Method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method

Abstract

The invention discloses a method for determining total phosphorus and total potassium in an organic fertilizer by a pressure tank digestion method, which comprises the following steps: S1, sample preparation, S2, sample solution preparation and standard solution preparation, S3, determination of water content of an air-dried sample, S4, determination of total phosphorus content, and S5, determination of total potassium content. The sample preparation process in the step S1 comprises air drying, grinding, sieving and collecting, and sieving equipment is a nylon sieve. The method for determining the total phosphorus and the total potassium in the organic fertilizer by the pressure tank digestion method comprises the following steps: feeding a treated organic fertilizer sample into a digestion inner tank, adding hydrogen peroxide and nitric acid, uniformly shaking, mixing, putting into an outer tank, feeding the outer tank into a constant-temperature drying box, heating, cooling, slowly unscrewing the outer tank, taking out the digestion inner tank, and carrying out pressure tank digestion on the organic fertilizer to obtain the total phosphorus and the total potassium in the organic fertilizer. Transferring the digestive juice into a 50mL volumetric flask, and performing a reagent blank test at the same time; the consumption of the digestion reagent can be reduced, the digestion time is shortened, and the digestion process basically does not need to be attended by a detector.

Description

Technical Field

[0001] The present invention relates to the technical field of organic fertilizer determination, and specifically to a method for determining total phosphorus and total potassium in organic fertilizer by a pressure tank digestion method. Background Art

[0002] Organic fertilizers improve soil fertility and promote plant growth by increasing the organic matter and nutrients utilized by bacteria, fungi, and other organisms in the soil, and play an important role in daily agricultural production. In agricultural production, there is a great demand for high-quality and efficient organic fertilizers, and the total nutrients composed of nitrogen, phosphorus, and potassium are important indicators for measuring the fertility of organic fertilizers.

[0003] When determining the phosphorus and potassium contents in organic fertilizers, a sample solution is required. In the prior art, when preparing the sample solution, wet digestion is mainly used, including the sulfuric acid-hydrogen peroxide method, the aqua regia-perchloric acid method, and the nitric acid-perchloric acid method. These preparation methods have the following problems: 1. The consumption of sample digestion reagents is large and uncertain, increasing the risks of experimental safety and environmental pollution. 2. To achieve the colorless or light yellow solution effect required by the standard, it is necessary to frequently supplement the digestion reagents during the digestion process, and repeatedly perform the operations of heating-cooling-replenishing liquid-heating, resulting in a long overall digestion time and large subjective differences in the judgment of the digestion end point by the tester. 3. The sample digestion process requires the tester to be on duty, constantly paying attention to the changes in the digestion situation and dealing with them in a timely manner, increasing the health risks to the tester and at the same time increasing the investment in human resources. 4. The nylon sieve aperture used in the standard NY / T525-2021 "Organic Fertilizer" is relatively large, resulting in a long pre-reaction time and difficulty in achieving consistent uniformity. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for determining total phosphorus and total potassium in organic fertilizer by a pressure tank digestion method, so as to solve the problems of long existing sample digestion time and large reagent consumption mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A method for determining total phosphorus and total potassium in organic fertilizer by a pressure tank digestion method, comprising the following steps:

[0006] S1. Sample preparation;

[0007] S2. Sample solution preparation and standard solution preparation;

[0008] S3. Determination of the moisture content of the air-dried sample;

[0009] S4. Determination of the total phosphorus content;

[0010] S5. Determination of the total potassium content.

[0011] Preferably, the sample preparation process in S1 includes air drying, grinding, sieving and collection. The sieving equipment is a nylon sieve with a filtration aperture of 0.25 mm.

[0012] Preferably, the sample solution preparation equipment in S2 is a pressure tank, which consists of an inner tank, a lower gasket, an outer tank, an upper pressing piece, an upper cover and a boosting rod.

[0013] Preferably, the sample solution in S2 is a test solution obtained by digesting the organic fertilizer sample with hydrogen peroxide and nitric acid. The standard solutions are specifically phosphorus standard solution and potassium standard solution. The concentration of hydrogen peroxide is 30%, the dosage of hydrogen peroxide added is 4 mL, the dosage of nitric acid added is 4 mL, and the mass of the sample material is 0.35 g.

