A QuEChERS extraction kit and its application

Abstract

The present invention provides a QuEChERS extraction kit and its application, wherein the QuEChERS extraction kit comprises a salting-out bag, a purification bag and a button magnet; wherein the salting-out bag comprises 4.0 g of MgSO4 and 1.0 g of NaCl; the purification bag comprises 2 mg of Fc‑MOF@NC; and the button magnet is used to provide an external magnetic field. The QuEChERS extraction kit of the present invention has good purification performance, is simple to operate and convenient to carry, and can be directly used for pretreatment of pesticide residues. The present invention uses Fc‑MOF@NC as a purifier in the QuEChERS extraction kit to adsorb interfering components of the sample, eliminate matrix interference during detection, and combines liquid chromatography-tandem mass spectrometry to establish an accurate, simple and efficient analysis method for THs in a variety of vegetables and fruits.

Description

Technical Field

[0001] The invention belongs to the technical field of analysis and detection, and particularly relates to a QuEChERS extraction kit and application thereof. Background Art

[0002] Pesticide residues in agricultural products are a highly concerned issue in food safety today. Triazine herbicides (THs), also known as triazine herbicides, are a class of broad-spectrum herbicides composed of a six-membered ring structure composed of symmetrically arranged carbon atoms and nitrogen atoms. This type of herbicide achieves the purpose of weed control by inhibiting the photosynthesis of weeds before and after germination. It has the characteristics of high selectivity, rapid drug effect, and stable chemical properties, and is widely used in crop cultivation. Excessive use and abuse of THs will lead to pesticide residues in fruits and vegetables. Long-term intake of foods containing residues of such herbicides by humans can cause endocrine and hormonal disorders, damage to the immune and reproductive systems, and even lead to diseases such as Alzheimer's disease and liver cancer.

[0003] The analysis of THs residues in food includes sample pretreatment and instrumental analysis. Since the components of food matrix samples such as vegetables and fruits are complex, containing a large amount of pigments, sugars, organic acids and other substances, direct injection interferes with the measurement and even damages the instrument; at the same time, THs are trace, so it is difficult to directly and accurately quantify them.

[0004] QuEChERS stands for Quick, Easy, Cheap, Effective, Rugged and Safe. QuEChERS technology combines the extraction and purification steps, using organic solvents to extract the target and purifiers to remove interferences, thereby achieving a method for pretreatment of pesticide residues in food. The QuEChERS purification step is mainly used to eliminate matrix interference, so the purifier determines the purification effect and recovery rate of the method. Currently, purifiers include N-propylethylenediamine bonded silica gel (PSA), C 18 Graphitized carbon black (GCB) and others are commonly used to remove interferences such as organic acids, lipids, sugars and polar pigments, but they are not effective for samples with high pigment content and high lipid content. The combined use of multiple purifiers can improve the purification effect, but the entire pretreatment process is relatively cumbersome.

[0005] Therefore, how to provide a QuEChERS extraction kit, using Fc-MOF@NC as a purifier to remove interfering components in vegetables and fruits, and thereby improve the accuracy of pesticide residue detection in vegetables and fruits, is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] The object of the present invention is to provide a QuEChERS extraction kit and application thereof, so as to solve at least one of the above technical problems.

[0007] To achieve the above objectives, the first aspect of the present invention provides a QuEChERS extraction kit, which includes: a salting-out package, a purification package and a button magnet; the salting-out package includes 4.0 g of MgSO4 and 1.0 g of NaCl; the purification package includes 2 mg of Fc-MOF@NC; and the button magnet is used to provide an external magnetic field.

[0008] In the first aspect, the Fc-MOF@NC is obtained by the following preparation method: (1) FeCl3·6H2O and NiCl2·6H2O are dissolved in DMF, and ultrasonically mixed to obtain solution A; (2) ferrocene dicarboxylic acid and PVP are dissolved in DMF, and ultrasonically mixed to obtain solution B; (3) the solution A and the solution B are mixed to obtain solution C; (4) the solution C is transferred to a high temperature and high pressure reactor to react to obtain a reactant; (5) the reactant is centrifuged, washed, and dried to obtain an Fc-MOF precursor; (6) the Fc-MOF precursor is carbonized at high temperature to obtain Fc-MOF@NC.

[0009] In the first aspect, in the step (4), the reaction conditions include: reaction temperature of 120 to 130° C.; reaction time of 10 to 14 h.

[0010] In the first aspect, the step (5) centrifuges, washes, and dries the reactant to obtain an Fc-MOF precursor, comprising the following steps: centrifuging the reactant to obtain a centrifuged product; washing the centrifuged product three times with DMF to obtain a first washed product; washing the first washed product three times with deionized water to obtain a second washed product; washing the second washed product three times with ethanol to obtain a third washed product; and drying the third washed product in a 60°C vacuum drying oven for 24 hours to obtain an Fc-MOF precursor.

[0011] In the first aspect, the step (6) of high-temperature carbonization of the Fc-MOF precursor comprises: placing the Fc-MOF precursor in a tubular furnace, setting the tubular furnace to heat the Fc-MOF precursor to 700°C at a heating rate of 1.5°C / min under argon protection, keeping the reaction warm for 1.5 hours, and naturally cooling to room temperature to obtain Fc-MOF@NC.

[0012] The second aspect of the present invention provides an application of the QuEChERS extraction kit as described in the first aspect in sample pretreatment for pesticide residue detection in vegetables and fruits, and the application method in sample pretreatment specifically comprises the following steps: crushing the sample to obtain a uniform slurry; adding acetonitrile to the slurry, oscillating and extracting for 30 minutes to obtain a first mixed solution; adding a salting-out bag to the first mixed solution, mixing evenly and centrifuging for 5 minutes to obtain a first supernatant; taking 2 mL of the first supernatant, mixing it with a purification bag, vortexing and oscillating for 5 minutes to obtain a second mixed solution; placing a button magnet on the outside of the second mixed solution for separation to obtain a second supernatant; filtering the second supernatant through a 0.22 μm organic filter membrane to obtain a sample solution to be detected.

