1. A method for extracting organic phosphorus from calcareous soil is characterized by comprising the following steps: the method comprises the following steps:

s1, adding acid into the calcareous soil for reaction, and washing with water to obtain a precipitate;

s2, adding N into the precipitate after freeze-dryinga₂Extracting with EDTA-NaOH extractant, and sequentially oscillating, centrifuging and filtering to obtain organic phosphorus extract, namely realizing extraction of organic phosphorus in the calcareous soil;

the Na is₂EDTA-NaOH extractant refers to Na₂Mixed aqueous solutions of EDTA and NaOH.

2. The method for extracting organophosphorus from calcareous soil according to claim 1, wherein: in step S1, the acid is any one of hydrochloric acid, nitric acid, and sulfuric acid;

the concentration of the acid is 1.44M, 2.88M, 4.32M or 5.78M;

the mass ratio of the alkaline calcareous soil to the acid is 1: 5 to 10.

3. The method for extracting organophosphorus from calcareous soil according to claim 1 or 2, wherein: in the step S1, after the acid is added, shaking for 5-10 min, and standing until no bubbles are generated; centrifuging for 10-15 min to obtain the precipitate;

the precipitate was washed with water to neutrality.

4. The method for extracting organophosphorus from calcareous soil according to claim 3, wherein: in step S2, the Na₂In EDTA-NaOH extractant, the Na₂The molar concentration of EDTA is 0.01-0.1M, and the molar concentration of NaOH is 0.1-0.5M.

5. The method for extracting organophosphorus from calcareous soil according to claim 4, wherein: in step S2, the extraction conditions are as follows:

the precipitate is mixed with the Na₂The mass ratio of the EDTA-NaOH extractant is 1: 10-20;

the conditions of the oscillation are as follows: the temperature is 20-25 ℃, and the time is 6-16 h;

the centrifugation conditions were: the rotating speed is 4500-5000 r/min, and the time is 10-20 min.

6. The method for extracting organophosphorus from calcareous soil according to claim 5, wherein: the alkaline calcareous soil is from Henan or Shaanxi.

7. Liquid phase of organic phosphorus in alkaline calcareous soil³¹A P-NMR detection method characterized by: the method comprises the following steps:

s I) extracting organic phosphorus from the calcareous soil by using the method for extracting the organic phosphorus from the calcareous soil according to any one of claims 1 to 6 to obtain an organic phosphorus extracting solution;

s II) the organophosphorus extracting solution is re-dissolved after being freeze-dried, and then liquid phase is carried out³¹And (4) detecting by using P-NMR.

8. Liquid phase of organophosphorus in alkaline calcareous soil according to claim 7³¹A P-NMR detection method characterized by: and before the step II), filtering the organic phosphorus extracting solution by adopting a 0.45um filter membrane.

Background

The organic phosphorus being of plantsImportant phosphorus sources are increasingly paid attention particularly with the continuous decrease of global phosphorus ore resources. Morphological information of soil organophosphorus is a prerequisite for understanding the effectiveness of organophosphorus and for exploring organophosphorus libraries for agricultural production. However, the chemical structure and biological effectiveness thereof are still poorly understood, mainly due to limitations in analytical methods.³¹P-NMR technology provides a powerful means for characterization and identification of organophosphorus in soil, but organophosphorus must be extracted from soil before testing so as to be quantified and identified, so that subsequent morphological and biological effectiveness researches can be facilitated. The ideal extractant for soil organophosphate chemical characterization should maximize recovery while minimizing chemical structural changes.

The most widely used extraction method at present is an EDTA-NaOH one-step extraction method, and EDTA in an alkaline solvent improves the extraction rate of organic phosphorus in soil by chelating metal cations. However, in case of calcareous soil, a large amount of soluble calcium ions are contained, and calcium salt precipitation is easily generated during extraction with an alkaline solution, so that organic phosphorus is fixed, and the extraction rate of the organic phosphorus is reduced. Therefore, there is a need for an improved method for extracting organophosphorus from calcareous soil, which is of practical significance for accurately evaluating phosphorus reserves, forms and biological effectiveness of calcareous soil.

