A hydrolyzable nitrogen absorbing device and a method for measuring a hydrolyzable nitrogen content at high throughput

Abstract

The application provides a hydrolytic nitrogen absorption device and a method for determining the content of hydrolytic nitrogen, and belongs to the technical field of analysis and detection. The hydrolytic nitrogen absorption device comprises an automatic sampling tube, a sealed tube for containing the automatic sampling tube, an elastic buckle support for fixing the automatic sampling tube on the upper part inside the sealed tube, and a sealing cover for sealing the opening at the top of the sealed tube. The device is used for pretreating the sample to be measured, and has the advantages of simple operation, high processing efficiency, high-throughput detection by using a full-automatic equipment, liberation of manpower, time and labor saving, more than 200 samples can be tested in one day (24 hours of unattended operation), low error probability, and accurate determination of the content of hydrolytic nitrogen in soil.

Description

Technical Field

[0001] This invention relates to the field of analytical testing technology, and in particular to a hydrolyzable nitrogen absorption device and a method for determining the content of hydrolyzable nitrogen. Background Technology

[0002] Hydrolyzable nitrogen (also known as alkaline nitrogen) in soil consists of ammonium nitrogen, nitrate nitrogen, and easily decomposable, relatively simple amino acid nitrogen, amide nitrogen, and easily hydrolyzable protein nitrogen from some organic matter. It is an important parameter reflecting soil nutrient content. Measuring hydrolyzable nitrogen in soil allows us to understand its nutrient supply capacity and reflect its recent nitrogen supply status. Hydrolyzable nitrogen content has a better correlation with plant nitrogen nutrition than inorganic nitrogen. Compared to total soil nitrogen, it better reflects the intensity, capacity, and rate of nitrogen supply in the soil, and is considered the best indicator for guiding fertilization.

[0003] Currently, the standard method for determining hydrolyzable nitrogen in soil is the alkaline hydrolysis diffusion method (LY / T1228-2015). This method uses a diffusion dish as the nitrogen release device. A certain concentration of alkaline solution, such as sodium hydroxide solution, is added to the soil sample, and the sample is heated at a constant temperature to hydrolyze the nitrogen into ammonium nitrogen, which is then absorbed by boric acid solution. Finally, the nitrogen is titrated with a standard hydrochloric acid solution. This method is cumbersome, time-consuming, and has many influencing factors, which can easily lead to large deviations in the test results. Summary of the Invention

[0004] The purpose of this invention is to provide a hydrolyzable nitrogen absorption device and a method for determining the content of hydrolyzable nitrogen. The device provided by this invention is simple to operate, has high processing efficiency, and is easy to implement with fully automated equipment for high-throughput detection.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The present invention provides a hydrolytic nitrogen absorption device, comprising an automatic injection tube, a sealing tube for holding the automatic injection tube, an elastic snap bracket for fixing the automatic injection tube inside the upper part of the sealing tube, and a sealing cap for sealing the top opening of the sealing tube.

[0007] Preferably, the elastic buckle bracket includes an arc support component, an upper ring, a lower ring, a first support rod, and a second support rod. The two ends of the first support rod are respectively connected to the upper ring and the lower ring, and the two ends of the second support rod are respectively connected to the upper ring and the lower ring. The upper ring is connected to the arc support component.

[0008] The diameter of the upper ring is greater than the diameter of the autosampler tube, and the diameter of the lower ring is smaller than the diameter of the autosampler tube.

[0009] Preferably, the diameter of the upper ring is 1 to 1.5 cm, the diameter of the lower ring is 0.5 to 0.8 cm, and the distance between the upper and lower rings is 1.5 to 4 cm.

[0010] Preferably, the elastic buckle bracket is a stainless steel bracket.

[0011] Preferably, the height of the sealing tube is 4 to 15 cm, and the diameter of the sealing tube is 2 to 6 cm.

[0012] Preferably, the sealing tube is a glass tube, a polytetrafluoroethylene tube, a polypropylene tube, or a perfluoroalkoxy resin plastic tube.

