Device and method for automatically analyzing carbon isotope in deep sea water dissolved gas

Abstract

The invention discloses an automatic analysis device and method for carbon isotope in deep sea water dissolved gas, and relates to the technical field of laser spectrum analysis, the device comprises an automatic sample introduction unit and a laser spectrum detection unit; the automatic sample injection unit is used for automatic sample injection of seawater separation sample gas and sample injection of standard gas; the laser spectrum detection unit is used for executing the functions of spectrum data acquisition, signal-to-noise ratio enhancement, data post-processing and carbon isotope composition calculation; the laser spectrum detection unit comprises three lasers, and the first laser is a methane laser corresponding to a main methane absorption spectral line; the second laser is a methane isotope laser and corresponds to 12CH4 and 13CH4 methane isotope absorption spectral lines; and the third laser is a carbon dioxide isotope laser and corresponds to carbon dioxide isotope absorption spectral lines of 12CO2 and 13CO2. The carbon isotope of methane and carbon dioxide gas dissolved in deep sea water is detected by using an automatic sample injection and automatic measurement method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser spectrum analysis, in particular to an automatic analysis device and method for carbon isotope of dissolved gas in deep-sea water. BACKGROUND

[0002] A large amount of carbon is stored in deep-sea natural hydrate, and the analysis of carbon isotope in deep-sea can help to understand the long-term behavior of the stored carbon in the natural environment and the potential release risk. The carbon isotope composition of dissolved methane and carbon dioxide gas in deep-sea water is a key indicator for revealing the response mechanism of seafloor hydrothermal activity, cold spring leakage, biogeochemical cycle and climate change. The traditional method relies on ship-borne sampling and laboratory analysis, but the sample is prone to be contaminated, gas to escape or isotopic fractionation during transportation, resulting in reduced data reliability.

[0003] The current commercial isotope analysis device is usually large in size and lacks self-calibration capability, and cannot realize long-term continuous monitoring. At the same time, the synchronous analysis of multi-component gas requires complicated pretreatment, and lacks online self-calibration function, and long-term measurement is prone to data drift. SUMMARY

[0004] In order to overcome the defects in the prior art, the present application provides an automatic analysis device for carbon isotope of dissolved gas in deep-sea water, which uses an automatic sampling and measuring method to detect the carbon isotope of dissolved methane and carbon dioxide gas in deep-sea water.

[0005] To achieve the above purpose, the present application adopts the following technical scheme, comprising:

[0006] The automatic analysis device for carbon isotope of dissolved gas in deep-sea water comprises an automatic sampling unit and a laser spectrum detection unit;

[0007] The automatic sampling unit comprises a gas inlet pipe, a filter, a sample gas solenoid valve, a three-way valve, a gas inlet solenoid valve, an optical cavity, a gas outlet solenoid valve, a gas outlet pipe, a check valve and a vacuum pump connected in sequence, and is used for automatic sampling of seawater separated sample gas, i.e. sample gas;

[0008] The laser spectrum detection unit comprises a first laser controller, a second laser controller, a third laser controller, a first laser, a second laser, a third laser, a first collimating optical fiber, a second collimating optical fiber, a third collimating optical fiber, an optical cavity, a focusing lens, a detector, an upper computer, a collection card and a noise source, and is used for performing functions of spectrum data collection, signal-to-noise ratio enhancement, data post-processing, and calculation of methane isotope concentration and abundance and calculation of carbon dioxide isotope concentration and abundance;

[0009] The first laser is a methane laser corresponding to a main methane absorption spectrum line; the second laser is a methane isotope laser corresponding to a methane isotope absorption spectrum line; and the third laser is a carbon dioxide isotope laser corresponding to a carbon dioxide isotope absorption spectrum line. 12CH4, 13 CH4methane isotope absorption spectrum line; the third laser is a carbon dioxide isotope laser, corresponding 12 CO2, 13 CO2carbon dioxide isotope absorption spectrum line;

[0010] Each laser controller introduces a suitable power noise source into the corresponding laser, each laser controller controls the corresponding laser to generate laser light, and the laser light is off-axis incident into the optical cavity through the corresponding collimating optical fiber. The optical cavity is an off-axis integrating cavity. The laser light emitted by the optical cavity is focused by a focusing lens and received by a detector. The detector collects the optical spectrum signal and sends it to the acquisition card, which then sends it to the host computer.

