Method for regulating and controlling ion energy in linear ion trap

Abstract

The invention discloses a method for regulating and controlling ion energy in a linear ion trap. The linear ion trap comprises an ion source, an inlet ion gate electrode, an outlet ion gate electrode and a radio frequency electrode, the geometric centers of the inlet ion gate electrode, the outlet ion gate electrode and the radio frequency electrode are located on the same axis and are distributed at intervals, and periodic radio frequency waves with the phase difference of 180 degrees are applied to the radio frequency electrode for ion radial constraint; and applying a direct current voltage to the inlet ion gate electrode and the outlet ion gate electrode to axially bind ions. In the short-line-shaped ion trap, direct-current voltage of an ion gate can permeate into the center of the ion trap to generate induced voltage, and the induced voltage can reduce the binding stability of a radio-frequency field to ions and promote the ions to obtain energy from the radio-frequency field. The ion energy can be regulated and controlled by changing the direct-current voltage of the ion gate.

Description

Technical Field

[0001] The invention belongs to a mass spectrometry instrument and particularly relates to a method for regulating ion energy in a linear ion trap. Background Art

[0002] Mass spectrometry can achieve qualitative and quantitative analysis of compounds. Mass spectrometers can characterize the structure of compounds through tandem mass spectrometry analysis. For the ions of the sample to be tested, ions with a specific mass-to-charge ratio (m / z) are selected and isolated as parent ions; then the energy of the parent ions is modulated to induce their excitation and dissociation to obtain fragment ions; this process is repeated to achieve multi-stage mass spectrometry analysis. The key to ion screening and dissociation is to excite ions to increase their energy. Collision excitation technology and electron or photon-mediated energy transfer methods have been used to change ion energy. Among them, collision excitation technology based on electric field manipulation is more convenient to operate and is a widely used method for ion energy regulation.

[0003] The two-dimensional linear ion trap is recognized as one of the most suitable devices for achieving collisional excitation. It can realize the isolation, dissociation, mass analysis and other steps of ions in a single trap, and has unique advantages in tandem mass spectrometry. After nearly two decades of development, resonant excitation technology has become a commonly used method for ion ejection and dissociation in ion traps. Although the resonant excitation technology can achieve a higher fragmentation efficiency, it still has drawbacks and shortcomings. Resonant excitation requires precise matching of the resonant frequency according to the mass-to-charge ratio of the target ion, is dependent on the mass-to-charge ratio of the ion, and is not conducive to performing continuous collisional dissociation. Non-resonant excitation does not require precise matching of the resonant frequency and is suitable for continuous collisional excitation. It is currently an important research direction in ion excitation technology.

[0004] The motion of ions in an ion trap can be described using the solution (a, q) of the Mathieu equation. The stability (energy state) of ions in an ion trap is related to (a, q) and can be expressed as:

[0005]

[0006] Where a is the trap parameter proportional to the DC voltage, q is the trap parameter proportional to the RF voltage, U is the DC voltage applied to the ion trap electrodes, V is the RF voltage applied to the ion trap electrodes, ω is the frequency of the RF voltage, and r0 is the field radius. In a short linear ion trap, due to the DC voltage permeation effect, the ion gate capture DC voltage induces a DC voltage U* at the center of the ion trap, affecting the value of the Mathieu stability parameter a, reducing the ion confinement potential well depth, encouraging ions to extract energy from the RF field, and increasing their kinetic energy. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention discloses a method for regulating the energy of ions in a linear ion trap. When ions generated by an ion source inside the trap or an ion source outside the trap enter the linear ion trap, they are confined in the linear ion trap under the combined action of a periodic radio frequency electric field and a DC electric field of an ion gate. In a short linear ion trap, the DC voltage of the ion gate penetrates to the center of the ion trap to generate an induced voltage. The induced voltage reduces the stability of the radio frequency field on the ions, prompting the ions to obtain energy from the radio frequency field. By changing the DC voltage of the ion gate, the ion energy can be regulated. The specific technical solution is:

[0008] The linear ion trap comprises an ion source, an entrance ion gate electrode, an exit ion gate electrode and a radio frequency electrode;

[0009] The geometric centers of the entrance ion gate electrode, the exit ion gate electrode, and the radio frequency electrode are located on the same axis and are spaced apart. A periodic radio frequency wave with a phase difference of 180° is applied to the radio frequency electrode to radially confine the ions, and a direct current voltage is applied to the entrance ion gate electrode and the exit ion gate electrode to axially confine the ions.