[0013] Preferably, the sealing cap is made of polytetrafluoroethylene, polypropylene, or perfluoroalkoxy resin.

[0014] Preferably, the sealing cap has a sealing gasket made of silicone.

[0015] This invention provides a method for determining the content of hydrolyzable nitrogen based on the hydrolyzable nitrogen absorption device described above, comprising the following steps:

[0016] The sample to be tested, alkaline solution and reducing agent are placed in a sealed tube. An automatic sample injection tube containing absorbent is placed on an elastic buckle bracket. Then, the elastic buckle bracket containing absorbent is placed inside the sealed tube containing the sample to be tested, alkaline solution and reducing agent. After sealing the sealed tube with a sealing cap, hydrolysis-absorption treatment is performed to obtain the sample to be tested in the automatic sample injection tube.

[0017] The content of hydrolyzable nitrogen in the sample was obtained by analyzing the test solution contained in the autosampler tube using a flow injection analyzer.

[0018] Preferably, the sample to be tested includes soil or sediment.

[0019] This invention provides a hydrolyzable nitrogen absorption device, comprising an automatic sample inlet tube, a sealing tube for holding the automatic sample inlet tube, an elastic snap-fit ​​bracket for fixing the automatic sample inlet tube inside the upper part of the sealing tube, and a sealing cap for sealing the top opening of the sealing tube. Using the device provided by this invention for sample pretreatment is simple to operate, highly efficient, and facilitates high-throughput detection using fully automated equipment. It frees up manpower, saves time and effort, and can test more than 200 samples per day (24 hours unattended). Furthermore, it has a low error rate, which is beneficial for accurately determining the hydrolyzable nitrogen content in soil. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the components in the hydrolytic nitrogen absorption device of the present invention;

[0021] Figure 2 This is a schematic diagram of the hydrolytic nitrogen absorption device of the present invention performing hydrolysis-absorption treatment on the sample to be tested;

[0022] 1 is a sealing tube, 2 is a sealing cap, 3 is an elastic buckle bracket, 3-1 is an arc support component, 3-2 is an upper ring, 3-3 is a lower ring, 3-4 is a first support rod, 3-5 is a second support rod, 4 is an automatic sample injection tube, and 5 is a sealing gasket.

[0023] Figure 3 This is the standard curve in Example 1. Detailed Implementation

[0024] The present invention provides a hydrolytic nitrogen absorption device, comprising an automatic injection tube, a sealing tube for holding the automatic injection tube, an elastic snap bracket for fixing the automatic injection tube inside the upper part of the sealing tube, and a sealing cap for sealing the top opening of the sealing tube.

[0025] The hydrolytic nitrogen absorption device provided by this invention includes an automatic sample injection tube for holding an absorption liquid. The absorption liquid absorbs the ammonium nitrogen released from the hydrolysis of the sample by the alkaline solution, thereby obtaining the test solution. This invention does not have specific limitations on the specifications of the automatic sample injection tube; conventional automatic sample injection tubes in the art can be used. This invention uses an automatic sample injection tube to hold the absorption liquid, and the test solution is obtained directly in the automatic sample injection tube after the hydrolysis-absorption treatment. This facilitates fully automated sample injection analysis, allows for repeated measurements more than three times without sample transfer, and avoids the problems of complex operation and inability to repeat measurements associated with traditional manual titration methods.

[0026] The hydrolytic nitrogen absorption device provided by this invention includes a sealed tube for holding the automatic sample inlet tube. The sealed tube is preferably a glass tube, a polytetrafluoroethylene (PTFE) tube, a polypropylene tube, or a perfluoroalkoxy resin plastic tube, more preferably a polypropylene tube. This invention preferably uses the above-mentioned materials for the sealed tube, resulting in a long service life. Using PTFE, polypropylene, or perfluoroalkoxy resin plastic tubes also avoids the problem of glass tubes being fragile. In this invention, the height of the sealed tube is preferably 4–15 cm, more preferably 4–8 cm, specifically 4 cm, 6 cm, or 8 cm; the diameter of the sealed tube is preferably 2–6 cm, more preferably 2–3 cm. This invention uses the above-mentioned sealed tube and can be used with ordinary centrifuge tube sample racks, such as ordinary 30–40 cm centrifuge tube sample racks. In actual operation, multiple hydrolytic nitrogen absorption devices (e.g., 40–60) assembled with the sealed tube can be directly placed on the centrifuge tube sample rack, and then the entire rack can be removed and placed in an incubator for hydrolysis-absorption treatment, greatly saving pretreatment and detection time.