[0011] Preferably, the automatic sampling unit further comprises a standard gas bottle and a standard gas electromagnetic valve for sampling standard gas; the standard gas bottle stores standard gas mixed with methane and carbon dioxide, and is connected to the three-way valve through the standard gas electromagnetic valve, and then connected to the optical cavity through the gas inlet electromagnetic valve;

[0012] The standard gas is introduced into the optical cavity to calibrate the device, and the obtained calibration data is used to correct the isotope calculation model.

[0013] Preferably, the device further comprises a signal acquisition unit; the signal acquisition unit comprises a temperature sensor and a pressure sensor arranged on the optical cavity, for acquiring temperature and pressure data of the optical cavity and sending them to the host computer.

[0014] Preferably, the device further comprises a circuit control unit, which drives the switches of the sample gas electromagnetic valve, the standard gas electromagnetic valve, the gas inlet electromagnetic valve, the gas outlet electromagnetic valve and the vacuum pump based on the pressure data of the optical cavity, to realize automatic control of sample gas sampling.

[0015] Preferably, the host computer inverses the methane concentration according to the measurement data of the first laser, and executes different calculation strategies according to the inverted methane concentration:

[0016] When the methane concentration is less than or equal to the first methane concentration threshold k1, the first laser and the second laser are used for measurement at the same time, and the methane concentration, the methane isotope concentration and the methane isotope abundance are calculated according to the measurement data of the first laser and the second laser and the line strength of the corresponding absorption spectrum line, wherein linear fitting is used between the methane concentration, the methane isotope concentration and the peak value;

[0017] When the methane concentration is greater than the first methane concentration threshold k1, switch to measuring only with the second laser, and calculate the methane concentration, methane isotope concentration, and methane isotope abundance based on the measurement data of the second laser and the line strength of the corresponding absorption line; among them, when the methane concentration is greater than the first methane concentration threshold k1 and less than or equal to the second methane concentration threshold k2, linear fitting is used between the methane concentration, methane isotope concentration, and the peak value, and when the methane concentration is greater than the second methane concentration threshold k2, polynomial fitting is used between the methane concentration, methane isotope concentration, and the peak value, where k2 > k1.

[0018] Preferably, the calculation method of the isotope abundance is as follows:

[0019]

[0020] Among them, R std is the VPDB standard value, with a value of 0.011125; C 13 is the concentration of the heavy isotope, that is 13 CH4 or 13 CO2 concentration, C 12 is the concentration of the light isotope, that is 12 CH4 or 12 CO2 concentration, δ 13 C(‰) is the isotope abundance.

[0021] Preferably, after measuring the standard gas, use the correction coefficient K = δ ref / δ meas to correct the isotope calculation model, where δ ref represents the standard value of the standard gas, and δ meas represents the measured value of the standard gas; multiply the measured value of the subsequent sample gas by the correction coefficient K.

[0022] The present invention also provides a working method applicable to the deep - sea seawater dissolved gas carbon isotope automatic analysis device described above, including the following steps:

[0023] S1. Cavity evacuation: Automatically open the vacuum pump and the outlet solenoid valve, and pump the pressure inside the optical cavity to be lower than the first pressure value V1;

[0024] S2. Quantitative sample injection: When the pressure inside the cavity is lower than the first pressure threshold V1, automatically open the sample gas solenoid valve and the inlet solenoid valve; when the pressure inside the cavity reaches the second pressure value V2, automatically close the sample gas solenoid valve and the inlet solenoid valve;

[0025] S3. Precise analysis: Automatically open the vacuum pump and the outlet solenoid valve to adjust the pressure inside the cavity to the third pressure value V3, where V1 < V3 < V2, close all solenoid valves, at this time the laser spectroscopy detection unit starts to work, and the detector collects spectral data for carbon isotope analysis;

[0026] S4, automatic cleaning and circulation: after the analysis is completed, the vacuum pump and the outlet electromagnetic valve are automatically opened to empty the cavity, and when the pressure in the optical cavity is extracted to be lower than the first pressure threshold V1, the next cycle is entered.

