15 Pretreatment system and method for nitrogen tracing nitrification-denitrification gas products

Abstract

The present invention belongs to the technical field of gas stable isotope determination, and provides 15 A pretreatment system and method for gas products of N tracer nitrification-denitrification. The pretreatment system of the present invention uses a chemical trap to remove CO2 and H2O from the gas products of nitrification-denitrification; the first cold trap can remove CO2, H2O, NH3, NO2 and N2O from the gas products of nitrification-denitrification; the oxygen is removed by using a high-temperature reduction furnace; then the trace carbon monoxide, small molecule organic matter and nitrogen are separated by using a separation column; and the residual CO2, H2O, NH3, NO2 and N2O are removed by using a second cold trap. The pretreatment system of the present invention can remove O2, NOx, CO2, H2O and small molecule organic matter from the gas products of nitrification-denitrification, which is beneficial to the accurate detection of N2 in the gas products of nitrification-denitrification.

Description

Technical Field

[0001] The present invention relates to the technical field of gas stable isotope determination, and in particular to 15 A system and method for pre-treating gas products of N-tracing nitrification-denitrification. Background Art

[0002] In recent years, commonly used 15 The loss of fertilizer nitrogen in rice fields was studied by using a field micro-plot test method using N tracing. The results showed that the loss of ammonium nitrogen fertilizer and urea could be as high as 60-80% of the applied nitrogen. The loss of fertilizer nitrogen in rice fields mainly occurs when a large amount of exchangeable ammonia is present. This is because ammonium is both a source of ammonia volatilization and a source of nitrification-denitrification loss; therefore, the determination of nitrification-denitrification loss has attracted the attention of many researchers. The nitrification gas products (N2+NO x ), denitrification gas products (N2+NO x ), nitrification-denitrification gas products (N2+NO x ) or directly measure the N2 in the above gas products to study the circulation and transformation of nitrogen in the plant-soil-environment.

[0003] The N2 produced by nitrification or denitrification is "non-randomly distributed". 14 N and 15 The N atoms are non-randomly distributed, and 15 The N abundance is neither very high (when it is above about 5%, the ion peak of mass number 30 can be measured with high accuracy); nor very low (when it is less than the natural abundance, it is difficult to measure the ion peak of mass number 30). To use the direct measurement method, it is necessary to determine the I 30 , and calculated as follows:

[0004]

[0005] The nitrification gas products, denitrification gas products and nitrification-denitrification gas products collected in the experiment are usually 30 N2 / 28 N2 or 30 N2 / ( 28 N2+ 29 N2) is very small (mainly due to the dilution effect of N2 in the air), which requires the mass spectrometer to have very high precision, even to the point where it is suitable for detecting test objects such as air, soil, and plants. 15 At the same time, the impurities such as O2, CO2 and H2O contained in the gas products have a certain influence on the 30 N2 / 28The determination of N2 ratio will produce great interference, among which O2 has the greatest impact. This is mainly due to interference with the determination of m / e30 peak, because O + +N2→NO + +N, which makes the measurement of peak 30 too high, and thus the gas produced by nitrification-denitrification cannot be accurately measured, limiting the in-depth study of the nitrification-denitrification process and mechanism. Therefore, before the gas products enter the mass spectrometer, the interference needs to be effectively removed to make the measurement results accurate and effective. This step is all 15 The most difficult and critical part of N analysis.

[0006] At present, the direct determination of nitrification-denitrification gas products is 15 The sample pretreatment of N tracer-mass spectrometry usually includes arc method (randomization) and non-randomized stable isotope mass spectrometer method (referred to as non-randomized direct method). The arc method uses a high-voltage arc to react N2 with O2 in the gas sample to generate NOx, making the gas sample to be tested random; then KMnO4-H2SO4 solution is used to absorb NOx and convert it into NH4 + , then quantified by conventional semi-micro distillation, and finally determined by a double-receiver mass spectrometer 15 N abundance, calculated 15 N loss. This method not only requires a special arc generating device, but also the entire measurement process is very cumbersome, the error is large, and it is difficult to control, so the potential for widespread application is not great.

