Electron multiplier, mass spectrometry system and method

Abstract

The invention relates to a mass spectrometry technology, and particularly provides an electron multiplier, a mass spectrometry system and a mass spectrometry method, the electron multiplier comprises a multi-stage dynode, a collector and a power supply, and the power supply applies voltage to the dynode and the collector; the power supply is connected with the voltage division circuit, and the voltage division circuit is connected with the third dynode to the Nth dynode; the switching unit is used for switching the working mode of the voltage division circuit, the voltage division circuit applies positive bias voltage to the third-stage dynode to the Nth-stage dynode in the detection mode, and the voltage applied to the third-stage dynode to the Nth-stage dynode is the same in the cleaning mode. The cleaning device has the advantages of good cleaning effect, convenience and the like.

Description

Technical Field

[0001] This invention relates to mass spectrometry, and more particularly to electron multipliers, mass spectrometry systems and methods. Background Technology

[0002] Mass spectrometry (MS) is a scientific instrument that separates ions with different mass-to-charge ratios using electric / magnetic fields to determine the molecular and structural composition of matter. Generally, a mass spectrometry system has three main components: an ionization source to ionize the analyte compound; a mass analyzer to separate different ions based on m / z differences; and a detector to amplify and detect the ion stream after screening by the mass analyzer. Electron multipliers are the most commonly used type in mass spectrometry. Their core principle is to amplify weak ion signals through secondary electron emission from the tampon surface. Depending on the tampon structure, they can be divided into continuous tampon electron multipliers and discrete tampon electron multipliers. The latter typically has 11-22 (or even more) discrete tampons, each biased with a positive voltage to create an electron avalanche, ultimately achieving a gain approximately 50%-100% higher than continuous multipliers. This characteristic is why they are widely used.

[0003] Technically, Al2O3 and Cu-BeO are commonly chosen as secondary electron emission materials for the dinter electrode surface. These alloys, through oxidation treatment, can form a low work function surface, effectively improving the secondary electron emission coefficient (γ=2-4). However, with increasing usage time, multipliers inevitably age. One major reason is that carbonaceous organic contaminants remaining in the vacuum system adsorb onto the dinter electrode surface. Under ion / electron beam bombardment, these organic contaminants undergo decomposition and polymerization reactions, forming carbonaceous deposits that bind to the electrode surface, leading to a decrease in secondary electron yield. Since contaminants preferentially contact the front-end dinter electrode during the transmission process from the ion source to the multiplier, the front-end dinter electrode is the most heavily contaminated. The contamination level of the first dinter electrode (conversion dinter electrode) directly affects the primary secondary electron yield, thus having the greatest impact on the multiplier gain performance. Taking this key issue as a starting point, this patent proposes a system and method for efficiently activating and regenerating multipliers.

[0004] Ordinary technicians have already used various methods to solve the above problems, such as: 1. Increasing the voltage of the multiplier electrode can further increase the number of secondary electrons and restore the original gain, but this operation will greatly reduce the service life of the multiplier. From the perspective of long-term use costs, this method is not worthwhile. 2. Disassemble the multiplier for cleaning / refurbishment. For example, multiplier manufacturers usually recommend using the conventional method of ultrasonic cleaning with organic solvents such as isopropanol followed by high-temperature baking. The article "Activation and Regeneration of Electron Multipliers" proposes a heating annealing method. First, the electron multiplier undergoes chemical decontamination, then it is placed in a high-vacuum system for high-frequency induction heating. The preheating temperature is gradually increased to approximately 400°C, and degassing takes about a full day. Afterward, oxygen is introduced for activation while maintaining a high-vacuum environment, with the temperature gradually increased from 550°C to 700-740°C. This oxygen absorption reaction is repeated more than 20 times. Finally, high-frequency heating continues for 20 minutes under high vacuum, followed by gradual cooling. This method can restore the gain of a multiplier with degraded performance, but it has not been disclosed in patent form.

[0005] Obviously, the above methods require removing the multiplier from the mass spectrometer chamber, which necessitates breaking the instrument's vacuum and interrupting normal instrument operation. After cleaning and reinstalling the multiplier, large laboratory mass spectrometers require several days to achieve high vacuum, and typically require professional disassembly guidance from the mass spectrometer manufacturer's engineers. Moreover, the latter method suffers from an overly complex cleaning process. Summary of the Invention

[0006] To address the shortcomings of the existing technical solutions, the present invention provides an electron multiplier.

