A device for improving the detection sensitivity of a photoionization source in a low pressure environment

Abstract

The application relates to the technical field of mass spectrometry instruments, in particular to a device for improving the detection sensitivity of a photoionization source in a low-pressure environment, which comprises a sample inlet tube, an ionization source cavity, a vacuum ultraviolet lamp, a push-pull electrode, a gas supplement capillary, an inert gas source and an ion funnel; one end of the gas supplement capillary is connected with the inert gas source; the other end of the gas supplement capillary penetrates into the ionization source cavity and extends to the position between the push-pull electrode and the ion funnel. The device can improve the detection sensitivity of the photoionization source in the low-pressure environment without increasing the sample amount; in addition to the function of sampling from the low-pressure environment, the ionization source cavity also uses the gas supplement capillary to introduce high-purity inert gas, so that the gas pressure in the ionization source cavity can be maintained in the gas pressure range in which the ion funnel can work efficiently, efficient transmission of sample ions in the source is realized, and the detection sensitivity of the instrument is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of mass spectrometry analysis instrument technology, specifically to a device for improving the detection sensitivity of photoionization sources in low-pressure environments. Background Technology

[0002] Photoionization technology based on commercially available vacuum ultraviolet lamps is an attractive soft ionization technology. Photoionization itself has advantages such as excellent ionization efficiency, high molecular ion yield and easy spectrum interpretation. Furthermore, using a simple and compact vacuum ultraviolet lamp as the light source further reduces the cost of use. Therefore, it is widely used in environmental analysis, clinical diagnosis and industrial process monitoring.

[0003] In photoionization sources, increasing the sample intake by raising the internal gas pressure and employing focusing techniques to improve transmission efficiency are effective methods for enhancing instrument sensitivity. However, when detecting samples in low-pressure environments (10-5000 Pa), the sample intake is limited by the sample inlet tubing and interface, resulting in lower instrument sensitivity. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a device for improving the detection sensitivity of photoionization sources in low-pressure environments.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A device for improving the detection sensitivity of a photoionization source in a low-pressure environment includes a sample inlet tube, an ionization source chamber, a vacuum ultraviolet lamp, a repulsion electrode, a gas supply capillary, an inert gas source, and an ion funnel.

[0007] The ionization source cavity is provided with a vacuum pump port and an ion output port, and the vacuum pump port is connected to an external vacuum pump.

[0008] The vacuum ultraviolet lamp, the repulsion electrode, and the ion funnel are sequentially installed inside the ionization source cavity. The light emitted from the light source of the vacuum ultraviolet lamp passes through the repulsion electrode and the ion funnel in sequence. The vacuum ultraviolet lamp is located on the side of the repulsion electrode away from the ion output port, and the ion funnel is located on the side of the repulsion electrode closer to the ion output port.

[0009] One end of the sample inlet tube is located in a low-pressure environment with the sample outside the ionization source chamber, and the other end of the sample inlet tube is inserted into the ionization source chamber and extends to the space between the repulsion electrode and the ion funnel. One end of the gas supply capillary is connected to the inert gas source, and the other end of the gas supply capillary is inserted into the ionization source chamber and extends to the space between the repulsion electrode and the ion funnel.

[0010] A DC voltage is applied to the repulsion electrode, and a DC voltage and a radio frequency voltage are applied to the ion funnel.

[0011] One end of the gas supply capillary is connected to the inert gas source via a mass flow controller.

[0012] A mass analyzer is provided on the outside of the ionization source cavity, and the sample input end of the mass analyzer is connected to the ion output port.

[0013] Both the vacuum extraction port and the ion output port are located at the bottom of the ionization source cavity. The axial centerline of the vacuum extraction port is parallel to the horizontal plane, and the axial centerline of the ion output port and the axial centerline of the light source emitting end of the vacuum ultraviolet lamp are perpendicular to the horizontal plane.

[0014] The axial centerline of the sample inlet tube and the axial centerline of the gas supply capillary are both perpendicular to the axial centerline of the light source emitting end of the vacuum ultraviolet lamp.

[0015] The repulsion electrode is an annular plate structure with a circular through hole in the middle;

[0016] The ion funnel is divided into several layers of parallel, equally spaced annular electrodes, each with a circular through-hole. The diameter of the circular through-holes in each annular electrode gradually decreases from the side closest to the repulsive electrode to the side furthest from the repulsive electrode.

[0017] All the annular electrodes of the ion funnel have the same thickness.

[0018] The DC voltage applied to each annular electrode of the repulsion electrode and ion funnel decreases sequentially along the direction of the light emitted from the light source of the vacuum ultraviolet lamp, forming a DC gradient electric field.