[0014] Preferably, after the test solution in S2 is mixed, it needs to be sent to a constant temperature drying oven for processing. The temperature of the constant temperature drying oven is set at 165 °C, and the heating time is set at 5 h.

[0015] Preferably, when preparing the phosphorus standard solution, 5.00 mL of phosphorus standard stock solution is added to a 100 mL volumetric flask and mixed with water. The concentration of the phosphorus standard stock solution is 1000 μg / mL, and the concentration of the prepared phosphorus standard solution is 50 μg / mL.

[0016] Preferably, when preparing the potassium standard solution, 10.00 mL of potassium standard stock solution is added to a 100 mL volumetric flask and mixed with water. The concentration of the potassium standard stock solution is 1000 μg / mL, and the concentration of the prepared potassium standard solution is 100 μg / mL.

[0017] Preferably, when measuring the total phosphorus content in S4, an ultraviolet-visible spectrophotometer and a colorimetric tube are required, and a phosphorus standard solution, a 2,4-dinitrophenol indicator with a concentration of 2 g / L, a sodium hydroxide solution with a concentration of 100 g / L and ammonium vanadomolybdate reagent are added to the colorimetric tube.

[0018] Preferably, when measuring the total potassium content in S5, a volumetric flask and a flame photometer are required, and a potassium standard solution is added to the volumetric flask.

[0019] Preferably, when measuring the moisture content of the air-dried sample in S3, an electric heating forced air constant temperature drying oven and a dryer are required, and the heating temperature of the electric heating forced air constant temperature drying oven is 105 °C.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The processed organic fertilizer sample is sent into the digestion inner tank, hydrogen peroxide and nitric acid are added and shaken well. After mixing, it is placed into the outer tank, and the outer tank is sent into a constant temperature drying oven for heating. After cooling, the outer tank is slowly loosened, the digestion inner tank is taken out, and the digestion solution is transferred into a 50 mL volumetric flask. At the same time, a reagent blank test is conducted. This method can reduce the dosage of digestion reagents, shorten the digestion time, and basically does not require the on-site monitoring of testers during the digestion process. After adding the phosphorus standard solution into 7 groups of colorimetric tubes and mixing it with 2,4-dinitrophenol indicator, sodium hydroxide solution and ammonium vanadomolybdate reagent, colorimetry can be carried out through a spectrophotometer to make a standard curve. After the determination of the sample solution is completed, the content of phosphorus pentoxide in the sample can be calculated through a formula; after adding the potassium standard solution into 6 groups of volumetric flasks and mixing it with water, the emission intensity values of each standard solution can be measured through a flame photometer to make a standard curve. After the determination of the sample solution is completed, the content of potassium oxide in the sample can be calculated through a formula. In this way, the determination of the total phosphorus and total potassium content in the organic fertilizer can be completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic flow chart of the method of the present invention;

[0022] Figure 2 It is a schematic structural diagram of the pressure tank of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figure 1 - Figure 2 , the present invention provides a technical solution: A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method, comprising the following steps:

[0025] S1. Sample preparation: The organic fertilizer sample is air-dried, ground, and sieved. The sieving equipment is a nylon sieve, and the filtration pore diameter of the nylon sieve is 0.25 mm;

[0026] S2. Preparation of sample solution and preparation of standard solution: By the pressure tank digestion method, 0.35 g of the sample is weighed into the digestion inner tank, 4 mL of hydrogen peroxide is added, shaken well, left for 30 min, 4 mL of nitric acid is added, shaken well, left for 30 min, the inner cover is covered, the stainless steel outer sleeve is tightened, and it is placed into a constant temperature drying oven and maintained at 165 °C for 5 h. After cooling, the digestion solution is transferred into a 50 mL volumetric flask. At the same time, a reagent blank test is conducted;

[0027] S3. Determine the moisture content of the air-dried sample. Measure the moisture content of the sample using an electrothermal blast oven for constant temperature and a desiccator.

[0028] S4. Determine the total phosphorus content: by spectrophotometry.

[0029] S5. Determine the total potassium content: by flame photometer.

