Method for characterizing particle size and composition of soil nanoparticles by asymmetric flow-field flow combined inductively coupled plasma mass spectrometry technology

Abstract

The invention provides a method for characterizing the particle size and composition of soil nanoparticles by an inductively coupled plasma mass spectrometry technology through asymmetric flow-field flow combination. The method comprises the following steps: S1, carrying out anaerobic environment pretreatment on an asymmetric flow field flow instrument; and S2, carrying out sample loading treatment on the soil nanoparticle suspension in an asymmetric flow field flow meter, and obtaining a characterization result after a sample injection stage, a flushing stage and a flushing stage. The application of the soil nanoparticles in the asymmetric flow field flow meter is researched and developed, the soil nanoparticles are separated and represented by adopting the asymmetric flow field flow meter combined with the ICP-MS method, and the method has the advantages of convenience in operation, simultaneous determination of multiple elements, simple pretreatment, small destructiveness, low detection limit and the like.

Description

Technical Field

[0001] The invention relates to a method for using an asymmetric flow field flow instrument, and in particular to a method for characterizing the particle size and composition of soil nanoparticles by using an asymmetric flow-field flow coupled inductively coupled plasma mass spectrometry technique. Background Art

[0002] Soil nanoparticles are a complex type of nanomaterials, including aluminosilicates (clay minerals), oxides and hydroxides of aluminum, iron and ions, enzymes, humus, viruses, and non-fixed colloids, with a much higher structural diversity and complexity than artificial nanomaterials. Most of the migration of nutrients, pollutants, organic matter and heavy metals occurs at the nanoscale, in or around nanoparticles.

[0003] At present, there is no method that can qualitatively and quantitatively characterize soil nanoparticles of various sizes, but there are a variety of known nanoparticle characterization methods, so they can be compared with existing nanoparticle characterization methods. Existing nanoparticle characterization methods include: Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

[0004] The transmission electron microscope has the resolution capability at the atomic level. It can not only observe the microscopic morphology of the sample, but also characterize the internal structure of the observed area. The principle of TEM is roughly that a high-voltage electron source releases high-speed electrons, which pass through a condenser system to form a parallel electron beam, which is incident on and passes through a local area of ​​the sample. The electron beam interacts with the soil nanoparticles and the sample modulates the phase and amplitude of the incident electron beam to form an outgoing electron beam. The outgoing electron beam passes through the objective lens system and converges on the focal plane of the objective lens to form a diffraction spot, which then propagates further downward to the objective lens image plane to form the first magnified image of the sample. The transmission electron microscope can study the size, shape and crystal structure at the single particle level.

[0005] Dynamic light scattering is a technique that measures the fluctuations in the intensity of scattered light from a sample to obtain information about the particle size of the sample. Because the molecules in the sample are constantly performing Brownian motion, this motion causes changes in the scattered light. The volatility of the scattered light over time is used to obtain the relevant equation, and then the average movement rate (Dt) of the particles in the sample is obtained, and finally the average hydrodynamic diameter is obtained. The particle size detection of the dynamic light scattering method has the advantages of being fast and simple, and has certain statistical significance, but because the scattered light intensity is proportional to the sixth power of the particle size, the scattering of large particles is relatively strong, so for a wide distribution sample, the average particle size result tends to be large particles. Therefore, DLS is suitable for particle size detection of monodisperse systems with a distribution that is not too wide, and the dynamic light scattering experiment is easily affected by dust or impurities, so sample filtration and centrifugation are very important.