[0010] When the linear ion trap adjusts the ion energy: when ions generated by the ion source inside the trap or the ion source outside the trap enter the linear ion trap, they are bound in the linear ion trap under the combined action of the periodic radio frequency electric field and the DC electric field of the ion gate. In the short linear ion trap, the ion gate capture DC voltage will penetrate into the center of the ion trap to generate an induced voltage. The induced voltage will reduce the binding stability of the radio frequency field on the ions, prompting the ions to obtain energy from the radio frequency field. By changing the DC voltage of the ion gate, the ion energy is regulated.

[0011] The length of the linear ion trap is 2 to 20 mm.

[0012] The ion gate DC voltage is 1~500V.

[0013] The storage time of the linear ion trap is 0.001 to 1000 ms.

[0014] The background gas in the linear ion trap is one or more of helium, argon, krypton, nitrogen, oxygen or dry air.

[0015] The gas pressure in the linear ion trap is 0.1~100Pa.

[0016] Linear ion traps include, but are not limited to, rectangular ion traps, multipole and segmented multipole structures.

[0017] The ion trap driving RF voltage is any periodic RF wave, including square wave, triangle wave or sine wave.

[0018] The ion source includes an in-trap ion source and an out-trap ion source. The out-trap ion source includes various types of ion sources at normal pressure and negative pressure.

[0019] Due to the adoption of the above-mentioned technical solution, the present invention provides a method for regulating the energy of ions in a linear ion trap. In this method, when ions generated by an ion source inside the trap or an ion source outside the trap enter the linear ion trap, they are confined within the linear ion trap under the combined action of a periodic radio frequency electric field and the DC electric field of the ion gate. In a short linear ion trap, the DC voltage of the ion gate will penetrate to the center of the ion trap to generate an induced voltage. This induced voltage will reduce the stability of the radio frequency field in binding the ions, prompting the ions to obtain energy from the radio frequency field. By changing the DC voltage of the ion gate, the ion energy can be regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 Schematic diagram of the structure of the linear ion trap in the present invention

[0022] Figure 2 The working sequence diagram of the linear ion trap in the present invention is

[0023] Figure 3 This is the ion optical simulation result of the kinetic energy of m / z 300 ions by adjusting the DC voltage of the ion gate in the present invention.

[0024] Figure 4 This is a diagram showing the experimental results of changing the kinetic energy of xylene ions by regulating the DC voltage of the ion gate in the present invention. DETAILED DESCRIPTION

[0025] To make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0026] like Figure 1 The linear ion trap shown includes an ion source, an entrance ion gate electrode 1 , an exit ion gate electrode 2 and a radio frequency electrode 3 .

[0027] The geometric centers of the entrance ion gate electrode 1, the exit ion gate electrode 2 and the radio frequency electrode 3 are located on the same axis and are spaced apart. A periodic radio frequency wave with a phase difference of 180° is applied to the radio frequency electrode 3 to radially confine the ions, and a direct current voltage is applied to the entrance ion gate electrode 1 and the exit ion gate electrode 2 to axially confine the ions.

[0028] When the linear ion trap adjusts the ion energy: when ions generated by the ion source inside the trap or the ion source outside the trap enter the linear ion trap, they are bound in the linear ion trap under the combined action of the periodic radio frequency electric field and the DC electric field of the ion gate. In the short linear ion trap, the DC voltage of the ion gate will penetrate to the center of the ion trap to generate an induced voltage. The induced voltage will reduce the binding stability of the radio frequency field on the ions, prompting the ions to obtain energy from the radio frequency field. By changing the DC voltage of the ion gate, the ion energy can be controlled.

