A biochar material and its preparation method and application

Abstract

The present invention relates to the field of biochar materials, and in particular to a biochar material and a preparation method and application thereof. The present invention provides a method for preparing a biochar material, characterized in that it comprises the following steps: S101 obtaining a first mixed solution; S102 obtaining a first precursor; S103 obtaining a second precursor; S104 obtaining a first material; S105 obtaining the biochar material. The biochar material prepared by the present invention can perform directional adsorption on pigments (such as lutein and chlorophyll) and is suitable for application to QuEChERS pretreatment.

Description

[0001] Priority application

[0002] This application claims priority to Chinese invention patent application CN2024112963579 “A biochar material, preparation method and application thereof” filed on September 14, 2024, which is incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to the field of biochar materials, and in particular to a biochar material and a preparation method and application thereof. Background Art

[0004] With the expansion of the planting area of ​​medicinal crops and the extension of the planting years, the occurrence of diseases, insect pests and weeds in medicinal crops is becoming more and more serious. At present, the prevention and control of diseases, insect pests and weeds in the production of medicinal crops in my country mainly rely on chemical pesticides. However, unreasonable use of pesticides may bring potential hazards of pesticide residues. Therefore, it is necessary to monitor people's food safety by detecting pesticide residues in medicinal crops.

[0005] Chrysanthemum is a multifunctional medicinal crop. Its pharmacological effects include clearing away heat and detoxifying, calming the liver and improving eyesight, antibacterial and anti-inflammatory, lowering blood lipids, anti-oxidation, vasodilation, lowering blood pressure, and anti-tumor. In recent years, with the in-depth exploration of the rich pharmacological effects of chrysanthemum, its planting area has shown a significant expansion trend. However, in the process of chrysanthemum cultivation, the problem of diseases and pests has become increasingly prominent. In order to pursue high yields and ensure the quality of chrysanthemums, growers have no choice but to take pesticide control measures to protect chrysanthemums from diseases and pests. This practice has also caused dual problems of food safety and ecological safety.

[0006] The pesticide residue analysis process includes two parts: sample pretreatment and instrumental analysis. The cumbersome sample pretreatment seriously limits the analysis efficiency. The development of the QuEChERS method has simplified the operational process of sample pretreatment, among which the selection of purifiers is crucial, mainly affecting the purification effect of the matrix and the recovery rate of pesticides. The specific surface area, porous structure and adjustable surface chemical properties of carbon materials have gradually emerged in the improvement of the QuEChERS method. Carbon materials such as carbon nanotubes, carbon dots, graphene / graphene oxide, fullerene and its derivatives have achieved good results, but the raw materials of the above carbon materials are mostly derived from petroleum substrates, which are not only not environmentally friendly, but also consume a huge amount of non-renewable resources such as petroleum.

[0007] Biochar material is a material derived from biomass as a carbon source. It not only has a wide range of sources, but also has a certain adsorption capacity. Therefore, it can be used as an adsorbent to adsorb pesticides to achieve the removal of pesticide residues. However, for pesticide residue analysis, the prior art usually uses metal ions (such as ZnCl2) or metal oxides (such as Fe3O4) to modify the biochar material, so as to apply the modified biochar material to the sample pretreatment stage of pesticide residue analysis. Chinese patent application CN117191536A discloses the use of a magnetic biochar material as a purifier in the QuEChERS pretreatment method, wherein the magnetic biochar material is Fe3O4-modified biochar. It clearly mentions that biochar is not easy to separate when used directly in the sample pretreatment process, so Fe3O4 needs to be assembled on the biochar material before it can be applied to pesticide residue analysis. Summary of the invention

[0008] In a first aspect, the present invention provides a method for preparing a biochar material, characterized in that it comprises the following steps:

[0009] S101 soaking straw powder in a hypochlorite solution for a first period of time to obtain a first mixed solution;

[0010] In some embodiments, the effective chlorine content of the hypochlorite solution comprises 2%-5% by mass.

[0011] In some embodiments, the first period of time comprises 4 - 6 hours.

[0012] In some embodiments, the stover is corn stover.

[0013] In some embodiments, the straw powder comprises 40-60 mesh.

[0014] In some embodiments, the ratio of the straw powder to the hypochlorite solution comprises 1.0 g: 40-60 mL.

[0015] S102 placing the straw powder in the first mixed solution in water and performing a hydrothermal reaction to obtain a first precursor;

[0016] In some embodiments, the temperature of the hydrothermal reaction comprises 200-240°C.

[0017] In some embodiments, the hydrothermal reaction time comprises 4-6 hours.

[0018] S103 vacuum drying the first precursor to obtain a second precursor;

[0019] S104 carbonizing the second precursor to obtain a first material;

[0020] In some embodiments, the carbonization temperature is set to be 600-800°C.

