Rapid nondestructive quantitative analysis method for mixed gas based on Raman spectrum

Abstract

The invention discloses a Raman spectrum-based rapid nondestructive quantitative analysis method for mixed gas, which relates to the technical field of internal standard method Raman spectrum quantification and can be used for rapid quantitative analysis of mixed gas. According to the internal standard method, an appropriate internal standard substance is selected from a Raman spectrum, an internal standard peak of the internal standard substance and a Raman peak of the mixed target gas are located in the same spectrum, the concentration of the internal standard gas does not change before and after the target substance is detected, and then the concentration change of the mixed target gas is inversed in real time by detecting the change before and after the air pressure in the cabin and calibrating the internal standard peak. According to the method, errors caused by factors such as equipment and environment are reduced through an internal standard method, and the air pressure change of the detection cabin is further used as calibration of the internal standard peak intensity, so that the more accurate target gas concentration is inverted, and the quantitative analysis speed of the mixed gas is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of mixed gas quantitative analysis, and more particularly to a mixed gas rapid non-destructive quantitative analysis method based on Raman spectroscopy. Background Art

[0002] Quantitative analysis of mixed gases is of great significance in many fields such as environmental monitoring, industrial production, scientific research and safety monitoring. It can not only be used to monitor and evaluate the quality of water resources, soil resources, etc., but also to monitor and warn of dangerous situations such as fire and explosion. It is an important means to protect human health and environmental safety. Therefore, how to quickly and accurately monitor the concentration changes of mixed gases in real time is very important. And the detection technology of obtaining the concentration changes of mixed gases quickly, in real time and with high precision has become a challenge.

[0003] At present, the quantitative analysis methods used for mixed gases mainly include: spectral analysis, electrochemistry, and mass spectrometry quantitative analysis methods. Different gases in infrared spectroscopy and ultraviolet spectroscopy will absorb infrared light of specific wavelengths, which limits the wavelength range of the laser. The mass spectrometry quantitative analysis method is costly and difficult to operate, and electrochemistry can be destructive to the target. Raman spectroscopy is an optical detection method that can quickly and non-contact quantitatively analyze the concentration of mixed gases in real time, but this technology is difficult to quickly perform quantitative analysis on dynamically changing mixed gases. Based on this, there is an urgent need for a fast, real-time, high-precision, non-contact detection method for the concentration of mixed gases. Summary of the invention

[0004] In view of this, the present invention provides a method for rapid dynamic quantitative analysis of the concentration of a mixed gas based on Raman spectroscopy, which combines the internal standard quantitative analysis method of the spectrum and the chemometric method, fully utilizes the two analysis methods to dynamically quantitatively analyze the concentration of the mixed gas, and simultaneously utilizes the difference between the absorption peak measured by the internal standard substance and the calibrated internal standard peak and the change in the pressure in the sealed sample chamber to correct the concentration of the mixed gas, thereby obtaining the concentration of the mixed gas with high precision.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A rapid non-destructive quantitative analysis method for mixed gases based on Raman spectroscopy comprises the following steps:

[0007] (1) Select an internal standard gas, collect the Raman peak of the internal standard gas as the calibration peak, read the air pressure value under the steady state, and calculate the concentration of the internal standard gas;

[0008] (2) collecting Raman peaks of the mixed gas to be tested and the internal standard gas mixture, wherein the Raman peak of the internal standard gas is used as the internal standard peak;

[0009] (3) calculating an error compensation coefficient based on the calibration peak of step (1) and the internal standard peak collected in step (2);

[0010] (4) Calculate the concentration of the mixed gas using the internal standard peak and the Raman peak area of ​​the mixed gas;

[0011] (5) Using the compensation coefficient obtained in step (3), perform pressure correction and calculate the concentration of the mixed gas after compensation.

[0012] Preferably, the internal standard gas in step (1) exists stably and does not react with the mixed gas to be measured.

[0013] Furthermore, the internal standard gas is nitrogen.

