A quantitative detection method for soil metal nanocolloids

Abstract

The application provides a soil metal nanocolloid quantitative detection method, which comprises the following steps: obtaining a soil sample, purifying the soil sample, adding deionized water containing a microbial inhibitor to the soil precipitate after purification, adjusting a soil-water ratio, and obtaining a suspension; releasing a target nanocolloid into the suspension to obtain a dispersed suspension; adopting a gradient membrane group to perform multi-stage cross-flow filtration on the dispersed suspension to obtain a soil colloid; performing asymmetric flow field flow fractionation on the soil colloid to obtain a metal nanocolloid; and performing quantitative analysis on the metal nanocolloid to obtain the concentration of different metals. The extraction of the soil metal nanocolloid adopts a cross-flow filtration gradient membrane separation extraction method, different aperture separation membranes are used in sequence, and under the premise of removing large-sized silt and clay, the problem of colloid structure damage caused by high-speed centrifugation can be effectively avoided, gradient separation of metal elements with different particle sizes in the soil metal nanocolloid is realized, and finally the target product is obtained.

Description

Technical Field

[0001] This invention relates to the field of soil chemistry, and in particular to a method for quantitative detection of soil metal nanocolloids. Background Technology

[0002] The rapid pace of industrialization and urbanization has led to increasingly prominent soil pollution problems. Recent studies show that soils surrounding metal mining areas are severely polluted with heavy metals, which has become a major environmental issue threatening soil ecological security. Metal nanocolloids are widely present in soil, exhibiting high reactivity and migration / diffusion capabilities. These metal nanocolloids not only significantly impact soil ecosystems but can also accumulate through the food chain, threatening human health through various exposure pathways. Research indicates that the ecotoxicity and migration / diffusion capabilities of metal nanocolloids are controlled by their particle size and composition. Therefore, clarifying the particle size distribution and metal concentration of metal nanocolloids in soil is a crucial foundation for revealing their environmental behavior and ecological effects. However, current research methodologies for soil nanocolloids still have significant shortcomings, particularly in achieving the separation and precise quantification of soil metal nanocolloids, which remains a major challenge.

[0003] Currently, the main technologies for further separation of soil nanocolloids include ultrafiltration, column chromatography, and asymmetric flow field separation (AF4). Among these, ultrafiltration, due to its fixed membrane pore size, struggles to achieve precise separation within specific particle size ranges and suffers from membrane fouling and clogging issues. While column chromatography offers high separation efficiency, it requires desalination of the soil solution sample to reduce the salt concentration. Asymmetric flow field separation, with its unique separation mechanism, shows promising application prospects in nanoparticle fractionation.

[0004] Existing AF4-based methods employ high-speed centrifugation for separation. The shearing and compressive forces generated during centrifugation can easily damage the natural structure of colloids. Therefore, a method is needed that can be performed under mild physical conditions, effectively avoiding the colloidal structure damage caused by high-speed centrifugation, to obtain soil metal nanocolloids that are closer to their natural state, thereby improving the accuracy of metal element measurement in soil metal nanocolloids. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the purpose of this invention is to provide a method for quantitative detection of soil metal nanocolloids. This method is applicable to rare earth nanocolloids with a wide size range and can also accurately recover low-concentration rare earth nanocolloids with various particle sizes.

[0006] A method for quantitative detection of soil metal nanocolloids, comprising:

[0007] A soil sample is obtained and purified to obtain a purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of the supernatant;

[0008] Deionized water containing microbial inhibitors was added to the purified soil precipitate to adjust the soil-to-water ratio and obtain a suspension.

[0009] The target nanocolloid is released into the suspension to obtain a dispersed suspension;

[0010] Soil colloids were obtained by multi-stage cross-flow filtration of the dispersed suspension using a gradient membrane array.

[0011] The soil colloids were subjected to asymmetric flow field separation to obtain metal nanocolloids;

[0012] The concentrations of different metals were obtained by quantitative analysis of the metal nanocolloids.