[0021] In some embodiments, the carbonization heating rate comprises 5-10°C / min;

[0022] S105 Soak the first material in a sulfuric acid solution for a second period of time, and obtain the biochar material after vacuum drying.

[0023] In some embodiments, the concentration of the sulfuric acid solution comprises 0.5-1 M.

[0024] In some embodiments, the second period of time comprises at least 8 hours.

[0025] In a second aspect, the present invention provides a biochar material prepared by the above preparation method.

[0026] In a third aspect, the present invention provides the use of the above-mentioned biochar material in the preparation of pesticide residue pretreatment reagents.

[0027] In some embodiments, the pesticide residue pretreatment reagent is used for targeted adsorption of pigments in the sample.

[0028] In the present invention, "directional adsorption" means that in the presence of a matrix of the sample, the pigment (such as chlorophyll and / or xanthophyll) contained in the sample is selectively adsorbed, while trace amounts of pesticides are hardly adsorbed.

[0029] In some embodiments, the pigment comprises chlorophyll and / or xanthophyll.

[0030] In some embodiments, the pesticide residue pre-treatment reagent is used for chrysanthemum samples.

[0031] In some embodiments, the biochar material is used in combination with an adsorbent material.

[0032] In some embodiments, the adsorbent material includes ethylenediamine-N-propylsilane (PSA).

[0033] In some embodiments, the mass ratio of the biochar material to the adsorption material comprises (5-8):1.

[0034] In some embodiments, the pesticide residue pre-treatment reagent includes the biochar material and ethylenediamine-N-propylsilane.

[0035] In some embodiments, the mass ratio of the biochar material and the ethylenediamine-N-propylsilane in the pesticide residue pretreatment reagent comprises (5-8):1.

[0036] In some embodiments, the mass ratio of the biochar material to the ethylenediamine-N-propylsilane is (6-8):1.

[0037] In a fourth aspect, the present invention also provides a QuEChERS-based sample pretreatment kit, characterized in that the sample pretreatment kit comprises a pesticide residue pretreatment reagent, the pesticide residue pretreatment reagent comprises the above-mentioned biochar material and an adsorption material, the adsorption material comprises ethylenediamine-N-propylsilane, and the mass ratio of the biochar material to the adsorption material comprises (5-8):1.

[0038] In some embodiments, the sample preparation kit is used for chrysanthemum samples.

[0039] In some embodiments, the pesticide residue pretreatment reagent is configured to be used for pretreatment and purification of a chrysanthemum sample, and the mass ratio of the pesticide residue pretreatment reagent to the chrysanthemum sample comprises 1:(8-15).

[0040] In some embodiments, the mass ratio of the pesticide residue pretreatment reagent to the chrysanthemum sample is 1:(9-12).

[0041] In some embodiments, when the mass of the chrysanthemum sample is 2.5 g, the pesticide residue pretreatment reagent may include 180-240 mg of biochar material and 30 mg of ethylenediamine-N-propylsilane.

[0042] In some embodiments, the sample pretreatment kit further comprises an anhydrous polar reagent, wherein the anhydrous polar reagent comprises one or more of ethyl acetate, acetonitrile and methanol.

[0043] In some embodiments, the anhydrous polar reagent is anhydrous acetonitrile.

[0044] In a fifth aspect, the present invention also provides a method for detecting various trace pesticide residues in chrysanthemum samples using HPLC-MS / MS, the method being based on the above-mentioned sample pretreatment kit and comprising the following steps:

[0045] S201 adding the anhydrous polar solvent to the chrysanthemum sample for extraction to obtain a chrysanthemum extract;

[0046] In some embodiments, the chrysanthemum sample is in the form of powder.

[0047] S202 adding the chrysanthemum extract (preferably 1 / 3 of the chrysanthemum extract obtained in S201) to the pesticide residue pretreatment reagent for extraction by shaking, then filtering the supernatant and injecting it into an HPLC-MS / MS instrument for trace pesticide residue detection;

[0048] In some embodiments, the mass ratio of the pesticide residue pretreatment reagent to the chrysanthemum sample comprises 1:(8-15).

[0049] S203 The supernatant of S202 is separated by high performance liquid chromatography, wherein the high performance liquid chromatography uses a C18 chromatographic column, the column temperature is 40° C., and 0.1% formic acid acetonitrile solution is used as mobile phase A and 0.1% formic acid water is used as mobile phase B for gradient elution;

[0050] S204 Analyze the substances separated by the high performance liquid chromatography described in S203 by tandem mass spectrometry, using ESI as an ion source and adopting a multiple reaction monitoring mode.

[0051] In some embodiments, the gradient elution conditions are:

[0052] 0min: A%-B%: 30-70;

[0053] 12min: A%-B%: 70-0;

[0054] 14min: A%-B%: 70-0;

[0055] 14.01 min: A%-B%: 30-70.

[0056] In some embodiments, the nebulizing gas flow rate of the tandem mass spectrometry is 3.0 L / min; the drying gas flow rate is 10 L / min; and the heating gas flow rate is 10 L / min.