[0027] Preferably, the working method further comprises the following steps:

[0028] S5, periodic calibration: the standard gas cylinder stores standard gas mixed with methane and carbon dioxide, the standard gas cylinder is connected to the three-way valve through the standard gas electromagnetic valve, and then connected to the optical cavity through the inlet electromagnetic valve, and the standard gas sampling process is automatically started periodically to introduce the standard gas into the optical cavity for analysis, and the obtained calibration data is used to correct the isotope calculation model in real time.

[0029] The application also provides a computer program product comprising computer programs / instructions which, when executed by a processor, implement the working method of the deep-sea seawater dissolved gas carbon isotope automatic analysis device.

[0030] The application has the advantages that:

[0031] (1) The core of the application is to propose an automatic carbon isotope analysis device integrating off-axis integrated cavity output spectrum technology and fully automatic sampling control, which breaks through the limitations of traditional shipborne sampling and indoor analysis, and is particularly suitable for the harsh requirements of deep-sea environment and the low-concentration and high-precision challenges of dissolved gas analysis. The off-axis integrated cavity output spectrum technology is applied to the deep-sea environment, and the long optical path feature makes it have high sensitivity, which is suitable for low-concentration dissolved gas. Combined with high-pressure sealed integrated packaging anti-vibration interference, the automatic sampling and automatic measurement method is used to detect the dissolved methane and carbon dioxide gas carbon isotopes in deep-sea water, and the periodic standard gas correction can realize unattended deep-sea exploration.

[0032] (2) The application configures special lasers for methane, methane isotopes and carbon dioxide isotopes respectively, accurately matches characteristic absorption spectral lines, reduces cross interference, and ensures detection specificity.

[0033] (3) The application introduces a standard gas cylinder and a calibration process, periodically automatically performs a calibration cycle of standard gas, calculates a correction coefficient through the measured value and the standard value of the standard gas, corrects the isotope calculation model in real time, and reduces system error.

[0034] (4) The degree of automation of the present application is high, reduces human error, and adapts to complex environments. The device realizes full-process automation through an automatic sampling unit (solenoid valve, vacuum pump, pressure sensor linkage) and a circuit control unit, from cavity emptying, quantitative sampling, pressure regulation to automatic cleaning cycle, without manual intervention. This feature not only reduces errors caused by human operation (such as inconsistent sample size and pollution risk), but is also particularly suitable for extreme environments such as deep sea where direct human operation is difficult, and can support long-term unattended monitoring.

[0035] (5) The detection range of the present application is wide, taking into account high and low concentration samples, improving applicability, and using a "segmented detection strategy" for different concentrations of dissolved gas: for low concentration, a combination of main methane laser and isotope laser is used to ensure detection sensitivity at low concentration; for high concentration, switch to isotope laser alone for detection, and further distinguish between linear fitting and polynomial fitting according to concentration, effectively avoiding nonlinear interference at high concentration. This design significantly expands the applicable concentration range of the device, which can accurately analyze low-concentration dissolved gas in deep sea and also cope with high-concentration samples, improving the adaptability to complex marine environments.

[0036] (6) The present application uses an off-axis integral cavity design to extend the optical path and enhance the intensity of the spectral signal. By introducing a noise source in cooperation with the laser controller, the signal-to-noise ratio (SNR) of the spectral signal is improved, and the recognition ability of low-concentration signals is improved. Equipped with temperature and pressure sensors, real-time acquisition of temperature and pressure data of the optical cavity can also be used to correct the influence of environmental factors on gas spectral characteristics.

