Method for fractionating soil organic carbon in wind erosion products and matrix purification

Abstract

The present application relates to the technical field of soil organic carbon extraction, and particularly relates to a method for grading extraction and matrix purification of soil organic carbon in wind erosion products, which provides a method for grading extraction and matrix purification of soil organic carbon with high adaptability to wind erosion products, high extraction efficiency and high extraction purity, through sample pretreatment, grading extraction, multi-stage matrix purification, freezing concentration and collection, and post-treatment; the method is precisely adapted to the characteristics of wind erosion products, such as a large amount of sand particles and easy oxidation and loss of organic carbon, by adopting a combined technology of gradient screening-low temperature grinding-density liquid pre-separation; a three-stage extraction system of 'active-semi-active-stable' is constructed, the extraction efficiency of organic carbon is improved, and the detection requirements of different active organic carbon components for carbon cycle research in the wind erosion area are met; in the multi-stage matrix purification, sand particles, metal ions and salt residues are removed step by step, the purity of the extraction liquid is significantly improved, and the method has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of soil organic carbon extraction technology, and in particular to a method for graded extraction and matrix purification of soil organic carbon from wind erosion products. Background Technology

[0002] Soil organic carbon is the core carrier of carbon cycling in terrestrial ecosystems. The migration and transformation patterns of its components, such as active organic carbon, semi-active organic carbon, and stable organic carbon, directly affect the maintenance of soil fertility and ecosystem stability in wind-eroded areas. As direct products of wind erosion in sandy areas, wind erosion products exhibit unique properties significantly different from those of ordinary farmland and forest soils: high sand content (up to 80% or more), low total organic carbon content (usually below 5 g / kg), extremely low proportion of active organic carbon (such as dissolved organic carbon (DOC) and easily oxidized organic carbon (LOC), and poor stability, with components easily oxidized and lost. Simultaneously, the matrix contains a large amount of sand impurities and metal ions such as iron and calcium, posing a significant challenge to the accurate extraction of soil organic carbon components.

[0003] In the prior art, for example, patent document CN120609955A discloses a method for detecting soil organic carbon components based on gas chromatography-mass spectrometry. This invention is mainly developed for ordinary soils (farmland, forest land, wetland soils) and has not been fully adapted to the special properties of wind erosion products, resulting in many technical defects in the extraction process, as follows:

[0004] I. Pretreatment technologies are incompatible with the characteristics of wind erosion products. Current soil pretreatment generally adopts a "conventional sieving + room temperature grinding" mode, using a 2mm single-aperture sieve and high-speed grinding at 300 rpm. This mode has three major problems: ① The sieving method is singular. Light sand particles in wind erosion products are easily carried away by airflow, and fine carbon components easily adhere to the surface of large-diameter sand particles. Single sieving cannot achieve the initial separation of carbon components from sand particles, resulting in low subsequent extraction efficiency; ② Room temperature high-speed grinding will cause the oxidative decomposition of organic carbon components. In particular, the active organic carbon in wind erosion products has extremely poor stability, and mechanical heat and oxygen contact during the grinding process will exacerbate its loss; ③ The lack of a sand-carbon component pre-separation step allows a large amount of sand impurities to enter the subsequent extraction stage, which not only interferes with the extraction process but also increases the difficulty of matrix purification.

[0005] II. The graded extraction technology cannot meet the requirements of low organic carbon characteristics of wind erosion products. Existing graded extraction methods are mainly designed for ordinary soils and have two major defects: ① The extraction parameters are mismatched. Ordinary soils have a high organic carbon content, and conventional soil-water ratio (1:5) and oscillation parameters (high amplitude, room temperature) can meet the detection requirements. However, the organic carbon content of wind erosion products is extremely low, and the concentration of active organic carbon is close to the detection limit. Conventional parameters will lead to insufficient concentration of target components and inaccurate quantification. ② The graded system is imperfect. Existing methods mostly focus on the binary separation of DOC and LOC and lack efficient extraction technology for stable organic carbon (such as mineral-bound organic carbon MAOC). As a key component of carbon sequestration in wind erosion areas, the extraction efficiency of MAOC directly affects the accuracy of the study of carbon cycle mechanism in wind erosion areas.

[0006] III. Matrix purification technology has failed to effectively address the interference problem of wind erosion products. The matrix of wind erosion products is complex, containing a large number of fine sand particles, metal ions (iron, calcium, etc.), and potential salt impurities. Existing purification technologies have significant shortcomings: ① Sand particle impurities are not thoroughly removed. Existing technologies mostly use ordinary filter membranes, which are difficult to retain fine sand particles with a diameter of less than 1μm. These sand particles will adsorb organic carbon components, affecting the extraction purity; ② Interference from metal ions has not been effectively eliminated. The dosage and flow rate parameters of conventional purification materials such as cation exchange resins have not been optimized for wind erosion products. Metal ions easily combine with organic carbon components to form complexes, leading to deviations in detection results; ③ Salt residue is a prominent problem. Some methods use calcium chloride isodense liquids for separation, but salt residues cannot be completely removed during subsequent purification processes, interfering with the accuracy of detection methods such as gas chromatography-mass spectrometry.

