A mass spectrometer based on image charge signal detection

Abstract

The application relates to a mass spectrometer based on mirror charge signal detection, comprising an electrostatic ion trap, the electrostatic ion trap comprising an electrode group for defining a boundary potential to generate an electrostatic field, the electrode group comprising a plurality of electrodes, at least two electrodes in the electrode group serving as mirror charge pickup electrodes, the mirror charge pickup electrodes being connected through a capacitor, one of the mirror charge pickup electrodes being connected with a mirror charge amplifier, and each mirror charge pickup electrode being electrically connected with a resistor and then with a direct current power supply; the application connects the direct current power supply with each mirror charge pickup electrode to electrify the mirror charge pickup electrode to meet the conditions for mass spectrum analysis of ions in the ion trap, and connects the mirror charge pickup electrodes through a capacitor to combine the mirror charge signals picked up by the plurality of mirror charge pickup electrodes and send the signals to a mirror charge amplifier for amplification and detection, so that the number of mirror charge amplifiers is reduced, and noise signals are reduced.

Description

Technical Field

[0001] This invention relates to the field of electrostatic orbital ion trap mass spectrometer equipment, and in particular to a mirror charge pickup circuit for an electrostatic ion trap. Background Technology

[0002] In Fourier transform mass spectrometry (FTMS) using electrostatic or magnetic field ion traps as analyzers, ions oscillate under the constraint of magnetic or electric fields, inducing a mirror current at the pickup electrode. As the ions oscillate continuously in the electric or magnetic field, the induced mirror current signal is amplified by a low-noise amplifier and then converted into a spectrum by Fourier transform, thus becoming the mass spectrum of the ions.

[0003] In existing mass spectrometers, due to the different potentials between the electrodes in the electrostatic ion trap, only one electrode is selected as the image charge pickup electrode and connected to an image charge amplifier to pick up the image charge signal; or a pair of electrodes are selected as anti-phase image charge pickup electrodes and connected to the two input terminals of a differential charge amplifier. Other electrodes are lost and wasted because they need to be applied with different DC potentials or the orientation distance between the electrodes is inconvenient to connect to the same amplifier. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a mass spectrometer based on image charge signal detection that can reduce the loss and waste of image charge signal pickup.

[0005] The technical solution adopted in this invention is a mass spectrometer based on image charge signal detection, comprising an electrostatic ion trap and an image charge amplifier. The electrostatic ion trap includes an electrode group for defining a boundary potential and generating an electrostatic field. The electrode group includes several electrodes, some of which serve as image charge pickup electrodes in conjunction with the image charge amplifier to pick up image charge signals. The electrode group includes at least one pickup electrode assembly, and the pickup electrode assembly includes at least two image charge pickup electrodes with similar phases for picking up image charge signals. Each image charge pickup electrode in the pickup electrode assembly is electrically connected to a DC voltage through a resistor to ensure that the electric field in the ion trap meets the conditions for mass spectrometry analysis of ions in the trap. Image charge pickup electrodes at different potentials in each pickup electrode assembly are electrically connected through a capacitor. At the same time, one of the image charge pickup electrodes in the pickup electrode assembly is electrically connected to the input terminal of the image charge amplifier.

[0006] The beneficial effects of this invention are as follows: This invention connects image charge pickup electrodes with similar phases to the input terminal of the same charge amplifier through capacitors, and applies power to the image charge pickup electrodes through resistors and DC voltage to meet the conditions for mass spectrometry analysis of ions in the ion trap. This allows multiple electrodes in the ion trap to pick up image charge signals, obtain stronger image charge signals, and reduce the loss and waste of image charge signals.

[0007] Preferably, the image charge amplifier is a differential amplifier. The electrodes of the electrode group are two symmetrically arranged outer shell electrodes that pick up image charge signals with opposite phases, and inner electrodes symmetrically arranged within the two outer shell electrodes. The outer shell electrodes and at least one inner electrode within the outer shell electrodes form the image charge pickup electrode assembly. The two outer shell electrodes, as image charge pickup electrodes, are respectively connected to the positive and negative input terminals of the differential amplifier. The inner electrodes and outer shell electrodes within the same pickup electrode assembly, which serve as image charge pickup electrodes, are electrically connected through a capacitor. In this way, the image charge signals picked up by the inner electrodes and the outer shell electrodes are combined and input into the differential amplifier, thereby enhancing the signal strength of the image charge signal.