[0057] In some embodiments, the interface temperature of the tandem mass spectrometry instrument is 300°C; the DL temperature is 150°C; and the heating block temperature is 400°C.

[0058] Compared with the prior art, the beneficial effects of the present invention include at least the following aspects:

[0059] In order to apply biochar materials to pesticide residue analysis, the existing technology usually uses metal ions (such as ZnCl2) or metal oxides (such as Fe3O4) to modify biochar materials. In fact, the existing technology also believes that biochar materials that have not been activated or magnetically modified with metal ions are difficult to apply to pesticide residue analysis, especially difficult to use as a purifier in the QuEChERS pretreatment method.

[0060] The method for preparing the biochar material provided by the present invention creatively combines hypochlorite treatment, hydrothermal treatment and pyrolysis, and it is found that these three steps synergistically ensure the directional adsorption of pigments (such as lutein and chlorophyll) by the biochar material prepared by the present invention (that is, it has no retention effect on a variety of pesticides but has a retention effect on pigments), and is suitable for application to QuEChERS pre-treatment.

[0061] Specifically, the present invention uses hypochlorite (such as sodium hypochlorite) to treat straw powder to oxidize and degrade lignin in the straw powder. However, the present invention finds that hypochlorite, as a broad-spectrum oxidant, will degrade part of the cellulose in the straw powder while oxidizing and degrading lignin, thereby destroying the pore structure of the straw powder, resulting in the pore structure of the straw powder being further destroyed in the subsequent hydrothermal treatment and pyrolysis, and ultimately unable to generate biochar material. The sensitivity of cellulose to hypochlorite degradation may be attributed to the chloride ions in the hypochlorite solution, which have a strong interaction with the terminal hydroxyl groups of the glucose units in cellulose. The present invention controls the soaking time (such as the first time period) and proportion of the straw powder in the hypochlorite solution, effectively reduces the binding force between lignin, cellulose, and hemicellulose in the straw powder, breaks the natural anti-degradation barrier of lignin, and maintains the integrity of the original structure of cellulose, giving the cellulose surface more oxygen-containing functional groups, and providing a structural basis for subsequent hydrothermal treatment and pyrolysis (i.e., ensuring the stability of the pore structure of biochar).

[0062] Furthermore, the present invention sequentially hydrothermally treats and pyrolyzes the straw powder treated with hypochlorite. Since the pore structure of the straw powder treated with hypochlorite has been changed to a certain extent, hydrothermally treating and pyrolyzing it still has an adverse effect on the stability of the pore structure of the biochar. In this regard, the present invention, by coordinating factors such as the temperature of the hydrothermal treatment and the pyrolysis, gives the cellulose surface retained by the straw powder treated with hypochlorite more oxygen-containing functional groups, while ensuring that the stability of the pore structure of the biochar is not affected, it also further expands the pores on the cellulose surface and increases the specific surface area of ​​the biochar material.

[0063] Furthermore, the present invention found that sulfuric acid impregnation can dissolve impurities in biochar, such as amorphous carbon and metal aggregates, oxidize carbon on the skeleton, and open pores formed by the escape of organic matter and gas during biomass pyrolysis, further increasing the surface area and pore volume of the biochar material.

[0064] Compared with the traditional adsorption material production process, the method provided by the present invention is cost-effective, the cost is significantly lower than that of petroleum or asphalt-based materials, and a large amount of energy can be saved, which is eco-friendly. In addition, the method provided by the present invention has a high yield, the prepared biochar material is of high quality, almost no by-products such as tar and ash are produced, the preparation difficulty and risk are low, and it has a good industrial application prospect.

[0065] In addition, it should be emphasized that the biochar material prepared by the present invention can unexpectedly be used as a directional adsorbent in the analysis of pesticide residues in the chrysanthemum composite matrix pre-treated by the QuEChERS method without metal ion activation modification and / or magnetic modification, and achieves effective purification of pigments and fats in the chrysanthemum extract, while the biochar material obtained by hydrothermal treatment or pyrolysis alone is difficult to achieve the purification effect of pigments and fats in complex matrices. Based on the biochar material prepared by the present invention, the detection limit of pesticides in the method of detecting multiple trace pesticide residues in chrysanthemum using HPLC-MS / MS is 0.00002 ~ 0.0054 mg / kg, and the quantitative limit is 0.00007 ~ 0.01638 mg / kg, which shows that the biochar material prepared by the present invention can better replace commercial adsorption materials (such as GCB). Compared with commercial adsorption materials, the preparation cost of the biochar material prepared by the present invention is lower (the preparation cost of each gram of biochar is about US$0.5), and it is more eco-friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without paying creative labor.