[0007] When the existing gas stable isotope mass spectrometer is used to measure the gas products of nitrification-denitrification using the non-randomized stable isotope mass spectrometer method, the impurity gases such as NOx, CO2 and H2O in the gas products are not completely removed, especially O2 cannot be removed, so the measurement results of the nitrogen 30 isotope of N2 produced during the denitrification process are not accurate. Summary of the invention

[0008] In view of this, the object of the present invention is to provide 15 N tracing nitrification-denitrification gas product pretreatment system and method. The pretreatment system provided by the present invention can remove O2, NOx, CO2, H2O and small molecular organic matter in the nitrification-denitrification gas product to obtain high-purity nitrogen, and realize accurate detection of nitrogen in the nitrification-denitrification gas product.

[0009] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0010] The present invention provides a 15 A pre-treatment system for N-tracing nitrification-denitrification gas products, comprising a closed gas injection needle valve 1;

[0011] A chemical trap 2 connected to the gas outlet of the sealed gas injection needle valve 1, wherein the chemical trap 2 can be used to load at least magnesium perchlorate and potassium hydroxide;

[0012] A first cold trap 3 connected to the gas outlet of the chemical trap 2;

[0013] a high-temperature reduction furnace 4 connected to the gas outlet of the first cold trap 3;

[0014] a separation column 5 connected to the gas outlet of the high-temperature reduction furnace 4, wherein the filler of the separation column 5 comprises a copolymer of ethylvinylbenzene and divinylbenzene;

[0015] A second cold trap 6 is connected to the gas outlet of the separation column 5 .

[0016] Preferably, it further comprises a first gas source q1 , and a gas outlet of the first gas source q1 is connected to a gas inlet of the sealed gas injection needle valve 1 .

[0017] Preferably, the filling height ratio of magnesium perchlorate to potassium hydroxide in the chemical trap 2 is 1:4.

[0018] Preferably, the separation column 5 comprises a Porapak Q chromatography column.

[0019] Preferably, the first cold trap 3 and the second cold trap 6 are liftable cold traps, and the first cold trap 3 and the second cold trap 6 are liquid nitrogen cold traps.

[0020] Preferably, it also includes a mass spectrometer 7 connected to the gas outlet of the second cold trap 6.

[0021] Preferably, a first four-way ball valve V1 is provided on the pipeline connecting the first cold trap 3 and the high-temperature reduction furnace 4;

[0022] A second four-way ball valve V2 is provided on the pipeline connecting the second cold trap 6 and the mass spectrometer 7 .

[0023] Preferably, it further comprises a second gas source q2, and the second gas source q2 is connected to the first four-way ball valve V1 and the second four-way ball valve V2 in sequence.

[0024] The present invention also provides a method for using the pre-treatment system described in the above technical solution to 15 The method for pre-treating the gas product of N-tracing nitrification-denitrification comprises the following steps:

[0025] Pending 15 The N-tracing nitrification-denitrification gas product is sampled through the closed gas sampling needle valve 1 and enters the chemical trap 2 for impurity removal under the action of the carrier gas;

[0026] The obtained impurity-free gas enters the first cold trap 3 for the first condensation;

[0027] The obtained first condensed gas enters the high-temperature reduction furnace 4 for high-temperature reduction reaction;

[0028] The obtained high-temperature reducing gas enters the separation column 5 for separation;

[0029] The obtained separated gas enters the second cold trap 6 for second condensation to obtain purified pre-treated gas.

[0030] Preferably, the high temperature reduction temperature is 850-900°C.

[0031] The present invention provides a 15 The pretreatment system of N-tracing nitrification-denitrification gas products includes a closed gas injection needle valve 1; a chemical trap 2 connected to the gas outlet of the closed gas injection needle valve 1, and the chemical trap 2 can be used to load at least magnesium perchlorate and potassium hydroxide; a first cold trap 3 connected to the gas outlet of the chemical trap 2; a high-temperature reduction furnace 4 connected to the gas outlet of the first cold trap 3; a separation column 5 connected to the gas outlet of the high-temperature reduction furnace 4, and the filler of the separation column 5 includes a copolymer of ethylvinylbenzene and divinylbenzene; and a second cold trap 6 connected to the gas outlet of the separation column 5. The chemical trap 2 filled with magnesium perchlorate and potassium hydroxide in the pretreatment system of the present invention can remove CO2 and H2O in the nitrification-denitrification gas product; the first cold trap 3 can remove CO2, H2O, NH3, NO2 and N2O in the nitrification-denitrification gas product; the high-temperature reduction furnace 4 is used to remove oxygen; the separation column 5 filled with a copolymer of ethylvinylbenzene and divinylbenzene is used to separate trace CO and small molecular organic matter from N2; and the second cold trap 6 is used to remove CO2, H2O, NH3, NO2 and N2O. The pretreatment system of the present invention can remove O2, NOx, CO2, H2O and small molecular organic matter in the nitrification-denitrification gas product to obtain pure nitrogen, which is conducive to the accurate detection of the nitrification-denitrification gas product N2.

