Iron removing agent and method for quantitative determination of lead in confectionery products

Abstract

The application belongs to the technical field of food quality monitoring, and particularly relates to an iron removing agent and a quantitative detection method for lead in preserved fruit products. The preparation method of the iron removing agent comprises the following steps: S1, providing Fe3O4 nanoparticles; S2, in-situ polymerization of pyrrole monomers and 4-carboxybutyl pyrrole to coat the Fe3O4 nanoparticles to obtain Fe3O4@PPy-COOH; and S3, coupling Fe3O4@PPy-COOH with DFO in the presence of EDC and NHS to obtain Fe3O4@PPy-DFO. The inert coating of the Fe3O4 nanoparticles by the polypyrrole and the introduction of a large number of carboxyl groups prepare for the subsequent connection of DFO, and the inert coating has better acid and alkali corrosion resistance than a silica coating layer. The iron removing agent can specifically complex Fe 3+ in a solution to form a stable chelate, Fe 3+ in a sample to be detected is removed through magnetic separation, so that the interference of Fe 3+ on the detection of the lead content in the preserved fruit products is avoided.

Description

Technical Field

[0001] This invention belongs to the field of food quality monitoring technology, specifically relating to a quantitative detection method for lead in iron removal agents and preserved fruit products. Background Technology

[0002] Preserved fruit products, as a popular snack, are susceptible to lead contamination during production, processing, and storage. Long-term consumption of preserved fruit products with excessive lead levels can lead to its accumulation in the body, causing serious harm to multiple systems. To protect consumer health and safety, relevant food safety standards have set clear limits on lead content in preserved fruit products: according to national standards, the limit for lead in candied fruit is 1 mg / kg. However, in actual production and market circulation, excessive lead levels in preserved fruit products remain common. Therefore, developing efficient and accurate detection methods for lead in preserved fruit products is of paramount practical importance.

[0003] Currently, there are various traditional methods for detecting lead in candied fruit products, mainly including atomic absorption spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry, atomic fluorescence spectrometry, ultraviolet-visible spectrophotometry, and anodic stripping voltammetry. While these traditional methods offer advantages such as low detection limits and high accuracy, enabling precise determination of lead content in candied fruit products, they also have several significant drawbacks. From an equipment perspective, the purchase cost of the necessary equipment is high, and subsequent maintenance costs are also substantial, placing a significant financial burden on many testing organizations. The sample pretreatment process is cumbersome and time-consuming, requiring digestion of the candied fruit samples, making the operation complex. Furthermore, these methods demand a high level of professional expertise from operators, requiring solid professional knowledge and extensive operational experience.

[0004] Due to the aforementioned shortcomings, traditional detection methods are insufficient to meet the needs of grassroots testing units for rapid on-site testing, and are particularly ineffective in scenarios requiring rapid screening of large batches of candied fruit samples, such as market supervision and inspection. To compensate for the deficiencies of traditional detection methods, immunoassays, with their advantages of simple operation, good specificity, and low testing cost, have gradually been applied in the field of lead detection in candied fruit products. Among them, colloidal gold immunochromatography and enzyme-linked immunosorbent assay (ELISA) are currently the most widely used mainstream technologies in this field.

[0005] Time-resolved fluorescence immunochromatography (TRFICA) combines colloidal gold immunochromatography with fluorescent dye labeling, integrating the advantages of immunoaffinity, immunolabeling, and immunochromatography. It not only retains the characteristics of rapid detection and ease of operation but also significantly improves detection performance. The core principle of this technology is to label antibodies or antigens using rare earth element chelates, leveraging the differences in fluorescence lifetimes of different substances to eliminate background interference. Therefore, it boasts comprehensive advantages such as high detection sensitivity, simple and rapid operation, and good stability of detection results.

[0006] However, when testing the lead content of candied fruit products, interference from iron is easily encountered, which seriously affects the accuracy of the test results. This is mainly because a large amount of iron is often introduced during the candied fruit production process due to factors such as the materials of the production equipment and the production operation procedures. In the quantitative analysis of lead content based on time-resolved fluorescence immunochromatography, Fe... 3+ The chelation constant with the chelating agent is approximately 26, while Pb 2+ The chelation constant with the chelating agent is approximately 18, due to Fe 3+ It has a stronger binding ability with chelating agents; the chelating agent will preferentially bind with Fe. 3+ A reaction occurs, which leads to Pb 2+ It cannot effectively bind with chelating agents, thus leading to false detections.

