A device for improving signal stability of a vacuum ultraviolet photoionization source through gas absorption.

Abstract

This invention relates to the field of mass spectrometry, specifically to a device for improving the signal stability of a vacuum ultraviolet photoionization source through gas absorption. Vacuum ultraviolet photoionization is a widely used ionization source for mass spectrometry. However, the light window of vacuum ultraviolet light can become contaminated due to organic phase deposition or dust adhesion, leading to a decrease in vacuum ultraviolet light intensity. According to Beer-Lambert law, the decrease in vacuum ultraviolet light intensity reduces ion yield, limiting the sensitivity and stability of optical mass spectrometry. By adding a gas-filled sink between the light source and the ionization chamber, and adjusting the type and pressure of the gas in the absorption cell to control the ultraviolet light transmittance, the device compensates for signal instability caused by fluctuations in the intensity of the vacuum ultraviolet light source. This gas absorption method has good linear compensation capability for signal attenuation caused by light intensity, which helps to improve the stability of photoionization mass spectrometry.

Description

Technical Field

[0001] This invention belongs to the field of mass spectrometry, specifically relating to a device for improving the signal stability of a vacuum ultraviolet photoionization source through gas absorption. Background Technology

[0002] Vacuum ultraviolet (VUV) light can soft ionize organic molecules with an ionization energy (IE) lower than their photon energy, primarily producing molecular ions with almost no fragment ions, making it suitable for rapid qualitative and quantitative analysis. Combining a VUV photoionization source with mass spectrometry yields organic mass spectra containing only molecular ion peaks, resulting in simple spectra that allow for rapid qualitative and quantitative analysis based on molecular weight and signal intensity. In recent years, photoionization sources based on Kr discharge VUV lamps have become an important ionization source technology and have been widely applied. However, the VUV lamp's light window is in direct contact with sample molecules, making it susceptible to contamination and reduced light intensity. Furthermore, the light intensity decreases with prolonged use. In addition to light intensity attenuation, electrode contamination, charge accumulation, and detector efficiency also contribute to signal attenuation. The stability of the photoionization mass spectrometry signal severely limits the quantitative capability of mass spectrometry; therefore, improving the stability of photoionization mass spectrometry is crucial.

[0003] Li Haiyang, Xie Yuanyuan, Hua Lei, and others invented an online automatic correction system and method for ion signal intensity (patent number CN201310691115.5), which includes a continuous signal monitoring program, an online automatic correction program, a voltage parameter control program, a power supply module, and a signal generating device. The continuous signal monitoring program sets the ideal signal value for a specific ion and obtains the current signal value, then feeds it back to the online automatic correction program, which controls the power supply module to automatically adjust the voltage. This invention adjusts the electron accelerating voltage in the ionization source by feeding back the mass spectrometry signal, enhancing electron ionization capability and compensating for signal attenuation caused by electrode contamination or reduced light intensity. However, in practical use, because electron ionization capability is not linearly related to voltage, compensation can easily fail. Li Haiyang, Jiang Jichun, and others invented a method for signal correction in photoionization mass spectrometry (patent number CN201911259722.8), which includes a photoionization source, mass spectrometer, sample introduction tubing, correction gas tubing, flow meter, and correction gas cylinder. The correction method includes standard value setting, spectrum acquisition, peak identification, peak position correction, intensity correction, and lamp current feedback. This invention, through signal feedback and lamp current adjustment, enables photoionization mass spectrometry to obtain a more stable mass spectrometry signal. However, there is no good linear correlation between light intensity and lamp current, which may also lead to nonlinearity and failure of the compensation. Summary of the Invention

[0004] This invention, based on the principle of light absorption, adds a gas-filled sink between the light source and the ionization chamber. By adjusting the type and pressure of the gas in the absorption cell, the ultraviolet light transmittance is controlled, compensating for signal instability caused by fluctuations in the intensity of the vacuum ultraviolet light source. This gas absorption method has good linear compensation capability for signal attenuation caused by light intensity, which helps to improve the stability of photoionization mass spectrometry. Specifically, it includes: a device for improving the signal stability of a vacuum ultraviolet photoionization source through gas absorption, comprising a vacuum ultraviolet light source, a gas absorption cell, a light window, an ionization chamber, an inlet valve, a sample inlet tube, a vacuum pump, and a vacuum gauge;