[0032] The present invention also provides a method for using the pre-treatment system described in the above technical solution to 15 The method for pre-treating the gas product of N-tracing nitrification-denitrification comprises the following steps: 15The N-tracing nitrification-denitrification gas product is sampled through a closed gas sampling needle valve 1, and enters a chemical trap 2 for impurity removal under the action of a carrier gas; the obtained impurity-removed gas enters a first cold trap 3 for a first condensation; the obtained first condensed gas enters a high-temperature reduction furnace 4 for a high-temperature reduction reaction; the obtained high-temperature reduced gas enters a separation column 5 for separation; the obtained separated gas enters a second cold trap 6 for a second condensation to obtain a purified pre-treatment gas. The use method provided by the present invention can remove O2, NOx, CO2, H2O and small molecular organic matter in the nitrification-denitrification gas product to obtain pure nitrogen, which is conducive to the accurate detection of the nitrification-denitrification gas product N2. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention provides 15 Schematic diagram of the pretreatment system for N-tracing nitrification-denitrification gas products, wherein 1 is a closed gas injection needle valve, 2 is a chemical trap, 3 is a first cold trap, 4 is a high-temperature reduction furnace, 5 is a separation column, 6 is a second cold trap, V1 is a first four-way ball valve, V2 is a second four-way ball valve, q1 is a first gas source, q2 is a second gas source, P1 is a first pressure gauge, and P2 is a second pressure gauge;

[0034] Figure 2 Figure 2 shows the nitrogen ion flow and its ratio. DETAILED DESCRIPTION

[0035] The present invention provides 15 A pre-treatment system for N-tracing nitrification-denitrification gas products, comprising a closed gas injection needle valve 1;

[0036] A chemical trap 2 connected to the gas outlet of the sealed gas injection needle valve 1, wherein the chemical trap 2 can be used to load at least magnesium perchlorate and potassium hydroxide;

[0037] A first cold trap 3 connected to the gas outlet of the chemical trap 2;

[0038] a high-temperature reduction furnace 4 connected to the gas outlet of the first cold trap 3;

[0039] a separation column 5 connected to the gas outlet of the high-temperature reduction furnace 4, wherein the filler of the separation column 5 comprises a copolymer of ethylvinylbenzene and divinylbenzene;

[0040] A second cold trap 6 is connected to the gas outlet of the separation column 5 .

[0041] Figure 1 The present invention provides 15 Schematic diagram of the pretreatment system of N tracer nitrification-denitrification gas products. Figure 1 The pre-treatment system provided by the present invention is described in detail.

[0042] The present invention provides 15 The pretreatment system of N-tracing nitrification-denitrification gas products comprises a closed gas injection needle valve 1. In the present invention, the 15 The pretreatment system of the N-tracing nitrification-denitrification gas product preferably further comprises a first gas source q1. In the present invention, the gas outlet of the first gas source q1 is connected to the gas inlet of the sealed gas injection needle valve 1. In the present invention, a first pressure gauge P1 is preferably provided on the pipeline connecting the sealed gas injection needle valve 1 and the first gas source q1.