[0027] The hydrolytic nitrogen absorption device provided by this invention includes an elastic snap-fit ​​bracket for fixing the automatic sample inlet tube to the upper part of the sealed tube. In this invention, the elastic snap-fit ​​bracket is disposed inside the sealed tube, and the outer dimensions of the elastic snap-fit ​​bracket are adapted to the inner diameter of the sealed tube. Preferably, the elastic snap-fit ​​bracket is made of stainless steel, which has strong elasticity, allowing it to be directly fixed inside the sealed tube (and the automatic sample inlet tube placed on the elastic snap-fit ​​bracket) without the need for other means, relying solely on its own elasticity, without slipping to the bottom of the sealed tube. Furthermore, the stainless steel bracket used in this invention prevents corrosion from alkaline solutions, has a long service life, requires virtually no replacement, and eliminates consumable consumption.

[0028] In one embodiment of the present invention, the elastic buckle bracket includes an arc-shaped support component, an upper ring, a lower ring, a first support rod, and a second support rod. The two ends of the first support rod are respectively connected to the upper ring and the lower ring, and the two ends of the second support rod are also respectively connected to the upper ring and the lower ring. The upper ring is connected to the arc-shaped support component. In another embodiment of the present invention, the first support rod, the second support rod, and the arc-shaped support component are arranged longitudinally, while the upper ring and the lower ring are arranged laterally. In this invention, the arc-shaped support component can specifically be a stainless steel wire with an arc, and the upper ring and the lower ring can specifically be circular stainless steel wires. The elastic buckle bracket with the above structure of the present invention facilitates stable fixation inside the sealing tube.

[0029] The elastic snap-fit ​​bracket described in this invention is used to hold the autosampler tube. The two should be sized to match. Specifically, the diameter of the upper ring is preferably larger than the diameter of the autosampler tube, and the diameter of the lower ring is preferably smaller than the diameter of the autosampler tube, facilitating the fixation of the autosampler tube to the elastic snap-fit ​​bracket. Specifically, the diameter of the upper ring is preferably 1-1.5 cm, and the diameter of the lower ring is preferably 0.5-0.8 cm, compatible with most mainstream flow analyzer autosampler tubes on the market. As an embodiment of this invention, the distance between the upper and lower rings is preferably adapted to the height of the autosampler tube; specifically, the distance between the upper and lower rings is preferably 1.5-4 cm, more preferably 2-3 cm. This invention provides two rings (i.e., an upper ring and a lower ring) to ensure stable fixation of the autosampler tube to the elastic snap-fit ​​bracket.

[0030] The hydrolytic nitrogen absorption device provided by this invention includes a sealing cap for sealing the top opening of the sealing tube. In this invention, the sealing cap is preferably made of polytetrafluoroethylene, polypropylene, or perfluoroalkoxy resin.

[0031] As an embodiment of the present invention, the sealing cap is equipped with a sealing gasket to enhance the sealing effect; the sealing gasket is preferably made of silicone.

