CN115565847A - Method for improving linear ion trap-flight time mass spectrum performance by digital wave phase modulation - Google Patents

Abstract

The invention relates to a method for improving the performance of a linear ion trap-time-of-flight mass spectrum by digital wave phase modulation.A digital wave radio frequency voltage is generated by a digital wave generating device and is applied to the linear ion trap, ions generated by an ion source enter the linear ion trap, and the cooling and storage of the ions are realized under the action of a digital wave radio frequency electric field; and (3) turning off the radio frequency of the digital wave at a certain phase point, and applying an extraction voltage to axially extract ions in the trap to a time-of-flight mass spectrometer detector. By changing the radio frequency phase during ion extraction, the IS-TOF performance can be regulated and controlled.

Description

Method for improving linear ion trap-flight time mass spectrum performance by digital wave phase modulation

Technical Field

The invention belongs to a mass spectrometer, and particularly relates to a method for improving the performance of a linear ion trap-time-of-flight mass spectrometer by digital wave phase modulation.

Background

In the ion trap, ion clouds are concentrated near the center of the ion trap by ion-molecule collisions, and their phase space distribution is less than 1mm. The ion trap can thereby provide a time-of-flight mass spectrometer with an ion source having a smaller spatial divergence. Compared with the 3D ion trap, ions in the linear ion trap are easy to gather in a shape of a smoke cloud along the Z axis, and the space charge influence is very small, so that the storage capacity of the linear ion trap is dozens of times or even hundreds of times higher than that of the 3D ion trap. Currently commonly used ion trapping methods typically use a sine wave and the RF voltage should be switched off when extracting ions into the TOF for more efficient extraction of ions in the trap. In fact, the sine wave is difficult to realize instantaneous closing, a residual ringing radio frequency field exists during closing, the residual radio frequency field brings an accelerating electric field which is difficult to predict, ion cloud phase space distribution is disturbed, loss of ion extraction efficiency is caused, and the resolution of a flight time mass spectrum is distorted.

Disclosure of Invention

The invention discloses a method for changing ion storage-time-of-flight mass spectrum performance by phase modulation. In the flight time mass spectrum with the ion trap preceding stage storage device, the IS-TOF performance can be regulated and controlled by changing the radio frequency phase during ion extraction.

The technical scheme adopted by the invention for realizing the purpose is as follows: the method for improving the performance of the linear ion trap-time-of-flight mass spectrum by digital wave phase modulation comprises the following steps:

generating digital wave radio frequency voltage by a digital wave generating device and applying the digital wave radio frequency voltage to a linear ion trap, enabling ions generated by an ion source to enter the linear ion trap, and realizing the cooling and storage of the ions under the action of a digital wave radio frequency electric field; and (3) turning off the digital wave radio frequency at a certain phase point, and applying an extraction voltage to axially extract ions in the trap to a time-of-flight mass spectrometer detector.

The ion generated by the ion source enters the linear ion trap, the voltage of the inlet electrode is reduced to negative voltage, the ion is injected into the linear ion trap, the inlet electrode is raised to positive voltage to prevent the ion from flowing out, and voltage is applied to the radio frequency electrode to capture the injected ion.

Turning off the radio frequency of the digital wave at a certain phase point, applying extraction voltage to axially extract ions in the trap to a time-of-flight mass spectrometer detector, and comprising the following steps:

respectively applying positive and negative pulse high voltages to the inlet electrode and the outlet electrode, wherein the absolute values of the positive and negative voltages are equal; and simultaneously, closing the digital wave radio frequency power supply, and extracting ions in the linear ion trap to a time-of-flight mass spectrometer according to the set extraction time.

The waveform, voltage, phase, duty ratio and frequency of the digital wave are adjusted at will.

The digital waves include, but are not limited to, square waves, triangular waves.

The digital wave phase realizes the modulation of any phase point between 0 and 360 degrees.

The gas pressure in the linear ion trap is regulated and controlled within the range of 0.1-thousands Pa.

A system for improving linear ion trap-time-of-flight mass spectral performance by digital wave phase modulation, comprising:

a linear ion trap for injecting and storing ions generated by the ion source;

a time-of-flight mass spectrometer detector for extracting ions in the ion trap; the inlet corresponds to the outlet of the linear ion trap, and the axis of the time-of-flight mass spectrometer detector is coincident with the axis of the linear ion trap;

and the digital wave generating device is connected with the radio frequency electrode of the linear ion trap and is used for applying a digital wave radio frequency voltage to the linear ion trap.

The linear ion trap is a rectangular ion trap, a quadrupole rod or a segmented quadrupole rod structure.

The ion source includes an in-trap source and an out-of-trap source.

The invention has the following beneficial effects and advantages:

1. the present invention applies a digital square wave to ion storage-multiple reflection time-of-flight mass spectrometry. The precise control of the radio frequency voltage can be realized, and the acceleration effect of a ringing electric field during ion extraction is effectively avoided.

2. The control of IS-TOF resolution and sensitivity can be realized by changing the radio frequency phase during ion extraction, namely controlling the phase space distribution of ion cloud during extraction.