[0013] In the second aspect, the mass of the slurry is 10 g; the amount of acetonitrile used is 10 mL.

[0014] The third aspect of the present invention provides a use of the QuEChERS extraction kit as described in the first aspect in the detection of pesticide residues in vegetables and fruits, comprising the following steps:

[0015] Treating the sample with the sample pretreatment method described in the second aspect to remove interfering components in the sample to obtain a solution to be tested;

[0016] The pesticide residues in the sample solution to be detected are analyzed by liquid chromatography-tandem mass spectrometry, wherein the detection conditions of the liquid chromatography-tandem mass spectrometry include: liquid chromatography conditions and mass spectrometry conditions;

[0017] The liquid chromatography conditions include: the chromatographic column is C 18 Column; mobile phase A is 0.1% formic acid water; mobile phase B is acetonitrile; gradient elution program: from 0 to 7 minutes, the volume of the mobile phase A accounts for 10% to 20%, and the volume of the mobile phase B accounts for 90% to 80%; the injection volume is 10 μL, the flow rate is 0.25 mL / min, and the column oven temperature is 35°C;

[0018] The mass spectrometry conditions include: electrospray ion source positive ion mode; ion spray voltage 5.5 kV, ion source temperature 450° C., curtain gas pressure 40 psi, spray gas pressure 40 psi, auxiliary heating gas pressure 40 psi.

[0019] In the third aspect, the interfering components include: chlorophyll, lutein, β-carotene and lycopene.

[0020] In a third aspect, the pesticide residues include triazine herbicides; the triazine herbicides include: atrazine, propazine, simazine, terbuthylazine, dichlorvos, promethazine and simethoxam.

[0021] Beneficial effects:

[0022] The present invention provides a QuEChERS extraction kit, comprising a salting-out bag, a purification bag and a button magnet; wherein the salting-out bag comprises 4.0 g of MgSO4 and 1.0 g of NaCl; the purification bag comprises 2 mg of Fc-MOF@NC; and the button magnet is used to provide an external magnetic field. The present invention uses 4.0 g of MgSO4 and 1.0 g of NaCl as the salting-out bag, which can not only remove the moisture during extraction, but also promote stratification when pre-treating the sample, so as to collect the upper clear night, which is beneficial to improve the purification efficiency of the QuEChERS extraction kit; using Fc-MOF@NC as the purifier in the purification bag, utilizing the adjustable pore structure and large specific surface area in Fc-MOF@NC, the interfering components in vegetables and fruits can be removed, and Fc-MOF@NC has good magnetic properties, and under the action of the button magnet, the purifier and the sample solution can be quickly separated, thereby improving the sample processing efficiency and detection accuracy.

[0023] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic diagram of the structure of a QuEChERS extraction kit in this application;

[0026] Figure 2 Scanning electron microscopy image a and transmission electron microscopy image c of the Fc-MOF precursor provided in the examples of the present application, scanning electron microscopy image b and transmission electron microscopy image d of Fc-MOF@NC in the purification package;

[0027] Figure 3 XRD graph a, hysteresis curve graph b, nitrogen adsorption-desorption isotherm graph c and pore size distribution graph d of Fc-MOF@NC in the purification package provided in the embodiment of the present application;

[0028] Figure 4 This is a graph showing the adsorption test results of Fc-MOF@NC on chlorophyll, lutein, β-carotene and lycopene in the purification package of the present application example;

[0029] Figure 5 The fitted pseudo-second-order kinetic equation for the adsorption of chlorophyll, lutein, β-carotene and lycopene by Fc-MOF@NC in the purification package of the embodiment of the present application;

[0030] Figure 6 This is the internal diffusion model of the adsorption of chlorophyll, lutein, β-carotene and lycopene by Fc-MOF@NC in the purification package of the embodiment of the present application;

[0031] Figure 7 The Langmuir adsorption isotherm model and the Freundlich adsorption isotherm model of the embodiments of the present application;

[0032] Figure 8 This is a graph showing the experimental results of the effect of the amount of Fc-MOF@NC on purification efficiency provided in the examples of this application;

[0033] Fig. 9 This is a graph showing the experimental results of the effect of purification time on purification efficiency provided in the embodiments of the present application;

[0034] Fig.10 These are the 7 standard MRM mass spectra of THs provided in the examples of this application. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are used to illustrate the present invention, rather than to limit the present invention.

[0036] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or obtained by existing methods.

[0038] The present invention provides a QuEChERS extraction kit, such as Figure 1 As shown, the extraction kit includes: a salting-out package, a purification package and a button magnet; the salting-out package includes 4.0 g of MgSO4 and 1.0 g of NaCl; the purification package includes 2 mg of Fc-MOF@NC; and the button magnet is used to provide an external magnetic field.

[0039] It should be noted that each salting-out package contains 4.0g of MgSO4 and 1.0g of NaCl, which can be directly placed in a plastic centrifuge tube of suitable size and sealed; each purification package contains 2mg of Fc-MOF@NC, which can be directly placed in another plastic centrifuge tube of suitable size and sealed; a QuEChERS extraction kit can include several salting-out packages and several purification packages, as well as a button magnet. The QuEChERS extraction kit is small in size and easy to carry.