[0037] (7) The present application can efficiently and continuously monitor, reducing the risk of cross-contamination. The automatic cleaning and circulation steps are designed in the working method, and the cavity is completely emptied by the vacuum pump after each analysis to avoid interference of residual samples on the next detection; the pressure is controlled to V2 during quantitative sampling and to V3 during accurate analysis to ensure consistency of each detection, support efficient and continuous monitoring, and be suitable for high-frequency data acquisition of deep-sea long-term observation stations.

[0038] (8) The present application is functionally integrated, easy to operate, and the device integrates automatic sampling, spectral detection, data acquisition, calibration and correction, result calculation and other functions, and realizes full-process control and data processing through the host computer without the need for additional equipment.

[0039] (9) The device of the present application realizes high sensitivity, high accuracy, wide range and automatic analysis of carbon isotopes of dissolved gas in deep sea water through automation design, multi-dimensional correction, segmented detection and integrated functions, providing reliable technical support for marine carbon cycle research, deep sea ecological environment monitoring and other fields. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of the gas path structure of the present application.

[0041] Figure 2 is a schematic diagram of the laser spectrum detection structure of the present application.

[0042] Legend of reference signs:

[0043] 1, gas inlet pipe; 2, filter; 3, sample gas solenoid valve; 4, three-way valve; 5, standard gas solenoid valve; 6, standard gas cylinder; 7, gas inlet solenoid valve; 8, optical cavity; 9, gas outlet solenoid valve; 10, check valve; 11, vacuum pump; 12, gas outlet pipe; 13, temperature sensor; 14, pressure sensor; 15, focusing lens; 16, detector; 17, host computer; 18, acquisition card; 19, noise source; 20, first laser controller; 21, second laser controller; 22, third laser controller; 23, first laser; 24, second laser; 25, third laser; 26, first collimating optical fiber; 27, second collimating optical fiber; 28, third collimating optical fiber. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0045] The deep-sea seawater dissolved gas carbon isotope automatic analysis device comprises an automatic sampling unit, a laser spectrum detection unit, a circuit control unit and a signal acquisition unit. All the units are packaged in a high-pressure sealed instrument, and seawater separated sample gas is provided by an external main control equipment.

[0046] As shown in Figure 1 , the automatic sampling unit comprises a gas inlet pipe 1, a filter 2, a sample gas solenoid valve 3, a three-way valve 4, a gas inlet solenoid valve 7, an optical cavity 8, a gas outlet solenoid valve 9, a check valve 10 and a vacuum pump 11. Among them: the gas inlet part is connected by the gas inlet pipe 1, the filter 2, the sample gas solenoid valve 3, the three-way valve 4, the gas inlet solenoid valve 7 and the optical cavity 8, when the automatic gas inlet, the optical cavity 8 is in a low pressure state, the sample gas is automatically absorbed into the cavity by the pressure, realizing the automatic sampling function; when the sample gas solenoid valve 3, the gas inlet solenoid valve 7 and the gas outlet solenoid valve 9 are all closed, the gas in the optical cavity 8 is in a relatively static state, realizing the measurement function; the gas outlet part is connected by the optical cavity 8, the gas outlet solenoid valve 9, the gas outlet pipe 12, the check valve 10 and the vacuum pump 11, the optical cavity 8 is pumped, and when the set threshold value is reached, the automatic stop is realized.

[0047] As shown in Figure 1As shown, the automatic sample introduction unit also includes a standard gas solenoid valve 5 and a standard gas cylinder 6. The standard gas cylinder 6 stores a standard gas mixture of methane and carbon dioxide. The standard gas cylinder 6 is connected to a three-way valve 4 via the standard gas solenoid valve 5, and then connected to the optical cavity 8 via the inlet solenoid valve 7. The circuit control unit periodically initiates the standard gas injection process to automatically calibrate the device and obtain correction coefficients used to correct the isotope calculation model.