[0019] The radio frequency peak amplitudes on any two adjacent annular electrodes of the ion funnel are equal and opposite in phase.

[0020] The center lines of the circular through holes of the repulsion electrode, the center lines of the circular through holes of all the annular electrodes of the ion funnel, the axial center line of the ion output port, and the axial center line of the light source emitting end of the vacuum ultraviolet lamp are all collinear.

[0021] The advantages and positive effects of this invention are as follows:

[0022] This invention can improve the detection sensitivity of photoionization sources in low-pressure environments without increasing the sample volume. In addition to introducing samples from a low-pressure environment, the ionization source cavity also uses a gas replenishment capillary to introduce high-purity inert gas, so that the gas pressure in the ionization source cavity can be maintained within the gas pressure range that allows the ion funnel to work efficiently. This achieves efficient transmission of sample ions within the source and greatly improves the detection sensitivity of the instrument. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] In the figure: 1 is the sample inlet tube, 2 is the ionization source chamber, 3 is the vacuum ultraviolet lamp, 4 is the repulsion electrode, 5 is the gas supply capillary, 6 is the mass flow controller, 7 is the inert gas source, 8 is the ion funnel, and 9 is the vacuum extraction port. Detailed Implementation

[0025] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0026] A device for improving the detection sensitivity of photoionization sources in low-pressure environments, such as... Figure 1 As shown, this embodiment includes a sample inlet tube 1, an ionization source chamber 2, a vacuum ultraviolet lamp 3, a repulsion electrode 4, a gas supply capillary 5, an inert gas source 7, and an ion funnel 8.

[0027] The ionization source chamber 2 is equipped with a vacuum extraction port 9 and an ion output port, respectively. The vacuum extraction port 9 is connected to an external vacuum pump. The external vacuum pump extracts the gas from the ionization source chamber 2 through the vacuum extraction port 9.

[0028] A vacuum ultraviolet lamp 3, a repulsion electrode 4, and an ion funnel 8 are sequentially installed inside the ionization source cavity 2. Light emitted from the light source of the vacuum ultraviolet lamp 3 passes sequentially through the repulsion electrode 4 and the ion funnel 8. The vacuum ultraviolet lamp 3 is located on the side of the repulsion electrode 4 furthest from the ion output port, and the ion funnel 8 is located on the side of the repulsion electrode 4 closest to the ion output port. The installation structure of the vacuum ultraviolet lamp 3, the repulsion electrode 4, and the ion funnel 8 adopts existing technology. A DC voltage is applied to the repulsion electrode 4, and both a DC voltage and a radio frequency voltage are applied to the ion funnel 8.

[0029] One end of the sample inlet tube 1 is located in a low-pressure environment (10-5000 Pa) containing the sample (gaseous state) outside the ionization source chamber 2. The other end of the sample inlet tube 1 is inserted into the ionization source chamber 2 and extends to the space between the repulsion electrode 4 and the ion funnel 8. One end of the gas supply capillary 5 is connected to the inert gas source 7. The other end of the gas supply capillary 5 is inserted into the ionization source chamber 2 and extends to the space between the repulsion electrode 4 and the ion funnel 8.

[0030] Specifically, in this embodiment, one end of the gas supply capillary 5 is connected to the inert gas source 7 via a mass flow controller 6. In this embodiment, the mass flow controller 6 is a commercially available product; the inert gas source 7 is set using existing technology, and can be a high-purity nitrogen source or a high-purity helium source. In this embodiment, the gas in the ionization source chamber 2 is extracted by an external vacuum pump connected to the vacuum extraction port 9, and the flow rate of the gas input from the inert gas source 7 to the ionization source chamber 2 is adjusted by the mass flow controller 6. This maintains the gas pressure in the ionization source chamber 2 between 0.5-500 Pa, and ensures that the gas pressure in the ionization source chamber 2 is always lower than the external low-pressure environment pressure at one end of the sample inlet tube 1.

[0031] Specifically, in this embodiment, a mass analyzer is provided on the outside of the ionization source cavity 2, and the sample input end of the mass analyzer is connected to the ion output port. The mass analyzer receives ions discharged from the ion output port for subsequent detection; the configuration of the mass analyzer is in the prior art. In this embodiment, the mass analyzer can be a commercially available time-of-flight mass analyzer, quadrupole mass analyzer, ion trap mass analyzer, sector magnetic field mass analyzer, or ion cyclotron resonance mass analyzer.