[0006] Nanoparticle tracking analysis is a method of irradiating a solution of suspended particles with a beam of concentrated laser energy through a glass prism, and using chrome-plated glass to minimize background signals, thereby detecting the intensity of scattered light from each particle, observing the Brownian motion of nanoparticles in the solution, and taking images. By tracking and analyzing the Brownian motion of the particles, the particle size of the nanoparticles is calculated according to the Stokes-Einstein equation, and the concentration is obtained by the number of particles. Nanoparticle tracking analysis is more accurate than dynamic light scattering, but like dynamic light scattering, since particles will scatter light, the signals between particles will block each other, and the particle size will still tend to be large particles. In addition, due to the limitation of the limited shooting focal plane, the movement of the particles in three-dimensional space is actually presented as a two-dimensional motion trajectory on the instrument, so there will still be a certain deviation in the final result.

[0007] Inductively coupled plasma optical emission spectrometry uses the high temperature formed by ICP plasma to atomize or ionize the element to be tested, forming an excited state and generating a characteristic emission spectrum. By detecting the wavelength and intensity of the spectrum line, it can be determined whether the sample to be tested contains the element to be tested and its content. Although ICP-OES has been widely used, when trace elements encounter a high concentration of matrix, the element test will be significantly interfered, which is particularly serious for Ca, A1, and Fe.

[0008] Inductively coupled plasma mass spectrometry uses the high temperature formed by plasma to ionize an electron from most elements in the sample to form monovalent positive ions. The mass spectrometer screens the ions of different mass-to-charge ratios, allowing specific ions to pass through and reach the detector. It can detect a certain ion and its intensity, and then analyze and calculate the content of a certain element. ICP-MS can achieve simultaneous determination of multiple elements, and has the advantages of lower detection limit and higher precision compared to ICP-OES.

[0009] The existing transmission electron microscopy method may lead to a lack of overall statistical results due to the small amount of nanopowder used for electron microscopy observation; since the surface activity of nanoparticles is very high and they are easy to agglomerate, ultrasonic dispersion must be performed before dropping the sample; it is difficult to obtain accurate results for some nanoparticle samples that are not resistant to strong electron beam bombardment. In addition, the nanoparticles must be electron transparent and able to withstand the high vacuum and beam energy used in the characterization process. In particular, due to the presence of high-energy electron beams, sample damage is common.

[0010] In the existing dynamic light scattering method, since the scattered light intensity is proportional to the sixth power of the particle size, the scattering is stronger for large particles, resulting in that for samples with a wide distribution, the average particle size results will be biased towards large particles. The results may not be accurate or representative, and are easily affected by dust or impurities, which will increase the error of the results and increase the complexity and difficulty of the operation.

[0011] In the existing nanoparticle tracking analysis method, due to the light scattering of particles, the signals between particles will be blocked by each other, and the obtained particle size will tend to be large particles. In addition, due to the limitation of the limited shooting focal plane, the movement of particles in three-dimensional space is actually presented as a two-dimensional motion trajectory on the instrument, resulting in a certain deviation in the final result.

[0012] The existing inductively coupled plasma emission spectrometry has complex spectral lines, serious spectral interference, large sample requirements, and requires acidification and other pre-treatments when used alone, which destroys the sample structure.

[0013] The prior art inductively coupled plasma mass spectrometry is greatly affected by matrix effects and requires internal standard correction. It also has poor tolerance to the salt content in the analyzed sample, which is usually less than 0.2%.

[0014] In order to overcome the shortcomings of existing technologies such as complex operation, over-reliance on separation and extraction technology and relatively single characterization capabilities, and to achieve efficient separation and characterization of soil nanoparticles, this method uses an asymmetric flow field flow instrument (AF4, hereinafter referred to as field flow instrument) combined with ICP-MS to separate and characterize soil nanoparticles. It has the advantages of convenient operation, simultaneous determination of multiple elements, simple pretreatment, low destructiveness and low detection limit. Summary of the invention

[0015] The invention provides a method for characterizing the particle size and composition of soil nanoparticles by using an asymmetric flow-field flow coupled inductively coupled plasma mass spectrometry technique, so as to realize the use of soil nanoparticles in an asymmetric flow field flow instrument.