[0048] like Figure 2 As shown, the laser spectral detection unit consists of a first laser controller 20, a second laser controller 21, a third laser controller 22, a first laser 23, a second laser 24, a third laser 25, a first collimating fiber 26, a second collimating fiber 27, a third collimating fiber, an optical cavity 8, a focusing lens 15, a detector 16, a data acquisition card 18, a host computer 17, and a noise source 19. It is used to perform functions such as spectral data acquisition, signal-to-noise ratio enhancement, data post-processing, and calculation of methane isotope concentration and abundance, and calculation of carbon dioxide isotope concentration and abundance.

[0049] Each laser controller controls its corresponding laser to generate laser light, which is then incident off-axis into the optical cavity 8 via its corresponding collimating fiber. The first laser 23 is a methane laser, corresponding to the main methane absorption line, and is controlled by the first laser controller 20. The emitted laser light is incident into the optical cavity 8 via the first collimating fiber 26. The second laser 24 is a methane isotope laser, corresponding to... 12 CH4 13 The CH4 methane isotope absorption spectrum is controlled by the second laser controller 21, and the emitted laser light is incident into the optical cavity 8 via the second collimating fiber 27. The third laser 25 is a carbon dioxide isotope laser, corresponding to... 12 CO2, 13 The CO2 carbon dioxide isotope absorption spectrum is controlled by the third laser controller 22, and the emitted laser is incident into the optical cavity 8 through the third collimating fiber 28.

[0050] Each laser controller introduces a noise source 19 of appropriate power into the corresponding laser to increase the laser linewidth and reduce cavity mode noise.

[0051] Optical cavity 8 is an off-axis integrating cavity. By adjusting the two high-reflectivity lenses with reflective films and reflectivity greater than 99.99% at both ends of optical cavity 8, the high-reflectivity lenses are made coaxial with optical cavity 8, and the laser is incident off-axis and forms optical resonance in optical cavity 8, forming a stable off-axis integrating cavity and increasing the effective absorption optical path.

[0052] The laser emitted from the optical cavity 8 is focused by the focusing lens 15 and received by the detector 16. The detector 16 collects the spectral signal and sends it to the acquisition card 18, which then sends it to the host computer 17.

[0053] The signal acquisition unit comprises a temperature sensor 13 and a pressure sensor 14 arranged on the optical cavity 8, for acquiring temperature and pressure data of the optical cavity 8 and sending to the host computer 17.

[0054] The circuit control unit comprises a power supply part and a control part, the power supply part realizes the power supply function of all electronic devices in the device, including the power supply of the detector 16, the first laser controller 20, the second laser controller 21, the third laser controller 22, the acquisition card 18, the noise source 19, and the host computer 17; the control part realizes the switching of all electromagnetic valves (sample gas electromagnetic valve 3, inlet gas electromagnetic valve 7, outlet gas electromagnetic valve 9) and the vacuum pump 11 in the device, specifically, the host computer 17 sends a binary instruction to the circuit control unit according to the temperature and pressure data of the optical cavity 8, the circuit control unit receives the binary instruction sent by the host computer 17, and then immediately performs the power-on and power-off operation on the corresponding electromagnetic valve and vacuum pump 11.

[0055] The acquisition card 18 time-division multiplexes to generate a triangular wave scanning signal, which is sequentially output to the first laser controller 20, the second laser controller 21 and the third laser controller 22, to drive the corresponding laser to scan the laser wavelength.

