Ionization and focusing integrated ion source and mass spectrometry instrument

Abstract

The utility model relates to an ionization and focusing integrated ion source and a mass spectrometry instrument, and belongs to the technical field of ion sources. The ion source comprises a vacuum ultraviolet krypton lamp and a repulsion electrode which are arranged along the axis, and a photoelectron electrode with a through hole, a multi-pole electrode and a differential electrode are sequentially arranged on the side, away from the krypton lamp, of the repulsion electrode. The multi-pole-rod electrode comprises a plurality of pole rods arranged around the axis, each pole rod is parallel to the axis, and each pole rod comprises a plurality of sub-rods in the extension direction of the axis; the photoelectron electrode is connected with a first radio frequency power supply, and the multi-pole rod electrode is connected with a second radio frequency power supply. The photoelectron electrode can apply a radio frequency electric field, so that passing ions spirally move on the photoelectron electrode to increase the ion molecule collision frequency; a quadrupole electric field formed in the segmented multi-pole-rod electrode can restrain ions to do sinusoidal motion in the pole rods in the direction perpendicular to the axis direction, the collision probability of reagent ions and sample molecules is increased, and the ion transmission efficiency and sensitivity of an instrument are improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of ion sources, and in particular relates to an ion source and mass spectrometry instrument integrated with ionization and focusing. Background Art

[0002] Mass spectrometry is an important means for qualitative and quantitative analysis of volatile organic compounds (VOCs), and has the highest sensitivity among existing VOCs analysis methods.

[0003] Traditional gas chromatography-mass spectrometry (GC-MS) measurement of VOCs in air requires not only sample pretreatment to isolate the target compounds but also the use of electron impact ionization (EI). The resulting compound spectra contain numerous fragments, requiring comparison and retrieval with a standard EI spectral library, making rapid and accurate online monitoring impossible. Radioactive ionization sources, such as Po sources, can effectively ionize and detect VOCs, but their radioactive hazards preclude online detection. Soft ionization sources, such as vacuum ultraviolet (VUV) photoionization sources, offer the advantages of low fragmentation and high safety, but their relatively low ionization energy (10.6 eV) makes it difficult to detect VOCs at high ionization energies. Chemical ionization (CIC) sources, as a low-pressure ionization source for mass spectrometry of VOCs in the atmosphere, have rapidly developed due to their strong molecular / quasi-molecular ion peaks and high sensitivity. They typically operate at pressures between 100 and 10,000 Pa and consist of two components: a reagent ion generation / guidance unit and a reagent ion molecular reaction unit. Although good detection of VOCs can be achieved, the device is relatively large and the generation of reagent ions must use standard gas cylinders, which adds a lot of inconvenience to its use on-site. Utility Model Content

[0004] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide an integrated ionization and focusing ion source and mass spectrometry instrument, which adds a radio frequency electric field to the photoelectron electrode and uses a fragment quadrupole structure in the chemical ionization region to increase the number of ion-molecule collisions, thereby improving the target ion yield and sensitivity; at the same time, the radio frequency electric field on the fragment quadrupole focuses to generate an ion beam, thereby improving the ion transmission efficiency.

[0005] In order to achieve the above purpose, the technical solution of the utility model is:

[0006] In a first aspect, an ionization and focusing integrated ion source comprises a vacuum ultraviolet krypton lamp and a repeller electrode arranged along an axis, wherein a photoelectron electrode, a multipole electrode and a differential electrode are sequentially arranged on a side of the repeller electrode away from the vacuum ultraviolet krypton lamp;

[0007] The repulsion electrode, the photoelectron electrode and the differential electrode are provided with through holes along the axis; the multipole electrode comprises a plurality of rods arranged around the axis, each rod being parallel to the axis, and each rod comprising a plurality of segments along the extension direction of the axis;

[0008] The photoelectron electrode is connected to a first radio frequency power source, and the multipole rod electrode is connected to a second radio frequency power source.

[0009] Optionally, the aperture of the through hole of the photoelectron electrode is smaller than that of the through hole of the repeller electrode, the photoelectron electrode is provided with a countersunk hole facing the multipole electrode, and the through hole of the photoelectron electrode is located at the center of the bottom surface of the countersunk hole.

