WO2021008617A1 - 一种化学转化法测定氮氧同位素的前处理方法和测定方法 - Google Patents

一种化学转化法测定氮氧同位素的前处理方法和测定方法 Download PDF

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WO2021008617A1
WO2021008617A1 PCT/CN2020/102818 CN2020102818W WO2021008617A1 WO 2021008617 A1 WO2021008617 A1 WO 2021008617A1 CN 2020102818 W CN2020102818 W CN 2020102818W WO 2021008617 A1 WO2021008617 A1 WO 2021008617A1
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acetic acid
buffer solution
sodium azide
acid buffer
low temperature
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PCT/CN2020/102818
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English (en)
French (fr)
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杨芳
廖海清
马文娟
吴丰昌
郭建阳
安宁
张润宇
冯伟莹
岑睿
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中国环境科学研究院
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Priority to AU2020312536A priority Critical patent/AU2020312536B2/en
Publication of WO2021008617A1 publication Critical patent/WO2021008617A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/42—Low-temperature sample treatment, e.g. cryofixation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode

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  • the present disclosure relates to the technical field of environmental protection and monitoring, in particular to a pretreatment method and a measurement method for determining nitrogen and oxygen isotopes by a chemical conversion method.
  • Nitrate is the main form of nitrogenous pollutants in freshwater systems. Excessive nitrate content can pose a potential health threat to humans, and high concentrations of nitrate can cause methemoglobinosis. Nitrate pollution in water bodies has become one of the important water environmental problems. Identifying the source of nitrate is the first condition to solve this problem. At present, the method of tracing nitrogen pollution sources using soluble nitrate nitrogen and oxygen double isotope technology in water bodies has been widely used in the research of food traceability, ecosystem circulation and pollutant migration process. Reducing the fractionation of nitrogen in pretreatment has always been a difficulty and hot spot in the analysis and detection of nitrogen isotopes.
  • the representative methods for determining nitrogen isotopes in freshwater samples mainly include: silver nitrate technology, denitrifying bacteria method, cadmium reduction method/azide method (chemical conversion method), and the three methods have their own advantages and disadvantages.
  • the silver nitrate method is currently considered to be a highly accurate nitrogen isotope pretreatment method.
  • the possibility of fractionation in the whole process is very low and no impurities are introduced.
  • the ion exchange process requires sufficient silver nitrate samples to be tested.
  • the bacteria must be cultured in large quantities, resulting in a low survival rate, and the culture cycle is about 7-10 days, which is very time-consuming; the second is the N 2 O produced by bacteria through the denitrification process
  • the nitrogen in the water may not come from the cultured water sample, but produced by its own catabolism.
  • the pre-treated water sample virtually increases the interference of external nitrogen sources, so there is still controversy and it has not become the mainstream pretreatment method.
  • the chemical conversion method avoids the deficiencies of the denitrifying bacteria method and silver nitrate technology and saves water samples. Each sample only needs 15-40mL of water sample, which is short in time, and only 3.5 in a single batch of 20-60 samples. Pre-processing work can be completed in an hour. However, at present, the pretreatment technology of chemical conversion method is not mature enough, and the test stability is low.
  • the purpose of the present disclosure includes, for example, providing a pretreatment method for determining nitrogen and oxygen isotopes by a chemical conversion method, so as to solve the technical problem of poor test stability in the prior art.
  • the present disclosure provides a pretreatment method for determining nitrogen and oxygen isotopes by a chemical conversion method, which includes the following steps:
  • the present disclosure proves that the sodium azide-acetic acid buffer solution is the main reagent that interferes with the blank by checking and testing the reagents that may affect the experimental results when the isotope is determined by the chemical conversion method.
  • the present disclosure can greatly reduce the sodium azide-acetic acid buffer solution to the N 2 O obtained by the reaction of nitrate in the sample during the test by performing low-temperature treatment under the condition of ⁇ 15°C. Interference to improve the accuracy of test results.
  • the sodium azide-acetic acid buffer solution is prepared as follows: Weigh an appropriate amount of sodium azide solid (GR), dissolve it in ultrapure water, and add 20% of the same volume. Acetic acid solution, mixed uniformly to obtain sodium azide-acetic acid buffer solution;
  • GR sodium azide solid
  • the preparation method of the 20% acetic acid solution is: taking glacial acetic acid (GR) and mixing with ultrapure water in a volume ratio of 1:4 to obtain a 20% acetic acid solution.
  • GR glacial acetic acid
  • the sodium azide-acetic acid buffer solution is treated at a low temperature under the condition of ⁇ 10°C; can be treated at a low temperature under the condition of ⁇ 4°C; or can be optionally treated at a condition of ⁇ 0°C Under low temperature processing. In one or more embodiments, the sodium azide-acetic acid buffer solution is treated at a low temperature at -5°C to 4°C.
  • the low-temperature treatment method includes: placing the buffer solution in a system of ⁇ 15°C, or ⁇ 10°C, or ⁇ 4°C, or ⁇ 0°C.
  • the low-temperature treatment time is ⁇ 2h.
  • the low temperature treatment time is within the above range, which can reduce the interference of the buffer solution on the test results.
  • the concentration of the sodium azide-acetic acid buffer solution can be prepared according to actual needs, and usually a concentration such as 2mol/L can be used.
  • the low-temperature treatment time can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h , 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h, 30h, 31h, 32h, etc.
  • the low temperature treatment time is preferably 2-30h, more preferably 4-24h.
