Trivalent iron magnetic solid phase masking agent and quantitative detection method for lead in vegetable product

Abstract

The invention belongs to the technical field of food quality monitoring, and particularly relates to a ferric iron magnetic solid-phase masking agent and a quantitative detection method for lead in vegetable products. The preparation method of the trivalent iron magnetic solid-phase masking agent comprises the following steps: S1, carrying out carboxylation on a terminal amino group of DFO to obtain DFO-COOH; s2, the surface of the Fe3O4 magnetic core is coated with a SiO2 layer, and Fe3O4 coated SiO2 is obtained; s3, carrying out amination modification on the Fe3O4 (at) SiO2, so as to obtain Fe3O4 (at) SiO2-NH2; and S4, the Ac-DFO is coupled with the Fe3O4 (at) SiO2-NH2, and the Fe3O4 (at) SiO2-DFO is prepared. Three hydroximic acid groups of DFO and Fe < 3 + > form a stable chelate, the Fe < 3 + > removal rate can be increased to 99% or above through magnetic separation, and quantitative detection of lead ions is faster and more accurate by further combining with a mature immunochromatography technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food quality monitoring, and particularly relates to a ferric magnetic solid-phase masking agent and a quantitative detection method for lead in vegetable products. BACKGROUND

[0002] Long-term consumption of vegetable products contaminated by lead by human body can cause lead enrichment in the body, and harm the nervous system, bone hematopoietic function, digestive system, reproductive system and the like; especially, the brain of children is in the sensitive period of nervous system development, and is prone to adverse consequences such as developmental retardation. Therefore, the relevant food safety standards clearly stipulate the limit of lead in vegetable products: 0.3 mg / kg for vegetable products (except pickled vegetables and dried vegetables), 0.5 mg / kg for pickled vegetables, and 0.8 mg / kg for dried vegetables. However, in practice, the phenomenon of lead exceeding the standard in vegetable products still occurs from time to time, so it is of important practical significance to study a high-efficiency detection method for lead in vegetable products.

[0003] At present, the traditional heavy metal lead detection methods mainly include atomic absorption spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry, atomic fluorescence spectrometry, ultraviolet-visible spectrophotometry, anodic stripping voltammetry and the like. Although such methods have low detection limit and high accuracy, they have defects such as high cost of equipment purchase and maintenance, tedious and time-consuming sample pretreatment process, need for sample digestion treatment, and high requirement for professional quality of operators, and cannot meet the needs of on-site rapid detection of grassroots detection units, and are difficult to adapt to batch sample screening work in scenes such as vegetable purchase monitoring and on-site supervision and inspection. In order to solve the shortcomings of traditional methods, immunological analysis methods are gradually applied due to the advantages of simple operation, good specificity and low detection cost, among which colloidal gold immunochromatography and enzyme-linked immunosorbent assay are the current mainstream technologies.

[0004] Time-resolved fluorescence immunochromatography technology is a new immunological detection method based on the development of fluorescence dye labeling technology, and is a combination of immunological affinity technology, immunological labeling technology and immunochromatography technology, and inherits the advantages of rapid detection and simple operation. The core of time-resolved fluorescence immunochromatography technology (TRFICA) is to label antibodies / antigens with rare earth element chelates, and to eliminate background interference by using fluorescence lifetime difference, and the technology has comprehensive advantages such as high detection sensitivity, simple operation and good stability.

