Method for measuring nitrate nitrogen content and test pipeline

Abstract

The invention discloses a nitrate nitrogen content determination method and a test pipeline, and relates to the technical field of agricultural chemical analysis, and the technical key points are that the determination method comprises the following steps: S1, under an alkaline condition, catalyzing nitrate in water or soil and an organic fertilizer extracting solution by using copper, and reducing the nitrate into nitrite by using hydrazine sulfate; s2, nitrite is subjected to a diazo coupling reaction with sulfanilamide and N-1-naphthyl ethylenediamine dihydrochloride under the acidic condition, and a red color base is formed; and S3, carrying out spectrophotometric determination on the color developing solution at the wavelength of 550nm. According to the method disclosed by the invention, the dosage of the reagent is reduced, precipitates generated by the oxidation-reduction reaction under the alkaline condition and impurities in the reagent are removed through the dialysis membrane, and the long-term problems that the determination of the nitrate peak map is interfered, the marking correlation coefficient is poor, the variation coefficient is large and the like are solved.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural chemical analysis, and in particular to a method for determining nitrate nitrogen content and a testing pipeline. Background Art

[0002] If the nitrate content in water is too high to a certain extent, it means that the water is polluted or causes eutrophication. High nitrate content in drinking water has adverse effects on human health and is one of the important indicators for drinking water testing. However, soil nitrate nitrogen is a fast-acting nitrogen that can be directly absorbed and utilized by plants. At the same time, soil nitrate and nitrite are also important sources of soil non-point source pollution, which plays an important role in monitoring soil nitrogen utilization and soil nitrogen pollution. Nitrate nitrogen is a fast-acting nitrogen in organic fertilizer nitrate nitrogen.

[0003] At present, the existing methods for detecting nitrate nitrogen in water, soil and organic fertilizer include ultraviolet spectrophotometry, phenol disulfonic acid colorimetry, distillation, copper-plated cadmium reduction-diazotization coupling colorimetry, etc. Under normal circumstances, the sample liquid to be tested can simultaneously determine ammonium nitrogen and nitrate nitrogen. The colorimetric method can only be used for simultaneous determination using a continuous flow analyzer. However, the existing continuous flow analyzer often has problems such as poor peak diagrams, poor calibration correlation coefficients and large coefficients of variation.

[0004] To this end, the present invention aims to provide a method for determining nitrate nitrogen content and a test pipeline to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of interference in the peak diagram of nitrate determination, poor correlation coefficient of calibration lines and large coefficient of variation in the prior art for a long time, and to provide a method for determining nitrate nitrogen content and a test pipeline.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a method for determining nitrate nitrogen content, comprising the following steps:

[0008] S1. Nitrates in water or soil and organic fertilizer extracts are reduced to nitrites by hydrazine sulfate under alkaline conditions using copper as catalyst;

[0009] S2, reacting nitrite with sulfonamide and N-1-naphthylethylenediamine dihydrochloride under acidic conditions to undergo diazo coupling reaction to form a red color base;

[0010] S3. Spectrophotometrically measure the color developing solution at a wavelength of 550 nm.

[0011] Furthermore, low concentration injection is adopted in the method.

[0012] Further, step S1 is specifically as follows: the test solution is subjected to alkaline conditions and the catalysis of copper, and the nitrite reduced by hydrazine sulfate by heating is filtered through a dialysis membrane, and undergoes a diazo coupling reaction with sulfonamide and N-1-naphthylethylenediamine dihydrochloride to form a red color base for photometric analysis, and the heating temperature is 37°C.

[0013] The present invention also provides a test pipeline for measuring the amount of nitrate nitrogen by a continuous flow analyzer, comprising an injection pipeline for a sample test liquid, an injection pipeline for an alkali solution, an injection pipeline for hydrazine sulfate, an injection pipeline for an acid buffer, and an injection pipeline for a color developing solution: the low-concentration injection pipeline of the method is merged with the lubricating liquid injection pipeline to form a first merged pipeline, the first merged pipeline is merged with the alkali solution injection pipeline to form a second merged pipeline, the second merged pipeline is merged with the hydrazine sulfate liquid injection pipeline to form a third merged pipeline, the third merged pipeline is merged with the color developing solution injection pipeline through a dialysis membrane to form a fourth merged pipeline, and the liquid outlet of the fourth merged pipeline is used to be connected to a detector of the continuous flow analyzer.

[0014] Furthermore, a mixing ring device is provided after the converging pipeline to mix the fluid in the pipeline.

[0015] Furthermore, a heating device is provided between the third merging pipeline and the fourth merging pipeline to prolong and accelerate the reduction reaction time.

