A method for improving the reflectron time-of-flight mass spectrometer interval resolution

Abstract

The patent proposes a method for improving the interval resolution of a reflective time-of-flight mass spectrometer. The principle of the invention is to apply a square wave pulse voltage on the reflector bottom plate during the spectrum acquisition process of the reflective time-of-flight mass spectrometer, and change the electric field intensity of the reflection area in the reflector, which can be used to improve the local resolution of the target ion mass range in the reflective time-of-flight mass spectrometer.

Description

Technical Field

[0001] This invention relates to the field of mass spectrometry analysis technology, and in particular to a method for improving the range resolution of reflectance time-of-flight mass spectrometry. Background Technology

[0002] In current ion source technologies, when neutral molecules are ionized into ions, the resulting ion clusters exhibit both energy and spatial divergence. This energy and spatial divergence of ion clusters is a crucial factor affecting the resolution of time-of-flight mass spectrometry.

[0003] Time-of-flight mass spectrometry (TOF-MS) primarily consists of a repulsion region, an accelerator, a field-free flight region, a reflector, and an ion detector. Based on the number of grids in the reflector, it is mainly classified into gridless reflectors, single-grid reflectors, and dual-grid reflectors. In a dual-grid reflector, the electric fields are respectively the deceleration region and the reflection region, where ions are decelerated and reflected, respectively. When the voltage of the electrode containing grid one and the voltage of the reflector base plate remain constant, the ion focusing plane can be moved by adjusting the voltage of the electrode containing grid two, i.e., adjusting the relative electric field strength between the deceleration and reflection regions. Therefore, the voltage of the electrode containing grid two is also called the focusing voltage. When the ion focusing plane coincides with the ion detector, the ions are precisely focused on the detector surface, and the resolution of the TOF-MS reaches its optimal value.

[0004] Through patent and paper searches, the relevant patents found concerning improving the resolution of reflective flight mass spectrometry are as follows:

[0005] 1. Brook Dalton Ltd. filed and disclosed a patent application on April 12, 2019, for a wide-range high-resolution method for reflective time-of-flight mass spectrometers. This method involves altering an operating voltage on the diaphragm of the reflector to generate high-resolution mass over a range exceeding 8 kilodaltons. However, this method is primarily applied to gridless reflectors, acting on the diaphragm to deform the local electric field shape within the reflector, changing the electric field strength and generating additional focusing ability, thus improving the mass spectrometry resolution.

[0006] 2. Brook Dalton Ltd. filed a patent application on November 15, 2002, for the design of a spatial angle focusing reflector for a time-of-flight mass spectrometer. This design introduces a slightly curved electrostatic field at the rear end of the reflector, thereby generating additional focusing within the reflector and improving the resolution of the mass spectrometer. However, this method alters the uniform electric field within the reflector and is not universally applicable to mass spectrometry instruments.

[0007] In summary, the currently published patents for improving reflective time-of-flight mass spectrometry are mainly applied to gridless reflectors. The voltage applied to the diaphragm changes the uniformity of the local electric field inside the reflector, generating a non-uniform electric field for focusing to improve the mass spectrometry resolution. Summary of the Invention

[0008] This invention proposes a method for improving the resolution of reflective time-of-flight mass spectrometry. The purpose is to apply a square wave pulse voltage to the reflector base plate when the target ion cluster enters the reflector, thereby changing the electric field intensity of the uniform electric field and reducing the spatial divergence of the ion cluster to the ion detector, i.e., the half-width at half-maximum (WHM) of the spectral peak, to improve the resolution of the ion cluster of interest.

[0009] Assume the ion to be detected is a positive ion. Due to energy and spatial divergence among ions of the same mass, the ion cluster has a certain length. Before the applied pulse voltage U4, the voltage on the reflector plate is U3. After the target ion has completely entered the reflector's reflection zone, a positive pulse voltage U4 is applied to the reflector plate, transforming the electric field in the reflection zone into a uniform electric field with increased intensity. The further back the ion cluster is, the longer it takes for it to leave the reflection zone; that is, ions at the rear of the cluster are subjected to the positive pulse voltage for a longer time than ions at the front. After the target ion has completely left the reflector, the ions at the rear of the cluster have a higher velocity than those at the front. When the ion cluster reaches the ion detector plane, the ions at the rear just catch up with the ions at the front. At this point, the spatial divergence of the ions is minimized, meaning the full width at half maximum (FWHM) of the ions in the spectrum decreases, thus improving the resolution of the time-of-flight reflection mass spectrometry (TOF-MS). By selecting an appropriate pulse voltage U4 and pulse start time, the resolution of the region near the target ion in TOF-MS can be improved.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] A method for improving the range resolution of a reflective time-of-flight mass spectrometer includes voltage setting operations for the reflective time-of-flight mass spectrometer and the reflector of the reflective time-of-flight mass spectrometer.

[0012] The aforementioned reflective time-of-flight mass spectrometer includes a repulsion region, an acceleration region, a field-free flight region, a reflector, and an ion detector. The reflector can be divided into a deceleration region and a reflection region, and is composed of a first grid, a second grid, an electrode array, and a reflector base plate. In the reflector, the voltage applied to the first grid is U1, the voltage applied to the second grid is U2, the voltage on the reflector base plate is U3, and the pulse voltage on the reflector base plate is U4.