[0005] However, in the detection of lead content in vegetable products such as dried plum, it is easy to be interfered by iron element. A large amount of iron element is introduced due to production equipment problems in the production process of dried plum. The highest Koda is 1.5 g / kg. The chelation constant of ferric ion and lead chelator is about 26, and the chelation constant of lead ion and chelator is about 18. The chelator will preferentially react with ferric ion, resulting in missed detection and misjudgment. The conventional method adopts DETA to shield iron ion. However, the stability of the complex of EDTA and iron is greatly affected by pH, and the iron ion is easily released again in the detection process, which greatly interferes with the detection of lead. Selective removal of iron ion from the sample will effectively avoid this situation. The vegetable products contain cellulose fragments. After iron precipitation, the centrifugal / filtration method is easy to form a viscous precipitate layer, which is difficult to effectively remove the iron precipitate. The lead ion originally leached into the solution is also easily wrapped by the precipitate, resulting in detection error. SUMMARY

[0006] (I) Technical problems to be solved In view of the above-mentioned defects and deficiencies of the prior art, the present application provides a ferric magnetic solid-phase masking agent and a quantitative detection method for lead in vegetable products. The iron ion is shielded and removed by the magnetic solid-phase masking agent to improve the detection accuracy of lead in vegetable products.

[0007] (II) Technical solutions In a first aspect, the present application provides a ferric magnetic solid-phase masking agent, and the preparation method is as follows: S1, the terminal amino group of DFO is carboxylated to obtain DFO-COOH; S2, a SiO2 layer is coated on the surface of Fe3O4 magnetic core to obtain Fe3O4@SiO2; S3, Fe3O4@SiO2 is modified by amination to obtain Fe3O4@SiO2-NH2; S4, Ac-DFO is coupled with Fe3O4@SiO2-NH2 to obtain Fe3O4@SiO2-DFO.

[0008] According to the preferred embodiment of the present application, in S1, the method for carboxylating the terminal amino group of DFO is as follows: according to the ratio of 1g:15-20mL, DFO is dissolved in anhydrous DMF, oxygen is removed by N2 for 10-15min, and stirring is carried out at room temperature; according to the molar ratio of DFO: succinic anhydride = 1:1.2, the DMF solution of succinic anhydride is slowly added, triethylamine is added dropwise as an acid binding agent, and reaction is carried out at room temperature for 3-5h. After the reaction is completed, ice water is added to the solution, and the pH is adjusted to 3.0-4.0 with HCl. White precipitate is precipitated, filtered, washed with ice water for 2-3 times, and dried at 60℃ under vacuum to obtain carboxylated deferoxamine DFO-COOH.

[0009] According to the preferred embodiment of the present application, in S2, the preparation method of Fe3O4@SiO2 is as follows: high-purity nano Fe3O4 with a particle size of 80-150 nm is dispersed in a mixed solution of ethanol / water at a ratio of 4:1 at 10-20 mg / mL, ultrasonic dispersion is performed for 20-30 min, 10% ammonia water is added to adjust the pH to 10-10.5, TEOS is added dropwise at a proportion of 20-30% of the mass of the magnetic powder, stirring is performed at room temperature overnight, the product is separated by magnetism, washed with ethanol for 2-4 times, dried, and Fe3O4@SiO2 is obtained.

[0010] According to the preferred embodiment of the present application, in S3, the preparation method of Fe3O4@SiO2-NH2 is as follows: Fe3O4@SiO2 is dispersed in anhydrous toluene and ultrasonic dispersion is performed; APTES is added at a proportion of 5-8% of the volume of the solution, refluxing is performed at 70-75°C under nitrogen protection overnight, the product is separated by magnetism, washed with ethanol for 2-3 times, vacuum dried, and Fe3O4@SiO2-NH2 is obtained.

[0011] According to the preferred embodiment of the present application, in S4, the preparation method of Fe3O4@SiO2-DFO is as follows: DFO-COOH is dissolved in MES buffer (pH 5.0), EDC / NHS is added, the molar ratio of Ac-DFO:EDC:NHS is 1:1.2:1.2, and ice bath stirring is performed for 20-40 min to activate the carboxyl group; Fe3O4@SiO2-NH2 prepared in step 3) is added, rotary incubation is performed at room temperature for 3-6 h; the product is collected by magnetism, washed with PBS for 3-4 times, vacuum dried, and Fe3O4@SiO2-DFO is obtained.

