A kind of extracting agent for extracting effective selenium element in soil and its extraction detection method

Abstract

The present invention relates to the technical field of effective selenium element detection in soil, and discloses an extractant for extracting effective selenium element in soil and its extraction detection method, wherein the extractant includes the following components in molar concentration meter: 0.1500mol / L potassium carbonate, 0.0050-0.0100mol / L trisodium hydroxyethyldiaminetetraacetic acid, 0.0100-0.0500mol / L diammonium hydrogen phosphate, 0.0010-0.0050mol / L methacrylic acid-3-sulfonic acid propyl potassium salt, 0.0020-0.0040mol / L crystalline aluminum chloride. The present invention can efficiently extract effective selenium element in soil in wet areas, and the extraction amount is better than AB-DTPA method, and no expensive atomic fluorescence spectrometer is required, no oscillator with large volume is required, the existing conventional method requires various instruments and equipment, and the price is high, while the present method saves cost, improves efficiency, does not require high operation skills of technical personnel, is suitable for testing by grassroots institutions lacking expensive equipment such as fields and grassroots laboratories, and is an effective supplement to conventional methods.

Description

Technical Field

[0001] The invention relates to the technical field of effective selenium element detection in soil, and more specifically discloses an extractant for extracting effective selenium element in soil and an extraction detection method thereof. Background Art

[0002] Selenium is a trace element necessary for the human body, which has the functions of anti-oxidation, enhancing immunity and protecting cell integrity. Selenium exists in the soil in the form of selenide, elemental selenium, selenite and selenate. The effective selenium in the soil of different regions exists in different forms, and the requirements for corresponding extractants are also different. Studies have shown that the selenium content of crops is significantly correlated with the effective selenium content in the soil. Therefore, the study of the extractant and extraction detection method of the effective selenium in the soil has important theoretical and practical significance in agricultural production and even crop ecological environment research.

[0003] Regarding the research on available selenium in soil, there is currently no effective extraction agent and unified determination method. Since the available selenium in soil in different regions exists in different forms, it is necessary to select a suitable extraction agent based on the soil type and acidity and alkalinity. Currently, there is a lack of research on the extraction and determination of available selenium in different types of soil in different regions. The operation of extracting and determining the available selenium content in soil is relatively complicated, and the requirements for instruments and equipment are relatively high.

[0004] The existing extractant formula and extraction detection method cannot meet the requirements of extraction and determination of effective selenium in different soils. Therefore, it is necessary to have an extractant and extraction detection method for effective selenium in soils of different regions. Summary of the invention

[0005] The present invention mainly provides an extractant for extracting effective selenium in soil and an extraction detection method thereof, which can solve the problem that the existing extractant formula and extraction detection method cannot meet the requirements of extraction and determination of effective selenium in different soils.

[0006] To solve the above technical problems, according to one aspect of the present invention, there is provided an extractant for extracting effective selenium in soil, comprising the following components in molar concentration: 0.1500 mol / L potassium carbonate, 0.0050-0.0100 mol / L trisodium hydroxyethyldiaminetetraacetic acid, 0.0100-0.0500 mol / L diammonium hydrogen phosphate, 0.0010-0.0050 mol / L methacrylate-3-sulfonic acid propyl ester potassium salt, 0.0020-0.0040 mol / L crystalline aluminum chloride, the balance being water, and the pH of the extractant solution being 7.8-9.2.

[0007] Furthermore, the preparation method of the leaching agent is:

[0008] S1. First, prepare a leaching agent powder composed of potassium carbonate, trisodium hydroxyethyldiaminetetraacetic acid, and diammonium hydrogen phosphate methacrylate-3-sulfonate propyl ester potassium salt;

[0009] S2. Dissolve the extractant powder composed of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate and diammonium hydrogen phosphate methacrylate-3-sulfonate propyl potassium salt in distilled water, add crystalline aluminum chloride under stirring until dissolved, and dilute to 1000 mL with distilled water to obtain an extractant solution.

