A triple iterative capture method for the separation and analysis of a full range of noble gas isotopes

Abstract

The present invention relates to the field of ultra-high vacuum mass spectrometry technology for rare gas separation and analysis, and in particular to a triple iterative capture type full-series rare gas isotope separation and analysis method. The present invention has developed a set of rare gas pretreatment system, which includes a stainless steel water vapor catcher, two SEAS ST-172getters, three stainless steel wire mesh liquid nitrogen cold traps, an activated carbon liquid nitrogen cold trap and an activated carbon temperature-controlled cold trap, and a single injection realizes the separation and analysis of a full range of rare gases such as helium, neon, argon, krypton and xenon. The capture and separation efficiency of krypton reaches 98%, reaching the international leading level. The capture and separation efficiency of the rare gas processing and analysis method for helium, neon, argon, krypton and xenon is all above 98%, and the content of each residual component is less than or equal to 2%. The present invention solves the problem of separation of rare gases, especially argon and krypton, and makes it possible to test all rare gas stable isotopes with high precision by single injection.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high vacuum mass spectrometry for separation and analysis of rare gases, and in particular to a triple iterative capture type full-series rare gas isotope separation and analysis method. Background Art

[0002] Noble gas isotopes are effective tracers in geological and environmental research. Suitable and powerful adsorbents and cryogenic trap separators are the key to the purification and separation of noble gases and the basis for high-precision isotope ratio mass spectrometer (IRMS) analysis. However, the content of argon in atmospheric standard samples and geological samples is more than 8,000 times that of krypton. A large amount of argon poses a severe challenge to the purification and separation of krypton and the safety of mass spectrometers. The existing technology mainly relies on expensive temperature-controlled cold traps to separate argon and krypton by repeated freezing capture and heating release, but the experimental process of this method is complicated and cannot quickly and efficiently separate argon and krypton in noble gases. Moreover, the pretreatment line required for the temperature cycle method is expensive, the installation and commissioning cycle is long, and the experimental process is cumbersome. At present, the separation and analysis of noble gases has been plagued by the separation of argon and krypton, which has become an international problem. Therefore, testing the entire series of noble gases such as helium, neon, argon, krypton, and xenon with a single injection has become a scientific and technological problem that researchers of noble gas isotopes need to solve urgently. Summary of the invention

[0003] The purpose of the present invention is to provide a triple iterative capture type full series of noble gas isotope separation and analysis method to solve the problems existing in the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a triple iterative capture type full series of noble gas isotope separation and analysis method, comprising the following steps:

[0006] Step 1) The sample gas enters an ethanol-liquid nitrogen cold trap to remove water vapor, and then the sample gas is introduced into two SEASST-172 Getters to remove impurities in the sample gas to obtain purified rare gas;

[0007] Step 2) The purified rare gas is passed through three stainless steel wire mesh liquid nitrogen cold traps in sequence to capture krypton and xenon therein; after krypton and xenon are captured, argon is captured by an activated carbon liquid nitrogen cold trap, and helium and neon are subsequently captured on an activated carbon temperature-controlled cold trap;

[0008] Step 3) releasing helium and neon by controlling the temperature of the activated carbon temperature-controlled cold trap, and respectively introducing them into a rare gas mass spectrometer for testing and analysis;

[0009] Step 4) After the helium-neon test and analysis are completed, three stainless steel wire mesh liquid nitrogen cold traps are heated to release krypton and xenon, and transferred to the activated carbon temperature-controlled cold trap for recapture. The krypton and xenon are released by controlling the temperature of the activated carbon temperature-controlled cold trap, and are respectively introduced into the rare gas mass spectrometer for test and analysis;

[0010] Step 5) The activated carbon liquid nitrogen cold trap is heated to release argon, which is then introduced into a rare gas mass spectrometer for testing and analysis.

[0011] Preferably, the temperature of the ethanol-liquid nitrogen cold trap is -90 to -50°C.

[0012] Preferably, of the two SEAS ST-172 Getters, one has a temperature of 15-30°C, the other has a temperature of 250-350°C, and the purification time is 5-20 min.

[0013] Preferably, the temperatures of the three stainless steel wire mesh liquid nitrogen cold traps are all 77K, and the capture time is all 5 to 20 minutes.

[0014] Preferably, the capture temperature of the argon is 77K, and the capture time is 5 to 20 minutes; the release temperature of the argon is 400 to 500K.

[0015] Preferably, the capture temperature of helium and neon is 1-10K, and the capture time is 5-20 minutes; the release temperature of helium is 20-50K; and the release temperature of neon is 60-100K.

[0016] Preferably, the release temperature of krypton and xenon from the stainless steel wire mesh liquid nitrogen cold trap is 400-500K; the temperature at which krypton and xenon are recaptured is 100-150K, and the capture time is 20-40 minutes; the release temperature of krypton is 150-250K; and the release temperature of xenon is 260-350K.