[0007] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a method for graded extraction and matrix purification of soil organic carbon from wind erosion products. Summary of the Invention

[0008] In view of this, the purpose of this invention is to propose a method for graded extraction and matrix purification of soil organic carbon in wind erosion products, so as to solve the problems of poor compatibility between soil organic carbon extraction technology and wind erosion products, low extraction accuracy, cumbersome operation and serious matrix interference in the prior art.

[0009] To achieve the above objectives, the present invention provides a method for graded extraction of soil organic carbon and matrix purification from wind erosion products.

[0010] A method for fractional extraction and matrix purification of soil organic carbon from wind erosion products includes the following steps:

[0011] Step S1. Sample pretreatment: The wind erosion product sample is added to the wind erosion product integrated device through the sample feeding module, and is pretreated by gradient sieving, low temperature grinding and density liquid pretreatment to obtain pretreated sample C;

[0012] Step S2. Fractional extraction: The pretreated sample C is sent into the fractional extraction module to extract active organic carbon (DOC), semi-active organic carbon (LOC), and stable organic carbon (MAOC) in sequence, to obtain pretreated extract 1, pretreated extract 2, and pretreated extract 3, respectively.

[0013] Step S3. Multi-stage matrix purification: Pretreated extract 1, pretreated extract 2 and pretreated extract 3 are respectively sent to the sand filtration unit of the multi-stage purification module. After filtration, they are passed through a cation exchange resin column for ion purification, and then transferred to a vacuum dialysis bag to remove salt residue, to obtain purified extract 1, purified extract 2 and purified extract 3.

[0014] Step S4. Freeze concentration and collection: Purified extract 1, purified extract 2 and purified extract 3 are respectively sent to the freeze concentration module, freeze-dried to semi-solid state, and then concentrated and collected using a nitrogen blower to obtain concentrated extract 1, concentrated extract 2 and concentrated extract 3.

[0015] Step S5. Post-processing: Concentrated extract 1, concentrated extract 2 and concentrated extract 3 are tested and analyzed. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, and neutralized with acid and alkali until it meets the standards before being discharged.

[0016] Preferably, the sample pretreatment includes the following steps:

[0017] Step A1. Add the wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration sieve parameters of the gradient sieve module. After three-stage sieve classification, collect the undersize material, record it as pre-treated sample A, and enter the low-temperature grinding module. Through three-stage gradient sieve, the sand particles and carbon components are initially classified. Low-amplitude vibration sieve avoids the loss of light carbon components and the particle size of the undersize material is uniform.

[0018] Step A2. Set the freezing parameters of the low-temperature grinding module. Grind the sieved material for 3-5 minutes at a grinding speed of 150-200 rpm to obtain pretreated sample B. The low-temperature environment inhibits the oxidative decomposition of organic carbon, and the low-speed grinding avoids the loss of carbon components caused by mechanical heat. At the same time, it ensures that the sample particle size meets the extraction requirements and increases the contact area between carbon components and the density liquid in the subsequent density liquid pre-separation module.

[0019] Step A3. Send the pretreated sample B into the density liquid pre-separation module, add density liquid, stir at a stirring speed of 30-50 rpm for 8-10 min, let it stand and settle for 20-25 min, then separate it through a 0.45 μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module. Utilize the density difference between sand particles and carbon components to remove ≥80% of sand impurities, reducing the processing pressure of subsequent extraction and purification steps.

[0020] Preferably, the vibration parameters in step A1 are: amplitude of 5-10 mm, frequency of 30-50 Hz, and time of 5-10 min.

[0021] The apertures of the three-stage sieves are 2 mm, 0.25 mm, and 0.053 mm, respectively.

[0022] The particle size of the pretreated sample B described in step A2 is ≤0.075 mm;

[0023] The temperature of the cryogenic grinding module is -25 to 20°C.

[0024] Preferably, the density liquid in step A3 is a modified sodium iodide density liquid with low toxicity and low residue, which can effectively avoid interference with organic carbon components.

[0025] The modified sodium iodide density solution comprises the following raw materials in parts by weight:

[0026] 700-800 parts anhydrous sodium iodide, 0.1-0.5 parts sodium thiosulfate pentahydrate, and 1000-1150 parts deionized water;

[0027] The ratio of the amount of pretreated sample B to the amount of modified sodium iodide density solution is 1g:9-11mL.