  • the sodium azide-acetic acid buffer solution can be treated at a low temperature of 0-4° C. for 20-28 hours, such as 24 hours. Or, treat the sodium azide-acetic acid buffer solution at a low temperature of -5°C to 0°C for 2-6 hours, such as 4 hours.
  • the sodium azide-acetic acid buffer solution before the low temperature treatment, is purged with gas.
  • the gas is a non-oxidizing gas.
  • the non-oxidizing gas is helium and/or nitrogen.
  • helium and/or nitrogen purging and low-temperature treatment can significantly reduce and eliminate interference.
  • the buffer solution may be subjected to low-temperature treatment, helium purge+low-temperature treatment, or nitrogen purge+low-temperature treatment to reduce interference.
  • the buffer solution can be stored in a headspace bottle.
  • the mouth of the bottle is sealed with a polyethylene cap and a matching rubber gasket.
  • the headspace bottle can be upside down first, and then used The clean syringe is inserted and taken from the mouth of the bottle to prevent outside air from entering and interfering with the experiment.
  • the present disclosure also provides a method for determining nitrogen and oxygen isotopes by a chemical conversion method, using the sodium azide-acetic acid buffer solution pre-treated with the above method to test the sample to be tested.
  • the stability test of the gas isotope mass spectrometer can be performed to ensure that the instrument is stable and free of interference factors.
  • the detection range of the gas isotope mass spectrometer that has been tested for stability is determined, wherein 20 ⁇ 5 ⁇ g of N 2 O is a suitable concentration range for MAT252.
  • the protective gas used in the test is air or helium.
  • the sampling device used in the test includes: a cross connecting tube, a hose, and a sample injection needle; each port of the cross connecting tube is provided with a first valve and a first valve in a clockwise direction.
  • the two ports of the cross connecting pipe provided with the first valve and the third valve are connected with the test pipeline of the gas isotope mass spectrometer, and are used for sending the gas sample into the test instrument.
  • the port of the cross connecting pipe provided with the fourth valve is connected to the vacuum pump, which can vacuumize the sampling device.
  • a drying column is provided in the hose.
  • the composition of the drying column is calcium oxide.
  • the hose is a polyethylene hose.
  • the injection needle is provided with a rubber stopper to block the injection needle. Since the injection is a gas-liquid mixed sample, and the water content is relatively large in the chemical conversion headspace bottle, the setting of a drying column can ensure that the content of water and carbon dioxide is reduced during the injection, the content of impurities is reduced, and the interference is reduced. Improve the accuracy of measurement results.
  • the injection needle is provided with a switch for turning the injection needle on or off.
  • the existing automatic sampling device can be used.
  • the sampling device of the present disclosure it can be ensured that the N 2 O generated from the reaction liquid in the sampling headspace bottle enters the mass spectrometer at a stable pressure and a suitable concentration, which improves the operability of precision control.
  • the present disclosure proves that the main reagent that interferes with the blank when the sodium azide-acetic acid buffer solution is the main reagent that interferes with the blank when the chemical conversion method is used for the determination of isotope Low temperature treatment under the condition of ⁇ 15°C can greatly reduce the interference of sodium azide-acetic acid buffer solution on the N 2 O obtained by the nitrate reaction in the sample during the test, and improve the accuracy of the test results; make the 18 O The accuracy is controlled at 0.1 ⁇ , and the accuracy of 15 N is controlled at 0.12 ⁇ ;
  • the present disclosure further optimizes the pretreatment method, which can eliminate the interference of the buffer solution from the measurement of the sample to be tested, and improve the stability and accuracy of the test;
  • the sampling device of the present disclosure can ensure that the N 2 O generated from the reaction liquid in the sampling headspace bottle enters the mass spectrometer at a stable pressure and suitable concentration, which further improves the operability of precision control.
  • Figure 1 is a schematic structural diagram of a sample injection device provided by an embodiment of the disclosure
  • Figure 2 is an instrument measurement curve of outdoor air bottle-outdoor-1 under vacuum conditions in an embodiment of the present disclosure
  • FIG. 3 is an instrument measurement curve of the indoor air blank-1 under vacuum conditions in an embodiment of the disclosure
  • FIG. 4 is a measurement curve of dummy bottle 1 with N 2 O gas (approximately 20 ⁇ g) added in an embodiment of the disclosure;
  • Figure 5 is a measurement curve of another dummy bottle 2 with N 2 O gas (approximately 20 ⁇ g) added in an embodiment of the disclosure;
  • Figure 6 is a measurement curve obtained by He1 under helium conditions in an embodiment of the disclosure.
  • Fig. 7 is a measurement curve obtained by Air1 under nitrogen in an embodiment of the disclosure.
  • Fig. 8 is a measurement curve obtained by N1-1 without adding cadmium chloride in an embodiment of the disclosure
  • Fig. 9 is a measurement curve obtained by N1-2 without adding cadmium chloride in an embodiment of the disclosure.
  • Figure 10 is a measurement curve obtained by N2-1 without adding ammonium chloride in an embodiment of the disclosure.
  • Figure 11 is a measurement curve obtained by N2-2 without adding ammonium chloride in an embodiment of the disclosure.
  • Figure 12 is a measurement curve obtained by N3-1 without adding zinc flakes in an embodiment of the disclosure.