[0014] Furthermore, the specific calculation process is as follows:

[0015] The Raman-Stokes scattering intensity of the object to be measured can be:

[0016] I=K′NσI L Formula 1

[0017] Where I represents the Raman Stokes scattering intensity; K′ represents the proportionality coefficient; σ represents the Raman scattering cross section; I L represents the intensity of the stimulated radiation, and N is the concentration;

[0018] It can be seen that the intensity of Raman scattering is related to the concentration of the analyte. The spectral information of the internal standard and the analyte under the same conditions are displayed on a spectrum. The ratio of the two is:

[0019]

[0020] Among them, I R is the Raman-Stokes scattering intensity of the internal standard, N R The concentration of the internal standard, σ R is the Raman scattering cross section of the internal standard;

[0021] From equations 1 and 2, we can see that the concentration of the substance being measured is:

[0022]

[0023] Among them, σ R / σ is used as a constant. If the absorption peaks of the internal standard and the analyte are obtained in the same system, the concentration of the analyte can be expressed as the relative Raman intensity I / I R To analyze;

[0024] When the concentration of the mixed gas in the sealed sample chamber changes dynamically, the state in the sealed sample chamber approximately conforms to the ideal gas state equation, as shown below:

[0025] pV=nRT Formula 4

[0026] Where p is the pressure, V is the gas volume, T is the temperature, n is the amount of gas, and R is the molar gas constant. Therefore, the concentration of the dynamic mixed gas can be expressed as

[0027]

[0028] Where p′=p c / p i , expressed as the pressure variation coefficient; p c 、p i are the initial and current pressures of the sealed sample chamber respectively;

[0029] In a homogeneous phase, the concentration ratio of two Raman-active species a and b can be calculated from the peak area ratio corresponding to a specific vibration band of each of them according to the following formula:

[0030]

[0031] Where A is the peak area of ​​the selected vibration band corresponding to the substance, C is the molar concentration, σ is the Raman scattering coefficient, η is the instrument efficiency coefficient, and F is the Raman quantification factor.

[0032] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a method for rapid non-destructive quantitative analysis of mixed gases based on Raman spectroscopy, which has the following beneficial effects:

[0033] The present invention reduces the errors caused by factors such as equipment and environment through the internal standard method, and further uses the air pressure change in the detection cabin as a calibration for the internal standard peak intensity, thereby inverting a more accurate target gas concentration, greatly improving the speed of quantitative analysis of mixed gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0035] Figure 1 is a flow chart of the method of the present invention;

[0036] Figure 2 This is the Raman map of Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0038] The specific calculation process of the method of the present invention is:

[0039] The Raman-Stokes scattering intensity of the object to be measured can be:

[0040] I=K′NσI L Formula 1

[0041] Where I represents the Raman Stokes scattering intensity; K′ represents the proportionality coefficient; σ represents the Raman scattering cross section; I L represents the intensity of the stimulated radiation, and N is the concentration;

[0042] It can be seen that the intensity of Raman scattering is related to the concentration of the analyte. The spectral information of the internal standard and the analyte under the same conditions are displayed on a spectrum. The ratio of the two is:

[0043]

[0044] Among them, I R is the Raman-Stokes scattering intensity of the internal standard, N R The concentration of the internal standard, σ R is the Raman scattering cross section of the internal standard;

[0045] From equations 1 and 2, we can see that the concentration of the substance being measured is:

[0046]

[0047] Among them, σ R / σ is used as a constant. If the absorption peaks of the internal standard and the analyte are obtained in the same system, the concentration of the analyte can be expressed as the relative Raman intensity I / I R To analyze;

[0048] When the concentration of the mixed gas in the sealed sample chamber changes dynamically, the state in the sealed sample chamber approximately conforms to the ideal gas state equation, as shown below:

[0049] pV=nRT Formula 4

[0050] Where p is the pressure, V is the gas volume, T is the temperature, n is the amount of gas, and R is the molar gas constant. Therefore, the concentration of the dynamic mixed gas can be expressed as

[0051]

[0052] Where p′=p c / p i , expressed as the pressure variation coefficient; p c 、p i are the initial and current pressures of the sealed sample chamber respectively;

[0053] In a homogeneous phase, the concentration ratio of two Raman-active species a and b can be calculated from the peak area ratio corresponding to a specific vibration band of each of them according to the following formula:

[0054]

[0055] Where A is the peak area of ​​the selected vibration band corresponding to the substance, C is the molar concentration, σ is the Raman scattering coefficient, η is the instrument efficiency coefficient, and F is the Raman quantification factor.