[0032] Figure 1 This is a schematic diagram of the components in the hydrolyzable nitrogen absorption device of the present invention, including an automatic sampling tube 4, a sealing tube 1 for holding the automatic sampling tube 4, an elastic buckle bracket 3 for fixing the automatic sampling tube 4 inside the upper part of the sealing tube 1, and a sealing cap 2 for sealing the top opening of the sealing tube 1, the sealing cap 2 having a sealing gasket 5; wherein the elastic buckle bracket 3 includes an arc support component 3-1, an upper ring 3-2, a lower ring 3-3, a first support rod 3-4, and a second support rod 3-5; using the device provided by the present invention for pretreatment of the sample to be tested is simple to operate, has high processing efficiency, and is easy to achieve high-throughput detection with fully automated equipment, freeing up manpower, saving time and effort, and can test more than 200 samples per day (24 hours unattended), while having a low probability of error, which is beneficial for accurately determining the hydrolyzable nitrogen content in soil.

[0033] This invention provides a method for determining the content of hydrolyzable nitrogen based on the hydrolyzable nitrogen absorption device described above, comprising the following steps:

[0034] The sample to be tested, alkaline solution and reducing agent are placed in a sealed tube. An automatic sample injection tube containing absorbent is placed on an elastic buckle bracket. Then, the elastic buckle bracket containing absorbent is placed inside the sealed tube containing the sample to be tested, alkaline solution and reducing agent. After sealing the sealed tube with a sealing cap, hydrolysis-absorption treatment is performed to obtain the sample to be tested in the automatic sample injection tube.

[0035] The content of hydrolyzable nitrogen in the sample was obtained by analyzing the test solution contained in the autosampler tube using a flow injection analyzer.

[0036] Figure 2 The following is a detailed description of a schematic diagram of the hydrolytic nitrogen absorption device of the present invention used to perform hydrolysis-absorption treatment on the sample to be tested.

[0037] This invention places the sample to be tested, an alkaline solution, and a reducing agent in a sealed tube. In this invention, the sample to be tested preferably includes soil or sediment, more preferably soil. In this invention, the alkaline solution is preferably a sodium hydroxide solution, and the concentration of the alkaline solution is preferably 1.5–2.0 mol / L, more preferably 1.8 mol / L. In this invention, the ratio of the sample to the alkaline solution is preferably 1:2–10 g / mL, more preferably 1:2–4 g / mL; specifically, the weight of the sample to be tested is preferably 0.2–0.5 g, and the volume of the alkaline solution is preferably not less than 1 mL. In this invention, the reducing agent is preferably a zinc-ferrous sulfate reducing agent, which is preferably obtained by mixing ferrous sulfate (FeSO4·7H2O, analytical grade) powder and zinc (Zn, analytical grade) powder. The mass ratio of ferrous sulfate powder to zinc powder is preferably 4-6:1, more preferably 5:1. Before mixing, the ferrous sulfate powder and zinc powder are preferably ground separately and passed through a 0.25mm sieve, and the sieve-passing material is used to prepare the zinc-ferrous sulfate reducing agent. In this invention, the mass ratio of the sample to the reducing agent is preferably 1:0.5-2, more preferably 1:1.

[0038] This invention places an autosampler containing an absorbent solution on a flexible clip holder. Preferably, the absorbent solution is placed in the autosampler, and then the autosampler containing the absorbent solution is placed on the flexible clip holder. In this invention, the absorbent solution is preferably a boric acid solution, and the concentration of the boric acid solution is preferably 10–40 g / L, more preferably 20 g / L. In this invention, the amount of absorbent solution used is sufficient to meet the requirements of detection (specifically, automatic sample injection detection).

[0039] This invention places the elastic clip holder containing the absorbent liquid above the interior of a sealed tube containing the sample to be tested, alkali solution, and reducing agent. After sealing the tube with a sealing cap, a hydrolysis-absorption treatment is performed, yielding the test solution in an autosampler. In this invention, the preferred temperature for the hydrolysis-absorption treatment is 35–45°C, more preferably 40°C; the preferred time is 20–30 hours, more preferably 24 hours. Preferably, the hydrolysis-absorption treatment is performed in an incubator, specifically by placing the sealed tube in the incubator. After the hydrolysis-absorption treatment, the preferred method is to open the sealed tube and remove the autosampler; the liquid inside the autosampler is the test solution.