[0010] Optionally, a reagent gas injection tube is provided between the repeller electrode and the photoelectron electrode.

[0011] Optionally, the reagent gas inlet tube is connected to a PEEK capillary or a metal capillary through a commercial capillary inverted cone joint. By changing the inner diameter and length of the capillary, the flow rate of the reagent gas can be controlled.

[0012] Optionally, the ion source includes a sample gas injection tube, and a tube opening of the sample gas injection tube is opened on the cylindrical side wall of the countersunk hole.

[0013] Optionally, the sample gas inlet tube is also connected to the PEEK capillary or metal capillary through a commercial capillary inverted cone joint. By changing the inner diameter and length of the capillary, the flow rate of the sample gas can be controlled.

[0014] Optionally, the multipole electrode is in the form of a quadrupole, hexapole or octapole. In each pole, multiple segments are coaxially fixed on an insulating rod (PEEK or ceramic material) at a set distance. Each segment is connected to an electrode ring, and the multiple electrode rings are insulated from each other. In addition to applying voltage and current, the electrode ring also serves as a connecting component to fix the pole on the insulating rod.

[0015] Optionally, the electrode rings are respectively connected to a DC voltage source via voltage-dividing resistors, and are respectively connected to a second radio frequency power source via the same capacitor.

[0016] Optionally, the voltage divider resistor connected to the electrode ring is 10 to 15 MΩ, the capacitor connected to the electrode ring is 100 to 150 nF, the DC voltage source forms a voltage difference of 5 to 7 V across a single pole, and the second RF power supply applies a second RF voltage to the pole with a peak-to-peak voltage of 50 to 800 V and an RF frequency of 1 to 3 MHz.

[0017] Optionally, the photoelectron electrode is connected to a first radio frequency power source via a capacitor.

[0018] Optionally, the capacitor connected to the photoelectronic electrode is 100-150 nF, and the first radio frequency power supply applies a radio frequency voltage with a peak value of 50-800 V and a radio frequency of 1-3 MHz to the photoelectronic electrode.

[0019] Optionally, the photoelectron electrode and the multipole rod electrode are located in a vacuum chamber, the repeller electrode and the differential electrode are respectively located at the two ends of the length direction of the multipole rod electrode, the light window of the vacuum ultraviolet krypton lamp is sealedly connected to the through hole of the repeller electrode, and the light window and the through hole of the repeller electrode have the same size, which are used to form a vacuum atmosphere and an ion transmission electric field.

[0020] Optionally, during sample injection, the gas pressure in the vacuum chamber is maintained at 100-1000 Pa.

[0021] Optionally, the surfaces of the repeller electrode, photoelectron electrode, multipole electrode and differential electrode are respectively provided with a gold-plated layer to prevent residual ion contamination during long-term use of the ionization source and improve the sensitivity of the mass spectrometer.

[0022] In a second aspect, a mass spectrometry instrument includes the above-mentioned ionization and focusing integrated ion source.

[0023] Optionally, the ionization and focusing integrated ion source is connected to a time-of-flight mass spectrometer, a quadrupole mass spectrometer or a magnetic mass spectrometer.

[0024] The beneficial effects of the utility model are:

[0025] The sample in the ionization focusing integrated ion source provided by the present invention can be ionized in three ways, including: (1) some VOCs with ionization energy lower than 10.6 eV can be directly photoionized to form sample ions; (2) most VOCs are ionized with O 2+ The reagent ions undergo chemical ionization to form sample ions; (3) Some OVOCs react with (H2O) n H3O + The reagent ions undergo a proton transfer reaction to form sample ions. The photoelectron electrode can apply a radio frequency electric field, which allows the ions passing through the photoelectron electrode to move in a spiral motion, increasing the frequency of ion-molecule collisions to improve sensitivity. During the chemical ionization process, under the action of pressure difference and potential difference, the quadrupole electric field formed in the segmented multipole electrode can constrain the ions to perform a quasi-sinusoidal motion perpendicular to the axis in the quadrupole, increasing the collision probability between the reagent ions and the sample molecules, promoting chemical ionization between the reagent ions and the sample molecules, and increasing the target ion yield; at the same time, the ions gradually decrease in energy and converge toward the central axis during the continuous collision motion, which increases the number of ions passing through the differential electrode and improves the ion transmission efficiency and sensitivity of the instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention.

