Ion modulation method for improving time-of-flight mass spectrometer resolution

Abstract

The application provides an ion modulation method for improving the resolution of time-of-flight mass spectrometry, wherein a double-slit structure is arranged between an ion source and an acceleration zone to remove ions with large kinetic energy dispersion along the ion flight direction; the acceleration zone is composed of four electrode sheets, wherein different pulse voltages are applied to the first electrode sheet, the second electrode sheet and the third electrode sheet; the initial kinetic energy dispersion and the initial position dispersion of the ions introduced into the acceleration zone are reduced by forming a modulation electric field through the three-electrode pulse; the double-slit structure and the fourth electrode sheet are connected with the shell of the instrument and grounded. The electric field reduces the kinetic energy of the ions, and makes the ions gather between the first electrode sheet and the third electrode sheet, thereby reducing the dispersion in the spatial position and the kinetic energy dispersion to some extent, and improving the resolution of time-of-flight mass spectrometry.

Description

Technical Field

[0001] This invention relates to the field of precision instrument manufacturing, and in particular to a method for improving the resolution of time-of-flight mass spectrometry. Background Technology

[0002] The main performance parameters of a mass spectrometer reflect its analytical capabilities, including resolution, sensitivity, detection mass range, and mass accuracy. Among these, the primary factors affecting the resolution of time-of-flight mass spectrometry (TOF-MS) are the flight time of ions within the mass analyzer and the temporal dispersion of ions during flight. The flight time of ions can be increased by extending the flight distance in the field-free region and by employing a reflective structure, while the temporal dispersion of ions during flight is mainly related to the initial dispersion conditions of vertically introduced ions.

[0003] Factors such as power supply stability, electrostatic field uniformity, and ion detector are relevant. The initial dispersion conditions for vertically introduced ions mainly include the initial spatial dispersion of ions and the initial energy dispersion of ions.

[0004] Due to the angular divergence of the initial kinetic energy of the ion beam, the space charge effect between ions, and the thermal motion of the ions themselves, the ion beam entering the pulse acceleration region has a certain width. Ions with the same mass-to-charge ratio will have different flight distances due to the dispersion of their initial spatial positions, resulting in inconsistent arrival times of the ions at the detector MCP. This causes peak broadening and reduces the resolution of the instrument. Summary of the Invention

[0005] The main technical problem to be solved by the present invention is to provide an ion modulation method for improving the resolution of time-of-flight mass spectrometry.

[0006] To address the aforementioned technical problems, this invention provides an ion modulation method for improving the resolution of time-of-flight mass spectrometry: a double-slit structure is set between the ion source and the acceleration region to remove ions with large kinetic energy dispersion along the ion flight direction;

[0007] The acceleration zone consists of four electrode plates, with different pulse voltages applied to the first, second, and third electrode plates. The three-electrode pulses form a modulated electric field to reduce the initial kinetic energy dispersion and initial position dispersion of the ions introduced into the acceleration zone.

[0008] The double-slit structure and the fourth electrode plate are connected to the instrument housing and grounded.

[0009] In a preferred embodiment: the longer the distance between the two slits in the double-slit structure, the more parallel the resulting ion beam and the smaller the initial energy dispersion of the ions.

[0010] In a preferred embodiment: the slit is a rectangular opening 1 mm wide, the slit opening is located between the first electrode plate and the second electrode plate, and is biased towards the position close to the second electrode plate.

[0011] In a preferred embodiment: the thickness of the four electrode plates is 1 mm, the length and width of the four electrode plates are the same, the third electrode plate and the fourth electrode plate are grid structures, and the second electrode plate has an arc-shaped groove on the side.

[0012] In a preferred embodiment: the grid is a high-purity tungsten wire mesh with a wire diameter of 0.05 mm, which is made by bonding one side of the electrode sheet with 0.06 mm thick single conductive copper foil tape and 80 mesh.

[0013] In a preferred embodiment, the surface protrusion of the grid is less than 0.5 mm.

[0014] In a preferred embodiment: the pulse voltage is a positive pulse with a rise time of less than 100 ns; the pulse voltage of the first electrode is much higher than the pulse voltage of the second electrode; and the pulse voltage of the second electrode is higher than the pulse voltage of the third electrode.

[0015] The pulse voltage difference between the first electrode and the second electrode is greater than the pulse voltage difference between the second electrode and the third electrode.