[0056] In the present application, the host computer 17 obtains the methane concentration by inversion according to the measurement data of the first laser 23, and performs different calculation strategies according to the inverted methane concentration:

[0057] When the methane concentration is in a low concentration range (1-20 ppm), i.e., less than or equal to the first methane concentration threshold k1 (k1=20 ppm), the measurement data of the first laser 23 (main methane) and the second laser 24 (methane isotope) and the line strength of the corresponding absorption spectrum are used to calculate the methane concentration, the methane isotope concentration and the methane isotope abundance. This strategy takes advantage of the higher line strength of the main methane absorption spectrum at low concentrations, achieving higher measurement accuracy and sensitivity. Among them, linear fitting is used between the methane concentration, the methane isotope concentration and the peak value.

[0058] When the methane concentration exceeds 20 ppm, the measurement is switched to use only the second laser 24 (methane isotope). The methane concentration, methane isotope concentration, and methane isotope abundance are calculated based on the measurement data from the second laser 24 and the line intensity of the corresponding absorption lines. This is because the main methane absorption line may saturate at high concentrations, while the isotope absorption lines are relatively weaker and less prone to saturation. This strategy avoids the saturation effect and effectively extends the instrument's measurement range in high concentration areas. Specifically, within the methane concentration range of 20 ppm to 50 ppm, linear fitting is used between the methane concentration, methane isotope concentration, and peak value. Within the methane concentration range of 50 ppm to 3000 ppm, polynomial fitting is used between the methane concentration, methane isotope concentration, and peak value.

[0059] Different measurement line strengths and fitting methods are used for different concentration ranges. This concentration-based measurement method switching not only expands the range of methane concentration that the instrument can measure, but also ensures high-precision measurement in the low concentration range and effective measurement in the high concentration range.

[0060] Isotopic abundance is calculated using the following formula:

[0061]

[0062] Among them, R s R represents the concentration ratio of the gas in the sample being tested. std The VPDB standard value is 0.011125; C 13 Heavy isotopes ( 13 CH4 or 13 CO2 concentration; C 12 Light isotopes ( 12 CH4 or 12 CO2 concentration; δ 13 C(‰) represents the isotopic abundance.

[0063] Standard gas is periodically introduced into optical cavity 8 for device calibration. The obtained calibration data is used to correct the isotope calculation model, addressing baseline drift, optical path attenuation, and laser wavelength shift issues during long-term operation, thus ensuring the long-term stability of isotope abundance measurements. After standard gas measurement, a correction coefficient K = δ is used. ref / δ meas Correction is performed, where δ ref δ represents the standard value of the abundance of a standard gas. meas This represents the abundance measurement of the standard gas. Subsequently, the abundance measurement of the sample gas is multiplied by the correction factor K.

[0064] In the present application, the core of the methane concentration, carbon dioxide concentration and carbon isotope abundance calculation based on laser absorption spectrum technology is to establish the correlation between the measurement signal and the gas concentration through the Beer-Lambert Law, and to realize quantitative analysis combined with spectral line intensity.

[0065] The working method of the deep-sea seawater dissolved gas carbon isotope automatic analysis device is as follows:

[0066] S1, cavity evacuation: automatically open the vacuum pump 11 and the outlet gas electromagnetic valve 9, and the pressure in the optical cavity 8 is extracted to be lower than the first pressure value 4torr;

[0067] S2, quantitative sampling: when the pressure in the cavity is lower than the first pressure value 4torr, automatically open the sample gas electromagnetic valve 3 and the inlet gas electromagnetic valve 7; when the pressure in the cavity reaches the set gas inlet requirement, that is, reaches the second pressure value 40torr, automatically close the sample gas electromagnetic valve 3 and the inlet gas electromagnetic valve 7;

[0068] S3, accurate analysis: automatically open the vacuum pump 11 and the outlet gas electromagnetic valve 9 to accurately adjust the pressure in the cavity to the third pressure value 32torr, close all electromagnetic valves, at this time the laser spectrum detection unit starts to work, the probe 16 collects spectrum data, and the host computer 17 carries out carbon isotope analysis; during this process, all pipelines and the optical cavity 8 are kept relatively static, and according to the measurement requirement, the set time is 3h;