[0012] According to the preferred embodiment of the present application, in S4, the prepared Fe3O4@SiO2-DFO can be sealed and stored in anhydrous ethanol under cold storage, anhydrous ethanol is added with 0.1% BHT (butylated hydroxytoluene) antioxidant to delay pyridinone epoxidation, the storage time is >12 months, the stability is good, DFO dissolution is negligible (<0.1%), and the specificity of combination with trivalent iron is strong.

[0013] In a second aspect, the present application provides a method for quantitatively detecting lead in vegetable products based on heavy metal lead time-resolved fluorescence immunochromatography technology, which comprises the following steps: Step 1: Preparation of sample crude extract The edible part of dried vegetables is cut and crushed by a high-speed pulverizer, and then passed through a 40-mesh sieve to obtain a sample powder; the edible part of pickled vegetables is homogenized to obtain a sample; A certain mass of powder sample or homogenate sample is weighed into a centrifugal tube, an extraction reagent is added in an amount of 1g:4-6mL according to the mass volume ratio, vortex oscillation is carried out, centrifugation is carried out at 3000-5000rpm, supernatant is separated, and a sample crude extract is obtained; the extraction reagent is nitric acid-hydrogen peroxide solution, wherein the concentration of nitric acid is 15v / v%; Step 2: preparation of a to-be-tested liquid The sample crude extract is added with the trivalent iron magnetic solid phase masking agent prepared in the above examples, trivalent iron is removed by magnetic separation, Na2HPO4-Na3PO4 buffer system is added to the remaining solution for neutralization to pH 7-8, and a to-be-tested liquid is obtained; Step 3: taking the to-be-tested liquid, and performing detection according to the operation instruction of the time-resolved fluorescence immunochromatographic test paper.

[0014] The heavy metal lead time-resolved fluorescence immunochromatographic test strip / test paper card is based on an existing product, for example, the existing brand Huaanmai Ke, Feicai Biology, Meizheng Biology and the like.

[0015] (Three) beneficial effects The technical effect of the present application is that: (1) The present application provides a trivalent iron magnetic solid phase masking agent which can be stably stored in anhydrous ethanol, the masking agent can specifically bind to 3-valent iron ions in a sample crude extract (basically not combined with lead ions), iron ions are directly removed by magnetic separation technology, the competition path of iron ions and chelating agents is cut off from the source, and the problems of large pH influence on the stability of the complex and easy release of iron ions in the traditional EDTA shielding method are completely solved, and the key interference obstacle for lead ion detection is cleared. The trivalent iron magnetic solid phase masking agent is stable in storage, and can be stored in anhydrous ethanol after preparation once, that is, it can be taken as needed.

[0016] The present application uses deferoxamine to prepare a trivalent iron magnetic solid phase masking agent, mainly because deferoxamine has strong selective complexation with iron and basically does not combine with lead, and deferoxamine has multiple hydroxyl groups and terminal amino groups, the terminal amino groups do not participate in the complexation of iron ions, and after the terminal amino carboxylation is connected to the surface of the magnetic iron particle, the remaining hydroxyl groups still have strong complexation with iron ions. After DFO is connected to the surface of Fe3O4@SiO2 magnetic core through terminal amino carboxylation, the molecular conformation is in an extended state of "magnetic core-connection arm-DFO main body", the length of the connection arm is about 0.6nm, which can make the DFO main body away from the surface of the magnetic core, avoid the spatial hindrance of the magnetic core to the hydroxamic acid group and Fe 3+ Combination.

[0017] (2) Avoid the error caused by the iron precipitate wrapping lead ions: compared with the conventional iron precipitation centrifugation / filtration method, the magnetic separation technology can quickly and completely separate the iron ion complex by means of the targeted combination of the magnetic shielding agent and the magnetic field adsorption characteristics, without going through the cumbersome process of precipitation centrifugation / filtration, effectively avoiding the wrapping of lead ions by the precipitate, and significantly reducing the detection error caused by improper separation method.

