Method for measuring concentration of trace elements in fertilizer production process

Abstract

The invention relates to the technical field of trace element concentration determination, and discloses a method for determining trace element concentration in a fertilizer production process. According to the method, an imine derivative synthesized by reaction of 4-amino-5-hydroxy-2, 7-naphthalene disulfonic acid and 1-hydroxy-2-naphthaldehyde is used as a color developing agent for determining the boron element, a flow analyzer is combined for multi-channel synchronous detection, and the concentration of the trace elements in the fertilizer production process is determined. The carbon-nitrogen double bond and the phenolic hydroxyl group in the imine derivative can form a stable complex with boron, and meanwhile, the water solubility of the product is remarkably improved by the disulfonic acid group, so that the precipitation interference is effectively avoided. The method is high in sensitivity, good in selectivity and simple and convenient to operate, and the accuracy and the automation degree of detection of trace elements such as boron in the fertilizer production process are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of trace element concentration determination technology, specifically a method for determining trace element concentration during fertilizer production. Background Technology

[0002] Fertilizers, as essential agricultural inputs, directly impact crop growth, development, and quality through their micronutrient content. Currently, the determination of micronutrient concentrations such as iron, manganese, zinc, copper, boron, and molybdenum in fertilizers typically employs spectrophotometry, relying on specific chromogenic reagents. However, existing methods generally suffer from cumbersome pretreatment steps, low detection efficiency, low automation, and difficulty in achieving simultaneous and rapid multi-element analysis. Particularly in boron determination, while traditional chromogenic reagents such as curcumin and 1,8-dihydroxyanthraquinone have some applications, they still exhibit limitations such as complex operation, susceptibility to interference, and narrow linear ranges, making them unsuitable for the rapid, accurate, and high-throughput detection demands of modern fertilizer production processes.

[0003] Imine derivatives are a class of promising chromogenic agents that form stable colored complexes with boron atoms. However, some imine derivatives have simple molecular structures and poor water solubility, easily forming precipitation when reacting with water-soluble borate ions. Developing chromogenic agents that combine high selectivity, good water solubility, and compatibility with automated analysis platforms has become crucial for improving the rapid detection performance of multiple elements in fertilizers. Patent CN118311126A discloses a method for determining the content of trace and meso-elements in water-soluble fertilizers, using inductively coupled plasma mass spectrometry (ICP-MS) to detect meso- and trace elements, improving detection sensitivity and accuracy. However, this patent does not address the problems of complex pretreatment and slow measurement speed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for determining the concentration of trace elements during fertilizer production, which solves the problems of slow determination speed and complex pretreatment.

[0005] A method for determining the concentration of trace elements during fertilizer production is as follows: Step (1): Add 7-9 parts by weight of ferrous ammonium sulfate, 4-6 parts by weight of manganese acetate, 4-6 parts by weight of zinc sulfate, 3-5 parts by weight of copper nitrate, 5-7 parts by weight of boric acid, and 2-4 parts by weight of ammonium molybdate to 6 polyethylene bottles respectively, dissolve them in deionized water, and obtain trace element standard solutions respectively.

[0006] Step (2): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to seven quartz volumetric flasks respectively, dilute with deionized water and mix well. Then add the diluted trace element standard solution, colorimetric reagent, and buffer solution to the six independent analytical channels of the flow analyzer respectively. The instrument parameters are: pump speed 0.5-1.0 mL / min, injection flow rate 0.05-0.1 mL / min, injection time 30-40 s, washing time 60-90 s, optical path 10-15 mm, reaction temperature 25-35℃, and absorbance is detected. The regression linear equation is obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0007] Step (3): Add deionized water and fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0008] Furthermore, in step (1), the maximum absorption wavelengths for determining the concentrations of iron, manganese, zinc, copper, boron, and molybdenum are 465nm, 526nm, 620nm, 562nm, 420nm, and 460nm, respectively.

[0009] Furthermore, in step (2), the colorimetric agents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively, and the buffer solutions are acetic acid-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixture, respectively.

[0010] Furthermore, the preparation method of the imine derivative is as follows: Deionized water, 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid, and 1-hydroxy-2-naphthaldehyde in a molar ratio of 1:(2.4-3.2) are added to a flask. The mixture is heated to 50-70℃, stirred for 2-4 hours, centrifuged, filtered, the precipitate is washed with ethanol, and dried to obtain the imine derivative. The reaction formula for preparation is: .