[0005] The gas absorption cell is a hollow, sealed chamber with a through hole on its upper wall. The gas absorption cell is positioned directly below the light outlet of the vacuum ultraviolet light source. The edges of the light outlet of the vacuum ultraviolet light source are sealed to the upper wall of the gas absorption cell. The through hole is coaxial with the light outlet of the vacuum ultraviolet light source. A light-transmitting window is provided on the lower wall of the gas absorption cell away from the light outlet of the vacuum ultraviolet light source.

[0006] The ionization chamber is a hollow cavity with an open top. The upper opening of the ionization chamber is sealed to the lower wall of the gas absorption cell, forming a closed chamber. A flat transfer electrode with a through hole in the middle is provided inside the ionization chamber. A through hole serving as an ion outlet is provided on the lower wall of the ionization chamber, and the ion outlet is coaxial with the through hole in the middle of the transfer electrode. A sample inlet is provided on the side wall of the ionization chamber. The light window is located in the area surrounded by the upper opening of the ionization chamber. Light emitted from the vacuum ultraviolet light source enters the gas absorption cell through the through hole, and then enters the through hole in the middle of the transfer electrode inside the ionization chamber through the light window.

[0007] Three through holes are provided on the side wall of the gas absorption cell, which are respectively connected to an inlet valve, a vacuum pump, and a vacuum gauge. The gas used to absorb light enters the gas absorption cell through the sample inlet tube and the inlet valve. The gas pressure inside the gas absorption cell is adjusted by the inlet valve and the vacuum pump, and the gas pressure is measured by the vacuum gauge. The light emitted by the vacuum ultraviolet light source enters the ionization chamber after passing through the gas absorption cell and the light window to ionize the sample molecules. The generated ions enter the mass spectrometer for detection under the action of the transfer electrode.

[0008] By controlling the injection volume of the inlet valve and the pumping speed of the pump, the gas pressure inside the gas absorption cell can be changed in real time to adjust the transmittance of vacuum ultraviolet light and suppress the influence of vacuum ultraviolet light intensity fluctuations on the stability of mass spectrometry signals.

[0009] The gas in the gas absorption cell can be a single-component gas or a mixture of two or more gases, specifically one or more of O2, He, H2O, N2, CO2, ethanol, methanol, acetonitrile, and acetone. The sample flow rate of the inlet valve and the pumping speed of the pump can be automatically controlled via circuitry. The transfer electrode is a stacked ring electrode structure commonly used in photoionization mass spectrometry, with insulating rings separating adjacent electrodes. The light emitted from the vacuum ultraviolet light source is transmitted along the axis of the through-hole in the middle of the transfer electrode.

[0010] Vacuum ultraviolet photoionization is a widely used ionization source for mass spectrometry. However, the light window of vacuum ultraviolet light can become contaminated due to organic phase deposition or dust adhesion, leading to a decrease in vacuum ultraviolet light intensity. According to Beer-Lambert law, the decrease in vacuum ultraviolet light intensity reduces ion yield, limiting the sensitivity and stability of photomass spectrometry. This invention adds a gas-filled sink between the light source and the ionization chamber. By adjusting the type and pressure of the gas in the absorption cell, the ultraviolet light transmittance is controlled, compensating for signal instability caused by fluctuations in the intensity of the vacuum ultraviolet light source. This gas absorption method has good linear compensation capability for signal attenuation caused by light intensity, which helps to improve the stability of photoionization mass spectrometry. Attached Figure Description

[0011] Figure 1 A device for improving the signal stability of a vacuum ultraviolet photoionization source through gas absorption. Detailed Implementation

[0012] A device for improving the signal stability of a vacuum ultraviolet photoionization source by gas absorption includes a vacuum ultraviolet light source 1, a gas absorption cell 2, a light window 3, an ionization chamber 8, an inlet valve 4, a sample inlet tube 5, a pump 6, and a vacuum gauge 7.