[0018] The trivalent iron magnetic solid phase shielding agent is combined with the trivalent iron ions after being added to the solution, a magnetic field is applied outside the container, the magnetic particles are adsorbed to the container wall, and the remaining solution is poured out to complete the separation. The iron ion removal adopts the magnetic separation technology, which is faster and more convenient than the centrifugation / filtration method, without waiting for the processing of the viscous precipitate.

[0019] (3) In the sample processing process, 15v / v% nitric acid-hydrogen peroxide solution is used as the extraction reagent, the mass volume ratio of 1g:4-6mL is extracted, and the sample crude extract is prepared by centrifugation at 3000-5000rpm. The extraction system can efficiently leach lead ions in vegetable products (dried vegetables, pickled vegetables), while avoiding excessive dissolution of impurities such as cellulose fragments, so that the iron ions remain in the form of 3-valence; The subsequent step 2 is neutralized to pH 7-8 in the buffer system, which provides a stable environment for lead ions and reduces the loss of lead ions during pretreatment, laying a accurate foundation for subsequent detection.

[0020] (4) The present application combines mature immunochromatography technology with efficient iron ion removal and sample pretreatment in the early stage, greatly reduces the influence of interference factors on the immune reaction, makes the quantitative detection result of lead ions more accurate, effectively avoids the detection deviation caused by interference in the traditional method, and meets the accuracy and reliability requirements of lead content detection in vegetable products. DETAILED DESCRIPTION

[0021] In order to better explain the present application, the following specific embodiments are used to describe the present application in detail. The preparation method of the trivalent iron magnetic solid phase shielding agent and the verification of its specific removal efficiency of iron ions are described in the following examples.

[0022] Example 1 This embodiment provides Fe 3+ Preparation method of magnetic solid phase shielding agent Fe3O4@SiO2-DFO: (1) Take 1 g of deferoxamine DFO and dissolve it in 15 mL of anhydrous DMF according to the ratio of 1 g:15 mL. Bubble N2 into the solution to remove oxygen for 12 min and stir at room temperature. Slowly add succinic anhydride (dissolved in 5 mL of anhydrous DMF) according to the molar ratio of DFO: succinic anhydride = 1:1.2, and drop 0.1 mL of triethylamine as an acid-binding agent. React at room temperature for 4 h. After the reaction is completed, add 50 mL of ice water to the solution, adjust the pH to 3.5 with 1M HCl, precipitate white sediment, filter, wash with ice water for 3 times, and dry the sediment in a 60°C vacuum drying oven for 5 h to obtain carboxylated deferoxamine DFO-COOH. -1 There is no obvious absorption at 3300-3500 cm -1 There is a strong absorption peak at 1720-1740 cm

[0023] (2) Take 5 g of high-purity nano Fe3O4 with an average particle size of 100 nm, disperse it in a mixture of ethanol / water (volume ratio 4:1) according to the ratio of 15 mg / mL, and ultrasonically disperse the mixture in an ultrasonic instrument for 35 min. Add 10% ammonia water to the dispersed solution, adjust the pH of the solution to 10.2, and then slowly add tetraethyl orthosilicate (TEOS) according to the ratio of 20% of the mass of the magnetic powder. Stir at room temperature overnight (about 12 h). After the reaction is completed, collect the product by magnetic separation, wash the product with anhydrous ethanol for 3 times, and dry the washed product in a 60°C oven for 6 h to obtain Fe3O4@SiO2.

[0024] FT-IR analysis of the product: compared with the spectrum of Fe3O4, there is a strong peak at 1080 cm -1 and the peak intensity at 570 cm -1 is weakened, indicating that SiO2 is successfully coated.

[0025] (3) Take 4 g of Fe3O4@SiO2, disperse it in 80 mL of anhydrous toluene, and ultrasonically disperse for 30 min until the solution is uniformly dispersed. Add 3-aminopropyltriethoxysilane (APTES) according to the ratio of 6% of the solution volume. Under the condition of nitrogen protection, heat the reaction system to 72°C and reflux for 10 h. After the reaction is completed, collect the product by magnetic separation, wash the product with anhydrous ethanol for 3 times, and dry the product in a 55°C vacuum drying oven for 8 h to obtain Fe3O4@SiO2-NH2.

