Method for efficiently and accurately measuring urease inhibitor content in stabilized fertilizer

Abstract

The invention relates to a method for efficiently and accurately measuring the content of a urease inhibitor in a stabilized fertilizer. The method comprises the following steps: preparing a sample solution; carrying out digestion treatment on the sample solution; carrying out chromogenic reaction; measuring the absorbance of the blue complex by using a 3cm cuvette under the wavelength of 710 nanometers by using a spectrophotometer; and calculating the content of the total effective components of the urease inhibitor in the sample according to a relational expression between the phosphorus content and the absorbance. According to the invention, accurate measurement of the content of the target component can be realized through chemical digestion, chromogenic reaction and photometric analysis, the measurement method is simple and reliable, the measurement method shows significant advantages in the aspect of urease inhibitor content measurement, and powerful technical support can be provided for quality control and performance evaluation of related products. Compared with the existing liquid chromatography, the method has the advantages that the cost advantage is obvious, the acquisition cost and the maintenance cost of a liquid chromatograph and matched equipment thereof can be saved, accurate determination can be carried out only by using a conventional detection appliance, and the method has good universality.

Description

Technical Field

[0001] The present invention belongs to the technical field of determining the content of urease inhibitors in fertilizers, and specifically relates to a method for efficiently and accurately determining the content of urease inhibitors in stable fertilizers, and in particular to quantitative analysis of NBPT (n-butyl thiophosphoric triamide) and NPPT (n-propyl thiophosphoric triamide) components contained in urease inhibitor urea products. Background Art

[0002] Stable fertilizers are nitrogen-containing fertilizers that have been added with urease inhibitors and / or nitrification inhibitors through a certain process. After being applied to the soil, they can inhibit the hydrolysis of urea through urease inhibitors and / or inhibit the nitrification of ammonium nitrogen through nitrification inhibitors, thereby extending the effective period of fertilizer application. Urease inhibitors play a key role in the long-term effect of fertilizers, and the content of urease inhibitors should be sufficient to effectively inhibit the activity of urease, thereby slowing down the hydrolysis rate of urea and slowing down the volatilization and nitrification of ammonium nitrogen. Therefore, it is undoubtedly very important to determine the content of urease inhibitors in stable fertilizers.

[0003] At present, only the Ministry of Agriculture's industry standard "Determination of the Content of Fertilizer Synergists n-Butylthiophosphoric Triamide (NBPT) and n-Propylthiophosphoric Triamide (NPPT)" NY / T 3038-2016 records the method for determining the content of fertilizer synergists n-butylthiophosphoric triamide (NBPT) and n-propylthiophosphoric triamide (NPPT) - high performance liquid chromatography.

[0004] The high performance liquid chromatography method mainly extracts n-butylthiophosphoric triamide (NBPT) and n-propylthiophosphoric triamide (NPPT) in the sample with water, separates them by liquid chromatography, detects them with a UV detector, and quantifies them by the external standard method. For organic compounds such as NBPT and NPPT, they interact with the mobile phase and the stationary phase on a specific chromatographic column. Different substances will flow out of the chromatographic column at different times. The detector detects and records their signals, and the content of the substance is determined based on the intensity and time of the signal. Although this determination method has the advantages of high separation efficiency, good selectivity, high detection sensitivity, and high level of automation, it also has the disadvantages of high performance liquid chromatography, high daily maintenance costs, difficulty in operation and maintenance, complex pre-treatment of the samples to be tested, and long analysis time. It is not universal for enterprises and laboratories.

[0005] In view of the above problems, the present invention aims to provide a universal method for determining the content of urease inhibitors and to improve the determination efficiency while ensuring accuracy. Summary of the invention

[0006] The invention provides a method for efficiently and accurately determining the content of urease inhibitors in stable fertilizers.