[0013] In a preferred embodiment of the present invention, the purification of the soil sample to obtain purified soil precipitate includes:

[0014] Sterile and deoxygenated ultrapure water was added to the soil sample to obtain a soil-water mixture;

[0015] The soil-water mixture is centrifuged to separate the precipitate and soluble substances, resulting in a separated solution.

[0016] The supernatant in the separated solution is removed to remove soluble interfering substances, resulting in purified soil precipitate.

[0017] In a preferred embodiment of the present invention, the microbial inhibitor comprises 0.02% NaN3 and 0.01% cyclohexylimide; the adjusted soil-to-water ratio is 1:100.

[0018] In a preferred embodiment of the present invention, the step of releasing the target nanocolloid into the suspension to obtain a dispersed suspension includes:

[0019] The suspension was placed in a low-temperature shaker at 4°C;

[0020] The dispersed suspension was obtained by gently shaking at a very low speed of 50 rpm for 2 hours.

[0021] In a preferred embodiment of the present invention, the step of using a gradient membrane array to perform multi-stage cross-flow filtration on the dispersed suspension to obtain soil colloids includes:

[0022] A filter membrane with a pore size of 20 μm is used to perform a first-stage separation on the dispersed suspension to obtain a first permeate; the first-stage separation is used to remove powder particles.

[0023] A filter membrane with a pore size of 2 μm is used to perform a second-stage separation on the first permeate to obtain a second permeate; the second-stage separation is used to remove clay particles.

[0024] A filter membrane with a pore size of 1 μm was used to perform a third-stage separation on the second permeate to obtain a soil metal nanocolloid dispersion.

[0025] The soil metal nanocolloid dispersion was freeze-dried to obtain soil colloid.

[0026] In a preferred embodiment of the present invention, the first-stage separation of the dispersed suspension to obtain a first permeate includes:

[0027] The dispersed suspension is pumped into a cross-flow filtration system;

[0028] Under the action of tangential flow and a 20 μm filter membrane, particles with a diameter less than 20 μm pass through the 20 μm filter membrane into the permeate, while powder and sand particles with a diameter greater than 20 μm are retained in the circulating liquid, resulting in the first permeate.

[0029] In a preferred embodiment of the present invention, the step of performing a second-stage separation on the first permeate to obtain a second permeate includes:

[0030] Under the action of tangential flow and a 2 μm filter membrane, particles with a diameter less than 2 μm pass through the 2 μm filter membrane into the permeate, while particles with a diameter greater than 2 μm are retained in the circulating liquid, resulting in a second permeate.

[0031] In a preferred embodiment of the present invention, the ratio of ultrapure water to soil is 1:5, the centrifugation temperature is 4°C, the rotation speed is 2000 rpm, and the centrifugation time is 10 min.

[0032] In a preferred embodiment of the present invention, the step of performing asymmetric flow field separation on the soil colloid to obtain metal nanocolloids includes:

[0033] During the sample introduction stage, the soil colloids are gathered near the channel inlet under the combined action of carrier flow, tangential flow, and focusing flow.

[0034] During the elution phase, the tangential flow rate was kept constant during the first time period; during the second time period, the tangential flow rate was increased from 2.5 mL / min using a power function flow with an exponent of 0.2. -1 Reduced to 0.15 mL·min -1 During the third time interval, the tangential flow velocity was reduced from 0.15 mL / min using a power function with an exponent of 0.8. -1 Reduce to 0 mL·min -1During the fourth time period, the tangential flow rate was maintained at 0 mL / min. -1 To efficiently separate metal nanocolloids across the entire particle size range.

[0035] In a preferred embodiment of the present invention, the quantitative analysis of the metal nanocolloids to obtain the concentrations of different metals includes:

[0036] Connect the sample outlet tube of the asymmetric flow field to the sample inlet tube of the multi-angle light scattering instrument;

[0037] The scattering angle of the multi-angle light scattering instrument was set to measure the concentration of different metals in the metal nanocolloid.