[0026] FT-IR analysis of the product: there is a N-H stretching vibration doublet (relatively wide) at 3300-3500 cm -1 , and a peak at 1490 cm -1N-H bending vibration peak, indicating that the primary amino group (-NH2) is successfully grafted; the SiO2 surface Si-OH peak (950 cm -1 ) is weakened, indicating that Si-OH has reacted; the C-H bending vibration peak at 1380 cm -1 further indicates that the product organic segment exists.

[0027] (4) 1.2 g of DFO-COOH was weighed and dissolved in 35 mL of 0.1M MES buffer (pH 5.0), and 1-ethyl-(3-dimethylaminopropyl) carbonyldiimidazole (EDC) and N-hydroxysuccinimide (NHS) (molar ratio of DFO-COOH:EDC:NHS is 1:1.2:1.2) were added, and the mixture was stirred in an ice bath for 30 min to activate the carboxyl group. Then 2 g of Fe3O4@SiO2-NH2 was added, and the mixture was incubated at room temperature for 4 h. After the reaction was completed, the product was collected by magnetic separation, washed with PBS buffer (pH 7.4) for 4 times, and dried in a vacuum drying oven at 60°C for 6 h to obtain the trivalent iron magnetic solid phase masking agent Fe3O4@SiO2-DFO. FT-IR analysis of the product: compared with the spectrum of the product of the previous step, the intensity of the hydroxyl peak (3400 cm -1 ) increased, indicating that the product introduced multiple hydroxyl groups; the C-H bending vibration peak at 1380 cm -1 significantly increased, and the 720 cm -1 also increased, indicating an increase in the number of methylene groups, indicating an increase in the C-H signal of the organic segment and an increase in the chain length.

[0028] The prepared Fe3O4@SiO2-DFO was sealed in anhydrous ethanol containing 0.1% BHT and stored in a refrigerator. After 12 months of storage, the DFO dissolution rate was <0.1%, and the specificity of trivalent iron binding did not decrease.

[0029] Example 2 This example provides a method for preparing the Fe 3+ magnetic solid phase masking agent Fe3O4@SiO2-DFO: (1) Take 1 g of deferoxamine DFO and dissolve it in 15 mL of anhydrous DMF according to a ratio of 1 g:18 mL. Bubble N2 into the solution to remove oxygen for 15 min and stir at room temperature. Slowly add succinic anhydride (dissolved in 5 mL of anhydrous DMF) according to a molar ratio of DFO: succinic anhydride = 1:1.2, and drop 0.15 mL of triethylamine as an acid-binding agent. React at room temperature for 3.5 h. After the reaction is completed, add 55 mL of ice water to the solution, adjust the pH to 3.4 with 1M HCl, and precipitate white sediment. After filtration, wash the sediment with ice water for 3 times, and dry the sediment in a 60°C vacuum drying oven for 6 h to obtain carboxylated deferoxamine DFO-COOH. FT-IR analysis: the characteristic peak of amino group disappears, and the stretching vibration peak (1730 cm -1 ) of carboxyl C=O is obvious.

[0030] (2) Take 4 g of high-purity nano Fe3O4 with an average particle size of 80 nm, and disperse it in a mixture of ethanol / water (volume ratio 4:1) according to a ratio of 12 mg / mL. Place the mixture in an ultrasonic instrument and ultrasonically disperse for 25 min. Drop 10% ammonia water into the dispersed solution to adjust the pH of the solution to 10.5, and then slowly drop tetraethyl orthosilicate (TEOS) according to a ratio of 20% of the mass of the magnetic powder. Stir at room temperature for 10 h. After the reaction is completed, collect the product by magnetic separation, wash the product with anhydrous ethanol for 3 times, and dry the washed product in a 60°C oven for 6 h to obtain Fe3O4@SiO2.