[0040] In some possible embodiments, the Fc-MOF@NC is obtained by the following preparation method: (1) dissolving FeCl3·6H2O and NiCl2·6H2O in DMF, and mixing them by ultrasonication to obtain solution A; (2) dissolving ferrocene dicarboxylic acid and PVP in DMF, and mixing them by ultrasonication to obtain solution B; (3) mixing the solution A and the solution B to obtain solution C; (4) transferring the solution C to a high temperature and high pressure reactor to react and obtain a reactant; (5) centrifuging, washing, and drying the reactant to obtain an Fc-MOF precursor; (6) carbonizing the Fc-MOF precursor at high temperature to obtain Fc-MOF@NC.

[0041] In this application, the solvothermal method is first used to construct a Fe 3+ and Ni 2+ The Fc-MOF precursor with a central metal ion and ferrocene dicarboxylic acid as an organic ligand provides a stable three-dimensional spatial structure and a high specific surface area for the purifier in the QuEChERS extraction kit; then, the Fc-MOF@NC with a porous structure and good magnetic properties is constructed through high-temperature carbonization, which can adsorb a large number of interfering components, thereby improving the purification efficiency of the QuEChERS extraction kit. In addition, the preparation method of Fc-MOF@NC can also be optimized to determine the optimal reaction conditions.

[0042] Based on a general inventive concept, the present invention provides an application of the QuEChERS extraction kit as described in the first aspect in sample pretreatment for pesticide residue detection in vegetables and fruits, and the application method in sample pretreatment specifically comprises the following steps: crushing the sample to obtain a uniform slurry; adding acetonitrile to the slurry, oscillating and extracting for 30 minutes to obtain a first mixed solution; adding a salting-out package to the first mixed solution, mixing evenly and centrifuging for 5 minutes to obtain a first supernatant; taking 2 mL of the first supernatant, mixing it with a purification package, vortexing and oscillating for 5 minutes to obtain a second mixed solution; placing a button magnet on the outside of the second mixed solution for separation to obtain a second supernatant; filtering the second supernatant through a 0.22 μm organic filter membrane to obtain a sample solution to be detected.

[0043] In conjunction with the second aspect of the present application, the mass of the slurry is 10 g; the amount of acetonitrile used is 10 mL.

[0044] Those skilled in the art will understand that the QuEChERS extraction kit provided by the present application can be used to pre-treat the sample to remove interfering components in vegetables and fruits. In a specific scheme, the present application studies the adsorption performance of Fc-MOF@NC in the purification package. At present, the common natural pigments in vegetables and fruits mainly include chlorophyll, lutein, β-carotene and lycopene, as shown in Table 1:

[0045] Table 1 Four common pigments and fruit and vegetable samples

[0046] pigment fruit vegetable Chlorophyll Apple, kiwi Lettuce, celery Lutein Orange, mango Carrots, lettuce Beta-carotene Citrus, Apple Carrots, spinach Lycopene Watermelon, papaya Tomato, carrot

[0047] Taking chlorophyll as an example, 2 mg of Fc-MOF@NC was dispersed in 5 mL of chlorophyll ACN standard solution with a concentration of 500 μg / mL. After oscillation adsorption at 25°C for 5 min, an external magnetic field was applied to separate Fc-MOF@NC from the sample solution, and the supernatant was collected and analyzed using a visible spectrophotometer.

[0048] The maximum adsorption capacity of Fc-MOF@NC at a certain time (t) is expressed as Q t It is expressed as follows, calculated by equation (1):

[0049]

[0050] Among them, C e is the initial concentration of chlorophyll; C t is the residual concentration of chlorophyll at time t; m is the mass of Fc-MOF@NC; V is the volume of the chlorophyll standard solution.

[0051] The maximum absorption wavelengths of chlorophyll, lutein, β-carotene and lycopene are 660, 445, 455 and 472 nm, respectively. The control ACN was used for zero calibration, and the effect of adsorption time (0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 10, 15 min) on the maximum adsorption capacity of the four pigments by Fc-MOF@NC was investigated.

[0052] Based on a general inventive concept, the present invention also provides a use of the QuEChERS extraction kit as described in the first aspect in the detection of pesticide residues in vegetables and fruits, comprising the following steps:

[0053] Treating the sample with the sample pretreatment method described in the second aspect to remove interfering components in the sample to obtain a solution to be tested;

[0054] The pesticide residues in the sample solution to be detected are analyzed by liquid chromatography-tandem mass spectrometry, wherein the detection conditions of the liquid chromatography-tandem mass spectrometry include: liquid chromatography conditions and mass spectrometry conditions;

[0055] The liquid chromatography conditions include: the chromatographic column is C 18 Column; mobile phase A is 0.1% formic acid water; mobile phase B is acetonitrile; gradient elution program: from 0 to 7 minutes, the volume of the mobile phase A accounts for 10% to 20%, and the volume of the mobile phase B accounts for 90% to 80%; the injection volume is 10 μL, the flow rate is 0.25 mL / min, and the column oven temperature is 35°C;

[0056] The mass spectrometry conditions include: electrospray ion source positive ion mode; ion spray voltage 5.5 kV, ion source temperature 450° C., curtain gas pressure 40 psi, spray gas pressure 40 psi, auxiliary heating gas pressure 40 psi.

[0057] In conjunction with the third aspect of the present application, the interfering components include: chlorophyll, lutein, β-carotene and lycopene.

[0058] In conjunction with the third aspect of the present application, the pesticide residues include triazine herbicides; the triazine herbicides include: atrazine, propazine, simazine, terbuthylazine, diclofenac, promethazine and simethoate.

[0059] Specifically, the detection method of the present application is multi-segment multiple reaction monitoring (MRM). The retention time, qualitative ion pair, quantitative ion pair, declustering voltage and collision energy reference values ​​of the seven THs are shown in Table 2.

[0060] Table 2 Retention time, qualitative ion pair, quantitative ion pair, declustering voltage and collision energy of THs

[0061]

[0062] The following will describe in detail a QuEChERS extraction kit and its application provided by the present application in combination with examples and experimental data.