[0038] The beneficial effects of this invention are as follows:

[0039] This invention provides a method for quantitative detection of soil metal nanocolloids, comprising acquiring a soil sample, purifying the soil sample to obtain a purified soil precipitate; wherein, purification includes low-speed centrifugation and removal of supernatant. Deionized water containing microbial inhibitors is added to the purified soil precipitate to adjust the soil-to-water ratio, obtaining a suspension. The target nanocolloids are released into the suspension to obtain a dispersed suspension. The dispersed suspension is subjected to multi-stage cross-flow filtration using a gradient membrane array to obtain soil colloids. The soil colloids are then subjected to asymmetric flow field separation to obtain metal nanocolloids. Quantitative analysis of the metal nanocolloids is performed to obtain the concentration of different metals. Before extracting soil metal nanocolloids, this invention uses low-speed centrifugation to remove the supernatant, thereby removing most soluble interfering substances such as soluble salts and free organic matter. The addition of deionized water containing microbial inhibitors can inhibit microbial activity. The preparation of the dispersed suspension using the target nanocolloids disperses soil aggregates while maximally protecting the original structure of the target nanocolloids from shear force damage. The present invention employs a cross-flow filtration gradient membrane separation extraction method for the extraction of soil metal nanocolloids. This method is based on the principle of cross-flow filtration. By using separation membranes with different pore sizes in sequence, it can effectively avoid the problem of colloidal structure destruction caused by high-speed centrifugation while removing larger powder and clay particles. This method achieves gradient separation of metal elements of different particle sizes in soil metal nanocolloids and finally obtains the target product. Attached Figure Description

[0040] Figure 1 This is a flowchart of the quantitative detection method for soil metal nanocolloids of the present invention;

[0041] Figure 2 The signal intensity of soil metal nanocolloids of different concentrations at different efflux times was measured by AF4-MALS according to the present invention.

[0042] Figure 3The signal intensity of Al in soil metal nanocolloids of different concentrations at different efflux times is shown in the present invention.

[0043] Figure 4 This is a linear relationship graph between the concentration of soil metal nanocolloids and the Al concentration therein, according to the present invention.

[0044] Figure 5 The signal intensity of Fe in soil metal nanocolloids of different concentrations at different efflux times is shown in the present invention.

[0045] Figure 6 This is a linear relationship graph between the concentration of soil metal nanocolloids and the Fe concentration therein, according to the present invention.

[0046] Figure 7 The signal intensity of Zn in soil metal nanocolloids of different concentrations at different efflux times is shown in the present invention.

[0047] Figure 8 This is a linear relationship graph between the concentration of soil metal nanocolloids and the concentration of Zn therein, according to the present invention. Detailed Implementation

[0048] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention more thorough and complete, and to fully convey the scope of the invention to those skilled in the art.

[0049] Example 1: Extraction and Detection of Soil Metal Nanoparticles with Pretreatment and Multi-Stage Purification Steps

[0050] like Figure 1 As shown, this embodiment provides a method for quantitative detection of soil metal nanocolloids, including:

[0051] S1: Obtain a soil sample, purify the soil sample to obtain purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of supernatant;

[0052] S2: Add deionized water containing microbial inhibitors to the purified soil precipitate, adjust the soil-to-water ratio, and obtain a suspension;

[0053] S3: Release the target nanocolloid into the suspension to obtain a dispersed suspension;

[0054] S4: The dispersed suspension is subjected to multi-stage cross-flow filtration using a gradient membrane module to obtain soil colloids;

[0055] S5: Perform asymmetric flow field separation on the soil colloids to obtain metal nanocolloids;

[0056] S6: Quantitatively analyze the metal nanocolloids to obtain the concentrations of different metals.

[0057] The soil sample of this invention contains multiple metallic elements, such as Al, Fe, and Zn. The purification of the soil sample to obtain a purified soil precipitate includes:

[0058] S12: Add sterile and deoxygenated ultrapure water to the soil sample to obtain a soil-water mixture;

[0059] S13: The soil-water mixture is centrifuged to separate the precipitate and soluble substances, resulting in a separated solution;

[0060] S14: Remove the supernatant from the separated solution to remove soluble interfering substances and obtain purified soil precipitate.

