Square wave driven ion storage - multiple reflection time-of-flight mass spectrometry system and method

Abstract

The application relates to a square wave driven ion storage-multiple reflection time-of-flight mass spectrometry system and method, which comprises the following steps: applying a direct current voltage DC1 and a direct current voltage DC2 to an inlet electrode and an outlet electrode of an ion trap respectively; applying a square wave radio frequency voltage with an arbitrary frequency and amplitude to a radio frequency electrode; allowing an ion beam with energy to pass through the inlet electrode and enter the region of the radio frequency electrode, so that ion injection is realized; then, under the action of a direct current potential well formed by the inlet electrode and the outlet electrode and a quadrupole potential well formed by the square wave radio frequency, ion storage and cooling in the ion trap are realized; after sufficient cooling, double pulse voltages are applied to the inlet electrode and the outlet electrode, so that the ions in the trap are extracted to a time-of-flight mass spectrometry detector along the axial direction. The application applies a digital square wave to replace a sine wave in ion storage-multiple reflection time-of-flight mass spectrometry. The performance of the IS-MRTOFMS can be improved, a deeper potential well can further improve the resolution of the IS-MRTOFMS, the storage capacity of the storage well is improved, and the sensitivity of the instrument is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to mass spectrometry instrument, and particularly relates to a square wave driven ion storage-multiple reflection time-of-flight mass spectrometry system and method. BACKGROUND

[0002] The ion storage trap-multiple reflection time-of-flight combined device (IS-MRTOFMS) uses the multiple reflection time-of-flight mass spectrometer as a mass analyzer, increases the ion flight path to obtain a higher mass resolution, and combines the ion trap storage function to effectively improve the ion utilization efficiency of the continuous ion source. Therefore, the performance of the IS-MRTOFMS is closely related to the ion storage trap. As is known, the longer the flight path of the TOF, the higher the resolution, and the lower the sensitivity. The ion enrichment function realized by the ion storage trap can improve the ion utilization rate and further improve the sensitivity of the IS-MRTOFMS. The ion trap confines the ion beam in the four-pole electrode and the ion storage area of the direct current potential trap. The ion storage capacity depends on the depth of the ion trap potential. Therefore, increasing the depth of the potential well can improve the ion capacity and further improve the sensitivity, and can reduce the spatial divergence of the ion cloud and improve the resolution. The existing device uses a digital voltage to drive the ion trap, and the ion is ejected from the radial opening into the time-of-flight analyzer. When the ion is ejected radially, the spatial distribution and kinetic energy divergence of the ion cloud in the radial direction vary periodically with the radio frequency, which indirectly causes the turnaround time to vary periodically with the radio frequency. Based on the stable axial direct current potential well, the spatial and kinetic energy divergence of the ion cloud in the axial direction is small. At present, there is no report on the square wave driven ion trap-multiple reflection time-of-flight mass spectrometer combined device for axial ion extraction. SUMMARY

[0003] The application discloses a square wave driven ion storage-multiple reflection time-of-flight mass spectrometry system and method (IS-MRTOFMS). In the time-of-flight mass spectrometer with an ion storage trap front-stage storage device, the driving radio frequency of the ion trap is changed from a sine wave to a square wave, which can improve the storage capacity of the IS-MRTOFMS and improve the resolution of the IS-MRTOFMS.

[0004] The technical scheme adopted by the application to achieve the above object is as follows: a square wave driven ion storage-multiple reflection time-of-flight mass spectrometry method, a square wave radio frequency voltage is applied to the radio frequency electrode of the ion trap, and the injection, cooling and extraction of ions in the ion trap are realized through time sequence control, including the following steps:

[0005] A direct current voltage DC1 and a direct current voltage DC2 are respectively applied to the inlet electrode and the outlet electrode of the ion trap; and a square wave radio frequency voltage of an arbitrary frequency and amplitude is applied to the radio frequency electrode.

[0006] An energetic ion beam passes through the inlet electrode and enters the region of the radio frequency electrode, thus achieving ion implantation;

[0007] Subsequently, under the action of the DC potential well formed by the inlet electrode and the outlet electrode and the quadrupole potential well formed by the square wave radio frequency, the storage and cooling of ions in the ion trap are realized.

