Method for separating and recycling soil colloid and representing occurrence characteristics of soil colloid

Abstract

The invention provides a method for separating and recycling soil colloids and characterizing the occurrence characteristics of the soil colloids. The method comprises the following steps: injecting a sample into a separation channel, and applying a carrier flow, a cross flow and a focused flow. And stopping applying the focusing flow, continuously applying the carrying flow and the cross flow, pushing the sample to move towards the detector and adjusting the flow speed of the cross flow so as to separate colloidal particles with different sizes. And adjusting the flow velocity of the carrier current so that the flow velocity of the colloidal particles reaching the detector is constant. The organic components and inorganic element distribution of colloid particles with different sizes are quantitatively detected by combining a plurality of detectors, and the occurrence characteristics of the soil colloid are obtained. According to the determination method disclosed by the invention, the soil colloid extracted from the soil can be separated without pre-treating the sample, and inorganic elements and organic components can be detected. According to the invention, the interference of complex background substances in the soil colloid sample on the determination result is eliminated, and the sample detection resolution is improved. And various instruments are combined for characterization, so that the occurrence characteristics of the soil colloid can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of soil chemistry, and in particular to a method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids. Background Art

[0002] Soil colloids refer to soil particles with diameters in the range of 1 - 1000 nm, which are the smallest particle size part in the soil solid phase, including inorganic colloids such as clay minerals, metal elements and oxides, organic colloids such as carbohydrates and humus, and biological colloids such as bacteria, viruses and protozoa. Soil colloids have a large specific surface area and special size effects, and are the most active part in the soil. They can adsorb and complex pollutants and affect the diffusion and migration of pollutants in the soil as carriers of pollutant migration. The elemental composition and environmental behavior of soil colloids vary with particle size, and the adsorption, complexation and co-migration effects of soil colloids on pollutants are also affected. Therefore, quantitative analysis of the elemental composition of soil colloids with different particle sizes is the key to characterizing the occurrence characteristics of soil colloids.

[0003] Currently, the main quantitative methods for the elemental composition of soil colloids with different particle sizes are as follows: First, soil colloids are divided into different particle size intervals, such as less than 100 nm, 100 - 200 nm, 200 - 450 nm and 450 - 1000 nm, by methods such as filtration and centrifugation. Then, the samples in different particle size intervals are digested, and the elements therein are measured. Patent CN118603706A discloses a method for quantitatively analyzing boron in soil colloids by centrifugal separation and isotope determination. This method separates samples in three particle size intervals of 2 - 0.45 μm, 0.45 - 0.2 μm and less than 0.2 μm. After purification, the boron concentration and boron isotope composition in the samples are measured by a multi-collector inductively coupled plasma mass spectrometer, i.e., MC-ICP-MS. However, this method has complex operations, and the obtained results are only the average values of the elemental composition within the particle size interval, and it is easy to produce errors in the actual application of centrifugal separation of different particle size intervals.

[0004] Single particle inductively coupled plasma mass spectrometry, i.e., spICP-MS, provides a method for simultaneously determining the particle size and elemental composition of particles. This method does not require prior separation of soil colloids in different particle size ranges. By simply diluting the sample, it is possible to simultaneously determine the particle size, concentration, and elemental composition of the particles. Soil colloid suspensions usually contain other background substances in addition to the colloids, such as colloidal dissolution products. When measured by spICP-MS, the substances outside the colloidal particles are also ionized, and signals of both the substances outside the colloidal particles and the target colloidal particles are detected in the ion detector. Therefore, the distinction between the signals of the target colloidal particles and the background substances is an important control factor affecting the accuracy of the spICP-MS detection results. To improve the detection accuracy of spICP-MS, CN111105979A discloses a method for improving the detection accuracy of spICP-MS by identifying the intersection points of the ion signals, i.e., the background components, and the particle signals, i.e., the target particles, in the signal distribution and setting the particle detection threshold. The optimization of the algorithm may have good accuracy for the detection of simple artificial nanocolloid materials, but it is difficult to determine the detection threshold of soil colloids containing complex matrices extracted from soil, which may cause errors in the determination of the elemental composition and concentration of soil colloids by spICP-MS.