Disclosure of Invention

The invention aims to provide a method for improving the extraction rate of organic phosphorus in calcareous soil and a liquid phase³¹The invention relates to a method for detecting the effect of P-NMR, which carries out acidification pretreatment on calcareous soil, ionizes soluble calcium carbonate and then cleans the calcium carbonate with ultrapure water, thereby removing a large amount of calcium ions in the soil; then EDTA-NaOH solution is adopted for extraction, the extract is redissolved by alkali solution after being freeze-dried, thereby improving the extraction rate of the organic phosphorus in the calcareous soil, and the organic phosphorus in the solution³¹Better spectral resolution was obtained in P-NMR.

The invention firstly provides a method for extracting organophosphorus in calcareous soil, which comprises the following steps:

s1, adding acid into the calcareous soil for reaction, and washing with water to obtain a precipitate;

s2, freeze-dryingAdding Na to the precipitate₂Extracting with EDTA-NaOH extractant, and sequentially oscillating, centrifuging and filtering to obtain organic phosphorus extract, namely realizing extraction of organic phosphorus in the calcareous soil;

0.5-1 ml of organic phosphorus extracting solution can be adopted, and the diluted organic phosphorus extracting solution is used for measuring the content of organic phosphorus;

the Na is₂EDTA-NaOH extractant refers to Na₂Mixed aqueous solutions of EDTA and NaOH.

In the above extraction method, in step S1, the acid is any one of hydrochloric acid, nitric acid and sulfuric acid, preferably hydrochloric acid;

the concentration of the acid is 1.44M, 2.88M, 4.32M or 5.78M, preferably 2.88M.

The mass ratio of the calcareous soil to the acid is 1: 5-10, preferably 1: 8;

in the extraction method, in step S1, after the acid is added, shaking is carried out for 5-10 min, and standing is carried out until no bubbles are generated; centrifuging for 10-15 min to obtain the precipitate;

the precipitate was washed with water to neutrality.

In the above extraction method, in step S2, the Na is₂In EDTA-NaOH extractant, the Na₂The molar concentration of EDTA can be 0.01-0.1M, preferably 0.05M, and the molar concentration of NaOH is 0.1-0.5M, preferably 0.25M.

In the above extraction method, in step S2, the extraction conditions are as follows:

the precipitate is mixed with the Na₂The mass ratio of the EDTA-NaOH extractant is 1: 10-20, preferably 1: 10 (adjusted according to the organic content of the sample);

the conditions of the oscillation are as follows: the temperature is 20-25 ℃, the time is 6-16 h, and the oscillation is preferably carried out for 6h under the condition of 20 ℃;

the centrifugation conditions were: the rotating speed is 4500-5000 r/min, the time is 10-20 min, and centrifugation is preferably carried out for 20min under the condition of 4800 r/min.

On the basis of the extraction method, the invention further provides a liquid phase of organic phosphorus in calcareous soil³¹The P-NMR detection method comprises the following steps:

the organic phosphorus extract is lyophilized and redissolved, and then liquid phase can be carried out³¹And (4) detecting by using P-NMR.

In the detection method, before freeze-drying, the organic phosphorus extracting solution is filtered by a 0.45um filter membrane;

in the above-mentioned detection method, the compound is dissolved in D₂O、H₂O、Na₂In a mixture of EDTA-NaOH extractant and NaOH, e.g. 0.65ml D₂O、0.65 ml H₂O、0.65ml 0.05 M Na₂EDTA-0.25M NaOH, 0.4ml 10M NaOH water solution, vortex shaking for 10min, then adding into 5mm nuclear magnetic tube, and testing on the machine.

Carrying out the liquid phase³¹When P-NMR is detected, the test parameters are as follows: d1=5s, TD =16400, TE =293K, P1=70usec, NS =3000~6000, and the remaining parameters are automatically set with reference to the machine.

