High-sensitivity soil available sulfur detection method

Abstract

The invention provides a high-sensitivity soil available sulfur detection method, and belongs to the technical field of determination of available sulfur in soil. The invention provides a high-sensitivity soil available sulfur detection method, which comprises: (1) drying and crushing soil to be detected, mixing with an extraction agent, and carrying out primary extraction; (2) adding tween-80 after the primary extraction, and carrying out secondary extraction; and (3) taking the filtrate subjected to secondary extraction, and measuring available sulfur by adopting a nephelometry. The detection method provided by the invention not only can accurately determine the content of available sulfur in the soil, but also has relatively high detection stability, the detection limit is 0.42 mg / kg, and the detection sensitivity is relatively high. Therefore, the invention provides a high-sensitivity, accurate and stable soil available sulfur detection method.

Description

Technical Field

[0001] The invention relates to the technical field of determination of available sulfur in soil, and in particular to a highly sensitive method for detecting available sulfur in soil. Background Art

[0002] As one of the 16 nutrients necessary for plant growth, sulfur plays an important role in the development of plants. It can have an important impact on the synthesis of secondary metabolites, protein synthesis, nitrogen fixation, photosynthesis and other processes of plants. It has been listed as the fourth major plant nutrient after nitrogen, phosphorus and potassium. Available sulfur is sulfur in the soil that can be directly absorbed and utilized by plants, including soluble sulfur, adsorbable sulfur and some organic sulfur. Available sulfur mainly exists in the soil solution in a dissolved state or is adsorbed on soil colloids. In soils with high concentrations, it precipitates as sulfate solids due to supersaturation. Most of these forms of sulfate are water-soluble, acid-soluble or exchangeable, and are easily absorbed by plants. Therefore, accurately determining the content of available sulfur in agricultural soil is of great significance to agricultural development.

[0003] At present, the methods for determining available sulfur in soil mainly include turbidity, inductively coupled plasma optical emission spectrometry (ICP-OES) and ion chromatography (IC method). Among them, inductively coupled plasma optical emission spectrometry and ion chromatography have higher detection sensitivity than turbidity, and are suitable for the detection of large quantities of samples, but the instrument configuration is complex and the flexibility is poor, while the turbidity has the characteristics of simple instrument configuration and flexible applicability, but the sensitivity is poor. Therefore, it is necessary to improve the detection sensitivity of turbidity to make up for the defects of the prior art. Summary of the invention

[0004] The invention aims to improve the sensitivity of turbidity method in detecting available sulfur in soil, and to achieve accurate, sensitive, simple and flexible determination of the content of available sulfur in soil.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a highly sensitive method for detecting available sulfur in soil, comprising the following steps:

[0007] (1) Dry and crush the soil to be tested, mix it with an extractant, and perform a primary extraction;

[0008] (2) adding Tween-80 after the primary extraction to perform a secondary extraction;

[0009] (3) Taking the filtrate after the secondary extraction, the effective sulfur is determined by turbidity method.

[0010] Preferably, the drying is to dry the soil to a moisture content of less than 5%; and the particle size of the crushed soil is 1 to 2 mm.

[0011] Preferably, when the soil is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution; when the soil is alkaline soil, the extractant is a calcium chloride solution.

[0012] Preferably, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 to 0.03 mol / L, and the concentration of acetic acid is 1 to 3 mol / L.

[0013] Preferably, the mass concentration of the calcium chloride solution is 0.1-0.2%.

[0014] Preferably, the mass volume ratio of the soil to the extractant is 1 g:5-7 mL.

[0015] Preferably, the temperature of the extraction is 25-30°C and the time is 30-50 minutes.

[0016] Preferably, the added amount of Tween-80 is 1-2% of the volume of the extractant.

[0017] Preferably, the secondary extraction is assisted by ultrasound, the frequency of the ultrasound is 40 to 50 kHz, the temperature of the secondary extraction is 25 to 30° C., and the time is 10 to 20 min.