[0007] To address the interference from iron ions, conventional methods involve using chelating agents such as EDTA to shield them. However, the stability of the complex formed by EDTA and iron ions is significantly affected by the pH of the solution. During detection, as the pH changes, the complex easily releases iron ions, thus interfering with the quantitative analysis of lead in candied fruit products. Selectively removing iron ions from candied fruit samples would effectively avoid this problem.

[0008] In the sample pretreatment process for lead detection in candied fruit products, the products are typically crushed, extracted with water, and then the test solution is prepared by centrifugation. However, candied fruit products contain a significant amount of viscous substances such as cellulose and fructose gum. If conventional iron precipitation agents are used, followed by centrifugation or filtration, not only is a viscous mixture more likely to form, making effective separation difficult, but the precipitate and filter media can also adsorb and carry away some lead ions during the separation process, ultimately leading to lower test results that fail to accurately reflect the actual lead content in the candied fruit products.

[0009] In view of the above problems, this solution aims to propose a highly efficient and specific iron ion removal agent that can be magnetically separated. It can remove ferric iron by means of magnetic separation technology, avoiding the technical problem of low quantitative lead ion concentration caused by the adsorption of lead ions by filter cake / filter media in centrifugation or vacuum filtration. Summary of the Invention

[0010] (a) Technical problems to be solved

[0011] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides an iron removal agent and a method for quantitative detection of lead in candied fruit products. The method uses a magnetic solid-phase iron removal agent to specifically and efficiently complex ferric ions in the sample solution and uses magnetic separation technology to remove the ferric ions, thereby avoiding interference from the large number of ferric ions in the sample solution on the quantitative detection of lead. The present invention can improve the accuracy, stability and reliability of lead detection in candied fruit products.

[0012] (II) Technical Solution

[0013] An iron removal agent, the preparation method of which is as follows:

[0014] S1 provides Fe3O4 nanoparticles;

[0015] S2. Fe3O4 nanoparticles were coated by in-situ polymerization of pyrrole monomer and 4-carboxybutylpyrrole to obtain Fe3O4@PPy-COOH;

[0016] S3. Fe3O4@PPy-COOH and DFO are coupled in the presence of EDC and NHS to obtain Fe3O4@PPy-DFO, which is the iron removal agent.

[0017] Preferably, in S1, Fe3O4 nanoparticles are prepared by co-precipitation. The method is as follows: water is pre-purged with nitrogen to remove oxygen for 20-60 min, then ferric chloride or its hydrate and ferrous chloride or its hydrate are dissolved in the deoxygenated water at a molar ratio of 2:1. 20-30% ammonia water is slowly added dropwise under stirring at 40-70℃ until the pH of the solution reaches 10-10.5. The reaction is continued for 20-40 min to generate black Fe3O4 particles. After magnetic separation, the particles are washed alternately with deionized water and ethanol until neutral, and then vacuum dried to obtain superparamagnetic Fe3O4 nanomagnetic cores.

[0018] The superparamagnetic Fe3O4 nano-cores prepared in this step provide a substrate for subsequent coating. Currently, there are commercially available mature superparamagnetic Fe3O4 nano-cores that can be purchased, or they can be prepared in-house.

[0019] Preferably, in S2, the preparation method of Fe3O4@PPy-COOH is as follows: Fe3O4 nanomagnetic cores are dispersed in an ethanol-water mixture and ultrasonically dispersed to form a uniform suspension; 4-carboxybutylpyrrole monomer and pyrrole monomer are added to the suspension in a molar ratio of 1:3~5, stirred evenly, and an initiator solution is slowly added dropwise under an ice-water bath to adjust the pH to 2-3. The reaction is carried out under nitrogen protection for 2-4 hours to generate brown-black Fe3O4@PPy-COOH; after filtration or magnetic separation, the solution is washed with deionized water and ethanol until the washing liquid is colorless and then vacuum dried.

