Method for extracting organic phosphorus in calcareous soil and detecting liquid phase < 31 > P-NMR (nuclear magnetic resonance)

Abstract

The invention relates to a method for extraction of organophosphorus in calcareous soil and liquid phase < 31 > P-NMR detection, and belongs to the technical field of environmental analysis, the method comprises the following steps: removing impurities from the soil, freeze-drying, preparing natural granularity, screening, fully and uniformly mixing, filling into a bottle, culturing at 20-30 DEG C in a shading manner for 8-15 days to obtain a soil sample, extracting a precipitate with a NaOH-EDTA mixed solution, and determining the content of organophosphorus in the soil; carrying out freeze drying on the supernatant II, and then carrying out NMR (nuclear magnetic resonance) testing; adding 10% of HCI into the third precipitate, standing for 20 min to enable CaCO3 to fully react to obtain a fourth precipitate, extracting the fourth precipitate with a NaOH-EDTA mixed solution to obtain a third supernatant, mixing the third supernatant and the first supernatant, performing freeze drying, and performing NMR testing. Phosphorus is detected from multiple and multi-stage extracting solutions, the extraction amount of organophosphorus in the calcareous soil can be accurately detected, and the detection accuracy is high. Soil available phosphorus mainly comes from freely diffused inorganic phosphorus and easily mineralized organic phosphorus.

Description

Technical Field

[0001] The present invention relates to the field of environmental analysis technology, and specifically refers to a method for extracting organic phosphorus from calcareous soil and liquid phase 31 P-NMR detection method. Background Art

[0002] The soil contains inorganic phosphorus and organic phosphorus, of which organic phosphorus accounts for 35-65% of the total soil phosphorus. Understanding the changing dynamics of soil organic phosphorus is of great significance for a deeper understanding of the biogeochemical cycle of soil phosphorus and the establishment of efficient and sustainable agricultural management measures.

[0003] The inorganic phosphorus in the soil is mainly orthophosphate, and its content can be determined by spectrophotometry and ICP-OES. The content of organic phosphorus in the soil can be estimated by subtracting the inorganic phosphorus extracted by acid from the total phosphorus extracted after digestion. At the same time, specific soil organic phosphorus forms can be extracted and analyzed by chromatography, such as using chloroform, methanol and water or dichloromethane and methanol to extract phospholipids, followed by chromatographic separation and content determination. However, this method cannot determine the form of organic phosphorus, but can only determine the content of a specific form of organic phosphorus. There are many types of organic phosphorus molecules in the soil, so it is necessary to analyze the form and composition of soil organic phosphorus at the molecular level.

[0004] The most widely used extraction method is the EDTA-NaOH one-step extraction method. EDTA in alkaline solvents improves the extraction rate of soil organic phosphorus by chelating metal cations. However, for calcareous soils, which contain a large amount of soluble calcium ions, calcium salt precipitation is easily generated when extracted with alkaline solutions, which leads to the fixation of organic phosphorus and reduces the organic phosphorus extraction rate. Therefore, it is necessary to improve the organic phosphorus extraction rate method of calcareous soils, which is of great practical significance for accurately evaluating the phosphorus reserves, forms and bioavailability in calcareous soils. Summary of the invention

[0005] The present invention aims to solve the above technical problems and provide a method for extracting organic phosphorus from calcareous soil and liquid phase 31 P-NMR detection method.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] A method for extracting organic phosphorus from calcareous soil comprises the following steps:

[0008] S1. Soil pretreatment:

[0009] The soil was cleaned of impurities, freeze-dried, and prepared into natural particle size, then sieved and fully mixed, put into bottles, and placed in a dark environment at 20-30°C for 8-15 days to obtain soil samples.

[0010] S2. Sampling:

[0011] Take a soil sample, add 10% HCl and let it stand for 20 minutes to allow CaCO3 to fully react, and obtain precipitate 1. The precipitate 1 is washed with deionized water three times to obtain precipitate 2.

[0012] The soil sample was extracted with a NaOH-EDTA mixed solution to obtain supernatant 1 and precipitate 3;

[0013] S4. Extraction:

[0014] The second precipitate was extracted with a NaOH-EDTA mixed solution to obtain a second supernatant, which was freeze-dried and then subjected to NMR testing.