[0061] Before step S12, step S11 is included: obtaining a soil sample. A soil sample that has been air-dried and passed through a 10-mesh sieve is taken and purified using a low-speed centrifugation-supernatant removal method. Sterile and deoxygenated ultrapure water is added to the soil sample at a soil-to-water ratio of 1:5. Centrifugation is performed at 4℃ and 2000 rpm for 10 minutes. This step precipitates large particles and most colloids in the soil, while retaining high concentrations of soluble salts and free organic matter in the supernatant. The supernatant is then discarded, thus removing most of the dissolved interfering substances. Steps S12-S14 are repeated 2-3 times based on the decrease in the conductivity of the supernatant until the conductivity of the supernatant stabilizes.

[0062] After extraction and purification of the soil precipitate, the colloidal components are gently released: sterile, deoxygenated deionized water containing microbial inhibitors, including 0.02% NaN3 and 0.01% cyclohexylimide, is added to the purified soil precipitate, adjusting the soil-to-water ratio to 1:100. The suspension is placed in a 4°C low-temperature shaker and gently shaken at an extremely low speed of 50 rpm for 2 hours. This step disperses the soil aggregates with minimal mechanical force, releasing the target nanocolloids into the suspension while maximally protecting the original structure of the target nanocolloids from shear force damage. The effects of NaN3 (sodium azide) on microorganisms are mainly manifested in inhibiting their metabolic activity and preventing pollution. The specific mechanism of action is as follows: NaN3 inhibits the activity of cytochrome oxidase, blocking the electron transport chain of microorganisms, thereby inhibiting their metabolic activities. It also inhibits the growth and reproduction of microorganisms by damaging their cell membranes, enzyme systems, and other target sites. Cyclohexylimide is a protein synthesis inhibitor in eukaryotes. Its inhibitory effect leads to cell growth arrest and even death, thereby inhibiting microorganisms in purified soil precipitates. This invention employs a combination of NaN3 and cyclohexylimide to inhibit the growth of microorganisms in purified soil precipitates, preventing the adsorption of metal components from soil samples by microbial cell walls, such as peptidoglycans and lipopolysaccharides, and simultaneously preventing microorganisms from altering the valence state of metals in the soil sample through redox reactions.

[0063] This embodiment provides a method for quantitative detection of soil metal nanocolloids, including obtaining a soil sample, purifying the soil sample to obtain a purified soil precipitate; wherein, purification includes low-speed centrifugation and removal of supernatant. Deionized water containing microbial inhibitors is added to the purified soil precipitate to adjust the soil-to-water ratio, obtaining a suspension. The target nanocolloids are released into the suspension to obtain a dispersed suspension. A gradient membrane array is used to perform multi-stage cross-flow filtration on the dispersed suspension to obtain soil colloids. The soil colloids are then subjected to asymmetric flow field separation to obtain metal nanocolloids. Quantitative analysis of the metal nanocolloids is performed to obtain the concentration of different metals. Before extracting soil metal nanocolloids, this invention uses low-speed centrifugation to remove the supernatant, thereby removing most soluble interfering substances such as soluble salts and free organic matter. Adding deionized water containing microbial inhibitors can inhibit microbial activity. The preparation of the dispersed suspension using the target nanocolloids disperses soil aggregates while maximally protecting the original structure of the target nanocolloids from shear force damage. The present invention employs a cross-flow filtration gradient membrane separation extraction method for the extraction of soil metal nanocolloids. This method is based on the principle of cross-flow filtration. By using separation membranes with different pore sizes in sequence, it can effectively avoid the problem of colloidal structure destruction caused by high-speed centrifugation while removing larger powder and clay particles. This method achieves gradient separation of metal elements of different particle sizes in soil metal nanocolloids and finally obtains the target product.