[0007] The objective of this invention is achieved through the following technical solution: An electron multiplier includes a multi-stage dynode, a collector, and a power source, wherein the power source applies a voltage to the dynode and the collector; the electron multiplier further includes: A voltage divider circuit is provided, wherein the power supply is connected to the voltage divider circuit, and the voltage divider circuit is connected to the third to the Nth stage terminals; A switching unit is used to switch the operating mode of the voltage divider circuit. When in detection mode, the voltage divider circuit applies a positive bias voltage to the electrodes of the 3rd to Nth stages. When in cleaning mode, the voltage applied to the electrodes of the 3rd to Nth stages is the same.

[0008] Another objective of this invention is to provide a method for operating an electron multiplier, wherein the method is as follows: When switched to detection mode, the voltage divider circuit applies an increasing voltage to the electrodes of the 3rd to Nth stages; When switched to cleaning mode, negative oxygen ions enter the electron multiplier and are captured by the tandoor, reacting with the carbon deposited on the tandoor surface.

[0009] The present invention also aims to provide a mass spectrometry system, comprising an ion source, a transmission device, a mass analyzer, and a detector arranged sequentially. The detector employs the electron multiplier of this application. In the cleaning mode, the ion source generates superoxide negative ions, which are then decomposed into oxygen negative ions.

[0010] The present invention also aims to provide a method for operating a mass spectrometry system, including a detection mode; the method further includes a cleaning mode, wherein the cleaning mode is: The ion source generates superoxide anions, which are then split into oxygen anions. The oxygen anions pass through the transmission device and the mass analyzer in sequence, enter the electron multiplier, and are captured by the tandem electrode. The oxygen anions react with the carbon deposited on the surface of the tandem electrode.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: By relying on the mass spectrometry system's own ion source to generate superoxide negative ions in situ, which are then decomposed into oxygen negative ions, the discrete darad multiplier can achieve "non-disassembly, non-damage, and high-efficiency" carbon pollution cleaning and functional regeneration through directional electric field guidance. Essentially, it breaks through the bottleneck of existing technologies that require vacuum destruction and reliance on external equipment, and uses mass spectrometry as the master controller for cleaning, solving the gain decay problem caused by carbon deposition during long-term use of discrete darad multipliers.

[0012] In-situ cleaning is achieved, converting oxygen negative ions from analytical ions to active ions for cleaning, allowing the cleaning process to be carried out directly in-situ inside the mass spectrometry system, avoiding the instrument interruption problem in existing technologies and avoiding a series of complex operations of disassembly and reassembly. Targeted cleaning is achieved by designing a voltage divider circuit and switching unit for the hierarchical structure of discrete dinoflagellates. This guides the transport of negative oxygen ions to the front-end dinoflagellate with the highest degree of contamination, while simultaneously realizing the reaction energy of negative oxygen ions colliding with the surface. This achieves precise cleaning while allowing for autonomous adjustment of cleaning power.

[0013] 1. Restore multiplier gain to improve detection signal-to-noise ratio; 2. Extend the service life of the multiplier and reduce maintenance costs; 3. Ensure stable operation of mass spectrometry and improve maintenance efficiency; 4. No additional consumables or equipment are required, reducing maintenance costs. Attached Figure Description

[0014] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are merely illustrative of the technical solutions of this invention and are not intended to limit the scope of protection of this invention. In the drawings: Figure 1 This is a schematic diagram of the electron multiplier according to the present invention; Figure 2 This is a schematic diagram of the mass spectrometry system according to the present invention; Figure 3 This is a schematic diagram of the ion travel path according to Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the ion travel path according to Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of the ion travel path according to Embodiment 4 of the present invention.

[0015] In the attached figure, 21-ion source, 22-sampling cone, 23-vacuum chamber, 24-transfer capillary, 241-intra-source fragmentation region, 25-Skimmer, 26-octupole, 27-mass analyzer, 28-detector, 29-purge cone. Detailed Implementation

[0016] Figures 1-5 The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to teach the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the optional embodiments described below, but is defined only by the claims and their equivalents.

[0017] Example 1

[0018] One embodiment of the electron multiplier, such as Figure 1 As shown, it includes: Multi-level attack, such as DY1-DY 19 A collector electrode and a power source, wherein the power source applies a voltage to the collector electrode and the collector electrode.

[0019] The power supply is connected to a voltage divider circuit, which is connected to the third to the Nth stage terminals. The switching unit is used to switch the operating mode of the voltage divider circuit. When in detection mode, the voltage divider circuit applies a positive bias voltage to the electrodes of the 3rd to Nth stages (e.g., N=19). When in cleaning mode, the voltage applied to the electrodes of the 3rd to Nth stages is the same.

