Gas stable isotope measurement method based on spectral analysis

Abstract

The invention belongs to the technical field of stable isotope measurement, and particularly discloses a gas stable isotope measurement method based on spectral analysis. The method comprises the following steps: collecting a gas sample containing a stable isotope to be detected; sequentially purifying and concentrating the gas sample to obtain a pretreated gas sample; the pretreated gas sample is introduced into a light path of an infrared spectrometer for analysis, and a spectral analysis result is obtained; performing data processing on the spectral analysis result to obtain a measurement result of the gas stable isotope; the gas sample contains carbon dioxide gas. The measuring method disclosed by the invention is high in sensitivity, high in accuracy, relatively small in error and simple and convenient to operate; and for the isotope with lower content, the method also has higher accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of stable isotope measurement, and in particular to a gas stable isotope measurement method based on spectral analysis. Background Art

[0002] An isotope is one of two or more atoms of the same chemical element with the same atomic number, occupying the same position in the periodic table, and having almost the same chemical properties, but different atomic masses or mass numbers, resulting in differences in their mass spectrometry properties, radioactive transitions, and physical properties. Isotopes include radioactive isotopes and stable isotopes, and the measurement of stable isotopes has far-reaching significance in many fields. For example, due to their unique properties, stable isotopes are widely used in water and soil management, environmental research, nutritional assessment research, and forensic identification. For example, by measuring and analyzing the distribution of stable isotopes, it is possible to trace the origin, history, source of substances, and their interaction processes in the environment. Stable isotopes can also be used as tracers and are intentionally added to the system being studied, such as agriculture or nutrition, to reveal the mechanism and rate of a specific process. In the field of medicine, the measurement of stable isotopes also plays an important role. For example, 13 The C breath test is a non-invasive medical test method that uses stable isotopes to evaluate digestion and absorption function, gastric acid secretion, and Helicobacter pylori detection. This test method is not only highly accurate, but also safe and non-invasive, providing strong support for the diagnosis and monitoring of gastrointestinal diseases.

[0003] At present, the methods for measuring stable isotopes in gas samples mainly include mass spectrometry, spectroscopy and chromatography. Mass spectrometry is an isotope analysis method that measures the mass-to-charge ratio of ions (i.e., the mass-to-charge ratio). It has the advantages of high precision and high sensitivity, and can accurately determine the isotope ratio. However, mass spectrometry has the problems of complex operation, cumbersome sample pretreatment, and the need for complex correction and verification of interfering elements; chromatography uses the separation effect of different isotopes on the chromatographic column for analysis. However, there are problems such as the separation effect is easily affected and the operation process is cumbersome. Spectroscopy is also widely used in the measurement of stable isotopes. It uses the slight differences in the spectrum of different isotopes for analysis. It has the advantages of being non-destructive, fast and relatively simple. However, the accuracy and sensitivity of spectroscopy are relatively low, especially for isotopes with low content, which are difficult to accurately measure.

[0004] Therefore, how to disclose a gas stable isotope measurement method based on spectral analysis and improve the accuracy and sensitivity of spectral analysis is a difficult problem that needs to be solved urgently in this field. Summary of the invention

[0005] In view of this, the present invention provides a method for measuring gas stable isotopes based on spectral analysis to solve the problem of low precision and sensitivity of existing spectral analysis methods, especially the difficulty in accurately measuring isotopes with low content.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for measuring gas stable isotopes based on spectral analysis comprises the following steps:

[0008] 1) Collecting a gas sample containing the stable isotope to be measured;

[0009] 2) Gas sample pretreatment: purifying and concentrating the gas sample in sequence to obtain a pretreated gas sample;

[0010] 3) Spectral scanning: introducing the pretreated gas sample into the optical path of the infrared spectrometer for analysis to obtain the spectral analysis results;

[0011] 4) Processing the spectrum analysis results to obtain the measurement results of gas stable isotopes;

[0012] The gas sample contains carbon dioxide gas.

[0013] Preferably, the purification in step 2) comprises filtration, adsorption and drying performed sequentially.

[0014] Preferably, the filtration is first performed using a particle filter and then a membrane separation filtration.

[0015] Preferably, the adsorption is performed using activated carbon.

[0016] Preferably, the drying is performed using a chemical drying agent.

[0017] Preferably, the concentration is to obtain concentrated carbon dioxide gas by a condensation method.

[0018] Preferably, the pressure measured in step 3) is 1.2-1.5 MPa.

[0019] Preferably, the data processing in step 4) includes integrating the spectral analysis results to obtain the peak areas corresponding to different isotopes, and using the peak areas to obtain the isotope abundance.