[0028] Preferably, the hierarchical extraction includes the following steps:

[0029] Step B1. Send the pretreated sample C into the first group of light-proof oscillation units of the fractionation extraction module, add solution A, set the oscillation parameters to a temperature of 18-23℃, an amplitude of 15-20mm, and a frequency of 60-80Hz, and oscillate in the dark for 24h. After solid-liquid separation, the pretreated extract 1 and residue A are obtained.

[0030] Step B2. Transfer residue A to the second group of light-proof oscillation units, add solution B, set the oscillation parameters to temperature of 18-23℃, amplitude of 15-20mm, and frequency of 60-80Hz, and oscillate in the dark for 24h. After solid-liquid separation, pretreated extract 2 and residue B are obtained.

[0031] Step B3. Transfer the residue B to the third group of light-protected oscillation units, add solution C, set the oscillation parameters to a temperature of 28-32℃, an amplitude of 15-20mm, and a frequency of 60-80Hz, and oscillate in the dark for 24 hours. After solid-liquid separation, the pretreated extract 3 and residue C are obtained.

[0032] Preferably, solution A in step B1 is ultrapure water;

[0033] The ratio of the amount of pretreated sample C to solution A is 1g:9.5-10.3mL.

[0034] Preferably, solution B in step B2 is an aqueous solution of potassium chloride with a concentration of 1 mol / L;

[0035] The mass ratio of residue A to solution B is 7.7-8 g: 1 mL.

[0036] Preferably, solution C in step B3 is obtained by mixing a 0.1 mol / L sodium hydroxide aqueous solution and a 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution;

[0037] The mass ratio of residue B to solution C is 9.5-10.5 g: 1 mL.

[0038] Preferably, the multi-stage matrix purification includes the following steps:

[0039] Pretreated extract 1, pretreated extract 2, and pretreated extract 3 were respectively fed into the sand filtration unit of the multi-stage purification module. They were filtered through a 0.22 μm polytetrafluoroethylene (PTFE) membrane at a pressure of 0.1-0.2 MPa to remove residual fine sand particles and prevent the adsorption of organic carbon components by sand particles, which could lead to a decrease in extraction purity. Subsequently, the extracts were passed through a 15 cm high 732 type cation exchange resin column at a flow rate of 1-2 mL / min for ion purification. The resin was then exchanged with the pretreated extracts... Extraction solution 1, pretreated extraction solution 2, and pretreated extraction solution 3 are brought into full contact to adsorb and remove iron and calcium metal ions, avoiding interference from the combination of metal ions and organic carbon. Then, they are transferred to a vacuum dialysis bag with a molecular weight cutoff of 800-1000 Da for dialysis for 12-24 hours. The dialysis solution is ultrapure water, and the dialysis solution is changed 3 times during the process to remove salt residues in the extract, so that the salt residue is <0.01g / L, avoiding interference with subsequent instrument detection. This yields purified extraction solution 1, purified extraction solution 2, and purified extraction solution 3.

[0040] Preferably, the cryogenic concentration and collection includes the following steps:

[0041] Purified extract 1, purified extract 2, and purified extract 3 were fed into a freeze-drying module and freeze-dried to a semi-solid state at -60 to -50°C and 10 to 20 Pa. Then, they were concentrated to 10 to 50 mg / L using a nitrogen blow-drying concentrator with a nitrogen flow rate of 5 to 10 mL / min. The concentrated extracts 1, 2, and 3 were collected. The combined concentration method of "freeze-drying + nitrogen blowing" reduced the loss rate of organic carbon volatilization.

[0042] The beneficial effects of this invention are:

[0043] This invention provides a method for graded extraction and matrix purification of soil organic carbon from wind erosion products. The method, involving sample pretreatment, graded extraction, multi-stage matrix purification, cryogenic concentration and collection, and post-processing, offers a highly adaptable, efficient, and pure extraction method for soil organic carbon. Specifically, it employs a combined technique of "gradient sieving-low-temperature grinding-density liquid pre-separation" to precisely address the characteristics of wind erosion products, which are characterized by abundant sand particles and easy oxidation and loss of organic carbon, effectively reducing carbon component loss and improving sand particle removal rate. In the graded extraction, a three-stage extraction system of "active-semi-active-stable" is constructed. Extraction reagents and conditions are optimized to address the low organic carbon content of wind erosion products, thereby improving organic carbon extraction efficiency and meeting the detection requirements for different active organic carbon components in carbon cycle research in wind erosion areas. In the multi-stage matrix purification, sand particles, metal ions, and salt residues are removed stepwise, significantly improving the purity of the extract. Compared with existing technologies, this method has broad application prospects. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0045] Example 1: A method for graded extraction and matrix purification of soil organic carbon from wind erosion products, comprising the following steps:

[0046] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 1 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0047] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 5mm amplitude, 30Hz frequency and 5min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0048] S3. Set the temperature of the low-temperature grinding module to -25℃, grind the sieved material for 3 minutes at a grinding speed of 150 rpm, and obtain pretreated sample B with a particle size ≤ 0.075 mm.

