Method for directly measuring silicon dioxide in soil through medium and low temperature alkali fusion-ICP-OES

Abstract

The invention provides a method for directly measuring silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer), which comprises the following steps: weighing a soil sample in a graphite or nickel crucible, and dropwise adding ethanol to uniformly spread the sample; adding sodium hydroxide to cover the sample; the crucible is placed in a muffle furnace, the temperature is increased to 700 DEG C according to the gradient, the temperature is kept for 30 minutes, water is added after cooling, and heating is conducted to enable melt to fall off; transferring the solution into a volumetric flask for constant volume; preparing a silicon standard working solution and an internal standard solution Eu, wherein all media are water; spraying a standard solution to ICP-OES, measuring the emission intensity of the standard solution, and drawing a standard curve; and measuring the emission intensity of the to-be-measured sample solution under the same condition, and calculating the concentration of the to-be-measured component according to the standard curve. The invention effectively solves the problems of high equipment cost, complex operation, high sample melting temperature and the like in the existing method, and provides a simple, convenient, low-cost, efficient and stable soil silicon dioxide determination method.

Description

Technical Field

[0001] The invention belongs to the field of environmental monitoring and soil analysis, and specifically relates to a method for directly determining silicon dioxide in soil by medium-low temperature alkali fusion-ICP-OES. Background Art

[0002] Silica in soil is an essential element for plant growth and plays a vital role in the soil ecosystem. It can improve soil texture and structure, increase soil porosity, promote soil looseness and aeration, and create good conditions for plant root growth and nutrient absorption. In addition, silica can enhance soil stability, effectively reduce surface soil erosion, and resist acid and alkali erosion and other physical damage. In agricultural production and ecological protection, accurate determination of soil silica content is of great significance for ensuring soil health, optimizing fertilization management, and improving crop disease resistance and stress resistance.

[0003] In recent years, with the rapid development of industrial and agricultural production, more and more silicon-containing compound fertilizers have been widely used in farmland. Although silicon has a certain promoting effect on crop growth, excessive application or improper fertilization methods may cause changes in soil structure, affect the plant's absorption efficiency of nutrients, and thus reduce the disease resistance, stress tolerance and yield of crops. Therefore, accurately and quickly measuring the silicon dioxide content in the soil and monitoring its changing trend is an important task in agricultural production and soil management.

[0004] At present, the determination of soil silica content mainly adopts HJ 974-2018 "Determination of 11 elements in soil and sediments - alkali fusion-inductively coupled plasma emission spectrometry". This method uses a platinum crucible for high-temperature melting and uses a variety of fluxes such as sodium carbonate, lithium tetraborate, and lithium metaborate. The melting process needs to be carried out at a high temperature of 1000 ° C. Although this method can accurately determine the silica content, it also has many problems. First, the platinum crucible is expensive, which increases the analysis cost. Secondly, there are many types of fluxes and they need to be added step by step, which makes the operation process complicated and the experimental repeatability difficult to ensure. In addition, the melt processing process is cumbersome. For example, the melted platinum crucible needs to be placed upright in a beaker filled with 100ml water. After cracks appear in the melt, the platinum crucible is taken out and water is continued to be added until the melt is completely detached, and then it is transferred to a 250ml beaker and 40ml nitric acid-hydrochloric acid mixed solution is added to dissolve it. These operations are not only time-consuming and laborious, but also easy to introduce errors, affecting the accuracy and stability of the detection. Therefore, this method is subject to certain limitations in large-scale soil monitoring applications.