[0029] Example

[0030] In the example, the linear ion trap is a quadrupole structure, and the time-of-flight mass analyzer is a reflective time-of-flight mass analyzer TOFMS. The linear ion trap consists of an entrance ion gate electrode, a quadrupole electrode, and an exit ion gate electrode. The field radius of the ion trap is 4 mm and the length is 8 mm. The inner diameter of the two ion gates is 1.5 mm, the outer diameter is 28 mm, and the thickness is 1 mm. A DC voltage is applied to the entrance ion gate electrode and the exit ion gate electrode, respectively. A periodic RF voltage is applied to the quadrupole electrodes, wherein the alternating quadrupole electrodes apply the same RF voltage, and the RF voltages applied to adjacent quadrupole electrodes differ in phase by 180°. The periodic RF wave used is a square wave with a voltage amplitude of 200 V, a frequency of 1.5 MHz, and a duty cycle of 0.5. Figure 2 The following is a working timing diagram, including the ion injection, cooling, and extraction processes. The mass spectrometry analysis cycle is controlled by the main trigger frequency, and each trigger cycle consists of ion injection, ion cooling, and ion extraction stages. During the ion injection period, the entrance ion gate electrode voltage is reduced to -5V, forming a potential energy gradient with the voltage at the front end of the entrance ion gate electrode to achieve ion injection into the linear ion trap. At the same time, the entrance ion gate electrode is raised to +3V to prevent ions from flowing out of the ion trap. The radio frequency electric field is used to capture ions. During the ion capture cooling period, the entrance ion gate electrode and the exit ion gate electrode are simultaneously raised to the same voltage U to achieve axial confinement of the ions. The square wave radio frequency field confines the ions radially. For an 8mm short linear ion trap, the ion gate DC voltage U penetrates to the center of the ion trap, inducing the generation of a DC voltage U*, which changes the ion confinement stability, prompting the ions to obtain energy from the radio frequency field and increasing the ion kinetic energy. By regulating the ion gate DC voltage, the ion energy can be changed. During the ion extraction period, dual-pulse extraction was used, applying pulsed high voltages of +300V and -300V to the entrance and exit ion gate electrodes, respectively. The extraction time was set to 10μs, and the ions were extracted to the TOFMS for mass analysis.

[0031] The ion optical simulation of m / z 300 ion beam was performed using simion 8.0 software, with the gas pressure set to 0.1 Pa and the collision gas to helium (m g =4), gas temperature T = 298K, change the ion gate DC voltage, calculate the m / z 300 ion (mi =300) of kinetic energy E k ,like Figure 3 As shown in FIG, as the ion gate voltage increases, the ion kinetic energy increases from 0.56 eV to 12.6 eV.

[0032] Experimentally, 10 ppbv p-xylene / nitrogen was used as the sample standard gas and ionized by a VUV lamp. The turnaround time error of the m / z 106 ion at different ion gate DC voltages was measured using TOFMS, and the effective kinetic energy of the ion was estimated based on the turnaround time error formula Δt = 2mv / zeE. Figure 4 As shown in FIG, as the DC voltage of the ion gate increases, the kinetic energy of the ions increases from 0.16 eV to 0.58 eV.

[0033] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for regulating ion energy in a linear ion trap, characterized by: The linear ion trap comprises an ion source, an entrance ion gate electrode (1), an exit ion gate electrode (2) and a radio frequency electrode (3); The geometric centers of the entrance ion gate electrode (1), the exit ion gate electrode (2), and the radio frequency electrode (3) are located on the same axis and are spaced apart. A periodic radio frequency wave with a phase difference of 180° is applied to the radio frequency electrode (3) to radially confine the ions, and a direct current voltage is applied to the entrance ion gate electrode (1) and the exit ion gate electrode (2) to axially confine the ions. When the linear ion trap adjusts the ion energy: when ions generated by the ion source inside the trap or the ion source outside the trap enter the linear ion trap, they are bound in the linear ion trap under the combined action of the periodic radio frequency electric field and the DC electric field of the ion gate. In the short linear ion trap, the DC voltage of the ion gate will penetrate to the center of the ion trap to generate an induced voltage. The induced voltage will reduce the binding stability of the radio frequency field on the ions, prompting the ions to obtain energy from the radio frequency field. By changing the DC voltage of the ion gate, the ion energy is regulated.

2. The method for regulating ion energy in a linear ion trap according to claim 1, characterized in that: The length of the linear ion trap is 2 to 20 mm.

3. The method for regulating ion energy in a linear ion trap according to claim 1, wherein: The ion gate DC voltage is 1~500V.

4. The method for regulating ion energy in a linear ion trap according to claim 1, wherein: The storage time of the linear ion trap is 0.001 to 1000 ms.

5. The method for regulating ion energy in a linear ion trap according to claim 1, wherein: The background gas in the linear ion trap is one or more of helium, argon, krypton, nitrogen, oxygen or dry air.

6. The method for regulating ion energy in a linear ion trap according to claim 1, characterized in that: The gas pressure in the linear ion trap is 0.1~100Pa.

7. The method for regulating ion energy in a linear ion trap according to claim 1, characterized in that: Linear ion traps include, but are not limited to, rectangular ion traps, multipole and segmented multipole structures.

8. The method for regulating ion energy in a linear ion trap according to claim 1, characterized in that: The ion trap driving RF voltage is any periodic RF wave, including square wave, triangle wave or sine wave.

9. The method for regulating ion energy in a linear ion trap according to claim 1, wherein: The ion source includes an in-trap ion source and an out-trap ion source. The out-trap ion source includes various types of ion sources at normal pressure and negative pressure.

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