[0005] Therefore, there is a need for a method that can exclude the interference of complex background substances in soil colloid samples on the measurement results, non-destructively separate soil colloids, and characterize the occurrence characteristics of soil colloids without pretreatment. Summary of the Invention

[0006] To overcome the problems existing in the related art, the purpose of the present invention is to provide a method for separating, recovering soil colloids and characterizing the occurrence characteristics of soil colloids. This method can exclude the interference of complex background substances in soil colloid samples on the measurement results, non-destructively separate soil colloids, and characterize the occurrence characteristics of soil colloids without pretreatment.

[0007] A method for separating, recovering soil colloids and characterizing the occurrence characteristics of soil colloids includes: S1: Inject the sample into the separation channel, apply a carrier flow, a cross flow, and a focusing flow to remove the dissolved substances in the sample and focus the colloidal particles; wherein, the direction of the focusing flow is opposite to the direction of the carrier flow; S2: Stop applying the focusing flow, continuously apply the carrier flow and the cross flow, push the sample towards the detector and adjust the flow rate of the cross flow to separate colloidal particles of different sizes; S3: Adjust the flow rate of the carrier flow so that the flow rate of the colloidal particles reaching the detector is constant; S4: Combine multiple detectors to quantitatively detect the organic components and the inorganic element distribution of the colloidal particles of different sizes to obtain the occurrence characteristics of the soil colloids.

[0008] In a preferred technical solution of the present invention, in step S2, pushing the sample towards the detector and adjusting the flow rate of the cross-flow to separate colloidal particles of different sizes includes flowing the carrier to push the sample towards the detector, and the sample is distributed at different heights in the separation channel under the action of the cross-flow, and separating small-particle colloids and large-particle colloids under the laminar flow formed by the carrier flow in the separation channel.

[0009] In a preferred technical solution of the present invention, the small-particle colloids are distributed near the center of the separation channel, and the large-particle colloids are distributed near the channel membrane at the bottom of the channel.

[0010] In a preferred technical solution of the present invention, during the focusing process of step S1, the flow rate of the focusing flow is 2.7 mL / min, and the maximum injection volume of the sample is 20 mL.

[0011] In a preferred technical solution of the present invention, when adjusting the flow rate of the cross-flow to separate colloidal particles of different sizes in step S2, it also includes gradually reducing the flow rate of the cross-flow in a non-linear manner.

[0012] In a preferred technical solution of the present invention, in step S4, a plasma mass spectrometer is used at different separation times to detect the composition and concentration of inorganic elements of different particle size components; in combination with a multi-angle static light scattering detector, a differential refractive index detector, and an organic carbon detector, the organic carbon concentration and molecular weight of different particle size components are obtained.

[0013] In a preferred technical solution of the present invention, after obtaining the organic carbon concentration and molecular weight of different particle size components, it also includes recovering the separated colloidal particles according to particle size, and using a transmission electron microscope and an in-situ infrared spectrometer to detect the morphology and functional group composition of different particle size components.

[0014] In a preferred technical solution of the present invention, gradually reducing the flow rate of the cross-flow in a non-linear manner includes, within the first time period, using a power function flow with an exponent of 0.2 to reduce the flow rate of the cross-flow from 2.5 mL / min to 0.15 mL / min; within the second time period, using a power function flow with an exponent of 0.8 to reduce the flow rate of the cross-flow from 0.15 mL / min to 0 mL / min; wherein, the first time period is 20 min, and the second time period is 10 min.

[0015] In a preferred technical solution of the present invention, in step S3, adjusting the flow rate of the carrier flow to make the flow rate of the colloidal particles reaching the detector constant includes adjusting the flow rate of the carrier flow according to the flow rate of the cross-flow to fix the flow rate reaching the detector at 0.5 mL / min.

[0016] In a preferred technical solution of the present invention, after the flow rate of the cross flow is reduced to 0 mL / min, it further includes controlling the carrier flow to flow at a flow rate of 0.5 mL / min within a third time period, where the third time period is 22 min.

