A sampling device for automatic Kjeldahl nitrogen analyzer

Abstract

The present invention discloses a sample injection device for an automatic Kjeldahl nitrogen analyzer, which relates to the field of Kjeldahl nitrogen analyzers and includes a Kjeldahl nitrogen analyzer body, wherein the upper part of the Kjeldahl nitrogen analyzer body has an equipment accommodating chamber, a mixing cylinder is installed at the inner bottom of the equipment accommodating chamber, a stirring assembly is provided in the mixing cylinder, and a liquid discharge pipe is provided at the bottom of the mixing cylinder, a first electromagnetic valve is installed on the liquid discharge pipe, and the bottom end of the liquid discharge pipe extends out of the bottom of the equipment accommodating chamber and extends into the inner top of the butt joint pipe, the butt joint pipe is fixed to the bottom surface of the equipment accommodating chamber, and the bottom end of the butt joint pipe is directly opposite to the top of the glass test tube, and a quantitative injection assembly is also provided at the top of the equipment accommodating chamber. The present invention realizes the purpose of accurately controlling the amount before the reaction through the quantitative injection assembly to ensure the accuracy of the subsequent test results, and this process is automatically carried out, reducing the amount of operation of the experimenter, and has a strong promotion effect.

Description

Technical Field

[0001] The invention relates to the field of Kjeldahl nitrogen analyzers, in particular to a sample feeding device for an automatic Kjeldahl nitrogen analyzer. Background Art

[0002] The Kjeldahl nitrogen analyzer is an instrument that calculates the protein content by measuring the nitrogen content in the sample based on the principle that the nitrogen content in protein is constant. Because the method of measuring and calculating protein content is called the Kjeldahl method, it is called the Kjeldahl nitrogen analyzer, also known as the nitrogen analyzer, protein analyzer, and crude protein analyzer.

[0003] During the measurement process, when a strong base is added to the test tube of the existing Kjeldahl nitrogen analyzer to neutralize the strong acid in the solution, a catalyst is often required to be added. In this way, a magnetic stirring base is generally provided on the test tube base to achieve this effect. However, the amount of reaction solution or water injected into the test tube by the existing Kjeldahl nitrogen analyzer cannot be accurately controlled, and the degree of automation is low, which increases the operation workload of the experimenter. Summary of the invention

[0004] The object of the present invention is to provide a sample introduction device for an automatic Kjeldahl nitrogen analyzer to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A sampling device for an automatic Kjeldahl nitrogen analyzer comprises a Kjeldahl nitrogen analyzer body, a test tube positioning seat for placing a glass test tube on the Kjeldahl nitrogen analyzer body, the glass test tube is used to inject acid solution and alkali solution, an equipment accommodating chamber is provided on the upper part of the Kjeldahl nitrogen analyzer body, a mixing cylinder is fixedly installed on the inner bottom of the equipment accommodating chamber, a stirring assembly is provided in the mixing cylinder, and a liquid discharge pipe is provided at the bottom of the mixing cylinder, a first electromagnetic valve is fixedly installed on the liquid discharge pipe, and the bottom end of the liquid discharge pipe extends out of the bottom of the equipment accommodating chamber and extends into the inner top of a butt joint pipe, the butt joint pipe is fixed on the bottom surface of the equipment accommodating chamber, and the bottom end of the butt joint pipe is directly opposite to the top of the glass test tube, a quantitative injection assembly is also provided on the top of the equipment accommodating chamber, and a purification tank for absorbing volatile gas in the mixing cylinder is also provided on the inner top of the equipment accommodating chamber;

[0007] The quantitative injection assembly includes a measuring cylinder with scale lines on the outer surface, a liquid level sensor for detecting the height of the liquid level inside the measuring cylinder is fixedly installed in the measuring cylinder, and the top and bottom of the measuring cylinder are fixedly connected to the liquid through pipe, the bottom end of the bottom liquid through pipe is fixedly connected to the top of the mixing cylinder, and the top end of the top liquid through pipe is fixedly connected to the water inlet bucket or the liquid inlet bucket, and the second solenoid valve and the third solenoid valve are respectively fixedly installed in the upper liquid through pipe and the lower liquid through pipe in each quantitative injection assembly.