[0049] S4. Mix 700g of anhydrous sodium iodide, 0.1g of sodium thiosulfate pentahydrate and 1000g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:9mL. Stir at 30rpm for 8min, let stand and settle for 20min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0050] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:9.5mL. Set the oscillation parameters to 18℃, 15mm amplitude, and 60Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0051] S6. Transfer residue A to the second group of light-protected oscillation units, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.7 g: 1 mL. Set the oscillation parameters to 18℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0052] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 9.5 g: 1 mL. Set the oscillation parameters to 28℃, 15 mm, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0053] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 are respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa. Then, the extracts are passed through a 732 type cation exchange resin with a column height of 15cm and the flow rate is set to 1mL / min for ion purification. Then, they are transferred to a vacuum dialysis bag with a molecular weight cutoff of 800Da and dialyzed for 12h. The dialysate is ultrapure water and the dialysate is changed 3 times during the period to remove salt residue in the extracts, so as to obtain purified extract 1, purified extract 2 and purified extract 3.

[0054] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -60℃ and 10Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 10mg / L using a nitrogen blow concentrator with a nitrogen flow rate of 5mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0055] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0056] Example 2: A method for graded extraction and matrix purification of soil organic carbon from wind erosion products, comprising the following steps:

[0057] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 10 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0058] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 7mm amplitude, 40Hz frequency and 7min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0059] S3. Set the freezing parameters of the low-temperature grinding module to -23℃, grind the sieved material at a grinding speed of 170 rpm for 4 min to obtain pretreated sample B with a particle size ≤0.075 mm;

[0060] S4. Mix 750g of anhydrous sodium iodide, 0.3g of sodium thiosulfate pentahydrate and 1100g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:10mL. Stir at 40rpm for 9min, let stand and settle for 23min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0061] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:10mL. Set the oscillation parameters to 20℃, 18mm amplitude, and 70Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0062] S6. Transfer residue A to the second group of light-proof oscillation unit, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.8 g: 1 mL. Set the oscillation parameters to 20℃, 17 mm amplitude, and 70 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0063] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 10 g: 1 mL. Set the oscillation parameters to 30℃, 18 mm, and 70 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0064] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 were respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa. Then, the extracts were passed through a 732 type cation exchange resin with a column height of 15cm and a flow rate of 1.5mL / min for ion purification. They were then transferred to a vacuum dialysis bag with a molecular weight cutoff of 900Da and dialyzed for 18h. The dialysate was ultrapure water and was changed 3 times during the process to remove salt residue in the extracts, resulting in purified extract 1, purified extract 2 and purified extract 3.

[0065] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -55℃ and 15Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 30mg / L using a nitrogen blow-dryer with a nitrogen flow rate of 7mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0066] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0067] Example 3: A method for graded extraction and matrix purification of soil organic carbon from wind erosion products, comprising the following steps:

[0068] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 20cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2g / kg, DOC content 0.15g / kg, LOC content 0.8g / kg, and MAOC content 2.25g / kg.

[0069] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 10mm amplitude, 50Hz frequency and 10min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0070] S3. Set the temperature of the low-temperature grinding module to -20℃, and grind the sieved material for 3-5 minutes at a grinding speed of 200 rpm to obtain pretreated sample B with a particle size ≤0.075 mm.

[0071] S4. Mix 800g of anhydrous sodium iodide, 0.5g of sodium thiosulfate pentahydrate and 1150g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the ratio of pretreated sample B to modified sodium iodide density solution is 1g:11mL. Stir at 50rpm for 10min, let stand and settle for 25min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0072] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:10.3mL. Set the oscillation parameters to 23℃, 20mm amplitude, and 80Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0073] S6. Transfer residue A to the second group of light-proof oscillation unit, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 8 g: 1 mL. Set the oscillation parameters to 23℃, 20 mm, and 80 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0074] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 10.5 g: 1 mL. Set the oscillation parameters to 32℃, 20 mm, and 80 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0075] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 were respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.2MPa. Then, the extracts were passed through a 732 type cation exchange resin with a column height of 15cm and the flow rate was set to 2mL / min for ion purification. Then, they were transferred to a vacuum dialysis bag with a molecular weight cutoff of 1000Da and dialyzed for 24h. The dialysate was ultrapure water and the dialysate was changed 3 times during the period to remove salt residue in the extracts, resulting in purified extract 1, purified extract 2 and purified extract 3.

[0076] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -50℃ and 20Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 50mg / L using a nitrogen blow concentrator with a nitrogen flow rate of 10mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0077] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0078] Comparative Example 1:

[0079] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 1 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0080] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the sieving module to 20mm amplitude, 30Hz frequency and 5min time. After being classified by a sieve with a pore size of 0.053mm, collect the carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the grinding module.