[0063] Example

[0064] This embodiment provides a QuEChERS extraction kit, a salting-out package, a purification package and a button magnet; the salting-out package is composed of 4.0 g of MgSO4 and 1.0 g of NaCl; the purification package is 2 mg of Fc-MOF@NC; the button magnet is used to provide an external magnetic field; wherein the purification package Fc-MOF@NC is obtained by the following method:

[0065] (1) Weigh 135.25 mg of FeCl3·6H2O and 119 mg of NiCl2·6H2O and dissolve them in 10 mL of NN dimethylformamide (DMF), sonicate for 30 min, and mix well to obtain solution A;

[0066] (2) Weigh 274.05 mg of ferrocene dicarboxylic acid and 3330 mg of polyvinyl pyrrolidone (PVP) and dissolve them in 10 mL of DMF. Ultrasonicate for 30 min and mix well to obtain solution B.

[0067] (3) Mixing solution A and solution B uniformly to obtain solution C;

[0068] (4) transferring solution C to a high temperature and high pressure reactor and reacting at 125° C. for 12 h to obtain a reactant;

[0069] (5) centrifuging the reactant to obtain a centrifugal product; washing the centrifugal product three times with DMF to obtain a first washed product; washing the first washed product three times with deionized water to obtain a second washed product; washing the second washed product three times with ethanol to obtain a third washed product; drying the third washed product in a vacuum drying oven at 60° C. for 24 hours to obtain an Fc-MOF precursor;

[0070] (6) The Fc-MOF precursor was placed in a tubular furnace and heated to 700°C at a heating rate of 1.5°C / min under an argon protection environment and kept warm for 1.5 h. After the reaction was completed, it was naturally cooled to room temperature to obtain a black powder Fc-MOF@NC.

[0071] The performance of Fc-MOF@NC in the purification package was further characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffractometer, vibrating sample magnetometer, and fully automatic specific surface area and porosity analyzer, and the adsorption performance of Fc-MOF@NC in the purification package on four natural pigments, chlorophyll, lutein, β-carotene, and lycopene, was tested.

[0072] Scanning electron microscopy and transmission electron microscopy were used to characterize the Fc-MOF precursor and Fc-MOF@NC: Figure 2 a and Figure 2 c shows that the Fc-MOF precursor is a typical spherical flower-like structure, which is composed of irregular spherical micron-sized particles composed of densely connected and uniform nanoscale flakes; after high-temperature carbonization, Fc-MOF@NC still maintains the original pore structure of the Fc-MOF precursor, and carbonization makes Fe 3+ and Ni 2+ are reduced to Fe and Ni nanoparticles and evenly distributed in the carbon skeleton (e.g. Figure 2 b and Figure 2 d).

[0073] The XRD characterization results of Fc-MOF precursor and Fc-MOF@NC in the purification package are shown in Figure 3 As shown in a, all typical diffraction peaks of Fc-MOF precursors (200), (400), (001), (201), (600), (310), (402) and (511) correspond to 6.9°, 12.9°, 15.8°, 17.9°, 19.2°, 27.2°, 33.0° and 36.6°, respectively. After high-temperature carbonization, Fc-MOF@NC shows a characteristic peak (002) of graphite carbon at 26.4°. At the same time, the characteristic peaks of iron (400) and nickel nanoparticles (200) and (220) appear at 43.7°, 50.9° and 74.8°, which give Fc-MOF@NC magnetic properties, proving that magnetic Fc-MOF@NC was successfully prepared.

[0074] From the hysteresis curve ( Figure 3 b) It can be seen that the saturation magnetic intensity of Fc-MOF@NC in the purification package is 79.76emu / g, indicating that the purification package has sufficient magnetism for magnetic separation. Under the action of an external magnetic field, the Fc-MOF@NC material and the sample matrix can be quickly separated.

[0075] The specific surface area and pore structure of Fc-MOF precursor and Fc-MOF@NC were analyzed by nitrogen adsorption-desorption experiment. Figure 3 c and Figure 3 As shown in d, the nitrogen adsorption-desorption curves of Fc-MOF precursor and Fc-MOF@NC are both type III curves, and their specific surface areas are 131.15 m 2 / g and 184.23m 2 / g, and the average pore sizes are 6.28nm and 7.90nm respectively. After the Fc-MOF precursor is carbonized, Fc-MOF@NC has a larger specific surface area and a larger pore size. This structural feature can increase the contact opportunity between the target and the adsorbent, thereby enhancing the adsorption performance.

[0076] Furthermore, lettuce, carrots, tomatoes and other samples contain natural pigments, sugars and unsaturated fatty acids. Among them, high content of natural pigments is the most important interfering substance in the analysis of pesticide residues. This application investigates the adsorption performance of Fc-MOF@NC in the purification package on chlorophyll, lutein, β-carotene and lycopene:

[0077] (1) Adsorption kinetics

[0078] The adsorption kinetics mainly investigated the purification rate of the purification package. The experiment investigated the effect of purification time of 0.2 to 15 min on the maximum adsorption capacity of Fc-MOF@NC material for four kinds of pigments. The pseudo-first-order kinetic equation (2) and pseudo-second-order kinetic equation (3) were used to fit the trend of the adsorption capacity of Fc-MOF@NC material over time, and the adsorption mechanism of Fc-MOF@NC material for four kinds of pigments was explained.

[0079] Pseudo-first-order kinetic equation (2):

[0080] Pseudo-second-order kinetic equation (3):

[0081] Among them, Q t represents the maximum adsorption capacity at time t; Q e represents the maximum adsorption capacity; t represents time; k1 represents the rate constant of the pseudo-first-order kinetic model; k2 represents the rate constant of the pseudo-second-order kinetic model.