[0008] As a further solution of the present invention: the first solenoid valve, the second solenoid valve, the third solenoid valve and the liquid level sensor are electrically connected to the PLC control mechanism built into the control panel on the main body of the Kjeldahl nitrogen analyzer, and the PLC control mechanism includes the following control method, according to the amount of water or acid and alkali solution to be added, a set value is input from the control panel, the PLC control mechanism sends a closing signal to the third solenoid valve, sends an opening signal to the second solenoid valve, and then injects into the cylinder through the water inlet bucket or the liquid inlet bucket, when the liquid level sensor detects that the liquid level reaches the set value, the liquid level sensor feeds back the signal to the PLC control mechanism, and then the PLC control mechanism sends an opening signal to the third solenoid valve and a closing signal to the second solenoid valve.

[0009] As a further solution of the present invention: a dosing tube is fixedly installed on the upper part of the equipment accommodating chamber, and the lower end of the dosing tube is fixedly connected to the liquid mixing cylinder.

[0010] As a further solution of the present invention: the stirring assembly includes a stirring rod in the middle of the mixing cylinder, a plurality of stirring rods are fixedly mounted on the stirring rod, and the top end of the stirring rod extends out of the top of the equipment accommodating chamber and is connected to the output shaft of the reduction motor through a coupling, and the reduction motor is fixedly mounted on one side of the top shell of the Kjeldahl nitrogen analyzer body.

[0011] As a further solution of the present invention: an appropriate amount of activated carbon particles are stored in the purification tank, and a gauze is fixedly connected to the bottom surface of the purification tank to prevent the activated carbon particles from leaking out. The bottom of the purification tank is fixedly connected to the air outlet opened at the top of the mixing cylinder through a plurality of evenly distributed air guide tubes, and at the same time, a plurality of exhaust pipes connected to the external atmosphere are also fixedly connected to the top of the purification tank.

[0012] As a further solution of the present invention: an activated carbon filter is fixedly installed on the inner top of the purification tank.

[0013] As a further solution of the present invention: the purification tank is penetrated by the upper part of the stirring rod, and the stirring rod in the purification tank is also fixedly sleeved with a stirring spiral.

[0014] As a further solution of the present invention: a slot for inserting the bottom of the glass test tube is opened in the middle of the upper surface of the test tube positioning seat, and one end of a plurality of evenly distributed first compression springs is fixedly connected to the bottom surface of the slot, while the other end of the first compression spring is vertically upward and fixedly connected to a support plate, the upper surface of the support plate is used to be placed in contact with the bottom surface of the glass test tube, and the slot also has a limit assembly for maintaining the vertical state of the glass test tube.

[0015] As a further solution of the present invention: the limiting assembly includes a plurality of placement grooves opened on the periphery of the top side of the slot, and the plurality of placement grooves are evenly distributed at equal angles, and the bottom surface of each placement groove is fixedly connected to one end of the second compression spring, and the other end of the second compression spring is fixedly connected to the limiting bead, and the limiting bead protrudes out of the corresponding placement groove and extends into the slot.

[0016] As a further solution of the present invention: a fixing ring is fixedly connected to the lower edge of the inner circumference of the bottom port of the docking tube, and a sealing ring is compositely connected to the outer edge of the lower circumference of the fixing ring, and a supporting ring is fixedly connected to the upper edge of the inner circumference of the top end of the glass test tube, and a sealing groove for the sealing ring to press into is formed on the upper surface of the supporting ring. When the sealing ring presses into the sealing groove, the first compression spring is in a compressed state, so that when the glass test tube is lifted by the support sheet, the sealing groove on it just presses against the sealing ring.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention injects liquid into a mixing cylinder through a water inlet hopper or a liquid inlet hopper. When a liquid level sensor detects that the liquid level reaches a set value, the liquid level sensor feeds back a signal to a PLC control mechanism. Then the PLC control mechanism sends an opening signal to a third solenoid valve and a closing signal to a second solenoid valve, so that an amount corresponding to the set value is added to the mixing cylinder, thereby reducing measurement errors and achieving the purpose of accurately controlling the amount before reaction to ensure the accuracy of subsequent detection results. Moreover, this process is automatically performed, reducing the amount of operation of experimenters and having a strong promotion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention;

[0020] Figure 2 It is a structural schematic diagram of the quantitative injection component in the present invention;

[0021] Figure 3 It is a schematic diagram of the installation of the fixing ring and the supporting ring in the present invention;

[0022] Figure 4 It is a schematic diagram of the installation of the sealing ring in the present invention;

[0023] Figure 5 for Figure 1 A magnified view of the structure at A;

[0024] Figure 6 for Figure 1 Enlarged view of the structure at point B in the figure.