[0020] This step involves in-situ polymer coating of Fe3O4 nanomagnetic cores, introducing a large number of carboxyl groups during the polymerization process. The polymer monomers used include 4-carboxybutylpyrrole monomer and pyrrole monomer. The 4-carboxybutylpyrrole monomer has a carboxyl group with a certain length of side chain to ensure that the side chain length is appropriate to reduce steric hindrance. The pyrrole monomer without side chain is a comonomer to ensure the stability of the coating layer. The molar ratio of the two monomers is 1:3~5, which can control the density of carboxyl groups (avoiding excessive density that would lead to steric hindrance) and the stability of the coating layer.

[0021] Preferably, in S2, the initiator is potassium persulfate or ammonium persulfate to initiate pyrrole polymerization to form a coating layer, thereby coating and modifying Fe3O4. This introduces carboxyl groups and improves the chemical inertness of Fe3O4, making it suitable for downstream solution environments.

[0022] Preferably, 10-20% of glutaraldehyde, representing the total molar amount of the monomers, is added to S2 to lightly crosslink the polymer coating and improve its resistance to degradation in acidic or oxidizing environments.

[0023] Preferably, in S3, the preparation method of Fe3O4@PPy-DFO is as follows: Fe3O4@PPy-COOH is dispersed in MES buffer at pH 5.0-6.0, and EDC and NHS in relative excess of carboxyl groups are added, with a molar ratio of EDC to NHS of 1:1. The carboxyl groups are activated by stirring at room temperature, and the activated product is separated by magnetic separation or vacuum filtration. The product is redispersed in PBS buffer at pH 7.0-7.5, DFO is added, and the reaction is carried out at 30-37°C in the dark for 4-6 hours. After the reaction is completed, the product is washed with PBS buffer and deionized water, and then vacuum dried to obtain the target product Fe3O4@PPy-DFO.

[0024] This step uses carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to activate the carboxyl groups (-COOH) of the polypyrrole layer, causing them to undergo an amidation reaction with the terminal amino group of DFO to form a stable amide bond (-CONH-), thereby attaching DFO to the exterior of the Fe3O4 nanomagnetic core. EDC / NHS activation requires pH control (activation under acidic conditions, coupling under neutral conditions) to avoid hydrolysis of the activation intermediates. DFO is attached to the exterior of the Fe3O4 nanomagnetic core with the terminal primary amino group removed, perfectly preserving the hydroxamic acid group (with Fe...). 3+ (Key chelation site) Since the hydroxamic acid group is less reactive than the amino group under neutral conditions, the coupling of the amino and carboxyl groups can be preferentially ensured by controlling the pH (7.0-7.5), thereby reducing the impact on the chelation site.

[0025] According to a preferred embodiment of the present invention, in S3, the prepared Fe3O4@PPy-DFO is stored in a dry powder state at room temperature in a light-proof and sealed manner to avoid contact with air and oil phase, which could lead to a loose coating structure or even the DFO peeling off from the PPy layer. The hydroxamic acid groups of DFO are photosensitive and easily oxidized by long-term light exposure; therefore, all storage containers must be brown bottles or wrapped in aluminum foil.

[0026] The dry powder can be stored at room temperature in a dark and sealed environment for more than 6 months. It has good stability and still has a strong binding specificity with ferric iron after 6 months of storage.

[0027] Secondly, the present invention provides a method for quantitative detection of lead in candied fruit products based on time-resolved fluorescence immunochromatography, which includes the following steps:

[0028] Step (1): Preparation of crude extract of sample

[0029] Take the edible portion of the candied fruit sample, chop it, then crush it. Weigh a certain mass of the crushed sample into a centrifuge tube. Add the extraction reagent at a mass-to-volume ratio of 1g:4-6mL. Extract using pulsed microwave-assisted extraction for 10-15 minutes. Centrifuge at 3000-5000 rpm, separate the supernatant, and obtain the crude extract. The extraction reagent is a hydrochloric acid-hydrogen peroxide solution, wherein the hydrochloric acid concentration is 10v / v%.