[0032] Specifically, in this embodiment, both the vacuum extraction port 9 and the ion output port are located at the bottom of the ionization source cavity 2. The axial centerline of the vacuum extraction port 9 is parallel to the horizontal plane, while the axial centerline of the ion output port and the axial centerline of the light source emitting end of the vacuum ultraviolet lamp 3 are perpendicular to the horizontal plane. The axial centerline of the sample inlet tube 1 and the axial centerline of the gas replenishment capillary 5 are both perpendicular to the axial centerline of the light source emitting end of the vacuum ultraviolet lamp 3. This design is easy to manufacture and ensures accurate detection. In this embodiment, the vacuum ultraviolet lamp 3 can be a commercially available low-pressure inert gas discharge lamp, such as a krypton (Kr) discharge lamp, a deuterium (D2) discharge lamp, or a xenon (Xe) discharge lamp. In this embodiment, the inner diameter of the sample inlet tube 1 is 1-10 mm, and the length can be adjusted arbitrarily according to usage requirements. The manufacturing material can be polytetrafluoroethylene (PTFE). In this embodiment, the gas replenishment capillary 5 is made of stainless steel, quartz, or polyetheretherketone (PEEK), with an inner diameter of 50-500 μm and a length of 10-60 cm.

[0033] Specifically, in this embodiment, the repulsion electrode 4 is an annular plate structure with a circular through hole in the middle. The thickness of the repulsion electrode 4 can be 1-4 mm, and the diameter of the circular through hole is 2-6 mm.

[0034] The ion funnel 8 consists of several layers of parallel, equally spaced annular electrodes, each with a circular through-hole. The diameter of the circular through-holes in each annular electrode gradually decreases from the side closest to the repulsive electrode 4 to the side furthest from the repulsive electrode 4. In this embodiment, all the annular electrodes of the ion funnel 8 are annular flat plates of the same thickness, with a circular through-hole in the center of the annulus. The diameter of the circular through-hole is 0.5-50 mm, and the number of annular electrodes is 2-200, with a thickness of 0.5 mm.

[0035] In this embodiment, the repulsion electrode 4 and all the annular electrodes of the ion funnel 8 are arranged parallel and spaced apart. The repulsion electrode 4 is 6 mm apart from the nearest annular electrode, and the two adjacent annular electrodes are 0.5 mm apart. The materials of the repulsion electrode 4 and all the annular electrodes of the ion funnel 8 can be conductive metal (such as stainless steel) or a plate with a conductive metal layer on its surface. The center line of the circular through hole of the repulsion electrode 4, the center line of the circular through hole of all the annular electrodes of the ion funnel 8, the axial center line of the ion output port, and the axial center line of the light source emitting end of the vacuum ultraviolet lamp 3 are all collinear.

[0036] Specifically, in this embodiment, the DC voltage applied to the repulsion electrode 4 and each annular electrode of the ion funnel 8 decreases sequentially along the direction of the light emitted from the light source of the vacuum ultraviolet lamp 3, forming a DC gradient electric field. The gradient voltage corresponding to this DC gradient electric field is 1-20V / cm. The radio frequency applied to the ion funnel 8 is 0.5-5MHz, and the radio frequency peak-to-peak value is 10-500V. The peak-to-peak values ​​of the radio frequency on any two adjacent annular electrodes of the ion funnel 8 are equal in amplitude and opposite in phase. The voltage setting method and the energizing method of each annular electrode of the repulsion electrode 4 and the ion funnel 8 adopt existing technology.

[0037] In a specific application example of the present invention: during operation, a DC gradient electric field with a gradient voltage of 2V / cm is applied to the repulsion electrode 4 and the ion funnel 8, which decreases sequentially along the ultraviolet light emission direction; the radio frequency applied to the ion funnel 8 is 1.99MHz, the radio frequency peak-to-peak value is 30V, and the radio frequency peak-to-peak value amplitudes on any two adjacent annular electrodes are equal and opposite in phase; in addition, the gas input flow rate is adjusted to 10ml / min by the mass flow controller 6, so that high-purity helium gas enters the ion source cavity 2 through the gas replenishment capillary 5, and the working gas pressure is increased from 5Pa to the gas pressure of 20Pa, which allows the ion funnel 8 to work efficiently.