[0005] In response to the above problems, there is an urgent need for a soil silica determination method that is simple to operate, low in cost, has a moderate melting temperature, requires fewer types of reagents, is easy to handle the molten material, has stable analysis results and high accuracy, so as to meet the needs of agricultural production and environmental monitoring for rapid and efficient detection technology. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for directly determining silicon dioxide in soil by medium-low temperature alkali fusion-ICP-OES, which effectively solves the problems of high equipment cost, multiple types of fluxes, complex operation, high melting temperature, cumbersome melt processing and poor stability of detection results in the existing determination methods.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is: A method for directly determining silicon dioxide in soil by medium-low temperature alkali fusion-ICP-OES, the method comprising the following steps: Sample pretreatment: weigh the soil sample into a graphite crucible or a nickel crucible, add ethanol dropwise, and shake slightly to spread the sample evenly; Flux addition: Weigh sodium hydroxide and evenly cover the surface of the sample to make the sample completely covered; Alkali melting treatment: wipe the surface of the crucible clean and place it in a muffle furnace. Heat it to a predetermined temperature according to the set gradient, keep it for a period of time, then stop heating and take out the crucible after cooling down. Dissolution: Add water to the crucible and heat on a hot plate to completely remove the melt; Filtration and dilution: After the sample has cooled, transfer the resulting solution completely to a volumetric flask, dilute to the mark with water, shake well, and let stand for testing; Preparation of standard solution: Prepare silicon standard series working solution and internal standard solution Eu at the same time, all media are water; ICP-OES determination: spray a series of standard solutions into ICP-OES in sequence, measure their emission intensity, and draw a standard working curve; Test and calculation: Under the same conditions, measure the emission intensity of the sample solution to be tested, and calculate the concentration of the component to be tested in the test solution according to the standard curve. At the same time, input the sample weight, fixed volume and conversion coefficient for calculation.

[0008] Preferably, the soil sample weighs 0.2000 g, and 3-5 drops of ethanol are added.

[0009] Preferably, the amount of sodium hydroxide used is 1.5 g.

[0010] Preferably, the heating procedure of the muffle furnace is: heating from 200°C to 400°C, then heating to 700°C and maintaining for 30 minutes.

[0011] Preferably, 10 ml of water is added to the crucible and heated on a hot plate at 200° C. to completely remove the melt.

[0012] Preferably, the fixed volume of the volumetric flask is 500 ml.

[0013] Preferably, the mass concentration range of the standard series solutions is 0, 5.0, 10.0, 50.0, 100.0, 200.0, 500.0 mg / L, the concentration of the internal standard solution is 2 mg / L Eu, and the medium is water.

[0014] Preferably, the working conditions of the ICP-OES include: RF power: 1150w; Nebulizer gas flow rate: 0.65 L / min; Auxiliary gas flow rate: 0.5 L / min; Cooling air flow: 12 L / min; Flushing pump speed: 50 r / min; Analysis pump speed: 50 r / min; Long wave exposure time: 10s; Shortwave exposure time: 5s; Maximum integration time: 30s; Sample flushing time: 20s; Analysis mode: Precision.

[0015] Preferably, during the test, the sample weight, fixed volume, and conversion factor are input into the ICP-OES software for calculation.

[0016] The present invention has novel structure, ingenious design, simple and convenient operation, and has the following advantages compared with the prior art: 1. Low cost and easy operation. The present invention uses a graphite crucible or a nickel crucible instead of a traditional platinum crucible, which greatly reduces the cost of experimental equipment. At the same time, only sodium hydroxide (NaOH) is used as a single flux, which avoids the cumbersome operation of adding multiple reagents such as sodium carbonate, lithium tetraborate, and lithium metaborate in steps in the existing method, making the entire melting process more concise and efficient. In addition, the molten product of the present method can be quickly dissolved in a small amount of water without the need for complex acid dissolution steps, thereby reducing the operating difficulty of the experimenter and improving the detection efficiency.

[0017] 2. Moderate temperature and low energy consumption. The existing alkali fusion method usually requires melting samples at high temperatures above 1000°C, while the present invention optimizes the melting system and only requires medium and low temperature conditions of about 700°C to complete the melting reaction, which significantly reduces the energy consumption of experimental equipment and reduces the safety risks caused by high-temperature operations. In addition, the molten material can quickly separate from the crucible under hot dissolution conditions, making sample pretreatment more efficient and further improving the convenience of detection.

[0018] 3. The test results are stable and accurate. This method uses ICP-OES (inductively coupled plasma emission spectroscopy) for quantitative analysis. Compared with traditional chemical titration or weight methods, it avoids human errors and has higher sensitivity and accuracy. At the same time, this method uses the internal standard method to correct possible matrix effects and instrument drift, which improves the stability of the test and the reproducibility of the data, making it more suitable for rapid detection of large quantities of samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of the method for directly determining silicon dioxide in soil by medium-low temperature alkali fusion-ICP-OES.

[0020] Figure 2 This is the standard curve of the silicon standard series solution determined by ICP-OES in Example 1 (with silicon mass concentration as the abscissa and spectral emission intensity as the ordinate).