[0030] Step (2): Prepare the test solution

[0031] The iron removal agent prepared in the above-described example was added to the crude extract of the sample, and Fe was removed from the crude extract of the sample by magnetic separation. 3+ The remaining solution was neutralized to pH 6.5-7.4 by adding a Na2HPO4-Na3PO4 buffer system to obtain the test solution.

[0032] Step (3): Take the predetermined volume of the test solution and perform the test according to the instructions of the time-resolved fluorescence immunochromatographic test strip. The time-resolved fluorescence immunochromatographic test strips / test cards for heavy metal lead are existing products, such as those from brands like Huaan Maike, Feice Bio, and Meizheng Bio.

[0033] (III) Beneficial Effects

[0034] The technical effects of this invention are as follows:

[0035] (1) This invention provides an iron removal agent that can be stored stably for a long time in a sealed, light-proof, and room-temperature environment. This iron removal agent can specifically bind to ferric ions in the crude extract of the sample (binding constant 30-31), and directly remove iron ions through magnetic separation technology. This cuts off the competitive path between iron ions and chelating agents at the source, completely solving the problem that the stability of the complex is greatly affected by pH and easily releases iron ions in the traditional EDTA shielding method, thus clearing a key interference obstacle for lead ion detection. The iron removal agent is stable and can be sealed at room temperature for a long time after preparation, which means it can be used as needed, which is convenient and quick.

[0036] DFO on Fe 3+ It exhibits strong selective complexation with Fe 3+ The complexation constant reaches 30-31, which is similar to that of Pb. 2+ The complexation constant is around 10, and it is even lower under weakly acidic conditions. Deferroamine DFO has multiple hydroxyl groups and terminal amino groups. The terminal amino groups undergo amidation reactions with the activated carboxyl groups on the magnetic core surface. The remaining hydroxyl groups are the main active sites for complexation, exhibiting strong complexing effects on iron ions. After DFO is linked to Fe3O4@PPy-COOH via the terminal amino groups, the molecular conformation adopts an extended state of "nanomagnetic core-connecting arm-DFO body," which allows the DFO body to be distanced from the nanomagnetic core surface, preventing the nanomagnetic core from affecting the hydroxyxamic acid groups and Fe... 3+ Spatial barriers to integration.

[0037] (2) In the polypyrrole layer of Fe3O4@PPy-COOH, the unreacted carboxyl group can also provide a complexation site to assist in the complexation of Fe. 3+ It also provides a weakly acidic environment to further reduce DFO and Pb. 2+ The combination of Fe 3+ Highly efficient and selective removal. Compared to silica coatings, polypyrrole layers exhibit better chemical inertness and resistance to alkali corrosion, making them suitable for weakly alkaline sample solutions.

[0038] (3) Compared with conventional iron precipitation agents, centrifugation / filtration is prone to forming a viscous precipitate layer after iron precipitation, which is difficult to effectively remove iron and is prone to adsorbing / encapsulating lead ions. Magnetic separation technology has the advantages of extremely fast response speed and convenient operation. Simply attach a permanent magnet (such as a strong magnetic rod or permanent magnet sheet) to the outside of the container and let it stand for 1-2 minutes. The magnetic powder that has bound iron ions will be firmly adsorbed onto the container wall by the permanent magnet, forming an obvious solid adsorption layer. Then, slowly pour the clear liquid in the container into a new clean container. The collected clear liquid can be used for subsequent lead content detection. Compared with centrifugation / filtration, it is faster and more convenient, and there is no need to wait for the viscous precipitate layer to be processed.

[0039] (4) During the sample processing, 10 v / v% hydrochloric acid-hydrogen peroxide solution was used as the extraction reagent. The extraction was carried out at a mass-volume ratio of 1 g: 4-6 mL. Pulsed microwave assisted extraction was used for 10-15 min. The crude extract was prepared by centrifugation at 3000-5000 rpm. This can quickly and efficiently destroy the structure of the candied fruit sample, fully release the lead ions, and keep the iron ions at the valence of 3. Subsequently, the pH was neutralized to 6.5-7.4 by the buffer system to accurately match the detection environment of the time-resolved fluorescence immunochromatographic test strip, ensuring that the subsequent detection reaction proceeds stably and reducing detection errors caused by pH fluctuations.

