Device for improving detection sensitivity of photo ionization source in low-voltage environment

Abstract

The invention relates to the technical field of mass spectrometry instruments, in particular to a device for improving the detection sensitivity of a photo ionization source in a low-pressure environment, which comprises a sample introduction tube, an ionization source cavity, a vacuum ultraviolet lamp, a repulsion electrode, a gas supplementing capillary tube, an inert gas source and an ion funnel, and the other end of the gas supplementing capillary tube penetrates into the ionization source cavity and extends to a position between the repulsion electrode and the ion funnel. The detection sensitivity of the photoionization source in the low-pressure environment can be improved under the condition that the sample injection amount is not increased, the ionization source cavity can inject samples from the low-pressure environment, and high-purity inert gas is introduced through the gas supplementing capillary tube. The air pressure in the ionization source cavity can be maintained within the air pressure range where the ion funnel can work efficiently, efficient transmission of sample ions in the source is achieved, and the detection sensitivity of an instrument is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of mass spectrometry instruments, and more specifically, to a device for improving the detection sensitivity of a photoionization source in a low-pressure environment. Background Art

[0002] The photoionization technology based on commercial vacuum ultraviolet lamps is an attractive soft ionization technology. Photoionization itself has excellent ionization efficiency, high molecular ion yield, and easy spectral analysis. Using a simple and compact vacuum ultraviolet lamp as the light source reduces the usage cost, so it is widely used in environmental analysis, clinical diagnosis, industrial process monitoring and other fields.

[0003] In a photoionization source, increasing the sample intake by increasing the gas pressure inside the ionization source and using certain focusing means to improve the transmission efficiency are good methods to improve the instrument sensitivity. However, when detecting samples in a low-pressure environment (10 - 5000 Pa), due to limitations in the sampling pipeline and interface, the sample intake is low, so the detection sensitivity of the instrument is low. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a device for improving the detection sensitivity of a photoionization source in a low-pressure environment.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A device for improving the detection sensitivity of a photoionization source in a low-pressure environment, comprising a sampling tube, an ionization source cavity, 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 respectively provided with a vacuum pumping port and an ion output port, and the vacuum pumping port is connected to an external vacuum pump;

[0008] The vacuum ultraviolet lamp, the repulsion electrode, and the ion funnel are respectively installed inside the ionization source cavity in sequence. The light emitted from the light source emitting end of the vacuum ultraviolet lamp sequentially passes through the repulsion electrode and the ion funnel. 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 close to the ion output port;

[0009] One end of the sampling tube is in the low-pressure environment with samples outside the ionization source cavity, and the other end of the sampling tube penetrates into the ionization source cavity and extends to the position 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 penetrates into the ionization source cavity and extends to the position between the repulsion electrode and the ion funnel;

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

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

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

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

[0014] The axial center lines of the sample injection tube and the gas replenishment capillary are both perpendicular to the axial center line of the light emitting end of the vacuum ultraviolet lamp.

[0015] The repulsion electrode has an annular flat plate structure with a circular through hole in the middle.

[0016] The ion funnel is divided into several layers of annular electrodes that are parallel, equally spaced, and each has a circular through hole. The diameters of the circular through holes of the annular electrodes gradually decrease from the side close to the repulsion electrode to the side far from the repulsion electrode.

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

[0018] The DC voltages applied to the repulsion electrode and the annular electrodes of the ion funnel decrease in sequence along the direction of the light emitted from the light emitting end of the vacuum ultraviolet lamp to form a DC gradient electric field.

[0019] The peak-to-peak amplitudes of the RF on any two adjacent annular electrodes of the ion funnel are equal and the phases are opposite.

[0020] The center line of the circular through hole 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 emitting end of the vacuum ultraviolet lamp are all collinear.

[0021] The advantages and positive effects of the present invention are:

[0022] The present invention can improve the detection sensitivity of the photoionization source in a low-pressure environment without increasing the sample injection volume. In addition to being able to inject samples from a low-pressure environment, the ionization source cavity also introduces high-purity inert gas through a gas supply capillary, so that the gas pressure in the ionization source cavity can be maintained within the gas pressure range in which the ion funnel can work efficiently, realizing the efficient transmission of sample ions in the source and greatly improving the detection sensitivity of the instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the present invention.

[0024] In the figure: 1 is a sampling tube, 2 is an ionization source cavity, 3 is a vacuum ultraviolet lamp, 4 is a repulsion electrode, 5 is a gas supply capillary, 6 is a mass flow controller, 7 is an inert gas source, 8 is an ion funnel, and 9 is a vacuum pumping port. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will further describe the present invention in detail Figure 1 in conjunction with the accompanying drawings.

[0026] A device for improving the detection sensitivity of a photoionization source in a low-pressure environment, as Figure 1 shown, in this embodiment, it includes a sampling tube 1, an ionization source cavity 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 cavity 2 is respectively 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 external vacuum pump extracts the gas in the ionization source cavity 2 through the vacuum pumping port 9.