[0013] The gas absorption cell 2 is a hollow, sealed chamber. A through hole is provided on the upper wall of the gas absorption cell 2. The gas absorption cell 2 is located directly below the light outlet of the vacuum ultraviolet light source 1. The four edges of the light outlet of the vacuum ultraviolet light source 1 are sealed to the upper wall of the gas absorption cell 2. The through hole is coaxially arranged with the light outlet of the vacuum ultraviolet light source 1. A light-transmitting window 3 is provided on the lower wall of the gas absorption cell 2 away from the light outlet of the vacuum ultraviolet light source 1.

[0014] The ionization chamber 8 is a hollow cavity with an open top. The upper opening of the ionization chamber 8 is sealed to the lower wall of the gas absorption cell 2, thus forming a sealed cavity. A flat plate-shaped transmission electrode 9 with a through hole in the middle is provided inside the ionization chamber 8. A through hole serving as an ion outlet is provided on the lower wall of the ionization chamber 8, and the ion outlet is coaxial with the through hole in the middle of the transmission electrode 9. A sample inlet is provided on the side wall of the ionization chamber 8. The light window 3 is located in the area surrounded by the upper opening of the ionization chamber 8. Light emitted from the vacuum ultraviolet light source 1 enters the gas absorption cell 2 through the through hole, and then enters the through hole in the middle of the transmission electrode 9 inside the ionization chamber 8 through the light window 3.

[0015] Three through holes are provided on the side wall of the gas absorption cell 2. The three through holes are respectively connected to the inlet valve 4, the pump 6 and the vacuum gauge 6. The gas used to absorb light enters the gas absorption cell 2 through the sample inlet tube 5 and the inlet valve 4. The gas pressure inside the gas absorption cell 2 is adjusted by the inlet valve 4 and the pump 6. The gas pressure is measured by the vacuum gauge 7. The light emitted by the vacuum ultraviolet light source (1) enters the ionization chamber 8 after passing through the gas absorption cell 2 and the light window 3 to ionize the sample molecules. The generated ions enter the mass spectrometer for detection under the action of the transmission electrode 9.

[0016] By controlling the injection rate of the inlet valve 4 and the pumping speed of the pump 6, the gas pressure inside the gas absorption cell 2 can be changed in real time to adjust the transmittance of vacuum ultraviolet light and suppress the influence of light intensity fluctuations of the vacuum ultraviolet light source 1 on the stability of the mass spectrometry signal. The gas in the gas absorption cell 3 can be a single-component gas or a mixture of two or more gases, specifically one or more of O2, He, H2O, N2, CO2, ethanol, methanol, acetonitrile, and acetone. The injection flow rate of the inlet valve 4 and the pumping speed of the pump 6 can be automatically controlled by the circuit. The transmission electrode 9 is a stacked ring electrode structure commonly used in photoionization mass spectrometry, with insulating gaskets between adjacent electrodes. The transmission direction of the light emitted by the vacuum ultraviolet light source 1 is on the axis of the through hole in the middle of the transmission electrode 9.

[0017] Example 1

[0018] A device for improving the signal stability of a vacuum ultraviolet photoionization source using gas absorption includes a Kr discharge VUV vacuum ultraviolet light source, a gas absorption cell, a MgF2 optical window, an ionization chamber, uniformly spaced transmission electrodes, an inlet valve, a sample inlet tube, a mechanical pump, and a vacuum gauge. The gas absorption cell is located directly below the VUV lamp's light outlet. The gas pressure in the gas absorption cell is regulated by the inlet valve and the pump, controlled between 10 and 10000 Pa, and measured by the vacuum gauge. The gas absorption cell is filled with a 500 ppm O2 / He mixture to absorb ultraviolet light. By controlling the sample inlet flow rate of the inlet valve and the pumping speed of the pump, the gas pressure inside the gas absorption cell can be changed in real time to adjust the transmittance of the vacuum ultraviolet light and suppress the impact of vacuum ultraviolet light source optical window contamination on the stability of the mass spectrometry signal. Based on the signal intensity feedback from the mass spectrometer, the sample inlet flow rate of the electrically controlled inlet valve can be changed to alter the gas pressure inside the gas absorption cell, compensating for changes in signal intensity.