[0008] After sufficient cooling, a dual-pulse voltage is applied to the inlet and outlet electrodes to extract ions from the trap along the axial direction to the time-of-flight mass spectrometer detector.

[0009] During ion implantation, ion implantation is achieved by using a DC electric field to reduce the inlet electrode voltage DC1 to -5V, forming a potential energy gradient with the inlet electrode front-end voltage, thereby achieving ion implantation into the ion trap. At the same time, the inlet electrode voltage DC1 is increased to +3V to prevent ion outflow. Radio frequency voltage is applied to the radio frequency electrode to capture the implanted ions.

[0010] During the storage and cooling of ions in the ion trap, the DC voltage DC1 at the inlet electrode and the DC voltage DC2 at the outlet electrode are simultaneously modulated to +10V to achieve axial constraint of the ions. The square wave radio frequency field binds the ions radially. After a certain period of cooling, the resulting ion cloud converges spatially onto the central axis of the quadrupole.

[0011] During ion extraction, a dual-pulse extraction method is used, with +300V and -300V pulsed high voltages applied to the inlet electrode DC1 and outlet electrode DC2, respectively, for an extraction time of 10μs, to extract ions from the trap to the time-of-flight mass spectrometer detector at the back end.

[0012] The ion trap storage time is in the range of 0-1000ms.

[0013] A square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry system includes: an ion trap consisting of an inlet electrode, an outlet electrode, and a radio frequency electrode;

[0014] Time-of-flight mass spectrometry, located at the rear end of the ion trap, is used to extract ions from the ion trap;

[0015] A square wave RF power supply, connected to RF electrodes, is used to apply a square wave RF voltage of arbitrary frequency and amplitude.

[0016] The square wave radio frequency power supply is connected to the radio frequency electrode through a capacitor.

[0017] The ion trap includes a 2D ion trap or a 3D ion trap.

[0018] The background gas in the ion trap is at least one of helium, argon, krypton, nitrogen, oxygen, or dry air.

[0019] The ion trap is extracted axially.

[0020] The present invention has the following beneficial effects and advantages:

[0021] 1. This invention replaces the sine wave with a digital square wave in ion storage-multiple reflection time-of-flight mass spectrometry. This is expected to improve the performance of IS-MRTOFMS; deeper potential wells will further enhance the resolution of IS-MRTOFMS, increase the storage capacity of the storage wells, and thus improve the instrument's sensitivity.

[0022] 2. This invention uses bipolar pulse extraction technology to axially extract the ion trap, thereby stabilizing the axial DC potential trap and reducing the divergence of the ion cloud backtracking time. Attached Figure Description

[0023] Figure 1 Schematic diagram of a two-dimensional ion trap-multiple reflection time-of-flight mass spectrometer structure driven by square wave radio frequency;

[0024] 1. Inlet electrode, 2. Outlet electrode, 3. Radio frequency electrode, 4. Square wave power supply, 5. Time-of-flight mass spectrometer detector;

[0025] Figure 2 shows a resolution comparison between the sine wave drive mode and the square wave drive mode;

[0026] Figure 3 shows a comparison of storage capacity in sine wave drive mode and square wave drive mode. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, a square wave driven ion storage-multiple reflection time-of-flight mass spectrometer includes an ion trap consisting of an inlet electrode, an outlet electrode, and a radio frequency electrode, a multiple reflection time-of-flight mass spectrometer, and a square wave radio frequency power supply.

[0029] DC voltages DC1 and DC2 are applied to the inlet and outlet electrodes, respectively; a square wave radio frequency voltage of arbitrary frequency and amplitude is applied to the radio frequency electrode via capacitive coupling; by controlling the voltage parameters of the above electrodes in a timing manner, ion implantation, cooling, and extraction can be achieved in the ion trap. An ion beam of a certain energy passes through the inlet electrode and enters the region of the radio frequency electrode; subsequently, under the action of the DC potential trap formed by the inlet and outlet electrodes and the quadrupole potential trap formed by the square wave radio frequency, the ions are stored and cooled in the ion trap; after sufficient cooling, a dual-pulse voltage is applied to the inlet and outlet electrodes to extract the ions in the trap axially to the time-of-flight mass spectrometer detector at the rear end.