[0027] Figure 1 Schematic diagram of the structure of the ionization and focusing integrated ion source in Example 1.

[0028] Figure 2 Schematic diagram of the connection relationship between the split rod and the voltage divider resistor and capacitor in Example 1.

[0029] Figure 3 Schematic diagram of the connection relationship between the multipole rod electrodes and the RF source in Example 1.

[0030] Figure 4 Schematic diagram of the connection relationship between the multipole electrodes and the DC source in Example 1.

[0031] Figure 5 Graphs showing simulation results of ions passing through differential electrodes in Example 1; a) is a graph showing simulation results without applying radio frequency voltage; b) is a graph showing simulation results with applying radio frequency voltage.

[0032] Figure 6 Schematic diagram of the structure of the mass spectrometer in Example 2.

[0033] Figure 7 Schematic diagram of the detection capability of the mass spectrometer in Example 2; a) is a schematic diagram of the detection capability of PAMs; b) is a schematic diagram of the detection capability of OVOCs.

[0034] Figure 8 This is a diagram of the long-term monitoring results of the mass spectrometry instrument in Example 2.

[0035] Figure 9 1. A comparison diagram of the detection results of whether or not radio frequency voltage is applied to the photoelectron electrode of the mass spectrometer in Example 2; a) is a diagram of the detection results when radio frequency voltage is applied; b) is a diagram of the detection results when radio frequency voltage is not applied.

[0036] Among them: 1. Vacuum ultraviolet krypton lamp; 2. Repeller electrode; 3. Photoelectron electrode; 4. Multipole electrode; 5. Splitter rod; 51. PEEK insulating rod; 6. Differential electrode; 7. First radio frequency power supply; 8. Reagent gas injection tube; 9. Sample gas injection tube; 10. Vacuum chamber; 11. Ionization and focusing integrated ion source; 12. Quadrupole chamber; 13. Lens chamber; 14. Time-of-flight mass analyzer; 15. Vacuum system; 16. Ions. DETAILED DESCRIPTION

[0037] Example 1

[0038] An integrated ion source with ionization and focusing, such as Figure 1 As shown, it comprises: a vacuum ultraviolet krypton lamp 1 and a repeller electrode 2 arranged along an axis, and a photoelectron electrode 3, a multipole electrode 4 and a differential electrode 6 are sequentially arranged on the side of the repeller electrode 2 away from the vacuum ultraviolet krypton lamp 1;

[0039] The repelling electrode 2, the photoelectron electrode 3 and the differential electrode 5 are provided with through holes along the axis; the multipole rod electrode 4 includes a plurality of rods arranged around the axis, each rod is parallel to the axis, and each rod includes a plurality of segmented rods 5 along the extension direction of the axis;

[0040] The photoelectron electrode is connected to a first radio frequency power supply 7, and the segmented multipole electrode 4 is connected to a second radio frequency power supply.

[0041] Among them, the photoelectron electrode 3 generates photoelectrons under the irradiation of the vacuum ultraviolet krypton lamp 1, which promotes the formation of reagent ions between the photoelectron electrode 3 and the repeller electrode 2. The repeller electrode 2 applies a high voltage to enable the reagent ions to obtain sufficient energy to move through the through holes along the axis in sequence. The multipole electrode 4 is used to promote chemical ionization between the reagent ions and the sample molecules, thereby increasing the target ion yield. In the continuous collision movement, the energy of the target ions gradually decreases and converges toward the central axis, thereby increasing the number of ions 16 passing through the differential electrode 6, thereby improving the ion transmission efficiency and sensitivity of the instrument.