[0030] The sample preparation process in S1 includes air-drying, grinding, sieving, and collection. The sieving equipment is a nylon sieve with a filtration aperture of 0.25 mm. The sample solution preparation equipment in S2 is a pressure tank, which consists of an inner tank, a lower gasket, an outer tank, an upper pressing plate, an upper cover, and a booster rod. The sample solution in S2 is the test solution obtained by digesting the organic fertilizer sample with hydrogen peroxide and nitric acid. The standard solutions are specifically phosphorus standard solution and potassium standard solution. The concentration of hydrogen peroxide is 30%, and the dosage of hydrogen peroxide added is 4 mL. The dosage of nitric acid added is 4 mL, and the mass of the sample material is 0.35 g. After the test solution in S2 is mixed, it needs to be sent to a constant temperature drying oven for heating. The temperature of the constant temperature drying oven is set at 165 °C, and the heating time is set at 5 h. When preparing the phosphorus standard solution, 5.00 mL of phosphorus standard stock solution needs to be added to a 100 mL volumetric flask and mixed with water. The concentration of the phosphorus standard stock solution is 1000 μg / mL, and the concentration of the prepared phosphorus standard solution is 50 μg / mL. When preparing the potassium standard solution, 10.00 mL of potassium standard stock solution needs to be added to a 100 mL volumetric flask and mixed with water. The concentration of the potassium standard stock solution is 1000 μg / mL, and the concentration of the prepared potassium standard solution is 100 μg / mL. When determining the total phosphorus content in S4, an ultraviolet-visible spectrophotometer and a colorimetric tube are required, and a phosphorus standard solution, a 2,4-dinitrophenol indicator with a concentration of 2 g / L, a sodium hydroxide solution with a concentration of 100 g / L, and ammonium vanadomolybdate reagent need to be added to the colorimetric tube. When determining the total potassium content in S5, a volumetric flask and a flame photometer are required, and a potassium standard solution needs to be added to the volumetric flask. When determining the moisture content of the air-dried sample in S3, an electrothermal blast oven for constant temperature and a desiccator are required, and the heating temperature of the electrothermal blast oven for constant temperature is 105 °C.

[0031] In specific implementation, when determining the phosphorus and potassium contents in organic fertilizers, a sample solution is required. When preparing the sample solution, the organic fertilizer sample is air-dried, ground, sieved, mixed evenly, and then collected in a clean sample bottle for standby. Take 0.35 g of the air-dried solid sample and put it into the digestion inner tank, add 4 mL of hydrogen peroxide, and let it stand for 30 min. During this period, gently shake it several times to fully immerse the sample in the reagent. Then add 4 mL of nitric acid and let it stand for 30 min. During this period, gently shake it several times. After mixing, cover the inner lid, and place the inner tank into the outer tank. There is a lower gasket inside the outer tank, and an upper pressing piece is placed on the top of the inner tank. Then tighten the stainless steel upper lid, and put it into a constant temperature drying oven, and keep it at 165 °C for 5 h. After cooling, slowly loosen the outer tank, take out the digestion inner tank, transfer the digestion solution to a 50 mL volumetric flask, wash the inner tank and the inner lid 3 to 5 times with a small amount of water, combine the washing solutions in the volumetric flask, and make up the volume to the scale with water, mix evenly for standby, and at the same time, conduct a reagent blank test. When preparing the standard solution, add 5.00 mL of 1000 μg / mL phosphorus standard stock solution to a 100 mL volumetric flask, make up the volume with water, and mix evenly to obtain a 50 μg / mL phosphorus standard intermediate solution; add 10.00 mL of 1000 μg / mL potassium standard stock solution to a 100 mL volumetric flask, make up the volume with water, and mix evenly to obtain a 100 μg / mL potassium standard intermediate solution, thus completing the preparation of the standard solution. This method can reduce the dosage of digestion reagents, optimize the ratio of digestion reagents, improve the preparation process of the sample solution, reduce environmental pollution at the same time, the digestion time is relatively short, generally completed within 7 h, the digestion solution can meet the requirements of the standard light yellow clear liquid, and basically no tester is required to be on duty during the digestion process, reducing the health risk of the tester and the investment in human resources.

[0032] Determine the moisture content of the air-dried sample:

[0033] 1. Place the aluminum box with the lid placed obliquely in an electrothermal blast drying oven at 105 °C for 30 min, take it out, cover it, transfer it to a desiccator containing silica gel for equilibration for 20 min, and then take it out for weighing. Bake for another 30 min and weigh under the same conditions until the difference in mass between two weighings does not exceed 1 mg, which is the constant weight.