[0008] Preferably, the image charge amplifier is a low-noise amplifier, and the electrode group consists of two coaxially arranged ring electrode arrays composed of several electrodes. Each ring electrode array is a coaxial circular structure composed of multiple electrodes. Each of the electrodes can serve as an image charge pickup electrode to cooperate with the image charge amplifier to pick up image charge signals. One image charge pickup electrode, serving as the central image charge pickup electrode, is located at the central axis of the two ring electrode arrays and passes through both ring electrode arrays. The image charge pickup electrodes within the same pickup electrode assembly are electrically connected to the central image charge pickup electrode via capacitors. The central image charge pickup electrode capacitively couples the image charge pickup electrodes in the two ring electrode arrays to an image charge amplifier. Furthermore, the central image charge pickup electrode can increase the amount of image charge picked up, reduce the charge interaction force between ions, and improve the sensitivity of image charge signal detection.

[0009] Preferably, within the electrode group, the mirror charge pickup electrodes connected by capacitors are adjacent to each other.

[0010] Preferably, the DC voltage includes a first DC voltage, a second DC voltage, and a third DC voltage that are electrically connected to the central mirror charge pickup electrode via a resistive device, wherein the second DC voltage is electrically connected to the mirror charge pickup electrode connected to the mirror charge amplifier via a resistive device, and the third DC voltage is connected to other mirror charge pickup electrodes within the same pickup electrode assembly via a resistive device.

[0011] Preferably, ensuring that the electric field within the ion trap meets the conditions for mass spectrometry analysis of ions within the trap includes:

[0012] (1) When analyzing positive ions, the first DC voltage is higher than the second DC voltage to form a potential difference;

[0013] (2) When analyzing negative ions, the first DC voltage is lower than the second DC voltage to form a potential difference.

[0014] The positive or negative potential difference created can generate an electric field within the ion trap that helps to focus ions both temporally and spatially.

[0015] Preferably, the central mirror charge pickup electrode is a cylindrical electrode with a diameter of less than 1.5 mm.

[0016] Preferably, the image charge pickup electrode with similar phase is the image charge pickup electrode whose fundamental frequency phase difference with the picked-up image charge pickup signal is less than 30°.

[0017] Preferably, the resistive device is a resistor, an inductor, or a resistor and an inductor connected in series. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a specific embodiment 1 of the present invention;

[0019] Figure 2 This is a schematic diagram of the structure of a specific embodiment 2 of the present invention;

[0020] Figure 3 This is a potential distribution diagram of the central mirror charge pickup electrode in a specific embodiment 2 of the present invention when the DC potential of the central mirror charge pickup electrode is higher than that of the adjacent mirror charge pickup electrode.

[0021] Figure 4 This is a potential distribution diagram of the central mirror charge pickup electrode in specific embodiment 2 of the present invention when the DC potential of the central mirror charge pickup electrode is equal to that of the adjacent mirror charge pickup electrode.

[0022] Figure 5 This is a schematic diagram of the ring electrode array in specific embodiment 2 of the present invention.

[0023] As shown in the figure: 1. Electrode group; 1-1. Electrode; 1-1-1. Outer shell electrode; 1-1-2. Inner electrode; 2. Mirror charge pickup electrode; 3. Pickup electrode assembly; 4. Capacitor; 5. Mirror charge amplifier; 6. Resistor; 7. DC voltage; 7-1. First DC voltage; 7-2. Second DC voltage; 8. Central mirror charge pickup electrode. Detailed Implementation

[0024] The invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can implement it based on the description. The scope of protection of the invention is not limited to these specific embodiments.