[0020] The voltage divider circuit includes (N-3) resistors connected in series, such as... Figure 1 In the orange section, the output terminal of the i-th resistor is connected to the (i+3)-th stage electrode, where i = 1, 2, ..., (N-3).

[0021] The switching unit includes: A series of (N-3) switches, such as K1-K 16 The i-th switch is connected in parallel with the i-th resistor, i = 1, 2, ... (N-3); one end of the (N-3)-th switch is connected through the (N-2)-th switch (such as switch K). 17 Connect the Nth stage dial electrode, and the Nth stage dial electrode is sequentially connected to the (N-1)th switch (e.g., switch K). 18), connection point, Nth switch (e.g., switch K) 19 The (N-2)th resistor and the collector are connected at the connection point to the (N-3)th switch, and through the (N-1)th resistor and the (N+1)th switch (such as switch K). 20 Grounding; In the detection mode, the (N-3)th, (N-2)th, and (N+1)th switches connected in series are open, while the (N-1)th and Nth switches are closed. In cleaning mode, the (N-3)th, (N-2)th, and (N+1)th switches connected in series are closed, while the (N-1)th and Nth switches are open.

[0022] To clean the first-stage tannin electrode, which has the most deposited carbon, further in the cleaning mode, the first-stage tannin electrode captures negative oxygen ions. The power supply applies positive voltages V1 to the first-stage tannin electrode and V2 to the second-stage tannin electrode, and negative voltages V3 to the third-stage tannin electrode, with -V3>V1>V2.

[0023] In order to skip the first-stage dano electrode and directly clean the second-stage dano electrode with more deposited carbon, further, in the cleaning mode, the second-stage dano electrode captures oxygen negative ions. The power supply applies a positive voltage V2 to the second-stage dano electrode and a negative voltage V3 to the third-stage dano electrode, with -V3>V2>abs(V1).

[0024] The working method of the electron multiplier according to an embodiment of the present invention is as follows: When switched to detection mode, the voltage divider circuit applies an increasing voltage to the electrodes of the 3rd to Nth stages; When switched to cleaning mode, negative oxygen ions enter the electron multiplier and are captured by the tandoor, reacting with the carbon deposited on the tandoor surface.

[0025] To prevent damage to the metal coating on the dara electrode surface when oxygen negative ions bombard it, it is necessary to ensure that the reaction between oxygen negative ions and carbon deposits is not physical sputtering, but gentle chemical etching, with oxygen negative ion energy ranging from 20eV to 100eV.

[0026] The mass spectrometry system of this invention, such as Figure 2 As shown, it includes an ion source 21, a transmission device, a mass analyzer 27, and a detector 28 arranged in sequence.

[0027] The detector 28 uses the electron multiplier of this embodiment. In the cleaning mode, the ion source 21 generates superoxide negative ions and decomposes them into oxygen negative ions.

[0028] The ion source 21 is an atmospheric pressure chemical ionization source, and the mass analyzer 27 is a multipole, such as a quadrupole.

[0029] The working method of the mass spectrometry system of this invention includes a detection mode; the working method further includes a cleaning mode, wherein the cleaning mode is: Ion source 21 generates superoxide negative ions, which are then broken down into oxygen negative ions. These ions pass through the transmission device and mass analyzer 27 in sequence, enter the electron multiplier, and are captured by the tandem electrode. The oxygen negative ions react with the carbon deposited on the surface of the tandem electrode.

[0030] Example 2

[0031] Application example of the mass spectrometry system and method in Example 1.

[0032] In this application example, such as Figure 2 As shown, the mass spectrometry system consists of an ion source 21, a sampling cone 22, a purge cone 29, a transport capillary 24, a skimmer 25, an octupole 26, a mass analyzer 27, and an end detector 28 arranged sequentially.

[0033] Vacuum chamber 23 has three levels of vacuum. The first level of vacuum (2-3 Torr) is upstream of Skimmer 25, and the octupole 26 is in the second level of vacuum (approximately 8 × 10⁻⁶). -3 Torr), mass analyzer 27 and detector 28 are in the third stage vacuum (approximately 5 × 10⁻⁶). - 5 Torr).

[0034] Ion source 21 is an atmospheric pressure chemical ionization (APCI) source. By increasing the voltage of the transmission capillary 24, intrasource ion fragmentation can be formed in the first-stage vacuum region between it and the Skimmer. Octuple 26 operates in RF-only mode and is used solely for ion transport. Mass analyzer 27 is a quadrupole with selected ion monitoring mode (SIM) to filter out only ions of specific masses; for example, in clean mode, only oxygen negative ions are allowed to pass. Detector 28 is a discrete danotron electron multiplier with 19 danotron stages.