[0021] Figure 3 The linear regression equation and correlation coefficient (within the concentration range of 0-500 mg / L) of the silicon standard solution in Example 1 are shown.

[0022] Figure 4 The precision and accuracy of ICP-OES determination of Example 1 (using GSS-10 and GSS-12 standard substances, 6 parallel experiments were carried out to analyze the relative standard deviation and relative error of SiO2 determination).

[0023] Figure 5 This is the standard curve of the silicon standard series solution determined by ICP-OES in Example 2 (with silicon mass concentration as the abscissa and spectral emission intensity as the ordinate).

[0024] Figure 6 The linear regression equation, correlation coefficient and detection limit (within the concentration range of 0-500 mg / L) of the silicon standard solution in Example 2 are shown.

[0025] Figure 7 This is the precision and accuracy analysis of the ICP-OES determination of standard soil samples in Example 2 (the method uses two standard substances, GSS-23 and GSS-37, and conducts 6 parallel experiments to analyze the precision and accuracy of the method).

[0026] Figure 8 This is the standard curve of the ICP-OES determination of the silicon standard series solution in Example 3 (with silicon mass concentration as the abscissa and spectral emission intensity as the ordinate).

[0027] Fig. 9 The linear regression equation, correlation coefficient and detection limit (within the concentration range of 0-500 mg / L) of the silicon standard solution in Example 3 are shown.

[0028] Fig.10 This is the precision and accuracy analysis of the ICP-OES determination of Example 3 (using GSD-31 and GSD-32 standard substances, 6 parallel experiments were carried out to analyze the relative standard deviation and relative error of SiO2 determination). DETAILED DESCRIPTION

[0029] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments.

[0030] The present invention provides a method for directly determining silicon dioxide (SiO2) in soil by medium-low temperature alkali fusion-ICP-OES. ICP-OES (inductively coupled plasma emission spectrometry) is a technique commonly used for elemental analysis, which can accurately measure the element content of the sample without destroying it. ICP-OES introduces the sample into high-temperature plasma, excites the elements therein and emits light of specific wavelengths, and quantitatively analyzes the element concentration in the sample by detecting the intensity of these spectra.

[0031] The technical solution of the present invention is based on ICP-OES and combines medium and low temperature alkali fusion to treat soil samples, which significantly reduces the equipment and energy consumption required for high temperature fusion in traditional methods. Through simple and fast operation steps, it not only improves the analysis accuracy, but also reduces the operation cost, providing a more efficient and economical solution for soil testing.

[0032] The method includes the following key steps: 1. Sample pretreatment: including weighing the soil sample and adding ethanol for uniform treatment.

[0033] 2. Flux addition: Sodium hydroxide (NaOH) is added as a flux to completely cover the sample.

[0034] 3. Alkali fusion treatment: The sample is subjected to medium-low temperature alkali fusion treatment in a muffle furnace.

[0035] 4. Dissolution: Dissolve the molten material by adding water and heating to facilitate subsequent analysis.

[0036] 5. Filtration and dilution: Filter the solution and dilute to the specified volume to ensure accurate measurement.

[0037] 6. Preparation of standard solution: Prepare standard solution and internal standard solution for drawing standard curve.

[0038] 7.ICP-OES determination: ICP-OES is used to obtain the emission intensity of the sample and draw a standard curve.

[0039] 8. Test and calculation: Calculate the concentration of silica in the sample to be tested using the standard curve, taking into account the conversion factor.

[0040] The advantages of the present invention are that by lowering the operating temperature and simplifying the processing steps, the silicon dioxide in the soil can be measured efficiently and accurately, while reducing the cost and time consumption in the experimental process. Example

[0041] like Figure 1-4 As shown, this example introduces a method for directly determining silicon dioxide (SiO2) in soil by medium-low temperature alkali fusion-ICP-OES. Through precise experimental operation steps and parameter settings, the silicon dioxide content in soil can be determined quickly and accurately. This method has the advantages of simple operation, low cost, high detection sensitivity, etc., and is suitable for large-scale soil analysis and monitoring.