[0081] S3. Grind the sieved material for 3 minutes at a grinding speed of 550 rpm and a grinding temperature of 15℃ to obtain pretreated sample B with a particle size ≤0.075 mm;

[0082] S4. Mix 700g of anhydrous sodium iodide, 0.1g of sodium thiosulfate pentahydrate and 1000g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:9mL. Stir at 30rpm for 8min, let stand and settle for 20min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0083] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:9.5mL. Set the oscillation parameters to 18℃, 15mm amplitude, and 60Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0084] S6. Transfer residue A to the second group of light-protected oscillation units, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.7 g: 1 mL. Set the oscillation parameters to 18℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0085] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 9.5 g: 1 mL. Set the oscillation parameters to 28℃, 15 mm, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0086] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 are respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa. Then, the extracts are passed through a 732 type cation exchange resin with a column height of 15cm and the flow rate is set to 1mL / min for ion purification. Then, they are transferred to a vacuum dialysis bag with a molecular weight cutoff of 800Da and dialyzed for 12h. The dialysate is ultrapure water and the dialysate is changed 3 times during the period to remove salt residue in the extracts, so as to obtain purified extract 1, purified extract 2 and purified extract 3.

[0087] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -60℃ and 10Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 10mg / L using a nitrogen blow concentrator with a nitrogen flow rate of 5mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0088] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0089] Comparative Example 2:

[0090] Compared with Example 1, this comparative example only replaces "modified sodium iodide density solution" with "sodium iodide density solution with a density of 1.8 g / cm³". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is the graded extraction of soil organic carbon and matrix purification from wind erosion products.

[0091] Comparative Example 3:

[0092] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 1 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0093] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 5mm amplitude, 30Hz frequency and 5min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0094] S3. Set the temperature of the low-temperature grinding module to -25℃, grind the sieved material for 3 minutes at a grinding speed of 150 rpm, and obtain pretreated sample B with a particle size ≤ 0.075 mm.

[0095] S4. Mix 700g of anhydrous sodium iodide, 0.1g of sodium thiosulfate pentahydrate and 1000g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:9mL. Stir at 30rpm for 8min, let stand and settle for 20min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0096] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:5mL. Set the oscillation parameters to 18℃, 15mm amplitude, and 60Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0097] S6. Transfer residue A to the second group of light-protected oscillation units, add potassium chloride aqueous solution with a concentration of 0.5 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.7 g: 1 mL. Set the oscillation parameters to 18℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 2 and residue B.

[0098] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is a 0.1 mol / L sodium hydroxide aqueous solution, and the mass ratio of residue B to solution C is 9.5 g: 1 mL. Set the oscillation parameters to 28℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to obtain pretreated extract 3 and residue C.

[0099] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 are respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa. Then, the extracts are passed through a 732 type cation exchange resin with a column height of 15cm and the flow rate is set to 1mL / min for ion purification. Then, they are transferred to a vacuum dialysis bag with a molecular weight cutoff of 800Da and dialyzed for 12h. The dialysate is ultrapure water and the dialysate is changed 3 times during the period to remove salt residue in the extracts, so as to obtain purified extract 1, purified extract 2 and purified extract 3.

[0100] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -60℃ and 10Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 10mg / L using a nitrogen blow concentrator with a nitrogen flow rate of 5mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0101] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0102] Comparative Example 4:

[0103] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 1 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0104] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 5mm amplitude, 30Hz frequency and 5min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0105] S3. Set the temperature of the low-temperature grinding module to -25℃, grind the sieved material for 3 minutes at a grinding speed of 150 rpm, and obtain pretreated sample B with a particle size ≤ 0.075 mm.

[0106] S4. Mix 700g of anhydrous sodium iodide, 0.1g of sodium thiosulfate pentahydrate and 1000g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:9mL. Stir at 30rpm for 8min, let stand and settle for 20min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0107] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:9.5mL. Set the oscillation parameters to 18℃, 15mm amplitude, and 60Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0108] S6. Transfer residue A to the second group of light-protected oscillation units, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.7 g: 1 mL. Set the oscillation parameters to 18℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0109] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 9.5 g: 1 mL. Set the oscillation parameters to 28℃, 15 mm, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0110] S8. Pretreatment extract 1, pretreatment extract 2 and pretreatment extract 3 are respectively sent to the sand filtration unit of the purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa to obtain purified extract 1, purified extract 2 and purified extract 3.

[0111] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and freeze-dried to semi-solid state at -60℃ and 10Pa. Then, the purified extract 1, purified extract 2 and purified extract 3 were concentrated to 10mg / L using a nitrogen blow concentrator with a nitrogen flow rate of 5mL / min. The concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0112] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0113] Comparative Example 5:

[0114] S1. Aeolian erosion product samples were selected from the sandy aeolian erosion area in northern my country. The collection depth was 1 cm. After removing obvious impurities such as stones and plant residues, the samples were sealed and stored in a refrigerator at 4℃ for later use. The basic properties of the samples were: sand content 85%, total organic carbon content 3.2 g / kg, DOC content 0.15 g / kg, LOC content 0.8 g / kg, and MAOC content 2.25 g / kg.