[0064] Example 2 Gradient Membrane Separation

[0065] This embodiment provides a method for quantitative detection of soil metal nanocolloids. This embodiment describes the differences from Embodiment 1, based on Embodiment 1. The method includes:

[0066] S1: Obtain a soil sample, purify the soil sample to obtain purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of supernatant;

[0067] S2: Add deionized water containing microbial inhibitors to the purified soil precipitate, adjust the soil-to-water ratio, and obtain a suspension;

[0068] S3: Release the target nanocolloid into the suspension to obtain a dispersed suspension;

[0069] S4: The dispersed suspension is subjected to multi-stage cross-flow filtration using a gradient membrane module to obtain soil colloids;

[0070] S5: Perform asymmetric flow field separation on the soil colloids to obtain metal nanocolloids;

[0071] S6: Quantitatively analyze the metal nanocolloids to obtain the concentrations of different metals.

[0072] The method of using a gradient membrane array to perform multi-stage cross-flow filtration on the dispersed suspension to obtain soil colloids includes:

[0073] S41: A filter membrane with a pore size of 20 μm is used to perform a first-stage separation on the dispersed suspension to obtain a first permeate; the first-stage separation is used to remove powder particles;

[0074] S42: A filter membrane with a pore size of 2 μm is used to perform a second-stage separation on the first permeate to obtain a second permeate; the second-stage separation is used to remove clay particles;

[0075] S43: A filter membrane with a pore size of 1 μm is used to perform a third-stage separation on the second permeate to obtain a soil metal nanocolloid dispersion.

[0076] S44: Freeze-dry the soil metal nanocolloid dispersion to obtain soil colloid.

[0077] All gradient membrane separation steps were carried out in a low-temperature environment of 4°C and in a closed system with continuous high-purity nitrogen gas to simultaneously inhibit microbial activity and prevent oxidation of metal nanocolloids.

[0078] First-stage separation (particle removal): The mildly dispersed suspension is pumped into a cross-flow filtration system using a 20 μm pore size filter membrane. Under tangential flow, particles smaller than 20 μm enter the permeate, while powder and sand particles larger than 20 μm are retained in the circulating liquid, achieving initial separation of powder and target components.

[0079] Second-stage separation (mucus removal): The permeate from the first-stage separation is collected and replaced with a 2 μm pore size filter membrane for secondary cross-flow filtration. At this stage, the permeate consists of particles smaller than 2 μm, and the retentate consists of mucus particles with a particle size of 2-20 μm.

[0080] Third-stage separation (obtaining nanocolloids): The permeate from the second-stage separation is collected and subjected to final cross-flow filtration using a 1 μm pore size membrane. After filtration, the permeate is the target product, namely a soil metal nanocolloid dispersion with a particle size of less than 1 μm.

[0081] Preparation of nanocolloid solutions: The collected nanocolloid dispersions with particle sizes less than 1 μm were freeze-dried to obtain solid samples. For use, the solid samples were redispersed in a solvent and precisely prepared to the desired concentration, with concentration gradients set at 0.5, 1.0, 2.0, 5.0, or 10.0 mg / L. -1 .

[0082] The cross-flow filtration gradient membrane separation and extraction method used in this embodiment can be operated under mild physical conditions, effectively avoiding the colloidal structure damage caused by high-speed centrifugation, thereby obtaining soil nanocolloids that are closer to their natural state. Three filter membranes with different pore sizes are used to remove powder and clay particles from the dispersed suspension, avoiding the significant impact of powder and clay particles on metal migration through mechanisms such as physical adsorption, chemical precipitation, and surface reactions.