  • Figure 13 is a measurement curve obtained by N4-1 without adding sodium azide-acetic acid buffer solution in an embodiment of the disclosure
  • Figure 14 is a measurement curve obtained by N4-2 without adding sodium azide-acetic acid buffer solution in an embodiment of the disclosure
  • Figure 15 is a measurement curve obtained by N5-1 without sodium hydroxide in an embodiment of the disclosure.
  • Figure 16 is a measurement curve obtained by using the sodium azide-acetic acid buffer solution treated in Example 1 of the present disclosure; wherein air2-1 and air2-2 are two parallel experiments respectively;
  • Example 17 is a measurement curve Air1-2 obtained by using the sodium azide-acetic acid buffer solution treated in Example 3 of the present disclosure and a measurement curve Air1 obtained by the sodium azide-acetic acid buffer solution treated in Comparative Example 2;
  • Example 18 is a measurement curve Air1-2 obtained by using the sodium azide-acetic acid buffer solution treated in Example 4 of the present disclosure and a measurement curve Air1-1 obtained by the sodium azide-acetic acid buffer solution treated in Comparative Example 2;
  • Figure 19 is a measurement curve air2 of sodium azide-acetic acid buffer solution treated in Comparative Example 1 and a measurement curve air1 of untreated sodium azide-acetic acid buffer solution;
  • FIG. 20 shows the measurement curve air4 of the sodium azide-acetic acid buffer solution treated in Comparative Example 2 and the measurement curve air3 of the untreated sodium azide-acetic acid buffer solution.
  • connection should be interpreted broadly. For example, they can be fixed or detachable. Connected or integrally connected; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication between two components.
  • connection should be interpreted broadly. For example, they can be fixed or detachable. Connected or integrally connected; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication between two components.
  • FIG. 1 is a schematic structural diagram of a sample injection device provided by an embodiment of the disclosure. It can be seen from the figure that the sample injection device includes a cross connecting pipe 1, a hose 2 and a sample injection needle 3. Each port of the cross connecting pipe 1 is provided with a first valve 11, a second valve 12, a third valve 13, and a fourth valve 14 in a clockwise direction. The two ports of the cross connecting pipe 1 provided with a first valve 11 and a third valve 13 communicate with the test pipeline of the gas isotope mass spectrometer. The port of the cross connecting pipe 1 provided with the second valve 12 communicates with the injection needle 3 through the hose 2. The port of the cross connecting pipe 1 provided with a fourth valve 14 communicates with the vacuum pump.
  • a drying column 21 is provided in the hose 2.
  • the component of the drying column 21 is preferably calcium oxide.
  • the hose 2 may be a polyethylene hose, but it is not limited thereto.
  • the injection needle 3 is provided with a switch, which can be used to turn the injection needle on or off. Or a rubber stopper can be used to plug the injection needle 3.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a volume ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) The sodium azide-acetic acid buffer solution obtained in step (1) is refrigerated for 4 hours at 0-4° C. to obtain a processed sodium azide-acetic acid buffer solution.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a volume ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) Treat the sodium azide-acetic acid buffer solution obtained in step (1) at a low temperature of 5-10° C. for 4 hours to obtain a processed sodium azide-acetic acid buffer solution.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a volume ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) The sodium azide-acetic acid buffer solution obtained in step (1) was purged with helium for 4 hours, and then treated in a cold storage at 0-4°C for 4 hours to obtain the treated sodium azide-acetic acid Buffer solution.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a volume ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) The sodium azide-acetic acid buffer solution obtained in step (1) was purged with nitrogen for 4 hours, and then refrigerated at 0-4°C for 4 hours to obtain the treated sodium azide-acetic acid buffer Solution.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) The sodium azide-acetic acid buffer solution obtained in step (1) is purged with nitrogen for 4 hours, and the processed sodium azide-acetic acid buffer solution is obtained without refrigeration treatment or low temperature treatment.
  • the preparation method of 20% acetic acid solution is: take glacial acetic acid (GR) and mix with ultrapure water in a ratio of 1:4 to obtain 20% acetic acid solution;
  • GR glacial acetic acid
  • step (2) The sodium azide-acetic acid buffer solution obtained in step (1) is purged with helium for 4 hours, and the processed sodium azide-acetic acid buffer solution is obtained without refrigeration treatment or low temperature treatment.
  • the test steps include: take 40mL of the sample to be tested in a 60mL headspace bottle, add 0.8mL of cadmium chloride solution (20g/L), then add 0.8mL of ammonium chloride solution (250g/L), and finally add 3 ⁇ 10cm 4N (or 3N) clean zinc flakes (cleaned with alcohol), shake on a shaker at 220r/min for 20min. Take out the zinc flakes, seal the headspace bottle, and complete the nitrate reduction step. Then add 2 mL of sodium azide-acetic acid buffer solution to the headspace bottle, shake vigorously to mix the sample and reagents. After shaking at 220r/min for 30 minutes, 1mL of NaOH solution (10mol/L) was added as a terminator to end the azide reaction. Then put the sample on the machine for testing.
  • the removed agent in Table 1 refers to the above test steps, no cadmium chloride, no ammonium chloride, no zinc flakes, no sodium azide-acetic acid buffer solution or no hydrogenation at the corresponding position Sodium oxide, these reagents, are tested on the machine after the sample to be tested (the sample to be tested is distilled water). The test results are shown in Figure 8-15.
  • the azide obtained by the treatment of Examples 1, 3 and 4 and Comparative Example 1-2 are used respectively.
  • Sodium-acetic acid buffer solution refer to the test procedure of Experimental Example 2. Distilled water was used in each Example and Comparative Example to obtain two blank parallel samples, and the test results are shown in Figure 16-18.