[0040] After obtaining the test solution, this invention uses a flow injection analyzer to detect the test solution contained in the automatic sample tube to obtain the content of hydrolyzable nitrogen in the test sample. In this invention, the flow injection analyzer is preferably a fully automated continuous flow injection analyzer (Skalar SNA++, Netherlands). In this invention, the detection conditions preferably include: injection time 80s; rinsing time 100s; air time 0s; sampling times 1; peak initiation value: 0.01ABS; peak width: 30%. In this invention, after the detection is completed, the content of hydrolyzable nitrogen in the test sample can be obtained based on the content of hydrolyzable nitrogen in the test solution and the sample weight.

[0041] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] The reagents and standard substances used in the following embodiments of the present invention are as follows:

[0043] Sodium hydroxide solution: Dissolve sodium hydroxide (analytical grade) powder in 700 mL of water, cool, and then bring the volume to 1 L.

[0044] Zinc-ferrous sulfate reducing agent: Finely ground ferrous sulfate (FeSO4·7H2O, analytical grade) powder that has passed through a 0.25mm sieve is mixed with zinc (Zn, analytical grade) powder at a mass ratio of 5:1.

[0045] 20 g / L boric acid solution: Dissolve 20.0 g of boric acid in 1 L of water to obtain a 2% boric acid solution (m / v).

[0046] The standard substance used was an ammonium nitrogen standard solution (1000 mg / L, GSB04-2832-201).

[0047] Standard soils: Heilongjiang black soil NSA-1, Hebei alluvial soil NSA-2, Shaanxi yellow cotton soil NSA-3, Sichuan purple soil NSA-4, Hunan paddy soil NSA-5, Guangzhou Shaoguan soil NSA-6.

[0048] The experimental equipment used in the following embodiments of the present invention is as follows:

[0049] Hydrolyzable nitrogen was released using a constant temperature incubator (Shanghai Yiheng GHP927), and the released absorbent was analyzed using a fully automated continuous flow injection analyzer (Skalar SNA++, Netherlands).

[0050] Example 1

[0051] 1. Method

[0052] (1) Sample pretreatment:

[0053] Using 20 g / L boric acid solution as the absorbent, 3 mL of the absorbent solution was placed in an autosampler tube, and the autosampler tube containing the absorbent solution was placed on a stainless steel elastic clip holder.

[0054] Weigh 0.5 g (accurate to 0.001 g) of air-dried soil sample that has passed through a 2 mm sieve into the bottom of a polypropylene tube. Add 1 mL of alkaline solution (1.8 mol / L sodium hydroxide solution) and 0.5 g of zinc-ferrous sulfate reducing agent. Then, quickly place the elastic clip holder with the absorbent liquid inside the polypropylene tube. Seal the polypropylene tube with a silicone sealing gasket and a sealing cap and place it in an incubator for hydrolysis-absorption treatment at 40°C for 24 h. After the incubation is complete, open the polypropylene tube and remove the autosampler tube. The liquid in the autosampler tube is used as the test solution.

[0055] The blank soil and the standard quality control soil were simultaneously subjected to hydrolysis-absorption treatment according to the above method;

[0056] (2) Sample testing

[0057] The test solution was analyzed using a flow injection analyzer, wherein the conditions of the flow injection analyzer included: injection time 80s; rinsing time 100s; air time 0s; sampling times 1; peak initiation value: 0.01ABS; peak width: 30%.

[0058] Standard curve plotting: Standard working solutions were prepared using a 1000 mg / L ammonium nitrogen (GSB04-2832-201) standard solution and 2% boric acid solution as the medium, with concentrations of 0.00 mg / L, 2.00 mg / L, 4.00 mg / L, 10.00 mg / L, 20.00 mg / L, 40.00 mg / L, and 60.00 mg / L. The standard working solutions were then tested according to the above method. A standard curve was plotted with the standard working solution concentrations on the x-axis and the detected signal values ​​on the y-axis, as detailed below. Figure 3 As shown, the linear equation is y = 0.0632x - 0.0162, R0 2 =0.9993.