[0042] The light window of the vacuum ultraviolet krypton lamp 1 has a diameter of 10 mm. The repeller electrode 2 has a through-hole of the same diameter, which is sealed to the through-hole of the repeller electrode 2 via an O-ring. The through-hole of the photoelectron electrode 3 has a smaller diameter than that of the repeller electrode 2, facilitating photon generation when photons strike the photoelectron electrode 3. The photoelectron electrode 3 has a countersunk hole facing the multipole rod electrode, located at the center of the bottom surface of the countersunk hole. The photoelectron electrode 3 is connected to a first RF power supply 7 via a 100 nF capacitor to generate a 1 MHz, 200 V RF electric field in the countersunk hole. This allows ions to spiral after passing through the photoelectron electrode 3, increasing the frequency of ion-molecule collisions and improving sensitivity. A 1 mm diameter through-hole is located in the center of the differential electrode 6, which is used for differential vacuum and ion transmission. During sample injection, the vacuum within the ionization source is maintained between 100 and 1000 Pa.

[0043] A reagent gas inlet tube 8 is provided between the repeller electrode 2 and the photoelectron electrode 3. The reagent gas preferably uses oxygen in the air (oxygen content in the air is 20%) and water as a natural reagent ion source, which is convenient for field deployment and avoids the need to carry standard gas cylinders during online detection. Acetone, ammonia, water, etc. can also be used.

[0044] The ion source includes a sample gas injection tube 9, which is a PEEK capillary with an inner diameter of 0.5 mm and a length of 1 m. The injection flow rate is 200 mL min -1 It can also be used in conjunction with other sampling systems; the opening of the sample gas injection tube 9 is opened on the cylindrical side wall of the countersunk hole. Similarly, the sample gas injection tube 9 is connected to the PEEK capillary or metal capillary through a commercial capillary inverted cone joint. By changing the inner diameter and length of the capillary, the flow rate of the sample gas can be controlled.

[0045] The multipole electrode 4 can be in the form of a quadrupole, hexapole or octapole. In each pole, multiple segmented rods 5 are coaxially and fixed at a set distance on an insulating rod (PEEK or ceramic material). Each segmented rod 5 is connected to an electrode ring, and the multiple electrode rings are insulated from each other. In addition to applying voltage and current, the electrode ring also serves as a connecting component to fix the pole on the insulating rod.

[0046] In this embodiment, the multipole electrode 4 is a quadrupole electrode, each of which includes six branch rods 5. Each branch rod 5 is coaxially fixed on a PEEK insulating rod 51 by an electrode ring with an inner diameter of 5 mm, an outer diameter of 9 mm, and a height of 4 mm. Each electrode ring is isolated by a PEEK insulating ring with an inner diameter of 5 mm, an outer diameter of 8 mm, and a height of 0.5 mm.

[0047] like Figure 2 As shown, the electrode rings are connected to 10MΩ voltage divider resistors and apply DC voltage (DC voltage range is 0-300V) to the rod 5 in the pole through the voltage divider resistor, forming a DC electric field along the axis direction. The voltage difference between the two ends of a single pole is 5V; and they are connected to a second RF power supply through the same capacitor (100nF) to apply RF voltage to the pole (RF voltage peak-to-peak value is 50-800V, RF frequency is 1-3MHz), and the minimum distance between the poles is D0 = 8mm. Figure 3 As shown, the opposite rods in the multipole electrode 4 are connected in parallel and connected to the RF source. Figure 4 As shown, adjacent rods in the multipole electrode 4 are connected in parallel and connected to a DC source.

[0048] The segmented quadrupoles form an ion-molecule reaction and focusing zone, where chemical ionization occurs between reagent ions and sample molecules. In the continuous collisions between ions and molecules, ions with gradually decreasing energy are converged on the central axis and then enter the mass spectrometry detection device for detection through a differential electrode 6 with a 1mm through-hole in the center.

[0049] The photoelectron electrode 3 and the multipole rod electrode 4 are located in the vacuum chamber 10, the repeller electrode 2 and the differential electrode 6 are respectively located at the two ends of the length direction of the multipole rod electrode 4, the light window of the vacuum ultraviolet krypton lamp 1 is sealedly connected to the through hole of the repeller electrode 2, and the light window and the through hole of the repeller electrode 2 are the same size, so that the vacuum inside the ionization source cavity is maintained at approximately 550Pa.