[0040] (5) This invention combines mature immunochromatographic technology with efficient iron ion removal and sample pretreatment in the early stage, which greatly reduces the influence of interference factors on the immune response, making the quantitative detection results of lead ions more accurate, effectively avoiding the detection deviation caused by interference in traditional methods, and meeting the accuracy and reliability requirements for lead content detection in candied fruit products. Detailed Implementation

[0041] To better explain and facilitate understanding of the present invention, specific embodiments are described in detail below. The preparation method of the iron removal agent and its specific removal efficiency for iron ions are illustrated below with reference to examples.

[0042] Example 1

[0043] This embodiment provides a method for preparing the iron removal agent Fe3O4@PPy-DFO:

[0044] (1) Measure 500 mL of deionized water into a three-necked flask and purge with nitrogen for 30 min to remove oxygen; weigh 0.09 mol of FeCl3·6H2O and 0.045 mol of FeCl2·4H2O (molar ratio 2:1), add them to the deoxygenated deionized water, and stir until completely dissolved. Place the three-necked flask in a 50℃ constant temperature water bath, and slowly add 25% ammonia water dropwise while stirring until the pH of the solution reaches 10.2. Continue stirring for 30 min to generate black Fe3O4 particles. After turning off the stirring, use an external magnet for magnetic separation, collect the black precipitate, and wash it 5 times alternately with deionized water and ethanol until the pH of the washing solution is neutral. Place the precipitate in a vacuum drying oven and vacuum dry at 60℃ for 8 h to obtain superparamagnetic Fe3O4 nanomagnetic cores.

[0045] (2) Weigh 1.0 g of the above Fe3O4 nanomagnetic cores and disperse them in 80 mL of ethanol-water mixture (ethanol to water volume ratio 1:1). Place the mixture in an ultrasonic instrument and sonicate for 20 min to form a uniform suspension. Add 0.01 mol of 4-carboxybutylpyrrole monomer and 0.03 mol of pyrrole monomer (molar ratio 1:3) to the suspension and stir for 10 min to mix them evenly. Place the system in an ice-water bath and slowly add 20 mL of 0.04 mol of ammonium persulfate aqueous solution. During the addition, adjust the pH of the system to 2.5 with 0.1 mol / L hydrochloric acid. Purge with nitrogen for protection and react for 3 h in an ice-water bath to generate brown-black Fe3O4@PPy-COOH. After the reaction is complete, use an external magnet for magnetic separation, collect the product, and wash it alternately with deionized water and ethanol until the washing solution is colorless. Place the product in a vacuum drying oven and vacuum dry at 50 °C for 6 h to obtain Fe3O4@PPy-COOH.

[0046] FT-IR analysis of the product: Compared with pure Fe3O4, the Fe3O4@PPy-COOH spectrum can be observed at ~1540 cm⁻¹. -1 and ~1450cm -1 Typical polypyrrole ring stretching vibration peaks appear at ~1720 cm⁻¹. -1 The presence of a distinct C=O stretching vibration peak (attributed to carboxylic acid-COOH) proves that PPy-COOH has successfully coated Fe3O4.

[0047] (3) Weigh 0.8 g of Fe3O4@PPy-COOH and disperse it in 50 mL of MES buffer (pH=5.5). Add 0.008 mol of EDC and 0.008 mol of NHS (molar ratio 1:1, relative carboxyl group excess) and stir at room temperature for 30 min to activate the carboxyl group. Use an external magnet to magnetically separate the activated product, discard the supernatant, and redisperse the activated product in 40 mL of PBS buffer (pH=7.2). Add 0.004 mol of DFO and place in a 35℃ constant temperature water bath. Stir and react for 5 h in the dark. After the reaction is complete, use an external magnet to magnetically separate the product and wash it 4 times each with PBS buffer and deionized water. Place the product in a vacuum drying oven and dry it at 45℃ for 7 h to obtain Fe3O4@PPy-DFO iron removal agent. Store it in a brown sealed bottle as a dry powder at room temperature in the dark.