[0007] The specific technical solution is: a method for efficiently and accurately determining the content of urease inhibitors in stable fertilizers, comprising the following steps: Step 1, preparation of sample solution: accurately weigh the urease inhibitor urea sample containing NBPT and NPPT, and add water to dissolve and dilute it to prepare a urea sample solution; Step 2: digesting the sample solution: adding sulfuric acid solution and potassium persulfate solution to the urea sample solution to digest the sample, so that the organic phosphorus contained in the active ingredients of urease inhibitors, NBPT and NPPT, is converted into inorganic orthophosphate that can be quantitatively detected; Step 3, color development reaction: under acidic environmental conditions, add ammonium molybdate solution to the converted orthophosphate to react to generate phosphomolybdic heteropoly acid, and at the same time add ascorbic acid solution as a reducing agent to further reduce to form a blue complex suitable for spectrophotometric determination; Step 4: using a spectrophotometer to measure the absorbance of the blue complex at a wavelength of 710 nanometers using a 3 cm cuvette; Step 5: Calculate the content of the total active ingredient of urease inhibitor in the sample according to the relationship between phosphorus content and absorbance, as follows: (1) In formula (1), A represents absorbance; b represents slope; 1.686 represents conversion coefficient, which is the ratio of 160.2 g / mol of NBPT and NPPT molar mass to 95 g / mol of phosphate molar mass; n represents dilution factor; M represents sample mass, in g.

[0008] Further, the specific operations of the above steps 1 to 3 are as follows: Step 1: Weigh 2 g of urease inhibitor urea product containing NBPT and NPPT into a 100 mL volumetric flask, add water to dissolve and dilute to the scale, shake well, and prepare a urea sample solution.

[0009] Step 2: Pipette 5 mL of the prepared urea sample solution into a 100 mL conical flask, add 1.0 mL of sulfuric acid solution and 5.0 mL of potassium persulfate solution, add water to 25 mL, then put in glass beads, place on an adjustable electric stove and slowly boil until the solution volume is 0.5 mL, and transfer to a 100 mL volumetric flask after cooling; in this process, the organic phosphorus contained in the active ingredients of urease inhibitors—NBPT and NPPT—is converted into inorganic orthophosphate that can be quantitatively detected; Step 3: Add 2.0 mL of ammonium molybdate solution and 3.0 mL of ascorbic acid solution to a volumetric flask, dilute to the mark with water, and shake well; during this process, the ammonium molybdate solution reacts with the inorganic orthophosphate to form phosphomolybdic heteropoly acid, and the addition of the reducing agent ascorbic acid solution further reduces the blue complex suitable for spectrophotometric determination; Furthermore, the slope b in formula (1) in step 5 is the slope of a standard curve established using a phosphate standard solution prepared with potassium dihydrogen phosphate.

[0010] Furthermore, the standard curve preparation method is: take different volumes of phosphate standard solution (0.02 mg / mL) to replace the analysis sample for testing, and after following the above-mentioned "step three and step four", measure and analyze the relationship between the phosphorus content and its absorbance, and draw a standard working curve and regression equation to obtain the slope b in the relationship between the phosphorus content in the analysis sample and its absorbance.

[0011] Furthermore, the mass volume concentration of the phosphate standard solution is 0.02 mg / mL.

[0012] Furthermore, the volume ratio of the sulfuric acid solution is 1 mL of concentrated sulfuric acid dissolved in every 35 mL of water.

[0013] Furthermore, the mass volume concentration of the potassium persulfate solution is 40 g / L.

[0014] Furthermore, the mass volume concentration of the ammonium molybdate solution is 26 g / L.

[0015] Furthermore, the mass volume concentration of the ascorbic acid solution is 20 g / L.

[0016] Beneficial effects of the present invention: The method for determining the content of urease inhibitors (NBPT and NPPT) in stable urea provided by the present invention can achieve accurate measurement of the content of the target component through chemical digestion, color reaction and photometric analysis. The measurement method is simple and reliable, and has shown significant advantages in the determination of urease inhibitor content, and can provide strong technical support for the quality control and performance evaluation of related products. Compared with the existing liquid chromatography method, it has significant cost advantages, can save the purchase cost and maintenance cost of liquid chromatographs and their supporting equipment, and only conventional detection instruments are needed for accurate determination, which has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a standard curve diagram of phosphorus in the embodiment, wherein the x-axis is absorbance and the y-axis is phosphorus content. DETAILED DESCRIPTION