[0010] Furthermore, the mass ratio of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate, diammonium hydrogen phosphate, potassium salt of 3-sulfonate propyl methacrylate, and crystalline aluminum chloride in the leaching agent solution is 83:7:5:1:2.

[0011] Furthermore, the purities of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate, diammonium hydrogen phosphate, potassium salt of 3-sulfonyl methacrylate, and crystalline aluminum chloride in the leaching agent solution are all analytically pure.

[0012] According to another aspect of the present invention, a method for extracting effective selenium from soil is provided. The method is implemented by using the above-mentioned extracting agent for extracting effective selenium from soil, and specifically comprises the following steps:

[0013] (1) Weigh 500.0×(1+soil water content)g of fresh soil sample and put it into a soil extraction bottle;

[0014] (2) Add 1000 mL of the extractant solution into the soil extraction bottle;

[0015] (3) Place the ultrasonic cleaner in an ultrasonic cleaning machine and extract at a frequency of 40-60kHz for 10 minutes;

[0016] (4) Then filter into a dry conical flask to obtain the soil effective selenium element test solution, which can be used to determine the effective selenium element in the soil;

[0017] (5) Take 1000 mL of the selenium-containing supernatant of the soil effective selenium element test solution and add it into a conical flask, and add 20 mL of concentrated hydrochloric acid to acidify;

[0018] (6) Filter and remove the precipitate produced during the acidification process;

[0019] (7) Add 10 g of sodium sulfite, stir and react for 1-2 hours to obtain a reduced solution, boil it and then cool it to room temperature;

[0020] (8) Add peptide violet indicator to the reduced solution obtained in step (7), dropwise add barium chloride to titrate and detect the sulfuric acid content, according to the formula:

[0021]

[0022] This allows the effective selenium content in the soil to be calculated.

[0023] Furthermore, in step (8), the concentration of the barium chloride titration solution is 0.0010 mol / L.

[0024] The beneficial effects of the extractant for extracting effective selenium in soil and the extraction detection method thereof of the present invention are as follows: the present invention can efficiently extract effective selenium in soil in humid areas, and the extraction amount is better than that of the AB-DTPA method, and no expensive atomic fluorescence spectrometer or large oscillator is required. The existing conventional methods require various instruments and equipment and are relatively expensive, while the present method saves costs, improves efficiency, and does not require high operating skills of technicians. The present method is suitable for testing in grassroots institutions such as fields and grassroots laboratories that lack expensive equipment, and is an effective supplement to conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the extraction detection method for effective selenium in soil. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below in conjunction with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0027] Example 1

[0028] Weigh 20.73 g of potassium carbonate solid, 1.72 g of trisodium hydroxyethyldiaminetetraacetate, 1.32 g of diammonium hydrogen phosphate, and 0.25 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 0.48 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0029] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0030] Add 20ml of concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g of sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, drop barium chloride to titrate and detect the sulfuric acid content, consume 4.80ml of barium chloride, according to the formula:

[0031]

[0032] The calculated effective selenium content in the soil of humid areas is 0.379 mg / kg.

[0033] Example 2

[0034] Weigh 69.11 g of potassium carbonate solid, 6.48 g of trisodium hydroxyethyldiaminetetraacetate, 4.32 g of diammonium hydrogen phosphate, and 0.83 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 1.60 g of crystalline aluminum chloride while stirring, stir to dissolve and make up to 1000 mL with distilled water, and make up to 1000 mL with distilled water, which is the soil effective selenium extractant solution.

[0035] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0036] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.74ml of barium chloride, according to the formula:

[0037]

[0038] The calculated effective selenium content in the soil of humid areas is 0.374 mg / kg.

[0039] Example 3

[0040] Weigh 138.21 g of potassium carbonate solid, 12.96 g of trisodium hydroxyethyldiaminetetraacetate, 8.64 g of diammonium hydrogen phosphate, and 1.67 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 3.20 g of crystalline aluminum chloride while stirring, stir to dissolve and make up to 1000 mL with distilled water, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0041] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0042] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.77ml of barium chloride, according to the formula:

[0043]

[0044] The calculated effective selenium content in the soil of humid areas is 0.377 mg / kg.