[0020] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention improves the purity of the gas sample through the pretreatment step, avoids the interaction of other impurities or particulate matter with the target gas molecules, avoids the interference generated during the spectral analysis process, and improves the accuracy of the measurement; at the same time, the increase in concentration also helps to enhance the intensity of the spectral signal, which can improve the sensitivity of the measurement and reduce the error in the measurement process.

[0022] 2. Use a spectral analysis instrument to perform spectral scanning on the carbon dioxide gas sample, and by obtaining the spectral data of the sample, accurately measure the stable isotope ratio in the sample; compared with traditional measurement methods, the present invention has the advantages of high measurement accuracy, simple operation, and short time consumption. DETAILED DESCRIPTION

[0023] The present invention provides a method for measuring gas stable isotopes based on spectral analysis, comprising the following steps:

[0024] 1) Collecting a gas sample containing the stable isotope to be measured;

[0025] 2) Gas sample pretreatment: purifying and concentrating the gas sample in sequence to obtain a pretreated gas sample;

[0026] 3) Spectral scanning: introducing the pretreated gas sample into the optical path of the infrared spectrometer for analysis to obtain the spectral analysis results;

[0027] 4) Processing the spectrum analysis results to obtain the measurement results of gas stable isotopes;

[0028] The gas sample contains carbon dioxide gas.

[0029] In the present invention, the carbon dioxide gas comprises 12 CO 2 and 13 CO 2 .

[0030] In the present invention, the purification in step 2) includes filtration, adsorption and drying performed in sequence.

[0031] In the present invention, the filtration is first performed by a particle filter and then by membrane separation filtration; the particle filter can block and capture particles in the airflow, and can effectively remove dust, fibers and other solid impurities therein; in membrane separation filtration, driven by pressure or concentration difference, the gas molecules pass through the membrane at different speeds, thereby achieving separation of different components, and can remove certain impurities in carbon dioxide gas.

[0032] In the present invention, the adsorption is performed using activated carbon.

[0033] In the present invention, the activated carbon adsorption is preferably to pass the gas sample through an adsorption layer filled with activated carbon for adsorption treatment; the thickness of the adsorption layer is preferably 3-10 cm, specifically 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm; the gas sample passage rate per 100 square centimeters is preferably 1-3 L / min, specifically 1.5 L / min, 2 L / min, 2.5 L / min; the number of adsorption treatments is preferably 1-5 times, specifically 2 times, 3 times, 4 times.

[0034] In the present invention, the drying is performed using a chemical drying agent, preferably silica gel drying.

[0035] In the present invention, the concentration is to obtain concentrated carbon dioxide gas by condensation. In the present invention, the concentration is to use the different boiling points of different substances to improve the purity of carbon dioxide gas and avoid the influence of other components. The concentration process will not affect the carbon dioxide gas. 13 The abundance of C.

[0036] In the present invention, the pressure measured in step 3) is 1.2-1.5 MPa.

[0037] In the present invention, under high pressure, the mean free path between carbon dioxide gas molecules will be shortened, which means that the collision frequency between molecules will increase, and the interaction between gas molecules will be enhanced, which will lead to an increase in the complexity of the spectral signal, making it difficult to distinguish the spectral lines and increasing the complexity of the spectrum. Although low pressure can reduce the collision and interaction between molecules, thereby simplifying the spectral structure, and improving the signal-to-noise ratio, and obtaining a clearer spectral signal. However, too low pressure will also cause the intensity of the spectral signal to become low. The present invention improves the arrangement and orientation of stable molecules by limiting the pressure of measurement, so that the spectral characteristics are more prominent.

[0038] In the present invention, the data processing in step 4) includes integrating the spectral analysis results to obtain the peak areas corresponding to different isotopes, and using the peak areas to obtain the isotope abundance.

[0039] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0040] Example 1

[0041] Will be known 13A carbon dioxide gas sample with a C abundance (55%) is collected in a gas cylinder. A particle filter is used to filter out dust, fibers and other solid impurities in the gas sample, and then the filtered gas sample is separated and filtered through a PDMS membrane. After the filtration is completed, activated carbon is used for adsorption twice (the activated carbon is ordinary commercially available coconut shell activated carbon, the thickness of the activated carbon adsorption layer is 5 cm, and the gas sample flow rate per 100 square centimeters is 2.5 L / min). After the adsorption is completed, silica gel drying is used to remove moisture from the gas sample. Then, the condensation method is used to obtain high-purity carbon dioxide gas. The treated carbon dioxide gas is pressurized to 1.3 MPa and then introduced into the optical path of the Fourier transform infrared spectrometer. The wavelength range is adjusted to cover the specific area of ​​the carbon dioxide gas absorption spectrum, and a spectral scan is performed. The scanning results are integrated to obtain the following results: 12 C. 13 The peak area corresponding to C. Calculation 13 The peak area of ​​C 12 C and 13 The ratio of the sum of the C peak areas is obtained. 13 The abundance of C is 54.96%.