[0018] In order to make the technical problems and technical solutions solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] 1. Experimental Principle The analysis of the active ingredients of urease inhibitors, NBPT and NPPT, shows that they are considered effective mainly because they contain the core element of organophosphorus. Organophosphorus exists in these molecules in a specific chemical bond form and plays a decisive role in the function of urease inhibitors. Therefore, determining the organophosphorus content in these active ingredients is not only an important indicator for evaluating the quality of urease inhibitors, but also a key link in understanding their mechanism of inhibiting urease activity, optimizing product performance and ensuring their effectiveness in fertilizer applications. By accurately measuring the content of organophosphorus, the activity level of NBPT and NPPT can be accurately understood.

[0020] In view of the above analysis, this experiment converted the organic phosphorus in the fertilizer into inorganic orthophosphate which can be quantitatively detected. By measuring the content of inorganic orthophosphate, the content of the total active ingredients of urease inhibitors (NBPT and NPPT) in the fertilizer was determined.

[0021] 2. Preparation of main instruments and reagents 2.1 Instruments Commonly used glass instruments in the laboratory; spectrophotometer, equipped with a 3cm cuvette.

[0022] 2.2 Reagents 2.2.1 Sulfuric acid solution (1+35) Measure 10mL of concentrated sulfuric acid, slowly add it into 350mL of water, stir well and cool (valid for six months).

[0023] 2.2.2 Potassium persulfate solution (40 g / L) Weigh 20g potassium persulfate (accurate to 0.5g) and dissolve it in 500mL water, mix well, and store in a brown bottle (valid for one month).

[0024] 2.2.3 Ammonium molybdate solution (26 g / L) Weigh 13g of ammonium molybdate (accurate to 0.5g) and 0.35g of potassium antimony tartrate (KSbOC4H4O6·1 / 2H2O, accurate to 0.01g), dissolve in 200mL of water; then add 230mL of sulfuric acid solution (1+1), mix well, dilute to 500mL with water after cooling, mix well, and store in a brown bottle (valid for two months).

[0025] 2.2.4 Ascorbic acid solution (20 g / L) Weigh 10 g ascorbic acid (accurate to 0.5 g) and 0.2 g disodium ethylenediaminetetraacetate (C10H14O8N2Na2·2H2O, accurate to 0.01 g), dissolve in 200 mL water, add 8.0 mL formic acid, dilute to 500 mL with water, mix well, and store in a brown bottle (valid for one month).

[0026] 2.2.5 Phosphate standard stock solution (0.5 mg PO3 4－ / mL) Weigh 0.7165 g of potassium dihydrogen phosphate dried at 100-105°C to constant weight, dissolve in 100 mL of water, transfer to a 1000 mL volumetric flask, dilute to scale with water and shake well.

[0027] 2.2.6 Phosphate standard working solution (0.02 mg PO3 4－ / mL) Accurately pipette 20.00 mL of phosphate standard stock solution into a 500 mL volumetric flask, dilute to the mark with water and shake well (prepare before use).

[0028] 2.2.7 NBPT and NPPT stock solutions (75% + 25%) Accurately weigh 563 mg NBPT and 187 mg NPPT into a 1000 mL volumetric flask, add about 200 mL of water, shake thoroughly to ensure that NBPT and NPPT are completely dissolved, then adjust to volume and set aside.

[0029] 2.2.8 Urea mixed solution containing NBPT and NPPT standard substances Weigh 2 g of common urea into a 100 mL volumetric flask, and pipette 1 mL of NBPT and NPPT stock solutions into a 100 mL volumetric flask, and then dilute to the mark with water.