Drawings

Figure 1 is a schematic of a linear ion trap-TOF configuration;

1. an inlet electrode 2, an outlet electrode 3, a radio frequency electrode 4, a digital wave generating device 5 and a time-of-flight mass spectrum detector;

fig. 2 illustrates the diagram: axial extraction ion trap-TOF structure schematic diagram;

FIG. 3 ion trap-TOF timing diagram;

FIG. 4 shows the variation trend of the signal intensity and resolution of the ion mass spectrum of m/z 106, m/z 164 and m/z 258 in the embodiment along with the extraction radio frequency phase of the digital wave;

wherein, a) ion peak signal intensity polar coordinate graph of mass-to-charge ratio m/z 106; b) A polar plot of the resolution of mass-to-charge ratio m/z 106 versus square wave phase; c) A polar graph of mass-to-charge ratio m/z 164 ion peak signal intensity; d) A polar plot of mass-to-charge ratio m/z 164 resolution versus square wave phase; e) A polar plot of mass to charge ratio m/z 258 ion peak signal intensity; f) Polar plot of mass to charge ratio m/z 258 resolution with square wave phase.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

The invention provides an axial series linear ion trap-time-of-flight mass spectrometer, wherein the ion trap and the time-of-flight mass spectrometer are coaxially arranged, and ion cloud is axially led out from the ion trap to a time-of-flight mass spectrometer detector. By changing the radio frequency phase during ion extraction, the IS-TOF performance can be regulated and controlled.

A method for improving linear ion trap-time-of-flight mass spectrum performance by digital wave phase modulation comprises an ion source, an ion trap consisting of an inlet electrode, an outlet electrode and a radio frequency electrode, a digital wave generating device and a time-of-flight mass spectrum. And generating a digital wave radio frequency voltage by a digital wave generating device and applying the digital wave radio frequency voltage to the linear ion trap.

The ion source in the trap or the ion source outside the trap generates ions and enters the linear ion trap, and the ions are cooled and stored under the action of the digital wave radio frequency electric field. And then, the digital wave radio frequency is closed at a specific phase position, and double pulse voltage is applied to axially extract ions in the trap to a time-of-flight mass spectrometer detector at the rear end.

The waveform, voltage, phase, duty cycle and frequency of the digital wave can be adjusted freely according to the measuring requirement, and the digital wave comprises but is not limited to square waves and triangular waves.

Linear ions include, but are not limited to, rectangular ion traps, quadrupole rods, and segmented quadrupole rod structures.

The linear ion trap storage time can be adjusted in the range of 0-1000 ms.

The digital wave phase can realize the modulation of any phase point between 0 and 360 degrees.

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

The gas pressure in the linear ion trap can be regulated and controlled within the range of 0.1-several thousand Pa.

The ion source comprises an inner trap ion source and an outer trap ion source, and the outer trap ion source comprises various ion sources with normal pressure and negative pressure.

The ion trap extraction mode is axial extraction.

Example 1

A method for improving linear ion trap-time-of-flight mass spectrometry performance by digital wave phase modulation. The device comprises a linear ion trap, a digital wave generation device and a time-of-flight mass spectrum. And generating a digital wave radio frequency voltage by a digital wave generating device and applying the digital wave radio frequency voltage to the linear ion trap.

The ion source in the trap or the ion source outside the trap generates ions and enters the linear ion trap, and the ions are cooled and stored under the action of the digital wave radio frequency electric field. And then, the radio frequency of the digital wave is closed at a specific phase position, and an extraction voltage is applied to axially extract ions in the trap to a time-of-flight mass spectrometer at the rear end.

As shown in fig. 2, the linear ion trap in the example is a segmented quadrupole rod structure, and consists of an inlet electrode, a segmented electrode and an outlet electrode. The segmented electrodes are respectively composed of four groups of parallel electrode arrays; each group of electrode arrays consists of one or more concentric cylindrical electrodes at even intervals, and the diameter of each cylinder is 9.04mm; the centers of the four groups of electrode arrays are uniformly arranged on the circumference with the radius of 8.52 mm; the thickness of the cylindrical electrodes is 4mm, and the interval is 0.5mm. The inlet electrode hole and the outlet electrode are both circular ring electrodes with the inner diameter of 1.5mm, the outer diameter of 28mm and the thickness of 1mm. Applying direct current voltage to the inlet electrode and the outlet electrode respectively; the concentric cylinder electrodes on any one of the four groups of electrode arrays of the segmented electrodes are uniformly divided by voltage dividing resistors, the segmented electrodes are respectively connected with equivalent capacitors, the cylinder electrodes on each group of segmented electrode arrays apply the same radio frequency voltage, the interphase segmented electrode array groups apply the same radio frequency voltage, and the adjacent cylinder electrode groups apply radio frequency voltages with opposite polarities and the same absolute values. The radio frequency voltage is digital square wave radio frequency voltage (the amplitude of the radio frequency voltage is 200V, the frequency is 1.5MHz, and the duty ratio is 0.5).