[0045] Example 4

[0046] Weigh 69.11 g of potassium carbonate solid, 6.48 g of trisodium hydroxyethyldiaminetetraacetate, 4.32 g of diammonium hydrogen phosphate, and 0.83 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 1.60 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0047] like Figure 1 As shown, weigh 500.0×(1+soil moisture content) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 60 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0048] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.81ml of barium chloride, according to the formula:

[0049]

[0050] The calculated effective selenium content in the soil of humid areas is 0.380 mg / kg.

[0051] Example 5

[0052] Weigh 69.11 g of potassium carbonate solid, 6.48 g of trisodium hydroxyethyldiaminetetraacetate, 4.32 g of diammonium hydrogen phosphate, and 0.83 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 1.60 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0053] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 80 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0054] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.75ml of barium chloride, according to the formula:

[0055]

[0056] The calculated effective selenium content in the soil of humid areas is 0.375 mg / kg.

[0057] Example 6

[0058] Weigh 69.11 g of potassium carbonate solid, 6.48 g of trisodium hydroxyethyldiaminetetraacetate, 4.32 g of diammonium hydrogen phosphate, and 0.83 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 1.60 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0059] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 20 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0060] Add 20ml concentrated hydrochloric acid to the test solution of soil effective selenium element, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.51ml of barium chloride, according to the formula:

[0061]

[0062] The calculated effective selenium content in the soil of humid areas is 0.356 mg / kg.

[0063] Example 7

[0064] Weigh 69.11 g of potassium carbonate solid, 6.48 g of trisodium hydroxyethyldiaminetetraacetate, 4.32 g of diammonium hydrogen phosphate, and 0.83 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 1.60 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0065] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 5 minutes, and filter the obtained mixed liquid into a dry triangular flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0066] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.20ml of barium chloride, according to the formula:

[0067]

[0068] The calculated effective selenium content in the soil of humid areas is 0.332 mg / kg.

[0069] Example 8

[0070] Weigh 20.73 g of potassium carbonate solid, 1.72 g of trisodium hydroxyethyldiaminetetraacetate, 1.32 g of diammonium hydrogen phosphate, and 0.25 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 0.48 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0071] like Figure 1 As shown, weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of soil effective selenium element extractant solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0072] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.77ml of barium chloride, according to the formula:

[0073]

[0074] The calculated effective selenium content in the soil of humid areas is 0.377 mg / kg.

[0075] Example 9

[0076] Weigh 20.73 g of potassium carbonate solid, 1.72 g of trisodium hydroxyethyldiaminetetraacetate, 1.32 g of diammonium hydrogen phosphate, and 0.25 g of potassium salt of 3-sulfonyl methacrylate to make an extractant powder, dissolve the extractant powder in distilled water, add 0.48 g of crystalline aluminum chloride while stirring, stir to dissolve, and make up to 1000 mL with distilled water, which is the soil effective selenium element extractant solution.

[0077] like Figure 1 As shown, 500.0×(1+soil moisture content) g of fresh soil sample was weighed and put into a soil extraction bottle, 1000 mL of soil effective selenium element extractant solution was added into the soil extraction bottle, and the bottle was put into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 60 minutes. The obtained mixed liquid was filtered into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0078] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 4.85ml of barium chloride, according to the formula:

[0079]

[0080] The calculated effective selenium content in the soil of humid areas is 0.383 mg / kg.

[0081] Comparison example

[0082] Weigh 79.06 g of NH4HCO3 solid and 1.97 g of DTPA to prepare an extractant powder, dissolve the extractant powder in distilled water, and dilute to 1000 mL with distilled water to obtain the AB-DTPA extractant solution.

[0083] Weigh 500.0×(1+soil moisture) g of fresh soil sample, put it into a soil extraction bottle, add 1000 mL of AB-DTPA extraction agent solution into the soil extraction bottle, put it into an ultrasonic cleaner for ultrasonic extraction at a frequency of 40 kHz for 10 minutes, and filter the obtained mixed liquid into a dry conical flask, which is the soil effective selenium element test solution. The soil effective selenium element test solution can be used to determine the soil effective selenium element.