[0017] Preferably, the impurity gas in step 1) comprises O2, N2, H2, H2S, CO2, CO and hydrocarbons.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention develops a rare gas pretreatment system, which includes a stainless steel water vapor catcher, two SEAS ST-172getters, three stainless steel wire mesh liquid nitrogen cold traps, an activated carbon liquid nitrogen cold trap and an activated carbon temperature-controlled cold trap. The triple iterative stainless steel wire mesh liquid nitrogen cold trap proposed and applied for the first time improves the separation efficiency of argon and krypton, and the capture efficiency of krypton reaches 98%, reaching the international leading level. The capture and separation efficiency of helium, neon, argon, krypton and xenon in this pretreatment method is above 98%, and the content of each residual component is less than or equal to 2%.

[0020] The method of the present invention treats argon separately, and does not capture and release it together with krypton on the activated carbon temperature-controlled cold trap, thereby avoiding wasting a lot of time on multiple temperature cycles on the activated carbon temperature-controlled cold trap. Under the same argon-krypton separation efficiency, the method of the present invention requires a lower cost for the pre-treatment line than the existing temperature cycle method. It is very beneficial for the long-term maintenance and operation of the laboratory and the promotion of the method. The method can ensure that the sensitivity to stable isotopes of helium, neon, argon, krypton, and xenon is close to the manufacturer's instrument reference value, thereby ensuring the accuracy of the absolute content test of each rare gas, and the isotope ratio test of rare gases has good precision and stability. The experimental error of the isotope ratio of multiple experiments is very small, and the value is maintained at a relatively stable level, which proves that the method has good stability and can be operated for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of the triple iterative capture-type full-series noble gas isotope separation and analysis method provided in Example 1;

[0022] Figure 2 This is a graph showing the variation of the signal intensity of each noble gas in the atmospheric standard sample using the triple iteration method in Example 1 over time;

[0023] Figure 3 The triple iteration method of Example 1 is as krypton is released 20 Ne and 40 Ar signal intensity plot. DETAILED DESCRIPTION

[0024] In the present invention, the ethanol-liquid nitrogen cold trap is a mixed liquid of ethanol and liquid nitrogen, and the required temperature is achieved by controlling the ratio of ethanol and liquid nitrogen;

[0025] SEAS ST-172Getters is a Zr-V-Fe alloy chemical getter pump produced by SEAS, Italy;

[0026] The stainless steel wire mesh liquid nitrogen cold trap was homemade in the laboratory, and the container material was stainless steel;

[0027] The activated carbon liquid nitrogen cold trap was homemade in the laboratory, and the container material was stainless steel;

[0028] The activated carbon temperature-controlled cold trap is a special version of the DE-204 cold trap customized by ARS (Advanced Research Systems);

[0029] The mass spectrometer was Helix SFT produced by Thermo-Fisher Scientific.

[0030] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0031] Example 1

[0032] The laboratory is kept at a constant temperature of 20°C and a constant humidity of 40%. Taking the gas sample stored in a copper tube as an example, the surface of the copper tube is cleaned, and the sample is placed in the pretreatment line sampling system in advance the night before, and the sampling system is re-evacuated to 10 - 6 Torr. The next morning, after all components of the pretreatment system are ready, the gas sample is released from the copper tube.

[0033] Step 1) Use -83°C ethanol-liquid nitrogen cold trap to remove water vapor from the sample; then introduce the sample gas into two SEAS ST-172Getters, one set at laboratory temperature 20°C and the other set at 300°C, for 10 minutes to remove impurities such as O2, N2, H2, CO, CO2, hydrocarbons, etc. in the sample;

[0034] Step 2) The purified rare gas is sequentially passed through three stainless steel wire mesh liquid nitrogen cold traps with a temperature of 77K to capture krypton and xenon therein, each lasting for 10 minutes; after the krypton and xenon are captured, argon is captured by an activated carbon liquid nitrogen cold trap 1 with a temperature of 77K, lasting for 10 minutes; helium and neon are then captured on an activated carbon temperature-controlled cold trap set at a temperature of 5K;

[0035] Step 3) raising the temperature of the activated carbon temperature-controlled cold trap to 30K to release helium and introduce it into a rare gas mass spectrometer for testing and analysis; then raising the temperature of the activated carbon temperature-controlled cold trap to 80K to release neon and introduce it into a rare gas mass spectrometer for testing and analysis, and then heating the activated carbon temperature-controlled cold trap to 300K for cleaning;

[0036] Step 4) After the helium-neon test analysis is completed, the three stainless steel wire mesh liquid nitrogen cold traps are heated to 473K to release krypton and xenon, and transferred to the activated carbon temperature-controlled cold trap set at 125K for secondary capture. The activated carbon temperature-controlled cold trap is raised to 205K to release krypton and introduce it into the rare gas mass spectrometer for test analysis, and then the temperature of the activated carbon temperature-controlled cold trap is raised to 325K to release xenon and introduce it into the rare gas mass spectrometer for test analysis.

[0037] Step 5) Use a turbo pump and an ion pump to clean the pretreatment line, heat the activated carbon liquid nitrogen cold trap 1 to 200°C (473K) to release argon, divide it into small portions suitable for the mass spectrometer, and then introduce it into the mass spectrometer for testing.