[0035] Generation of superoxide negative ions: When the APCI source ionizes the air in the environment, the following gas-phase reaction occurs in sequence, in which superoxide negative ions are one of the main product ions.

[0036] To ensure that the superoxide negative ions are always kept at a high concentration level, backflush gas is introduced into the reaction zone of ion source 21 to blow out the intermediate products ozone (O3) and nitrogen oxides (NO2) from the reaction zone as much as possible, thereby avoiding further reactions of equations (2)-(7).

[0037] Increasing the pressure difference between the transport capillary 24 and Skimme 25 can provide additional energy for superoxide anions, allowing them to collide with background neutral molecules, thereby causing superoxide anions to split into oxygen anions in the source-internal splitting region 241 between the capillary 24 and Skimme 25r.

[0038] like Figure 1 As shown, the electron multiplier includes 19 stages of electrodes and a collector, with the electrodes being DY1-DY. 19 .

[0039] The voltage divider circuit consists of 16 resistors connected in series. Figure 1 In the orange section, the output terminal of the i-th resistor is connected to the (i+3)-th stage electrode, i=1,2···16.

[0040] The switching unit consists of 16 switches connected in series, namely K1-K 16 The i-th switch is connected in parallel with the i-th resistor, i = 1, 2, ..., 16; the 16th switch (K 16 One end of the switch is connected to the 17th switch (switch K). 17 Connect the 16th stage dial electrode, and the 16th stage dial electrode is then connected to the 18th switch (K). 18 ), connection point, 19th switch (K) 19 The 17th resistor and the collector, the connection point is connected to the 16th switch, and through the 18th resistor and the 20th switch (K) 20 Grounding.

[0041] In detection mode, the 16 switches K1-K are connected in series. 16 Switch K 17 and switch K 20 Disconnect, switch K 18 and switch K 19 Close the circuit. The power supply applies a voltage of +4kV to the first stage electrode DY1, +4.2kV to DY2, and +4.4kV to DY3. The collector isolation voltage is set to +7.8kV, thus enabling the circuit from DY1 to DY2. 19 A positive voltage bias of +0.2kV is formed on it, thus putting it into the conventional mode of ion detection.

[0042] In cleaning mode, the 16 switches K1-K connected in series... 16 Switch K 17 and switch K 20 Open / close, switch K 18 and switch K 19 Disconnect. Set the collector voltage to 0V. The power supply is DY1 with applied voltage V1 and DY2 with applied voltage V2, both of which are positive voltages. The voltage is DY3-DY. 19 The applied voltage V3 is a negative voltage.

[0043] To achieve cleaning of the first stage DY1, the specific steps are as follows: Perform mass spectrometry sensitivity calibration periodically (e.g., every 1 week, 2 weeks, 1 month). If a significant decrease in signal-to-noise ratio is observed (typically 70%, 50%, or 30% of the original gain), after ruling out any abnormalities in ion source 21 and the ion transmission unit, initiate multiplier cleaning at the mass spectrometry control system. Typical settings include: The APCI discharge needle voltage is set to -4kV, the current is set to 5uA, air is used as the discharge gas, and gas is introduced into the ion reaction zone for backflushing.

[0044] Increase the voltage of the transmission capillary 24. The voltage difference between the capillary 24 and Skimer 25 can be selected as 80V, 100V, 120V, etc.

[0045] The quadrupole RF is 1.2MHz with a field radius of 4mm. According to the a and q stability conditions of the Mathieu equation, in order to allow only oxygen negative ions with m / z = -16 to pass through, the operating point can be set as the peak of the stable region. The specific configuration of RF is U = (4.5V) and V = (26.5V) ((zero peak value)).

[0046] The multiplier inlet structure is a grounded shielded grid (0V).

[0047] Switch to cleaning mode, V1=80V, V2=30V, V3=-140V, satisfying -V3>V1>V2.

[0048] After cleaning for 5-10 minutes, switch to the traditional detection mode.

[0049] like Figure 3 As shown, oxygen anions are directionally transferred to the first-stage dinoflagellate electrode DY1.

[0050] Example 3

[0051] The application example of the mass spectrometry system and method in Example 1 differs from that in Example 2 in that: If the multiplier gain drops to 10-30% of normal, activate the "powerful cleaning" mode: V1=80V, V2=30V, V3=-140V, oxygen negative ion bombardment energy is 85eV. Figure 4 As shown in (a).