[0067] Figure 1 The result diagram is a graph showing the pigment content in the matrix before and after purification by the biochar material of the present invention;

[0068] Figure 2 This is the result diagram of the effect of different amounts of biochar materials on the spiked recoveries of 31 pesticides;

[0069] Figure 3 This is a comparison chart of the purification effect of biochar composite materials and commercially available materials;

[0070] Figure 4 This is a comparison chart of the purification effects of different materials;

[0071] Figure 5 This is a comparison of the matrix effects of 31 pesticides in chrysanthemum extracts purified by optimized purification materials;

[0072] Figure 6 This is the SEM result of the morphological changes of biochar materials before and after adsorption;

[0073] Figure 7 is the adsorption isotherm of biochar material. DETAILED DESCRIPTION

[0074] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0075] Herein "and / or" includes any and all combinations of one or more of the associated listed items.

[0076] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0077] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0078] As used in this specification, the term "about" typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0079] In this specification, some embodiments may be disclosed in a format of being in a range. It should be understood that this description of "being in a range" is only for convenience and brevity, and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered to have specifically disclosed all possible sub-ranges and independent numerical values ​​within this range. For example, the description of the range 1-6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5 and 6. Regardless of the breadth of the range, the above rules apply.

[0080] Detailed description with drawings

[0081] Figure 1 :A is a comparison of the unpurified chrysanthemum extract and the chrysanthemum extract purified by 180 / 240 mg biochar materials. From left to right, they are the chrysanthemum extracts that were not purified, purified by 180 mg biochar materials, purified by 180 mg biochar materials, purified by 240 mg biochar materials, and purified by 240 mg biochar materials. B is the chrysanthemum extract purified by 30, 60, 90, and 120 mg biochar materials (from left to right). C is the quantitative result of the comparison of the chlorophyll and lutein content in the solution after purification by different amounts of biochar materials.

[0082] Figure 2 :A is the spiked recoveries of 15 pesticides (methamidophos, chlorfenthion, chlorsulfuron, cadastrene, metsulfuron, chlorsulfuron, cadastrene, chlorfenthion, coumaphos, thiophanate-methyl, phosphamidon, monocrotophos, chlorfenthion, chlordimeform, methyl isofenphos, the same below) in the solution purified by different amounts of biochar materials. B is the spiked recoveries of 4 pesticides (fenamidophos, phorate, aldicarb and terbuthion, the same below) in the solution purified by different amounts of biochar materials. C is the spiked recoveries of 2 pesticides (carbofuran and demeton, the same below) in the solution purified by different amounts of biochar materials. D is the qualified rate of spiked recoveries of different pesticides in the solution purified by different amounts of biochar materials.

[0083] Figure 3 : A is the spiked recovery rate of 15 pesticides in the solution after purification by different biochar composite materials. B is the spiked recovery rate of 4 pesticides in the solution after purification by different biochar composite materials. C is the spiked recovery rate of 2 pesticides in the solution after purification by different biochar composite materials. D is the spiked recovery rate of 15 pesticides in the solution after purification by commercial materials and biochar materials. E is the spiked recovery rate of 4 pesticides in the solution after purification by commercial materials and biochar materials. F is the spiked recovery rate of 2 pesticides in the solution after purification by commercial materials and different biochar composite materials.

[0084] Figure 4 : From left to right: unpurified; purified by GCB-80mg; purified by MWCNTS-180mg; purified by PSA-180mg; purified by C18-180mg; purified by biochar material-180mg+C18-30mg; purified by biochar material-180mg+PSA-30mg; purified by biochar material-180mg+PSA-30mg+C18-30mg.

[0085] Example 1: Materials and methods

[0086] 1.1 Reagents and Instruments

[0087] Corn stover was collected from Hebei Province, China. 31 pesticide reference materials (see table below) were obtained from Tanmo Quality Inspection Reference Material Center. NaOCl was obtained from Tianjin Fuchen Chemical, H2SO4 was obtained from Beijing Reagent, NaCl was obtained from Sinopharm Group, and formic acid was obtained from Aladdin. Acetonitrile was obtained from Merck. MWCNTs were obtained from Suzhou Hengqiu Technology (Suzhou, China), GCB-N and C18 were obtained from Beijing Codenos Technology Co., Ltd. (Beijing, China), PSA was obtained from Tianjin Bonaiger Technology Co., Ltd. (Tianjin, China), and Oasis HLB solid phase extraction cartridges were obtained from Waters Technologies.

[0088]

[0089] LC-40A liquid chromatography-mass spectrometer LCMS-8045 was purchased from Shimadzu Corporation, Japan. N5000 spectrophotometer was purchased from Shanghai Youke Instrument Co., Ltd. Universal high-speed pulverizer was purchased from Tianjin Testing Instrument Co., Ltd. Powerful multi-tube vortex mixer was purchased from Beijing Codenos Technology Co., Ltd. Tube furnace was purchased from Beijing Foreman Laboratory Equipment Co., Ltd. JJ 500 electronic balance (0.01 g) was purchased from Changshu Shuangjie Testing Instrument Factory. AL104-IC electronic balance (0.0001 g) was purchased from Mettler-Toledo. Eppendorf range: 20-200 μL and 100-1000 μL. MPE series high-throughput parallel evaporator was purchased from RayKol Group Corp., Ltd. (Xiamen, China). The samples were characterized by using a specific surface area tester-BelSorp Max (MicrotracBEL, Japan) and a scanning electron microscope Zeiss Ultra 55 (Shanghai, China).