[0017] The beneficial effects of the present invention are as follows: A method for separating, recovering soil colloids and characterizing the occurrence characteristics of soil colloids provided by the present invention includes injecting a sample into a separation channel, applying a carrier flow, a cross flow and a focusing flow to remove dissolved substances in the sample and focus the colloidal particles. The separation channel is a flat rectangle, the flow field along the long axis direction of the channel is the carrier flow, the vertical force field perpendicular to the carrier flow direction is the cross flow, and the direction of the focusing flow is opposite to the direction of the carrier flow. Under the combined action of the carrier flow, the cross flow and the focusing flow, the colloidal particles are compressed into a narrow band, that is, the focusing band, ensuring that all components start to separate at the same position and improving the resolution. After the focusing process ends, the application of the focusing flow is stopped, the carrier flow and the cross flow are continuously applied, the sample is pushed towards the detector and the flow rate of the cross flow is adjusted. Different particle size components move along the long axis direction of the channel, thus forming a laminar flow. The small particle colloids have strong diffusion ability, are less affected by the cross flow, are distributed closer to the center of the channel, move faster and reach the detector earlier. The large particle colloids have weak diffusion ability, are more affected by the cross flow, are pushed towards the channel membrane at the bottom of the channel, move slower and reach the detector later, thereby separating colloidal particles of different sizes. The flow rate of the cross flow is reduced twice at different attenuation rates to improve the separation efficiency, and the flow rate of the carrier flow is adjusted according to the flow rate of the cross flow to ensure that the flow rates of different particle size components reaching the detector are constant. Combining a variety of detectors to quantitatively detect the organic components and inorganic element distributions of colloidal particles of different sizes to obtain the occurrence characteristics of soil colloids. Online coupling with an inductively coupled plasma mass spectrometer can obtain the inorganic element composition and concentration of samples with different separation times, that is, different particle sizes in real time. Coupling with a multi-angle static light scattering detector, a differential refractive index detector and an organic carbon detector to obtain the organic carbon concentration and molecular weight information of different particle size components. The measurement method of the present invention can separate the soil colloids extracted from the soil without pretreatment of the sample and detect inorganic elements and organic components. The focusing process during sample injection of the present invention separates different particle size components through three different flow fields, excluding the interference of complex background substances in the soil colloid sample on the measurement results and improving the sample detection resolution. The present invention separates and recovers soil colloids without damage, combines a variety of instruments for characterization, and can obtain the occurrence characteristics of soil colloids. Description of the Drawings

[0018] Figure 1 is a flowchart of the method for separating, recovering soil colloids and characterizing the occurrence characteristics of soil colloids of the present invention; Figure 2It is a result graph of separating and determining the inorganic element composition and concentration on each particle size of soil colloids by combining asymmetrical flow - field flow fractionation with ICP - MS according to the present invention; Figure 3 It is a result graph of separating and measuring the organic components of each particle size of soil colloids by combining asymmetrical flow - field flow fractionation with MALS, RI and OCD according to the present invention; Figure 4 It is a schematic diagram of regulating the flow rate of the cross - flow by using a power - function flow according to the present invention. Detailed implementation manners

[0019] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0020] Example 1 As Figure 1 shown, this example provides a method for separating, recovering soil colloids and characterizing the occurrence characteristics of soil colloids, including: S1: Inject the sample into the separation channel, apply the carrier flow, cross - flow and focusing flow to remove the dissolved substances in the sample and focus the colloidal particles; wherein, the direction of the focusing flow is opposite to the direction of the carrier flow.

[0021] S2: Stop applying the focusing flow, continuously apply the carrier flow and cross - flow, push the sample to move towards the detector and adjust the flow rate of the cross - flow to separate colloidal particles of different sizes.

[0022] S3: Adjust the flow rate of the carrier flow to make the flow rate of the colloidal particles reaching the detector constant.

[0023] S4: Combine multiple detectors to quantitatively detect the organic components and the distribution of inorganic elements of the colloidal particles of different sizes, and obtain the occurrence characteristics of soil colloids.

