CN112992646B - Radio frequency voltage applying method of small ion trap mass spectrometer - Google Patents
Radio frequency voltage applying method of small ion trap mass spectrometer Download PDFInfo
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- CN112992646B CN112992646B CN202110172359.7A CN202110172359A CN112992646B CN 112992646 B CN112992646 B CN 112992646B CN 202110172359 A CN202110172359 A CN 202110172359A CN 112992646 B CN112992646 B CN 112992646B
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- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
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Abstract
The invention discloses a radio frequency voltage applying method of a small-sized ion trap mass spectrometer, which applies voltages to an ion trap at different time sequence stages of the small-sized ion trap mass spectrometer by using two independent radio frequency power supplies so as to enable the ion trap to work in different ion processing modes at different time sequence stages. In the cooling time sequence stage, the radio frequency voltage applied to the small ion trap mass spectrometer by the radio frequency power supply is coupled with the air pressure change in the cavity of the mass spectrometer, so that the ion loss in the cavity is reduced, the signal intensity of the instrument is improved, and the detection limit is reduced.
Description
Technical Field
The invention relates to the field of mass spectrometer control methods, in particular to a radio frequency voltage applying method of a small-sized ion trap mass spectrometer.
Background
Mass spectrometers, which are instruments used to determine the mass-to-charge ratio and abundance of ions, generally comprise an ion source, an ion trap and a detector, wherein the ion trap separates sample ions generated in the ion source according to different ways according to their mass-to-charge ratio. The ion trap is located between the ion source and the detector, and the finally ionized ions are received and detected by the detector.
The working process of the small ion trap mass spectrometer can be divided into four time sequence stages of sample introduction, cooling, scanning and idling according to time sequence, namely four stages of ion movement in the ion trap: ion incidence, cooling, mass analysis, and scavenging stages. The conventional small ion trap is mostly a rectangular ion trap mechanism, electrodes are respectively arranged at two ends in the X direction in the rectangular ion trap, an X direction electric field is formed when resonance excitation voltage AC is loaded to the two electrodes in the X direction, electrodes are respectively arranged at two ends in the Y direction in the rectangular ion trap, and a quadrupole constraint electric field is formed when radio frequency voltage RF is loaded to the two electrodes in the Y direction. After ions in a certain mass range are incident into the ion trap, the ions are captured and stored by the ion trap in a cooling time sequence stage under the conditions of a cooling constraint electric field with specific size and background gas in the vacuum cavity. When the ions are accumulated to a certain number, the ion trap enters a scanning time sequence stage, the voltage values of the AC and the RF are adjusted to perform scanning, and the ions sequentially leave the ion trap from high to low according to the mass and are detected by a detector.
In the existing mass spectrometer, the same radio frequency power supply is used for providing radio frequency voltage in four time sequence stages of sample introduction, cooling, scanning and idling. In the whole mass spectrum detection time sequence, when the cooling time sequence stage is used for cooling and constraining ions, the loss of the ions is serious, so that the ion detection limit of the whole instrument can not be reduced finally. It is therefore important to improve the ion-binding efficiency of the cooling stage.
Disclosure of Invention
The invention aims to provide a radio frequency voltage applying method of a small-sized ion trap mass spectrometer, which aims to solve the problem of serious ion loss in a cooling time sequence stage in the ion trap of the mass spectrometer in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a radio frequency voltage applying method for a small ion trap mass spectrometer is characterized in that a radio frequency voltage is loaded on a pair of X-direction electrodes in an ion trap to form an X-direction electric field, a radio frequency voltage is loaded on a pair of Y-direction electrodes to form a Y-direction electric field, and in a cooling time sequence stage of the ion trap, the radio frequency voltage corresponding to one electric field is controlled to enable the electric field change corresponding to the controlled radio frequency voltage to be coupled with the air pressure change in the ion trap in the cooling time sequence stage.
In the invention, an independent radio frequency power supply is used, and radio frequency voltage is loaded to two electrodes in the X direction in a cooling time sequence stage; or, loading radio frequency voltage to the two electrodes in the Y direction in the cooling time sequence stage; alternatively, the radio frequency voltage is applied to the electrodes in the X direction and the Y direction at the same time in the cooling timing stage.
In the cooling time sequence stage, the amplitude of the radio frequency voltage provided by the radio frequency power supply is always less than or equal to 500V, and the upper limit value of the resonance frequency of the radio frequency power supply is changed to be 2.5MHz aiming at different sample injection targets, so that a better cooling effect is achieved.
In the invention, in the cooling time sequence stage, the radio frequency voltage is controlled to be constant and then increased in the cooling time sequence stage; or controlling the radio frequency voltage to gradually increase at the cooling time sequence stage, wherein the early-stage gradual increase rate is smaller than the later-stage gradual increase rate; or the radio frequency voltage is controlled to be increased suddenly for a plurality of times in the cooling time sequence stage.