[0018] The present invention provides a method for detecting effective sulfur in soil with high accuracy and good stability, which can not only accurately determine the content of effective sulfur in soil, but also has high calibration stability, and the detection limit is 0.42 mg / kg, which has high detection sensitivity. Therefore, the present invention provides a method for detecting effective sulfur in soil with high sensitivity, accuracy and stability. DETAILED DESCRIPTION

[0019] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0020] Example 1

[0021] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, mixed with the extractant at a solid-liquid ratio of 1 g: 5 mL, and extracted at 28°C for 40 min. After the first extraction was completed, 1.5% of the volume of the extractant, Tween-80, was added, and a second extraction was continued at 28°C, assisted by ultrasound at a frequency of 45 kHz. After extraction for 15 min, the filtrate was filtered to obtain a filtrate, and the filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0022] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 mol / L, and the concentration of acetic acid is 2 mol / L.

[0023] When the soil to be tested is alkaline soil, the extractant is a calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.15%.

[0024] Example 2

[0025] The soil to be tested was dried to a moisture content of less than 5%, crushed to 1 mm, mixed with the extractant at a solid-liquid ratio of 1 g: 7 mL, and extracted at 25°C for 50 min. After the first extraction was completed, 1% Tween-80 by volume of the extractant was added, and a second extraction was continued at 25°C, assisted by ultrasound at a frequency of 40 kHz. After extraction for 20 min, the filtrate was filtered to obtain a filtrate, and the filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0026] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.02 mol / L, and the concentration of acetic acid is 3 mol / L.

[0027] When the soil to be tested is alkaline soil, the extractant is calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.1%.

[0028] Example 3

[0029] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, mixed with the extractant at a solid-liquid ratio of 1 g: 6 mL, and extracted at 30°C for 30 min. After the first extraction was completed, 2% Tween-80 by volume of the extractant was added, and a second extraction was continued at 30°C, assisted by ultrasound at a frequency of 50 kHz. After extraction for 10 min, the filtrate was filtered to obtain a filtrate, and the filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0030] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.03 mol / L, and the concentration of acetic acid is 1 mol / L.

[0031] When the soil to be tested is alkaline soil, the extractant is calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.2%.

[0032] Comparative Example 1

[0033] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, mixed with the extractant at a solid-liquid ratio of 1 g:5 mL, extracted at 28 °C for 1 h, filtered to obtain a filtrate, and the filtrate was filtered through a 0.45 μm filter membrane to obtain a test solution.

[0034] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 mol / L, and the concentration of acetic acid is 2 mol / L.

[0035] When the soil to be tested is alkaline soil, the extractant is a calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.15%.

[0036] Comparative Example 2

[0037] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, mixed with the extractant at a solid-liquid ratio of 1 g:5 mL, and ultrasonically extracted at 28°C for 1 h with an ultrasonic frequency of 45 kHz. After the ultrasonic extraction was completed, the filtrate was filtered to obtain a filtrate, and the filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0038] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 mol / L, and the concentration of acetic acid is 2 mol / L.

[0039] When the soil to be tested is alkaline soil, the extractant is a calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.15%.

[0040] Comparative Example 3

[0041] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, mixed with the extractant at a solid-liquid ratio of 1 g:5 mL, and then 1.5% of the volume of the extractant, Tween-80, was added, and ultrasonic extraction was performed at 28°C for 1 h with an ultrasonic frequency of 45 kHz. After the ultrasonic extraction was completed, the filtrate was filtered to obtain a filtrate, and the filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0042] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 mol / L, and the concentration of acetic acid is 2 mol / L.

[0043] When the soil to be tested is alkaline soil, the extractant is a calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.15%.