[0016] The present invention provides a method for characterizing the particle size and composition of soil nanoparticles by using an asymmetric flow-field flow coupled inductively coupled plasma mass spectrometry technique, comprising:

[0017] S1. Pre-treating the asymmetric flow field flow instrument in an oxygen-free environment;

[0018] S2. The soil nanoparticle suspension is loaded into an asymmetric flow field flow instrument, and the characterization results are obtained after the injection stage, the flushing stage and the rinsing stage.

[0019] Furthermore, the soil nanoparticle suspension to be tested also contains metal ions, and the metal ions are Fe 2 + , Fe 3+ , Cu 2+ 、Al 3+ One or more of .

[0020] Furthermore, the concentration of the metal ions is 100-400 μmol·L -1 .

[0021] Furthermore, the preparation method of the soil nanoparticle suspension to be tested is:

[0022] S101. 100-300mg·L -1 Soil nanoparticle suspension with 300-500 μmol·L -1 The pH of the nitrate metal ions was adjusted to 6.0;

[0023] S102. Mix the two solutions in a volume ratio of 1:1, and react with horizontal oscillation for 24 hours to obtain a sample to be tested.

[0024] Furthermore, the nitrate metal ion is specifically Cu(NO 3 ) 2 .

[0025] Furthermore, the horizontal oscillation reaction is specifically: reacting at 31° C. and 150 rpm for 24 hours.

[0026] Furthermore, the S1. pre-treating the asymmetric flow field flow instrument in an oxygen-free environment comprises:

[0027] Prepare 25 μM NaCl solution with oxygen-free water, select a low flow rate of 0.05 mL / min, and control the asymmetric flow field flow meter to run for 12-36 hours to ensure that the asymmetric flow field flow meter is an anaerobic environment.

[0028] Further, the S2. subjects the soil nanoparticle suspension to a sample loading process in an asymmetric flow field flow instrument, and after a sample loading stage, a flushing stage and a rinsing stage, obtains a characterization result, including:

[0029] S201. In the anaerobic workstation, take 2.5 mL of the soil nanoparticle suspension after 24 h of reaction into a 1 mL injection bottle for measurement;

[0030] S202. After the injection stage, the flushing stage and the rinsing stage, the characterization result is obtained.

[0031] Furthermore, the injection stage includes: taking the soil nanoparticle suspension in the injection bottle, setting the program of the asymmetric flow field flow instrument to a detector flow rate of 0.5 mL / min; during the focusing process: injection speed: 0.20 mL / min, injection time 5 min, injection volume: 200 μL, lateral flow rate: 1.00 mL / min, focusing pump: 1.3 mL / min.

[0032] Furthermore, the flushing stage includes: setting the elution process conditions as follows: (1) lateral flow rate 1.00 mL / min, mode constant, time 15 min; (2) lateral flow rate 1.00 mL / min, mode Power, Exponent 0.20, time 30 min; (3) lateral flow rate 0.05 mL / min, mode Power, Exponent 0.80, time 10 min; (4) lateral flow rate 0.00 mL / min, mode constant, time 30 min.

[0033] Compared with the prior art, the present invention develops a set of soil nanoparticles for use in an asymmetric flow field flow meter, and the asymmetric flow field flow meter can be used to effectively study and characterize the soil nanoparticles. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the AF4-UV curve change diagram before and after the reaction of soil nanoparticles with Cu2+;

[0035] Figure 2 The changes in component distribution at different particle sizes before and after the reaction of soil nanoparticles with Cu2+; (a) UV signal distribution before reaction; (b) UV signal distribution after reaction; (c) Fe and Cu mass spectrometry signal distribution before reaction; (d) Fe and Cu mass spectrometry signal distribution after reaction; (e) Al and Si mass spectrometry signal distribution before reaction; (f) Al and Si mass spectrometry signal distribution after reaction. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only embodiments of a part of the present invention, rather than all embodiments.