[0082] like Figure 4 As shown in the figure, as the adsorption time increases from 0.2min to 5min, the adsorption of chlorophyll, β-carotene and lycopene by Fc-MOF@NC quickly reaches saturation, and the maximum adsorption capacities are 1163.25mg / g, 249.47mg / g and 124.91mg / g, respectively. When the adsorption time is further increased to 15min, the adsorption capacities of the three do not change significantly; the adsorption capacity of lutein changes slowly, reaching saturation at 3min, with a maximum adsorption capacity of 25.10mg / g. When the adsorption time is further increased, the adsorption capacity does not change significantly. The results show that Fc-MOF@NC has excellent adsorption performance for chlorophyll, lutein, β-carotene and lycopene.

[0083] The pseudo-first-order kinetic equation and pseudo-second-order kinetic equation were used to fit the adsorption behavior of Fc-MOF@NC on the four pigments. The results are shown in Table 3 and Figure 5 As shown, the pseudo-second-order kinetic equation is fitted with R 2 The value is 0.9983-0.9999, which is greater than the pseudo-first-order kinetic equation fitting R 2 The adsorption rates of the four pigments on Fc-MOF@NC were 0.2793-0.8451, indicating that the adsorption process of Fc-MOF@NC on the four pigments was more consistent with the pseudo-second-order kinetic equation, and the adsorption process was mainly chemical adsorption.

[0084] Table 3 Kinetic parameters of Fc-MOF@NC adsorption of four natural pigments

[0085]

[0086] Using the intraparticle diffusion model of adsorption kinetics, t 0.5 is the horizontal axis, Qe Linear fitting is performed on the ordinate to describe the adsorption process of Fc-MOF@NC on the four pigments. The adsorption process of Fc-MOF@NC on the pigments is divided into three stages: extracellular diffusion, intracellular diffusion and adsorption equilibrium. The straight line does not pass through the origin, indicating that the adsorption process is jointly regulated by the three adsorption stages; comparing the slopes of the three adsorption stages ( Figure 6 ) It can be seen that the rates of the extramembrane diffusion process of the four pigments are all fast, indicating that extramembrane diffusion plays a major role in the entire adsorption process.

[0087] (2) Adsorption isotherm

[0088] At a certain temperature, the adsorption isotherm can reflect the equilibrium relationship between the adsorption capacity of the purification package Fc-MOF@NC and the residual concentration of the sample target. The Langmuir isotherm adsorption model (4) and the Freundlich isotherm adsorption model (6) are used to describe the adsorption process of Fc-MOF@NC on the four pigments.

[0089] Langmuir isotherm adsorption model (4):

[0090] The above Langmuir isotherm adsorption model is converted into model (5):

[0091] Freundlich isotherm adsorption model (6):

[0092] The above Freundlich isotherm adsorption model is converted into model (7):

[0093] Among them, Q e represents the maximum adsorption capacity; C e represents the concentration of pigment in the sample solution at adsorption equilibrium; K L represents the Langmuir adsorption constant; K F represents the Freundlich adsorption constant; 1 / n represents the adsorption intensity.

[0094] At a certain temperature, the Langmuir isotherm adsorption model and the Freundlich isotherm adsorption model were used to describe the purification mechanism of Fc-MOF@NC for the four pigments. Figure 7 It can be seen that the Freundlich adsorption isotherm model fits R 2 The Langmuir adsorption isotherm model fitting R 2 The adsorption equilibrium constant KL 0.0057~0.0142(0 <K L <1), indicating that the adsorption of the four pigments by Fc-MOF@NC is easy to occur, and the adsorption process tends to be a uniform monolayer chemical adsorption on the surface.

[0095] Table 4 Isothermal adsorption parameters of four pigments on Fc-MOF@NC

[0096]

[0097] (3) Adsorption thermodynamics

[0098] The experiment investigated the effect of Fc-MOF@NC on the maximum adsorption capacity of four pigments at different temperatures, calculated thermodynamic parameters such as ΔG (kJ / mol), ΔH (kJ / mol) and ΔS (J / mol·K), and used thermodynamic equations to analyze the adsorption mechanism of Fc-MOF@NC on the four pigments. According to formula (8), k e 、Calculate lnk using formula (9) e and ΔG; a scatter plot was drawn with 1 / T as the horizontal axis and lnke as the vertical axis and a linear fit was performed. Based on the slope and intercept of the fit, ΔH was calculated by formula (10) and ΔS was calculated by formula (11). The results are shown in Table 5. ΔG is less than 0, while ΔH and ΔS are greater than 0, indicating that the adsorption behavior of Fc-MOF@NC on the four pigments is a spontaneous endothermic process with an increase in entropy.

[0099] Formula (8):

[0100] Formula (9): ΔG = -RT lnk e ;

[0101] Formula (10): ΔH = -Slope × R;

[0102] Formula (11): ΔS=Intercept×R;

[0103] Among them, Slope represents the slope; Intercept represents the intercept; k e represents the adsorption equilibrium constant; T represents temperature; R represents the universal gas constant, 8.314 J / (mol·K).

[0104] Table 5 Thermodynamic parameters of Fc-MOF@NC adsorption of pigments

[0105]

[0106] In order to establish the QuEChERS conditions, the amount of Fc-MOF@NC in the purification package and the purification time were studied in this application.

[0107] (1) Fc-MOF@NC dosage

[0108] Taking lettuce samples as an example, the purification time was fixed at 5 minutes in the experiment to investigate the effect of Fc-MOF@NC dosage on the purification effect of lettuce sample matrix. The full wavelength scanning results of UV-visible spectrophotometer are as follows: Figure 8 As shown in a, from top to bottom are 0mg (unpurified), 0.5mg, 1mg, 1.5mg, 2mg and 2.5mg. Compared with the direct analysis results of the unpurified lettuce sample, as the amount of purifier increases from 0.5mg to 2mg, the impurity peak response decreases significantly, and the impurity peak does not change significantly when the amount continues to increase to 2.5mg. The results show that when the amount of Fc-MOF@NC is 2mg, it can effectively adsorb the matrix interference of the lettuce sample.

