powder are added to water and are preferably mixed by ultrasonic treatment. The frequency of ultrasonic treatment is 20-40 kHz, preferably 25-35 kHz, and more preferably 30 kHz. The ultrasonic treatment time is 1-3 min, preferably 2 min.

[0036] In this invention, in step (2), the volume ratio of the mixed dispersion to the Paramecium culture medium is 0.5-1.5:2.5-4.5, preferably 0.7-1.3:3.0-4.0, and more preferably 0.9-1.1:3.2-3.8; the OD580-660 value of the Paramecium culture medium is 10-150, preferably OD600 is 50-100, and more preferably OD600 is 60-80.

[0037] In this invention, the preparation process of the Paramecium culture medium is as follows:

[0038] First, prepare the paramecium culture medium: The paramecium culture medium consists of wheat straw powder, sodium dihydrogen phosphate, Klebsiella pneumoniae, and water. Add 2.5g of wheat straw powder and 0.75g of sodium dihydrogen phosphate to 1L of deionized water, mix well, boil, then cool to room temperature, filter to remove wheat straw particles, and autoclave the resulting solution. Then add Klebsiella pneumoniae culture medium (purchased from Sigma-Aldrich, model Klebsiella pneumoniae WDCM 00097 Vitroids). TM (Cut off a piece of agar rich in Klebsiella pneumoniae, about the size of a thumbnail, and add it directly to the mixed solution.) Incubate at 37°C for 8–12 hours. After incubation, transfer to a larger container and inoculate with Paramecium germplasm (inoculation amount: 10). 5 The paramecium population (CFU / mL) is then placed in a constant temperature incubator for incubation at 18–24°C. During incubation, the paramecium population expands within 1–3 days. The size of the paramecium population can be confirmed under a microscope, thus obtaining the paramecium culture medium. In this invention, as long as the nutrients in the culture medium are sufficient, the longer the culture time, the higher the concentration of paramecium and the higher the OD value will be when preparing the paramecium culture medium.

[0039] In this invention, the settling time in step (2) is 8 to 12 hours, preferably 9 to 11 hours, and more preferably 10 hours.

[0040] In this invention, after settling, the mixed solution of the mixed dispersion and Paramecium culture medium is preferably dispensed into 16 centrifuge tubes and placed in a high-speed centrifuge for centrifugation; the centrifugation speed is 6000-10000 rpm, preferably 7000-9000 rpm, and more preferably 8000 rpm; the centrifugation time is 10-20 min, preferably 12-18 min, and more preferably 15 min.

[0041] In this invention, it is preferable to decant the supernatant in the centrifuge tube and combine the remaining precipitate before carbonization.

[0042] In this invention, the carbonization process in step (3) is preferably carried out in a nitrogen atmosphere.

[0043] In this invention, in step (3), the carbonization temperature is 200-240°C, preferably 210-230°C, and more preferably 220°C; the carbonization time is 6-10 hours, preferably 7-9 hours, and more preferably 8 hours; the freeze-drying temperature is -20--10°C, preferably -18--12°C, and more preferably -15°C; the freeze-drying time is 8-16 hours, preferably 9-15 hours, and more preferably 10-14 hours.

[0044] This invention provides a method for preparing carbon dot-modified molecular sieves as described above, resulting in carbon dot-modified molecular sieves.

[0045] This invention also provides a method for preparing a food sample pretreatment extract, comprising the following steps:

[0046] By mixing the carbon dot-modified molecular sieve described above or the carbon dot-modified molecular sieve prepared by the above method with a salt solution, a food sample pretreatment extract can be obtained.

[0047] The salt solution consists of sodium chloride, magnesium salt, and water.

[0048] In this invention, the magnesium salt comprises magnesium chloride and / or magnesium sulfate; the mass ratio of sodium chloride, magnesium salt, and water is 3-5:1-3:30-70, preferably 4:2:40-60, and more preferably 4:2:50; the mass-volume ratio of the carbon dot-modified molecular sieve to the salt solution is 10-50 mg:500-1500 mL, preferably 20-40 mg:600-1400 mL, and more preferably 30 mg:800-1200 mL.

[0049] The present invention also provides a food sample pretreatment extract prepared by the above-mentioned method.

[0050] The present invention also provides an application of the above-mentioned food sample pretreatment extract in food sample pretreatment, wherein the food sample pretreatment extract and the food sample are mixed and centrifuged to obtain the food sample eluent.

[0051] The mass-to-volume ratio of the food sample and the food sample pretreatment extract is 1g:2-20mL, preferably 1g:5-15mL, and more preferably 1g:10mL.