[0042] Example 2

[0043] Will be known 13 A carbon dioxide gas sample with a C abundance (5%) is collected in a gas cylinder. A particle filter is used to filter out dust, fibers and other solid impurities in the gas sample, and then the filtered gas sample is separated and filtered through a PDMS membrane. After the filtration is completed, activated carbon is used for adsorption 3 times (the activated carbon is ordinary commercially available coconut shell activated carbon, the thickness of the activated carbon adsorption layer is 3 cm, and the gas sample flow rate per 100 square centimeters is 1.5 L / min). After the adsorption is completed, silica gel drying is used to remove moisture from the gas sample. Then, the condensation method is used to obtain high-purity carbon dioxide gas. The treated carbon dioxide gas is pressurized to 1.5 MPa and then introduced into the optical path of the Fourier transform infrared spectrometer. The wavelength range is adjusted to cover the specific area of ​​the carbon dioxide gas absorption spectrum, and a spectral scan is performed. The scanning results are integrated to obtain the following results: 12 C. 13 The peak area corresponding to C. Calculation 13 The peak area of ​​C 12 C and 13 The ratio of the sum of the C peak areas is obtained. 13 The abundance of C is 4.93%.

[0044] Embodiment 3:

[0045] The detection method described in Example 2 was used to detect the known 13 The test results of the carbon dioxide gas sample with a C abundance of 2% are 13 The abundance of C is 2.06%.

[0046] Embodiment 4:

[0047] The carbon dioxide gas sample is collected in a gas cylinder, and a particle filter is used to filter out dust, fiber and other solid impurities in the gas sample. The filtered gas sample is then separated and filtered through a PDMS membrane. After the filtration is completed, activated carbon is used for adsorption twice (the activated carbon is ordinary commercially available coconut shell activated carbon, the thickness of the activated carbon adsorption layer is 5 cm, and the gas sample flow rate per 100 square centimeters is 2.5 L / min). After the adsorption is completed, silica gel drying is used to remove moisture from the gas sample. Then, a condensation method is used to obtain high-purity carbon dioxide gas. The treated carbon dioxide gas is pressurized to 1.3 MPa and then introduced into the optical path of the Fourier transform infrared spectrometer. The wavelength range is adjusted to cover the specific area of ​​the carbon dioxide gas absorption spectrum, and a spectral scan is performed. The scanning results are integrated to obtain the following results: 12 C. 13 The peak area corresponding to C. Calculation 13 The peak area of ​​C 12 C and 13 The ratio of the sum of the C peak areas is obtained. 13 The abundance of C was 0.67%, which was verified by mass spectrometry to be 0.67%.

[0048] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0049] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring gas stable isotopes based on spectral analysis, It is characterized in that The steps include: 1) Collecting a gas sample containing the stable isotope to be measured; 2) Gas sample pretreatment: purifying and concentrating the gas sample in sequence to obtain a pretreated gas sample; 3) Spectral scanning: introducing the pretreated gas sample into the optical path of the infrared spectrometer for analysis to obtain the spectral analysis results; 4) Processing the spectrum analysis results to obtain the measurement results of gas stable isotopes; The gas sample contains carbon dioxide gas.

2. A method for measuring gas stable isotopes based on spectral analysis according to claim 1, It is characterized in that The purification in step 2) includes filtration, adsorption and drying performed in sequence.

3. A method for measuring gas stable isotopes based on spectral analysis according to claim 2, It is characterized in that The filtration is first performed using a particle filter and then a membrane separation filter.

4. A method for measuring gas stable isotopes based on spectral analysis according to claim 3, It is characterized in that The adsorption is performed using activated carbon.

5. A method for measuring gas stable isotopes based on spectral analysis according to claim 4, It is characterized in that The drying is performed using a chemical drying agent.

6. A method for measuring gas stable isotopes based on spectral analysis according to any one of claims 1 to 5, It is characterized in that The concentration is to obtain concentrated carbon dioxide gas by condensation.

7. A method for measuring gas stable isotopes based on spectral analysis according to claim 6, It is characterized in that The pressure measured in step 3) is 1.2-1.5 MPa.

8. The method for measuring gas stable isotopes based on spectral analysis according to claim 7, It is characterized in that The data processing in step 4) includes integrating the spectral analysis results to obtain the peak areas corresponding to different isotopes, and using the peak areas to obtain the isotope abundance.