[0115] S2. Add 100g of wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration parameters of the gradient sieving module to 5mm amplitude, 30Hz frequency and 5min time. After being classified by three-stage sieves with apertures of 2mm, 0.25mm and 0.053mm, collect carbon-containing components with a particle size ≤0.053mm, record them as pre-treated sample A and enter the low temperature grinding module.

[0116] S3. Set the temperature of the low-temperature grinding module to -25℃, grind the sieved material for 3 minutes at a grinding speed of 150 rpm, and obtain pretreated sample B with a particle size ≤ 0.075 mm.

[0117] S4. Mix 700g of anhydrous sodium iodide, 0.1g of sodium thiosulfate pentahydrate and 1000g of deionized water to obtain modified sodium iodide density solution. Send the pretreated sample B into the density solution pre-separation module, add the modified sodium iodide density solution, and the volume ratio of pretreated sample B to modified sodium iodide density solution is 1g:9mL. Stir at 30rpm for 8min, let stand and settle for 20min, and then separate through a 0.45μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

[0118] S5. Send the pretreated sample C into the first light-proof oscillation unit of the fractionation extraction module, add ultrapure water, and the ratio of pretreated sample C to ultrapure water is 1g:9.5mL. Set the oscillation parameters to 18℃, 15mm amplitude, and 60Hz. After oscillation in the dark for 24h, solid-liquid separation is performed to obtain pretreated extract 1 and residue A.

[0119] S6. Transfer residue A to the second group of light-protected oscillation units, add potassium chloride aqueous solution with a concentration of 1 mol / L, and the mass ratio of residue A to potassium chloride aqueous solution is 7.7 g: 1 mL. Set the oscillation parameters to 18℃, 15 mm amplitude, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is obtained to get pretreated extract 2 and residue B.

[0120] S7. Transfer residue B to the third group of light-protected oscillation unit, add solution C, which is obtained by mixing 0.1 mol / L sodium hydroxide aqueous solution and 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution. The mass ratio of residue B to solution C is 9.5 g: 1 mL. Set the oscillation parameters to 28℃, 15 mm, and 60 Hz. After oscillation in the dark for 24 h, solid-liquid separation is performed to obtain pretreated extract 3 and residue C.

[0121] S8. Pretreated extract 1, pretreated extract 2 and pretreated extract 3 were respectively sent to the sand filtration unit of the multi-stage purification module and filtered through a 0.22μm polytetrafluoroethylene filter membrane at a pressure of 0.1MPa. Then, the extracts were passed through a 732 type cation exchange resin with a column height of 15cm and the flow rate was set to 1mL / min for ion purification. Then, they were transferred to a vacuum dialysis bag with a molecular weight cutoff of 800Da and dialyzed for 12h. The dialysate was ultrapure water and the dialysate was changed 3 times during the period to remove salt residue in the extracts, resulting in purified extract 1, purified extract 2 and purified extract 3.

[0122] S9. The purified extract 1, purified extract 2 and purified extract 3 were respectively sent to the freeze concentration module and concentrated by freeze drying at -60℃ and 10Pa. The purified extract 1, purified extract 2 and purified extract 3 were concentrated to 10mg / L respectively, and the concentrated extract 1, concentrated extract 2 and concentrated extract 3 were collected.

[0123] S10. Conduct detection and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3. Waste liquid generated during sample pretreatment and multi-stage matrix purification is collected through waste liquid recovery pipeline, filtered to remove impurities, neutralized with acid and alkali until it meets the standards and then discharged.

[0124] Performance testing:

[0125] After the wind erosion product samples were subjected to graded extraction in Examples 1-3 and Comparative Examples 1-5, the extraction rates of each group of pretreated extract 1, pretreated extract 2 and pretreated extract 3 were detected by an elemental analyzer.

[0126] After the wind erosion product samples were purified by the matrices in Examples 1-3 and Comparative Examples 1-5, the total residual amount of sand particles, the total concentration of iron ions, the total concentration of calcium ions, and the total residual amount of salt in each group of purified extract 1, purified extract 2, and purified extract 3 were measured.

[0127] After being frozen concentrated and collected in Examples 1-3 and Comparative Examples 1-5, the wind erosion product samples were analyzed by gas chromatography-mass spectrometry for each group of concentrated extract 1, concentrated extract 2 and concentrated extract 3, and the relative standard deviation (RSD) of each group was recorded.