[0052] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] The preparation process of the Paramecium culture medium used in this embodiment of the invention is as follows: First, prepare the Paramecium culture medium: The Paramecium culture medium consists of wheat straw powder, sodium dihydrogen phosphate, Klebsiella pneumoniae, and water. Add 2.5g of wheat straw powder and 0.75g of sodium dihydrogen phosphate to 1L of deionized water, mix well, boil, then cool to room temperature, filter to remove wheat straw particles, and autoclave the resulting mixed solution. Then add Klebsiella pneumoniae culture medium (purchased from Sigma-Aldrich, model Klebsiella pneumoniae WDCM 00097 Vitroids). TM (Cut off a piece of agar rich in Klebsiella pneumoniae, about the size of a thumbnail, and add it directly to the mixed solution.) Incubate at 37°C for 10 hours. After incubation, transfer to a larger container and inoculate with Paramecium germplasm (inoculation amount: 10). 5 The culture solution (CFU / mL) was then placed in a constant temperature incubator at 22°C. During the incubation process, the Paramecium population expanded within 3 days. The size of the Paramecium population could be confirmed under a microscope. As needed, culture medium could be added to prepare Paramecium culture medium that meets the requirements of Examples 1, 2 and 3.

[0054] Example 1

[0055] 2.0g of ZSM-5 molecular sieve ground into powder, 1.0g of iron oxide powder, and 15g of deionized water were mixed and then ultrasonically treated at 30kHz for 2 minutes in an ultrasonic vibrator to obtain a mixed dispersion. The mixed dispersion and Paramecium culture medium (with an OD600 value of 100) were mixed at a volume ratio of 1:3 and allowed to stand for 10 hours. After standing, the mixed solution was dispensed into 16 centrifuge tubes and centrifuged at 8000rpm for 15 minutes in a high-speed centrifuge. The supernatant in the centrifuge tubes was decanted and the precipitates were combined and transferred to a container lined with polytetrafluoroethylene. The container was then placed in a muffle furnace, nitrogen was introduced to purge the air, and carbonization was carried out at 220℃ for 8 hours. The carbonized ash was then transferred to a freeze dryer and freeze-dried at -15℃ for 12 hours. Finally, the freeze-dried ash was ground into powder, which is the carbon-dot modified molecular sieve.

[0056] The carbon-dot-modified molecular sieve and salt solution were mixed, wherein the mass-to-volume ratio of the carbon-dot-modified molecular sieve and salt solution was 30 mg: 1000 mL. The salt solution was prepared by 4 g of sodium chloride, 2 g of magnesium sulfate and 50 g of deionized water to obtain the food sample pretreatment extract.

[0057] Figure 1 SEM images of ZSM-5 molecular sieve and the carbon dot-modified molecular sieve prepared in Example 1. Figure 1It can be seen that, compared with ZMS-5 molecular sieve, the surface of carbon dot modified molecular sieve has polypeptide chains from carbon dots wrapped around it, forming nanoscale tiny cavities.

[0058] Example 2

[0059] 1.5g of ZSM-5 molecular sieve ground into powder, 1.5g of iron oxide powder, and 20g of deionized water were mixed and then ultrasonically treated at 40kHz for 3 minutes in an ultrasonic vibrator to obtain a mixed dispersion. The mixed dispersion and Paramecium culture medium (with an OD600 value of 150) were mixed at a volume ratio of 0.5:4.5 and allowed to stand for 12 hours. After standing, the mixed solution was dispensed into 16 centrifuge tubes and centrifuged at 10,000rpm for 10 minutes in a high-speed centrifuge. The supernatant in the centrifuge tubes was decanted and the precipitates were combined and transferred to a container lined with polytetrafluoroethylene. The container was then placed in a muffle furnace, nitrogen was introduced to purge the air, and carbonization was carried out at 200℃ for 10 hours. The carbonized ash was then transferred to a freeze dryer and freeze-dried at -20℃ for 16 hours. Finally, the freeze-dried ash was ground into powder, which is the carbon-dot modified molecular sieve.

[0060] The carbon dot-modified molecular sieve and salt solution were mixed, wherein the mass-to-volume ratio of the carbon dot-modified molecular sieve and salt solution was 50 mg: 1500 mL. The salt solution was prepared by 3 g of sodium chloride, 3 g of magnesium sulfate and 70 g of deionized water to obtain the food sample pretreatment extract.

[0061] Example 3

[0062] 2.5g of ZSM-5 molecular sieve ground into powder, 0.5g of iron oxide powder, and 10g of deionized water were mixed and then ultrasonically treated at 20kHz for 1 minute in an ultrasonic vibrator to obtain a mixed dispersion. The mixed dispersion and Paramecium culture medium (with an OD600 value of 10) were mixed at a volume ratio of 1.5:2.5 and allowed to stand for 8 hours. After standing, the mixed solution was dispensed into 16 centrifuge tubes and centrifuged at 6000rpm for 20 minutes in a high-speed centrifuge. The supernatant in the centrifuge tubes was decanted and the precipitates were combined and transferred to a container lined with polytetrafluoroethylene. The container was then placed in a muffle furnace, nitrogen was introduced to purge the air, and carbonization was carried out at 240℃ for 6 hours. The carbonized ash was then transferred to a freeze dryer and freeze-dried at -10℃ for 8 hours. Finally, the freeze-dried ash was ground into powder, which is the carbon-dot modified molecular sieve.