[0083] Example 3 Separation of metal nanocolloids

[0084] This embodiment provides a method for quantitative detection of soil metal nanocolloids. This embodiment describes the differences from Embodiment 1, based on Embodiment 1. The method includes:

[0085] S1: Obtain a soil sample, purify the soil sample to obtain purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of supernatant;

[0086] S2: Add deionized water containing microbial inhibitors to the purified soil precipitate, adjust the soil-to-water ratio, and obtain a suspension;

[0087] S3: Release the target nanocolloid into the suspension to obtain a dispersed suspension;

[0088] S4: The dispersed suspension is subjected to multi-stage cross-flow filtration using a gradient membrane module to obtain soil colloids;

[0089] S5: Perform asymmetric flow field separation on the soil colloids to obtain metal nanocolloids;

[0090] S6: Quantitatively analyze the metal nanocolloids to obtain the concentrations of different metals.

[0091] The asymmetric flow field separation of the soil colloids to obtain metal nanocolloids includes:

[0092] S51: During the sample introduction stage, the soil colloids are gathered near the channel inlet under the combined action of the carrier flow, tangential flow and focusing flow;

[0093] S52: During the elution phase, the tangential flow rate is kept constant during the first time period; during the second time period, the tangential flow rate is increased from 2.5 mL / min using a power function flow with an exponent of 0.2. -1 Reduced to 0.15 mL·min -1 During the third time interval, the tangential flow velocity was reduced from 0.15 mL / min using a power function with an exponent of 0.8. -1 Reduce to 0 mL·min -1 During the fourth time period, the tangential flow rate was maintained at 0 mL / min. -1 To efficiently separate metal nanocolloids across the entire particle size range.

[0094] Before sample injection, the extracted soil metal nanoparticles with a particle size of less than 1000 nm were ultrasonically treated to disrupt particle aggregation through cavitation, mechanical, and thermal effects, resulting in uniform particle dispersion. An appropriate amount of the ultrasonically dispersed sample was placed in a sample vial, which was then placed on the sample tray of the asymmetric flow field separator.

[0095] In the injection step, the settings for injection flow rate, injection time, and related flow parameters are optimized based on the physical properties of the sample and the separation principle. The determination of the injection flow rate and injection time comprehensively considers the sample concentration and hydrodynamic characteristics, helping to introduce as much sample as possible into the system while avoiding overloading and clogging of the separation channel.

[0096] In this embodiment, in the asymmetric flow field separation system, the flow rate of the fluid entering the detector, i.e., the carrier flow rate, is kept constant at 0.5 mL·min. -1The cross flow is always perpendicular to the separation channel, and the initial flow rate is set to 2.5 mL / min. -1 The focus pump flows in the opposite direction to the final movement of the nanocolloids, concentrating sample particles near the channel inlet during the injection phase and preventing the sample from being flushed out.

[0097] The elution step employs a power-law tangential flow rate variation pattern. In this step, the tangential flow rate is initially maintained at 2.5 mL / min. -1 For 1 minute, small-diameter particles are preferentially separated. Then, a power function flow with an exponent of 0.2 is used, increasing the tangential flow rate from 2.5 mL / min over 20 minutes. -1 Reduced to 0.15 mL·min -1 In this stage, sample particles are gradually flushed out as the tangential flow changes, separating along the velocity gradient. The relatively rapid decrease in velocity avoids peak broadening of small particles and creates conditions for subsequent separation. Then, a power-law flow with an exponent of 0.8 is used, with the tangential flow rate decreasing from 0.15 mL / min over 30 min. -1 Reduced to 0 mL·min -1 The extremely slow deceleration ensures that large-diameter particles are fully separated under low-disturbance conditions. Finally, the tangential flow rate is maintained at 0 mL / min. 1 In 25 minutes, all remaining large particles in the channel were flushed out. This segmented flow rate control can achieve efficient separation of metal nanocolloids across the entire particle size range by dynamically matching the migration characteristics of particles of different sizes.

[0098] In this embodiment, a 1 kDa polyethersulfone membrane was selected as the AF4 channel membrane because its pore size can effectively filter dissolved substances, leaving only metal nanoparticles, thus achieving specific separation of the target substance. A 25 μM sodium chloride solution was chosen as the eluent because it provides suitable ionic strength and fluid properties, which helps maintain the stable dispersion of the metal nanoparticles and avoids particle aggregation or adsorption during the separation process.