[0128] Table 1. Summary of experimental data from Examples 1-3 and Comparative Examples 1-5

[0129]

[0130] Table 2 Summary of experimental data from Examples 1-3 and Comparative Examples 1-5

[0131]

[0132] Table 3 Summary of experimental data from Examples 1-3 and Comparative Examples 1-5

[0133]

[0134] Data Analysis:

[0135] As can be seen from Tables 1-3, the soil organic carbon graded extraction and matrix purification method of this invention has strong compatibility with wind erosion products, high extraction efficiency, and high extraction purity. This is likely because this invention employs a combined technology of "gradient sieving-low temperature grinding-density liquid pre-separation" through sample pretreatment, graded extraction, multi-stage matrix purification, freeze concentration and collection, and post-processing. This technology precisely adapts to the characteristics of wind erosion products, which have many sand particles and are prone to oxidation and loss of organic carbon, effectively reducing the carbon component loss rate and improving the sand particle removal rate. In the graded extraction, a three-stage extraction system of "active-semi-active-stable" is constructed. To address the low organic carbon content of wind erosion products, extraction reagents and conditions were optimized, thereby improving the extraction efficiency of organic carbon and meeting the detection requirements for different active organic carbon components in carbon cycle research in wind erosion areas. Multi-stage matrix purification enabled the stepwise removal of sand particles, metal ions, and salt residues, significantly improving the purity of the extract. In contrast, Comparative Example 1, due to the lack of gradient sieving and low-temperature grinding, failed to achieve homogenization of the initial fractionation of sand particles and carbon components, thus affecting the extraction efficiency of organic carbon. Furthermore, the organic carbon underwent oxidative decomposition at this temperature, easily leading to carbon component loss due to mechanical heat, which adversely affected subsequent processing. In Comparative Example 2, replacing the "modified sodium iodide density solution" with "sodium iodide density solution with a density of 1.8 g / cm³" resulted in a decrease in the extraction rate because the iodide ions in sodium iodide are easily oxidized by air to elemental iodine, which is highly toxic and causes chemical interference with the organic carbon components. In Comparative Example 3, changing the ratio of the extraction reagent to the extracted component and the composition of the extraction reagent also led to a decrease in the extraction rate. This is because the organic carbon content of wind erosion products is low, requiring a larger volume of ultrapure water to ensure accurate DOC extraction. The low concentration of potassium chloride aqueous solution lacks sufficient ionic strength to effectively extract DOC. Desorption of moderately bound LOCs resulted in a low extraction rate. EDTA, as a chelating agent, can break the bonds between minerals and organic carbon, improve the extraction efficiency of MAOCs, avoid damage to the MAOC structure, and achieve efficient extraction of stable organic carbons. In Comparative Example 4, due to the lack of multi-stage matrix purification, the residual metal ions and salts in the extract could not be completely removed, which also affected the relative standard deviation (RSD). In Comparative Example 5, due to the use of only freeze-drying technology, it was difficult to accurately control the actual concentration of the concentrated extract, resulting in an increased organic carbon volatilization loss rate and an increased relative standard deviation (RSD).

[0136] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0137] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for graded extraction and matrix purification of soil organic carbon from wind erosion products, characterized in that, Includes the following steps: Step S1. Sample pretreatment: The wind erosion product sample is added to the wind erosion product integrated device through the sample feeding module, and is pretreated by gradient sieving, low temperature grinding and density liquid pretreatment to obtain pretreated sample C; Step S2. Fractional extraction: The pretreated sample C is sent into the fractional extraction module to extract active organic carbon (DOC), semi-active organic carbon (LOC), and stable organic carbon (MAOC) in sequence, to obtain pretreated extract 1, pretreated extract 2, and pretreated extract 3, respectively. Step S3. Multi-stage matrix purification: Pretreated extract 1, pretreated extract 2 and pretreated extract 3 are respectively sent to the sand filtration unit of the multi-stage purification module. After filtration, they are passed through a cation exchange resin column for ion purification, and then transferred to a vacuum dialysis bag to remove salt residue, to obtain purified extract 1, purified extract 2 and purified extract 3. Step S4. Freeze concentration and collection: Purified extract 1, purified extract 2 and purified extract 3 are respectively sent to the freeze concentration module, freeze-dried to semi-solid state, and then concentrated and collected using a nitrogen blower to obtain concentrated extract 1, concentrated extract 2 and concentrated extract 3. Step S5. Post-processing: Conduct testing and analysis on concentrated extract 1, concentrated extract 2 and concentrated extract 3, and collect the waste liquid generated in sample pretreatment and multi-stage matrix purification through the waste liquid recovery pipeline, filter out impurities, neutralize acid and alkali until it meets the standards and then discharge it. The hierarchical extraction includes the following steps: Step B1. Send the pretreated sample C into the first group of light-proof oscillation units of the fractionation extraction module, add solution A, set the oscillation parameters to a temperature of 18-23℃, an amplitude of 15-20mm, and a frequency of 60-80Hz, and oscillate in the dark for 24h. After solid-liquid separation, the pretreated extract 1 and residue A are obtained. Step B2. Transfer residue A to the second group of light-proof oscillation units, add solution B, set the oscillation parameters to temperature of 18-23℃, amplitude of 15-20mm, and frequency of 60-80Hz, and oscillate in the dark for 24h. After solid-liquid separation, pretreated extract 2 and residue B are obtained. Step B3. Transfer the residue B to the third group of light-proof oscillation units, add solution C, set the oscillation parameters to a temperature of 28-32℃, an amplitude of 15-20mm, and a frequency of 60-80Hz, and oscillate in the dark for 24h. After solid-liquid separation, the pretreated extract 3 and residue C are obtained. Solution A mentioned in step B1 is ultrapure water; The ratio of the amount of pretreated sample C to solution A is 1g:9.5-10.3mL; Solution B mentioned in step B2 is an aqueous solution of potassium chloride with a concentration of 1 mol / L; The mass ratio of residue A to solution B is 7.7-8 g: 1 mL; Solution C in step B3 is obtained by mixing a 0.1 mol / L sodium hydroxide aqueous solution and a 0.01 mol / L disodium ethylenediaminetetraacetate aqueous solution; The mass ratio of residue B to solution C is 9.5-10.5 g: 1 mL.