The invention verifies the influence of the acid pretreatment step in the method on the chemical structure of phosphorus in soil, and the method can be carried out according to the following steps: selecting typical soil organic phosphorus standard sample, respectively extracting according to the invention and only adopting Na₂The EDTA-NaOH extractant is extracted by the method, and the change of the chemical structure of the soil phosphorus in the two modes is detected by NMR, and experimental results show that the chemical structure of the organic phosphorus can be influenced only by nitric acid treatment in the three treatment environments, and the chemical structure of the organic phosphorus can not be influenced by the acid treatment of hydrochloric acid and sulfuric acid, so that the subsequent nuclear magnetic analysis and test can be met.

Specifically, the soil phosphorus standard sample can be phytic acid (IHP), glucose 6 phosphate (G-6-P), and Deoxyribonucleotide (DNA).

Specifically, the simulation of the method of the present invention can be implemented as follows: taking 0.03g of the soil organophosphorus standard sample (0.01 g of DNA due to solubility), dissolving in 1ml of acid, and fully mixing; then adding 1ml of NaOH with corresponding concentration, and neutralizing the solution to be neutral; adding 1ml of 0.75M NaOH-0.15M EDTA extractant (here, 3 times the concentration of NaOH-EDTA is prepared to reduce the actual extraction environment pH);

the use of Na alone can be achieved as follows₂Simulation of the procedure for EDTA-NaOH extraction: take 0.03g or 0.01g of the soil phosphorus standard sample is dissolved in 3ml of 0.25M NaOH-0.15M EDTA solution and mixed well.

The simulation of the redissolution environment of the dried substance is realized according to the following steps: taking 0.65ml of each of the above two simulated extractive solutions, respectively dissolving in 0.65ml of H₂O，0.65ml D₂O, 0.4ml of 10M NaOH mixture.

Proved by verification, the pretreatment effect of 2.88M HCl is best, and the method can improve the extraction rate of organic phosphorus in calcareous soil and improve the liquid phase³¹P-NMR detection Effect: the acid pretreatment can obviously improve the extraction rate of the NaOH-EDTA organic phosphorus; at the same time, NMR results also show that the acid pretreatment has increased organic phosphorus species compared with the NaOH-EDTA one-step extraction method. Therefore, the method can improve the recognition degree of organophosphorus characteristic peaks in an NMR spectrogram;

specifically, ICP method can be adopted to measure total phosphorus content, molybdenum blue colorimetric method is adopted to measure inorganic phosphorus content, and subtraction method is adopted to obtain organic phosphorus content.

The method is suitable for extracting and detecting the organic phosphorus in the calcareous soil in Henan, Shaanxi and other places.

Compared with the prior art, the method has the following beneficial effects:

(1) can obviously improve the extraction amount of organic phosphorus in calcareous soil, in particular to phosphate monoester.

(2) The recognition degree of the organophosphorus characteristic peak in the NMR spectrum can be improved.

Drawings

FIG. 1 is a comparison of the chemical structure of soil phosphorus in three environments for three typical soil organophosphorus standards according to the embodiment of the present invention.

FIG. 2 is an NMR spectrum of two kinds of high-calcium soils in Shanxi and Henan after acid pretreatment and one-step extraction of EDTA-NaOH.

FIG. 3 shows the morphological contents of various phosphorus in the soil after hydrochloric acid treatment at different concentrations.

FIG. 4 shows the phosphorus content of various forms in soil after different kinds of acid treatment.

FIG. 5 shows the morphological content of phosphorus extracted from NaOH-EDTA after pretreatment with acids of different concentrations.

FIG. 6 shows the morphological content of phosphorus extracted from NaOH-EDTA after pretreatment with different acids.

FIG. 7 shows the morphological content of various phosphorus in the soil residue after NaOH-EDTA extraction.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Example 1 extraction and detection of organic phosphorus in calcareous soil

1) Pretreatment with acids of different concentrations

1.44M, 2.88M, 4.32M, 5.76M HCl was mixed in 1: adding the soil-liquid ratio of 8 into calcareous soil taken from Shaanxi and Henan, shaking for 10min, and standing until no bubbles are generated; centrifuging for 10min, 5000r/min, washing with deionized water for 5 times until pH is greater than 5, collecting washing liquid each time to obtain target precipitate, and lyophilizing.