[0042] Step 1: Sample processing and testing Sample processing: First, weigh 0.2000g (accurate to 0.0001g) of soil sample and put it into a 30ml graphite crucible or nickel crucible. Add 3-5 drops of ethanol and shake the crucible slightly horizontally to spread the sample evenly. Then, accurately weigh 1.5g of sodium hydroxide (NaOH) and add it to the crucible, ensuring that the soil sample is completely covered. Next, wipe the surface of the crucible and heat it in a muffle furnace. Set the gradient temperature (200℃, 400℃, 700℃) to 700℃ and maintain for 30 minutes, then stop heating and let the crucible cool down naturally to room temperature, and take out the crucible after about 1 hour.

[0043] Dissolve: Add 10ml of water to the crucible, place the crucible on a heating plate and heat it to 200°C, and use the hot melt method to completely separate the melt from the crucible. After the sample cools down, transfer the solution in the crucible to a 500mL volumetric flask, dilute to the mark with water, shake well, and let it stand for testing.

[0044] Preparation of standard working solution: Take different volumes of 10000 µg / mL silicon standard solution (0.00 ml, 0.05 ml, 0.10 ml, 0.50 ml, 1.00 ml, 2.00 ml, 5.00 ml respectively) and add them to a set of 100mL volumetric flasks, then dilute to the mark with water, shake well, and obtain a series of standard working solutions with mass concentrations of 0, 5.0, 10.0, 50.0, 100.0, 200.0, 500.0 mg / L. At the same time, the internal standard solution is 2 mg / L Eu, and the medium is water. Eu is the chemical symbol of europium, which is a rare earth element. In ICP-OES determination, the internal standard solution often uses a europium (Eu) solution of known concentration to calibrate the instrument response. Due to the stable spectral characteristics of europium, it is used as an internal standard solution in ICP-OES to help eliminate errors caused by instrument drift or changes in sample matrix, thereby improving the accuracy of the measurement results.

[0045] ICP-OES determination: Each standard series solution is sprayed into the ICP-OES instrument from low concentration to high concentration, and its emission intensity is measured. The standard working curve is drawn with the concentration of silicon as the horizontal axis and the emission intensity as the vertical axis. The content of silicon dioxide (SiO2) in the sample to be tested can be accurately calculated through this curve. During the test, the sample weight of 0.2000g, the fixed volume of 500mL, and the conversion coefficient of silicon to silicon dioxide (2.1394) are input into the software for calculation to ensure the accuracy of the results.

[0046] Inductively coupled plasma optical emission spectrometer working conditions: The operating parameters of ICP-OES are as follows: RF power: 1150w Nebulizer gas flow rate: 0.65 L / min Auxiliary gas flow: 0.5 L / min Cooling air flow: 12 L / min Flushing pump speed: 50 r / min Analysis pump speed: 50 r / min Long wave exposure time: 10s Shortwave exposure time: 5s Maximum integration time: 30s Sample flushing time: 20s Analysis Mode: Precision Mode These working conditions have been optimized for the determination of silica, ensuring the stability of instrument performance and the accuracy of measurement results.

[0047] Step 2: Method Validation Detection limit verification: First, according to the set working conditions of the ICP-OES instrument, the silicon standard series solution was measured and the standard curve was drawn. In the concentration range of 0-500 mg / L, the measurement results of the silicon standard series solution had a good linear relationship, and the correlation coefficient reached 0.9998, which met the requirements. Based on this standard curve, the detection limit of this method was determined in accordance with the requirements of Appendix A of the Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Methods (HJ168-2020). By preparing 7 parallel blank solutions and measuring them, the results showed that the detection limit of SiO2 was 0.05%, which was lower than the detection limit of the existing method (such as 0.07% in HJ974-2018). This method not only provides higher sensitivity, but also simplifies the operation process, reduces costs, and improves experimental efficiency.

[0048] Precision and accuracy: In order to verify the precision and accuracy of the method, two standard substances, GSS-10 and GSS-12, were selected and 6 parallel experiments were carried out. The experimental results showed that when determining SiO2 in standard soil samples, the relative standard deviation (RSD) of the method was in the range of 1.06%-1.79%, and the absolute value of the relative error was in the range of 0.23%-0.61%, indicating that the method has good precision and accuracy and fully meets the requirements for laboratory environmental sample determination.