[0050] The surfaces of the repeller electrode 2, the photoelectron electrode 3, the multipole electrode 4 and the differential electrode 6 are respectively provided with a gold-plated layer to prevent ion residual contamination during long-term use of the ionization source and improve the sensitivity of the mass spectrometer.

[0051] In this embodiment, when the ionization source is performing sample detection, the sample gas enters the ionization source through the sample gas inlet and is ionized in the ionization source through three pathways: first, some VOCs with ionization energies lower than 10.6 eV can be directly photoionized as shown in formula (1); second, most VOCs are ionized by O2 + The reagent ions undergo chemical ionization, forming sample ions according to the principles of equations (2) to (4). Chemical ionization is the main ionization mode of this ionization source. n H3O + The reagent ions undergo a proton transfer reaction to form sample ions according to the principle shown in formula (5).

[0052] M+hv→M + , (1);

[0053] Metal+hv→e - , (2);

[0054]

[0055]

[0056] H3O + (H2O) n +M→M·H + +(H2O) n+1 , (5).

[0057] Among them, M represents sample, hv represents vacuum ultraviolet light, Metal represents metal, O2 represents oxygen, and H2O represents water.

[0058] When the ionization source is performing online monitoring: the pressure difference can be used to directly collect ambient gas through the sample gas injection tube 9, avoiding the pre-treatment of the sample, and the time for generating sample ions is in microseconds. By connecting to the mass spectrometer, a response in seconds can be achieved, which is convenient for real-time and rapid monitoring of the atmospheric environment.

[0059] During the detection process, the vacuum ultraviolet krypton lamp 1 irradiates the metal surface of the photoelectron electrode 4, and the sputtered photoelectrons collide with oxygen and water in the air under the acceleration of the electric field to generate O2 + with (H2O) n H3O + Reagent ions (Formula 2-5), then under the action of pressure difference and potential difference, the reagent ions and sample molecules move forward into the fragment quadrupole ion-molecule reaction and focusing area.

[0060] Use SIMION 2020 software to simulate the motion state of ions in the ionization focusing integrated ionization source, such as Figure 5 As shown, the voltage on the photoelectron electrode 3 is 20 V, the voltage difference across the multipole electrode 4 is 5 V (20 V–15 V), and the voltage on the differential electrode 6 is 7 V; the initial ion conditions are: 500 ions with a mass-to-charge ratio of m / z = 100, uniformly dispersed in a cylinder with a radius of 2 mm and a height of 25 mm.

[0061] When RF=0V is applied to the multipole electrode 4 and the RF voltage frequency is 0 Hz, most of the ions 16 generated in the ionization source cannot pass through the differential electrode 6. Figure 5 As shown in a); when RF = 300V, the RF voltage frequency is 2×10 6 Hz, the efficiency of ions 16 passing through the differential electrode 6 is greatly improved after collision cooling, such as Figure 5 The simulation results show that the number of ion-molecule collisions increased by 6459 / 3125 = 2 times, and the ion transmission efficiency increased by 16 times.

[0062] Example 2

[0063] A mass spectrometer, comprising an ionization and focusing integrated ion source 11, a quadrupole chamber 12, a lens chamber 13, and a time-of-flight mass analyzer chamber 14 in Example 1 connected in sequence, and a vacuum system 15 is connected to each of the above chambers, maintaining the differential vacuum between the vacuum chamber 10 of the ionization and focusing integrated ion source 11 of the mass spectrometer and the other three chambers, and the vacuum degrees of the four regions are 550, 1.5, 10, and 15 respectively. -3 and 10 -5 Pa.

[0064] Figure 7 a) in Figure 2 shows the detection results of 57 PAMs. Figure 7 b) in the figure shows the detection results of 12 OVOCs. Table 1 shows the detection limits of the mass spectrometer of this embodiment for 57 ozone precursors (PAMs) and 12 aldehydes and ketones, showing good detection capabilities. The data in Table 1 show that the detection limit can reach the pptv level.