[0015] Preferably, the centrifugation is carried out using a centrifuge with parameters of 7000-8000 r·min-1 for 8-10 min.

[0016] Liquid phase of organic phosphorus in alkaline calcareous soil 31 The P-NMR detection method comprises the following steps: a mixture of the supernatant three, the supernatant one or the supernatant two obtained by the method for extracting organic phosphorus from calcareous soil is placed in a nuclear magnetic resonance instrument for liquid phase 31P-NMR detection.

[0017] Preferably, the operating conditions of the nuclear magnetic resonance instrument are temperature 20-25°C, resonance frequency 120-135MHz, pulse 10-12usec, pulse power 2.5-3dB, cycle delay 2-4s, and scan 5000-9000 times.

[0018] After adopting the above method, the present invention has the following advantages:

[0019] The present invention detects phosphorus from multiple and multi-level extracts. A NaOH-EDTA mixed solution is used to extract a second precipitate to obtain a second supernatant, which is freeze-dried and then subjected to an NMR test. 10% HCI is added to a third precipitate and allowed to stand for 20 minutes to allow CaCO3 to fully react to obtain a fourth precipitate. The fourth precipitate is extracted with a NaOH-EDTA mixed solution to obtain a third supernatant. The third supernatant and the first supernatant are mixed, freeze-dried, and subjected to an NMR test. The organic phosphorus extraction amount of the calcareous soil can be accurately detected. The effective phosphorus in the soil mainly comes from freely diffusible inorganic phosphorus and easily mineralized organic phosphorus.

[0020] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] none DETAILED DESCRIPTION

[0022] Specific embodiments of the present invention will now be mentioned in detail. Although the present invention is described in conjunction with these specific embodiments, it should be appreciated that it is not intended to limit the present invention to these specific embodiments. On the contrary, these embodiments are intended to cover substitutions, changes or equivalent embodiments that may be included in the spirit and scope of the invention defined by the claims. In the following description, a large number of specific details are set forth in order to provide a comprehensive understanding of the present invention. The present invention can be implemented without some or all of these specific details. In other cases, in order not to make the present invention unnecessarily obscure, well-known process operations are not described in detail.

[0023] When used in conjunction with "including," "methods comprising," or similar language in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0024] The present invention is further described in detail below in conjunction with the full text.

[0025] In combination with the full text, a method for extracting organic phosphorus in calcareous soil comprises the following steps:

[0026] S1. Soil pretreatment:

[0027] The soil was cleaned of impurities, freeze-dried, and prepared into natural particle size, then sieved and fully mixed, put into bottles, and placed in a dark environment at 20-30°C for 8-15 days to obtain soil samples.

[0028] S2. Sampling:

[0029] Take a soil sample, add 10% HCl and let it stand for 20 minutes to allow CaCO3 to fully react, and obtain precipitate 1. The precipitate 1 is washed with deionized water three times to obtain precipitate 2.

[0030] The soil sample was extracted with a NaOH-EDTA mixed solution to obtain supernatant 1 and precipitate 3;

[0031] S4. Extraction:

[0032] The second precipitate was extracted with a NaOH-EDTA mixed solution to obtain a second supernatant, which was freeze-dried and then subjected to NMR testing.

[0033] 10% HCl was added to the precipitate 3 and allowed to stand for 20 min to allow CaCO3 to fully react, thereby obtaining the precipitate 4. The precipitate 4 was extracted with a NaOH-EDTA mixed solution to obtain the supernatant 3. The supernatant 3 and the supernatant 1 were mixed and freeze-dried for NMR testing.

[0034] The centrifugation is carried out using a centrifuge with a parameter of 7000-8000 r·min-1 for 8-10 min.

[0035] Liquid phase of organic phosphorus in alkaline calcareous soil 31 The P-NMR detection method comprises the following steps: a mixture of the supernatant three, the supernatant one or the supernatant two obtained by the method for extracting organic phosphorus from calcareous soil is placed in a nuclear magnetic resonance instrument for liquid phase 31P-NMR detection.