[0044] Comparative Example 4

[0045] The soil to be tested was dried to a moisture content of less than 5%, crushed to 2 mm, and mixed with the extractant at a solid-liquid ratio of 1 g: 5 mL. Ultrasonic extraction was performed at 28°C for 40 min at an ultrasonic frequency of 45 kHz. After one extraction was completed, 1.5% Tween-80 by volume of the extractant was added, and a second ultrasonic extraction was performed at 28°C at an ultrasonic frequency of 45 kHz. After extraction for 15 min, the soil was filtered to obtain a filtrate. The filtrate was filtered with a 0.45 μm filter membrane to obtain a test solution.

[0046] When the soil to be tested is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution, the concentration of phosphate in the phosphate-acetic acid solution is 0.01 mol / L, and the concentration of acetic acid is 2 mol / L.

[0047] When the soil to be tested is alkaline soil, the extractant is a calcium chloride solution, and the mass concentration of the calcium chloride solution is 0.15%.

[0048] Experimental Example 1

[0049] Instrument: UV1201 UV-visible spectrophotometer produced by Beijing North Branch Rayleigh, wavelength range 200nm-800nm;

[0050] Reagents: calcium dihydrogen phosphate, acetic acid, calcium chloride, hydrogen peroxide, Tween-80, all of analytical grade or above; commercially available certified sulfur standard solution in water, 1000 mg / L.

[0051] The certified national standard materials are GBW(E)070332, GBW(E)070333, GBW(E)070334, GBW(E)070335, GBW(E)070336, GBW(E)070337, GBW(E)070338, GBW(E)070339, GBW(E)070340 and GBW(E)070341, involving 10 soil types, including paddy soil in Jiujiang, Jiangxi, red soil in Yingtan, Jiangxi, and gray tidal soil in Huadu, Guangdong, covering acidic, neutral and alkaline soils.

[0052] The test solution was prepared by the methods of Examples 1 to 3 and Comparative Examples 1 to 4 and the turbidity method was used for determination. Each standard substance and each method were weighed 3 times independently and the average value was taken. The results are shown in Table 1.

[0053] Table 1 Verification values ​​of standard substances

[0054]

[0055] From the measurement results in Table 1, it can be seen that the measurement accuracy of Examples 1 to 3 and Comparative Examples 1 to 2 is relatively high and can meet the quality control requirements of soil analysis, while the accuracy of Comparative Examples 3 to 4 is relatively poor.

[0056] Experimental Example 2

[0057] Six soil samples from different regions were selected as soil samples to be tested, and the basic information of the six soil samples to be tested is shown in Table 2. Extraction and determination were performed according to the methods of Examples 1 to 3 and Comparative Examples 1 to 4, in parallel for 3 times, and the determination results are shown in Table 3.

[0058] Table 2 Basic information of six soil samples to be tested

[0059]

[0060]

[0061] Table 3 Available sulfur content in six soil samples to be tested (mg / kg)

[0062] serial number 1 2 3 4 5 6 Example 1 2.47 7.77 8.30 8.67 4.47 4.67 Example 2 2.37 7.80 8.23 8.63 4.53 4.63 Example 3 2.43 7.73 8.33 8.70 4.47 4.57 Comparative Example 1 2.47 7.67 8.47 8.80 4.53 4.53 Comparative Example 2 2.43 7.70 8.60 8.77 4.60 4.57 Comparative Example 3 2.13 7.27 7.77 8.23 4.03 4.10 Comparative Example 4 2.23 7.40 7.67 8.30 3.83 4.07

[0063] It can be seen from Table 3 that the test results of the actual soil samples are consistent with those of the standard substances.

[0064] Examples 1 to 3 have higher accuracy.

[0065] Experimental Example 3

[0066] In order to further verify the stability of several methods, the coefficient of variation between replicates was calculated for 6 soil samples to be tested. The results are shown in Table 4.