[0030] 3. Experimental Methods During the experiment, potassium dihydrogen phosphate was first used to prepare a phosphate standard solution to establish a standard curve as a benchmark for subsequent quantitative analysis. Secondly, the urease inhibitor urea sample containing NBPT and NPPT was digested to effectively extract the active ingredients of the urease inhibitor. Subsequently, the sample was made suitable for spectrophotometric determination by chemical conversion and quantitative analysis was performed. At the same time, in order to verify the accuracy and reliability of this experimental method, some samples were sent to BASF Rudong Laboratory and compared using high performance liquid chromatography. In addition, a simulation experiment was also carried out, in which NBPT and NPPT standard substances of known concentrations were added to ordinary urea according to the actual production addition ratio. The feasibility of the analysis method was further verified by comparing the corresponding relationship between the determination results of the standard substances and the known true concentrations. Finally, the stable urea sample containing urease inhibitors was determined using a proven analytical method to accurately calculate the content of NBPT and NPPT in the product. The specific analysis method is as follows: 3.1 Preparation of standard curve Take 7 100ml volumetric flasks and add 0.0, 1.0, 5.0, 10.0, 15.0, 20.0 and 25.0mL of phosphate standard working solution (2.2.6) respectively. Add water to 25mL, then add 2mL of ammonium molybdate solution (2.2.3) and mix well. After 30 seconds, add 3mL of ascorbic acid solution (2.2.4) and mix well and let stand for 10min.

[0031] Using the reagent blank as a reference, measure the absorbance at a wavelength of 710nm using a 3cm cuvette. After deducting the absorbance of the blank test, draw a working curve using the corresponding phosphorus content (see Table 1, Figure 1 ).

[0032] Table 1: Relationship between phosphorus content (ug) and absorbance (A) (working curve)

[0033] Draw a standard curve using the data in Table 1. Figure 1 It can be seen that the relationship between phosphorus content and absorbance is y=192.35x, where x is absorbance, y is phosphorus content, and slope b=192.35. Through the above relationship, the organic phosphorus in the fertilizer can be converted into inorganic orthophosphate that can be quantitatively detected. By measuring the content of inorganic orthophosphate, the content of the total active ingredients of urease inhibitors (NBPT and NPPT) in the fertilizer can be determined in reverse.

[0034] 3.2 Preparation of sample solution Accurately weigh 2 g (accurate to 0.0001 g) of urea sample into a 100 mL volumetric flask, dissolve and dilute to the scale with water, shake well, and prepare a urea sample solution.

[0035] 3.3 Sample digestion Pipette 5mL of the prepared sample solution (3.2) into a 100mL conical flask, add 1.0mL of sulfuric acid solution (2.2.1) and 5.0mL of potassium persulfate solution (2.2.2). Rinse the flask wall with a small amount of water, and when the total volume of the solution in the conical flask is about 25mL, add glass beads, place it on an adjustable electric stove and slowly boil until the solution volume remains 0.5mL, and transfer it to a 100mL volumetric flask after cooling. In this process, the acidic environment created by sulfuric acid, combined with the strong oxidizing ability of potassium persulfate, can quickly break the PC bond in the organophosphorus compound, so that the organophosphorus contained in the active ingredients of urease inhibitors - NBPT and NPPT is converted into inorganic orthophosphate that can be quantitatively detected.

[0036] 3.4 Color reaction Add 2.0 mL of ammonium molybdate solution (2.2.3) and 3.0 mL of ascorbic acid solution (2.2.4) to the volumetric flask, dilute to the mark with water, and shake well. In this process, the ammonium molybdate solution reacts with the inorganic orthophosphate to form phosphomolybdic heteropoly acid, and the addition of the reducing agent ascorbic acid solution further reduces the solution to form a blue complex suitable for spectrophotometric determination.

[0037] 3.5 Sample testing After standing for 10 min, the absorbance of the blue complex was measured using a spectrophotometer at a wavelength of 710 nm using a 3 cm cuvette.

[0038] 3.5.1 According to the relationship between phosphorus content and absorbance, calculate the content of total active ingredients of urease inhibitor in the sample as follows: (1) The percentage content is expressed as: (2) In formula (1) and (2), A represents absorbance; b represents slope (i.e., the slope b = 192.35 in the standard curve established by preparing phosphate standard solution with potassium dihydrogen phosphate); 1.686 represents the conversion coefficient, which is the ratio of the molar mass of NBPT and NPPT (160.2 g / mol) to the molar mass of phosphate (95 g / mol); n represents the dilution factor; and M represents the sample mass, in g.