[0043] The present invention provides 15 The pretreatment system of N-tracing nitrification-denitrification gas products includes a chemical trap 2 connected to the gas outlet of the closed gas injection needle valve 1. In the present invention, the chemical trap 2 can at least be used to load magnesium perchlorate and potassium hydroxide. In the present invention, the filling height ratio of the magnesium perchlorate and potassium hydroxide is preferably 1:4. In the present invention, the magnesium perchlorate and potassium hydroxide are preferably filled in a fat quartz tube or a glass tube, and are further preferably filled in a fat quartz tube. In the present invention, the fat quartz tube preferably includes a fat part and two end parts; the inner diameter of the fat part is preferably 1 cm, and the length is preferably 16 cm; the inner diameter of the two end parts is independently preferably 0.5 cm, and the length is independently 4.5 cm. In the present invention, the magnesium perchlorate and potassium hydroxide are preferably filled in the fat part of the fat quartz tube; in the present invention, the chemical trap 3 is preferably connected to the closed gas injection needle valve 1 and the first cold trap 3 respectively through a 1 / 4 inch to 1 / 16 inch joint.

[0044] The present invention provides 15 The pretreatment system of the N-tracing nitrification-denitrification gas product includes a first cold trap 3 connected to the gas outlet of the chemical trap 2. In the present invention, the first cold trap 3 is preferably a liftable cold trap. In the present invention, the first cold trap 3 is preferably a liquid nitrogen cold trap. In the present invention, the first cold trap is preferably made of a stainless steel pipe. In the present invention, the first cold trap is preferably controlled by a pneumatic valve, and the height is suitable for placing a Dewar flask containing liquid nitrogen. In the present invention, the outer ring of the first cold trap is preferably wrapped with a circle of electric heating furnace wire.

[0045] The present invention provides 15 The pretreatment system of the N-tracing nitrification-denitrification gas product includes a high-temperature reduction furnace 4 connected to the gas outlet of the first cold trap 3. In the present invention, the high-temperature reduction furnace 4 preferably includes a quartz tube and a reduction copper wire filled in the quartz tube. In the present invention, both ends of the quartz tube are preferably connected to the first cold trap 3 through a 1 / 4 inch to 1 / 16 inch joint, which reduces the dead volume and facilitates the replacement of consumables.

[0046] In the present invention, a first four-way ball valve V1 is preferably provided on the pipeline connecting the first cold trap 3 and the high-temperature reduction furnace 4 .

[0047] The present invention provides 15 The pretreatment system of the N-tracing nitrification-denitrification gas product comprises a separation column 5 connected to the gas outlet of the high-temperature reduction furnace 4. In the present invention, the filler of the separation column 5 comprises a copolymer of ethylvinylbenzene and divinylbenzene. In the present invention, the separation column 5 preferably comprises a Porapak Q chromatographic column.

[0048] The present invention provides 15 The pretreatment system of the N-tracing nitrification-denitrification gas product comprises a second cold trap 6 connected to the gas outlet of the separation column 5. In the present invention, the second cold trap 6 is preferably a liftable cold trap. In the present invention, the second cold trap 6 is preferably a liquid nitrogen cold trap. In the present invention, the second cold trap is preferably made of a stainless steel pipe. In the present invention, the second cold trap is preferably controlled by a pneumatic valve, and the height of the Dewar flask containing liquid nitrogen is suitable. In the present invention, the outer ring of the second cold trap is preferably wound with a circle of electric heating furnace wire.

[0049] The present invention provides 15 The pretreatment system of N-tracing nitrification-denitrification gas products preferably further comprises a mass spectrometer 7 connected to the gas outlet of the second cold trap 6. In a specific embodiment of the present invention, the mass spectrometer 7 is preferably a stable isotope mass spectrometer MAT-253.

[0050] In the present invention, a second four-way ball valve V2 is preferably provided on the pipeline connecting the second cold trap 6 and the mass spectrometer 7 .

[0051] The present invention provides 15 The pretreatment system of the N-tracing nitrification-denitrification gas product preferably further includes a second gas source q2. In the present invention, the second gas source q2 is connected to the first four-way ball valve V1 and the second four-way ball valve V2 in sequence. In the present invention, the second gas source q2, the first four-way ball valve V1 and the second four-way ball valve V2 constitute a cleaning gas path.

[0052] The present invention also provides a method for using the pre-treatment system described in the above technical solution to 15 The method for pre-treating the gas product of N-tracing nitrification-denitrification comprises the following steps:

[0053] Pending 15 The N-tracing nitrification-denitrification gas product is sampled through the closed gas sampling needle valve 1 and enters the chemical trap 2 for impurity removal under the action of the carrier gas;

[0054] The obtained impurity-free gas enters the first cold trap 3 for the first condensation;

[0055] The obtained first condensed gas enters the high-temperature reduction furnace 4 for high-temperature reduction reaction;

[0056] The obtained high-temperature reducing gas enters the separation column 5 for separation;

[0057] The obtained separated gas enters the second cold trap 6 for second condensation to obtain purified pre-treated gas.