[0016] In a preferred embodiment: the amplitude of the pulse voltage of the first electrode plate is a fixed value, while the amplitudes of the pulse voltages of the second and third electrode plates are adjustable.

[0017] In a preferred embodiment: the timing of the pulse voltage of the first electrode plate is consistent with that of the pulse voltage of the third electrode plate, and the timing of the pulse voltage of the second electrode plate lags behind that of the pulse voltage of the first electrode plate and the pulse voltage of the third electrode plate, with the lag time being 5ns to 20ns.

[0018] In a preferred embodiment: the exit direction of the acceleration zone is perpendicular to the opening direction of the slit.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1. This invention improves instrument resolution by reducing initial kinetic energy and initial position dispersion. It employs a double-slit structure to remove ions with large dispersion angles. Simultaneously, the ions introduced into the acceleration zone are modulated by a triode pulse to reduce the initial kinetic energy dispersion and initial position dispersion of the introduced ions.

[0021] 2. This invention investigates pulse voltage circuits with introduced bias voltages. Employing a simple circuit structure, it achieves a maximum rise time of less than 100 ns for the output high-voltage pulse while reducing overall circuit power consumption. Instrument resolution is improved by reducing initial kinetic energy and initial position dispersion. A double-slit structure removes ions with large dispersion angles. Furthermore, by introducing a bias voltage into the pulse circuit, a potential difference between the pulse electrode and the slits creates an electric field that focuses the ion beam passing through the slits, reducing initial ion position dispersion. Additionally, the introduced bias voltage also decelerates ions entering the pulse acceleration region, reducing ion kinetic energy dispersion. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of ion introduction;

[0023] Figure 2 This is a schematic diagram of the time-of-flight mass spectrometry structure;

[0024] Figure 3 This is a schematic diagram of the first electrode plate structure;

[0025] Figure 4 This is a schematic diagram of the second electrode plate structure;

[0026] Figure 5 This is a schematic diagram of the third electrode plate structure;

[0027] Figure 6 This is a schematic diagram of the double slits and the acceleration zone;

[0028] Figure 7 This is a waveform diagram of the rising edge of a three-pulse pulse;

[0029] Figure 8 This is a diagram of a three-pulse circuit.

[0030] Figure 9 It is a mass spectrometry signal diagram. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0034] like Figure 1 As shown, this embodiment reduces the initial kinetic energy and initial position dispersion of the mass spectrometer by introducing a pulsed bias voltage. To further improve the instrument resolution, this embodiment proposes a method to improve the resolution of time-of-flight mass spectrometry by setting a double-slit structure between the ion source and the acceleration region to remove ions with large kinetic energy dispersion along the ion flight direction. Figure 2 As shown, the acceleration zone consists of four electrode plates. Different pulse voltages are applied to the first, second, and third electrode plates. The modulated electric field generated by the three-electrode pulses modulates the introduced ions, thereby reducing the initial kinetic energy dispersion and initial position dispersion of the ions introduced into the acceleration zone through the modulated electric field formed by the three-electrode pulses. The double-slit structure and the fourth electrode plate are connected to the instrument housing and grounded.

[0035] Specifically, the electric field reduces the kinetic energy of ions while causing them to converge between the first and third plates, thereby reducing spatial dispersion and kinetic energy dispersion to a certain extent and improving the resolution of time-of-flight mass spectrometry.

[0036] A double-slit structure is used between the acceleration zone and the ion source. The double-slit structure can further remove ions with large divergence angles. The longer the distance between the two slits, the more parallel the resulting ion beam, and the smaller the initial energy dispersion of the ions.

[0037] like Figure 1 As shown, the slit is a rectangular opening 1 mm wide, located between the first electrode plate and the second electrode plate, and biased towards the position of the second electrode plate.

[0038] like Figure 3 , Figure 4 , Figure 5 As shown, the thickness of the four electrodes is 1 mm, and the length and width of the four electrodes are the same. The third and fourth electrodes adopt the same grid structure, and the second electrode has an arc-shaped groove on the side to facilitate the introduction of ions.

[0039] The grid is made by attaching an 80-mesh, 0.05mm diameter high-purity tungsten wire mesh to one side of the electrode sheet using 0.06mm thick single-conductive copper foil tape. To ensure a uniform electric field distribution, the grid surface needs to be flat; therefore, the surface protrusion of the grid is less than 0.5mm.