[0090] 1.2 Preparation of biochar materials

[0091] To prepare biochar, corn stalks were first ground into powder and passed through a 40-mesh sieve. Then, the sieved corn stalk powder was soaked in NaOCl (effective chlorine content of about 5%) at a ratio of 1 g corn stalk powder to 50 mL NaOCl for 4 h. The NaOCl remaining on the surface of the stalks was washed off with deionized water until no obvious chlorine smell could be smelled.

[0092] The cleaned corn stalk powder and an appropriate amount of deionized water were placed in a reactor and treated in an oven at 220°C for 4 h to prepare a precursor. After the heating was completed, the reactor was completely cooled, the corn stalk powder was opened and taken out, and washed with deionized water until the color in the aqueous solution no longer changed. The corn stalk powder was placed in a vacuum drying oven and vacuum dried at 60°C to obtain a carbonized precursor.

[0093] The dried carbonized precursor was passed through a 40-mesh sieve and placed in a quartz boat. The temperature of the tube furnace was set to 800°C and the heating rate was 5°C / min to carbonize the corn stalk powder. The entire carbonization process was carried out under a N2 atmosphere. The biochar after carbonization was soaked in 0.5M sulfuric acid overnight, washed with water until the aqueous solution was neutral, and then vacuum dried to obtain the biochar material of the present invention.

[0094] 1.3 Pretreatment of chrysanthemum

[0095] For the pretreatment of chrysanthemum, first crush the chrysanthemum and pass it through a 40-mesh sieve for later use. Take 2.5g of the sieved chrysanthemum powder in a 50 mL centrifuge tube, add 1g of sodium chloride and a ceramic homogenizer suitable for 50 mL centrifuge tubes, and add 25 mL of acetonitrile. Vortex for 5 minutes on a powerful multi-tube vortex mixer at 3000r / min. Centrifuge and take the supernatant. Add 25 mL of acetonitrile to the centrifuge tube again, repeat the vortex and centrifuge to take the supernatant, repeat 3 times, and combine the supernatants for concentration on a parallel concentrator. After concentration, add 5 mL of acetonitrile to the tube for re-dissolution to obtain the chrysanthemum extract.

[0096] 1.4 Purification of chrysanthemum extract

[0097] Take 3 mL of chrysanthemum extract into a centrifuge tube containing biochar material, vortex at 3000 r / min for 5 min on a strong multi-tube vortex mixer, and centrifuge at 13000 r / min for 8 min to obtain the supernatant, which is the chrysanthemum purified liquid.

[0098] 1.5 Determination of lutein, chlorophyll and fat content in solution

[0099] The chlorophyll test is carried out in accordance with the provisions of the "Spectrophotometric Method for the Determination of Chlorophyll Content in Fruits, Vegetables and Their Products" (NY / T1783082-2017), and the lutein test is carried out in accordance with the provisions of the "National Food Safety Standard for the Determination of Lutein in Foods" (GB 5009.248-2016). The fat test is carried out in accordance with the provisions of the "National Food Safety Standard for the Determination of Fat in Foods" (GB 5009.6-2016).

[0100] 1.6 HPLC-MS / MS conditions

[0101] Pesticides were detected by liquid chromatography mass spectrometer LCMS-8045, and the chromatographic column was Shim-pack GIST-HP C18 (2.1×100 mm, 3 μm) (Shimadzu Corporation, Japan) (Kyoto). The column temperature was 40℃, and the injection volume was 5 μL. The mobile phase was 0.1% formic acid acetonitrile solution (A) and 0.1% formic acid aqueous solution (B), and the flow rate was 0.3 mL / min. The chromatographic conditions were: 30-70% A within 0-12 min, held for 2 min; 70-30% A within 14-14.01 min, held until 17 min. Pesticide analysis was performed in ESI positive ion mode, and the scanning mode was multiple reaction monitoring (MRM); the nebulizer gas flow rate was 3.0 L / min, the drying gas flow rate was 10 L / min, the heating gas flow rate was 10 L / min, the interface temperature was 300℃, the DL temperature was 150℃, and the heating block temperature was 400℃.