[0063] The carbon dot-modified molecular sieve and salt solution were mixed, wherein the mass-to-volume ratio of the carbon dot-modified molecular sieve and salt solution was 10 mg: 500 mL. The salt solution was prepared by 5 g of sodium chloride, 1 g of magnesium chloride and 30 g of deionized water to obtain the food sample pretreatment extract.

[0064] Application Example 1

[0065] 5g of pulverized pork sample was placed in a 50mL plastic centrifuge tube. 10mL of clenbuterol standard solution, 10mL of salbutamol standard solution, and 10mL of ractopamine (acetonitrile) standard solution (all with a concentration of 50ng / mL) were added. The mixture was then vortexed for 1min to ensure complete dispersion of the standard solutions in the pork sample. 100mL of the food sample pretreatment extract from Example 1 was then added. The mixture was shaken at 20kHz for 3min and then centrifuged at 13000rpm for 5min. The supernatant was removed. 1mL of acetonitrile was added to the remaining powder in the centrifuge tube, and the mixture was shaken at 20kHz for 3min and then centrifuged at 13000rpm for 5min to obtain the eluent. 100mL of the food sample pretreatment extract from Example 1 was added to the eluent again, and the subsequent steps were repeated for a second elution to obtain the secondary eluent.

[0066] 200 μL of N,O-bis(trimethylsilyl)trifluoroacetamide containing 1 wt% trimethylchlorosilane was added to the secondary eluent, and the derivatization reaction was carried out in a drying oven at 60 °C for 1 h. After the reaction was completed, the eluent was cooled to room temperature and finally analyzed by GC-MS.

[0067] In this invention, the GC-MS analysis used a DB-5ms column (30m*0.25mm*0.25μm), a flow rate of 5mL / min, an ion source temperature of 230℃, an interface temperature of 300℃, an injection port temperature of 300℃, ultrapure helium (purity ≥99.999%) as the carrier gas, an oven temperature of 70℃, and a solvent delay time of 3min. The temperature gradient was set as follows: initial temperature 70℃, held for 2min, increased to 200℃ at a rate of 25℃ / min, held for 6min, then increased to 280℃ at a rate of 20℃ / min, held for 5min, and finally increased to 300℃ at a rate of 10℃ / min, held for 2min. Quantitative analysis was performed using selective ion monitoring (SIM) mode. The mass spectra of the three food additives are shown below. Figure 2 As shown.

[0068] Performance comparison test:

[0069] The performance of the carbon-dot modified molecular sieve prepared in Example 1 was compared with that of commercially available C18 (purchased from Shimadzu Corporation, Japan), N-propylethylenediamine (PSA) (purchased from Shimadzu Corporation, Japan), graphitized carbon (GCB) (purchased from Shanghai Anpu Experimental Technology Co., Ltd.), and nitrogen-doped carbon dots (NCD) synthesized using L-glutamic acid and ethylenediamine as nitrogen sources. The specific procedure is as follows: Clenbuterol standard solution, salbutamol standard solution, and ractopamine standard solution were added to five different containers. The spiking levels of clenbuterol, salbutamol, and ractopamine were all 50 ng / mL, and the addition volume was 10 mL for each. Then, carbon-dot modified molecular sieve, C18, N-propylethylenediamine (PSA), graphitized carbon (GCB), and NCD were added to the five different containers, respectively, with an addition volume of 20 mg for each. The recoveries of clenbuterol, salbutamol, and ractopamine and the data repeatability (represented by relative standard deviation RSD) were tested.

[0070] The preparation method of the above nitrogen-doped carbon dots (NCDs) is as follows:

[0071] (1) Add ethylenediamine to an aqueous solution of L-glutamic acid (the concentration of L-glutamic acid is 1 mol / L), wherein the molar ratio of L-glutamic acid to ethylenediamine is 1:1. Then add sulfuric acid solution to the mixed solution so that the concentration of sulfuric acid in the mixed solution is 7.3 mol / L.

[0072] (2) The above mixed solution was reacted at 210℃ for 10h. The reaction product was cooled to room temperature and then centrifuged to remove larger particles. Finally, the supernatant was purified by dialysis membrane to obtain nitrogen-doped carbon dots (NCD).