The invention simultaneously uses another independent radio frequency power supply to load radio frequency voltage to the two electrodes in the Y direction in the scanning time sequence stage. In the scanning time sequence stage, the radio frequency voltage provided by the radio frequency power supply is greater than or equal to 2000V.
The invention can adopt two independent radio frequency power supplies to apply radio frequency voltage to different stages of the same ion trap time sequence differently, and specifically comprises that one radio frequency power supply is used in a cooling time sequence stage, and the other radio frequency power supply is used in a scanning time sequence stage;
in the cooling time sequence stage, the radio frequency voltage loaded to the electrode by the radio frequency power supply is controlled, so that the voltage amplitude applied to the ion trap by the radio frequency power supply is coupled with the air pressure change in the cavity of the ion trap of the mass spectrometer, the force of the ion in the cavity under a bound electric field is coupled with the force controlled by the air pressure, and meanwhile, the voltage frequency applied to the ion trap by the radio frequency power supply is coupled with the relative molecular weight of a sample injection target object of the mass spectrometer, so that the ion loss is reduced. Specifically, the radio frequency power supply voltage application process in the cooling time sequence stage is divided into two parts: a first part, in the first stage of the cooling time sequence stage, the air pressure in the cavity is higher, and at the moment, the radio frequency voltage amplitude with small change or almost unchanged and small amplitude is applied to prevent the radio frequency voltage from discharging under high air pressure; in the second part, the air pressure in the cavity becomes lower in the second stage of the cooling time sequence stage, and the amplitude of the radio frequency voltage is increased at the moment so as to increase the constraint electric field and enable the ions to be contracted and stored.
The invention provides a radio frequency voltage applying method of a small-sized ion trap mass spectrometer, which can independently control a cooling time sequence stage and a scanning time sequence stage, and couple the voltage of the cooling time sequence stage with the air pressure change of the time sequence stage, thereby improving the ion binding efficiency of the cooling time sequence stage to the maximum extent, further improving the detection efficiency of the mass spectrometer and reducing the ion detection limit.
Drawings
Figure 1 is a schematic diagram of an ion trap electrode distribution according to the present invention.
Figure 2 is a schematic diagram of the ion trap timing stages of the present invention.
Detailed Description
As shown in fig. 1, the method for applying rf voltage to a compact ion trap mass spectrometer of the present invention includes providing a pair of electrodes X1 and X2 in the X direction of the ion trap, and providing a pair of electrodes Y1 and Y2 in the Y direction of the ion trap. The X-direction electrode and the Y-direction electrode can be used for loading radio-frequency voltage provided by a radio-frequency power supply.
As shown in fig. 2, P1 in fig. 2 represents a sample injection timing stage, P2 represents a cooling timing stage, P3 represents a scan timing stage, and P4 represents an idle timing stage.
In the invention, an independent radio frequency power supply is adopted to supply power in the stage P2, another independent radio frequency power supply is adopted to supply power in the stage P3, and the radio frequency power supplies are not used for the stage P1 of sample introduction and the stage P4 of idle.
The process of cooling the rf voltage applied during the sequence phase P2 needs to be divided into two parts, so that the division is coupled to the pressure change in the vacuum chamber during the cooling sequence phase P2. After pulse sampling, the gas pressure change trend in the vacuum cavity is similar to a normal distribution, and the gas pressure change trend chart is shown in fig. 2, so that the radio frequency power supply voltage applying process of the cooling time sequence stage P2 is divided into two parts: the first part is that the air pressure in the cavity is higher in the first cooling stage, the collision contraction force of ion movement is high, and the radio frequency voltage amplitude with small change or almost unchanged and small amplitude is applied; and in the second part, the air pressure in the cavity becomes lower in the second cooling stage, the contraction effect of the ion motion track caused by collision is weakened, the amplitude of the radio frequency voltage is increased, and the binding voltage is increased, so that the ions are contracted and stored. And controlling the bound electric field according to the two processes, so that the change of the bound electric field is coupled with the change of the airflow field to achieve the purpose of better controlling ions in the trap.
Specifically, the following cases are classified when the cooling sequence stage P2 performs the radio frequency voltage adjustment:
1. in the cooling time sequence stage of the ion trap, the two electrodes X1 and X2 in the X direction are connected with a radio frequency power supply to load radio frequency voltage, and the two electrodes Y1 and Y2 in the Y direction are loaded with another radio frequency voltage. In this case, the rf voltage applied to the electrodes X1 and X2 is changed to change the X-direction electric field between the electrodes X1 and X2, and then the confinement electric field is changed to couple the confinement electric field change with the air pressure change.
2. In the cooling time sequence stage of the ion trap, the two electrodes X1 and X2 in the X direction are connected with a radio frequency power supply to load radio frequency voltage, and the two electrodes Y1 and Y2 in the Y direction are connected with the radio frequency power supply to load radio frequency voltage. In this case, by changing the rf voltage applied to the electrodes X1 and X2 and changing the rf voltage applied to the electrodes Y1 and Y2, the X-direction electric field between the electrodes X1 and X2 and the Y-direction electric field between the electrodes Y1 and Y2 can be changed, so as to finally change the confinement electric field, so that the confinement electric field change is coupled with the air pressure change.