[0102] 1.7 Methodological considerations

[0103] According to document SANTE / 11312 / 2021 v2 (SANTE, 2021), the developed method was validated for its feasibility using the following parameters: linearity, matrix effect, accuracy, precision, limit of detection (LOD) and limit of quantification (LOQ). The instrument was calibrated daily during the experiment. The linearity of the method was verified by spiking a mixed standard solution of 31 pesticides at 7 levels (1, 5, 10, 50, 100, 200, 300, 500 μg / L) in a blank matrix solution of chrysanthemum. The matrix effect of the method was evaluated by comparing the slope ratio of the solvent-based and matrix-matched calibration curves for all target pesticides. The spike recovery (n=6) and reproducibility test of the 31 pesticides at three levels (0.02, 0.1 and 0.2 mg / kg) were tested to verify the accuracy and precision of the method, respectively.

[0104] 1.8 Material pore structure analysis

[0105] The specific surface area and pore structure of biochar materials were analyzed and tested using a fully automatic specific surface area and pore size analyzer. The samples were weighed, placed in a test tube, vacuum dried for 12 h after pretreatment, and tested under 77 K liquid nitrogen after impurities were removed. The specific surface area was calculated using the Brunauer-Emmett-Teller method and the Langmuir method, and the results were processed using the Barret, Joyner, and Halenda method (BJH method for short) to better reflect the pore structure of the sample.

[0106] 1.9 SEM structural analysis of materials

[0107] A Zeiss UL TRA 55 scanning electron microscope was used. The samples were vacuum dried at 120 °C for 12 h before testing. Then, the powder samples were pasted on the copper pillar with conductive glue. Gold was sprayed on its surface under 10-2 mbar vacuum conditions for 60 s. Then, the copper pillar was fixed on the sample stage with conductive glue for scanning. The working distance was set to 4.6 mm and the acceleration voltage was set to 3.00 kV.

[0108] Embodiment 2

[0109] Purification effect of biochar materials on pigments in the matrix

[0110] There are many active ingredients in chrysanthemum, which not only make chrysanthemum a complex matrix in pesticide detection, but also cause certain troubles to the detection instruments. Among all the ingredients, pigments and fats cause the greatest trouble to detection. The inventors found that a large amount of pigments will significantly affect the accuracy of the results and lead to false positives. The presence of fat in the matrix may cause some lipophilic pesticides to be enriched in fat, which in turn affects the quality of the results, the sensitivity of the method, the sample throughput, and the maintenance and downtime of the instrument. Therefore, the ability to remove pigments and fats is an important indicator for evaluating the pretreatment level of purification materials.

[0111] like Figure 1 As shown in Table 1, after purification by biochar materials, the color of the purified liquid became significantly lighter, and the contents of lutein and chlorophyll in the matrix decreased by 71.03% and 85.34%, respectively. The fat content of the chrysanthemum extract without biochar purification was 1.2 g / 100 g -1 After purification by biochar material, the fat content in the solution is 1.0 g·100g -1 This proves that the prepared biochar material has a high ability to purify pigments. Although its ability to purify fat is weaker, it can also remove a small part of fat and can be used for the pretreatment of pesticide residues in chrysanthemums.

[0112] Table 1

[0113]

[0114] In order to determine the specific amount of biochar material, the spike recovery rate test was carried out. According to the requirements of the Chinese Pharmacopoeia (2020 edition), the pesticide residue detection method should meet the spike recovery rate of each pesticide between 70% and 120%, which can be appropriately relaxed to between 60% and 130% if repeatability is met. The spiked recoveries of fenamiphos (calculated as the sum of fenamiphos, fenamiphos sulfone and fenamiphos sulfoxide), phorate (calculated as the sum of phorate, phorate sulfone and phorate sulfoxide), aldicarb (calculated as the sum of aldicarb, aldicarb sulfone and aldicarb sulfoxide), and terbufos (calculated as the sum of terbufos, terbufos sulfone and terbufos sulfoxide) were in the qualified range of 180-390%, and the spiked recoveries of carbofuran (calculated as the sum of carbofuran and 3-hydroxycarbofuran) and idemeton (calculated as the sum of idemeton-O and idemeton-S) were between 120-260%, which was considered qualified. Specifically, in the process of preparing the chrysanthemum extract, a mixed standard solution prepared by 31 kinds of pesticides was added to the centrifuge tube, and the rest of the operations were consistent with the methods under 1.2 and 1.3.

[0115] The recovery rates of pesticide spikes in the matrix after purification with different amounts of biochar materials are as follows: Figure 2 shown. Figure 2 A is the comparison of the spiked recoveries of 15 pesticides at 6 levels. Figure 2 It can be observed in A that with the increase in the amount of biochar material used, the spiked recoveries of six pesticides, chlorpyrifos, chlorfenvinphos, chlordimeform, methyl isothioate, and terbuthion, gradually increased to the qualified limit. The reason may be that when the amount of biochar material used is small, the purification of interfering substances in the chrysanthemum extract is not thorough enough, which causes masking of trace amounts of pesticides, and thus the spiked recoveries do not meet the standards. The spiked recoveries of chlorpyrifos and chlorpyrifos decreased to a certain extent with the increase in the amount of biochar material used. As for systemic phos, its spiked recovery rate is always lower than the specified range ( Figure 2 C). Figure 2 D is the qualified rate of spiked recovery of 15 pesticides except 6 pesticides such as fenamiphos. It can be seen from the figure that the spiked recovery of 15 pesticides shows a significant upward trend with the increase of biochar material dosage, and the types of pesticides with spiked recovery in the range of 60-120% increase with the increase of biochar material dosage. Considering the pigment removal ability and the qualified rate of spiked recovery, this example finally selected 180 mg of biochar material for subsequent experiments.