  • the present disclosure proves that the main reagent that interferes with the blank when the sodium azide-acetic acid buffer solution is the main reagent that interferes with the blank when the chemical conversion method is used for the determination of isotope Low temperature treatment under the condition of ⁇ 15°C can greatly reduce the interference of sodium azide-acetic acid buffer solution on the N 2 O obtained by the nitrate reaction in the sample during the test, and improve the accuracy of the test results; make the 18 O The accuracy is controlled at 0.1 ⁇ , and the accuracy of 15 N is controlled at 0.12 ⁇ ;
  • the present disclosure further optimizes the pretreatment method, which can eliminate the interference of the buffer solution from the measurement of the sample to be tested, and improve the stability and accuracy of the test;
  • the sampling device of the present disclosure can ensure that the N 2 O generated from the reaction liquid in the sampling headspace bottle enters the mass spectrometer at a stable pressure and suitable concentration, which further improves the operability of precision control.

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Abstract

一种化学转化法测定氮氧同位素的前处理方法和测定方法，涉及环境保护和监测技术领域。该前处理方法包括如下步骤：将叠氮化钠-醋酸缓冲溶液于≤15℃的条件下低温处理。该方法通过对叠氮化钠-醋酸缓冲溶液于≤15℃的条件下进行低温处理，能够极大地降低叠氮化钠-醋酸缓冲溶液对测试时样品中硝酸盐反应得到的N2O的干扰，提高测试结果的精度。

Description

一种化学转化法测定氮氧同位素的前处理方法和测定方法
相关申请的交叉引用
本申请要求于2019年07月18日提交中国专利局的申请号为2019106493698、名称为“一种化学转化法测定氮氧同位素的前处理方法和测定方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本公开涉及环境保护和监测技术领域，尤其是涉及一种化学转化法测定氮氧同位素的前处理方法和测定方法。
背景技术
硝酸盐是淡水系统中含氮污染物的主要存在形态，硝酸盐含量过高会对人类造成潜在的健康威胁，高浓度硝酸盐会引起高铁血红蛋白症。水体硝酸盐污染已成为重要的水环境问题之一。识别硝酸盐来源是解决该问题的首要条件，目前利用水体中可溶性硝酸盐中氮氧双同位素技术示踪氮污染源的方法已经广泛应用于食品溯源、生态系统循环及污染物迁移过程研究中，如何在预处理中降低氮元素的分馏作用，一直是氮同位素的分析检测的难点和热点。
目前，测定淡水样品中氮同位素的代表性方法主要有：硝酸银技术、反硝化细菌法、镉还原法/叠氮法(化学转化法)三种，三种方法各有优劣。硝酸银法是目前认为的准确度较高的氮同位素预处理方法，整个过程中分馏的可能性很低且无杂质带入，但其离子交换过程要获得足够的硝酸银待测样品需要2-3L水样，单批次样品耗时24-48h，而化学转化法每个样品仅需15-40mL水样，且单批次样品前处理耗时仅需2-3h，相比于硝酸银法，化学转化法大大降低了水样需求和采集运输难度，并且节省大量预处理的时间。反硝化细菌法的优点在于一旦细菌培养成熟，便可以大批量进行氮同位素预处理工作，单次可满足200-400样品的测试需求，被科研单位和分析测试机构广泛采用，但反硝化细菌法在培养成功率和精度上都有缺陷，一是细菌必须大量培养导致成活率较低，且培养周期在7-10天左右，非常耗时；二是细菌通过反硝化过程产出的N 2O中的氮元素可能不是来源于培养水样，而是自身分解代谢产生，经过预处理的水样无形中增加了外来氮源的干扰，所以还存在争议，未能成为主流预处理方法。
相对来说，化学转化法避免了反硝化细菌法和硝酸银技术的不足，节省水样，每个样品仅需15-40mL水样，耗时短，单批次20-60个样品仅用3.5个小时即可完成前处理工作。然而目前，化学转化法前处理技术还不够成熟，试验稳定性低。
有鉴于此，特提出本公开。
发明内容