[0052] If the multiplier gain drops to 30-50% of normal, activate the "Standard Cleaning" mode: V1=40V, V2=30V, V3=-125V, oxygen negative ion bombardment energy is 45eV. Figure 4 As shown in (b).

[0053] If the multiplier gain drops to 50-70% of normal, activate the "light cleaning" mode: V1=20V, V2=30V, V3=-125V, oxygen negative ion bombardment energy is 25eV. Figure 4 As shown in (c).

[0054] Example 4

[0055] The application example of the mass spectrometry system and method in Example 1 differs from that in Example 2 in that: To achieve targeted cleaning of the second-stage dynamo electrode DY2, V1=1V, V1=59V, V3=-175V.

[0056] Oxygen negative ions directly bypass DY1 and are directionally transferred to the surface of DY2, with a bombardment energy of approximately 64 eV, achieving the cleaning purpose. Figure 5 As shown.

Claims

1. An electron multiplier, comprising a multi-stage dynode, a collector, and a power supply, wherein the power supply applies a voltage to the dynode and the collector; characterized in that, The electron multiplier also includes: A voltage divider circuit is provided, wherein the power supply is connected to the voltage divider circuit, and the voltage divider circuit is connected to the third to the Nth stage terminals; A switching unit is used to switch the operating mode of the voltage divider circuit. When in detection mode, the voltage divider circuit applies a positive bias voltage to the electrodes of the 3rd to Nth stages. When in cleaning mode, the voltage applied to the electrodes of the 3rd to Nth stages is the same.

2. The electron multiplier according to claim 1, characterized in that, The voltage divider circuit includes (N-3) resistors connected in series, with the output terminal of the i-th resistor connected to the (i+3)-th stage terminal, i=1,2···(N-3).

3. The electron multiplier according to claim 2, characterized in that, The switching unit includes: (N-3) switches are connected in series, with the i-th switch connected in parallel with the i-th resistor, i=1,2...(N-3); one end of the (N-3)-th switch is connected to the N-th electrode through the (N-2)-th switch, and the N-th electrode is connected in sequence to the (N-1)-th switch, the connection point, the N-th switch, the (N-2)-th resistor, and the collector. The connection point is connected to the (N-3)-th switch and grounded through the (N-1)-th resistor and the (N+1)-th switch. In the detection mode, the (N-3)th, (N-2)th, and (N+1)th switches connected in series are open, while the (N-1)th and Nth switches are closed. In cleaning mode, the (N-3)th, (N-2)th, and (N+1)th switches connected in series are closed, while the (N-1)th and Nth switches are open.

4. The electron multiplier according to claim 1, characterized in that, In cleaning mode, the first stage tandem electrode captures negative oxygen ions. The power supply applies positive voltages V1 and V2 to the first stage tandem electrode, and negative voltages V3 to the third stage tandem electrode, with -V3>V1>V2.

5. The electron multiplier according to claim 1, characterized in that, In cleaning mode, the second-stage tandem electrode captures negative oxygen ions. The power supply is a positive voltage V2 applied to the second-stage tandem electrode and a negative voltage V3 applied to the third-stage tandem electrode, where -V3>V2>abs(V1).

6. The method of operating the electron multiplier according to any one of claims 1-5, characterized in that, The working method is as follows: When switched to detection mode, the voltage divider circuit applies a positive bias voltage to the electrodes of stages 3 through N; When switched to cleaning mode, negative oxygen ions enter the electron multiplier and are captured by the tandoor, reacting with the carbon deposited on the tandoor surface.

7. The working method according to claim 6, characterized in that, The energy of oxygen negative ions is 20eV-100eV.

8. A mass spectrometry system, comprising an ion source, a transmission device, a mass analyzer, and a detector arranged sequentially; characterized in that, The detector employs an electron multiplier as described in any one of claims 1-5. In clean mode, the ion source generates superoxide negative ions, which are then decomposed into oxygen negative ions.

9. The mass spectrometry system according to claim 8, characterized in that, The ion source is an atmospheric pressure chemical ionization source, and the mass analyzer is a multipole.

10. The method of operating the mass spectrometry system according to claim 8 or 9, comprising a detection mode; characterized in that, The working method also includes a cleaning mode, which is: The ion source generates superoxide anions, which are then broken down into oxygen anions. The oxygen anions pass through the transmission device and the mass analyzer in sequence, enter the electron multiplier, and are captured by the tandem electrode. The oxygen anions react with the carbon deposited on the surface of the tandem electrode.

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