[0030] Linear ions include ion traps, including 2D and 3D ion traps.

[0031] The square wave voltage and frequency can be adjusted arbitrarily according to the measurement requirements.

[0032] The ion trap storage time can be adjusted within the range of 0-1000ms.

[0033] The background gas in the ion trap is one or more of helium, argon, krypton, nitrogen, oxygen, or dry air.

[0034] The gas pressure in the ion trap can be adjusted within the range of 0.1 to several thousand Pa.

[0035] Linear ion sources include in-trap sources and out-of-trap ion sources. Out-of-trap ion sources include various types of ion sources at atmospheric pressure and negative pressure.

[0036] Example 1

[0037] A square-wave driven ion storage system—multiple reflection time-of-flight mass spectrometry. It includes an ion trap consisting of an inlet electrode, an outlet electrode, and a radio frequency electrode, a multiple reflection time-of-flight mass spectrometer, and a square-wave radio frequency power supply.

[0038] DC voltages DC1 and DC2 are applied to the inlet and outlet electrodes, respectively; a square wave radio frequency voltage of arbitrary frequency and amplitude is applied to the radio frequency electrode via capacitive coupling; by controlling the voltage parameters of the above electrodes in a timing manner, ion implantation, cooling, and extraction can be achieved in the ion trap. An ion beam of a certain energy passes through the inlet electrode and enters the region of the radio frequency electrode; subsequently, under the action of the DC potential trap formed by the inlet and outlet electrodes and the quadrupole potential trap formed by the square wave radio frequency, the ions are stored and cooled in the ion trap; after sufficient cooling, a dual-pulse voltage is applied to the inlet and outlet electrodes to extract the ions in the trap axially to the time-of-flight mass spectrometer detector at the rear end.

[0039] In this example, the ion storage trap employs a 2D segmented quadrupole structure, consisting of an inlet electrode, a radio frequency (RF) electrode, and an outlet electrode. The RF electrode comprises four parallel electrode arrays; each array consists of one or more concentric cylindrical electrodes evenly spaced, with a cylinder diameter of 9.04 mm. The centers of the four electrode arrays are evenly positioned on a circle with a radius of 8.52 mm. The cylindrical electrodes are 4 mm thick and spaced 0.5 mm apart. The inlet electrode aperture and outlet electrode are both annular electrodes with an inner diameter of 1.5 mm, an outer diameter of 28 mm, and a thickness of 1 mm. A DC voltage is applied to the inlet and outlet electrodes. The concentric cylindrical electrodes in any of the four RF electrode arrays are evenly divided by voltage-dividing resistors. Each RF electrode is connected to an equivalent capacitor. The same RF voltage is applied to the cylindrical electrodes in each RF electrode array, with the same RF voltage applied to alternating RF electrode arrays and RF voltages of opposite polarity but the same absolute value applied to adjacent cylindrical electrode arrays. By controlling the voltage parameters of these electrodes in a timing sequence, ion implantation, cooling, and extraction can be achieved within the ion trap. The mass spectrometry analysis cycle is controlled by the master trigger frequency, which allows for the regulation of the ion trap storage time. Each trigger cycle consists of three segments: ion implantation, ion cooling, and ion extraction. During the ion implantation segment, ion implantation is achieved through a DC electric field, reducing the inlet electrode voltage to -5V to create a potential energy gradient with the inlet electrode front voltage, thus implanting ions into the ion trap. Simultaneously, the inlet electrode voltage is raised to +3V to prevent ion outflow, and the RF power supply is turned on to capture the implanted ions. Finally, in the cooling segment, both the inlet and outlet electrodes are modulated to +10V to constrain the ions axially, while the square wave RF field confines the ions radially. After a certain cooling time, the ion cloud gradually converges spatially to the central axis of the quadrupole. During the ion extraction segment, dual-pulse extraction is used, applying pulsed high voltages of +300V and -300V to the inlet and outlet electrodes, respectively, while simultaneously turning off the digital wave RF power supply. The extraction time is set to 10μs, extracting the ions from the trap to the time-of-flight mass spectrometer detector at the rear.