[0040] To ensure the flatness of the grid surface, two electrode plates are fixed with polyetheretherketone (PEEK) pillars that have good insulation properties and are not easily deformed. A 0.5mm nylon insulating pad is used to isolate the two electrode plates. A multimeter is used to test whether the two electrode plates are short-circuited. When the two electrode plates are not short-circuited, the grid of the electrode plates is relatively flat.

[0041] The second electrode plate adopts a gridless structure, while the third electrode plate and the fourth electrode plate adopt the same single-sided grid structure.

[0042] To better modulate the electric field to act on the ions, the grid surface of the third electrode is located close to the second electrode. To shield the electric field and prevent its penetration, the grid surface of the fourth electrode is located close to the field-free region.

[0043] like Figure 7 The pulse voltages are all positive pulses with a rise time of less than 100 ns. The pulse voltage of the first electrode is much higher than that of the second electrode. The pulse voltage of the second electrode is higher than that of the third electrode. The difference between the pulse voltages of the first and second electrodes is greater than the difference between the pulse voltages of the second and third electrodes.

[0044] In terms of timing, the pulse voltage of the first electrode plate is consistent with that of the third electrode plate, while the pulse voltage of the second electrode plate lags behind that of the first and third electrode plates. The lag time is adjustable from 5ns to 20ns.

[0045] The amplitude of the pulse voltage of the first electrode is fixed, while the amplitude of the pulse voltage of the second and third electrodes is adjustable.

[0046] like Figure 8 As shown, the three pulses consist of a pulse-driven low-voltage circuit, a transformer, and a pulse-driven high-voltage circuit. The transformer is used for isolation between the high-voltage and low-voltage circuits.

[0047] The aforementioned method for improving time-of-flight mass spectrometry resolution utilizes a double-slit structure to further remove ions with large divergence angles. The longer the distance between the two slits, the more parallel the resulting ion beam, and thus the smaller the initial energy dispersion of the ions. The time-of-flight mass spectrometry employs a vertical introduction method to reduce kinetic energy divergence caused by inconsistencies in kinetic energy along the ion's flight direction. Since the vertically introduced ion beam has a wide beam shape, the fabrication of the positive and negative pulse high-voltage power supply significantly affects the wide-beam resolution.

[0048] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. An ion modulation method for improving the resolution of time-of-flight mass spectrometry, characterized in that: A double-slit structure is set between the ion source and the acceleration zone to remove ions with large kinetic energy divergence angles along the ion flight direction. The acceleration zone consists of four electrode plates, with different pulse voltages applied to the first, second, and third electrode plates. The three-electrode pulses form a modulated electric field to reduce the initial kinetic energy dispersion and initial position dispersion of the ions introduced into the acceleration zone. The double-slit structure and the fourth electrode plate are connected to the instrument housing and grounded. The pulse voltage is a positive pulse with a rise time of less than 100 ns. The pulse voltage of the first electrode is much higher than that of the second electrode, and the pulse voltage of the second electrode is higher than that of the third electrode. The pulse voltage difference between the first electrode and the second electrode is greater than the pulse voltage difference between the second electrode and the third electrode. The timing of the pulse voltages of the first electrode plate is consistent with that of the third electrode plate, while the timing of the pulse voltage of the second electrode plate lags behind that of the first and third electrode plate pulse voltages, with a lag time ranging from 5ns to 20ns.

2. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 1, characterized in that: The longer the distance between the two slits in the double-slit structure, the more parallel the resulting ion beam and the smaller the initial energy dispersion of the ions.

3. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 2, characterized in that: The slit is a rectangular opening 1 mm wide, located between the first electrode plate and the second electrode plate, and biased towards the position close to the second electrode plate.

4. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 3, characterized in that: The thickness of the four electrode plates is 1 mm. The length and width of the four electrode plates are the same. The third and fourth electrode plates have a grid structure, and the second electrode plate has an arc-shaped groove on the side.

5. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 4, characterized in that: The grid is made by attaching an 80-mesh, 0.05-mm diameter high-purity tungsten wire mesh to one side of the electrode sheet with 0.06 mm thick single-conductive copper foil tape.

6. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 5, characterized in that: The surface protrusion of the grid is less than 0.5 mm.

7. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 1, characterized in that: The amplitude of the pulse voltage of the first electrode plate is a fixed value, while the amplitude of the pulse voltage of the second and third electrode plates is adjustable.

8. The ion modulation method for improving time-of-flight mass spectrometry resolution according to claim 1, characterized in that: The exit direction of the acceleration zone is perpendicular to the opening direction of the slit.

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