2) Pretreatment with different kinds of acids

Adding 1.44M HCl and HNO₃And 0.72M H₂SO₄According to the following steps: adding the soil-liquid ratio of 8 into calcareous soil taken from Shaanxi and Henan, shaking for 10min, and standing until no bubbles are generated; centrifuging for 10min, 5000r/min, washing with deionized water for 5 times until pH is greater than 5, collecting washing liquid each time to obtain target precipitate, and lyophilizing.

3) NaOH-EDTA extraction

Freeze-drying the above centrifugation precipitate in a 1: 10 soil-to-liquid ratio, 0.05M Na was added₂Extracting with EDTA-0.25M NaOH, shaking at 20 deg.C for 6 hr, centrifuging for 20min, 4800r/min, filtering to obtain organic phosphorus extractive solution, and filtering with 0.45um filter membrane.

3) Taking the lml organophosphorus extracting solution for measuring the content of organophosphorus, and freeze-drying the rest part. Redissolving the lyophilized extract in 0.65ml D₂O，0.65ml H₂O，0.65ml 0.05M Na₂EDTA-0.25M NaOH, 0.4ml 10M NaOH, vortex shaking for 10min, mixing the solution to 5mm nuclear magnetic tube, and NMR analysis.

Conditions for NMR analysis: d1=5s, TD =16400, TE =293K, P1=70usec, NS =3000~6000, and the remaining parameters are automatically set with reference to the machine.

Comparative example 1 extraction and detection of organic phosphorus in calcareous soil

1) NaOH-EDTA extraction

Taking calcium soil of Shanxi and Henan, mixing the materials in a proportion of 1: 10 soil-to-liquid ratio, 0.05M Na was added₂Extracting EDTA-0.25M NaOH, and shaking at 20 deg.C and 200r/min for 6 hr; centrifuging for 20min at 4800r/min, filtering to obtain organic phosphorus extractive solution, and filtering with 0.45um filter membrane.

2) Taking the lml organophosphorus extracting solution for measuring the content of organophosphorus, and freeze-drying the rest part. Redissolving the lyophilized extract in 0.65ml D₂O，0.65ml H₂O，0.65ml 0.05M Na₂EDTA-0.25M NaOH, 0.4ml 10M NaOH, vortex shaking for 10min, mixing the solution to 5mm nuclear magnetic tube, and NMR analysis.

Conditions for NMR analysis: d1=5s, TD =16400, TE =293K, P1=70usec, NS =3000~6000, and the remaining parameters are automatically set with reference to the machine.

The content of phosphorus in the original soil and in each form after hydrochloric acid treatment at different concentrations is shown in FIG. 3.

As can be seen from the data in FIG. 3, total phosphorus and inorganic phosphorus content are essentially inversely related to acid concentration, with organic phosphorus being lost in relatively small amounts when treated with 1.44M and 2.88M HCl. Suitable acid concentrations were determined to be 1.44M and 2.88M.

The results of the phosphorus contents of the different types of the acid-treated soil are shown in FIG. 4.

As can be seen from the data in FIG. 4, the treatment effect of hydrochloric acid and nitric acid is better than that of sulfuric acid, and particularly in Henan soil, the loss amount of organic phosphorus after the sulfuric acid treatment is the largest. Suitable acids were thus determined to be hydrochloric acid and nitric acid.

The results of the morphological contents of phosphorus extracted by NaOH-EDTA after pretreatment with hydrochloric acid of different concentrations are shown in FIG. 5.

As can be seen from the data in FIG. 5, the soil pretreated with 2.88M HCl and further extracted with NaOH-EDTA exhibited the greatest amount of organic phosphorus extracted, and the most suitable acid concentration was 2.88M in combination with FIG. 3.

The morphological content of each phosphorus in the solution extracted by NaOH-EDTA after pretreatment with different kinds of acids is shown in FIG. 6.

From the data in FIG. 6, HCl and HNO₃After pretreatment, the content of extracted organic phosphorus is higher than H₂SO₄And (4) extracting. It was further determined that the most suitable acid species was HCl or HNO₃。

Via HCl or HNO₃The morphological contents of phosphorus in the pretreated soil and the soil residue after NaOH-EDTA extraction are shown in FIG. 7.