本公开的目的包括，例如提供一种化学转化法测定氮氧同位素的前处理方法，以解决现有技术中存在的试验稳定性差的技术问题。
本公开提供了一种化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
将叠氮化钠-醋酸缓冲溶液于≤15℃的条件下低温处理。
本公开通过对化学转化法测定同位素时可能影响实验结果的试剂等进行排查测试，证明叠氮化钠-醋酸缓冲溶液是干扰空白的主要试剂。本公开通过对叠氮化钠-醋酸缓冲溶液于≤15℃的条件下进行低温处理，能够极大的降低叠氮化钠-醋酸缓冲溶液对测试时样品中硝酸盐反应得到的N 2O的干扰，提高测试结果的精度。
在一种或多种实施方式中，所述叠氮化钠-醋酸缓冲溶液以如下方法配制：称取适量叠氮化钠固体(GR)溶于超纯水定容，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮 化钠-醋酸缓冲溶液；
其中，所述20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液。
在一种或多种实施方式中，将叠氮化钠-醋酸缓冲溶液于≤10℃的条件下低温处理；可选于≤4℃的条件下低温处理；或可选于≤0℃的条件下低温处理。在一种或多种实施方式中，将叠氮化钠-醋酸缓冲溶液于-5℃～4℃的条件下低温处理。
在一种或多种实施方式中，所述低温处理的方法包括：将所述缓冲溶液置于≤15℃、或≤10℃、或≤4℃、或≤0℃的体系中。
在一种或多种实施方式中，所述低温处理的时间为≥2h。低温处理的时间在上述范围内，可以降低缓冲溶液对测试结果的干扰。
叠氮化钠-醋酸缓冲溶液的浓度可根据实际需求进行配制，通常可采用如2mol/L的浓度。
在一种或多种实施方式中，，低温处理的时间可以为2h、3h、4h、5h、6h、7h、8h、9h、10h、11h、12h、13h、14h、15h、16h、17h、18h、19h、20h、21h、22h、23h、24h、25h、26h、27h、28h、29h、30h、31h、32h等等。为了兼顾测试结果精度以及测试效率，优选低温处理的时间为2-30h，更优选为4-24h。
在一种或多种实施方式中，可以将叠氮化钠-醋酸缓冲溶液于0-4℃的条件下低温处理20-28h，如24h。或者将叠氮化钠-醋酸缓冲溶液于-5℃～0℃的条件下低温处理2-6h，如4h。通过上述处理条件，可以基本排除试剂对测试结果的干扰，提高测试结果的精度。
在一种或多种实施方式中，低温处理前，采用气体对叠氮化钠-醋酸缓冲溶液进行吹扫。
在低温处理前，配合气体的吹扫，能够进一步降低缓冲溶液中的N 2O对测试结果的干扰。
在一种或多种实施方式中，所述气体为非氧化气体。在一种或多种实施方式中，所述非氧化气体为氦气和/或氮气。
采用氦气和/或氮气吹扫，配合低温处理，能够显著降低并排除干扰。
在一种或多种实施方式中，可对缓冲溶液进行低温处理、氦气吹扫+低温处理或氮气吹扫+低温处理，以降低干扰。
通过上述方法对所述缓冲溶液处理后，可将缓冲溶液保存至顶空瓶中，瓶口采用聚乙烯盖子以及与其配套的橡胶垫片密封，取用时，可先将顶空瓶倒立，然后用洁净针筒从瓶口插入取用，防止外界空气进入干扰实验等。
本公开还提供了一种化学转化法测定氮氧同位素的方法，使用如上所述方法进行前处理后的叠氮化钠-醋酸缓冲溶液对待测样品进行测试。
通过对叠氮化钠-醋酸缓冲溶液进行上述前处理，基本排除了其中的N 2O对测试结果的干扰，能够极大的提高待测样品中氮氧同位素的测试结果。
在一种或多种实施方式中，在测试前，可对气体同位素质谱仪进行稳定性检验，保证仪器稳定且无干扰因素。
在一种或多种实施方式中，在测试前，对经过稳定性检验的气体同位素质谱仪的检测范围进行确定，其中20±5μg的N 2O是MAT252比较适宜的浓度范围。
在一种或多种实施方式中，所述测试时所用的保护气体为空气或氦气。
在空气条件下吹扫与惰性气体条件下的N 2O信号值相差不大，如为了降低成本，可配合采用空气代替惰性气体如氦气。
在一种或多种实施方式中，测试时采用的进样装置包括：十字连通管、软管和进样针；所述十字连通管的各个端口按顺时针方向分别设置有第一阀门、第二阀门、第三阀门和第四阀门；所述十字连通管设置有第二阀门的端口通过软管与进样针连通。十字连通管设置有第一阀门和第三阀门的两个端口与气体同位素质谱仪的测试管路连通，用于将气体样品送入测试仪器中。十字连通管设置有第四阀门的端口与真空泵连通，可对进样装置进行抽 真空处理。
在一种或多种实施方式中，所述软管内设置有干燥柱。在一种或多种实施方式中，所述干燥柱的成分为氧化钙。
在一种或多种实施方式中，所述软管为聚乙烯软管。
在一种或多种实施方式中，所述进样针设置有橡胶塞以将所述进样针堵上。由于进样是气液混合样，并且水的含量在化学转化的顶空瓶中比例较大，设置干燥柱，能够保证在进样时，降低水和二氧化碳的含量，降低杂质含量且减少干扰，提高测量结果精度。
在一种或多种实施方式中，所述进样针设置有开关，用于开启或关闭进样针。
在实际测试时，可采用现有的自动进样装置。但采用本公开的进样装置，能够确保进样顶空瓶中反应液体产生的N 2O以稳定的压强和适合的浓度进入质谱仪，提高了精度控制的可操作性。
与现有技术相比，本公开的有益效果如下：
(1)本公开通过对化学转化法测定同位素时可能影响实验结果的试剂等进行排查测试，证明叠氮化钠-醋酸缓冲溶液时干扰空白的主要试剂；通过对叠氮化钠-醋酸缓冲溶液于≤15℃的条件下进行低温处理，能够极大的降低叠氮化钠-醋酸缓冲溶液对测试时样品中硝酸盐反应得到的N 2O的干扰，提高测试结果的精度；使 18O的精度控制在0.1‰， 15N的精度控制在0.12‰；