[0073] The results are as follows: When GCB was used as the adsorbent, the recovery rate ranged from 24.1% to 31.2%, with an RSD of 2.2% to 6.0%, indicating that GCB had poor adsorption capacity for the target analyte. When PSA and C18 were used as adsorbents, the recovery rates were 36.8% to 48.9% (PSA) and 45.7% to 60.9% (C18), with RSDs of 6.2% to 12.8% (PSA) and 6.4% to 12.1% (C18), respectively. This indicates that the adsorption capacity of PSA and C18 was improved compared to GCB, but still relatively low. When NCD was used as the adsorbent, the recovery rate was significantly improved compared to the previous three materials (recovery rate 61.8% to 73.2%, RSD 4.4% to 9.4%), which may be due to the π-π stacking effect of NCD on the target analyte; however, the recovery rate of NCD still did not meet the requirements. When the carbon dot-modified molecular sieve prepared in Example 1 was used as an adsorbent, the recovery rate was 83.0–94.2%, and the RSD was 3.0–5.9%, indicating that the carbon dot-modified molecular sieve is an effective selective adsorbent. A summary table of the recovery rates and RSDs of various adsorbents is shown in Table 1.

[0074] Table 1. Comparison of recovery rates and RSDs of three common food additives by different types of adsorbents.

[0075]

[0076] As shown in the above embodiments, this invention provides a carbon-dot-modified molecular sieve and its preparation method, a food sample pretreatment extract and its preparation method, and its application. First, ZSM-5 molecular sieve and iron oxide powder are dispersed in water to obtain a mixed dispersion. Then, the mixed dispersion is mixed with Paramecium culture medium and subjected to static settling and centrifugation to obtain a supernatant and a precipitate. Finally, the precipitate is subjected to carbonization, freeze-drying, and magnetic separation to obtain the carbon-dot-modified molecular sieve. The carbon-dot-modified molecular sieve can be mixed with a salt solution to obtain the food sample pretreatment extract. In this invention, the micropores of the molecular sieve can adsorb biomolecules such as proteins and fats, and the tiny pores formed by the intertwining of polypeptides in the carbon dots on the molecular sieve surface can adsorb additives such as pigments and flavorings.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon dot-modified molecular sieve, characterized in that, Includes the following steps: (1) Disperse ZSM-5 molecular sieve and iron oxide powder in water to obtain a mixed dispersion; (2) After mixing the mixed dispersion and Paramecium culture medium, the mixture was allowed to stand and then centrifuged in sequence to obtain the supernatant and precipitate. (3) The precipitate was sequentially carbonized, freeze-dried, and magnetically separated to obtain a carbon dot-modified molecular sieve; The carbonization treatment temperature is 200–240°C, and the carbonization treatment time is 6–10 hours.

2. The method for preparing carbon dot-modified molecular sieves according to claim 1, characterized in that, In step (1), the mass ratio of ZSM-5 molecular sieve, iron oxide powder and water is 1.5-2.5:0.5-1.5:10-20.

3. The method for preparing carbon dot-modified molecular sieves according to claim 1 or 2, characterized in that, In step (2), the volume ratio of the mixed dispersion to the Paramecium culture medium is 0.5-1.5:2.5-4.5; the OD580-660 value of the Paramecium culture medium is 10-150.

4. The preparation method according to claim 3, characterized in that, In step (2), the settling time is 8 to 12 hours; the centrifugation speed is 6000 to 10000 rpm, and the centrifugation time is 10 to 20 minutes.

5. The method for preparing carbon dot-modified molecular sieves according to claim 2 or 4, characterized in that, In step (3), the freeze-drying temperature is -20 to -10°C, and the freeze-drying time is 8 to 16 hours.

6. The carbon dot-modified molecular sieve prepared by the method for preparing carbon dot-modified molecular sieves according to any one of claims 1 to 5.

7. A method for preparing a food sample pretreatment extract, characterized in that, The process includes the following steps: mixing the carbon dot-modified molecular sieve of claim 6 or the carbon dot-modified molecular sieve prepared by any one of claims 1 to 5 with a salt solution to obtain a food sample pretreatment extract. The salt solution consists of sodium chloride, magnesium salt, and water.

8. The method for preparing the food sample pretreatment extract according to claim 7, characterized in that, The magnesium salt comprises magnesium chloride and / or magnesium sulfate; the mass ratio of sodium chloride, magnesium salt and water is 3-5:1-3:30-70; the mass-volume ratio of the carbon dot-modified molecular sieve and the salt solution is 10-50 mg:500-1500 mL.

9. The food sample pretreatment extract prepared by the method of claim 7 or 8.

10. The application of the food sample pretreatment extract according to claim 9 in food sample pretreatment, characterized in that, The food sample pretreatment extract and the food sample were mixed and centrifuged to obtain the food sample eluent. The mass-to-volume ratio of the food sample and the food sample pretreatment extract is 1g:2-20mL.

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