[0049] Results analysis and advantages: The results obtained by this method show that it has significant advantages over traditional high-temperature and high-cost determination methods. This method not only simplifies the sample processing process and reduces the requirements for equipment, but also improves the detection limit, precision and accuracy, making it have broad application prospects in the determination of soil silica content. Compared with traditional methods, this method is easier to operate, the cost is significantly reduced, and accurate analysis results can be obtained in a shorter time. It is suitable for large-scale soil testing and soil health monitoring in agricultural production. Example

[0050] like Figure 1 , 5 As shown in Figures 6 and 7, this embodiment introduces a method for directly determining silicon dioxide (SiO2) in soil by medium-low temperature alkali fusion-ICP-OES. This method can accurately and quickly determine the silicon dioxide content in soil, and has the advantages of simple operation, low cost and high detection sensitivity. It is suitable for large-scale soil testing and soil health monitoring in agricultural production.

[0051] Step 1: Sample processing and testing Sample processing: First, weigh 0.2000g (accurate to 0.0001g) of soil sample and put it into a 30ml graphite crucible or nickel crucible. Add 3-5 drops of ethanol and shake the crucible slightly to spread the soil sample evenly. Then, accurately weigh 1.5g of sodium hydroxide (NaOH) and add it to the crucible, ensuring that the soil sample is completely covered. Next, wipe the surface of the crucible and heat it in a muffle furnace. Set the gradient temperature (200℃, 400℃, 700℃) to 700℃ and maintain for 30 minutes, then stop heating and let the crucible cool down naturally to room temperature (about 1 hour), and finally take out the crucible.

[0052] Dissolve: Add 10ml of water to the crucible, place the crucible on a heating plate and heat it to 200°C, and use the hot melt method to completely separate the melt from the crucible. After the sample cools down, transfer the solution in the crucible to a 500mL volumetric flask, dilute to the mark with water, shake well, and let it stand for testing.

[0053] Preparation of standard working solution: Take different volumes of 10000 µg / mL silicon standard solution (0.00 ml, 0.05 ml, 0.10 ml, 0.50 ml, 1.00 ml, 2.00 ml, 5.00 ml respectively) and add them to a set of 100mL volumetric flasks, then dilute to the mark with water, shake well, and obtain a series of standard working solutions with mass concentrations of 0, 5.0, 10.0, 50.0, 100.0, 200.0, 500.0 mg / L. At the same time, the internal standard solution is 2 mg / L Eu, and the medium is water.

[0054] ICP-OES determination: The standard series of solutions are sprayed into the ICP-OES instrument from low concentration to high concentration, and their emission intensity is measured. The standard working curve is drawn with the concentration of silicon as the horizontal axis and the emission intensity as the vertical axis. The content of silicon dioxide (SiO2) in the sample to be tested can be accurately calculated through this curve. During the test, the sample weight of 0.2000g, the fixed volume of 500mL, and the conversion coefficient of silicon to silicon dioxide (2.1394) are input into the software for calculation to ensure the accuracy of the results.

[0055] Inductively coupled plasma optical emission spectrometer working conditions: The operating parameters of ICP-OES are as follows: RF power: 1150w Nebulizer gas flow rate: 0.65 L / min Auxiliary gas flow: 0.5 L / min Cooling air flow: 12 L / min Flushing pump speed: 50 r / min Analysis pump speed: 50 r / min Long wave exposure time: 10s Shortwave exposure time: 5s Maximum integration time: 30s Sample flushing time: 20s Analysis Mode: Precision Mode These working conditions have been optimized for the determination of silica, ensuring the stability of instrument performance and the accuracy of measurement results.

[0056] Step 2: Method Validation Detection limit verification: First, according to the set ICP-OES instrument working conditions, the silicon standard series solution was measured and the standard curve was drawn (see Figure 5 ). In the concentration range of 0-500 mg / L, the determination results of the silicon standard series solutions showed good linear relationship, and the correlation coefficient reached 0.9999, which met the requirements. Based on this standard curve, the detection limit of this method was determined in accordance with the requirements of Appendix A of the Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Methods (HJ168-2020). By preparing 7 parallel blank solutions and measuring them, the results showed that the detection limit of SiO2 was 0.05%, which is lower than the detection limit of the existing method (such as 0.07% in HJ974-2018). This method not only provides higher sensitivity, but also simplifies the operation process, reduces costs, and improves experimental efficiency.