[0099] Example 4: Quantitative Detection and Recovery of Metal Nanocolloids

[0100] This embodiment provides a method for quantitative detection of soil metal nanocolloids. This embodiment describes the differences from Embodiment 1, based on Embodiment 1. The method includes:

[0101] S1: Obtain a soil sample, purify the soil sample to obtain purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of supernatant;

[0102] S2: Add deionized water containing microbial inhibitors to the purified soil precipitate, adjust the soil-to-water ratio, and obtain a suspension;

[0103] S3: Release the target nanocolloid into the suspension to obtain a dispersed suspension;

[0104] S4: The dispersed suspension is subjected to multi-stage cross-flow filtration using a gradient membrane module to obtain soil colloids;

[0105] S5: Perform asymmetric flow field separation on the soil colloids to obtain metal nanocolloids;

[0106] S6: Quantitatively analyze the metal nanocolloids to obtain the concentrations of different metals.

[0107] The quantitative analysis of the metal nanocolloids to obtain the concentrations of different metals includes:

[0108] S61: Connect the sample outlet tube of the asymmetric flow field to the sample inlet tube of the multi-angle light scattering instrument.

[0109] S62: Set the scattering angle of the multi-angle light scattering instrument and measure the concentration of different metals in the metal nanocolloid.

[0110] The sample outlet tube of the asymmetric flow field analyzer (AF4) was connected to the inlet tube of a multi-angle light scattering (MALS) instrument to determine the concentration of metal nanocolloids in the soil. During the experiment, the 90° scattering angle data from the MALS was used as the basis, as the scattered light signal at this angle is most sensitive to changes in particle size and can more accurately reflect the particle size distribution of the metal nanocolloids. Then, the asymmetric flow field analyzer was coupled with ICP-MS to accurately quantify the concentration of various metal elements in the metal nanocolloids.

[0111] Figure 2 The results of measuring different concentrations of soil metal nanocolloids at a 90° scattering angle were demonstrated by using an asymmetric flow field analyzer coupled with a multi-angle light scattering analyzer (MALS). Figure 3 These are the results of the determination of Al concentration in soil metal nanocolloids. Figure 5 This is the result of the determination of Fe concentration in soil metal nanocolloids. Figure 7 This is the result of the determination of Zn concentration in soil metal nanocolloids. Figure 4 This is a linear relationship between the concentration of soil metal nanoparticles and the Al concentration therein. Figure 6 This is a linear relationship between the concentration of soil metal nanoparticles and the Fe concentration therein. Figure 8 This is a linear relationship between the concentration of soil metal nanocolloids and the concentration of Zn within them. The concentrations of Al, Fe, and Zn were obtained by integrating the peak areas of the ICP-MS measurements. Figure 2 , Figure 3 , Figure 5 and Figure 7 It can be seen that asymmetric flow field separation can separate soil nanocolloids, and as the concentration of soil metal nanocolloids increases from 0.5 mg·L⁻¹, the separation effect is achieved. -1 Gradually increase to 10.0 mg·L -1 The signal intensities of Al, Fe, and Zn at each peak gradually increase. Figure 4 , Figure 6 and Figure 8 As can be seen, the concentration of soil metal nanocolloids has a good linear relationship with the signals of Al, Fe, and Zn (R0). 2 The value >0.9 indicates that AF4-ICP-MS can accurately quantify the concentration of metal elements in soil metal nanocolloids.

[0112] In this embodiment, the specific time period for fraction collection is determined based on the peak elution time of the sample. Compared with changing the membrane pore size to recover nanocolloids, the recovery method in this embodiment expands the particle size range of recovered metal nanocolloids by recovering them in different time periods through the particle size range of soil metal nanocolloids.