As can be seen from the data in FIG. 7, HCl or HNO₃The residual quantity of organic phosphorus in the pretreated soil is not very different. Based on the above data, 2.88M HCl and HNO are known₃The pretreatment agent is most suitable.

In order to verify the influence of the pretreatment steps of hydrochloric acid and nitric acid on the chemical structure of phosphorus in soil in the method, the method comprises the following steps: selecting typical soil organic phosphorus standard samples (phytic acid (IHP), glucose 6 phosphate (G-6-P) and Deoxyribonucleotide (DNA) respectively according to the extraction method of the invention and only adopting Na₂EDTA-NaOH extraction method for dissolution, and NMR for detection of changes in soil phosphorus chemical structure.

The simulation of the method of the invention is realized according to the following steps: 0.03g of soil organophosphorus standard sample (0.01 g of DNA due to low solubility) was dissolved in 1ml of 2.88M HCl and HNO₃Fully mixing; then adding 1ml of 2.88M NaOH, and neutralizing the solution to be neutral; adding 1ml of 0.75M NaOH-0.15M EDTA extractant (here, 3 times the concentration of NaOH-EDTA is prepared to reduce the actual extraction environment pH);

the method is realized by adopting Na only according to the following steps₂Simulation of the procedure for EDTA-NaOH extraction: 0.03g of soil organophosphorus standard sample (0.01 g of DNA) was dissolved in 3ml of 0.25M NaOH-0.15M EDTA solution and mixed thoroughly.

Taking 0.65ml of the standard sample preparation solution in the two states, and adding 0.65ml of D₂O，0.65ml H₂O, 0.4ml of 10M NaOH, mixed well and subjected to NMR analysis.

Conditions for NMR analysis: d1=5s, TD =16400, TE =293K, P1=70usec, NS =300, and the remaining parameters are automatically set with reference to the machine.

The phosphorus chemical structure pairs of three typical soil organophosphorus standards in three environments are shown in figure 1, wherein A represents HNO₃Acidifying and then extracting with an alkali solution, wherein B represents firstly acidifying with HCl and then extracting with an alkali solution, and C represents extracting with an alkali solution by one step.

From the data in FIG. 1, it can be seen that:

influence of pretreatment on phosphorus chemical structure: selecting three typical soil organic phosphorus standard samples, simulating acidification treatment, alkali solution extraction and alkali solution one-step extraction, and detecting the change of the soil phosphorus chemical structure in the three environments by using NMR (nuclear magnetic resonance), wherein the phosphorus standard samples are HNO (hydrogen sulfide oxide) in the three treatment environments₃The chemical structure of the treated standard was altered, especially DNA, probably due to HNO₃The oxidation of (a) results in the decomposition of organic phosphorus; the hydrochloric acid treatment had less effect on the samples.

NMR spectra of two kinds of high-calcium soils in Shaanxi and Henan, which are subjected to hydrochloric acid pretreatment (example 1) and one-step extraction of EDTA-NaOH (comparative example 1), are shown in FIG. 2, wherein the NMR spectra are marked in the figure, and the Shanxi-HCl represents the hydrochloric acid pretreatment, the Shanxi represents the one-step extraction of EDTA-NaOH, and the Shanxi-HNO₃Indicating a pretreatment with nitric acid, wherein the HCl concentration is 2.88M, HNO₃The concentration of (2) was 2.88M.

From the data in FIG. 2, it can be seen that: the HCl pretreatment will remove a large amount of inorganic phosphorus, when using HNO of the same concentration₃The residual inorganic phosphorus in the treated soil is more than that in the HCl treatment, which shows that the nitric acid not only has an acidifying effect, but also has an oxidizing effect, so that other organic phosphorus is oxidized into orthophosphate. And the HCl pretreatment has an increased number of detectable organophosphorus species compared to conventional NaOH-EDTA extraction.

To sum up, 2.88M HCl is preferred as the pretreatment.