[0038] At this point, the entire process is over. The entire process takes about 4 hours and 30 minutes. See the process diagram Figure 1 .

[0039] Figure 2 is the variation of the signal intensity of each rare gas over time using the triple iteration method. Figure 2 It can be seen that the signal intensity of each noble gas is stable under this method, and the sensitivity of the mass spectrometer to each noble gas is stable, which proves that the method has high repeatability and the experimental method is reliable.

[0040] Figure 3 It is a triple iteration method released with krypton 20 Ne and 40 Ar signal intensity diagram, by Figure 3 It can be seen that the signal value of argon released by krypton is lower than 20000fA, and the separation of argon and krypton is relatively thorough. The signal value of residual argon is much smaller than the detection upper limit of the mass spectrometer 500000fA, and the argon released by krypton will not affect the analysis and test of krypton.

[0041] The argon and krypton in the rare gases are separated by the stainless steel wire mesh capture method of triple iteration capture. Multiple experiments have confirmed that the capture efficiency of krypton has reached 98%, reaching the international leading level. And the capture and separation efficiency of helium, neon, argon, krypton, and xenon by this pre-treatment method is above 98%, and the content of each residual component is less than or equal to 2%. As krypton releases the residual argon content to a very low level, the sensitivity to each rare gas is relatively stable.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that only two stainless steel wire mesh liquid nitrogen cold traps are used to capture krypton and xenon. The capture and separation efficiency of krypton is about 95%, which is not as good as the triple iterative method of Example 1.

[0044] It can be seen from the above embodiments that the present invention provides a triple iterative capture type full series of rare gas isotope separation and analysis methods. The method of the present invention treats argon separately, and does not capture and release it together with krypton on the temperature-controlled cold trap, thereby avoiding wasting a lot of time on multiple temperature cycles on the activated carbon temperature-controlled cold trap. Under the same argon-krypton separation efficiency, the cost of the pre-treatment line required by the method of the present invention is lower than that of the existing temperature cycle method. It is very beneficial for the long-term maintenance and operation of the laboratory and the promotion of this method. The main advantage of this method is that all stable isotopes of helium, neon, argon, krypton, and xenon can be tested with high precision in one injection, which can ensure that the sensitivity of stable isotopes of helium, neon, argon, krypton, and xenon is close to the manufacturer's instrument reference value, thereby ensuring the accuracy of the absolute content test of each rare gas, and the isotope ratio test of rare gases has good accuracy and stability. The isotope ratios of multiple experiments have small experimental errors, and the values ​​are maintained at a relatively stable level, proving that the method has good stability and can be operated for a long time.

[0045] 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 triple iterative capture full range of noble gas isotope separation and analysis method, characterized in that: All stable noble gas isotopes can be tested in one injection, which includes the following steps: Step 1) The sample gas enters an ethanol-liquid nitrogen cold trap to remove water vapor, and then the sample gas is introduced into two SEAS ST-172 Getters to remove impurities in the sample gas to obtain a purified rare gas, wherein the temperature of the ethanol-liquid nitrogen cold trap is -90 to -50°C, and the temperature of the two SEAS ST-172 Getters is 15 to 30°C and 250 to 350°C, and the purification time is 5 to 20 minutes; Step 2) The purified rare gas is passed through three stainless steel wire mesh liquid nitrogen cold traps in sequence to capture krypton and xenon therein; after the krypton and xenon are captured, argon is captured by an activated carbon liquid nitrogen cold trap, and helium and neon are subsequently captured on an activated carbon temperature-controlled cold trap, the temperatures of the three stainless steel wire mesh liquid nitrogen cold traps are all 77K, and the capture time is 5 to 20 minutes; the capture temperature of argon is 77K, and the capture time is 5 to 20 minutes; the capture temperature of helium and neon is 1 to 10K, and the capture time is 5 to 20 minutes; Step 3) releasing helium and neon by controlling the temperature of the activated carbon temperature-controlled cold trap, and respectively introducing them into a rare gas mass spectrometer for testing and analysis, wherein the release temperature of the helium is 20 to 50 K; and the release temperature of the neon is 60 to 100 K; Step 4) After the helium-neon test and analysis are completed, three stainless steel wire mesh liquid nitrogen cold traps are heated to release krypton and xenon, and transferred to the activated carbon temperature-controlled cold trap for recapture. The krypton and xenon are released by controlling the temperature of the activated carbon temperature-controlled cold trap, and are respectively introduced into the rare gas mass spectrometer for test and analysis. The release temperature of the krypton and xenon from the stainless steel wire mesh liquid nitrogen cold trap is 400-500K; the temperature at which the krypton and xenon are recaptured is 100-150K, and the capture time is 20-40min; the release temperature of the krypton is 150-250K; the release temperature of the xenon is 260-350K; Step 5) The activated carbon liquid nitrogen cold trap is heated to release argon, which is then introduced into a rare gas mass spectrometer for testing and analysis. The release temperature of the argon is 400-500K.

2. A triple iterative capture full range of noble gas isotope separation and analysis method according to claim 1, characterized in that: The impurity gas in step 1) includes O2, N2, H2, H2S, CO2, CO and hydrocarbons.

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