[0011] Compared with existing technologies, the beneficial effects of this invention are: This invention uses an imine derivative synthesized by reacting 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid and 1-hydroxy-2-naphthaldehyde as a boron colorimetric agent, and combines it with a flow analyzer for multi-channel synchronous detection to determine the concentration of trace elements during fertilizer production.

[0012] The 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid of this invention contains a phenolic hydroxyl group, an amino group, and a sulfonic acid group. The amino group undergoes dehydration condensation with the aldehyde group of 1-hydroxy-2-naphthaldehyde to form a Schiff base condensation product, which then forms a complex with boron as a chromogenic agent. The disulfonic acid group improves the water solubility of the complex, preventing precipitation during detection. The imine derivative prepared by this invention significantly expands the detection range and improves the accuracy, sensitivity, and automation of trace element concentration determination. Detailed Implementation

[0013] The present invention will now be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0014] Example 1: The method for determining the concentration of trace elements during fertilizer production is as follows: Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0015] Step (2): Add 100 mL of water, 0.1 mol of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid, and 0.32 mol of 1-hydroxy-2-naphthaldehyde to the flask, heat to 70 °C, stir for 2 h, centrifuge, filter, wash the precipitate with ethanol, and dry to obtain the imine derivative.

[0016] Step (3): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks, respectively. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively. The buffer solutions are added separately. The buffer solutions used were acetic acid-ammonium acetate buffer, ammonia-ammonium chloride buffer, carbonate buffer, borate buffer, acetate buffer, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0017] Step (4): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0018] Example 2: The method for determining the concentration of trace elements during fertilizer production is as follows: Step (1): Add 0.9g ferrous ammonium sulfate, 0.4g manganese acetate, 0.6g zinc sulfate, 0.4g copper nitrate, 0.5g boric acid, and 0.2g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0019] Step (2): Add 100 mL of water, 0.1 mol of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid, and 0.28 mol of 1-hydroxy-2-naphthaldehyde to the flask, heat to 60 °C, stir for 4 h, centrifuge, filter, wash the precipitate with ethanol, and dry to obtain the imine derivative.

[0020] Step (3): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 1 mL of colorimetric reagent, and 1.5 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively. The buffer solutions are respectively... The following buffer solutions were used: acetate-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 1.0 mL / min, injection flow rate 0.05 mL / min, injection time 40 s, washing time 75 s, optical path 10 mm, and reaction temperature 30 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0021] Step (4): Add 60 mL of water and 20 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0022] Example 3: The method for determining the concentration of trace elements during fertilizer production is as follows: Step (1): Add 0.8g ferrous ammonium sulfate, 0.5g manganese acetate, 0.5g zinc sulfate, 0.5g copper nitrate, 0.6g boric acid, and 0.3g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0023] Step (2): Add 100 mL of water, 0.1 mol of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid, and 0.24 mol of 1-hydroxy-2-naphthaldehyde to the flask, heat to 50 °C, stir for 3 h, centrifuge, filter, wash the precipitate with ethanol, and dry to obtain the imine derivative.

[0024] Step (3): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 1.2 mL of colorimetric reagent, and 1.75 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively. The buffer solutions are respectively... The buffer solutions used were acetic acid-ammonium acetate buffer, ammonia-ammonium chloride buffer, carbonate buffer, borate buffer, acetate buffer, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.75 mL / min, injection flow rate 0.075 mL / min, injection time 35 s, washing time 90 s, optical path 12.5 mm, and reaction temperature 35 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0025] Step (4): Add 60 mL of water and 23 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0026] The difference between Comparative Example 1 and Example 1 is that no imine derivative is added: Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0027] Step (2): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to seven quartz volumetric flasks respectively, dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the five independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, and potassium thiocyanate, respectively. Do not add imine derivatives to the channel for determining boron concentration. The buffer solutions used were acetic acid-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0028] Step (3): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 5 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0029] The difference between Comparative Example 2 and Example 1 is that curcumin is used instead of the imine derivative: Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0030] Step (2): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to seven quartz volumetric flasks respectively, dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, curcumin, and potassium thiocyanate, respectively. The buffer solutions are respectively... The following buffer solutions were used: acetate-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0031] Step (3): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0032] The difference between Comparative Example 3 and Example 1 is that 1,8-dihydroxyanthraquinone is used instead of the imine derivative: Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0033] Step (2): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, 1,8-dihydroxyanthraquinone, and potassium thiocyanate, respectively. The buffer solutions used were acetic acid-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0034] Step (3): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0035] The difference between Comparative Example 4 and Example 1 is that 5-aminonaphthalene-2-sulfonic acid is used instead of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid. Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0036] Step (2): Add 100 mL of water, 0.1 mol of 5-aminonaphthalene-2-sulfonic acid, and 0.32 mol of 1-hydroxy-2-naphthaldehyde to the flask, heat to 70 °C, stir for 2 h, centrifuge, filter, wash the precipitate with ethanol, and dry to obtain the imine derivative. The reaction formula for preparation is: .