[0038] The mixed standard gas (BTX) of benzene, toluene, and paraxylene at a flow rate of 0 and 10 ml / min was detected at 100 ppbv, and the results are as follows. When the flow rate of high-purity helium was 0, the internal pressure of the ionization source chamber 2 was 5 Pa, which is equivalent to the invention not being used. The detection intensities of BTX were 2649, 2355, and 1633 counts·5s, respectively. When the flow rate of high-purity helium was 10 ml / min, the internal pressure of the ionization source chamber 2 was 20 Pa, which is the state in which the invention is used. The detection intensities of BTX were 7819, 7239, and 5231 counts·5s, respectively. The overall signal intensity was improved by about three times. It can be seen that the invention can effectively improve the detection sensitivity in low-pressure environment without increasing the sample volume.

[0039] Working principle:

[0040] During operation, the sample to be tested enters the ionization source chamber 2 through the sample inlet tube 1. The gas in the ionization source chamber 2 is extracted by an external vacuum pump connected to the vacuum extraction port 9. The flow rate of the gas input from the inert gas source 7 into the ionization source chamber 2 is adjusted by the mass flow controller 6. This ensures that the gas pressure inside the ionization source chamber 2 is always lower than the low-pressure environment outside the sample inlet tube 1, thereby raising the working gas pressure inside the ionization source chamber 2 to the range where the ion funnel 8 can operate efficiently. This greatly improves the output ion efficiency and solves the problem of low detection sensitivity when sample is introduced in a low-pressure environment.

Claims

1. A device for improving the detection sensitivity of a photoionization source in a low-pressure environment, characterized in that: Includes sample inlet tube (1), ionization source chamber (2), vacuum ultraviolet lamp (3), repulsion electrode (4), gas supply capillary (5), inert gas source (7), and ion funnel (8); The ionization source cavity (2) is provided with a vacuum pumping port (9) and an ion output port, and the vacuum pumping port (9) is connected to an external vacuum pump. The vacuum ultraviolet lamp (3), the repulsion electrode (4), and the ion funnel (8) are respectively installed inside the ionization source cavity (2). The light emitted from the light source emitting end of the vacuum ultraviolet lamp (3) passes through the repulsion electrode (4) and the ion funnel (8) respectively. The vacuum ultraviolet lamp (3) is located on the side of the repulsion electrode (4) away from the ion output port, and the ion funnel (8) is located on the side of the repulsion electrode (4) close to the ion output port. One end of the sample inlet tube (1) is located in a low-pressure environment with a sample outside the ionization source chamber (2). The other end of the sample inlet tube (1) is inserted into the ionization source chamber (2) and extends to the space between the repulsion electrode (4) and the ion funnel (8). One end of the gas supply capillary (5) is connected to the inert gas source (7). The other end of the gas supply capillary (5) is inserted into the ionization source chamber (2) and extends to the space between the repulsion electrode (4) and the ion funnel (8). A DC voltage is applied to the repulsion electrode (4), and a DC voltage and a radio frequency voltage are applied to the ion funnel (8); The repulsion electrode (4) is an annular plate structure with a circular through hole in the middle; The ion funnel (8) is divided into several layers of parallel and equally spaced annular electrode plates, each with a circular through hole. The diameter of the circular through hole of each annular electrode plate gradually decreases from the side closer to the repulsion electrode (4) to the side farther away from the repulsion electrode (4). The DC voltage applied to each annular electrode of the repulsion electrode (4) and the ion funnel (8) decreases sequentially along the direction of the light emitted from the light source end of the vacuum ultraviolet lamp (3) and forms a DC gradient electric field. The radio frequency peaks and amplitudes on any two adjacent annular electrodes of the ion funnel (8) are equal and opposite in phase.

2. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: One end of the gas supply capillary (5) is connected to the inert gas source (7) via a mass flow controller (6).

3. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: A mass analyzer is provided on the outside of the ionization source cavity (2), and the sample input end of the mass analyzer is connected to the ion output port.

4. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: The vacuum extraction port (9) and the ion output port are both located at the bottom of the ionization source cavity (2). The axial center line of the vacuum extraction port (9) is parallel to the horizontal plane, and the axial center line of the ion output port and the axial center line of the light source emitting end of the vacuum ultraviolet lamp (3) are both perpendicular to the horizontal plane.

5. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: The axial centerline of the sample inlet tube (1) and the axial centerline of the gas supply capillary (5) are both perpendicular to the axial centerline of the light source emitting end of the vacuum ultraviolet lamp (3).

6. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: All the annular electrodes of the ion funnel (8) have the same thickness.

7. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 1, characterized in that: The center lines of the circular through holes of the repulsion electrode (4), the center lines of the circular through holes of all the annular electrodes of the ion funnel (8), the axial center line of the ion output port, and the axial center line of the light source emitting end of the vacuum ultraviolet lamp (3) are all collinear.

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