[0025] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention. Specific Implementation Example 1:

[0027] like Figure 1 As shown, a mass spectrometer based on image charge signal detection includes an electrostatic ion trap and an image charge amplifier 5 for picking up image charge signals within the electrostatic ion trap. The electrostatic ion trap includes an electrode group 1 for defining a boundary potential and generating an electrostatic field. The electrode group 1 includes several electrodes 1-1, each of which can serve as an image charge pickup electrode 2 in conjunction with the image charge amplifier 5 to pick up image charge signals. The electrode group 1 includes at least one pickup electrode assembly 3, which includes at least two image charge pickup electrodes 2 for picking up image charge signals with similar phases. Each image charge pickup electrode 2 in each pickup electrode assembly 3 is electrically connected via a resistor 6 to a DC voltage 7 used to ensure that the electric field within the ion trap meets the conditions for mass spectrometry analysis of ions within the trap. Image charge pickup electrodes 2 at different potentials within each pickup electrode assembly 3 are electrically connected via a capacitor 4. Simultaneously, one of the image charge pickup electrodes 2 in the pickup electrode assembly 3 is connected to the input terminal of the image charge amplifier 5.

[0028] In this specific embodiment, the ion trap is a Cassinian electrostatic trap. The electrode group 1 comprises several electrodes 1-1, consisting of two symmetrically arranged outer shell electrodes 1-1-1 with opposite phases for picking up mirrored charge signals, and inner electrodes 1-1-2 symmetrically arranged within the two outer shell electrodes 1-1-1. The outer shell electrodes 1-1-1 and at least one inner electrode 1-1-2 together form a pickup electrode assembly 3, serving as mirrored charge pickup electrodes 2. The two outer shell electrodes 1-1-1 with opposite phases for picking up mirrored charge signals are electrically connected to the positive and negative input terminals of a differential amplifier, respectively. Simultaneously, the inner electrode 1-1-2 within the same pickup electrode assembly 3, serving as the mirrored charge pickup electrode 2, is electrically connected to the outer shell electrodes 1-1-1 via a capacitor 4. Thus, the mirrored charge signals picked up by the inner electrode 1-1-2 and the outer shell electrode 1-1-1 are combined and input into the differential amplifier, enhancing the signal strength of the mirrored charge signals. Specific Implementation Example 2:

[0030] like Figure 2 As shown, the difference between this specific embodiment and specific embodiment 1 is that the mirror charge amplifier 5 is a low-noise amplifier, such as... Figure 5As shown, the electrode group 1 in this specific embodiment consists of two coaxially arranged ring electrode arrays composed of several electrodes 1-1, and the two ring electrode arrays are symmetrical. Each ring electrode array is a coaxial circular structure composed of multiple electrodes. Several electrodes 1-1 can be used as mirror charge pickup electrodes 2 to cooperate with mirror charge amplifier 5 to pick up mirror charge signals. One mirror charge pickup electrode, as the central mirror charge pickup electrode, is located at the central axis of the two ring electrode arrays, and the central mirror charge pickup electrode passes through the two ring electrode arrays. At the same time, the central mirror charge pickup electrode 8 is insulated from the ring electrode arrays it passes through. In this specific embodiment, the central mirror charge pickup electrode 8 is a cylindrical structure made of metal wire, and the diameter of the central mirror charge pickup electrode 8 is less than 1.5 mm. Here, the diameter of the central mirror charge pickup electrode 8 used in this specific embodiment is 0.6 mm. The mirror charge pickup electrodes in one ring electrode array are 21a, 22a, 23a... from the inside out. The mirror charge pickup electrodes in the other symmetrical ring electrode array are... The charge pickup electrodes are numbered 21b, 22b, 23b... from the inside out. At least two image charge pickup electrodes with similar phases of the image charge signals form a pickup electrode assembly. The image charge pickup electrodes 2 in the same pickup electrode assembly 3 are electrically connected to the central image charge pickup electrode 8 through a capacitor. Each image charge pickup electrode 2 in the same pickup electrode assembly 3 is electrically connected to a DC voltage 7 through a resistor 6 to ensure that the electric field in the ion trap meets the conditions for mass spectrometry analysis of ions in the trap. The DC voltage 7 includes a first DC voltage 7-1, a second DC voltage 7-2, and a third DC voltage 7-3 that are electrically connected to the central image charge pickup electrode 8 through a resistor. The first DC voltage 7-1 for the central image charge pickup electrode 8 is 65V. In the same pickup electrode assembly 3, the image charge pickup electrode connected to the image charge amplifier is electrically connected to the second DC voltage through a resistor 6. The second DC voltage is 0V. The remaining image charge pickup electrodes 2 in the same group are electrically connected to the third DC voltage through a resistor 6. The third DC voltage is 515V. A DC voltage is superimposed on the central mirror charge pickup electrode 8 and the mirror charge pickup electrode 2 by a high-impedance resistor device 6, thereby forming an electric field that satisfies the mass spectrometry analysis of ions in the electrostatic ion trap.