3. In the cooling time sequence stage of the ion trap, two electrodes Y1 and Y2 in the Y direction are connected with a radio frequency power supply to load radio frequency voltage, and two electrodes X1 and X2 in the X direction are loaded with a constant voltage AC. In this case, the rf voltage applied to the electrodes Y1 and Y2 is changed to change the Y-direction electric field between the electrodes Y1 and Y2, and then the confinement electric field is changed to couple the confinement electric field change with the air pressure change.
In the three processes, the radio frequency voltage provided by the radio frequency power supply is small and can be provided by the radio frequency power supply with the output voltage less than or equal to 500V.
In the three processes, the specific rf voltage adjustment can be based on the change rule of the air pressure at the P2 stage shown in fig. 2. The P2 phase can be divided into two parts: the first part is higher in air pressure, and the loaded radio frequency voltage can be kept constant or changed gradually according to a smaller change rate; the second part is low in air pressure, and the radio frequency voltage can be increased suddenly or changed gradually at a high change rate.
In the present invention, another independent rf power source is used to provide the rf voltage during the scan timing phase P3. Specifically, during the phase P3, the electrodes Y1 and Y2 can be connected to the new RF power source to apply RF voltage. And in the scanning time sequence stage, the radio frequency voltage provided by the new radio frequency power supply is greater than or equal to 2000V.
The embodiments of the present invention are described only for the preferred embodiments of the present invention, and not for the limitation of the concept and scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall into the protection scope of the present invention, and the technical content of the present invention which is claimed is fully set forth in the claims.
Claims (7)
1. A radio frequency voltage applying method of a small-sized ion trap mass spectrometer is characterized in that a radio frequency voltage is applied to a pair of X-direction electrodes in an ion trap to form an X-direction electric field, and a radio frequency voltage is applied to a pair of Y-direction electrodes to form a Y-direction electric field, and the method comprises the following steps: an independent radio frequency power supply is used, at the cooling time sequence stage of the ion trap, radio frequency voltage corresponding to at least one electric field is controlled, the voltage amplitude corresponding to the controlled radio frequency voltage is coupled with the air pressure change inside the ion trap at the cooling time sequence stage, so that the force of the ions in the cavity body under the constraint electric field is coupled with the force controlled by the air pressure, meanwhile, the voltage frequency applied to the ion trap by the radio frequency power supply is coupled with the relative molecular weight of a sample introduction target object of a mass spectrometer, and the ion loss is reduced; specifically, the independent rf power voltage application process in the cooling sequence stage is divided into two parts: a first part, in the first stage of the cooling time sequence stage, the air pressure in the cavity is higher, and at the moment, the radio frequency voltage amplitude with small change or almost unchanged and small amplitude is applied to prevent the radio frequency voltage from discharging under high air pressure; the second part, the air pressure in the cavity becomes lower in the second stage of the cooling time sequence stage, and the radio frequency voltage amplitude is increased at the moment to increase the bound electric field so as to shrink and store the ions; in the cooling time sequence stage, the amplitude of the radio frequency voltage provided by the independent radio frequency power supply is always less than or equal to 500V, the resonance frequency of the independent radio frequency power supply is changed aiming at different sample injection targets, and the upper limit value of the change of the resonance frequency of the independent radio frequency power supply is 2.5MHz;
and applying radio frequency voltage to the two electrodes in the Y direction in a scanning time sequence stage by using another independent radio frequency power supply, wherein the radio frequency voltage provided by the other independent radio frequency power supply in the scanning time sequence stage is greater than or equal to 2000V.
2. The method of claim 1, wherein the rf voltage is applied to the ion trap mass spectrometer by: and applying radio frequency voltage to the two electrodes in the X direction in the cooling time sequence stage.
3. The method of claim 1, wherein the rf voltage is applied to a compact ion trap mass spectrometer by: and applying radio frequency voltage to the two electrodes in the Y direction in the cooling time sequence stage.
4. The method of claim 1, wherein the rf voltage is applied to a compact ion trap mass spectrometer by: and simultaneously applying radio frequency voltage to the electrodes in the X direction and the Y direction in the cooling time sequence stage.
5. The method for applying radio frequency voltage of a compact ion trap mass spectrometer as claimed in any one of claims 1 to 4, wherein: the RF voltage is controlled to be constant and then increased during the cooling time period.
6. The method for applying radio frequency voltage of a compact ion trap mass spectrometer as claimed in any one of claims 1 to 4, wherein: the radio frequency voltage is controlled to gradually increase in the cooling time sequence stage, and the early stage gradual increase rate is smaller than the later stage gradual increase rate.
7. The method for applying radio frequency voltage of a compact ion trap mass spectrometer as claimed in any one of claims 1 to 4, wherein: the RF voltage is controlled to increase abruptly a plurality of times during the cooling time period.
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