[0109] At the same time, the experiment investigated the effect of Fc-MOF@NC dosage of 0.5, 1, 1.5, 2 and 2.5 mg on the recovery rate of 7 THs. Figure 8 As shown in Figure b, when the dosage of Fc-MOF@NC is 0.5-1.5 mg, the recovery rate of the target product is 96.6%-117%, and the RSD is 2.2%-8.7%; when the dosage of Fc-MOF@NC is increased to 2 mg, the recovery rate is 94.5%-104%, and the RSD is 1.0%-4.9%; when the dosage of Fc-MOF@NC is further increased to 2.5 mg, the recovery rate does not change significantly. Considering the purification effect and economic cost, the experiment finally chose 2 mg Fc-MOF@NC to be filled into the purification bag.

[0110] (2) Purification time

[0111] Taking lettuce samples as an example, the experiment fixed the amount of Fc-MOF@NC at 2 mg to investigate the effect of purification time on the matrix purification effect and target recovery rate of lettuce samples. The full wavelength scanning results of the UV-visible spectrophotometer are shown in Fig. 9 a, from top to bottom, 0min (unpurified), 2min, 3min, 4min, 5min and 6min. Compared with the direct analysis results of the unpurified lettuce sample, the impurity peak response decreased with the increase of purification time within 2-5min, and continued to increase to 6min, and the impurity peak had no significant change, indicating that 2mg Fc-MOF@NC had a good effect when purifying the lettuce sample matrix for 5min. The experiment further investigated the effect of purification time on the recovery rate of THs. Fig. 9 b shows that the recovery rate of the target substance changes slowly during the observation period. After comprehensive consideration, the optimal purification time of the experiment is determined to be 5 minutes.

[0112] The present invention also provides an application of a QuEChERS extraction kit in the detection of pesticide residues in vegetables and fruits, which is used to remove interfering components in samples and detect pesticide residues (THs) in samples. The experiment evaluates the matrix effect, linear range, detection limit (LODs), quantification limit (LOQs), accuracy and precision of the liquid chromatography-tandem mass spectrometry detection method, and conducts actual sample analysis:

[0113] (1) Matrix effect

[0114] During mass spectrometry analysis, the matrix components in vegetable and fruit samples are prone to interfere with the ionization of the target, showing a matrix effect (ME) that enhances or inhibits the response of the target, affecting the accuracy of the method. The experiment used acetonitrile and blank orange, citrus, apple, watermelon, tomato, carrot and lettuce sample matrix extraction solutions to prepare solvent standard curves and matrix standard curves, and evaluated the method ME by the slope ratio of the two. When the value is 0.8-1.2, the ME is negligible. The results are shown in Table 6. The slope ratio is 0.81-1.19, indicating that the ME of this method is not significant, and it can effectively purify the sample matrix and achieve accurate analysis of THs in a variety of vegetables and fruits.

[0115] Table 6 Matrix effects of THs in 7 matrices

[0116] Target orange Tangerine apple watermelon tomato carrot lettuce Atrazine 1.05 1.04 1.00 1.01 1.00 0.98 0.98 Pulmonary 1.13 1.13 0.99 0.83 1.05 0.81 1.08 simazine 1.04 1.05 1.03 1.04 1.01 1.00 1.08 Terbutinzine 1.19 1.17 1.03 1.01 1.00 1.00 0.99 Dichlorvos 1.10 1.12 1.11 0.90 1.04 0.84 0.86 Promethazine 0.94 0.86 1.00 0.82 0.83 0.83 0.81 Simetidine 1.02 1.11 1.10 1.01 0.98 1.12 1.07

[0117] (2) Linear range, detection limit, and quantification limit

[0118] Under the optimal experimental conditions, an analytical method for 7 THs in fruit and vegetable matrices was established based on the QuEChERS improved extraction kit combined with LC-MS / MS analysis. Three different mass concentrations of THs were analyzed by LC-MS / MS, and linear regression was performed with THs mass concentration as the horizontal axis and peak area as the vertical axis. The signal-to-noise ratio (S / N) of 3 and 10 were used as the detection limit (LOD) and quantification limit (LOQ). The results are shown in Table 7. The 7 THs in fruit and vegetable samples showed a good linear relationship in the range of 0.0015-200 μg / kg, and the correlation coefficients (r) were all higher than 0.9990. The detection limit was 0.0005-0.2500 μg / kg, and the quantification limit was 0.0015-0.8000 μg / kg. The above results show that this method has a wide linear range, low detection limit and good sensitivity.

[0119] Table 7 Linear range, regression equation, detection limit and quantification limit of the method

[0120]

[0121]

[0122]

[0123] (3) Accuracy and precision

[0124] Spike recovery experiments were performed on blank orange, tangerine, apple, watermelon, tomato, carrot and lettuce sample homogenates at three concentration levels (5, 50 and 200 μg / kg), and the precision of the method was evaluated by the RSD of the chromatographic peak area measured three times within the day (n=3) and between days (n=3). Table 8 shows that the recoveries of the seven THs in orange samples were 85.6% to 102%, the intra-day precision was 0.2% to 4.3%, and the inter-day precision was 1.0% to 6.1%; the recoveries of the seven THs in citrus samples were 86.1% to 95.8%, the intra-day precision was 0.1% to 5.0%, and the inter-day precision was 0.6% to 7.1%; the recoveries of the seven THs in apple samples were 88.1% to 110%, the intra-day precision was 0.1% to 4.7%, and the inter-day precision was 1.0% to 6.4%; the recoveries of the seven THs in watermelon samples were 87.4% to 105%, and the intra-day precision was 0.3% to 10.5%. ~6.8%, and the inter-day precision was 0.7%~8.8%; the recovery rate of 7 THs in tomato samples was 86.2%~103%, the intra-day precision was 0.1%~4.3%, and the inter-day precision was 1.2%~7.5%; the recovery rate of 7 THs in carrot samples was 85.0%~110%, the intra-day precision was 0.7%~5.8%, and the inter-day precision was 1.2%~8.9%; the recovery rate of 7 THs in lettuce samples was 86.0%~106%, the intra-day precision was 0.1%~3.3%, and the inter-day precision was 1.3%~7.4%; the above results show that the accuracy and precision of this method are good. The standard MRM mass spectra of 7 THs (50μg / kg) are shown in Fig.10 .