[0058] The present invention is pending 15 The N-tracing nitrification-denitrification gas product is injected through the closed gas injection needle valve 1 and enters the chemical trap 2 for impurity removal under the action of the carrier gas.

[0059] The present invention is to be treated 15 The operation of injecting the N tracer nitrification-denitrification gas product through the closed gas injection needle valve 1 is not specifically limited, and the gas injection operation familiar to those skilled in the art can be used. 15 The flow rate of the N-traced nitrification-denitrification gas product is preferably 20 to 25 mL / min, more preferably 23 mL / min.

[0060] In the present invention, the impurity removal can remove CO2 and H2O.

[0061] After impurities are removed, the impurity-removed gas obtained in the present invention enters the first cold trap 3 for first condensation.

[0062] In the present invention, the temperature of the first condensation is preferably -196 to 150°C.

[0063] After the first condensation, the present invention will allow the obtained first condensed gas to enter the high-temperature reduction furnace 4 for high-temperature reduction reaction.

[0064] In the present invention, the temperature of the high temperature reduction reaction is preferably 850-900°C.

[0065] After the high-temperature reduction, the present invention allows the obtained high-temperature reduction gas to enter the separation column 5 for separation.

[0066] In the present invention, the type of the separation chromatographic column and the filler in the chromatographic column are preferably consistent with the above technical solution, which will not be described in detail here.

[0067] The separated gas obtained by the separation enters the second cold trap 5 for second condensation to obtain the pre-treated gas.

[0068] In the present invention, the temperature of the first condensation is preferably -196 to 150°C.

[0069] In the present invention, long-term and large-scale sampling will lead to the accumulation of trace impurity gases in the pretreatment system, affecting the impurity removal effect of the pretreatment system and thus affecting the measurement results; therefore, after completing the processing of 10 samples, the present invention preferably also includes cleaning the pretreatment system; specifically including the following steps: the first four-way ball valve V1 and the second four-way ball valve V2 rotate in opposite directions, and simultaneously raise the first cold trap 3 and the second cold trap 6, respectively open the electric heating furnace wires of the first cold trap 3 and the second cold trap 6, and open the first gas source q1 and the second gas source q2 to achieve the purging of the accumulated impurity gases.

[0070] Specifically, the cleaning of the first cold trap 3 preferably includes the following steps: adjusting the direction of the first four-way valve, raising the first cold trap and starting the electric heating wire of the first cold trap, and opening the first gas source q1 to blow away impurity gases.

[0071] In the present invention, the cleaning of the second cold trap 6 preferably includes the following steps: adjusting the direction of the second four-way valve, raising the second cold trap and starting the electric heating wire of the second cold trap, and opening the second gas source q2 to blow away impurity gases.

[0072] The present invention is provided below in conjunction with embodiment 15 The pretreatment system and method of the N-tracing nitrification-denitrification gas product are described in detail, but they should not be understood as limiting the scope of protection of the present invention.

[0073] Example

[0074] use Figure 1 The pre-treatment system shown is used to pre-treat the gas products of nitrification-denitrification to be detected:

[0075] The states of the first four-way ball valve and the second four-way ball valve are adjusted in sequence, the chemical trap, the high-temperature reduction furnace, the separation column and the second cold trap are connected to form an injection mode, and the gas flow rate is controlled to be 23 mL / min; the gas product of nitrification-denitrification to be detected enters the pretreatment system through the closed gas injection needle valve 1, and then passes through the chemical trap (the chemical trap is a filler filled with 16 cm in a fat-bellied quartz tube, the inner diameter of the fat-bellied part of the fat-bellied quartz tube is 1 cm, and the length is 16 cm; the inner diameter of the two end parts is preferably 0.5 cm, and the length is 4.5 cm; the filler is filled in the fat-bellied part; the filler is magnesium perchlorate with a particle size of 0.85-2 mm and potassium hydroxide with a particle size of 0.8-1.6 mm in a mass ratio of 4:1 mixture), and then passed through the first liquid nitrogen trap cold trap (the temperature of the first liquid nitrogen trap cold trap is -196°C, the first cold trap is made of a stainless steel tube with a length of 45 cm and an inner diameter of 1 mm, and is controlled by a pneumatic valve to a height suitable for placing a Dewar flask containing liquid nitrogen; an electric heating furnace wire is wound around the outer ring of the first cold trap) to remove CO2, H2O, NH3, NO2 and N2O, and passed through a high-temperature reduction furnace at 850°C (the high-temperature reduction furnace is a copper reduction furnace, specifically: a quartz tube with an inner diameter of 3 mm and a length of 30 cm and filled with about 15 g of reduced copper wire, and both ends are connected to the gas path with a 1 / 4 to 1 / 16 joint) to remove oxygen, and then passed through a 45°C separation column (the chromatographic column is Porapak Q chromatographic column, the filler is a copolymer of ethylvinylbenzene and divinylbenzene) to remove CO and small organic molecules, and then enter the second liquid nitrogen trap cold trap (the temperature of the first liquid nitrogen trap cold trap is -196°C, the second cold trap is made of a stainless steel tube with a length of 45 cm and an inner diameter of 1 mm, controlled by a pneumatic valve, and the height is suitable for placing a Dewar flask containing liquid nitrogen; the outer circle of the second cold trap is wrapped with a circle of electric heating furnace wire) to obtain pure nitrogen; the pure nitrogen after pretreatment is connected to the multi-channel reference gas box through a high-flow diluter, and then introduced into the gas stable isotope mass spectrometer for measurement.

[0076] System Accuracy Verification:

[0077] Verification 1: Select N2 in the natural abundance state of outdoor air as the gas sample. Use a closed gas injection needle valve to inject the collected air sample, desorb gas impurities other than oxygen through the chemical trap and the first cold trap, remove O2 in the sample through a high-temperature reduction furnace, and then separate and remove the remaining trace impurity gases through the separation column and the second cold trap. The gas entering the mass spectrometer is actually high-purity N2. The mass spectrometer measures the gas output relative to the reference gas. 15 N isotope ratio. The isotope ratio of the prepared air samples (6) was measured 6 times (with different injection volumes) to complete the detection of air samples. The results are shown in Tables 1 to 2 and Figure 2 shown.

[0078] Table 1 Air samples 15 Error in determination of natural abundance of N

[0079]

[0080] Table 2 Raw data of air sample measurement

[0081]

[0082] From Tables 1 to 2 and Figure 2 It can be seen that the mass spectrometer detects the same air sample 15 The coefficient of variation (CV%) of natural abundance of N was 0.007% to 0.01%, and the precision was <0.007% to 0.03%. 15 The coefficient of variation (CV%) of natural abundance of N was 0.004%, and the precision was <0.008%. 15 The average value of natural abundance of N is 0.3668% (theoretical value is 0.3665%), and the average value of absolute error is 0.0008%, which meets the accuracy requirement of mass spectrometer.

[0083] Verification 2: Use a sealed gas injection needle valve to extract randomly selected different 15 N abundance in gas samples, through reference gas and gas sample 29 N2 / 28 N2 ratio and 30 N2 / 28 The N2 ratio is processed through the same chemical trap as the air sample → the first cold trap → the reduction copper furnace → the high-efficiency separation column → the second cold trap, and finally detected by the mass spectrometer to obtain the gas sample. 29 N2 / 28 N2 ratio and 30 N2 / 28 N2 ratio, and the gas sample 15 N abundance, and perform error analysis. At the same time, calculate the corresponding 15 The coefficient of variation of the percentage of N atoms is listed in Table 3.

[0084] Table 3 Gas 15 Determination results and error analysis of N abundance

[0085]

[0086] From Table 3 we can see that: 15 For N abundance, the coefficient of variation and 15 The trend of increasing with increasing nitrogen abundance is relatively small (coefficient of variation 0.03-0.7%), while the coefficient of variation of atomic percentage excess varies with the gas sample. 15The N% abundance decreases and increases, with a relatively large amplitude (coefficient of variation 0.50-3.22%). Especially when the gas abundance is lower than 0.380%, the coefficient of variation becomes larger, indicating that the measurement error increases significantly. 15 The nitrogen loss is calculated on an atomic percent basis, so when collecting or preparing gas samples, try to minimize the nitrogen loss. 15 The N abundance should not be less than 0.380% to reduce the error.