[0067] Table 4 Coefficient of variation between repeated determination results of available sulfur in six soil samples by several methods (%)

[0068] serial number 1 2 3 4 5 6 average Example 1 2.34 1.97 1.20 2.40 3.42 3.27 2.43 Example 2 2.44 1.28 1.85 2.41 3.37 4.49 2.64 Example 3 2.37 1.97 2.50 3.04 3.42 3.34 2.77 Comparative Example 1 4.68 5.27 3.60 4.54 7.75 7.10 5.49 Comparative Example 2 6.28 5.95 5.07 4.61 9.96 6.69 6.43 Comparative Example 3 2.71 2.10 1.97 1.85 5.16 4.88 3.11 Comparative Example 4 2.58 1.35 2.71 2.09 3.01 3.76 2.58

[0069] From the calculation results in Table 4, it can be seen that the coefficients of variation of Examples 1 to 3 and Comparative Examples 3 to 4 are low, and have good stability, while the coefficients of variation of Comparative Examples 1 to 2 are high, and the stability is poor.

[0070] Experimental Example 4

[0071] The blank test was repeated 11 times using the method of Example 1 and Comparative Examples 1 to 2, and each measurement result was converted into the effective sulfur content in the sample. The standard deviation of the 11 parallel measurements was calculated, and the method detection limit was calculated according to the method characteristic index determination method A.1 formula in Appendix A of the Technical Guidelines for the Development of Environmental Monitoring Analysis Methods HJ168-2020. The results are shown in Table 5.

[0072] MDL=t (n-1，0.99) ×S

[0073] Where: MDL—method detection limit; n—number of parallel determinations of the sample;

[0074] t—t distribution value (one-sided) when the degrees of freedom are n-1 and the confidence level is 99%;

[0075] S is the standard deviation of n parallel measurements.

[0076] Among them, when the degree of freedom is 10 and the confidence level is 99%, the t value is 2.764 according to Table A.1.

[0077] Table 5 Detection limit and quantification limit of the method

[0078]

[0079] From the above content, it can be seen that the present invention provides a method for detecting available sulfur in soil with high accuracy and good stability, which can not only accurately determine the content of available sulfur in soil, but also has high calibration stability, and the detection limit is 0.42 mg / kg, which has high detection sensitivity. Therefore, the present invention provides a method for detecting available sulfur in soil with high sensitivity, accuracy and stability.

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A highly sensitive method for detecting available sulfur in soil, characterized in that: The steps include: (1) Dry and crush the soil to be tested, mix it with an extractant, and perform a primary extraction; (2) adding Tween-80 after the primary extraction to perform a secondary extraction; (3) Taking the filtrate after the secondary extraction, the effective sulfur is determined by turbidity method.

2. The detection method according to claim 1, characterized in that The drying process is to dry the soil until the water content is less than 5%; the particle size of the soil after crushing is 1 to 2 mm.

3. The detection method according to claim 2, characterized in that When the soil is acidic soil or neutral soil, the extractant is a phosphate-acetic acid solution; when the soil is alkaline soil, the extractant is a calcium chloride solution.

4. The detection method according to claim 3, characterized in that The concentration of phosphate in the phosphate-acetic acid solution is 0.01-0.03 mol / L, and the concentration of acetic acid is 1-3 mol / L.

5. The detection method according to claim 3, characterized in that: The mass concentration of the calcium chloride solution is 0.1-0.2%.

6. The detection method according to claim 3, characterized in that: The mass volume ratio of the soil to the extractant is 1 g:5-7 mL.

7. The detection method according to claim 6, characterized in that The temperature of the primary extraction is 25-30° C. and the time is 30-50 min.

8. The detection method according to claim 7, characterized in that The added amount of Tween-80 is 1-2% of the volume of the extractant.

9. The detection method according to any one of claims 1 to 8, characterized in that: The secondary extraction is assisted by ultrasound, the frequency of the ultrasound is 40-50 kHz, the temperature of the secondary extraction is 25-30° C., and the time is 10-20 min.

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