[0057] Precision and accuracy: In order to verify the precision and accuracy of the method, two standard substances, GSS-23 and GSS-37, were selected and six parallel experiments were performed (see Figure 5 and Figure 6 ). The experimental results show that when determining SiO2 in standard soil samples, the relative standard deviation (RSD) of the method is in the range of 2.29%-2.37%, and the absolute value of the relative error is in the range of 0.89%-0.90%, indicating that the method has good precision and accuracy and fully meets the requirements for laboratory environmental sample determination.

[0058] Results analysis and advantages: The results obtained by this method show that it has significant advantages over traditional high-temperature and high-cost determination methods. This method not only simplifies the sample processing process and reduces the requirements for equipment, but also improves the detection limit, precision and accuracy, making it have broad application prospects in the determination of soil silica content. Compared with traditional methods, this method is easier to operate, the cost is significantly reduced, and accurate analysis results can be obtained in a shorter time. It is suitable for large-scale soil testing and soil health monitoring in agricultural production. Example

[0059] like Figure 1 , 8 As shown in Figures 9 and 10, this embodiment introduces a method for directly determining silicon dioxide (SiO2) in soil by medium-low temperature alkali fusion-ICP-OES. This method uses ICP-OES technology and can quickly and accurately determine the silicon dioxide content in soil under precise experimental operation steps and parameter settings. This method has the advantages of simple operation, low cost, high detection sensitivity, etc., and is suitable for large-scale soil analysis and monitoring.

[0060] Step 1: Sample processing and testing Sample processing: First, weigh 0.2000g (accurate to 0.0001g) of soil sample and put it into a 30ml graphite crucible or nickel crucible. Add 3-5 drops of ethanol and shake the crucible slightly to spread the soil sample evenly. Then, accurately weigh 1.5g of sodium hydroxide (NaOH) and add it to the crucible, ensuring that the soil sample is completely covered. Next, wipe the surface of the crucible and heat it in a muffle furnace. Set the gradient temperature (200℃, 400℃, 700℃) to 700℃ and maintain it for 30 minutes, then stop heating and let the crucible cool down naturally to room temperature. Take out the crucible after about 1 hour.

[0061] Dissolve: Add 10ml of water to the crucible, place the crucible on a heating plate and heat it to 200°C, and use the hot melt method to completely separate the melt from the crucible. After the sample cools down, transfer the solution in the crucible to a 500mL volumetric flask, dilute to the mark with water, shake well, and let it stand for testing.

[0062] Preparation of standard working solution: Take different volumes of 10000 µg / mL silicon standard solution (0.00 ml, 0.05 ml, 0.10 ml, 0.50 ml, 1.00 ml, 2.00 ml, 5.00 ml respectively) and add them to a set of 100mL volumetric flasks, then dilute to the mark with water, shake well, and obtain a series of standard working solutions with mass concentrations of 0, 5.0, 10.0, 50.0, 100.0, 200.0, 500.0 mg / L. At the same time, the internal standard solution is 2 mg / L Eu, and the medium is water.

[0063] ICP-OES determination: The standard series of solutions are sprayed into the ICP-OES instrument from low concentration to high concentration, and their emission intensity is measured. The standard working curve is drawn with the concentration of silicon as the horizontal axis and the emission intensity as the vertical axis. The content of silicon dioxide (SiO2) in the sample to be tested can be accurately calculated through this curve. During the test, the sample weight of 0.2000g, the fixed volume of 500mL, and the conversion coefficient of silicon to silicon dioxide (2.1394) are input into the software for calculation to ensure the accuracy of the results.

[0064] Inductively coupled plasma optical emission spectrometer working conditions: The operating parameters of ICP-OES are as follows: RF power: 1150w Nebulizer gas flow rate: 0.65 L / min Auxiliary gas flow: 0.5 L / min Cooling air flow: 12 L / min Flushing pump speed: 50 r / min Analysis pump speed: 50 r / min Long wave exposure time: 10s Shortwave exposure time: 5s Maximum integration time: 30s Sample flushing time: 20s Analysis Mode: Precision Mode These working conditions have been optimized for the determination of silica, ensuring the stability of instrument performance and the accuracy of measurement results.