[0065] Table 1 shows the detection limits of 57 ozone precursors and 12 aldehydes and ketones

[0066]

[0067]

[0068]

[0069] Figure 8 The data show the long-term monitoring data of the concentrations of three OVOCs (propionaldehyde, valeraldehyde and benzaldehyde) in the atmosphere by the mass spectrometer in this embodiment. Over a period of 15 days, their concentrations in the atmosphere fluctuated between 1 and 3 ppbv, reflecting the sensitivity and stability of the detection.

[0070] The effect of the radio frequency voltage applied to the photoelectron electrode 3 is evaluated based on the peak intensity of the detection result, such as Figure 9 As shown: Figure 9 b) is the detection result of benzene, toluene and xylene obtained when no radio frequency voltage is applied to the photoelectron electrode 3; according to the same detection parameters, a radio frequency voltage with a peak value of 200V and a radio frequency frequency of 1MHz is applied to the photoelectron electrode 3, and the detection results obtained are as follows Figure 9 As shown in a), it can be seen that after increasing the radio frequency voltage on the photoelectron electrode 3, the peak intensity of the target ion is significantly improved, and the relative value is about 1.5 times, indicating that the detection sensitivity can be effectively improved.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An integrated ion source with ionization and focusing, characterized in that: The device comprises a vacuum ultraviolet krypton lamp and a repeller electrode arranged along an axis, wherein a photoelectron electrode, a multipole electrode and a differential electrode are sequentially arranged on a side of the repeller electrode away from the vacuum ultraviolet krypton lamp; The repulsion electrode, the photoelectron electrode and the differential electrode are provided with through holes along the axis; the multipole electrode comprises a plurality of rods arranged around the axis, each rod being parallel to the axis, and each rod comprising a plurality of segments along the extension direction of the axis; The photoelectron electrode is connected to a first radio frequency power source, and the multipole rod electrode is connected to a second radio frequency power source.

2. The ionization and focusing integrated ion source according to claim 1, characterized in that: The aperture of the through hole of the photoelectron electrode is smaller than that of the through hole of the repeller electrode. The photoelectron electrode is provided with a countersunk hole facing the multipole electrode. The through hole of the photoelectron electrode is located at the center of the bottom surface of the countersunk hole.

3. The ionization and focusing integrated ion source according to claim 2, characterized in that: A reagent gas injection tube is provided between the repeller electrode and the photoelectron electrode.

4. The ionization and focusing integrated ion source according to claim 2, characterized in that: It comprises a sample gas injection tube, the tube mouth of which is opened on the cylindrical side wall of the counterbore.

5. The ionization and focusing integrated ion source according to claim 1, characterized in that: The multipole electrode is in the form of a quadrupole, a hexapole or an octapole. In each pole, multiple segments are coaxially fixed on an insulating rod at set intervals. Each segment is connected to an electrode ring, and the multiple electrode rings are insulated from each other.

6. The ionization and focusing integrated ion source according to claim 5, characterized in that: The electrode rings are respectively connected to a DC voltage source via voltage-dividing resistors, and are respectively connected to a second radio frequency power source via the same capacitor.

7. The ionization and focusing integrated ion source according to claim 1, characterized in that: The photoelectron electrode is connected to a first radio frequency power supply via a capacitor.

8. The ionization and focusing integrated ion source according to claim 1, characterized in that: The photoelectron electrode and the multipole rod electrode are located in a vacuum chamber, the repeller electrode and the differential electrode are respectively located at the two ends of the length direction of the two sides of the multipole rod electrode, the light window of the vacuum ultraviolet krypton lamp is sealed and connected to the through hole of the repeller electrode, and the light window and the through hole of the repeller electrode have the same size.

9. The ionization and focusing integrated ion source according to claim 1, characterized in that: The surfaces of the repulsion electrode, the photoelectron electrode, the multipole rod electrode and the differential electrode are respectively provided with a gold-plated layer.

10. A mass spectrometry instrument, characterized in that: It comprises the ionization and focusing integrated ion source as described in any one of claims 1-9.

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