(2)本公开对前处理的方法进一步优化，能够排除缓冲溶液对待测样品测定的干扰，提高测试稳定性和精度；
(3)本公开的进样装置，能够确保进样顶空瓶中反应液体产生的N 2O以稳定的压强和适合的浓度进入质谱仪，进一步提高了精度控制的可操作性。
附图说明
为了更清楚地说明本公开具体实施方式或现有技术中的技术方案，下面将对具体实施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本公开的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本公开实施例提供的进样装置的结构示意图；
图2为本公开一个实施例中，在真空条件下对室外空气bottle-outdoor-1条件下仪器测量曲线；
图3为本公开一个实施例中，在真空条件下对室内空气blank-1条件下仪器测量曲线；
图4为本公开一个实施例中，加入N 2O气体(约为20μg)dummy bottle 1的测量曲线；
图5为本公开一个实施例中，另一加入N 2O气体(约为20μg)dummy bottle 2的测量曲线；
图6为本公开一个实施例中，在氦气条件下He1得到的测量曲线；
图7为本公开一个实施例中，在氮气条件下Air1得到的测量曲线；
图8为本公开一个实施例中，在不加氯化镉的条件下N1-1得到的测量曲线；
图9为本公开一个实施例中，在不加氯化镉的条件下N1-2得到的测量曲线；
图10为本公开一个实施例中，在不加氯化铵的条件下N2-1得到的测量曲线；
图11为本公开一个实施例中，在不加氯化铵的条件下N2-2得到的测量曲线；
图12为本公开一个实施例中，在不加锌片的条件下N3-1得到的测量曲线；
图13为本公开一个实施例中，在不加叠氮化钠-醋酸缓冲溶液的条件下N4-1得到的测量曲线；
图14为本公开一个实施例中，在不加叠氮化钠-醋酸缓冲溶液的条件下N4-2得到的测量曲线；
图15为本公开一个实施例中，在不加氢氧化钠的条件下N5-1得到的测量曲线；
图16为采用本公开实施例1处理后的叠氮化钠-醋酸缓冲溶液得到的测量曲线；其中air2-1 和air2-2分别为两组平行实验；
图17为采用本公开实施例3处理后的叠氮化钠-醋酸缓冲溶液得到的测量曲线Air1-2以及比较例2处理后的叠氮化钠-醋酸缓冲溶液得到的测量曲线Air1；
图18为采用本公开实施例4处理后的叠氮化钠-醋酸缓冲溶液得到的测量曲线Air1-2以及比较例2处理后的叠氮化钠-醋酸缓冲溶液得到的测量曲线Air1-1；
图19为采用比较例1处理后的叠氮化钠-醋酸缓冲溶液的测量曲线air2以及用未经处理的叠氮化钠-醋酸缓冲溶液的测量曲线air1；
图20为采用比较例2处理后的叠氮化钠-醋酸缓冲溶液的测量曲线air4以及用未经处理的叠氮化钠-醋酸缓冲溶液的测量曲线air3。
附图标记：
1-十字连通管；        2-软管；              3-进样针；
11-第一阀门；         12-第二阀门；         13-第三阀门；
14-第四阀门；         21-干燥柱。
具体实施方式
下面将结合附图和具体实施方式对本公开的技术方案进行清楚、完整地描述，但是本领域技术人员将会理解，下列所描述的实施例是本公开一部分实施例，而不是全部的实施例，仅用于说明本公开，而不应视为限制本公开的范围。基于本公开中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本公开保护的范围。实施例中未注明具体条件者，按照常规条件或制造商建议的条件进行。所用试剂或仪器未注明生产厂商者，均为可以通过市售购买获得的常规产品。
在本公开的描述中，需要说明的是，术语“中心”、“上”、“下”、“左”、“右”、“竖直”、“水平”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本公开和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本公开的限制。此外，术语“第一”、“第二”、“第三”仅用于描述目的，而不能理解为指示或暗示相对重要性。
在本公开的描述中，需要说明的是，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以具体情况理解上述术语在本公开中的具体含义。
图1为本公开实施例提供的进样装置的结构示意图。从图中可知，该进样装置包括十字连通管1、软管2和进样针3。所述十字连通管1的各个端口按顺时针方向分别设置有第一阀门11、第二阀门12、第三阀门13和第四阀门14。所述十字连通管1设置有第一阀门11和第三阀门13的两个端口与气体同位素质谱仪的测试管路连通。所述十字连通管1设置有第二阀门12的端口通过软管2与进样针3连通。所述十字连通管1设置有第四阀门14的端口与真空泵连通。
可选地，软管2内设置有干燥柱21。所述干燥柱21的成分优选为氧化钙。
可选地，软管2可选聚乙烯软管，但不局限于此。
可选地，进样针3设置有开关，可用于开启或关闭进样针。或者可以采用橡胶塞将进样针3堵上。
每测试一个待测样品前，将进样针3关闭，也可采用橡胶塞将进样针3堵上。然后关闭第一阀门11和第三阀门13，打开第二阀门12和第四阀门14，同时开启真空泵，对进样装置抽真空，约3-5min后，关闭第四阀门14，将进样针3穿过橡胶塞插入待测样品瓶中，得到适量的待测样品后，关闭第二阀门12，打开第一阀门11和第三阀门13，使待测样品 通过第一阀门11和第三阀门13的通路进入气体同位素质谱仪的测试管路连通，进行测试。