[0059] 2. Experimental Optimization and Methodological Results

[0060] (1) Optimization of soil sample weighing and alkali solution dosage

[0061] The standard soil sample, Hunan paddy soil (NSA-5), was used as the sample for optimizing soil sample weight and alkali solution dosage. The standard value was 180±10 mg / kg. The specific results are shown in Table 1. As shown in Table 1, when the soil sample weight was 0.2–0.5 g and the soil-to-alkali solution ratio was 1:2 (g / mL), good recovery rates (95–105%) were observed, fully meeting the requirements for accurate quantification.

[0062] Table 1 Results of the optimization experiment on soil sample size and alkali solution dosage

[0063]

[0064] (2) Optimization of hydrolytic nitrogen absorption device

[0065] The standard soil sample, Hunan paddy soil (NSA-5), was used as the sample for optimizing the hydrolyzable nitrogen absorption device. The standard value was 180±10 mg / kg. Specifically, 0.5 g of soil sample was weighed, and the ratio of soil to alkali solution was 1:2 (g / mL). The height of the polypropylene tube was optimized, and the specific results are shown in Table 2. Table 2 shows that the recovery rate (85-105%) was optimal when the polypropylene tube height was set between 4 and 15 cm, with a precision of less than 5%, fully meeting the requirements for accurate quantification. When the height was 20 cm, the recovery rate was only 80.56%, and the precision was 7.90%, failing to meet the requirements for accurate quantification.

[0066] Table 2. Experimental results of optimizing the height of the polypropylene tube in the hydrolytic nitrogen absorption device.

[0067]

[0068]

[0069] The standard soil sample, Hunan paddy soil (NSA-5), was used as the sample for optimizing the hydrolyzable nitrogen absorption device. The standard value was 180±10 mg / kg. Specifically, 0.5g of soil sample was weighed, and the ratio of soil to alkali solution was 1:2 (g / mL). The height of the polypropylene tube was set to 6cm, and the diameter of the polypropylene tube was optimized. The specific results are shown in Table 3. As shown in Table 3, regardless of the diameter of the polypropylene tube (2-6cm), a good recovery rate (95-105%) was achieved, fully meeting the requirements for accurate quantification. However, if the diameter of the polypropylene tube is too small, the operation is cumbersome, and some models of automatic sample feeding tubes may not be able to fit; if the diameter is too large, the sample rack size will be larger, thereby reducing the throughput. In this invention, a polypropylene tube diameter of 3cm was selected because this size can be matched with a universal 50cm centrifuge tube rack, which has a large sample throughput. A single centrifuge tube rack can hold 60 samples, which is counted as one treatment. A 50L incubator can perform more than 300 treatments.

[0070] Table 3. Experimental results of optimizing the diameter of polypropylene tubes in the hydrolytic nitrogen absorption device.

[0071]

[0072] (3) Standard soil test results

[0073] The optimized method was used to determine the content of hydrolyzable nitrogen in six different types of standard soils, and the specific results are shown in Table 4. Table 4 shows that the optimized method can accurately determine the content of hydrolyzable nitrogen in different types of soils.

[0074] Table 4. Results of Standard Soil Tests

[0075]

[0076] (4) Method detection limit

[0077] The method detection limit was determined by measuring the values ​​of 11 blank samples and calculating their standard deviation (SD value, the specific results are shown in Table 5). Then, it was calculated based on the soil sample weight and the volume of the absorbent liquid. With a soil sample weight of 0.2 g and an absorbent liquid volume of 3 mL, the detection limit of the method of this invention is 0.4 mg / L, while the detection limit of the traditional standard method (LY / T1228-2015) is 5 mg / L. That is, the detection limit of the method of this invention is more than 10 times lower than that of the standard method.

[0078] Table 5. Detection results of blank samples in this invention.

[0079]

[0080]

[0081] 3. Testing of actual soil samples

[0082] Actual soil samples were tested using the method of this invention, and the results were compared with those of the traditional standard method (LY / T1228-2015). The specific results are shown in Table 6. Table 6 shows that there was no significant difference between the test results of the method of this invention and the traditional standard method (LY / T1228-2015) (p>0.05). Furthermore, the precision of the method of this invention is superior to that of the traditional standard method (LY / T1228-2015).