[0024] Asymmetrical Flow Field Flow Fractionation (AF4) was originally a technology applied to protein separation, with advantages such as a relatively mild separation method, little damage to the sample, and no problem of filler adsorption. AF4 realizes the separation of components with different particle sizes through the synergistic action of the carrier flow field along the long axis direction of the flat rectangular separation channel and the vertical force field perpendicular to the carrier flow direction, that is, the cross - field.

[0025] Before separation begins, focusing is first carried out. The sample is injected into the channel while applying a carrier flow, a cross flow, and a focusing flow. At this time, among all the samples injected into the channel, the dissolved, smaller molecular weight, and / or the part with a particle size smaller than the pore size of the channel membrane at the bottom of the channel is drawn out of the channel under the action of the cross flow. The channel membrane allows the solvent and small molecules to pass through and retains the sample to be measured. The colloidal particles are compressed into a narrow band, namely the focusing band, under the combined action of the three flows to ensure that all components start to be separated at the same position, thereby improving the resolution.

[0026] In this embodiment, the injection speed of the sample is set to 0.3 mL / min and the injection time is 10 min. The soil colloid extracted from the soil is directly injected into the separation channel, and the injection volume is adjusted according to the number of particles in the sample, with a maximum injection volume of 20 mL. During the focusing process in step S1, the flow rate of the focusing flow is 2.7 mL / min, and the maximum injection volume of the sample is 20 mL.

[0027] In step S4, at different separation times, an inductively coupled plasma mass spectrometer is used to detect the composition and concentration of inorganic elements of different particle size components; combined with a multi-angle static light scattering detector, a differential refractive index detector, and an organic carbon detector, the organic carbon concentration and molecular weight of different particle size components are obtained.

[0028] After obtaining the organic carbon concentration and molecular weight of different particle size components, it further includes recovering the separated colloidal particles according to particle size, and using a transmission electron microscope and an in-situ infrared spectrometer to detect the morphology and functional group composition of different particle size components.

[0029] When using asymmetric flow field-flow fractionation (AF4) to separate soil colloid samples, an inductively coupled plasma mass spectrometer (ICP-MS) is online coupled to obtain the composition and concentration of various inorganic elements of different particle size components at different separation times in real time. By coupling a multi-angle static light scattering detector (MALS), a differential refractive index detector (RI), and an organic carbon detector (OCD), the organic carbon concentration and molecular weight of different particle size components are obtained.

[0030] The OCD oxidizes the soil colloids of different particle sizes separated by AF4 in real time to determine the organic carbon concentration of the soil colloids of different particle sizes. AF4 separates the same soil colloid sample, and according to the peak time of the sample, the fractions in different particle size ranges after separation are recovered. A transmission electron microscope and an in-situ infrared spectrometer are used to characterize the fractions in different particle size ranges to further obtain the morphology and functional group composition of different particle size components of the soil colloid, so as to characterize the occurrence characteristics of the soil colloid.