[0016] Compared with the prior art, this solution has the following beneficial effects:

[0017] The method of the invention reduces the amount of reagents used, removes the precipitate produced by the redox reaction under alkaline conditions and impurities in the reagents through the dialysis membrane, and solves the long-standing problems of interference in the determination of nitrate peaks, poor correlation coefficient of the calibration line and large coefficient of variation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of a test pipeline for measuring nitrate nitrogen content using a continuous flow analyzer in an embodiment of the present invention;

[0019] In the figure: 1-reagent pipeline, 2-air pipeline, 3-reagent pipeline, 4-injection pipeline, 5-reagent pipeline, 6-reagent pipeline, 7-air pipeline, 8-reagent pipeline, 9-reagent pipeline, 10-waste liquid pipe, 11-air T-type tee, 12-reagent T-type tee, 13-5 circles of mixing rings, 14-reagent T tee, 15-5 circles of mixing rings, 16-reagent T-type tee, 17-5 circles of mixing rings, 18-heating tank, 19-10 circles of mixing rings, 20-dialysis membrane, 21-air T tee, 22-reagent T tee, 23-10 circles of mixing rings, 24-10 circles of mixing rings. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0022] The solution provided by the present invention is: a method for determining the nitrate nitrogen content in water, soil and organic fertilizer, comprising the following steps:

[0023] (1) After the sample is mixed with the lubricating liquid, it is mixed with the alkaline solution and reduced to a nitrite nitrogen test solution by the hydrazine sulfate solution under the catalytic action of copper under alkaline conditions. The solution is then passed through a dialysis membrane and reacted with the acidic color developer sulfonamide and N-1-naphthylethylenediamine dihydrochloride (NEDD) to obtain a color developing solution.

[0024] (2) Perform spectrophotometric analysis on the color developing solution obtained online.

[0025] (3) The test solution reduced to nitrite nitrogen by hydrazine sulfate solution is passed through a dialysis membrane to remove the precipitate produced by the redox reaction under alkaline conditions and impurities in the reagent.

[0026] (4) Water is used instead of acid buffer, and the amount of alkali used is reduced from the original 4% to 2%; the amount of acid and alkali used is reduced.

[0027] Under alkaline conditions, the test solution is reduced to nitrite by hydrazine sulfate under the catalytic effect of copper by heating, which accelerates the speed of the redox reaction; after filtration through a dialysis membrane, the precipitation produced by the reaction and the impurities in the reagents are reduced.

[0028] A heating device is provided after the third confluence pipeline, and the processing temperature is set to 37°C by default.

[0029] The nitrate nitrogen in the soil can be extracted with 1 mol / L sodium chloride or 0.01 mol / L calcium chloride to obtain the test solution, with a soil-water ratio of 1:5; the nitrate nitrogen in the organic fertilizer can be extracted with 0.05N sulfuric acid solution or water to obtain the test solution, with a fertilizer-water ratio of 1:10.

[0030] The technical solution of the test pipeline for measuring nitrate nitrogen content by a continuous flow analyzer of the present invention is:

[0031] A test pipeline for measuring nitrate nitrogen content by a continuous flow analyzer comprises a sample test liquid injection pipeline, an alkali solution injection pipeline, a hydrazine sulfate injection pipeline, an acid buffer injection pipeline and a color development liquid injection pipeline: a low-concentration injection pipeline and a lubricating liquid injection pipeline are merged to form a first merged pipeline, the first merged pipeline and the alkali solution injection pipeline are merged to form a second merged pipeline, the second merged pipeline and the hydrazine sulfate liquid injection pipeline are merged to form a third merged pipeline, the third merged pipeline is heated online and then merged with the color development liquid injection pipeline through a dialysis membrane to form a fourth merged pipeline, and the liquid outlet of the fourth merged pipeline is used to be connected to a detector of the continuous flow analyzer.

[0032] The detector is equipped with a colorimetric cell and a filter, and the filter wavelength is 550nm.

[0033] A mixing ring device is provided after the converging pipeline to mix the fluid in the pipeline.

[0034] Unless otherwise specified, the reagents used in the present invention are all analytically pure, and the water is deionized water. The preparation is as follows:

[0035] 1- Reagent pipeline fluid: water or sample extract.

[0036] 3- Reagent pipeline liquid: Brij-35, 30% solution, take 1 mL and add it to 1000 mL deionized water and mix well.

[0037] 5-Reagent pipeline liquid: Add 20 grams of sodium hydroxide to 1000 mL of deionized water and mix well.

[0038] 6-Reagent pipeline liquid: Take 14mL of 0.1% copper sulfate, 10mL of 1% zinc sulfate and 6g of hydrazine sulfate and add them to 1000mL of deionized water, mix well and store for 1 week.

[0039] 8-Reagent pipeline liquid: Dissolve 3mL of phosphoric acid in water, add 4g of tetrasodium triphosphate and mix well, then add 1mL of Brij-35 (30% solution) to dilute to 1L.