[0013] During the acquisition of the mass spectrometry spectrum, the electrode voltages U1 and U2 of grid one and grid two in the reflector remain unchanged; when the target ion has not completely entered the reflection region, the voltage on the reflector base plate is U3; when the target ion cluster has completely entered and has not left the reflection region, a pulse voltage U4 is applied to the reflector base plate, and the actual voltage on the reflector base plate is; at any time when the target ion cluster has completely left the reflection region, the pulse voltage U4 is turned off, and the reflector base plate voltage U3 is restored.

[0014] The electrode plates in the reflector are circular or square ring-shaped with a through hole in the middle; the reflector consists of four or more electrode plates arranged in parallel from left to right, with the through holes in the middle coaxial and spaced apart, forming an electrode plate array, and the distance between adjacent electrode plates in the reflector is equal;

[0015] A grid one and a reflector base plate are respectively provided on the left and right sides of the electrode array, and a grid two is provided between the grid one and the reflector base plate;

[0016] The grid mesh one, grid mesh two, and reflector base plate are arranged in parallel and spaced intervals.

[0017] The area between grid one and grid two is the deceleration zone, and the area between grid two and the reflector base plate is the reflection zone.

[0018] When the ion is a positive ion, the applied square wave pulse voltage U4 is a positive voltage; when the ion is a negative ion, the applied square wave pulse voltage U4 is a negative voltage. Generally, the amplitude of the square wave pulse voltage is above 200 volts, the pulse width is 0.5-10us, and the pulse frequency is 5-40kHz.

[0019] The principle of this invention is to apply a square wave pulse voltage to the reflector base plate during the acquisition of a reflection time-of-flight mass spectrometry spectrum, thereby changing the electric field intensity in the reflection region of the reflector, which can be used to improve the local resolution of the target ion mass range in reflection time-of-flight mass spectrometry. Attached Figure Description

[0020] The accompanying drawings further illustrate the present invention, but the content of the drawings does not constitute any limitation on the present invention.

[0021] Figure 1 This is a schematic diagram of a reflection time-of-flight mass spectrometer according to one embodiment of the present invention; Detailed Implementation

[0022] The aforementioned reflective time-of-flight mass spectrometer includes a repulsion region, an acceleration region, a field-free flight region, a reflector, and an ion detector; wherein the reflector is divided into a deceleration region and a reflection region, and is composed of a grid one, a grid two, an electrode array, and a reflector base plate;

[0023] The target ion to be detected is a positive ion. In reflective time-of-flight mass spectrometry, the voltages of grid one, grid two, and the reflector base plate in the reflector are -5000V, -800V, and 600V, respectively. After acceleration in the repulsion and acceleration regions, the target ion reaches an energy of 5000 eV. It then flies at a constant speed in the field-free flight region before entering the reflector deceleration region, where its energy decreases to 800 eV upon exiting. As the ion's velocity approaches zero in the reflection region, a square wave pulse voltage with an amplitude of 500 eV, a frequency of 20 kHz, and a valley of 0V is applied to the reflector base plate, accelerating the ion out of the reflector. Before the ion detector, ions behind the target ion cluster just catch up with those in front, minimizing spatial divergence, narrowing the full width at half maximum (FWHM) of the spectral peak, and improving resolution.

Claims

1. A method for improving the interval resolution of a reflective time-of-flight mass spectrometer, wherein the reflective time-of-flight mass spectrometer includes a repulsion region (1), an acceleration region (2), a field-free flight region (3), a reflector (4), and an ion detector (5); wherein the reflector (4) is divided into a deceleration region (6) and a reflection region (7), and is composed of a grid one (8), a grid two (9), an electrode array, and a reflector base plate (10); characterized in that: In the reflector, the voltage applied to the first grid (8) is U1, the voltage applied to the second grid (9) is U2, the voltage applied to the reflector base plate (10) is U3, and the pulse voltage applied to the reflector base plate (10) is U4. During the acquisition of the mass spectrometry spectrum, the voltages U1 and U2 of grid one (8) and grid two (9) in the reflector remain unchanged; when the target ion has not completely entered the reflection area (7), the voltage on the reflector base plate (10) is U3; when the target ion cluster has completely entered and has not left the reflection area (7), a pulse voltage U4 is applied to the reflector base plate (10), and the actual voltage on the reflector base plate (10) is (U3+U4); at any time when the target ion cluster has completely left the reflection area (7), the pulse voltage U4 is turned off and the voltage U3 on the reflector base plate (10) is restored.

2. The method according to claim 1, characterized in that: The electrode sheet in the reflector (4) is a circular ring or square ring with a through hole in the middle; the reflector (4) consists of four or more electrode sheets arranged in parallel from left to right, with the through holes in the middle coaxial and spaced apart, forming an electrode sheet array; the distance between adjacent electrode sheets in the reflector (4) is equal. A grid 1 (8) and a reflector base plate (10) are respectively provided on the left and right sides of the electrode array, and a grid 2 (9) is provided between the grid 1 (8) and the reflector base plate (10); The grid one (8), grid two (9), and reflector base plate (10) are arranged in parallel and spaced intervals; The area between grid one (8) and grid two (9) is the deceleration zone (6), and the area between grid two (9) and reflector base plate (10) is the reflection zone (7).

3. The method according to claim 1, characterized in that: When the ion is a positive ion, the applied square wave pulse voltage U4 is a positive voltage; when the ion is a negative ion, the applied square wave pulse voltage U4 is a negative voltage. Generally, the amplitude of the square wave pulse voltage is above 200 volts, the pulse width is 0.5-10us, and the pulse frequency is 5-40kHz.

Images