[0037] Asymmetric flow field instrument (Poatnova, AF2000MT, GERMAN), hereinafter referred to as field flow instrument. Field flow instrument separation involves an asymmetric flow field. Under the action of the asymmetric flow field force and the opposing diffusion field, the sample forms different equilibrium layers in the channel. In the injection stage, that is, before the separation begins, after the sample enters the channel from the injection port, it will be subjected to the same-direction cross-flow flow field force from the top of the channel. The pressure generated by the cross-flow will cause the colloidal particles of the sample to be retained on a dialysis membrane that can only pass small molecular solutes. At this time, the sample will diffuse in the vertical direction of the channel, and the diffusion coefficient depends on factors such as the size and density of different colloidal particles. Colloidal particles with large particle size or density have a small diffusion coefficient and gather in the lower part of the channel near the membrane, while those with smaller particle size or density will be close to the middle position of the channel space. At the same time, the sample will also be subjected to the focusing flow field force opposite to the elution direction. Under the combined action of the channel flow and the focusing flow, the sample will be gathered near the injection port, and only small molecular solutes can be eluted through the dialysis membrane. After the injection is completed, the flow rate of the focused flow returns to zero, and the colloidal particles are eluted with the channel flow and then flow to the detector. According to the boundary layer theory, for the fluid on the same cross-section in the channel, the fluid flow rate near the boundary is slower, and the fluid flow rate near the center of the channel is faster. The fluid flow rate is a parabolic streamline along the cross section. Therefore, smaller particles are flushed out first with the faster fluid and enter the detector first, while larger particles are flushed out one after another as the cross-flow gradually decreases.

[0038] Field flow instrument can be coupled with many detectors, such as ultraviolet-visible spectrophotometer (UV-vis), multi-angle static laser particle size analyzer (MALS), fluorescence detector, differential detector, ICP-MS, etc. Different characteristics of colloidal particles can be analyzed by different detectors, and then the colloidal particles can be detected, separated and characterized simultaneously online.

[0039] By combining field flow spectroscopy and ICP-OES, nanoparticles of different sizes can be separated and then their elemental composition and particle size can be characterized. The relationship between the particle size and elemental composition of nanoparticles can be explored, which has important reference value for the study of the environmental effects and biological toxicity of nanoparticles at the nanoscale.

[0040] Although ICP-MS can characterize the elemental composition of soil nanoparticles, the complex interactions between colloidal particles easily lead to their adsorption and aggregation to form colloidal particles of different sizes, which may have different elemental ratios and characteristics. Therefore, by combining field flow spectroscopy and ICP-MS, soil nanoparticles of different purity can be separated and then characterized for their elemental composition and particle size, so as to explore the relationship between the particle size and elemental composition of soil nanoparticles, which has important reference value for the study of the environmental effects and biological toxicity of nanoparticles at the nanoscale.

[0041] Specifically, the embodiments of the present invention are as follows:

[0042] Step 1. Add 200 mg·L -1 Soil nanoparticle suspension and 400 μmol·L -1 Cu(NO 3 ) 2 The pH of the solution was adjusted to 6.0, and then added into a 50 mL centrifuge tube at a volume ratio of 1:1 (20 mL each), mixed, and manually shaken and reacted with horizontal oscillation for 24 h (31 °C, 150 rpm);

[0043] Step 2. Before separation, prepare a 25 μM NaCl background solution with oxygen-free water and run it overnight at a low flow rate of 0.05 mL / min to ensure an anaerobic environment during separation.

[0044] Step 3. In the anaerobic workstation, take 2.5 mL of the sample after 24 hours of reaction into the 1 mL injection bottle of AF4 for measurement. The sample was separated using an asymmetric flow field instrument (AF2000MT, Postnova, Germany), and the operation method was set on the field flow instrument software. The operation method was divided into three steps, namely the injection stage, the flushing stage and the rinsing stage.