By controlling the voltage parameters of the electrodes in a time sequence mode, the ions can be injected, cooled and extracted in the linear ion trap. The time sequence control is as shown in fig. 3, the mass spectrometry period is controlled by the main trigger frequency, and the storage time of the linear ion trap is regulated and controlled by controlling the main trigger frequency. Each trigger cycle consists of three sections, ion implantation, ion cooling and ion extraction. In the ion implantation period, ion implantation is realized through a direct current electric field, the voltage of an inlet electrode is reduced to-5V, potential energy gradient is formed between the voltage of the inlet electrode and the voltage of the front end of the inlet electrode, implantation of ions into a linear ion trap is realized, an outlet electrode is raised to +3V at the same time, ion outflow is prevented, and a radio frequency power supply is turned on to capture implanted ions; and finally, a cooling area is formed, the inlet electrode and the outlet electrode are modulated by +10V at the same time, the axial constraint of the ions is realized, the ions are bound by the digital wave radio frequency field in the radial direction, and after a certain time of cooling, the ion cloud gradually converges on the central axis of the quadrupole rod in space. In the ion extraction period, double-pulse extraction is adopted, pulse high voltages of +300V and-300V are applied to the inlet electrode and the outlet electrode respectively, a digital wave radio frequency power supply is closed, the extraction time is set to be 10 mu s, and ions in the trap are extracted to a flight time mass spectrum detector at the rear end.

The ion source is a low-pressure photoionization source, and the detector is a multi-reflection time-of-flight mass spectrum. The change trend of the signal intensity and the resolution of the m/z 106, m/z 164 and m/z 258 ion mass spectrum along with the radio frequency phase of digital wave extraction is tested by taking 10ppbv of acetone-benzene-p-xylene-tetrachloroethylene-1, 3 hexachlorobutadiene as a sample standard gas and setting the storage time of a linear ion trap under the condition of 2ms and MR-TOF flight behavior, and the experimental results are shown in a) to f) in FIG. 4. It can be seen that the corresponding mass spectral peak resolution and signal intensity exhibit periodic variations with the square wave phase, which is the best extraction phase point for the phase point at a square wave voltage of 0.

Claims (10)

1. The method for improving the linear ion trap-time-of-flight mass spectrum performance by digital wave phase modulation is characterized by comprising the following steps of:

generating digital wave radio frequency voltage by a digital wave generating device and applying the digital wave radio frequency voltage to the linear ion trap, enabling ions generated by the ion source to enter the linear ion trap, and realizing the cooling and storage of the ions under the action of a digital wave radio frequency electric field; and (3) turning off the radio frequency of the digital wave at a certain phase point, and applying an extraction voltage to axially extract ions in the trap to a time-of-flight mass spectrometer detector.

2. The method of claim 1 wherein ions generated by the ion source enter the linear ion trap, the voltage at the entrance electrode is reduced to a negative voltage to inject ions into the linear ion trap, the entrance electrode is raised to a positive voltage to prevent ions from flowing out, and a voltage is applied to the rf electrode to trap the injected ions.

3. The method of claim 1, wherein the digital wave phase modulation is used to improve linear ion trap-time-of-flight mass spectrometry performance, wherein the digital wave radio frequency is turned off at a certain phase point, and an extraction voltage is applied to axially extract ions in the trap to the time-of-flight mass spectrometry detector, comprising the steps of:

respectively applying positive and negative pulse high voltages to the inlet electrode and the outlet electrode, wherein the absolute values of the positive and negative voltages are equal; and simultaneously, closing the digital wave radio frequency power supply, and extracting ions in the linear ion trap to a flight time mass spectrum detector according to the set extraction time.

4. The method of digital wave phase modulation for improving linear ion trap-time-of-flight mass spectrometry performance of claim 1, wherein: the waveform, voltage, phase, duty cycle and frequency of the digital wave are adjusted at will.

5. The method of digital wave phase modulation for improving linear ion trap-time-of-flight mass spectrometry performance of claim 1, wherein: the digital waves include, but are not limited to, square waves, triangular waves.

6. The method of digital wave phase modulation for improving linear ion trap-time-of-flight mass spectrometry performance of claim 1, wherein: the digital wave phase realizes the modulation of any phase point between 0 and 360 degrees.

7. The method of digital wave phase modulation for improving linear ion trap-time-of-flight mass spectrometry performance of claim 1, wherein: the gas pressure in the linear ion trap is regulated and controlled within the range of 0.1-thousands Pa.

8. A system for improving linear ion trap-time-of-flight mass spectral performance by digital wave phase modulation, comprising:

a linear ion trap for injecting and storing ions generated by the ion source;

a time-of-flight mass spectrometer detector for extracting ions in the ion trap; the inlet corresponds to the outlet of the linear ion trap, and the axis of the time-of-flight mass spectrometry detector is coincident with the axis of the linear ion trap;

and the digital wave generating device is connected with the radio frequency electrode of the linear ion trap and is used for applying a digital wave radio frequency voltage to the linear ion trap.

9. The system of claim 8, wherein the linear ion trap is a rectangular ion trap, a quadrupole, or a segmented quadrupole structure.

10. The system of claim 8, wherein the ion sources comprise an in-trap and an out-of-trap ion source.

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