[0048] FT-IR analysis of the product: Compared with pure Fe3O4@PPy-COOH, the Fe3O4@PPy-DFO spectrum shows an increase of ~1650 cm⁻¹. -1 (Amide I band) and 3300cm -1 (NH stretching), CN peak of PPy (~1400 cm⁻¹) -1 The occurrence of a blue shift indicates that the DFO grafting was successful.

[0049] Example 2

[0050] This embodiment provides a method for preparing the iron removal agent Fe3O4@PPy-DFO:

[0051] (1) Purchase commercially available superparamagnetic Fe3O4 nano-magnetic cores (10~200nm).

[0052] (2) Weigh 1.2 g of Fe3O4 nanomagnetic cores and disperse them in 100 mL of ethanol-water mixture (ethanol to water volume ratio 1:2). Sonicate for 30 min to form a uniform suspension. Add 0.015 mol of 4-carboxybutylpyrrole monomer and 0.06 mol of pyrrole monomer (molar ratio 1:4) and stir for 15 min. Under ice-water bath conditions, slowly add 25 mL of aqueous solution of 0.08 mol potassium persulfate (initiator). Adjust the pH to 2.0 with 0.1 mol / L hydrochloric acid. Proceed under nitrogen protection for 2.5 h to generate brown-black Fe3O4@PPy-COOH. Filter to separate the product, wash with deionized water and ethanol until the washings are colorless, and dry under vacuum at 55 °C for 5 h to obtain Fe3O4@PPy-COOH.

[0053] (3) Weigh 1.0 g of Fe3O4@PPy-COOH, disperse it in 60 mL of MES buffer (pH=5.0), add 0.01 mol EDC and 0.01 mol NHS, and stir at room temperature for 30 min to activate the carboxyl group. Filter to separate the activated product, redisperse it in 50 mL of PBS buffer (pH=7.0), add 0.005 mol DFO, and stir at 30 °C in the dark for 6 h. Magnetically separate the product, wash it 5 times each with PBS buffer and deionized water, and vacuum dry it at 50 °C for 6 h to obtain Fe3O4@PPy-DFO iron removal agent, which is stored in a brown sealed bottle at room temperature in the dark.

[0054] Example 3

[0055] This embodiment provides a method for preparing the iron removal agent Fe3O4@PPy-DFO:

[0056] (1) Measure 500 mL of deionized water into a three-necked flask and purge with nitrogen for 60 min to remove oxygen; weigh 0.06 mol of FeCl3・6H2O and 0.03 mol of FeCl2・4H2O (molar ratio 2:1), add deionized water and stir to dissolve. Place the three-necked flask in a 70℃ constant temperature water bath, add 30% ammonia dropwise with stirring until the solution pH=10.5, then stop and continue the reaction for 35 min to generate black Fe3O4 particles. Magnetically separate the precipitate, wash it 4 times alternately with deionized water and ethanol until neutral, and vacuum dry at 65℃ for 9 h to obtain superparamagnetic Fe3O4 nanomagnetic cores.

[0057] (2) Weigh 1.0 g of Fe3O4 nanomagnetic cores and disperse them in 90 mL of ethanol-water mixture (ethanol to water volume ratio 2:1). Sonicate for 15 min to form a uniform suspension. Add 0.008 mol of 4-carboxybutylpyrrole monomer, 0.04 mol of pyrrole monomer (molar ratio 1:5), and 0.0096 mol of glutaraldehyde (15% of the total molar amount of monomers), and stir for 12 min. Add 18 mL of 0.05 mol of ammonium persulfate aqueous solution dropwise in an ice-water bath, adjust the pH to 3.0 with 0.1 mol / L hydrochloric acid, and purge the reaction under nitrogen for 4 h to generate brown-black Fe3O4@PPy-COOH. Magnetically separate the product, wash until the washings are colorless, and vacuum dry at 50 °C for 7 h to obtain Fe3O4@PPy-COOH.