[0045] The parameters of the specific operation method are set as follows: detector flow rate 0.5mL / min. During the focusing process: injection speed: 0.20mL / min, injection time 5min, injection volume: 200μL, lateral flow rate: 1.00mL / min, focusing pump: 1.3mL / min. Elution process: (1) lateral flow rate 1.00mL / min, mode constant, time 15min. (2) lateral flow rate 1.00mL / min, mode Power, Exponent 0.20, time 30min. (3) lateral flow rate 0.05mL / min, mode Power, Exponent 0.80, time 10min. (4) lateral flow rate 0.00mL / min, mode constant, time 30min. The total running time for one sample is 90min.

[0046] The UV signal and mass spectrometry signal were obtained by combining UV-vis and inductively coupled plasma mass spectrometry (ICP-MS, NexION 350D, PerkinElmer, USA). The corresponding relationship between the elution time and the particle size was obtained by running the latex standard sample for calibration. The particle size distribution of the nanoparticles in the sample and the element signal intensity of Fe, Cu, Al, and Si were determined.

[0047] The present invention uses AF4-UV to analyze the soil nanoparticles and Cu 2+The UV signal in the suspension system changes with the effluent time before and after the reaction. The relationship between the effluent time and the particle size is corrected by running the latex standard sample, and then the particle size distribution characteristics of the soil nanoparticles and the particle size redistribution behavior after the reaction are semi-quantitatively determined. Figure 1 As shown in the figure, the initial state of soil nanoparticles before reaction has two absorption peaks of 1-20nm and 200-300nm, indicating that there are at least two types of nanoparticle components. 2+ After the reaction, the particle size distribution of soil nanoparticles changed significantly, and three absorption peaks appeared in the UV curve. According to the relatively independent relationship between the absorption peaks, it can be seen that there are particle components with three particle size ranges (20nm, 50nm, 300-400nm) in the system at the same time, and the original 200-300nm particle component before the reaction basically disappeared, and was replaced by a smaller particle size (50nm) and a larger particle size (300-400nm) particle component.

[0048] The AF4-UV-MALS-ICP-MS coupling technique further analyzed the distribution characteristics of the main elements such as Fe, Cu, Al, and Si in particle size, and then explored the main components of different particle size components of soil nanoparticles before and after the reaction. It should be emphasized that the ordinate of the distribution curve of the element with particle size here is the mass spectrometry signal intensity value (cps), which does not represent the actual concentration, so it only provides reference information on whether the element exists and the relative change of the element. Figure 2 As shown in the figure, before the reaction, Fe, Al, and Si mineral elements were distributed in both particle size components of soil nanoparticles, and were relatively more in 200-300 nm particles, while Cu was basically concentrated in the small particle size components; after the reaction, with the redistribution of particle size, the particle components also changed. Fe, Al, and Si were basically concentrated in the newly formed agglomerated particles, while the distribution of Cu did not change much.

[0049] The distribution of Cu is not strongly correlated with Fe, Al, and Si, and it tends to be distributed in small-size particle components (mainly organic components), indicating that Cu exists mainly in the form of combining with organic matter in soil nanoparticles, and has a weak relationship with minerals. The changes in Fe, Cu, Al, and Si after the reaction are basically consistent with the redistribution trend of particle size. Most of Fe, Al, and Si are concentrated in the 300-400nm particle components, which fully demonstrates that the stability of particles dominated by mineral components in soil nanoparticles is more susceptible to interference, resulting in agglomeration effects; and the distribution particle size of Cu increases slightly as the stability of the system deteriorates and the agglomeration increases, but overall it is still weakly correlated with the mineral components, further confirming that the distribution, adsorption, and binding of Cu in soil nanoparticles are dominated by organic components.