[0113] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0114] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for quantitative detection of soil metal nanocolloids, characterized in that, include: A soil sample is obtained and purified to obtain a purified soil precipitate; wherein, the purification includes low-speed centrifugation and removal of the supernatant; Deionized water containing microbial inhibitors was added to the purified soil precipitate to adjust the soil-to-water ratio and obtain a suspension. The target nanocolloid is released into the suspension to obtain a dispersed suspension; Soil colloids were obtained by multi-stage cross-flow filtration of the dispersed suspension using a gradient membrane array. The soil colloids were subjected to asymmetric flow field separation to obtain metal nanocolloids; The concentrations of different metals were obtained by quantitative analysis of the metal nanocolloids. The step of releasing the target nanocolloid into the suspension to obtain a dispersed suspension includes: The suspension was placed in a low-temperature shaker at 4°C; The dispersed suspension was obtained by gently shaking at a very low speed of 50 rpm for 2 hours. The method of using a gradient membrane array to perform multi-stage cross-flow filtration on the dispersed suspension to obtain soil colloids includes: A filter membrane with a pore size of 20 μm is used to perform a first-stage separation on the dispersed suspension to obtain a first permeate; the first-stage separation is used to remove powder particles. A filter membrane with a pore size of 2 μm is used to perform a second-stage separation on the first permeate to obtain a second permeate; the second-stage separation is used to remove clay particles. A filter membrane with a pore size of 1 μm was used to perform a third-stage separation on the second permeate to obtain a soil metal nanocolloid dispersion. The soil metal nanocolloid dispersion was freeze-dried to obtain soil colloid.

2. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The purification of the soil sample to obtain purified soil precipitate includes: Sterile and deoxygenated ultrapure water was added to the soil sample to obtain a soil-water mixture; The soil-water mixture is centrifuged to separate the precipitate and soluble substances, resulting in a separated solution. The supernatant in the separated solution is removed to remove soluble interfering substances, resulting in purified soil precipitate.

3. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The microbial inhibitors include 0.02% NaN3 and 0.01% cyclohexylimide; the adjusted soil-to-water ratio is 1:

100.

4. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The first-stage separation of the dispersed suspension to obtain the first permeate includes: The dispersed suspension is pumped into a cross-flow filtration system; Under the action of tangential flow and a 20 μm filter membrane, particles with a diameter less than 20 μm pass through the 20 μm filter membrane into the permeate, while powder and sand particles with a diameter greater than 20 μm are retained in the circulating liquid, resulting in the first permeate.

5. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The second-stage separation of the first permeate to obtain the second permeate includes: Under the action of tangential flow and a 2 μm filter membrane, particles with a diameter less than 2 μm pass through the 2 μm filter membrane into the permeate, while particles with a diameter greater than 2 μm are retained in the circulating liquid, resulting in a second permeate.

6. The method for quantitative detection of soil metal nanocolloids according to claim 2, characterized in that, The ultrapure water has a soil-to-water ratio of 1:5, the centrifugation temperature is 4℃, the rotation speed is 2000rpm, and the centrifugation time is 10min.

7. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The asymmetric flow field separation of the soil colloids to obtain metal nanocolloids includes: During the sample introduction stage, the soil colloids are gathered near the channel inlet under the combined action of carrier flow, tangential flow, and focusing flow. During the elution phase, the tangential flow rate was kept constant during the first time period; during the second time period, the tangential flow rate was increased from 2.5 mL / min using a power function flow with an exponent of 0.

2. -1 Reduced to 0.15 mL·min -1 During the third time interval, the tangential flow velocity was reduced from 0.15 mL / min using a power function with an exponent of 0.

8. -1 Reduce to 0 mL·min -1 During the fourth time period, the tangential flow rate was maintained at 0 mL / min. -1 To efficiently separate metal nanocolloids across the entire particle size range.

8. The method for quantitative detection of soil metal nanocolloids according to claim 1, characterized in that, The quantitative analysis of the metal nanocolloids to obtain the concentrations of different metals includes: Connect the sample outlet tube of the asymmetric flow field to the sample inlet tube of the multi-angle light scattering instrument; The scattering angle of the multi-angle light scattering instrument was set to measure the concentration of different metals in the metal nanocolloid.

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