Claims

1. A device for improving the signal stability of a vacuum ultraviolet photoionization source through gas absorption, characterized in that: It includes a vacuum ultraviolet light source (1), a gas absorption cell (2), a light window (3), an ionization chamber (8), an inlet valve (4), a sample inlet tube (5), a vacuum pump (6), and a vacuum gauge (7); The gas absorption cell (2) is a hollow, sealed chamber. A through hole is provided on the upper wall of the gas absorption cell (2). The gas absorption cell (2) is located directly below the light outlet of the vacuum ultraviolet light source (1). The edges of the light outlet of the vacuum ultraviolet light source (1) are sealed to the upper wall of the gas absorption cell (2). The through hole is coaxially arranged with the light outlet of the vacuum ultraviolet light source (1). A light-transmitting window (3) is provided on the lower wall of the gas absorption cell (2) away from the light outlet of the vacuum ultraviolet light source (1). The ionization chamber (8) is a hollow cavity with an open top. The upper opening of the ionization chamber (8) is sealed to the lower wall of the gas absorption cell (2), so that the ionization chamber (8) forms a sealed cavity. A flat plate-shaped transmission electrode (9) with a through hole in the middle is provided inside the ionization chamber (8). A through hole as an ion outlet is provided on the lower wall of the ionization chamber (8), and the ion outlet is coaxial with the through hole in the middle of the transmission electrode (9). A sample inlet is provided on the side wall of the ionization chamber (8). The light window (3) is located in the area surrounded by the upper opening of the ionization chamber (8). The light emitted by the vacuum ultraviolet light source (1) enters the gas absorption cell (2) through the through hole, and then enters the through hole in the middle of the transmission electrode (9) in the ionization chamber (8) through the light window (3). Three through holes are provided on the side wall of the gas absorption cell (2), and the three through holes are respectively connected to the inlet valve (4), the pump (6) and the vacuum gauge (6); the gas used to absorb light enters the gas absorption cell (2) through the sample inlet tube (5) and the inlet valve (4); the gas pressure inside the gas absorption cell (2) is adjusted by the inlet valve (4) and the pump (6), and the gas pressure is measured by the vacuum gauge (7); the light emitted by the vacuum ultraviolet light source (1) enters the ionization chamber (8) after passing through the gas absorption cell (2) and the light window (3) to ionize the sample molecules, and the generated ions enter the mass spectrometer for detection under the action of the transfer electrode (9); By controlling the injection volume of the inlet valve (4) and the pumping speed of the pump (6), the gas pressure inside the gas absorption cell (2) can be changed in real time to adjust the transmittance of vacuum ultraviolet light and suppress the influence of the intensity fluctuation of the vacuum ultraviolet light source (1) on the stability of the mass spectrometry signal.

2. The apparatus according to claim 1, characterized in that: The gas in the gas absorption cell (2) can be a single component gas or a mixture of two or more gases, specifically one or more of O2, He, H2O, N2, CO2, ethanol, methanol, acetonitrile, and acetone.

3. The apparatus according to claim 1, characterized in that: The sample flow rate of the inlet valve (4) and the pumping speed of the pump (6) can be automatically controlled by the circuit.

4. The apparatus according to claim 1, characterized in that: The transfer electrode (9) is a stacked ring electrode structure commonly used in photoionization mass spectrometry, with insulating pad rings separating adjacent electrodes.

5. The apparatus according to claim 1, characterized in that: The direction of light transmission emitted by the vacuum ultraviolet light source (1) is on the axis of the through hole in the middle of the transmission electrode (9).

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