实施例1
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水后定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液于0-4℃的条件下，冷藏处理4h，得到处理后的叠氮化钠-醋酸缓冲溶液。
实施例2
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液于5-10℃的条件下，低温处理4h，得到处理后的叠氮化钠-醋酸缓冲溶液。
实施例3
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液采用氦气吹扫4h，然后于0-4℃的条件下，冷藏处理4h，得到处理后的叠氮化钠-醋酸缓冲溶液。
实施例4
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液采用氮气吹扫4h，然后于0-4℃的条件下，冷藏处理4h，得到处理后的叠氮化钠-醋酸缓冲溶液。
比较例1
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的比例混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液采用氮气吹扫4h，不经过冷藏处理 或低温处理即得到处理后的叠氮化钠-醋酸缓冲溶液。
比较例2
本实施例的化学转化法测定氮氧同位素的前处理方法，包括如下步骤：
(1)配制叠氮化钠-醋酸缓冲溶液：称取6.501g叠氮化钠固体(GR)溶于25mL超纯水定容至50mL，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
其中，20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的比例混合，得到20％的醋酸溶液；
(2)将步骤(1)中得到的叠氮化钠-醋酸缓冲溶液采用氦气吹扫4h，不经过冷藏处理或低温处理即得到处理后的叠氮化钠-醋酸缓冲溶液。
实验例1
(1)在测试前，对仪器的稳定性进行检验：
为确认所使用的MAT252气体同位素质谱仪有较好的稳定性及环境气体对仪器的干扰程度，测试了真空条件下室外空气bottle-outdoor-1以及室内空气blank-1，如图2-3所示，在四组对比气体过后(3分钟48秒)，曲线在5分10-15秒内只显示CO 2一个峰，且在正常范围内，可以忽略，证明使用的仪器较稳定且无干扰因素。
(2)进行仪器适宜检测范围确定：
分别在两个60mL顶空瓶中加入定量的N 2O气体(约为20μg)，编号分别为dummy bottle 1-1和dummy bottle 2-1，上机测试，测试结果如图4-5所示，结果显示N 20信号值较稳定，说明20μg左右的N 2O是比较适宜的浓度范围。
(3)不同保护气体精度控制：
分别制备空气条件和氦气条件下样品各5瓶(60mL顶空瓶)，每个样品中加入40mL的超纯水，编号为Air1、Air2、Air3、Air4、Air5均处于空气条件下，编号为He1、He2、He3、He4、He5均处于氦气条件下，且两种均使用新配制的叠氮化钠-醋酸缓冲溶液(以下简称缓冲液)。测试(参考实验例2的测试步骤)结果显示空气条件下和氦气条件下N 2O的信号值相差不大，后期可使用空气代替氦气，但从曲线图中可以很明显的看出两种空白样品中含有大量氧化亚氮气体，无法达到空白要求。如图6-7分别为He1和Air1对应的测试结果。
实验例2
为了验证在化学转化法测定氮氧同位素时可能对测试结果产生干扰，导致精度降低的影响因素时，对可能影响测试结果的试剂进行排查，进行如下实验，条件如下：
在每种条件下设置两个平行样品，如下表1，分别为N1-1、N1-2、N2-1、N2-2、N3-1、N3-2、N4-1、N4-2、N5-1、N5-2；该实验在空气条件下进行。
表1影响条件排查表
去除的药剂 去除药剂样品平行样编号
不加氯化镉 N1-1，N1-2
不加氯化铵 N2-1，N2-2
不加锌片 N3-1、N3-2
不加叠氮化钠-醋酸缓冲溶液 N4-1，N4-2
不加氢氧化钠 N5-1、N5-2
测试步骤包括：取待测样品40mL于60mL顶空瓶中，加入0.8mL的氯化镉溶液(20g/L)，然后加入0.8mL的氯化铵溶液(250g/L)，最后加入3×10cm 4N(或者3N)洁净锌片(酒精擦拭干净)，在摇床上以220r/min转速振荡20min。取出锌片，密闭顶空瓶，完成硝酸盐还原步骤。然后向顶空瓶中加入2mL的叠氮化钠-醋酸缓冲溶液，剧烈振荡使样品和试剂混匀。之后以220r/min转速振荡30min，最后加入1mL的NaOH溶液(10mol/L)作为终止剂，结束叠氮化反应。然后将样品上机进行测试。
表1中的去除的药剂是指，参考上述测试步骤，在对应的位置不加氯化镉、不加氯化铵、不加锌片、不加叠氮化钠-醋酸缓冲溶液或不加氢氧化钠这几种试剂，对待测样品(待测样品为蒸馏水)处理后上机进行测试。测试结果如图8-15所示。
从图8-15中可知，不加叠氮化钠-醋酸缓冲溶液的样品测量曲线不存在氧化亚氮信号值，其余样品测量曲线均有氧化亚氮，且信号值相差不大，证明了叠氮化钠-醋酸缓冲溶液是干扰空白的主要试剂。
实验例3
为了对比说明本公开各实施例和比较例对叠氮化钠-醋酸缓冲溶液进行前处理对测试结果的影响，分别采用实施例1、3和4以及比较例1-2处理得到的叠氮化钠-醋酸缓冲溶液，参考实验例2的测试步骤，每个实施例和比较例分别采用蒸馏水得到两个空白平行样品，上机测试，测试结果如图16-18。