[0058] (3) Weigh 0.9 g of Fe3O4@PPy-COOH and disperse it in 75 mL of MES buffer (pH=6.0). Add 0.005 mol EDC and 0.005 mol NHS and stir at room temperature for 35 min to activate the carboxyl groups. Magnetically separate the activated product and redisperse it in 45 mL of PBS buffer (pH=7.5). Add 0.003 mol DFO and stir at 37 °C in the dark for 4 h. Magnetically separate the product, wash it, and vacuum dry it at 55 °C for 5 h to obtain Fe3O4@PPy-DFO iron removal agent. Store it in a brown sealed bottle at room temperature in the dark.

[0059] Example 4

[0060] This embodiment uses the Fe3O4@PPy-DFO method prepared in Example 1 to determine the removal efficiency of iron and the retention rate of lead ions in the simulated sample.

[0061] Purchase a high-quality candied fruit product from a certain brand. Take the edible portion, chop it, and then crush it. Weigh 1.0g of the crushed sample into a centrifuge tube. Add extraction reagent at a mass-to-volume ratio of 1g:5mL. Extract using pulsed microwave-assisted extraction for 15min. Centrifuge at 4000rpm, separate the supernatant, and obtain the crude extract. The extraction reagent is a hydrochloric acid-hydrogen peroxide solution, where the hydrochloric acid concentration is 10v / v% and the hydrogen peroxide concentration is 5wt%. Take 120μL of the crude extract and use a Plasma 1500 ICP-OES to detect the concentrations of lead and iron ions. The concentrations are only a few tens of ppb, which are negligible. Divide the sample into 3 portions and add known concentrations of lead and iron ions to each portion. Then, 0.06 g of iron removal agent Fe3O4@PPy-DFO was added, and the mixture was shaken at 30℃ and 200 rpm for 15 min. Magnetic separation with a permanent magnet was used to remove Fe3O4@PPy-DFO. The remaining supernatant was neutralized to pH 6.9 by adding a Na2HPO4-Na3PO4 buffer system to obtain the test solution. The blank sample was treated in the same way, but without the iron removal agent. The iron removal efficiency and lead ion retention rate in the test solution were detected using a Plasma 1500 ICP-OES analyzer. The experimental results are shown in Table 1.

[0062]

[0063] The above experimental results demonstrate that, in the iron and lead content system of candied fruit products, the iron removal agent provided by this invention has high efficiency in removing iron and lead. 3+ Adsorption and removal capacity, removal rate, and Pb 2+ The retention rate is consistently above 95%, with good repeatability, making it suitable for high-precision detection of batch samples.

[0064] Example 5

[0065] Purchase candied fruit from the market, cut the edible portion into small pieces, and then crush it with a garlic press for 20 minutes. Weigh 1.0g (accurate to 0.01g) of the sample into a 10mL centrifuge tube, add 5mL of extraction reagent, and extract using pulsed microwave assisted extraction for 10min. Centrifuge at 3000rpm, separate the supernatant, and obtain the crude extract. The extraction reagent is hydrochloric acid-hydrogen peroxide solution, with hydrochloric acid concentration of 10v / v% and hydrogen peroxide concentration of 5wt%. Take 30μL of the crude extract and add it to a 2mL centrifuge tube, add 0.04g of the iron removal agent prepared in Example 1, shake at 30℃ and 220rpm for 30min, magnetically separate to remove ferric iron, and add 310μL of Na2HPO4-Na3PO4 buffer system to the remaining solution to neutralize to pH 7.0, which is the test solution.

[0066] The lead content level was obtained by testing with a commercially available time-resolved fluorescence immunochromatographic test strip (Meizheng Biotechnology) based on heavy metal lead.

[0067] Taking into account the lead content in the actual samples, the lead limit standard in GB2762-2022, and the concentration requirements in GB / T 27404-2008 "Laboratory Quality Control Standard for Physicochemical Testing of Food", lead content of 0.215, 0.624, and 1.578 mg / kg was selected for candied fruit products, with six replicates for each concentration level. Specific results are shown in Table 1. As shown in Table 1, the recoveries of the three lead content levels in fruit products ranged from 88.4% to 116.3%, with a coefficient of variation (CV) ≤ 10.7%.