[0037] Step (3): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks, respectively. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively. The buffer solutions are added separately. The buffer solutions used were acetic acid-ammonium acetate buffer, ammonia-ammonium chloride buffer, carbonate buffer, borate buffer, acetate buffer, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0038] Step (4): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0039] The difference between Comparative Example 5 and Example 1 is that 3-amino-4-hydroxybenzenesulfonic acid is used instead of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid: Step (1): Add 0.7g ferrous ammonium sulfate, 0.6g manganese acetate, 0.4g zinc sulfate, 0.3g copper nitrate, 0.7g boric acid, and 0.4g ammonium molybdate to 6 polyethylene bottles respectively, and dissolve them in 1L of deionized water to obtain trace element standard solutions.

[0040] Step (2): Add 100 mL of water, 0.1 mol of 3-amino-4-hydroxybenzenesulfonic acid, and 0.32 mol of 1-hydroxy-2-naphthaldehyde to the flask, heat to 70 °C, stir for 2 h, centrifuge, filter, wash the precipitate with ethanol, and dry to obtain the imine derivative. The reaction formula for preparation is: .

[0041] Step (3): Add deionized water or 1.0, 2.5, 7.5, 10.0, 15.0, and 20.0 mL of trace element standard solution to each of the seven quartz volumetric flasks, respectively. Dilute with deionized water to 100 mL and mix well. Then, add 1 mL of trace element standard solution, 0.8 mL of colorimetric reagent, and 2 mL of buffer solution to each of the six independent analytical channels of the flow analyzer. The colorimetric reagents are sulfosalicylic acid, formaldehyde oxime, sodium 2-(2-hydroxy-5-sulfophenylazo)benzylhydrazine benzoate, 2,2'-biquinoline, imine derivative, and potassium thiocyanate, respectively. The buffer solutions are added separately. The buffer solutions used were acetic acid-ammonium acetate buffer, ammonia-ammonium chloride buffer, carbonate buffer, borate buffer, acetate buffer, and sulfuric acid-copper sulfate-thiourea mixture. The instrument parameters were: pump speed 0.5 mL / min, injection flow rate 0.1 mL / min, injection time 30 s, washing time 60 s, optical path 15 mm, and reaction temperature 25 ℃. The absorbance at 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm was measured. The regression linear equation was obtained by plotting the trace element concentration on the x-axis and the absorbance on the y-axis.

[0042] Step (4): Add 60 mL of water and 25 g of fertilizer sample to a polyvinyl fluoride beaker, boil, cool and dilute to obtain the test solution, add it to the 6 independent analysis channels of the flow analyzer, add colorimetric reagent and buffer solution respectively, detect absorbance, and calculate the concentration of trace elements in fertilizer according to the regression linear equation.

[0043] Table 1. Regression linear equations and correlation coefficients of trace elements

[0044] The absorbance (y-value) of the test solution in each of the six analytical channels was substituted into the corresponding regression linear equation to calculate the concentration (x-value) of the trace elements.

[0045] Table 2 Concentration of micronutrients in fertilizers , , , , , , , .

[0046] Compared to Comparative Example 1, Examples 1-3 used an imine derivative synthesized from 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid and 1-hydroxy-2-naphthaldehyde as the chromogenic agent for boron, while the chromogenic agents for other trace elements remained unchanged. Combined with a flow analyzer for multi-channel simultaneous detection, this significantly improved the accuracy, automation, and detection speed of trace element concentration determination. The measured concentration of boron was significantly higher than in the comparative example, with a smaller standard deviation. This is mainly because 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid contains phenolic hydroxyl, amino, and sulfonic acid groups. The amino group undergoes dehydration condensation with the aldehyde group of 1-hydroxy-2-naphthaldehyde to form a Schiff base condensation product containing a carbon-nitrogen double bond. This product then forms a complex with boron as the chromogenic agent. Under the action of the disulfonic acid group, the water solubility of the complex is improved, preventing precipitation during detection.