[0031] (3) Take 3 g of Fe3O4@SiO2, disperse it in 70 mL of anhydrous toluene, and ultrasonically disperse for 30 min until the solution is uniformly dispersed. Add 3-aminopropyltriethoxysilane (APTES) according to a ratio of 5.5% of the volume of the solution. Under the condition of nitrogen protection, heat the reaction system to 75°C and reflux for 10 h. After the reaction is completed, collect the product by magnetic separation, wash the product with anhydrous ethanol for 3 times, and dry the product in a 55°C vacuum drying oven for 8 h to obtain Fe3O4@SiO2-NH2.

[0032] (4) Take 1.1 g of DFO-COOH, dissolve it in 32 mL of 0.1M MES buffer (pH 5.0), and add 1-ethyl-(3-dimethylaminopropyl) carbonyldiimidazole (EDC) and N-hydroxysuccinimide (NHS) (the molar ratio of DFO-COOH:EDC:NHS is 1:1.2:1.2). Stir in an ice bath for 30 min to activate the carboxyl group. Then add 2.2 g of Fe3O4@SiO2-NH2, and rotate and incubate at room temperature for 4 h. After the reaction is completed, collect the product by magnetic separation, wash it with PBS buffer (pH 7.4) for 3 times, and dry the product in a 60°C vacuum drying oven for 6 h to obtain trivalent iron magnetic solid masking agent Fe3O4@SiO2-DFO. Example 3 The present example provides Fe 3+ Preparation method of magnetic solid phase masking agent Fe3O4@SiO2-DFO: (1) Take 1 g of DFO, dissolve in 20 mL of anhydrous DMF at a ratio of 1 g:20 mL, deoxygenate with N2for 15 min, and stir at room temperature; add succinic anhydride (dissolved in 7 mL of anhydrous DMF, DFO: succinic anhydride = 1:1.2), drop 0.15 mL of triethylamine, and react at room temperature for 5 h. After the reaction, add 60 mL of ice water, adjust the pH to 4.0 with 1M HCl, precipitate white sediment, filter, wash with ice water 3 times, and dry at 60°C under vacuum for 6 h to obtain DFO-COOH. Infrared detection result: no amino absorption peak, carboxyl characteristic peak (1725 cm -1 ) is clear. (2) Take 6 g of high-purity nano Fe3O4with a particle size of 50 nm, disperse in a mixture of ethanol / water (4:1) at a concentration of 20 mg / mL, and ultrasonic disperse for 30 min; drop 10% ammonia water to adjust the pH to 10.5, drop TEOS at a ratio of 30% of the mass of the magnetic powder, stir at room temperature overnight, wash with ethanol 4 times after magnetic separation, and dry at 65°C for 7 h to obtain Fe3O4@SiO2. (3) Take 5 g of Fe3O4@SiO2, disperse in 100 mL of anhydrous toluene, ultrasonic disperse for 30 min; add APTES at a ratio of 8% of the solution volume, reflux at 75°C under N2protection overnight, wash with ethanol 3 times after magnetic separation, and dry at 60°C under vacuum for 9 h to obtain Fe3O4@SiO2-NH2. (4) Take 1.3 g of DFO-COOH, dissolve in 38 mL of 0.1M MES buffer (pH 5.0), add EDC and NHS (molar ratio 1:1.2:1.2), and stir in an ice bath for 40 min to activate the carboxyl group; add 2.2 g of Fe3O4@SiO2-NH2, rotate incubate at room temperature for 6 h, wash with PBS 4 times after magnetic separation, and dry at 60°C under vacuum for 7 h to obtain Fe3O4@SiO2-DFO.

[0033] Example 4 The present example uses the Fe3O4@SiO2-DFO prepared by the method of Example 1 to remove the removal efficiency of iron and the retention rate of lead ions in the simulated sample.