[0116] Embodiment 3

[0117] In order to achieve better purification effect, this example selects commercially available common degreasing purifiers PSA and C18 to be compounded with biochar materials. Figure 3 and Figure 4As shown. From the figure, it can be seen that compared with the unpurified chrysanthemum extract, the pigment removal effect is obvious after purification by the material compounded with biochar material and PSA and / or C18. From the results of the spiked recovery rate, it can also be seen that after the biochar material is compounded with PSA and / or C18, the qualified rate of the spiked recoveries of 31 pesticides is also improved. After the biochar material is compounded with PSA, among the 31 pesticides, only the spiked recoveries of chlorpyrifos, chlorpyrifos, methyl parathion and chlorpyrifos did not meet the spiked recovery rate standard, and the spiked recoveries were 54.21%, 134.18%, 1413.41% and 111.05% respectively. Figure 4 As shown in the figure, the results obtained by compounding the biochar material with PSA and C18 are similar to those obtained by compounding the biochar with PSA, but the recovery rate of chlordimeform in the compounding of the biochar material with PSA and C18 is reduced to the qualified line. Finally, 180 mg of biochar + 30 mg of PSA was selected as the adsorbent (purification material) for the QuEChERS method for the recovery rate detection of 31 pesticides in chrysanthemum.

[0118] In order to test whether the prepared biochar material can replace the adsorbent commonly used in the QuEChERS method currently on the market, this example selected GCB, MWCNTs, PSA, and C18 to compare the purification effects of biochar materials. Figure 3 As shown in the figure, it can be seen that compared with the unpurified chrysanthemum extract, the most outstanding pigment purification ability among the commercially available purification materials is GCB (graphitized carbon black), followed by MWCNTs (multi-walled carbon nanotubes), and then PSA, while the purification ability of C18 pigment is poor. Comparing the spiked recovery rates of several groups, at the same addition amount, 16.13%, 16.13%, 16.13%, and 19.36% of the pesticide spiked recoveries did not meet the requirements. From the specific spiked recovery rate values, GCB has a strong adsorption capacity for chlordimeform, resulting in a spiked recovery rate of chlordimeform of only 14.22%; while MWCNTs performed better than GCB. Another commercially available QuEChERS method commonly used adsorption material PSA with strong adsorption capacity has a lower spiked recovery rate for sulfonyl pesticides (including ethametsulfuron, metsulfuron-methyl, and chlorsulfuron) than all test groups. The biochar materials and the purification materials obtained by combining biochar materials with PSA can solve the above two problems. The spiked recoveries of chlordimeform and sulfone-methyl pesticides (including ethametsulfuron-methyl, metsulfuron-methyl, and chlorsulfuron-methyl) are all within the acceptable limits.

[0119] Tables 2 and 3 list the linear regression equation, linear range, detection limit, quantification limit and recovery rate of 31 pesticides in chrysanthemum matrix after purification by optimized purification materials (180 mg biochar + 30 mg PSA). The purified chrysanthemum matrix solution was spiked with 0.02 mg / kg, 0.1 mg / kg and 0.2 mg / kg, and the spike recovery rate was determined (n=6). The results showed that the peak area and concentration had good linearity, and the correlation coefficient (R 2 ) was in the range of 0.9980-0.9998. The detection limit (LOD) and minimum detection limit (LOD) of all pesticides were calculated as 3 times and 10 times the signal-to-noise ratio (S / N) of the quantitative ion pair, respectively. The detection limit of the method was 0.00002-0.0054 mg / kg, the quantification limit range was 0.00007-0.01638 mg / kg, and the spiked recoveries of 31 pesticides were within the qualified range except for demeton, with relative standard deviations of 0.93-21.54%.

[0120] Table 2 Linear regression equation, linear range, LOD (mg / kg), LOQ (mg / kg), recovery, precision and relative standard deviation (RSD) of 15 pesticides in chrysanthemum matrix (n=6)

[0121]

[0122] Table 3 Linear regression equation, linear range, LOD (mg / kg), LOQ (mg / kg), recovery, precision and relative standard deviation (RSD) of 6 pesticides (n=6)

[0123]

[0124] Figure 5 This is a comparison of the matrix effects of 31 pesticides in chrysanthemum extracts purified by optimized purification materials. As can be seen from the figure, all 31 pesticides have matrix effects, and 19.35% of the 31 pesticides have matrix effects within ±20%, which are basically not affected by matrix effects. Other pesticides have medium and high matrix effects, which affect the accuracy of pesticide quantification. Therefore, chrysanthemum matrix extracts were used to prepare standard curves during the experiment to accurately quantify 31 pesticides.