[0031] A method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids provided by this embodiment includes injecting a sample into a separation channel, applying a carrier flow, a cross flow, and a focusing flow to remove dissolved substances in the sample and focus the colloidal particles. The separation channel is a flat rectangle. The flow field along the long axis of the channel is the carrier flow, the vertical force field perpendicular to the carrier flow direction is the cross flow, and the direction of the focusing flow is opposite to the direction of the carrier flow. Under the combined action of the carrier flow, the cross flow, and the focusing flow, the colloidal particles are compressed into a narrow band, i.e., the focusing band, to ensure that all components start to separate at the same position and improve the resolution. After the focusing process ends, the application of the focusing flow is stopped, the carrier flow and the cross flow are continuously applied, the sample is pushed towards the detector, and the flow rate of the cross flow is adjusted. Different particle size components move along the long axis of the channel, thus forming a laminar flow. The small particle colloids have strong diffusion ability, are less affected by the cross flow, are distributed closer to the center of the channel, move faster, and reach the detector earlier. The large particle colloids have weak diffusion ability, are more affected by the cross flow, are pushed towards the channel membrane at the bottom of the channel, move slower, and reach the detector later, thereby separating colloidal particles of different sizes. The flow rate of the cross flow is reduced twice at different attenuation rates to improve the separation efficiency, and the flow rate of the carrier flow is adjusted according to the flow rate of the cross flow to ensure that the flow rates of different particle size components reaching the detector are constant. Combining multiple detectors to quantitatively detect the organic components and the distribution of inorganic elements of colloidal particles of different sizes to obtain the occurrence characteristics of soil colloids. Online coupling with an inductively coupled plasma mass spectrometer can obtain the inorganic element composition and concentration of samples with different separation times, i.e., different particle sizes, in real time. Coupling with a multi-angle static light scattering detector, a differential refractive index detector, and an organic carbon detector to obtain the organic carbon concentration and molecular weight information of different particle size components. The measurement method of the present invention can separate the soil colloids extracted from the soil without pre-treating the sample and detect inorganic elements and organic components. The focusing process during sample injection of the present invention separates different particle size components through three different flow fields, eliminates the interference of complex background substances in the soil colloid sample on the measurement result, and improves the sample detection resolution. The present invention separates and recovers soil colloids without damage, combines multiple instruments for characterization, and can obtain the occurrence characteristics of soil colloids.

[0032] Example 2 This embodiment provides a method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids. On the basis of Embodiment 1, the differences from Embodiment 1 are described. The method includes: S1: Inject the sample into the separation channel, apply a carrier flow, a cross flow, and a focusing flow to remove dissolved substances in the sample and focus the colloidal particles; wherein, the direction of the focusing flow is opposite to the direction of the carrier flow.

[0033] S2: Stop applying the focusing flow, continuously apply the carrier flow and the cross flow, push the sample towards the detector, and adjust the flow rate of the cross flow to separate colloidal particles of different sizes.

[0034] S3: Adjust the flow rate of the current-carrying fluid so that the flow rate of the colloidal particles reaching the detector is constant.

[0035] S4: Combine multiple detectors to quantitatively detect the organic components and inorganic element distributions of the colloidal particles of different sizes, and obtain the occurrence characteristics of soil colloids.

[0036] In step S2, pushing the sample towards the detector and adjusting the flow rate of the cross-flow to separate colloidal particles of different sizes includes the current-carrying fluid pushing the sample towards the detector, and the sample is distributed at different heights in the separation channel under the action of the cross-flow. Under the laminar flow formed by the current-carrying fluid in the separation channel, small-particle colloids and large-particle colloids are separated.

[0037] The small-particle colloids are distributed close to the center of the separation channel, and the large-particle colloids are distributed close to the channel membrane at the bottom of the channel.

[0038] Laminar flow is a flow state of a fluid, referring to the fluid flowing in layers. When the fluid flows at a low speed in a pipe, it presents laminar flow, and the fluid particles move in a straight line along the direction parallel to the pipe axis. According to the boundary layer theory, the fluid velocity near the center of the channel is faster, and the fluid velocity near the channel boundary is slower. The diffusion ability of small-particle colloids is strong, less affected by the cross-flow, distributed closer to the center of the channel, with a fast moving speed and reaching the detector earlier. The diffusion ability of large-particle colloids is weak, more affected by the cross-flow, the large-particle colloids are pushed near the channel membrane at the bottom of the channel, with a slow moving speed and reaching the detector later.

[0039] When adjusting the flow rate of the cross-flow to separate colloidal particles of different sizes in step S2, it also includes gradually reducing the flow rate of the cross-flow in a non-linear manner.

[0040] Gradually reducing the flow rate of the cross-flow in a non-linear manner includes, after the focusing ends, within the first time period, using a power function flow with an exponent of 0.2 to reduce the flow rate of the cross-flow from 2.5 mL / min to 0.15 mL / min; within the second time period, using a power function flow with an exponent of 0.8 to reduce the flow rate of the cross-flow from 0.15 mL / min to 0 mL / min; where the first time period is 20 min and the second time period is 10 min.