[0034] The sample was simulated by crushing tea leaves without iron and lead, and the sample powder was obtained by passing through a 40-mesh sieve; 1 g of the powder sample or homogenate sample was weighed into a 10 mL centrifuge tube, 4 mL of extraction reagent was added, vortexed for 3 min, then centrifuged at 4000 rpm, and the supernatant was separated to obtain the sample crude extract; the extraction reagent was a nitric acid-hydrogen peroxide solution, wherein the concentration of nitric acid was 15 v / v%, and the concentration of hydrogen peroxide was 5 wt%. 60 μL of the sample crude extract was taken and divided into two parts, and known concentrations of lead ions and iron ions were added, then 0.05 g of Fe3O4@SiO2-DFO trivalent iron magnetic solid-phase masking agent was added, and oscillation was carried out at 25°C and 180 rpm for 35 min, the trivalent iron was removed by magnetic separation, and Na2HPO4-Na3PO4 buffer system was added to the remaining solution for neutralization to pH 7.4 to prepare the test solution. The blank sample was treated in the same way, but without using the trivalent iron magnetic solid-phase masking agent.

[0035] The removal efficiency of iron and the retention rate of lead ions in the test solution were detected by ICP-MS, and the experimental results are shown in Table 1. The above experimental results show that in the system of iron and lead in conventional vegetable products, the masking agent still has high Fe 3+ removal capacity, and the Pb 2+ retention rate is stable at more than 96%, with good repeatability, and is suitable for high-precision detection of batch samples.

[0036] Example 5 10 g of dried plum was purchased from the market, the edible part was cut and crushed uniformly by a high-speed pulverizer, and then passed through a 40-mesh sieve. 1.0 g (accurate to 0.01 g) of the crushed / homogenized sample was accurately weighed into a 10 mL centrifuge tube, 4 mL of extraction reagent was added, vortexed for 3 min, and centrifuged at 3000 r / min for 1 min to obtain a crude extract. The extraction reagent was a nitric acid-hydrogen peroxide solution, wherein the concentration of nitric acid was 15 v / v%, and the concentration of hydrogen peroxide was 5 wt%.

[0037] 30 μL of the crude extract was taken and added to a 2 mL centrifuge tube, 0.04 g of Fe3O4@SiO2-DFO trivalent iron magnetic solid-phase masking agent was added, oscillation was carried out at 25°C and 180 rpm for 30 min, the trivalent iron was removed by magnetic separation, and 310 μL of Na2HPO4-Na3PO4 buffer system was added to the remaining solution for neutralization to pH 7.2 to obtain the test solution.

[0038] According to the commercially available heavy metal lead time-resolved fluorescence immunochromatographic test strip (Meizheng Biology), the lead content level was detected.

[0039] Considering the lead content in the actual sample, the lead limit standard in GB2762-2022 and the addition concentration regulation in GB / T 27404-2008 "laboratory quality control specification food physical and chemical test", the lead content of vegetable products is selected as 0.496, 1.083 and 2.404 mg / kg, and 6 repeated experiments are carried out at each concentration level. The specific results are shown in Table 1. As shown in Table 1, the recovery rate of the three lead content levels in the vegetable products is 84.4%~112.9%, and the coefficient of variation CV≤11.4%.

[0040] Table 2: Recovery rate determination of lead content in vegetable products Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements, or in the case of technical features in the above embodiments do not conflict with each other, can be combined in the manner recorded in the embodiments, and these modifications, replacements or combinations do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A ferric iron magnetic solid-phase masking agent, characterized in that, Prepared according to the following method: S1, the terminal amino group of DFO is carboxylated to obtain DFO-COOH; S2, a SiO2 layer is coated on the surface of Fe3O4 magnetic core to obtain Fe3O4@SiO2; S3, the Fe3O4@SiO2 is modified by amination to obtain Fe3O4@SiO2-NH2; S4, Ac-DFO is coupled with Fe3O4@SiO2-NH2 to prepare Fe3O4@SiO2-DFO.