2. The method for graded extraction and matrix purification of soil organic carbon from wind erosion products according to claim 1, characterized in that, The sample pretreatment includes the following steps: Step A1. Add the wind erosion product sample to the wind erosion product integrated device through the sample feeding module, and set the vibration sieve parameters of the gradient sieve module. After being classified by three-stage sieves, collect the material under the sieve, record it as pre-treated sample A, and enter the low-temperature grinding module. Step A2. Set the freezing parameters of the low-temperature grinding module. Grind the sieved material at a grinding speed of 150-200 rpm for 3-5 minutes to obtain pretreated sample B. Step A3. Send the pretreated sample B into the density liquid pre-separation module, add density liquid, stir at a stirring speed of 30-50 rpm for 8-10 min, let it stand and settle for 20-25 min, then separate it through a 0.45 μm filter membrane to obtain the supernatant, which is recorded as pretreated sample C and sent to the fractionation extraction module.

3. The method for graded extraction and matrix purification of soil organic carbon from wind erosion products according to claim 2, characterized in that, The vibration parameters for the vibrating screen mentioned in step A1 are: amplitude of 5-10 mm, frequency of 30-50 Hz, and time of 5-10 min. The apertures of the three-stage sieves are 2 mm, 0.25 mm, and 0.053 mm, respectively. The particle size of the pretreated sample B described in step A2 is ≤0.075 mm; The temperature of the cryogenic grinding module is -25 to 20°C.

4. The method for graded extraction and matrix purification of soil organic carbon from wind erosion products according to claim 2, characterized in that, The density liquid mentioned in step A3 is a modified sodium iodide density liquid; The modified sodium iodide density solution comprises the following raw materials in parts by weight: 700-800 parts anhydrous sodium iodide, 0.1-0.5 parts sodium thiosulfate pentahydrate, and 1000-1150 parts deionized water; The ratio of the amount of pretreated sample B to the amount of modified sodium iodide density solution is 1g:9-11mL.

5. The method for graded extraction and matrix purification of soil organic carbon from wind erosion products according to claim 1, characterized in that, The multi-stage matrix purification includes the following steps: Pretreated extract 1, pretreated extract 2, and pretreated extract 3 were respectively fed into the sand filtration unit of the multi-stage purification module and filtered through a 0.22 μm polytetrafluoroethylene (PTFE) membrane at a pressure of 0.1-0.2 MPa. Subsequently, the extracts were passed through a 15 cm high 732 type cation exchange resin column at a flow rate of 1-2 mL / min for ion purification. Then, they were transferred to a vacuum dialysis bag with a molecular weight cutoff of 800-1000 Da and dialyzed for 12-24 h with ultrapure water as the dialysate. The dialysate was replaced 3 times during the process to remove residual salts in the extracts, resulting in purified extract 1, purified extract 2, and purified extract 3.

6. The method for graded extraction and matrix purification of soil organic carbon from wind erosion products according to claim 1, characterized in that, The cryogenic concentration and collection process includes the following steps: Purified extract 1, purified extract 2, and purified extract 3 were respectively fed into a freeze-drying module and freeze-dried to a semi-solid state at -60 to -50℃ and 10 to -20 Pa. Then, purified extract 1, purified extract 2, and purified extract 3 were concentrated to 10 to 50 mg / L using a nitrogen blow-drying concentrator with a nitrogen flow rate of 5 to 10 mL / min. The concentrated extracts 1, concentrated extract 2, and concentrated extract 3 were collected.

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