[0041] The method of using power function flow is an adjustment made for the sample, which can reduce the time used to separate components of different particle sizes, and laminar flow exists throughout the separation channel. As Figure 4As shown, the blue part is the injection time, and the red part is the change time of the cross-flow. In the time range of 10 - 30 minutes, the cross-flow decreases in the form of a power function with an exponent of 0.2. The cross-flow changes rapidly during this period because the previous linear decrease showed that small particle size fractions began to appear approximately when the cross-flow was 1 mL / min. To save time, the cross-flow was decreased rapidly.

[0042] In the time range of 30 - 40 minutes, the cross-flow changes relatively slowly to extend the time for large particle size samples to reach the detector. Compared with the linearly changing cross-flow in this embodiment with a power function form, small particle size samples reach the detector earlier, and large particle size samples reach the detector later, improving the resolution of asymmetric flow - field flow fractionation for sample separation.

[0043] During the process of field flow fractionation, the flow rate of colloidal particles reaching the detector = carrier flow rate + focusing flow rate - cross-flow rate. In this embodiment, when adjusting the cross-flow rate, the instrument system will synchronously adjust the carrier flow rate and the focusing flow rate to keep the flow rate of colloidal particles reaching the detector constant.

[0044] When adjusting the cross-flow rate to separate colloidal particles of different sizes in step S2 of this embodiment, it also includes gradually reducing the cross-flow rate in a non-linear manner. At 10 - 30 minutes, the cross-flow decreases in the form of a power function with an exponent of 0.2. The cross-flow changes rapidly during this period because the previous linear decrease showed that small particle size fractions began to appear approximately when the cross-flow was 1 mL / min. To save time, the cross-flow was decreased rapidly. At 30 - 40 minutes, the cross-flow changes relatively slowly to extend the time for large particle size samples to reach the detector. Compared with the linearly changing cross-flow in this embodiment with a power function form, small particle size samples reach the detector earlier, and large particle size samples reach the detector later, improving the resolution of asymmetric flow - field flow fractionation for sample separation.

[0045] Example 3 This embodiment provides a method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids. Based on Example 1, this embodiment describes the differences from Example 1. The method includes: S1: Inject the sample into the separation channel, apply the carrier flow, cross-flow, and focusing flow to remove dissolved substances in the sample and focus the colloidal particles; wherein, the direction of the focusing flow is opposite to the direction of the carrier flow.

[0046] S2: Stop applying the focusing flow, continuously apply the carrier flow and cross-flow, push the sample towards the detector, and adjust the cross-flow rate to separate colloidal particles of different sizes.

[0047] S3: Adjust the flow rate of the carrier current so that the flow rate of the colloidal particles reaching the detector is constant.

[0048] S4: Combine multiple detectors to quantitatively detect the organic components and the distribution of inorganic elements of the colloidal particles of different sizes, and obtain the occurrence characteristics of soil colloids.

[0049] When adjusting the flow rate of the cross-flow to separate colloidal particles of different sizes in step S2, it further includes gradually reducing the flow rate of the cross-flow in a non-linear manner.

[0050] The gradually reducing the flow rate of the cross-flow in a non-linear manner includes, within the first time period, reducing the flow rate of the cross-flow from 2.5 mL / min to 0.15 mL / min using a power function flow with an exponent of 0.2; within the second time period, reducing the flow rate of the cross-flow from 0.15 mL / min to 0 mL / min using a power function flow with an exponent of 0.8; wherein, the first time period is 20 min and the second time period is 10 min.

[0051] In step S3, the adjusting the flow rate of the carrier current so that the flow rate of the colloidal particles reaching the detector is constant includes adjusting the flow rate of the carrier current according to the flow rate of the cross-flow to fix the flow rate reaching the detector at 0.5 mL / min.

[0052] After the flow rate of the cross-flow is reduced to 0 mL / min, it further includes controlling the carrier current to flow at a flow rate of 0.5 mL / min within the third time period, wherein the third time period is 22 min, to ensure that all particles in the separation channel are eluted, and a better soil colloid separation effect is achieved through the above method.