[0125] Table 8 Recovery and precision of the method

[0126]

[0127]

[0128]

[0129] (4) Actual sample analysis

[0130] Ten samples of seven THs in orange, tangerine, apple, watermelon, tomato, carrot and lettuce were analyzed by liquid chromatography-tandem mass spectrometry. The results are shown in Tables 9 to 15:

[0131] Table 9 Analysis results of 7 THs in orange

[0132]

[0133]

[0134] Table 10 Analysis results of 7 THs in citrus

[0135]

[0136]

[0137] Table 11 Analysis results of 7 THs in apple

[0138]

[0139]

[0140] Table 12 Analysis results of 7 THs in watermelon

[0141]

[0142]

[0143] Table 13 Analysis results of 7 THs in tomatoes

[0144]

[0145]

[0146] Table 14 Analysis results of 7 THs in carrots

[0147]

[0148]

[0149] Table 15 Analysis results of 7 THs in lettuce

[0150]

[0151]

[0152]

[0153] From the data in the above table, we can know that among the orange samples, simazine was detected in 9 samples, and the detection concentration was 0.12±0.01~0.78±0.02; atrazine was detected in 1 sample, and the detection concentration was 0.16±0.02; promethazine was detected in 7 samples, and the detection concentration was 0.03±0.01~1.47±0.04; diquat was detected in 3 samples, and the detection concentration was 0.02±0.01~0.08±0.02; fametamine was detected in 2 samples, and the detection concentrations were 0.08±0.01 and 0.09±0.01; terbuthylazine was detected in 2 samples, and the detection concentrations were 0.08±0.01 and 1.06±0.04; simethoate was detected in all 10 samples, and the detection concentrations were 0.41±0.03 and 4.55±0.04.

[0154] Among the citrus samples, simazine was detected in 9 samples with a detection concentration of 0.02±0.01~0.30±0.02; atrazine was detected in 3 samples with a detection concentration of 0.13±0.02~2.28±0.04; cypermethrin was detected in 3 samples with a detection concentration of 0.05±0.01~0.21±0.02; diquat was detected in 3 samples with a detection concentration of 0.08±0.01~0.15±0.04; cypermethrin was detected in 1 sample with a detection concentration of 0.01±0.01; terbuthylazine was detected in 1 sample with a detection concentration of 2.26±0.02; simetropium was detected in 8 samples with a detection concentration of 0.17±0.02~1.40±0.06.

[0155] Among the apple samples, simazine was detected in 4 samples with a detection concentration of 0.08±0.02~0.13±0.02; atrazine was detected in 1 sample with a detection concentration of 0.25±0.03; promethazine was detected in 6 samples with a detection concentration of 0.12±0.02~0.57±0.06; diquat was detected in 5 samples with a detection concentration of 0.11±0.02~0.28±0.03; terbuthylazine was detected in 4 samples with a detection concentration of 0.19±0.02~0.45±0.03; simethoate was detected in 4 samples with a detection concentration of 0.43±0.03 and 0.55±0.04.

[0156] Among the watermelon samples, simazine was detected in 8 samples with the detection concentration of 0.06±0.01~0.12±0.02; cypermethrin was detected in 2 samples with the detection concentration of 0.07±0.02 and 0.08±0.02; diquat was detected in 7 samples with the detection concentration of 0.04±0.02~0.17±0.04; terbuthylazine was detected in 1 sample with the detection concentration of 0.06±0.02; simenochlorvamine was detected in 8 samples with the detection concentration of 0.73±0.03 and 14.72±0.05.

[0157] Among the tomato samples, simazine was detected in 7 samples with the detection concentration of 0.04±0.01~0.19±0.02; cypermethrin was detected in 2 samples with the detection concentration of 0.65±0.03 and 0.94±0.03; diquat was detected in 1 sample with the detection concentration of 0.24±0.03; terbuthylazine was detected in all 10 samples with the detection concentration of 0.03±0.02 and 0.42±0.04; simenochlorvamine was detected in 4 samples with the detection concentration of 1.01±0.04~5.51±0.05.

[0158] Among the carrot samples, simazine was detected in 2 samples with concentrations of 0.02±0.02 and 0.09±0.03; cypermethrin was detected in 1 sample with a concentration of 0.06±0.02; terbuthylazine was detected in 3 samples with concentrations of 0.11±0.01 to 0.98±0.03; and simethoprim was detected in all 3 samples with concentrations of 1.22±0.03 to 2.68±0.07.

[0159] Among the lettuce samples, simazine was detected in 2 samples with concentrations of 0.02±0.01 and 0.02±0.02; atrazine was detected in 1 sample with a concentration of 0.01±0.01; promethazine was detected in 5 samples with a concentration of 0.01±0.01~0.28±0.04; terbuthylazine was detected in 9 samples with a concentration of 0.02±0.01~0.41±0.02; simethoate was detected in 5 samples with a concentration of 1.15±0.03~11.69±0.04.