[0050] In summary, the present invention has the following beneficial effects:

[0051] 1. For the first time, an asymmetric flow field instrument was used in conjunction with inductively coupled plasma mass spectrometry to characterize soil nanoparticles, and good characterization results were obtained, which can be used as a means of separating and characterizing soil nanoparticles;

[0052] 2. Explore the field flow instrument method suitable for the sample, including axial flow velocity, cross flow velocity, injection time, flushing time, etc., to improve the elution and detection effect of the sample;

[0053] 3. Practice has proved that the method parameters of asymmetric flow field flow instrument are effective method parameters for separating colloidal particles and nanoparticles.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the specification of this application, the technicians can still modify or replace the specific implementation mode of the present invention with equivalents, but these modifications or changes do not deviate from the scope of protection of the pending claims of the present application.

Claims

1. A method for characterizing the particle size and composition of soil nanoparticles using asymmetric flow-field flow coupling inductively coupled plasma mass spectrometry, characterized in that: include: S1. Pre-treating the asymmetric flow field flow instrument in an oxygen-free environment; S2. The soil nanoparticle suspension is loaded into an asymmetric flow field flow instrument, and the characterization results are obtained after the injection stage, the flushing stage and the rinsing stage.

2. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 1, characterized in that: The soil nanoparticle suspension to be tested also contains metal ions, and the metal ions are Fe 2+ , Fe 3+ , Cu 2+ 、Al 3+ One or more of .

3. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 2, characterized in that: The concentration of the metal ion is 100-400 μmol·L -1 .

4. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 3, characterized in that: The preparation method of the soil nanoparticle suspension to be tested is: S101. 100-300mg·L -1 Soil nanoparticle suspension with 300-500 μmol·L -1 The pH of the nitrate metal ions was adjusted to 6.0; S102. Mix the two solutions in a volume ratio of 1:1, and react with horizontal oscillation for 24 hours to obtain a sample to be tested.

5. The method for characterizing the particle size and composition of soil nanoparticles using asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 4, characterized in that: The nitrate metal ion is specifically Cu(NO3)2.

6. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 4, characterized in that: The horizontal oscillation reaction is specifically: reacting at 31° C. and 150 rpm for 24 hours.

7. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chromatographic inductively coupled plasma mass spectrometry according to claim 1, characterized in that: S1. performing oxygen-free environment pretreatment on the asymmetric flow field flow instrument, comprising: Prepare 25 μM NaCl solution with oxygen-free water, select a low flow rate of 0.05 mL / min, and control the asymmetric flow field flow meter to run for 12-36 hours to ensure that the asymmetric flow field flow meter is an anaerobic environment.

8. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 1, characterized in that: S2. The soil nanoparticle suspension is subjected to sample treatment in an asymmetric flow field flow instrument, and after a sample injection stage, a flushing stage and a rinsing stage, a characterization result is obtained, including: S201. In the anaerobic workstation, take 2.5 mL of the soil nanoparticle suspension after 24 h of reaction into a 1 mL injection bottle for measurement; S202. After the injection stage, the flushing stage and the rinsing stage, the characterization result is obtained.

9. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chemistry and inductively coupled plasma mass spectrometry according to claim 8, characterized in that: The injection stage includes: taking a soil nanoparticle suspension in an injection bottle, setting the program of the asymmetric flow field flow instrument to a detector flow rate of 0.5 mL / min; during the focusing process: injection speed: 0.20 mL / min, injection time 5 min, injection volume: 200 μL, lateral flow rate: 1.00 mL / min, focusing pump: 1.3 mL / min.

10. The method for characterizing the particle size and composition of soil nanoparticles by asymmetric flow-field flow chromatographic inductively coupled plasma mass spectrometry according to claim 9, characterized in that: The flushing stage includes: setting the elution process conditions as follows: (1) lateral flow rate 1.00 mL / min, mode constant, time 15 min; (2) lateral flow rate 1.00 mL / min, mode Power, Exponent 0.20, time 30 min; (3) lateral flow rate 0.05 mL / min, mode Power, Exponent 0.80, time 10 min; (4) lateral flow rate 0.00 mL / min, mode constant, time 30 min.

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