[0025] In the figure: 1. Kjeldahl nitrogen analyzer body; 2. test tube positioning seat; 3. glass test tube; 4. equipment accommodating chamber; 5. mixing cylinder; 6. water inlet bucket; 7. liquid inlet bucket; 8. dosing tube; 9. butt joint tube; 10. measuring cylinder; 11. liquid pipe; 12. stirring rod; 13. first solenoid valve; 14. liquid discharge pipe; 15. activated carbon filter; 16. stirring spiral; 17. reduction motor; 18. stirring rod; 19. purification tank; 20. scale line; 21. second solenoid valve; 22. liquid level sensor; 23. third solenoid valve; 24. fixing ring; 25. sealing ring; 26. sealing groove; 27. supporting ring; 28. activated carbon particles; 29. ​​gauze; 30. air guide tube; 31. slot; 32. support plate; 33. a compression spring; 34. limit bead; 35. second compression spring; 36. placement groove. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 are within the scope of protection of the present invention.

[0027] See also Figures 1 to 6 In an embodiment of the present invention, a sample introduction device for an automatic Kjeldahl nitrogen analyzer comprises a Kjeldahl nitrogen analyzer body 1, a test tube positioning seat 2 for placing a glass test tube 3 is provided on the Kjeldahl nitrogen analyzer body 1, and the glass test tube 3 is used to inject acid solution and alkali solution, and an equipment accommodating chamber 4 is provided on the upper part of the Kjeldahl nitrogen analyzer body 1, a mixing liquid cylinder 5 is fixedly installed on the inner bottom of the equipment accommodating chamber 4, a stirring component is provided in the mixing liquid cylinder 5, and a liquid discharge pipe 14 is provided at the bottom of the mixing liquid cylinder 5, and a first solenoid valve 13 is fixedly installed on the liquid discharge pipe 14, and the bottom end of the liquid discharge pipe 14 extends out of the bottom of the equipment accommodating chamber 4 and extends into the inner top of the butt joint 9, the butt joint 9 is fixed on the bottom surface of the equipment accommodating chamber 4, and the bottom end of the butt joint 9 is directly opposite to the top of the glass test tube 3, and a quantitative injection component is also provided on the top of the equipment accommodating chamber 4, and a purification tank 19 for absorbing volatile gases in the mixing liquid cylinder 5 is also provided on the inner top of the equipment accommodating chamber 4;

[0028] The quantitative injection assembly includes a measuring cylinder 10 having scale lines 20 on its outer surface, a liquid level sensor 22 for detecting the height of the liquid level inside the measuring cylinder 10 is fixedly installed inside the measuring cylinder 10, and the top and bottom of the measuring cylinder 10 are fixedly connected to the liquid through pipe 11, the bottom end of the bottom liquid through pipe 11 is fixedly connected to the top of the mixing cylinder 5, and the top end of the top liquid through pipe 11 is fixedly connected to the water inlet bucket 6 or the liquid inlet bucket 7, and the second solenoid valve 21 and the third solenoid valve 23 are respectively fixedly installed in the upper liquid through pipe 11 and the lower liquid through pipe 11 in each quantitative injection assembly.