[0034] 2. Weigh 5 g of the air-dried sample passing through a 1 mm sieve, accurate to 0.001 g, spread it evenly in the known constant weight aluminum box, cover the lid, and transfer it to an electrothermal blast drying oven preheated to 105 °C. Open the lid of the box and place it obliquely, close the oven door, and heat at 105 °C for 8 h. Cover the lid of the box, take it out, transfer it to a desiccator containing silica gel for equilibration for 30 min, and then take it out for weighing.

[0035] 3. The moisture content is expressed as a mass percentage (%), and is calculated according to the following formula:

[0036]

[0037] In the formula:

[0038] m1———mass of air-dried test sample and aluminum box, unit: gram (g);

[0039] m2———mass of dried test sample and aluminum box, unit: gram (g);

[0040] m0———mass of aluminum box, unit: gram (g).

[0041] Determination of total phosphorus:

[0042] Accurately pipette 0 mL, 1.00 mL, 2.50 mL, 5.00 mL, 7.50 mL, 10.00 mL, and 15.00 mL of phosphorus standard solution into 7 50-mL colorimetric tubes respectively, add water to about 30 mL in each group of colorimetric tubes, then add 2 drops of 2,4-dinitrophenol indicator, adjust to just slightly yellow with sodium hydroxide solution, add 10.0 mL of ammonium vanadomolybdate reagent, make up the volume with water, and shake well. At this time, the phosphorus contents in the standard series solutions in each group of colorimetric tubes are 0 μg, 50 μg, 125 μg, 250 μg, 375 μg, 500 μg, and 750 μg respectively. After standing at room temperature for 20 min, perform colorimetry at a wavelength of 450 nm with a 1-cm colorimetric cell in a spectrophotometer. Zero with the 0 point of the standard solution, then measure the absorbances of each standard solution from low concentration to high concentration respectively. Use the mass of phosphorus (μg) in the standard series solutions as the abscissa and the corresponding absorbances as the ordinate to make a standard curve;

[0043] Pipette 5 mL to 10 mL of the test sample solution into a 50-mL colorimetric tube, add water to about 30 mL, perform color development and colorimetry under the same conditions as the standard series solutions, zero with the blank test solution, read the absorbance, compare with the standard series for quantitative determination, and complete the determination of the test sample solution;

[0044] When calculating the content of phosphorus pentoxide in the test sample, the phosphorus pentoxide is calculated as the mass fraction ω, and the value is expressed as a percentage, and is calculated according to the following formula:

[0045]

[0046] In the formula:

[0047] m2———mass of phosphorus in the test sample solution, unit: microgram (μg);

[0048] V1———constant volume of the test sample digestion solution, unit: milliliter (mL);

[0049] 2.292———coefficient for converting phosphorus mass to phosphorus pentoxide mass;

[0050] m———mass of the test sample taken, unit: gram (g);

[0051] V2 ——— The volume of the digested sample solution taken, in milliliters (mL);

[0052] f ——— The value of the moisture content of the air-dried sample;

[0053] 10 6 ——— The coefficient for converting grams to micrograms, in micrograms per gram (μg / g).

[0054] Determination of total potassium:

[0055] Accurately pipette 0 mL, 2.50 mL, 5.00 mL, 10.00 mL, 15.00 mL, and 20.00 mL of the potassium standard solution into 6 100-mL volumetric flasks respectively, add water to the mark, and mix well. At this time, the mass concentrations of potassium in the standard series solutions in each volumetric flask are 0 μg / mL, 2.5 μg / mL, 5.00 μg / mL, 10.00 μg / mL, 15.00 μg / mL, and 20.00 μg / mL respectively. On the flame photometer under the selected working conditions, adjust the zero point and full scale of the instrument with the 0 point and the highest concentration point of the standard solution respectively, and then measure the emission intensity values of each standard solution from low concentration to high concentration. Using the mass concentration of potassium in the standard series solution (μg / mL) as the abscissa and the corresponding emission intensity as the ordinate, prepare a standard curve;

[0056] After the sample solution is directly or appropriately diluted, measure the emission intensity of potassium under the same experimental conditions as for the determination of the standard solution, compare it with the standard series for quantitative determination, and complete the determination of the sample solution;

[0057] When calculating the potassium oxide content in the sample, the potassium oxide content in the sample is expressed as the mass fraction ω, and the value is expressed as a percentage, and is calculated according to the following formula:

[0058]

[0059] In the formula:

[0060] ρ1 ——— The mass concentration of potassium in the sample solution, in micrograms per liter (μg / mL);

[0061] ρ0 ——— The mass concentration of potassium in the blank solution, in micrograms per liter (μg / mL);

[0062] D ——— The dilution factor of the sample solution during determination;

[0063] V1 ——— The volume of the sample digestion solution made up to the mark, in milliliters (mL);

[0064] 1.205 ——— The coefficient for converting potassium mass to potassium oxide mass;

[0065] m———The weighed sample amount of the specimen, unit: gram (g);

[0066] f———The value of the water content of the air-dried specimen;

[0067] 10 6 ———The coefficient for converting grams to micrograms, unit: microgram per gram (μg / g).

[0068] Through the above operations, the determination of the total phosphorus and total potassium contents in the organic fertilizer is completed.

[0069] In summary, when determining the total potassium and total phosphorus contents in the organic fertilizer, the specimen solution is prepared by a pressure tank. The standard curve can be made by a spectrophotometer and a flame photometer, and finally the total potassium and total phosphorus contents in the organic fertilizer are calculated through the formula. The content not described in detail in this description belongs to the prior art well-known to those skilled in the art.

[0070] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for determining total phosphorus and total potassium in organic fertilizers by pressure tank digestion method, characterized in that, It includes the following steps: S1. Specimen preparation; S2. Preparation of specimen solution and preparation of standard solution; S3. Determination of water content of air-dried specimen; S4. Determination of total phosphorus content; S5. Determination of total potassium content.

2. The method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: The specimen preparation process in S1 includes air-drying, grinding, sieving and collection. The sieving equipment is a nylon sieve, and the filtration aperture of the nylon sieve is 0.25 mm.

3. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: The equipment for preparing the specimen solution in S2 is a pressure tank, which consists of an inner tank, a lower gasket, an outer tank, an upper pressing piece, an upper cover and a booster rod.

4. A method for determining total phosphorus and total potassium in organic fertilizer by a pressure tank digestion method according to claim 1, characterized in that: The specimen solution in S2 is the test solution obtained by digesting the organic fertilizer specimen with hydrogen peroxide and nitric acid. The standard solution is specifically a phosphorus standard solution and a potassium standard solution. The concentration of the hydrogen peroxide is 30%, the dosage of the hydrogen peroxide added is 4 mL, the dosage of the nitric acid added is 4 mL, and the mass of the specimen material is 0.35 g.

5. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: After the test solution in S2 is mixed, it needs to be sent to a constant temperature drying oven for heating. The temperature of the constant temperature drying oven is set at 165 °C, and the heating time is set at 5 h.

6. The method for determining total phosphorus and total potassium in organic fertilizer by a pressure tank digestion method according to claim 1, characterized in that: When preparing the phosphorus standard solution, 5.00 mL of the phosphorus standard stock solution needs to be added to a 100 mL volumetric flask and mixed with water. The concentration of the phosphorus standard stock solution is 1000 μg / mL, and the concentration of the prepared phosphorus standard solution is 50 μg / mL.

7. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: When preparing the potassium standard solution, 10.00 mL of the potassium standard stock solution needs to be added to a 100 mL volumetric flask and mixed with water. The concentration of the potassium standard stock solution is 1000 μg / mL, and the concentration of the prepared potassium standard solution is 100 μg / mL.

8. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: When determining the total phosphorus content in S4, an ultraviolet-visible spectrophotometer and a colorimetric tube are needed, and a phosphorus standard solution, a 2,4-dinitrophenol indicator with a concentration of 2 g / L, a sodium hydroxide solution with a concentration of 100 g / L and an ammonium vanadomolybdate reagent need to be added to the colorimetric tube.

9. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: When determining the total potassium content in S5, a volumetric flask and a flame photometer are needed, and a potassium standard solution needs to be added to the volumetric flask.

10. A method for determining total phosphorus and total potassium in organic fertilizer by pressure tank digestion method according to claim 1, characterized in that: When determining the water content of the air-dried specimen in S3, an electrothermal blast constant temperature drying oven and a dryer are needed, and the heating temperature of the electrothermal blast constant temperature drying oven is 105 °C.

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