[0028] The vacuum ultraviolet lamp 3, the repulsion electrode 4, and the ion funnel 8 are respectively installed inside the ionization source cavity 2 in sequence. The light emitted from the light source emitting end of the vacuum ultraviolet lamp 3 sequentially passes 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 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. The installation structures of the vacuum ultraviolet lamp 3, the repulsion electrode 4, and the ion funnel 8 adopt existing technologies. 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.

[0029] One end of the sampling tube 1 is located in a low-pressure environment (10 - 5000 Pa) with a sample (gaseous state) outside the ionization source cavity 2, and the other end of the sampling tube 1 penetrates into the ionization source cavity 2 and extends to the position between the repulsion electrode 4 and the ion funnel 8. One end of the gas supply capillary 5 is communicated with the inert gas source 7, and the other end of the gas supply capillary 5 penetrates into the ionization source cavity 2 and extends to the position 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 through a mass flow controller 6. In this embodiment, the mass flow controller 6 is a commercially available product; the inert gas source 7 is arranged using the prior art, and the inert gas source 7 can be a high-purity nitrogen gas source or a high-purity helium gas source. In this embodiment, the gas in the ionization source cavity 2 is pumped out by an external vacuum pump connected to the vacuum pumping port 9, and the gas flow rate input from the inert gas source 7 into the ionization source cavity 2 is adjusted by the mass flow controller 6, so that the air pressure in the ionization source cavity 2 can be maintained at 0.5 - 500 Pa, and the air pressure in the ionization source cavity 2 is always lower than the air pressure of the external low-pressure environment at one end of the sampling tube 1.

[0031] Specifically, in this embodiment, a mass analyzer is provided outside 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 the ions discharged from the ion output port for subsequent detection, and the setting method of the mass analyzer is 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 pumping port 9 and the ion output port are located at the bottom of the ionization source cavity 2. The axial center line of the vacuum pumping port 9 is parallel to the horizontal plane, and the axial center lines of the ion output port and the light emitting end of the vacuum ultraviolet lamp 3 are perpendicular to the horizontal plane; the axial center lines of the sampling tube 1 and the gas supply capillary 5 are both perpendicular to the light emitting end of the vacuum ultraviolet lamp 3, which is easy to manufacture and can ensure the detection accuracy. In this embodiment, the vacuum ultraviolet lamp 3 can be a commercially available low-pressure inert gas discharge lamp, such as: krypton (Kr) discharge lamp, deuterium (D2) discharge lamp, xenon (Xe) discharge lamp, etc. In this embodiment, the inner diameter of the sampling tube 1 is 1 - 10 mm, and the length can be adjusted arbitrarily according to the use requirements, and the manufacturing material can be polytetrafluoroethylene. In this embodiment, the material of the gas supply capillary 5 is stainless steel, quartz or polyether ether ketone (PEEK), etc., the inner diameter is 50 - 500 μm, and the length is 10 - 60 cm.

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

[0034] The ion funnel 8 is divided into a plurality of annular electrodes arranged in parallel at equal intervals and each having a circular through-hole, and the aperture of the circular through-holes of the annular electrodes gradually decreases from the side close to the repulsion electrode 4 to the side far from the repulsion electrode 4. In this embodiment, all the annular electrodes of the ion funnel 8 are annular flat structures with the same thickness, the middle of the annulus is a circular through-hole, the diameter of the circular through-hole is 0.5 - 50 mm, the number of annular electrodes is 2 - 200, and the thickness is 0.5 mm.

[0035] In this embodiment, the repulsion electrode 4 is arranged in parallel and at intervals with all the annular electrodes of the ion funnel 8. The distance between the repulsion electrode 4 and the nearest annular electrode is 6 mm, and the distance between two adjacent annular electrodes is 0.5 mm; the materials of the repulsion electrode 4 and all the annular electrodes of the ion funnel 8 can be conductive metals (such as stainless steel, etc.) or flat plates with a conductive metal layer plated on the surface; the axial centerlines of the circular through-holes of the repulsion electrode 4, all the annular electrodes of the ion funnel 8, the axial centerline of the ion output port, and the axial centerline of the light-emitting end of the light source of the vacuum ultraviolet lamp 3 are collinear.

[0036] Specifically, in this embodiment, the DC voltages applied to the repulsion electrode 4 and each annular electrode of the ion funnel 8 decrease successively along the direction of the light emitted from the light-emitting end of the vacuum ultraviolet lamp 3 to form a DC gradient electric field, and the gradient voltage corresponding to this DC gradient electric field is 1 - 20 V / cm; the radio frequency applied to the ion funnel 8 has a frequency of 0.5 - 5 MHz and a radio frequency peak-to-peak value of 10 - 500 V. The radio frequency peak-to-peak amplitudes of any two adjacent annular electrodes of the ion funnel 8 are equal and the phases are opposite. The setting method of each voltage and the energizing method of the repulsion electrode 4 and each annular electrode of the ion funnel 8 both adopt the prior art.