[0036] Preferably, the operating conditions of the nuclear magnetic resonance instrument are temperature 20-25°C, resonance frequency 120-135MHz, pulse 10-12usec, pulse power 2.5-3dB, cycle delay 2-4s, and scan 5000-9000 times.

[0037] Embodiment 1:

[0038] A method for extracting organic phosphorus from calcareous soil comprises the following steps:

[0039] S1. Soil pretreatment:

[0040] The soil was cleaned of impurities, freeze-dried, and prepared into natural particle size, then sieved and fully mixed, put into bottles, and placed in the dark at 20°C for 8 days to obtain soil samples.

[0041] S2. Sampling:

[0042] Take the soil sample, add 10% HCl and let it stand for 20 minutes to allow CaCO3 to fully react, and obtain precipitate 1. The precipitate 1 is washed with deionized water 3 times to obtain precipitate 2.

[0043] The second precipitate was extracted with a NaOH-EDTA mixed solution to obtain a second supernatant, which was freeze-dried and then subjected to NMR testing.

[0044] Embodiment 2:

[0045] A method for extracting organic phosphorus from calcareous soil comprises the following steps:

[0046] S1. Soil pretreatment:

[0047] The soil was cleaned of impurities, freeze-dried, and prepared into natural particle size, then sieved and fully mixed, put into bottles, and cultured at 30°C in the dark for 15 days to obtain soil samples.

[0048] S2. Sampling:

[0049] A soil sample was extracted with a NaOH-EDTA mixed solution to obtain a supernatant 1 and a precipitate 3. 10% HCl was added to the precipitate 3 and allowed to stand for 20 minutes to allow CaCO3 to fully react to obtain a precipitate 4. The precipitate 4 was extracted with a NaOH-EDTA mixed solution to obtain a supernatant 3. The supernatant 3 and the supernatant 1 were mixed and freeze-dried for NMR testing.

[0050] The present invention and its embodiments are described above, and such description is not restrictive. What is shown in the full text is only one of the embodiments of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A method for extracting organic phosphorus from calcareous soil, characterized in that: The following steps are involved: S1. Soil pretreatment: The soil was cleaned of impurities, freeze-dried, and prepared into natural particle size, then sieved and fully mixed, put into bottles, and placed in shaded culture at 20-30°C for 8-15 days to obtain soil samples. S2. Sampling: Take a soil sample, add 10% HCl and let it stand for 20 minutes to allow CaCO3 to fully react, and obtain precipitate 1. The precipitate 1 is washed with deionized water three times to obtain precipitate 2. The soil sample was extracted with a NaOH-EDTA mixed solution to obtain supernatant 1 and precipitate 3; S4. Extraction: The second precipitate was extracted with a NaOH-EDTA mixed solution to obtain a second supernatant, which was freeze-dried and then subjected to NMR testing; 10% HCl was added to the precipitate three and allowed to stand for 20 min to allow CaCO3 to fully react to obtain precipitate four. The precipitate four was extracted with a NaOH-EDTA mixed solution to obtain supernatant three. The supernatant three and supernatant one were mixed and freeze-dried for NMR testing.

2. The method for extracting organic phosphorus from calcareous soil according to claim 1, characterized in that: The centrifugation is carried out using a centrifuge with parameters of 7000-8000 r·min-1 for 8-10 min.

3. A liquid phase 31P-NMR detection method for organic phosphorus in alkaline calcareous soil, characterized in that: The method comprises the following steps: mixing one or more of the supernatant three, the supernatant one or the supernatant two obtained by the method for extracting organic phosphorus in calcareous soil according to any one of claim 1, placing the mixture in a nuclear magnetic resonance apparatus, and then performing liquid phase 31P-NMR detection.

4. The liquid phase 31P-NMR detection method for organic phosphorus in alkaline calcareous soil according to claim 3, characterized in that: The operating conditions of the nuclear magnetic resonance instrument are as follows: temperature 20-25° C., resonance frequency 120-135 MHz, pulse 10-12 usec, pulse power 2.5-3 dB, cycle delay 2-4 s, and scan 5000-9000 times.