[0084] Add 20ml concentrated hydrochloric acid to the test solution of effective selenium in soil, filter to remove the precipitate produced in the acidification process, add 10g sodium sulfite, stir to dissolve and react for 1-2h, boil the reduced solution and cool to room temperature, add peptide violet indicator to the cooled reduced solution, add barium chloride to titrate and detect the sulfuric acid content, consuming 2.85ml of barium chloride, according to the formula:

[0085]

[0086] The calculated effective selenium content in the soil in humid areas is 0.225 mg / kg.

[0087] Table 1 The effective selenium content of soil detected under the implementation conditions of the present invention and the effective selenium content of soil detected under the control implementation conditions

[0088]

[0089]

[0090] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention also fall within the protection scope of the present invention.

Claims

1. A method for detecting the effective selenium content in soil, characterized in that: The detection method comprises the following steps: (1) weighing 500.0×(1+soil water content) g of a fresh soil sample and placing it in a soil extraction bottle; (2) Add 1000 mL of the extractant solution into the soil extraction bottle; (3) Place the sample in an ultrasonic cleaner and extract it at a frequency of 40-60kHz for 10 minutes; (4) Then filter it into a dry conical flask to obtain the soil effective selenium element test solution; (5) Take 1000 mL of the selenium-containing supernatant of the soil effective selenium element test solution and add it into a conical flask, then add 20 mL of concentrated hydrochloric acid to acidify; (6) Filter and remove the precipitate produced during the acidification process; (7) Add 10 g of sodium sulfite, stir and react for 1-2 hours to obtain a reduced solution, boil it and then cool it to room temperature; (8) Add phthalocyanine indicator to the reducing solution obtained in step (7), add barium chloride dropwise to titrate and detect the sulfuric acid content, according to the formula: Thus, the effective selenium content in the soil can be calculated; The leaching agent comprises the following components in molar concentration: 0.1500 mol / L potassium carbonate, 0.0050-0.0100 mol / L trisodium hydroxyethyldiaminetetraacetate, 0.0100-0.0500 mol / L diammonium hydrogen phosphate, 0.0010-0.0050 mol / L methacrylate-3-sulfonic acid propyl ester potassium salt, 0.0020-0.0040 mol / L crystalline aluminum chloride, and the balance is water, and the pH value of the leaching agent solution is 7.8-9.

2.

2. The method for detecting effective selenium content in soil according to claim 1, characterized in that: The preparation method of the leaching agent is: S1. First, prepare a leaching agent powder composed of potassium carbonate, trisodium hydroxyethyldiaminetetraacetic acid, and diammonium hydrogen phosphate methacrylate-3-sulfonate propyl ester potassium salt; S2. Dissolve the extractant powder composed of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate and diammonium hydrogen phosphate methacrylate-3-sulfonate propyl potassium salt in distilled water, add crystalline aluminum chloride under stirring until dissolved, and dilute to 1000 mL with distilled water to obtain an extractant solution.

3. A method for detecting effective selenium content in soil according to claim 2, characterized in that: The mass ratio of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate, diammonium hydrogen phosphate, potassium salt of 3-sulfonate propyl methacrylate and crystalline aluminum chloride in the leaching agent solution is 83:7:5:1:

2.

4. The method for detecting effective selenium content in soil according to claim 3, characterized in that: The purity of potassium carbonate, trisodium hydroxyethyldiaminetetraacetate, diammonium hydrogen phosphate, potassium salt of 3-sulfonyl methacrylate and crystalline aluminum chloride in the leaching agent solution are all analytically pure.

5. The method for detecting effective selenium content in soil according to claim 1, characterized in that: The soil extraction bottle is a glass triangular flask.

6. The method for detecting effective selenium content in soil according to claim 1, characterized in that: The state to be extracted is selenite which is easily soluble in water.

7. The method for detecting effective selenium content in soil according to claim 1, characterized in that: In the step (8), the concentration of the barium chloride titration solution is 0.0010 mol / L.

Images