[0083] Table 6 Comparison results of the method of the present invention and the traditional standard method

[0084]

[0085] As can be seen from the above embodiments, the hydrolyzable nitrogen absorption device provided by the present invention can pretreat soil samples and simultaneously achieve fully automated flow injection, thereby realizing the detection of hydrolyzable nitrogen in soil samples. This solves the problems of cumbersome pretreatment operations and high manpower consumption in traditional methods. The method of the present invention can achieve simple pretreatment operations and fully automated unattended injection. Compared with traditional standard methods, the method of the present invention has the advantages of high sensitivity, good precision, and accurate results.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the content of hydrolyzable nitrogen based on a hydrolyzable nitrogen absorption device, characterized in that, The hydrolytic nitrogen absorption device includes an automatic injection tube, a sealing tube for holding the automatic injection tube, an elastic buckle bracket for fixing the automatic injection tube inside the upper part of the sealing tube, and a sealing cap for sealing the top opening of the sealing tube. The height of the sealing tube is 4-8 cm, and the diameter of the sealing tube is 2-5 cm; the sealing tube is a polytetrafluoroethylene tube, a polypropylene tube, or a perfluoroalkoxy resin plastic tube; the material of the sealing cap is polytetrafluoroethylene, polypropylene, or perfluoroalkoxy resin. The sealing cap has a sealing gasket, and the sealing gasket is made of silicone. The method includes the following steps: The sample to be tested, the alkali solution, and the reducing agent are placed in a sealed tube. An automatic sample injection tube containing the absorbent is placed on an elastic clip bracket. Then, the elastic clip bracket containing the absorbent is placed above the inside of the sealed tube containing the sample to be tested, the alkali solution, and the reducing agent. After sealing the tube with a sealing cap, hydrolysis-absorption treatment is performed to obtain the test solution in the automatic sample injection tube. The sample weight is 0.2~0.5g, the concentration of the alkali solution is 1.5~1.8mol / L, and the ratio of the sample to the alkali solution is 1:2~4g / mL. The content of hydrolyzable nitrogen in the test sample was obtained by analyzing the test solution contained in the autosampler tube using a flow injection analyzer. The detection conditions included: injection time of 80 s, rinsing time of 100 s, air time of 0 s, sampling number of times of sampling, peak initiation value of 0.01 ABS, and peak width of 30%. The content of hydrolyzable nitrogen in the sample to be tested was calculated based on a standard curve. The standard curve was plotted as follows: a standard working solution was prepared using a 1000 mg / L ammonium nitrogen standard solution and a 2% boric acid solution as the medium, with concentrations of 0.00 mg / L, 2.00 mg / L, 4.00 mg / L, 10.00 mg / L, 20.00 mg / L, 40.00 mg / L, and 60.00 mg / L, respectively. The standard working solutions were tested according to the above method, and a standard curve was plotted with the concentration of the standard working solution as the abscissa and the detected signal value as the ordinate.

2. The method according to claim 1, characterized in that, The elastic buckle bracket includes an arc support component, an upper ring, a lower ring, a first support rod, and a second support rod. The two ends of the first support rod are respectively connected to the upper ring and the lower ring, and the two ends of the second support rod are respectively connected to the upper ring and the lower ring. The upper ring is connected to the arc support component. The diameter of the upper ring is greater than the diameter of the autosampler tube, and the diameter of the lower ring is smaller than the diameter of the autosampler tube.

3. The method according to claim 2, characterized in that, The diameter of the upper ring is 1~1.5cm, the diameter of the lower ring is 0.5~0.8cm, and the distance between the upper and lower rings is 1.5~4cm.

4. The method according to claim 1 or 2, characterized in that, The elastic buckle bracket is a stainless steel bracket.

5. The method according to claim 1, characterized in that, The samples to be tested include soil or sediment.

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