[0029] Further, the first solenoid valve 13, the second solenoid valve 21, the third solenoid valve 23 and the liquid level sensor 22 are all electrically connected to the PLC control mechanism built into the control panel on the main body 1 of the Kjeldahl nitrogen analyzer. The PLC control mechanism includes the following control methods. According to the amount of water or acid and alkali solution to be added, a set value is input from the control panel. The PLC control mechanism sends a closing signal to the third solenoid valve 23 and an opening signal to the second solenoid valve 21, and then injects into the vector cylinder 10 through the water inlet bucket 6 or the liquid inlet bucket 7. When the liquid level sensor 22 detects that the liquid level reaches the set value, the liquid level sensor 22 feeds back the signal to the PLC control mechanism, and then the PLC control mechanism sends an opening signal to the third solenoid valve 23 and a closing signal to the second solenoid valve 21, so that the amount corresponding to the set value is added to the mixing cylinder 5, reducing the measurement error, achieving the purpose of precise control of the amount before the reaction to ensure the accuracy of the subsequent test results, and this process is automatically carried out, reducing the amount of operation of the experimenter, and has a strong promotion effect.

[0030] Furthermore, a dosing tube 8 is fixedly installed on the upper part of the equipment accommodating chamber 4, and the lower end of the dosing tube 8 is fixedly connected to the liquid mixing cylinder 5. The dosing tube 8 is used to add solid particulate matter such as catalysts.

[0031] Further, the stirring assembly includes a stirring rod 18 in the middle of the mixing tube 5, and a plurality of stirring rods 12 are fixedly mounted on the stirring rod 18, and the top end of the stirring rod 18 extends out of the top of the equipment accommodating chamber 4 and is connected to the output shaft of the reduction motor 17 through a coupling, and the reduction motor 17 is fixedly mounted on one side of the top shell of the Kjeldahl nitrogen analyzer body 1. When the quantitative injection is completed, the first solenoid valve 13 is closed, and the reduction motor 17 is turned on to stir the relevant reaction liquid and catalyst in the mixing tube 5, which helps to accelerate the reaction rate.

[0032] Furthermore, an appropriate amount of activated carbon particles 28 are stored in the purification tank 19, and a gauze 29 for preventing the activated carbon particles 28 from leaking out is fixedly connected to the inner bottom surface of the purification tank 19. The bottom of the purification tank 19 is fixedly connected to the air outlet opened at the top of the mixing cylinder 5 through a plurality of evenly distributed air guide tubes 30. At the same time, a plurality of exhaust pipes connected to the external atmosphere are also fixedly connected to the top of the purification tank 19. The gas generated by the reaction in the mixing cylinder 5 is introduced into the purification tank 19 through the exhaust pipe, and is fully adsorbed by the activated carbon particles 28 to achieve the treatment effect.

[0033] Furthermore, an activated carbon filter 15 is fixedly installed on the inner top of the purification tank 19 to further serve the purpose of absorbing irritating, harmful and toxic gases.

[0034] Furthermore, the purification tank 19 is penetrated by the upper part of the stirring rod 18, and the stirring rod 18 in the purification tank 19 is also fixedly mounted with a stirring spiral 16. The stirring spiral 16 can turn over the activated carbon particles 28 so that each adsorption surface can participate in the adsorption purification process, thereby maximizing the adsorption effect.

[0035] Furthermore, a slot 31 is provided in the middle of the upper surface of the test tube positioning seat 2 for inserting the bottom of the glass test tube 3, and one end of a plurality of evenly distributed first compression springs 33 is fixedly connected to the bottom surface of the slot 31, and the other end of the first compression spring 33 is vertically upward and fixedly connected to a support piece 32, and the upper surface of the support piece 32 is used to contact the bottom surface of the glass test tube 3. The slot 31 also has a limiting component for maintaining the vertical state of the glass test tube 3. The purpose of arranging the first compression spring 33 below the support piece 32 is that the support piece 32 is directly in contact with the bottom surface of the glass test tube 3 when it is needed. When placing the glass test tube 3 on the test tube positioning seat 2, first slide the glass test tube 3 into the slot 31 of the test tube positioning seat 2, and then hold the glass test tube 3 and press it down, so that the support piece 32 compresses the first compression spring 33. When the top end of the glass test tube 3 is aligned directly below the bottom circumference of the docking tube 9, the glass test tube 3 is slowly released, and the first compression spring 33 is restored to its original state, lifting the support piece 32, thereby lifting the glass test tube 3 upward, and directly lowering the top end of the glass test tube 3 into the lower port of the docking tube 9, so that the reaction liquid discharged from the liquid discharge tube 14 is introduced into the glass test tube 3.