[0069] S4, automatic cleaning and circulation: after the analysis is completed, the vacuum pump 11 and the outlet gas electromagnetic valve 9 are automatically opened to evacuate the cavity, and when the pressure is extracted to be lower than the first pressure value 4torr, the next cycle is entered;

[0070] S5, regular calibration, the standard gas bottle 6 stores standard gas mixed with methane and carbon dioxide, the standard gas bottle 6 is connected to the three-way valve 4 through the standard gas electromagnetic valve 5, and then connected to the optical cavity 8 through the inlet gas electromagnetic valve 7, the circuit control unit automatically starts the standard gas sampling process at regular intervals, that is, automatically opens the standard gas electromagnetic valve 5 and the inlet gas electromagnetic valve 7, and closes the sample gas electromagnetic valve 3, and the standard gas is introduced into the optical cavity 8 for analysis, and the obtained calibration data is used for real-time correction of the isotope calculation model.

[0071] The above is only a preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An apparatus for automatic analysis of carbon isotope of dissolved gas in deep-sea water, characterized by, The device comprises an automatic sampling unit and a laser spectrum detection unit. The automatic sampling unit comprises a gas inlet pipe (1), a filter (2), a sample gas solenoid valve (3), a three-way valve (4), a gas inlet solenoid valve (7), an optical cavity (8), a gas outlet solenoid valve (9), a gas outlet pipe (12), a check valve (10) and a vacuum pump (11) connected in sequence, for automatic sampling of seawater separated sample gas. The laser spectrum detection unit comprises a first laser controller (20), a second laser controller (21), a third laser controller (22), a first laser (23), a second laser (24), a third laser (25), a first collimating optical fiber (26), a second collimating optical fiber (27), a third collimating optical fiber (28), an optical cavity (8), a focusing lens (15), a detector (16), a host computer (17), a data acquisition card (18) and a noise source (19), for performing functions of spectrum data acquisition, signal-to-noise ratio enhancement, data post-processing, methane isotopic concentration and abundance calculation, and carbon dioxide isotopic concentration and abundance calculation. Wherein, the first laser (23) is a methane laser, corresponding to a main methane absorption spectrum line; the second laser (24) is a methane isotope laser, corresponding to a 12 CH4, 13 CH4a methane isotope absorption spectrum line; the third laser (25) is a carbon dioxide isotope laser, corresponding to a 12 CO2, 13 CO2a carbon dioxide isotope absorption spectrum line; Each laser controller introduces a suitable power noise source (19) into the corresponding laser, each laser controller controls the corresponding laser to generate laser light, and the laser light is incident into the optical cavity (8) through the corresponding collimating optical fiber off-axis, the optical cavity (8) is an off-axis integrating cavity, the laser light emitted from the optical cavity (8) is focused by the focusing lens (15) and then received by the detector (16), the detector (16) acquires the spectrum signal and sends it into the data acquisition card (18), and then the data acquisition card (18) sends the spectrum signal to the host computer (17).

2. The apparatus according to claim 1, wherein The automatic sampling unit further comprises a standard gas bottle (6) and a standard gas solenoid valve (5) for sampling of standard gas; the standard gas bottle (6) stores standard gas mixed with methane and carbon dioxide, and is connected to the three-way valve (4) through the standard gas solenoid valve (5), and then connected to the optical cavity (8) through the gas inlet solenoid valve (7); The standard gas is introduced into the optical cavity (8) for device calibration, and the obtained calibration data are used for correcting the isotopic calculation model.

3. The apparatus according to claim 1, wherein The device further comprises a signal acquisition unit; the signal acquisition unit comprises a temperature sensor (13) and a pressure sensor (14) arranged on the optical cavity (8), for acquiring temperature and pressure data of the optical cavity (8) and sending them to the host computer (17).

4. The apparatus according to claim 1, wherein The device further comprises a circuit control unit, which drives the switches of the sample gas solenoid valve (3), the standard gas solenoid valve (5), the gas inlet solenoid valve (7), the gas outlet solenoid valve (9) and the vacuum pump (11) based on the pressure data of the optical cavity (8), to realize automatic control of sample gas sampling.