[0053] Couple a multi-angle static light scattering detector MALS, a differential refractive index detector RI and an organic carbon detector OCD to obtain the organic carbon concentration and molecular weight of different particle size fractions. The OCD measures the organic carbon concentration of soil colloids of different particle sizes by real-time oxidation of the soil colloids of different particle sizes separated by AF4.

[0054] MALS and RI use the Zimm equation to calculate the molecular weight information of the organic matter: ; ; wherein, R(θ) is the Rayleigh ratio at the scattering angle θ, K is the optical constant, n0 is the refractive index of the solvent, λ is the wavelength of the incident light, N A is the Avogadro constant, c is the organic carbon concentration, A2 is the second virial coefficient, and the second virial coefficient is used to reflect the interaction between molecules;

[0055] is the radius of gyration, which is used to reflect the molecular size. When θ approaches 0 and c approaches 0, the intercept is , is the refractive index increment, which is obtained by RI measurement. MALS measures R(θ) and the radius of gyration at different incident light angles .

[0056] During instrument calibration, the optical constant K is determined by a standard sample. Combining the results of OCD, the is deduced through the results of AF4-MALS-RI, that is, the reciprocal of the molecular weight of soil colloids with different particle sizes. At the same time, the soil colloid organic carbon concentration and molecular weight of different particle size components after AF4 separation are obtained.

[0057] Figure 2 is the result diagram of the separation and determination of the inorganic element composition and concentration on each particle size of soil colloids by the combination of asymmetric flow-field flow fractionation and ICP-MS in the present invention, Figure 3 is the result diagram of the separation and measurement of the organic components of soil colloids on each particle size by the combination of asymmetric flow-field flow fractionation and MALS, RI and OCD in the present invention. As can be seen from Figure 2 , there are two peaks for various inorganic elements. One concentration peak is located near 5 nm, and the other concentration peak is located between 250 - 500 nm. The waveforms of the first group of inorganic elements Fe, Si and Al are similar, and the first group of inorganic elements has a relatively large concentration near 5 nm and also a relatively large concentration between 250 - 500 nm. P is not detected in each component of this sample; the waveforms of the second group of inorganic elements Mn, Ca and Mg are similar, and among the second group of inorganic elements, Mg has a relatively large concentration near 5 nm, while the concentrations of Mn and Ca are much smaller than that of Mg, and the concentrations of Mn, Ca and Mg are relatively small between 250 - 500 nm; the waveforms of the third group of inorganic elements La, Gd and Yb are similar, the waveforms of the fourth group of inorganic elements Ce, Pr and Nd are similar, and the waveforms of the fifth group of inorganic elements Sm, Eu and Tb are similar; the waveforms of the sixth group of inorganic elements Dy, Ho and Er are similar, and the sixth group of inorganic elements has a relatively concentrated concentration distribution near 5 nm and a relatively dispersed concentration distribution between 250 - 500 nm.

[0058] Figure 3 The MALS results and OCD results in are read by converting the instrument into an electrical signal. According to the external standard curve method, the OCD results are converted into concentration units, and the units of both MALS results and OCD results are volts. Figure 3 The MALS intensity in has two peaks. The first peak is located near 5 nm, and the second peak is located between 250 - 500 nm. The MALS intensity in other intervals outside the peaks is close to 0. Figure 3The OCD in [it] has multiple peaks, where the first peak is located near 5 nm, the second peak is between 70 - 250 nm, and the third peak is between 250 - 500 nm.