[0031] In this specific embodiment, 21a, 22a, 21b, and 22b form a group of pickup electrodes. The mirror charge pickup electrode 21b is electrically connected to the low noise amplifier. At the same time, the mirror charge pickup electrode 21b and the symmetrical mirror charge pickup electrode 21a are both electrically connected to the second DC power supply through the resistor device 6, while the mirror charge pickup electrodes 22a and 22b are electrically connected to the third DC power supply through the resistor device 6.

[0032] Therefore, the mirror charge pickup electrodes 2 in the two sets of ring electrode arrays are coupled to a low-noise amplifier through a capacitor 4 via the central mirror charge pickup electrode 8. The low-noise amplifier amplifies and detects the signal, and then the signal is converted by a computer to obtain a mass spectrum. Considering that the trajectory of ions when they move to the center is very close to the central axis of the two sets of ring electrode arrays, the central mirror charge pickup electrode 8 has a certain shielding effect. While increasing the amount of ion charge, it reduces the charge interaction force between ions in space. Therefore, while improving the detection sensitivity of the mirror charge signal, it also increases the analytical dynamic range of the analyzer. How the mass spectrometer detects the signal after it is amplified by the mirror charge amplifier 5 is existing technology and will not be elaborated here.

[0033] In addition, in this specific embodiment, the second DC voltage 7-2 supplies 500V to the mirror charge pickup electrode. When the voltage potential of the mirror charge pickup electrode 2 is 0V, the second DC voltage 7-2 is a ground wire.

[0034] The electric field condition for mass spectrometry analysis of ions within an electrostatic ion trap is as follows:

[0035] (1) When analyzing positive ions, such as Figure 3 As shown, the first DC voltage is higher than the second DC voltage to form a potential difference; this positive potential difference enables the distribution of the potential around the central mirror charge pickup electrode 8 and on the central plane of the electrostatic field to have a continuously positive second derivative with respect to the radius. This continuously positive second derivative enables positive ions with different initial tangential kinetic energies to achieve isochronous focusing.

[0036] Otherwise, such as Figure 4 As shown, when the DC potential of the central mirror charge pickup electrode 8 is 0V, the adjacent mirror charge pickup electrode is also 0V. Therefore, the radial potential gradient in the ion trap decreases as the radius R of the ion trap increases, which fails to meet the condition of focusing the initial tangential velocity on the orbital period time.

[0037] (2) When analyzing negative ions, the first DC voltage is lower than the second DC voltage to form a potential difference. This negative potential difference enables the distribution of the potential around the central mirror charge pickup electrode 8 and on the central plane of the electrostatic field to have a continuously negative second derivative with respect to the radius. This continuously negative second derivative enables negative ions with different initial tangential kinetic energies to achieve isochronous focusing.

[0038] The positive or negative potential difference created can generate an electric field within the ion trap that helps to focus ions both temporally and spatially.

[0039] Furthermore, regarding the structure of the central mirror charge pickup electrode 8 passing through the central axis of the two-electrode annular array, in this specific embodiment, the electrodes 1-1 constituting the annular electrode array are annular electrode structures with different diameters, and the diameter of the central mirror charge pickup electrode 8 is less than 1.5 mm. Therefore, the central mirror charge pickup electrode 8 can be easily passed through the central axis of the two-electrode annular array, thereby shortening the directional distance between the electrodes 1-1 in the two annular electrode arrays, which facilitates the formation of the pickup electrode assembly 3.