5. The apparatus according to claim 1, wherein The host computer (17) obtains the methane concentration by inversion according to the measurement data of the first laser (23), and performs different calculation strategies according to the inverted methane concentration: When the methane concentration is less than or equal to the first methane concentration threshold k1, the first laser (23) and the second laser (24) are used to measure simultaneously, and the methane concentration, the methane isotope concentration and the methane isotope abundance are calculated according to the measurement data of the first laser (23) and the second laser (24) and the line strength of the corresponding absorption spectral line, wherein linear fitting is used between the methane concentration, the methane isotope concentration and the peak value; When the methane concentration is greater than the first methane concentration threshold k1, only the second laser (24) is used to measure, and the methane concentration, the methane isotope concentration and the methane isotope abundance are calculated according to the measurement data of the second laser (24) and the line strength of the corresponding absorption spectral line; wherein when the methane concentration is greater than the first methane concentration threshold k1 and less than or equal to the second methane concentration threshold k2, linear fitting is used between the methane concentration, the methane isotope concentration and the peak value, and when the methane concentration is greater than the second methane concentration threshold k2, polynomial fitting is used between the methane concentration, the methane isotope concentration and the peak value, k2>k1.

6. The apparatus according to claim 1 or 5, wherein The isotope abundance calculation method is as follows: wherein R std is the VPDB standard value, which is 0.011125; C 13 is the heavy isotope, i.e. 13 CH4or 13 CO2concentration, C 12 is the light isotope, i.e. 12 CH4or 12 CO2concentration, δ 13 C (‰) is the isotopic abundance.

7. The apparatus according to claim 2, wherein After the standard gas measurement, the correction factor K = δ ref / δ meas The isotope calculation model is corrected, where δ ref represents the standard value of the standard gas, δ meas represents the measured value of the standard gas; the measured value of the subsequent sample gas is multiplied by the correction factor K.

8. A method of operation for the deep-sea seawater dissolved gas carbon isotope automatic analyzer according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: S1, cavity evacuation: automatically open the vacuum pump (11) and the outlet electromagnetic valve (9), and evacuate the cavity pressure of the optical cavity (8) to be lower than the first pressure value V1; S2, quantitative sampling: after the cavity pressure is lower than the first pressure threshold V1, automatically open the sample gas electromagnetic valve (3) and the inlet electromagnetic valve (7); when the cavity pressure reaches the second pressure value V2, automatically close the sample gas electromagnetic valve (3) and the inlet electromagnetic valve (7); S3, accurate analysis: automatically open the vacuum pump (11) and the outlet electromagnetic valve (9) to adjust the cavity pressure to the third pressure value V3, V1 S4, automatic cleaning and circulation: after the analysis is completed, the vacuum pump (11) and the outlet electromagnetic valve (9) are automatically opened for cavity evacuation, and when the cavity pressure of the optical cavity (8) is evacuated to be lower than the first pressure threshold V1, the next cycle is entered.

9. The method of claim 8, wherein the deep-sea seawater dissolved gas carbon isotope autoanalyzer is operated by the steps of: Further comprising the following steps: S5, regular calibration: the standard gas bottle (6) stores standard gas mixed with methane and carbon dioxide, the standard gas bottle (6) is connected to the three-way valve (4) through the standard gas electromagnetic valve (5), and then connected to the optical cavity (8) through the inlet electromagnetic valve (7), the sampling process of the standard gas is automatically started regularly, the standard gas is introduced into the optical cavity (8) for analysis, and the obtained calibration data is used for real-time correction of the isotope calculation model.

10. A computer program product, characterised in that, It comprises computer programs / instructions which are executed by a processor to realize the working method of the deep-sea seawater dissolved gas carbon isotope automatic analysis device according to any one of claims 8-9.

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