[0047] In Comparative Example 1, the absence of a colorimetric reagent resulted in a significantly lower boron concentration, indicating that the reagent possesses irreplaceable selectivity and sensitivity for boron detection. Comparative Examples 2 and 3 used curcumin and 1,8-dihydroxyanthraquinone as alternative colorimetric reagents, respectively. These methods were cumbersome, susceptible to interference, had limited applicability, led to unstable boron determination results, decreased accuracy, and time-consuming measurement processes. Comparative Examples 4 and 5 used 5-aminonaphthalene-2-sulfonic acid and 3-amino-4-hydroxybenzenesulfonic acid, respectively, instead of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid. The synthesized imine derivatives contained only one sulfonic acid group, failing to improve the water solubility of the complex. Precipitation may occur during detection, leading to decreased sensitivity and accuracy in boron detection.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the concentration of trace elements in a fertilizer production process, characterized by, The determination method is as follows: Step (1) 7-9 parts by weight of ferrous ammonium sulfate, 4-6 parts by weight of manganese acetate, 4-6 parts by weight of zinc sulfate, 3-5 parts by weight of copper nitrate, 5-7 parts by weight of boric acid, and 2-4 parts by weight of ammonium molybdate are respectively added into polyethylene bottles, and deionized water is added to dissolve, to obtain trace element standard solutions respectively; Step (2) deionized water or trace element standard solution is respectively added into a quartz volumetric flask, and deionized water is added to dilute and mix uniformly, then the diluted trace element standard solution, color developing agent, and buffer solution are added into the channel of a flow analyzer, instrument parameters are set, absorbance is detected, and a regression linear equation is obtained with trace element concentration as the abscissa and absorbance as the ordinate; Step (3) deionized water and a fertilizer sample are added into a polyfluoroethylene beaker, boiled, and cooled to obtain a to-be-tested solution after dilution, which is added into the analysis channel of the flow analyzer, and then color developing agent and buffer solution are added, and the absorbance is detected, and the concentration of trace elements in the fertilizer is calculated according to the regression linear equation.

2. The method for determining the concentration of trace elements in the production of fertilizers according to claim 1, characterized in that, The color developing agent used for determining the concentrations of iron, manganese, zinc, copper, boron, and molybdenum in step (1) is sulfosalicylic acid, formaldehyde oxime, 2-(2-hydroxy-5-sulfophenylazo) benzylidene hydrazine benzoic acid sodium salt, 2,2'-biquinoline, imine derivative, and potassium thiocyanate.

3. The method for determining the concentration of trace elements in the production of fertilizers according to claim 1, characterized in that, The buffer solution used for determining the concentrations of iron, manganese, zinc, copper, boron, and molybdenum in step (1) is acetic acid-ammonium acetate buffer solution, ammonia-ammonium chloride buffer solution, carbonate buffer solution, borate buffer solution, acetate buffer solution, and sulfuric acid-copper sulfate-thiourea mixed solution.

4. The method of claim 1, wherein the method is characterized by, The instrument parameters in step (1) are pump speed of 0.5-1.0 mL / min, sample flow rate of 0.05-0.1 mL / min, sample injection time of 30-40 s, cleaning time of 60-90 s, optical path of 10-15 mm, and reaction temperature of 25-35℃.

5. The method of claim 1, wherein the method is characterized by, The maximum absorption wavelengths for determining the concentrations of iron, manganese, zinc, copper, boron, and molybdenum in step (1) are 465 nm, 526 nm, 620 nm, 562 nm, 420 nm, and 460 nm respectively.

6. The method of claim 2, wherein the method is characterized by, The preparation method of the imine derivative is as follows: deionized water, 4-amino-5-hydroxy-2,7-naphthalene disulfonic acid, and 1-hydroxy-2-naphthaldehyde are added into a flask, heated and stirred to react, centrifuged and separated, filtered, and the precipitate is washed with ethanol and dried to obtain the imine derivative.

7. The method for determining the concentration of trace elements in the production of fertilizers according to claim 6, characterized in that, The molar ratio of 4-amino-5-hydroxy-2,7-naphthalene disulfonic acid to 1-hydroxy-2-naphthaldehyde is 1: (2.4-3.2).

8. The method of claim 6, wherein the method is characterized by, The heating and stirring reaction is carried out at a temperature of 50-70℃ for 2-4 h.

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