[0056] Example 1

[0057] A pressure gauge is installed at the sealed sample hatch, and the internal standard gas in the initial state is injected into the sealed sample hatch (the volume inside the hatch remains unchanged). The initial reading is read through the pressure gauge equipped at the bottle mouth, and the concentration of the internal standard gas is calculated by the pressure;

[0058] Inject the sample (such as mixed gas, gas production sample) into the sample chamber. After stabilization, the current pressure correction coefficient (p′=p c / p i , p c 、p i are the initial and current pressures of the sealed sample chamber respectively);

[0059] Based on the relationship between the peak areas of the internal standard gas and the mixed gas in the Raman spectrum collected at the current moment (the ratio of the internal standard to the analyte concentration is positively correlated with the Raman peak area ratio), the concentrations of each substance in the mixed gas are inverted.

[0060] The relationship between the concentration ratio and the peak area ratio is as follows Figure 2 as shown in .

[0061] A1 and A2 are the Raman peak areas of the unknown mixed gas, C1 and C2 are the concentrations of the unknown mixed gas, and A R , C R is the peak area and concentration of the internal standard, and p′ is the current pressure correction coefficient.

[0062] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0063] 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 rapid non-destructive quantitative analysis method for mixed gases based on Raman spectroscopy, characterized in that: The following steps are involved: (1) Select an internal standard gas, collect the Raman peak of the internal standard gas as the calibration peak, read the air pressure value under the steady state, and calculate the concentration of the internal standard gas; (2) collecting Raman peaks of the mixed gas to be tested and the internal standard gas mixture, wherein the Raman peak of the internal standard gas is used as the internal standard peak; (3) calculating an error compensation coefficient based on the calibration peak of step (1) and the internal standard peak collected in step (2); (4) Calculate the concentration of different gases in the mixed gas using the Raman peak area of ​​the internal standard peak and the mixed gas; (5) Using the compensation coefficient obtained in step (3), perform pressure correction and calculate the concentrations of different gases in the mixed gas after compensation.

2. The method for rapid non-destructive quantitative analysis of mixed gases based on Raman spectroscopy according to claim 1, characterized in that: The internal standard gas in step (1) exists stably and does not react with the mixed gas to be measured.

3. A method for rapid non-destructive quantitative analysis of mixed gases based on Raman spectroscopy according to claim 1 or 2, characterized in that: The internal standard gas in step (1) is nitrogen.

4. The method for rapid non-destructive quantitative analysis of mixed gases based on Raman spectroscopy according to claim 1, characterized in that: The specific calculation process is: The Raman-Stokes scattering intensity of the object to be measured is: I=K′NσI L Formula 1 Where I represents the Raman Stokes scattering intensity; K′ represents the proportionality coefficient; σ represents the Raman scattering cross section; I L represents the intensity of the stimulated radiation, and N is the concentration; The intensity of Raman scattering is related to the concentration of the analyte. The spectral information of the internal standard and the analyte under the same conditions are displayed on a spectrum. The ratio of the two is: Among them, I R is the Raman-Stokes scattering intensity of the internal standard, N R The concentration of the internal standard, σ R is the Raman scattering cross section of the internal standard; From equations 1 and 2, we can see that the concentration of the substance being measured is: Among them, σ R / σ is used as a constant, and the absorption peaks of the internal standard and the analyte are obtained in the same system. The concentration of the analyte is expressed by the relative Raman intensity I / I R analyze; The concentration of the mixed gas in the sealed sample chamber changes dynamically. At this time, the state in the sealed sample chamber approximately conforms to the ideal gas state equation, as shown below: pV=nRT Formula 4 Where p is the pressure, V is the gas volume, T is the temperature, n is the amount of gas, R is the molar gas constant, and the concentration of the dynamic mixed gas is: Where p′=p c / p i , expressed as the pressure variation coefficient; p c 、p i are the initial and current pressures of the sealed sample chamber respectively; In a homogeneous phase, the concentration ratio of two Raman-active species a and b is calculated from the peak area ratio corresponding to one of their specific vibration bands according to the following formula: Where A is the peak area of ​​the selected vibration band corresponding to the substance, C is the molar concentration, σ is the Raman scattering coefficient, η is the instrument efficiency coefficient, and F is the Raman quantification factor.

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