[0036] Furthermore, the limiting assembly includes a plurality of mounting grooves 36 opened on the top side periphery of the slot 31, and the plurality of mounting grooves 36 are evenly distributed at equal angles, and the bottom surface of each mounting groove 36 is fixedly connected to one end of the second compression spring 35, and the other end of the second compression spring 35 is fixedly connected to the limiting bead 34, and the limiting bead 34 extends out of the corresponding mounting groove 36 into the slot 31, so that when the glass test tube 3 is drawn into the slot 31, the spherical shape of the limiting bead 34 can slide well with the outer surface of the glass test tube 3, and will not block the movement of the glass test tube 3. At the same time, the limiting bead 34 can support the peripheral wall of the glass test tube 3 from all directions under the support effect of the second compression spring 35, so as to maintain the vertical state of the glass test tube 3, avoid the glass test tube 3 from being unstable or even falling over, and is also conducive to the slow release of the glass test tube 3, which can be smoothly docked with the docking tube 9.

[0037] Furthermore, a fixing ring 24 is fixedly connected to the lower edge of the inner circumference of the bottom end of the butt-jointed tube 9, and a sealing ring 25 is compositely connected to the outer edge of the lower circumference of the fixing ring 24, and a supporting ring 27 is fixedly connected to the upper edge of the inner circumference of the top end of the glass test tube 3, and a sealing groove 26 for the sealing ring 25 to press into is provided on the upper circumference of the supporting ring 27. When the sealing ring 25 presses into the sealing groove 26, the first compression spring 33 is in a compressed state, so that when the glass test tube 3 is lifted by the support sheet 32, the sealing groove 26 thereon just presses against the sealing ring 25. Since the first compression spring 33 is in a compressed state, the sealing groove 26 exerts a certain upward pressure on the sealing ring 25, so that the sealing ring 25 and the sealing groove 26 maintain a relatively close fitting state, the purpose of which is to prevent the relevant acidic volatile gas in the glass test tube 3 from escaping from between the glass test tube 3 and the butt-jointed tube 9, thereby helping to ensure the health of the experimenters.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0039] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, 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 sample injection device for an automatic Kjeldahl nitrogen analyzer, comprising a Kjeldahl nitrogen analyzer body (1), the Kjeldahl nitrogen analyzer body (1) having a test tube positioning seat (2) for placing a glass test tube (3), the glass test tube (3) being used for injecting acid solution and alkali solution, characterized in that: The upper part of the main body (1) of the Kjeldahl nitrogen analyzer is provided with an equipment accommodating chamber (4), a mixing cylinder (5) is fixedly installed at the inner bottom of the equipment accommodating chamber (4), a stirring assembly is provided in the mixing cylinder (5), and a liquid discharge pipe (14) is fixedly installed at the bottom of the mixing cylinder (5), a first electromagnetic valve (13) is fixedly installed on the liquid discharge pipe (14), and the bottom end of the liquid discharge pipe (14) extends out of the bottom of the equipment accommodating chamber (4) and extends into the inner top of the butt joint pipe (9), the butt joint pipe (9) is fixed on the bottom surface of the equipment accommodating chamber (4), and the bottom end of the butt joint pipe (9) is directly opposite to the top of the glass test tube (3), the top of the equipment accommodating chamber (4) is also provided with a quantitative injection assembly, and at the same time, a purification tank (19) for absorbing volatile gases in the mixing cylinder (5) is also provided at the inner top of the equipment accommodating chamber (4); The quantitative injection assembly comprises a measuring cylinder (10) having scale lines (20) on its outer surface, a liquid level sensor (22) for detecting the height of the liquid level inside the measuring cylinder (10) being fixedly installed inside the measuring cylinder (10), and the top and bottom of the measuring cylinder (10) are both fixedly connected to a liquid through pipe (11), the bottom end of the liquid through pipe (11) at the bottom is fixedly connected to the top of a liquid mixing cylinder (5), and the top end of the liquid through pipe (11) at the top is fixedly connected to a water inlet hopper (6) or a liquid inlet hopper (7), and a second solenoid valve (21) and a third solenoid valve (23) are respectively fixedly installed in the upper liquid through pipe (11) and the lower liquid through pipe (11) in each quantitative injection assembly; The first solenoid valve (13), the second solenoid valve (21), the third solenoid valve (23) and the liquid level sensor (22) are all electrically connected to a PLC control mechanism built into a control panel on the main body (1) of the Kjeldahl nitrogen analyzer. The PLC control mechanism includes the following control method: according to the amount of water or acid and alkali solution to be added, a set value is input from the control panel, the PLC control mechanism sends a closing signal to the third solenoid valve (23), sends an opening signal to the second solenoid valve (21), and then injects the liquid into the cylinder (10) through the water inlet hopper (6) or the liquid inlet hopper (7). When the liquid level sensor (22) detects that the liquid level has reached the set value, the liquid level sensor (22) feeds back a signal to the PLC control mechanism, and then the PLC control mechanism sends an opening signal to the third solenoid valve (23), and sends a closing signal to the second solenoid valve (21); A dosing tube (8) is also fixedly mounted on the upper portion of the equipment accommodating chamber (4), and the lower end of the dosing tube (8) is fixedly connected to the liquid mixing cylinder (5).

2. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: The stirring assembly comprises a stirring rod (18) provided in the middle of a liquid mixing cylinder (5), a plurality of stirring rods (12) being fixedly mounted on the stirring rod (18), and a top end of the stirring rod (18) extending out of the top of the equipment accommodating chamber (4) and connected to an output shaft of a reduction motor (17) via a coupling, wherein the reduction motor (17) is fixedly mounted on one side of a top shell of a Kjeldahl nitrogen analyzer body (1).

3. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: An appropriate amount of activated carbon particles (28) is stored in the purification tank (19), and a gauze (29) for preventing the activated carbon particles (28) from leaking out is fixedly connected to the inner bottom surface of the purification tank (19). The bottom of the purification tank (19) is fixedly connected to the air outlet opening opened at the top of the mixing cylinder (5) through a plurality of evenly distributed air guide pipes (30), and a plurality of exhaust pipes connected to the external atmosphere are also fixedly connected to the top of the purification tank (19).

4. The sample introduction device for an automatic Kjeldahl nitrogen analyzer according to claim 1 or 3, characterized in that: An activated carbon filter screen (15) is fixedly mounted on the inner top of the purification tank (19).

5. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 4, characterized in that: The purification tank (19) is penetrated by the upper part of the stirring rod (18), and a stirring spiral (16) is fixedly mounted on the stirring rod (18) in the purification tank (19).

6. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: A slot (31) is provided in the middle of the upper surface of the test tube positioning seat (2) for inserting the bottom of the glass test tube (3), and one end of a plurality of evenly distributed first compression springs (33) are fixedly connected to the bottom surface of the slot (31), while the other end of the first compression spring (33) is vertically upward and fixedly connected to a support sheet (32), the upper surface of the support sheet (32) is used to contact the bottom surface of the glass test tube (3), and the slot (31) also has a limit assembly for maintaining the vertical state of the glass test tube (3).

7. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 6, characterized in that: The limiting assembly comprises a plurality of placement grooves (36) provided on the periphery of the top side of the slot (31), the plurality of placement grooves (36) being evenly distributed at equal angles, the bottom surface of each placement groove (36) being fixedly connected to one end of a second compression spring (35), the other end of the second compression spring (35) being fixedly connected to a limiting bead (34), and the limiting bead (34) protruding out of the corresponding placement groove (36) and extending into the slot (31).

8. The sample injection device for an automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: A fixing ring (24) is fixedly connected to the lower edge of the inner circumference of the bottom end of the butt-jointed tube (9), and a sealing ring (25) is compositely connected to the outer edge of the lower circumference of the fixing ring (24), and a supporting ring (27) is fixedly connected to the upper edge of the inner circumference of the top end of the glass test tube (3). A sealing groove (26) for the sealing ring (25) to be pressed into is formed on the upper circumference of the supporting ring (27). When the sealing ring (25) is pressed into the sealing groove (26), the first compression spring (33) is in a compressed state, so that when the glass test tube (3) is lifted up by the support sheet (32), the sealing groove (26) thereon just contacts the sealing ring (25).

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