[0040] The ionization source was an external low-pressure photoionization source, and 10 ppbv toluene was used as the sample standard gas. Under MRTOF flight conditions of 2 orbits, toluene mass spectra were obtained under different storage times. The resolution and storage capacity of IS-MRTOFMS under sinusoidal and square wave driving at different storage times were compared and analyzed. The experimental results are as follows: Figure 2a , Figure 2b , Figure 3a , Figure 3b As shown. Figure 2a , Figure 2bAs shown, for both sine wave and square wave driving modes, when the storage time is less than 1ms, the m / z 92 half-width at half-maximum (HWHM) decreases rapidly with the storage time; in the 1–5ms range, the HWHM shows a gradual trend; when the storage time is greater than 5ms, the HWHM begins to increase slowly; within the stable range of 1–5ms, the resolution of the square wave driving mode is 1.83 times that of the sine wave driving mode. Figure 3a , Figure 3b As shown, when the storage time is less than 20 ms, the storage capacity of the ion trap under the two modes is compared. The results show that when the storage time is less than 20 ms, the storage capacity of the square wave is greater than that of the sine wave, which is 2.33 times that under the sine condition.

Claims

1. A square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry method, characterized in that, Applying a square wave radio frequency voltage to the radio frequency electrodes of the ion trap, and controlling the timing, enables ion implantation, cooling, and extraction within the ion trap, including the following steps: DC voltage DC1 and DC voltage DC2 are applied to the inlet and outlet electrodes of the ion trap, respectively; a square wave radio frequency voltage of arbitrary frequency and amplitude is applied to the radio frequency electrode. An energetic ion beam passes through the inlet electrode and enters the region of the radio frequency electrode, thus achieving ion implantation; Subsequently, under the action of the DC potential well formed by the inlet electrode and the outlet electrode and the quadrupole potential well formed by the square wave radio frequency, the storage and cooling of ions in the ion trap are realized. After sufficient cooling, a dual-pulse voltage is applied to the inlet and outlet electrodes to extract ions from the trap along the axial direction to the time-of-flight mass spectrometer detector; During ion implantation, ion implantation is achieved by using a DC electric field to reduce the inlet electrode voltage DC1 to -5V, forming a potential energy gradient with the inlet electrode front voltage to achieve ion implantation into the ion trap. At the same time, the inlet electrode voltage DC1 is increased to +3V to prevent ion outflow. Radio frequency voltage is applied to the radio frequency electrode to capture the implanted ions. During the storage and cooling of ions in the ion trap, the DC voltage DC1 of the inlet electrode and the DC voltage DC2 of the outlet electrode are simultaneously modulated to +10V to achieve axial constraint of the ions. The square wave radio frequency field binds the ions radially. After a certain period of cooling, the ion cloud formed is spatially converged on the central axis of the quadrupole. During ion extraction, a dual-pulse extraction method is used, with +300V and -300V pulsed high voltages applied to the inlet electrode DC1 and outlet electrode DC2, respectively, for an extraction time of 10μs, to extract ions from the trap to the time-of-flight mass spectrometer detector at the back end.

2. The square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry method according to claim 1, characterized in that: The ion trap storage time is in the range of 0-1000ms.

3. A square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry system, characterized in that, include: The ion trap consists of an inlet electrode (1), an outlet electrode (2), and a radio frequency electrode (3); Time-of-flight mass spectrometry (4) is located at the rear end of the ion trap and is used to extract ions from the ion trap; A square wave radio frequency power supply (5) is connected to the radio frequency electrode (3) and is used to apply a square wave radio frequency voltage of arbitrary frequency and amplitude. The square wave radio frequency power supply (5) is connected to the radio frequency electrode through a capacitor; The ion trap includes a 2D ion trap or a 3D ion trap.

4. The square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry system according to claim 3, characterized in that, The background gas in the ion trap is at least one of helium, argon, krypton, nitrogen, oxygen, or dry air.

5. The square-wave driven ion storage-multiple reflection time-of-flight mass spectrometry system according to claim 3, characterized in that, The ion trap is extracted axially.

Images