[0068] Table 2: Determination of lead recovery rate in candied fruit products

[0069]

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An iron removing agent, characterized by, The preparation method is as follows: S1, providing Fe3O4 nanoparticles; The Fe3O4 nanoparticles are prepared by a coprecipitation method, and the method is as follows: the water is pre-deoxygenated by nitrogen for 20-60 min, then the ferric chloride or its hydrate and ferrous chloride or its hydrate are dissolved in the deoxygenated water in a molar ratio of 2:1, 20-30% ammonia water is slowly added under stirring at 40-70 DEG C until the pH of the solution reaches 10-10.5, and the reaction is continued for 20-40 min to generate black Fe3O4 particles; after magnetic separation, the particles are washed with deionized water and ethanol alternately until neutral, and then vacuum dried to obtain superparamagnetic Fe3O4 nano magnetic cores; S2, the Fe3O4 nanoparticles are coated with pyrrole monomers and 4-carboxybutyl pyrrole by in-situ polymerization to obtain Fe3O4@PPy-COOH; The preparation method of Fe3O4@PPy-COOH is as follows: the Fe3O4 nano magnetic cores are dispersed in an ethanol-water mixture, ultrasonic dispersion is performed to form a uniform suspension; 4-carboxybutyl pyrrole monomers and pyrrole monomers are added to the suspension in a molar ratio of 1:3-5, stirring is performed, an initiator solution is slowly added under ice water bath, the pH is adjusted to 2-3, the reaction is carried out under nitrogen protection for 2-4 h to generate brown-black Fe3O4@PPy-COOH; after separation by suction filtration or magnetic separation, the product is washed with deionized water and ethanol until the washing liquid is colorless, and then vacuum dried; S3, the Fe3O4@PPy-COOH is coupled with DFO in the presence of EDC and NHS to obtain Fe3O4@PPy-DFO, and the iron removal agent is obtained; The preparation method of Fe3O4@PPy-DFO is as follows: the Fe3O4@PPy-COOH is dispersed in a MES buffer solution with a pH of 5.0-6.0, EDC and NHS are added in an excess amount relative to the carboxyl group, the molar ratio of EDC to NHS is 1:1, the carboxyl group is activated at room temperature by stirring, the activated product is separated by magnetic separation or suction filtration, and then dispersed in a PBS buffer solution with a pH of 7.0-7.5, DFO is added, and the reaction is carried out at 30-37 DEG C under stirring and light shielding for 4-6 h; after the reaction is completed, the product is washed with a PBS buffer solution and deionized water, and then vacuum dried to obtain the target product Fe3O4@PPy-DFO.

2. The iron removing agent according to claim 1, characterized by, In S2, the initiator is potassium persulfate or ammonium persulfate.

3. The iron removing agent according to claim 1, characterized by, Glutaraldehyde is added to the in-situ polymerization system of S2, and the amount of glutaraldehyde added is 10-20% of the total molar amount of monomers.

4. The iron removing agent according to claim 1, characterized by The Fe3O4@PPy-DFO prepared in S3 is stored in a dry powder state at room temperature under light shielding and sealing.

5. A method for quantitative detection of lead in preserved fruits based on heavy metal lead time-resolved fluorescence immunochromatography technology, characterized in that, The method comprises the following steps: Step (1): preparing a sample crude extract The edible part of the preserved fruit sample is cut and then crushed, a certain amount of crushed sample is weighed into a centrifuge tube, an extraction reagent is added in an amount of 1 g:4-6 mL according to the mass volume ratio, pulse microwave assisted extraction is performed for 10-15 min, centrifugation is performed at 3000-5000 rpm, the supernatant is separated, and a sample crude extract is obtained; the extraction reagent is a hydrochloric acid-hydrogen peroxide solution, and the concentration of hydrochloric acid is 10 v / v%; Step (2): preparing a test solution The iron removing agent of any one of claims 1-4 is added to the sample crude extract solution, and Fe in the sample crude extract solution is removed by magnetic separation 3+ The remaining solution is neutralized to pH 6.5-7.4 with a Na2HPO4-Na3PO4 buffer system to obtain a test solution; Step (3): Take a predetermined volume of the sample to be tested and detect according to the operation instruction of the time-resolved fluorescence immunochromatography test paper.

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