[0059] In this embodiment, the flow rate of the cross-flow is gradually reduced in a non-linear manner, including that within the first time period, the flow rate of the cross-flow is reduced from 2.5 mL / min to 0.15 mL / min using a power function flow with an exponent of 0.2; within the second time period, the flow rate of the cross-flow is reduced from 0.15 mL / min to 0 mL / min using a power function flow with an exponent of 0.8; where the first time period is 20 min and the second time period is 10 min. By adopting the form of exponential decay, the flow rate of the cross-flow can be adjusted faster. Samples with smaller particle sizes reach the detector earlier, and samples with larger particle sizes reach the detector later, improving the resolution of field flow for sample separation. Combining asymmetric flow-field flow fractionation and inductively coupled plasma mass spectrometry, the composition and concentration of inorganic elements in different particle size components of soil colloids can be obtained. Combining asymmetric flow-field flow fractionation, a multi-angle static light scattering detector, a differential refractive index detector, and an organic carbon detector, the molecular weight of organic carbon and the concentration of organic carbon in each particle size component of soil colloids can be measured.

[0060] It should be noted that in this article, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, apparatus, article or method including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, apparatus, article or method. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, apparatus, article or method including that element.

[0061] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structural or equivalent process transformation made using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, are equally included in the patent protection scope of the present application.

Claims

1. A method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids, characterized in that, Including: S1: Inject the sample into the separation channel, apply carrier flow, cross flow and focusing flow to remove dissolved substances in the sample and focus the colloidal particles; wherein, the direction of the focusing flow is opposite to the direction of the carrier flow. S2: Stop applying the focusing flow, continuously apply the carrier flow and cross flow, push the sample towards the detector and adjust the flow rate of the cross flow to separate colloidal particles of different sizes. S3: Adjust the flow rate of the carrier flow to make the flow rate of the colloidal particles reaching the detector constant. S4: Combine multiple detectors to quantitatively detect the organic components and inorganic element distribution of the colloidal particles of different sizes, and obtain the occurrence characteristics of soil colloids.

2. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 1, wherein In step S2, the pushing the sample towards the detector and adjusting the flow rate of the cross flow to separate colloidal particles of different sizes includes the carrier flow pushing the sample towards the detector, and the sample is distributed at different heights in the separation channel under the action of the cross flow, and the small particle colloids and large particle colloids are separated under the laminar flow formed by the carrier flow in the separation channel.

3. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 2, characterized in that, The small particle colloids are distributed near the center of the separation channel, and the large particle colloids are distributed near the channel membrane at the bottom of the separation channel.

4. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 1, wherein During the focusing process of step S1, the flow rate of the focusing flow is 2.7 mL / min, and the maximum injection volume of the sample is 20 mL.

5. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 1, wherein When adjusting the flow rate of the cross flow to separate colloidal particles of different sizes in step S2, it also includes gradually reducing the flow rate of the cross flow in a non-linear manner.

6. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 1, wherein In step S4, at different separation times, use an inductively coupled plasma mass spectrometer to detect the composition and concentration of inorganic elements in different particle size components; combine a multi-angle static light scattering detector, a differential refractive index detector and an organic carbon detector to obtain the organic carbon concentration and molecular weight of different particle size components.

7. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 6, characterized in that, After obtaining the organic carbon concentration and molecular weight of different particle size components, it also includes recovering the separated colloidal particles according to particle size, and using a transmission electron microscope and an in-situ infrared spectrometer to detect the morphology and functional group composition of different particle size components.

8. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 5, characterized in that, The gradually reducing the flow rate of the cross flow in a non-linear manner includes, within the first time period, using a power function flow with an exponent of 0.2 to reduce the flow rate of the cross flow from 2.5 mL / min to 0.15 mL / min; within the second time period, using a power function flow with an exponent of 0.8 to reduce the flow rate of the cross flow from 0.15 mL / min to 0 mL / min; wherein, the first time period is 20 min and the second time period is 10 min.

9. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 1, wherein In step S3, the adjusting the flow rate of the carrier flow to make the flow rate of the colloidal particles reaching the detector constant includes adjusting the flow rate of the carrier flow according to the flow rate of the cross flow to fix the flow rate reaching the detector at 0.5 mL / min.

10. The method for separating and recovering soil colloids and characterizing the occurrence characteristics of soil colloids according to claim 8, wherein After the flow rate of the cross flow is reduced to 0 mL / min, it also includes controlling the carrier flow to flow at a flow rate of 0.5 mL / min within the third time period, wherein the third time period is 22 min.

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