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

[0038] The mixed standard gas (BTX) of benzene, toluene and p-xylene at 100 ppbv was detected when the high-purity helium gas flow rates were 0 and 10 ml / min respectively, and the detection results are as follows. When the high-purity helium gas flow rate was 0, the internal pressure of the ionization source cavity 2 was 5 Pa. At this time, it was equivalent to the non-operation of the present invention, and the detection intensities of BTX were 2649, 2355 and 1633 counts·5 s respectively. When the high-purity helium gas flow rate was 10 ml / min, the internal pressure of the ionization source cavity 2 was 20 Pa. At this time, it was the state of using the present invention, and the detection intensities of BTX were 7819, 7239 and 5231 counts·5 s respectively. The signal intensity was generally increased by about three times. It can be seen that the use of the present invention can effectively improve the detection sensitivity during low-pressure environment sampling without increasing the sample input volume.

[0039] Working principle:

[0040] During operation, the sample to be measured enters the ionization source cavity 2 from the sampling tube 1. The gas in the ionization source cavity 2 is pumped out by an external vacuum pump connected to the vacuum pumping port 9, and the gas flow rate input from the inert gas source 7 to the ionization source cavity 2 is adjusted by the mass flow controller 6, so that the internal pressure of the ionization source cavity 2 can always be kept lower than the external low-pressure environment pressure at one end of the sampling tube 1, and the working pressure inside the ionization source cavity 2 is increased to the pressure range in which the ion funnel 8 can work efficiently, greatly improving the output ion efficiency, thereby solving the problem of low detection sensitivity during low-pressure environment sampling.

Claims

1. A device for improving the detection sensitivity of a photoionization source in a low-pressure environment, characterized in that: It includes a sampling tube (1), an ionization source cavity (2), a vacuum ultraviolet lamp (3), a repelling electrode (4), a gas replenishment capillary (5), an inert gas source (7), and an ion funnel (8); The ionization source cavity (2) is respectively 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 repelling electrode (4), and the ion funnel (8) are respectively and sequentially installed inside the ionization source cavity (2). The light emitted from the light source emitting end of the vacuum ultraviolet lamp (3) sequentially passes through the repelling electrode (4) and the ion funnel (8). The vacuum ultraviolet lamp (3) is located on one side of the repelling electrode (4) away from the ion output port direction, and the ion funnel (8) is located on one side of the repelling electrode (4) close to the ion output port direction; One end of the sampling tube (1) is located in a low-pressure environment with a sample outside the ionization source cavity (2), and the other end of the sampling tube (1) penetrates into the ionization source cavity (2) and extends to the position between the repelling electrode (4) and the ion funnel (8). One end of the gas replenishment capillary (5) is connected to the inert gas source (7), and the other end of the gas replenishment capillary (5) penetrates into the ionization source cavity (2) and extends to the position between the repelling electrode (4) and the ion funnel (8); A DC voltage is applied to the repelling electrode (4), and a DC voltage and an RF voltage are applied to the ion funnel (8).

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 replenishment capillary (5) is connected to the inert gas source (7) through 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 outside 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: Both the vacuum pumping port (9) and the ion output port are located at the bottom of the ionization source cavity (2). The axial center line of the vacuum pumping port (9) is parallel to the horizontal plane, and the axial center lines of the ion output port and 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 center line of the sampling tube (1) and the axial center line of the gas replenishment capillary (5) are both perpendicular to the axial center line 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: The repelling electrode (4) is a ring-shaped flat plate structure with a circular through-hole in the middle; The ion funnel (8) is divided into several layers of ring-shaped electrodes that are parallel, equally spaced, and each has a circular through-hole. The aperture of the circular through-holes of the ring-shaped electrodes gradually decreases from the side close to the repelling electrode (4) to the side far from the repelling electrode (4).

7. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 6, characterized in that: The thicknesses of all the ring-shaped electrodes of the ion funnel (8) are the same.

8. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 6, characterized in that: The DC voltages applied to the repelling electrode (4) and the ring-shaped electrodes of the ion funnel (8) decrease sequentially along the direction of the light emitted from the light source emitting end of the vacuum ultraviolet lamp (3) to form a DC gradient electric field.

9. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 6, characterized in that: The peak-to-peak amplitudes of the RF on any two adjacent ring-shaped electrodes of the ion funnel (8) are equal and the phases are opposite.

10. The device for improving the detection sensitivity of a photoionization source in a low-pressure environment according to claim 6, characterized in that: The central axis of the circular through-hole of the repulsion electrode (4), the central axes of the circular through-holes of all the annular pole pieces of the ion funnel (8), the axial central axis of the ion output port, and the axial central axis of the light-emitting end of the light source of the vacuum ultraviolet lamp (3) are all collinear.

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