[0125] Embodiment 4

[0126] In this example, the biochar material before and after adsorption was characterized using a specific surface area analyzer and a scanning electron microscope.

[0127] Figure 6The following are scanning electron microscope images of biochar materials before and after adsorption. As a whole, it can be seen that the biochar material presents a three-dimensional porous structure. Compared with graphitized carbon black with a highly ordered structure, the structure of the biochar material is more disordered, which may be the reason why the biochar material has no retention effect on many pesticides but has a retention effect on pigments. After adsorption, the structure of the biochar material collapsed to a certain extent, and the pores changed from nearly circular to crescent-shaped. After adsorption, the pores of the biochar material became smaller, the pore edge boundaries were no longer clear, and were covered with more fine particles. After magnification, it can be observed that the surface of the biochar material before adsorption is relatively flat, while the surface three-dimensionality of the biochar material after adsorption increases, and more regular spherical particles can be observed.

[0128] In order to explore the pore structure of biochar materials, the specific surface area and pore structure of biochar materials were analyzed and tested using a fully automatic specific surface area and pore size analyzer. Figure 7 As shown in the figure, as the pressure increases, the adsorption amount increases rapidly, and the adsorption amount reaches saturation after reaching a certain pressure. This phenomenon is generally called type I adsorption isotherm, which is mainly caused by the fact that the adsorption amount of the narrow micropores in the material quickly reaches saturation at a lower pressure. Pore size analysis can also confirm this. It can be seen in the figure that the pore size of the biochar material is <5 nm, indicating that the biochar material prepared by the present invention is microporous biochar. The specific surface area of ​​the obtained biochar material was measured to be 351.43 m² / g.

[0129] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. Application of biochar material in the preparation of QuEChERS-based pesticide residue pretreatment reagent; characterized in that: The biochar material is prepared by the following method: S101 soaking straw powder in a hypochlorite solution for a first period of time to obtain a first mixed solution; S102 placing the straw powder in the first mixed solution in water and performing a hydrothermal reaction to obtain a first precursor; S103 vacuum drying the first precursor to obtain a second precursor; S104 carbonizing the second precursor to obtain a first material; S105 soaking the first material in a sulfuric acid solution for a second period of time, and obtaining the biochar material after vacuum drying; The first time period is 4-6 hours; the temperature of the hydrothermal reaction in step S102 is 200-240°C, and the time of the hydrothermal reaction is 4-6 hours; the set temperature of the carbonization in step S104 is 600-800°C, and the heating rate of the carbonization is 5-10°C / min; the effective chlorine content of the hypochlorite solution is 2%-5% by mass; the ratio of the straw powder to the hypochlorite solution is 1.0g:40-60mL.

2. The use according to claim 1, characterized in that The pesticide residue pretreatment reagent comprises the biochar material and ethylenediamine-N-propylsilane.

3. The use according to claim 2, characterized in that The mass ratio of the biochar material and the ethylenediamine-N-propylsilane in the pesticide residue pretreatment reagent is (5-8):

1.

4. A sample pretreatment kit based on QuEChERS, characterized in that: The sample pretreatment kit comprises a pesticide residue pretreatment reagent, the pesticide residue pretreatment reagent comprises a biochar material and an adsorption material, the adsorption material comprises ethylenediamine-N-propylsilane, and the mass ratio of the biochar material to the adsorption material is (5-8):1; the biochar material is prepared by the following method: S101 soaking straw powder in a hypochlorite solution for a first period of time to obtain a first mixed solution; S102 placing the straw powder in the first mixed solution in water and performing a hydrothermal reaction to obtain a first precursor; S103 vacuum drying the first precursor to obtain a second precursor; S104 carbonizing the second precursor to obtain a first material; S105 soaking the first material in a sulfuric acid solution for a second period of time, and obtaining the biochar material after vacuum drying; The first time period is 4-6 hours; the temperature of the hydrothermal reaction in step S102 is 200-240°C, and the time of the hydrothermal reaction is 4-6 hours; the set temperature of the carbonization in step S104 is 600-800°C, and the heating rate of the carbonization is 5-10°C / min; the effective chlorine content of the hypochlorite solution is 2%-5% by mass; the ratio of the straw powder to the hypochlorite solution is 1.0g:40-60mL.

5. The kit according to claim 4, characterized in that The pesticide residue pretreatment reagent is configured to be used for pretreatment and purification of a chrysanthemum sample, and the mass ratio of the pesticide residue pretreatment reagent to the chrysanthemum sample is 1:(8-15).

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