[0065] Step 2: Method Validation Detection limit verification: First, according to the set ICP-OES instrument working conditions, the silicon standard series solution was measured and the standard curve was drawn (see Figure 8 ). In the concentration range of 0-500 mg / L, the determination results of the silicon standard series solutions showed good linear relationship, and the correlation coefficient reached 0.9999, which met the requirements. Based on this standard curve, the detection limit of this method was determined in accordance with the requirements of Appendix A of the Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Methods (HJ168-2020). By preparing 7 parallel blank solutions and measuring them, the results showed that the detection limit of SiO2 was 0.05%, which is lower than the detection limit of the existing method (such as 0.07% in HJ974-2018). This method not only provides higher sensitivity, but also simplifies the operation process, reduces costs, and improves experimental efficiency.

[0066] Precision and accuracy: In order to verify the precision and accuracy of the method, two standard substances, GSD-31 and GSD-32, were selected and six parallel experiments were performed (see Fig. 9 and Fig.10 ). The experimental results show that when determining SiO2 in standard soil samples, the relative standard deviation (RSD) of the method is in the range of 1.32%-1.78%, and the absolute value of the relative error is in the range of 0.44%-1.67%, indicating that the method has good precision and accuracy and fully meets the requirements for laboratory environmental sample determination.

[0067] Results analysis and advantages: The results obtained by this method show that it has significant advantages over traditional high-temperature and high-cost determination methods. This method not only simplifies the sample processing process and reduces the requirements for equipment, but also improves the detection limit, precision and accuracy, making it have broad application prospects in the determination of soil silica content. Compared with traditional methods, this method is easier to operate, the cost is significantly reduced, and accurate analysis results can be obtained in a shorter time. It is suitable for large-scale soil testing and soil health monitoring in agricultural production.

[0068] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for directly determining silicon dioxide in soil by medium-low temperature alkali fusion-ICP-OES, characterized in that: The method comprises the following steps: Sample pretreatment: weigh the soil sample into a graphite crucible or a nickel crucible, add ethanol, and shake it slightly to spread the sample evenly; Flux addition: Weigh sodium hydroxide and evenly cover the surface of the sample to make the sample completely covered; Alkali melting treatment: wipe the surface of the crucible clean and place it in a muffle furnace. Heat it to a predetermined temperature according to the set gradient, keep it for a period of time, then stop heating and take out the crucible after cooling down. Dissolution: Add water to the crucible and heat on a hot plate to completely remove the melt; Filtration and dilution: After the sample has cooled, transfer the resulting solution completely to a volumetric flask, dilute to the mark with water, shake well and let stand for testing; Preparation of standard solution: Prepare silicon standard series working solution and internal standard solution Eu at the same time, all media are water; ICP-OES determination: spray a series of standard solutions into ICP-OES in sequence, measure their emission intensity, and draw a standard working curve; Test and calculation: Under the same conditions, measure the emission intensity of the sample solution to be tested, and calculate the concentration of the component to be tested in the test solution according to the standard curve. At the same time, input the sample weight, fixed volume and conversion coefficient for calculation.

2. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The soil sample weighs 0.2000 g, and 3-5 drops of ethanol are added.

3. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The amount of sodium hydroxide used is 1.5 g.

4. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The heating procedure of the muffle furnace is: heating from 200°C to 400°C, then heating to 700°C and maintaining for 30 minutes.

5. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: Add 10 ml of water to the crucible and heat it on a hot plate at 200°C to completely remove the melt.

6. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The fixed volume of the volumetric flask is 500 ml.

7. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The mass concentration ranges of the standard series solutions are 0, 5.0, 10.0, 50.0, 100.0, 200.0, and 500.0 mg / L, the concentration of the internal standard solution is 2 mg / L Eu, and the medium is all water.

8. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: The ICP-OES working conditions include: RF power: 1150w; Nebulizer gas flow rate: 0.65 L / min; Auxiliary gas flow rate: 0.5 L / min; Cooling air flow: 12 L / min; Flushing pump speed: 50 r / min; Analysis pump speed: 50 r / min; Long wave exposure time: 10s; Shortwave exposure time: 5s; Maximum integration time: 30s; Sample flushing time: 20s; Analysis mode: Precision.

9. The method for directly determining silicon dioxide in soil by medium and low temperature alkali fusion-ICP-OES according to claim 1, characterized in that: During the test, the sample weight, fixed volume, and conversion factor are input into the ICP-OES software for calculation.

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