采用比较例1处理后的叠氮化钠-醋酸缓冲溶液与采用未经处理的叠氮化钠-醋酸缓冲溶液的测量曲线如图19所示，其中，air2为比较例1的氮气吹扫，air1为未处理的测量曲线。
采用比较例2处理后的叠氮化钠-醋酸缓冲溶液与采用未经处理的叠氮化钠-醋酸缓冲溶液的测量曲线如图20所示，其中，air4为比较例2的氦气吹扫，air3为未处理的测量曲线。
从上图中可知，对配制好的叠氮化钠-醋酸缓冲溶液进行氦气吹扫再低温冷藏处理后，效果最佳；氮气吹扫，再低温冷藏处理，效果次之。同时，通过实验验证，吹扫的时间越长，效果相对越好，实验干扰越小。并且，冷藏处理比吹扫处理见效快，冷藏时间越长，实验干扰越小，甚至可以排除实验干扰。说明了冷藏条件下可抑制杂质气体的产生。
最后应说明的是：以上各实施例仅用以说明本公开的技术方案，而非对其限制；尽管参照前述各实施例对本公开进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本公开各实施例技术方案的范围。
工业实用性
(1)本公开通过对化学转化法测定同位素时可能影响实验结果的试剂等进行排查测试，证明叠氮化钠-醋酸缓冲溶液时干扰空白的主要试剂；通过对叠氮化钠-醋酸缓冲溶液于≤15℃的条件下进行低温处理，能够极大的降低叠氮化钠-醋酸缓冲溶液对测试时样品中硝酸盐反应得到的N 2O的干扰，提高测试结果的精度；使 18O的精度控制在0.1‰， 15N的精度控制在0.12‰；
(2)本公开对前处理的方法进一步优化，能够排除缓冲溶液对待测样品测定的干扰，提高测试稳定性和精度；
(3)本公开的进样装置，能够确保进样顶空瓶中反应液体产生的N 2O以稳定的压强和适合的浓度进入质谱仪，进一步提高了精度控制的可操作性。

Claims (18)

  1. 一种化学转化法测定氮氧同位素的前处理方法，其特征在于，包括如下步骤：
    将叠氮化钠-醋酸缓冲溶液于≤15℃的条件下低温处理。
  2. 根据权利要求1所述的前处理方法，其特征在于，所述叠氮化钠-醋酸缓冲溶液以如下方法配制：称取适量叠氮化钠固体(GR)溶于超纯水定容，加入同样体积的20％的醋酸溶液，混合均匀得到叠氮化钠-醋酸缓冲溶液；
    其中，所述20％的醋酸溶液的制备方法为：取冰醋酸(GR)，与超纯水以1﹕4的体积比混合，得到20％的醋酸溶液。
  3. 根据权利要求1或2所述的前处理方法，其特征在于，将所述叠氮化钠-醋酸缓冲溶液于≤10℃的条件下低温处理；
    优选的，将所述叠氮化钠-醋酸缓冲溶液于≤4℃的条件下低温处理；
    优选的，将所述叠氮化钠-醋酸缓冲溶液于-5℃～4℃的条件下低温处理。
  4. 根据权利要求1或2所述的前处理方法，其特征在于，将所述叠氮化钠-醋酸缓冲溶液置于≤15℃、或≤10℃、或≤4℃、或≤0℃的体系中。
  5. 根据权利要求1-4中任一项所述的前处理方法，其特征在于，所述低温处理的时间≥2h；
    优选的，所述低温处理的时间为2-30h。
  6. 根据权利要求1-4中任一项所述的前处理方法，其特征在于，所述低温处理的时间为2h、3h、4h、5h、6h、7h、8h、9h、10h、11h、12h、13h、14h、15h、16h、17h、18h、19h、20h、21h、22h、23h、24h、25h、26h、27h、28h、29h、30h、31h或32h。
  7. 根据权利要求3所述的前处理方法，其特征在于，将所述叠氮化钠-醋酸缓冲溶液于0-4℃的条件下低温处理20-28h。
  8. 根据权利要求3所述的前处理方法，其特征在于，将所述叠氮化钠-醋酸缓冲溶液于-5℃～0℃的条件下低温处理2-6h。
  9. 根据权利要求1-8中任一项所述的前处理方法，其特征在于，在将所述叠氮化钠-醋酸缓冲溶液于≤15℃的条件下低温处理前，采用非氧化气体对所述叠氮化钠-醋酸缓冲溶液进行吹扫。
  10. 根据权利要求9所述的前处理方法，其特征在于，所述非氧化气体为氮气和/或氦气；
    优选的，所述非氧化气体为氦气。
  11. 一种化学转化法测定氮氧同位素的方法，其特征在于，使用权利要求1-10任一项所述方法进行前处理后的叠氮化钠-醋酸缓冲溶液对待测样品进行测试；
    优选的，所述测试时所用的保护气体为空气或氦气。
  12. 根据权利要求11所述的方法，其特征在于，在测试前，对气体同位素质谱仪进行稳定性检验，保证仪器稳定且无干扰因素。
  13. 根据权利要求12所述的方法，其特征在于，在测试前，对经过稳定性检验的气体同位素质谱仪的检测范围进行确定。
  14. 根据权利要求11-13中任一项所述的方法，其特征在于，测试时采用的进样装置包括：十字连通管、软管和进样针；所述十字连通管的各个端口按顺时针方向分别设置有第一阀门、第二阀门、第三阀门和第四阀门；所述十字连通管设置有第二阀门的端口通过软管与进样针连通。
  15. 根据权利要求14所述的方法，其特征在于，所述软管内设置有干燥柱；
    优选的，所述干燥柱的成分为氧化钙；
    优选的，所述十字连通管设置有第四阀门的端口与真空泵连通。
  16. 根据权利要求14或15所述的方法，其特征在于，所述软管为聚乙烯软管。
  17. 根据权利要求14-16中任一项所述的方法，其特征在于，所述进样针设置有开关，用于开启或关闭进样针。
  18. 根据权利要求14-16中任一项所述的方法，其特征在于，所述进样针设置有橡胶塞以将所述进样针堵上。
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