[0039] 3.5.2 Calculation results statistics The urease inhibitor product was tested according to the operating steps from 3.2 to 3.5, and the results were compared with the test results of BASF Rudong Laboratory (liquid chromatography) after substitution into the calculation. The test results are detailed in Table 2: Table 2: Spectrophotometric test results statistics

[0040] 4. Specific experimental process 4.1 Standard sample comparison method Take 12 portions of 5 mL of the prepared urea mixed solution containing NBPT and NPPT standard substances (2.2.8) and place them in 12 100 mL volumetric flasks respectively. Digestion and testing are carried out according to steps 3.3 and 3.4. A total of 12 measurements are carried out to obtain the following data. Then, the t-test method is used to compare the average value with the fixed value of the standard sample (confidence level 95%) to determine whether there is a systematic error in this method. The analysis data are detailed in Table 3.

[0041] Table 3: Statistical table of NBPT and NPPT reference material determination results

[0042] Through the data collection in Table 3, combined with the following formula, when the confidence level is 95%, by consulting the t-test critical value table, t 0.05,12 =2.179 (3) Since the t value of 2.111 is less than the critical value of 2.179, this indicates that there is no statistically significant difference between the experimental results obtained by the method of the present invention and the standard sample results. Therefore, it can be considered that the present invention does not show significant systematic errors in the measurement.

[0043] 4.2 Comparison with standard analytical methods The same sample was measured several times by the method of the present invention and liquid chromatography, and the two sets of data were compared. The difference between the two average values ​​was calculated and compared (confidence level 95%) to illustrate whether the method is reliable. The analysis data are shown in Table 4.

[0044] Table 4: Statistical table of the determination results of the total active ingredient content of urease inhibitors in the samples

[0045] From the data in Table 4, we can see that when the degree of freedom f=n1+n2-2=2 and the confidence level is 95%, we can check the t value table and get t 0.05,2 =4.303, and the t value was calculated using the following formula to determine whether there was a significant difference between the methods.

[0046] (4) (5) According to formula (4) and (5), the t value is calculated. From the t value data obtained in Table 4, it can be seen that all t values ​​are less than 4.303. This result shows that there is no significant difference between the two methods of BASF Rudong Laboratory (liquid chromatography) and Dawei Ammonia Laboratory (spectrophotometry), so it can be considered that the spectrophotometry of the present invention is reliable.

[0047] 4.3 Determination of error in parallel determination results For the company's products that add urease inhibitor raw materials, the indicator range is set between 320 mg / kg and 360 mg / kg. In order to evaluate the running difference between the parallel sample measurement results, we used formula (4) and formula (5) to calculate the t value. For specific difference calculation statistical results, please see Table 5.

[0048] Table 5: Calculation table of differences between parallel samples

[0049] According to the results in Table 5, when the absolute difference of the parallel samples is in the range of 19 mg / kg to 23 mg / kg, the corresponding t value is within the allowable range, and the relative error is between 5.76% and 6.61%. This shows that within this range, there is no significant difference between the parallel sample measurement results. In order to further strictly control the quality, the relative error control standard of the two parallel measurement results in the same laboratory is set to no more than 5%. Example 1

[0050] For the enhanced version of the product with added urease inhibitor raw materials, the content index requirement is set to be no less than 320 mg / kg. During the production process and process adjustment, for some products with large content fluctuations, preliminary testing was first carried out in the company laboratory using the method described in the present invention. Subsequently, these samples were sent to BASF Rudong Laboratory and tested using a liquid chromatograph. For details of the comparison of the test results, see Table 6.

[0051] Table 6: Comparative statistics of product data analysis with large fluctuations

[0052] It is obvious from the data analysis of Table 6 that the difference range between the analysis results of the two laboratories is between -14mg / kg and 9mg / kg, and the relative error of the parallel samples is between 0.57% and 3.08%, which meets the setting standard that the relative error of the two parallel determination results of the same laboratory is not more than 5%. These data show that the method of the present invention has good parallelism, and its analysis result is highly consistent with the liquid chromatography analysis method. Therefore, it can be confirmed that the method of the present invention has reached expectations in terms of accuracy and reliability, and has laid a solid foundation for subsequent widespread application.