[0040] 9- Reagent pipeline liquid: a. 10% phosphoric acid sulfonamide solution: add 100mL phosphoric acid to water, add 40g sulfonamide to dissolve and dilute to 1L; b. 10% phosphoric acid N-(1-tetrayl)ethylenediamine dihydrochloride solution: add 100mL phosphoric acid to water, add 1g N-(1-tetrayl)ethylenediamine dihydrochloride to dilute to 1L. Mix a and b in a 1:1 ratio and filter if necessary.

[0041] The following is a specific implementation of the scheme of the present invention:

[0042] Example 1

[0043] In this embodiment, the extracted test liquid for simultaneous determination of ammonia and nitrate nitrogen in soil is used in a continuous flow analyzer and is measured through a measurement pipeline for measuring nitrate nitrogen content in the continuous flow analyzer. The steps are as follows:

[0044] (1) Preparation of sample solution: Weigh 5 g of soil sample, add 25 ml of 1 mol / L NaCl, and shake on an oscillator at 180 r.min +- 20 r.min for 30 minutes at 20-25°C. Dry filter to obtain a clear extract.

[0045] (2) Online determination: The sample liquid to be tested is connected to the 4-injection pipe and merged with the main flow 3-reagent pipe lubricating liquid to form the first confluence pipe. After being mixed in the mixing circle, it meets the 5-reagent pipe alkali liquid to form the alkaline liquid to be tested, forming the second confluence pipe and merging with the reducing agent of the 6-reagent pipe liquid to form the third confluence pipe. After 20 mixing circles and heating to accelerate the reduction of nitrate nitrogen to nitrite nitrogen, the impurities and most of the liquid are filtered out by the dialysis membrane, and a small amount of liquid enters the 8-reagent pipe liquid to react with the 9-reagent pipe liquid to form a red color developing liquid to form the fourth confluence pipe. It enters the detector (equipped with a colorimetric cell and a filter, the filter wavelength is 550nm) for analysis, and the nitrate nitrogen concentration is obtained through the data processing system, and the content is calculated.

[0046] The detection line of the test pipeline for measuring the nitrate nitrogen content by a continuous flow analyzer of the present invention is 0.16 mg / kg, the reagent absorption is 0.013, the sensitivity is 0.93, the correlation coefficient is 0.9999, and the coefficient of variation is less than 1.5%.

[0047] The above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for determining nitrate nitrogen content, characterized in that: The following steps are involved: S1. Nitrates in water or soil and organic fertilizer extracts are reduced to nitrites by hydrazine sulfate under alkaline conditions using copper as catalyst; S2, reacting nitrite with sulfonamide and N-1-naphthylethylenediamine dihydrochloride under acidic conditions to undergo diazo coupling reaction to form a red color base; S3. Spectrophotometrically measure the color developing solution at a wavelength of 550 nm.

2. The method for determining the nitrate nitrogen content according to claim 1, wherein: Low concentration injection is used in the method.

3. The method for determining nitrate nitrogen content and the test pipeline according to claim 1, characterized in that: Step S1 is specifically as follows: the test solution is heated under alkaline conditions and under the catalytic action of copper to reduce the nitrite to hydrazine sulfate, filter it through a dialysis membrane, and react with sulfonamide and N-1-naphthylethylenediamine dihydrochloride to form a red color base for photometric analysis, and the heating temperature is 37°C.

4. A test pipeline for measuring nitrate nitrogen by a continuous flow analyzer, characterized in that: The method comprises an injection pipeline for a sample test liquid, an injection pipeline for an alkaline solution, an injection pipeline for hydrazine sulfate, an injection pipeline for an acid buffer, and an injection pipeline for a color developing liquid: the low-concentration injection pipeline and the lubricating liquid injection pipeline of the method are merged to form a first merged pipeline, the first merged pipeline and the alkaline solution injection pipeline are merged to form a second merged pipeline, the second merged pipeline and the hydrazine sulfate liquid injection pipeline are merged to form a third merged pipeline, the third merged pipeline is merged with the color developing liquid injection pipeline through a dialysis membrane to form a fourth merged pipeline, and the liquid outlet of the fourth merged pipeline is used to be connected to a detector of a continuous flow analyzer.

5. A test pipeline for measuring nitrate nitrogen by a continuous flow analyzer as claimed in claim 4, characterized in that: A mixing ring device is provided after the converging pipeline to mix the fluid in the pipeline.

6. A test pipeline for measuring nitrate nitrogen by a continuous flow analyzer as claimed in claim 4, characterized in that: A heating device is provided between the third converging pipeline and the fourth converging pipeline to prolong and accelerate the reduction reaction time.

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