2. The ferric ferromagnetic solid-phase mask of claim 1, wherein, In S1, the method for carboxylating the terminal amino group of DFO is as follows: DFO is dissolved in anhydrous DMF at a ratio of 1 g: 15-20 mL, oxygen is removed by N2 for 10-15 min, and stirring is performed at room temperature; succinic anhydride is slowly added in a DMF solution at a molar ratio of DFO: succinic anhydride = 1:1.2, triethylamine is added dropwise as an acid-binding agent, reaction is performed at room temperature for 3-5 h, after the reaction is completed, ice water is added to the solution, and the pH is adjusted to 3.0-4.0 with HCl, a white precipitate is precipitated, the precipitate is filtered and washed with ice water for 2-3 times, and vacuum drying is performed at 60°C to obtain carboxylated deferoxamine DFO-COOH.

3. The ferric ferromagnetic solid-phase mask of claim 1, wherein, In S2, the preparation method of Fe3O4@SiO2 is as follows: high-purity nano Fe3O4 with a particle size of 80-150 nm is taken, dispersed in a mixed solution of ethanol / water at a ratio of 4:1 at 10-20 mg / mL, ultrasonic dispersion is performed for 20-30 min, 10% ammonia water is added to adjust the pH to 10-10.5, TEOS is added dropwise at a ratio of 20-30% of the mass of the magnetic powder, stirring is performed at room temperature overnight, the product is separated by magnetism, washed with ethanol for 2-4 times, and dried to obtain Fe3O4@SiO2.

4. The ferric ferromagnetic solid-phase mask of claim 1, wherein, In S3, the preparation method of Fe3O4@SiO2-NH2 is as follows: Fe3O4@SiO2 is dispersed in anhydrous toluene and ultrasonic dispersion is performed; APTES is added at a ratio of 5-8% of the volume of the solution, reflux is performed at 70-75°C under nitrogen protection overnight, the product is separated by magnetism, washed with ethanol for 2-3 times, and vacuum dried to obtain Fe3O4@SiO2-NH2.

5. The ferric iron magnetic solid-phase maskant of claim 1, wherein, In S4, DFO-COOH is dissolved in a MES buffer, EDC / NHS is added, and the molar ratio of Ac-DFO: EDC: NHS is 1:1.2:1.2; ice bath stirring is performed for 20-40 min to activate the carboxyl group; Fe3O4@SiO2-NH2 prepared in step 3) is added, and rotary incubation is performed at room temperature for 3-6 h; the product is collected by magnetism, washed with PBS for 3-4 times, and vacuum dried to obtain Fe3O4@SiO2-DFO.

6. The ferric iron magnetic solid-phase maskant of claim 1, wherein, In S4, the prepared Fe3O4@SiO2-DFO can be sealed and stored in anhydrous ethanol in a cold storage, and 0.1% BHT is added to the anhydrous ethanol.

7. A method for quantitatively detecting lead in a vegetable product based on heavy metal lead time-resolved fluorescence immunochromatography technology, characterized in that, Comprising the following steps: Step 1: preparation of sample crude extract The edible part of dried vegetables is cut and crushed by a high-speed pulverizer, and then sieved through a 40-mesh sieve to obtain sample powder; the edible part of pickled vegetables is homogenized to obtain a sample; A certain mass of powder sample or homogenate sample is weighed into a centrifuge tube, an extraction reagent is added in an amount of 1g:4-6mL according to the mass volume ratio, vortexed, centrifuged at 3000-5000rpm, the supernatant is separated, and a sample crude extract is obtained; the extraction reagent is a nitric acid-hydrogen peroxide solution, wherein the concentration of nitric acid is 15v / v%; Step 2: preparation of the test solution The sample crude extract is added with the ferric magnetic solid-phase masking agent according to any one of claims 1-6, the ferric iron is removed by magnetic separation, and the remaining solution is added with a Na2HPO4-Na3PO4 buffer system for neutralization to pH 7-8, and a test solution is obtained; Step 3: the test solution is taken and detected according to the operation instruction of the time-resolved fluorescence immunochromatography test paper.

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