[0053] The present invention is described in detail above through specific and preferred embodiments, but those skilled in the art should understand that the present invention is not limited to the embodiments described above, and any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for efficiently and accurately determining the content of urease inhibitors in stable fertilizers, characterized in that: The steps include: Step 1, preparation of sample solution: accurately weigh the urease inhibitor urea sample containing NBPT and NPPT, and add water to dissolve and dilute it to prepare a urea sample solution; Step 2: digesting the sample solution: adding sulfuric acid solution and potassium persulfate solution to the urea sample solution to digest the sample, so that the organic phosphorus contained in the active ingredients of urease inhibitors, NBPT and NPPT, is converted into inorganic orthophosphate that can be quantitatively detected; Step 3, color development reaction: under acidic environmental conditions, add ammonium molybdate solution to the converted orthophosphate to react to generate phosphomolybdic heteropoly acid, and at the same time add ascorbic acid solution as a reducing agent to further reduce to form a blue complex suitable for spectrophotometric determination; Step 4: using a spectrophotometer to measure the absorbance of the blue complex at a wavelength of 710 nanometers using a 3 cm cuvette; Step 5: Calculate the content of the total active ingredient of urease inhibitor in the sample according to the relationship between phosphorus content and absorbance, as follows: (1) In formula (1), A represents absorbance; b represents slope; 1.686 represents conversion coefficient, which is the ratio of 160.2 g / mol of NBPT and NPPT molar mass to 95 g / mol of phosphate molar mass; n represents dilution factor; M represents sample mass, in g.

2. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 1, characterized in that: The specific operations of steps 1 to 3 above are as follows: Step 1, weigh 2 g of urease inhibitor urea product containing NBPT and NPPT into a 100 mL volumetric flask, add water to dissolve and dilute to the scale, shake well, and prepare a urea sample solution; Step 2: Pipette 5 mL of the prepared urea sample solution into a 100 mL conical flask, add 1.0 mL of sulfuric acid solution and 5.0 mL of potassium persulfate solution, add water to 25 mL, then put in glass beads, place on an adjustable electric stove and slowly boil until the solution volume is 0.5 mL, and transfer to a 100 mL volumetric flask after cooling; in this process, the organic phosphorus contained in the active ingredients of urease inhibitors—NBPT and NPPT—is converted into inorganic orthophosphate that can be quantitatively detected; Step 3: Add 2.0 mL of ammonium molybdate solution and 3.0 mL of ascorbic acid solution to a volumetric flask, dilute to the mark with water, and shake well; during this process, the ammonium molybdate solution reacts with the inorganic orthophosphate to form phosphomolybdic heteropoly acid, and the addition of the reducing agent ascorbic acid solution further reduces the blue complex suitable for spectrophotometric determination.

3. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 1 or 2, characterized in that: The slope b in formula (1) in step 5 is the slope of the standard curve established by the phosphate standard solution prepared with potassium dihydrogen phosphate.

4. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 3, characterized in that: The standard curve preparation method is as follows: different volumes of phosphate standard solution are taken to replace the analysis sample for testing, and after the above-mentioned "step three and step four" are operated, the relationship between the phosphorus content and its absorbance is measured and analyzed, and a standard working curve and a regression equation are drawn to obtain the slope b in the relationship between the phosphorus content in the analysis sample and its absorbance.

5. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 4, characterized in that: The mass volume concentration of the phosphate standard solution is 0.02 mg / mL.

6. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 1 or 2, characterized in that: The volume ratio of the sulfuric acid solution is 1 mL of concentrated sulfuric acid dissolved in every 35 mL of water.

7. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 6, characterized in that: The mass volume concentration of the potassium persulfate solution is 40 g / L.

8. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 7, characterized in that: The mass volume concentration of the ammonium molybdate solution is 26 g / L.

9. The method for efficiently and accurately determining the content of urease inhibitor in stable fertilizer according to claim 8, characterized in that: The mass volume concentration of the ascorbic acid solution is 20 g / L.

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