[0087] Verification 3: Preparation of high-abundance markers 15 In order to verify the removal of impurity gases in high-abundance samples and the accuracy of sample measurement, the previously purchased 15 Ammonium sulfate with a nitrogen abundance of 99.14atom% and homogeneous 15 Ammonium sulfate with a natural abundance of 0.366atom% N is prepared according to the mass balance formula 15 The labeled ammonium nitrogen samples with N atom% of 10.30, 20.24, 30.18, 40.11, and 50.05 were then oxidized with sodium hypobromite in a sealed vacuum sample bottle to produce labeled 15 N2, N, and finally sampled and removed interference through the pre-treatment system and then measured using a stable isotope mass spectrometer 15 The results are shown in Table 4.

[0088] Table 4 Different markers 15 N2 sample measurement results

[0089]

[0090] It can be seen from Table 4 that the results of three repeated determinations under the same abundance conditions were very stable, with coefficients of variation less than 3%, which was consistent with the prepared standard values. 15 Compared with N abundance, the relative error is less than 1%, indicating that the expected function of the pretreatment system to remove impurities is obvious.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method of using a pre-processing system to 15 The method for pre-treating the gas product of nitrification-denitrification by N tracing is characterized in that: The pre-treatment system comprises a closed gas injection needle valve (1); A chemical trap (2) connected to the gas outlet of the sealed gas injection needle valve (1), wherein the chemical trap (2) can be used to at least load magnesium perchlorate and potassium hydroxide, and the loading height ratio of magnesium perchlorate to potassium hydroxide in the chemical trap (2) is 1:4; a first cold trap (3) connected to the gas outlet of the chemical trap (2); A high-temperature reduction furnace (4) connected to the gas outlet of the first cold trap (3); the high-temperature reduction furnace (4) comprises a quartz tube and a reduction copper wire filled in the quartz tube; A separation column (5) connected to the gas outlet of the high-temperature reduction furnace (4), wherein the filler of the separation column (5) comprises a copolymer of ethylvinylbenzene and divinylbenzene; a second cold trap (6) connected to the gas outlet of the separation column (5); The separation column (5) comprises a Porapak Q chromatographic column; The method comprises the following steps: Pending 15 The N-tracing nitrification-denitrification gas product is sampled through a closed gas sampling needle valve (1) and enters a chemical trap (2) for impurity removal under the action of a carrier gas; The obtained impurity-free gas enters the first cold trap (3) for first condensation; the temperature of the first condensation is -196 to -150°C; The obtained first condensed gas enters a high-temperature reduction furnace (4) for a high-temperature reduction reaction; the temperature of the high-temperature reduction reaction is 850-900° C.; The obtained high-temperature reducing gas enters the separation column (5) for separation; The obtained separated gas enters the second cold trap (6) for second condensation to obtain purified pre-treated gas; the temperature of the second condensation is -196 to -150°C.

2. The method according to claim 1, characterized in that The pretreatment system further comprises a first gas source (q1), the gas outlet of the first gas source (q1) being connected to the gas inlet of the sealed gas injection needle valve (1).

3. The method according to claim 1, characterized in that The first cold trap (3) and the second cold trap (6) are liftable cold traps, and the first cold trap (3) and the second cold trap (6) are liquid nitrogen cold traps.

4. The method according to claim 1, characterized in that: The pre-treatment system further comprises a mass spectrometer (7) connected to the gas outlet of the second cold trap (6).

5. The method according to claim 1, characterized in that A first four-way ball valve (V1) is provided on the pipeline connecting the first cold trap (3) and the high-temperature reduction furnace (4); A second four-way ball valve (V2) is arranged on the pipeline connecting the second cold trap (6) and the mass spectrometer (7).

6. The method according to claim 5, characterized in that The pre-treatment system further comprises a second gas source (q2), and the second gas source (q2) is connected to the first four-way ball valve (V1) and the second four-way ball valve (V2) in sequence.

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