Claims

1. A mass spectrometer based on image charge signal detection, comprising an electrostatic ion trap and an image charge amplifier (5), wherein the electrostatic ion trap includes an electrode assembly (1) for defining a boundary potential and generating an electrostatic field, the electrode assembly (1) comprising a plurality of electrodes (1-1), characterized in that, Several electrodes (1-1) can be used as image charge pickup electrodes (2) to cooperate with image charge amplifier (5) to pick up image charge signals. The electrode group (1) includes at least one pickup electrode assembly (3). The pickup electrode assembly (3) includes at least two image charge pickup electrodes (2) with similar phases for picking up image charge signals. Each image charge pickup electrode (2) in the pickup electrode assembly (3) is electrically connected to a DC voltage (7) through a resistor device (6) to ensure that the electric field in the ion trap meets the conditions for mass spectrometry analysis of ions in the trap. Image charge pickup electrodes (2) with different potentials in each pickup electrode assembly (3) are electrically connected through a capacitor (4). At the same time, one of the image charge pickup electrodes (2) in the pickup electrode assembly (3) is electrically connected to the input terminal of the image charge amplifier (5).

2. The mass spectrometer based on mirror charge signal detection according to claim 1, characterized in that, The mirror charge amplifier (5) is a differential amplifier. The electrode group (1) consists of several electrodes (1-1) that are two symmetrically arranged outer shell electrodes (1-1-1) and inner electrodes (1-1-2) symmetrically arranged inside the two outer shell electrodes (1-1-1). The outer shell electrode (1-1-1) and at least one inner electrode (1-1-2) inside the outer shell electrode (1-1-1) form the pickup electrode assembly (3) as mirror charge pickup electrodes (2). The two outer shell electrodes (1-1-1) are connected to the positive and negative input terminals of the differential amplifier as mirror charge pickup electrodes (2). The inner electrode (1-1-2) and the outer shell electrode (1-1-1) of the same pickup electrode assembly (3) are electrically connected through a capacitor (4).

3. A mass spectrometer based on mirror charge signal detection according to claim 1, characterized in that, The mirror charge amplifier (5) is a low-noise amplifier. The electrode group (1) consists of two coaxial ring electrode arrays composed of several electrodes (1-1). Each ring electrode array is a coaxial ring structure composed of multiple electrodes. Several electrodes (1-1) can be used as mirror charge pickup electrodes (2) to cooperate with the mirror charge amplifier (5) to pick up mirror charge signals. One of the mirror charge pickup electrodes is located at the central axis of the two ring electrode arrays as the central mirror charge pickup electrode, and the central mirror charge pickup electrode passes through the two ring electrode arrays. The mirror charge pickup electrode (2) in the same pickup electrode assembly (3) is electrically connected to the central mirror charge pickup electrode (8) through a capacitor.

4. A mass spectrometer based on mirror charge signal detection according to claim 3, characterized in that, Within the electrode group (1), the mirror charge pickup electrodes (2) connected by capacitors (4) are adjacent to each other.

5. A mass spectrometer based on mirror charge signal detection according to claim 3, characterized in that, The DC voltage (7) includes a first DC voltage (7-1), a second DC voltage (7-2), and a third DC voltage (7-3) electrically connected to the central mirror charge pickup electrode (8) via a resistor (6), wherein the second DC voltage is electrically connected to the mirror charge pickup electrode connected to the mirror charge amplifier via a resistor, and the third DC voltage is connected to other mirror charge pickup electrodes within the same pickup electrode assembly via a resistor.

6. A mass spectrometer based on mirror charge signal detection according to claim 5, characterized in that, The conditions for ensuring that the electric field within the ion trap satisfies the requirements for mass spectrometry analysis of ions within the trap include: (1) When analyzing positive ions, the first DC voltage is higher than the second DC voltage to form a potential difference; (2) When analyzing negative ions, the first DC voltage is lower than the second DC voltage to form a potential difference.

7. A mass spectrometer based on mirror charge signal detection according to claim 3, characterized in that, The central mirror charge pickup electrode (8) is a cylindrical electrode with a diameter of less than 1.5 mm.

8. A mass spectrometer based on mirror charge signal detection according to claim 3, characterized in that, The image charge pickup electrode (2) with similar phase is the image charge pickup electrode (2) with a fundamental frequency phase difference of less than 30° for the picked-up image charge pickup signal.

9. A mass spectrometer based on mirror charge signal detection according to claim 1, characterized in that, The resistive device (6) is a resistor or an inductor or a resistor and an inductor connected in series.

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