[0160] All samples were spiked with THs at a concentration of 50 ng / mL, and the recoveries of orange, citrus, apple, watermelon, tomato, carrot, and lettuce were 85.1%-95.4%, 84.1%-97.8%, 85.7%-102%, 85.3%-102%, 84.6%-96.5%, 84.6%-107, and 85.5%-100%, respectively. This indicates that the method has good accuracy and can be used for the analysis of THs in actual fruit and vegetable matrices.

[0161] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0162] (1) The QuEChERS extraction kit provided in the present application comprises a salting-out package, a purification package and a button magnet; wherein the salting-out package comprises 4.0 g of MgSO4 and 1.0 g of NaCl; the purification package comprises 2 mg of Fc-MOF@NC; the button magnet is used to provide an external magnetic field; the kit has good purification performance, is simple to operate and is easy to carry, and can be directly used for pretreatment of pesticide residues.

[0163] (2) The present invention uses Fc-MOF@NC as a purifier in the QuEChERS extraction kit to adsorb interfering components of the sample and eliminate matrix interference during detection. It is combined with liquid chromatography-tandem mass spectrometry to establish an accurate, simple and efficient analysis method for THs in a variety of vegetables and fruits.

[0164] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article, or apparatus.

[0165] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0166] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A QuEChERS extraction kit, characterized in that: The extraction kit includes: a salting-out package, a purification package and a button magnet; the salting-out package includes 4.0 g of MgSO4 and 1.0 g of NaCl; the purification package includes 2 mg of Fc-MOF@NC; the button magnet is used to provide an external magnetic field; The Fc-MOF@NC is obtained by the following preparation method: (1) Dissolve FeCl3·6H2O and NiCl2·6H2O in DMF and mix them evenly by ultrasonication to obtain solution A; (2) dissolving ferrocene dicarboxylic acid and PVP in DMF and mixing them uniformly by ultrasonication to obtain solution B; (3) mixing the solution A and the solution B evenly to obtain a solution C; (4) transferring the solution C to a high temperature and high pressure reactor to react and obtain a reactant; (5) centrifuging, washing, and drying the reactants to obtain an Fc-MOF precursor; (6) carbonizing the Fc-MOF precursor at high temperature to obtain Fc-MOF@NC; Step (5) centrifuging, washing and drying the reactant to obtain an Fc-MOF precursor comprises the following steps: Centrifuging the reactant to obtain a centrifugal product; The centrifuged product is washed three times with DMF to obtain a first washed product; Washing the first washed product three times with deionized water to obtain a second washed product; washing the second washed product three times with ethanol to obtain a third washed product; The third washed product was placed in a vacuum drying oven at 60° C. and dried for 24 h to obtain an Fc-MOF precursor.

2. The QuEChERS extraction kit according to claim 1, characterized in that: In step (4), the reaction conditions include: reaction temperature of 120-130° C.; reaction time of 10-14 h.

3. The QuEChERS extraction kit according to claim 1, characterized in that: Step (6) high-temperature carbonization of the Fc-MOF precursor comprises: The Fc-MOF precursor was placed in a tube furnace, and under argon protection, the tube furnace was set to heat the Fc-MOF precursor to 700° C. at a heating rate of 1.5° C. / min, and the reaction was kept at this temperature for 1.5 h, and the mixture was naturally cooled to room temperature to obtain Fc-MOF@NC.

4. An application of the QuEChERS extraction kit as claimed in any one of claims 1 to 3 in sample pretreatment for pesticide residue detection in vegetables and fruits, characterized in that: The application method in sample pretreatment specifically includes the following steps: The sample is crushed to obtain a uniform slurry; Add acetonitrile to the slurry, and extract by shaking for 30 min to obtain a first mixed solution; Adding a salting-out bag to the first mixed solution, mixing evenly and centrifuging for 5 minutes to obtain a first supernatant; Take 2 mL of the first supernatant, mix it with the purification package, and vortex for 5 minutes to obtain a second mixed solution; placing a button magnet outside the second mixed solution to separate the second mixed solution to obtain a second supernatant; The second supernatant is filtered through a 0.22 µm organic filter membrane to obtain a sample solution to be tested; The mass of the slurry is 10 g; the amount of acetonitrile is 10 mL; The pesticide residues include triazine herbicides.

5. Use of the QuEChERS extraction kit according to any one of claims 1 to 3 in the detection of pesticide residues in vegetables and fruits, characterized in that: The following steps are involved: Treating the sample by the application method in sample pretreatment as described in claim 4 to remove interfering components in the sample to obtain a solution to be tested; The pesticide residues in the test solution are analyzed by liquid chromatography-tandem mass spectrometry, and the detection conditions of the liquid chromatography-tandem mass spectrometry include: liquid chromatography conditions and mass spectrometry conditions; The liquid chromatography conditions include: the chromatographic column is C 18 Column; mobile phase A is 0.1% formic acid water; mobile phase B is acetonitrile; gradient elution program: from 0 to 7 min, the volume of the mobile phase A accounts for 10% to 20%, and the volume of the mobile phase B accounts for 90% to 80%; injection volume is 10 μL, flow rate is 0.25 mL / min, and column oven temperature is 35°C; The mass spectrometry conditions include: electrospray ion source positive ion mode; ion spray voltage 5.5 kV, ion source temperature 450° C., curtain gas pressure 40 psi, spray gas pressure 40 psi, and auxiliary heating gas pressure 40 psi.

6. Use of the QuEChERS extraction kit according to claim 5 in the detection of pesticide residues in vegetables and fruits, characterized in that: The interfering components include: chlorophyll, lutein, β-carotene and lycopene.

7. Use of the QuEChERS extraction kit according to claim 6 in the detection of pesticide residues in vegetables and fruits, characterized in that: The pesticide residues include triazine herbicides; the triazine herbicides include: atrazine, propazine, simazine, terbuthylazine, diclofenac, promethazine and simethoxam.

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