JPH10208692A - Ion trap mass spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection sensitivity of an ion and the sensitivity of an ion trap mass spectrograph without giving asymmetry to the electric field in the vicinity of the center in an ion trap electrode. SOLUTION: An ion trap mass spectrograph is provided with a ring electrode 2 of at least one side of end cap electrodes 3 and 4 and auxiliary electrodes 11 and 12 on the opposite side, and voltage is applied between auxiliary electrodes 11 and 12 and end cap electrodes 3 and 4. The ion is trapped by trapping electric field by the ring electrode 2 formed inside an ion trap electrode 10 and auxiliary high frequency electric field by end cap electrodes 3 and 4. Then, when DC or high frequency voltage is applied between auxiliary electrodes 11 and 12 and end cap electrodes 3 and 4, an electric field which is different from trapping electric field or auxiliary high frequency electric field is formed inside the ion trap electrode 10 through holes bored through end cap electrodes 3 and 4. This electric field promotes the extracting action of ions to the outside, increases amounts of detection by a detector and improves detection sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a mass spectrometer, and more particularly to a mass spectrometer provided with an ion trap electrode.

[0002]

2. Description of the Related Art A mass spectrometer is a device for selecting and separating molecules in a sample for each mass in accordance with a mass-to-charge ratio. The molecules in a sample are ionized in a dissociated or bound state by various means. The separation is performed by moving the ionized molecules by a magnetic field, an electric field, or both according to a mass-to-charge ratio. For example, in a quadrupole mass spectrometer, ions are incident in the axial direction of the electrode in a high-frequency electric field and a direct-current electric field formed by applying a voltage obtained by superimposing a high-frequency voltage and a direct-current voltage to an electrode of a specific shape, and the ions and the electric field Ions are selectively separated by the interaction of

On the other hand, an ion trap mass spectrometer is a device which acts on ions in three directions to trap and confine selected ions inside an electrode. Thus, the ions are confined inside the electrode, and the ions are emitted toward the detector by a change in a high-frequency voltage or application of an auxiliary high-frequency electric field. Also, inside the electrode, the confined parent ions are collided and separated, and the mass spectrum of the released daughter ions is also detected.

FIG. 6 is a schematic view of a conventionally known ion trap electrode. 6, the ion trap electrode 21 includes a ring electrode 22 having a hyperboloid of revolution and first and second end cap electrodes 23 and 24.
An AC voltage and a DC voltage are applied to capture ions. As the frequency of the AC voltage, a radio wave (RF) region is used. When a DC voltage U and an AC voltage Vcos ωt are applied to the electrodes, charged particles having mass m and charge e are (m / e, r0
, U, V, ω) are stably trapped in the electrode under certain conditions. Here, r0 is the minimum radius of the ring electrode 22. Therefore, given r0 and ω, m
In order to stably trap the ion species of / e, the size of U and V is limited. FIG. 7 is a diagram showing a trappable voltage condition, where m / e is 78, 51, 3
9 and 26, the shaded area indicates an area where the trap is stable when m / e is 51.

The ions trapped in the electrode oscillate at the angular frequency ω of the applied AC electric field, and harmonically oscillate with a period slower than ω in the r and z directions, and slowly move near the center of the electrode cell. It vibrates in a small amplitude with a period of ω while vibrating in the shape of ∞.

FIG. 8 is a view for explaining a conventional ion trap mass spectrometer using the above-described ion trap electrode. In FIG. 8, the ion trap electrode 21
Includes a ring electrode 22 having a hyperboloid of revolution, and first and second end cap electrodes 23 and 24 provided at open ends of the ring electrode 22.
Are connected, and the first and second end cap electrodes 23, 2
4 is connected to an auxiliary RF power supply 26 via a transformer 28, and both power supplies are controlled by a control circuit 27.

[0007] Through holes are formed in the central portions of the first and second end cap electrodes 23 and 24. The through hole on the first end cap electrode 23 side is used for introducing ions generated in a sample ionization chamber (not shown) or an electron beam for ionization into the ion trap electrode, and the through hole on the second end cap electrode 24 side. Is used for extracting ions to a detector 29 such as a secondary electron multiplier provided outside. The measurement device 39 obtains a mass spectrum using the detection signal of the detector 29.

[0008]

The conventional ion trap mass spectrometer has a problem that the ion detection sensitivity is low. In the ion trap electrode used in the conventional ion trap mass spectrometer, ions inside the electrode are ejected to the outside through through holes formed in the end cap electrodes on both sides, but the ion detector uses one of the two end cap electrodes. Since it is configured to be installed only on the side, ions emitted from the other through-hole do not contribute to ion detection, and the detection of emitted ions is not effectively performed.

Conventionally, in order to improve the ion detection sensitivity, a method has been proposed in which a ring electrode or an end cap electrode is formed into a special shape, or a bias is applied to both end cap electrodes to apply an unbalanced voltage. ing. However, processing a ring electrode or an end cap electrode into a special shape is expensive, and the voltage applied to the electrode requires high-precision frequency control.
In addition, when an imbalanced voltage is applied, there is a problem that an electric field in the ion trap electrode is deviated from the mechanical center of the electrode and the influence of the magnitude of the bias occurs.

Therefore, the present invention solves the above-mentioned problems and improves the sensitivity of ion trap mass spectrometry by improving the ion detection sensitivity without imparting asymmetry to the electric field near the center in the ion trap electrode. The purpose is to let them.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to an ion trap mass spectrometer in which an ion is selectively emitted from at least one end cap electrode to reduce an electric field near the center of the ion trap electrode. The object of the present invention is to improve the sensitivity of an ion trap mass spectrometer by improving the ion detection sensitivity without giving asymmetry.

[0012] The ion trap mass spectrometer of the present invention comprises:
A ring electrode, a pair of end cap electrodes having through holes provided at both open ends of the ring electrode, and a main RF power supply for applying an AC voltage having an amplitude V at an RF frequency ω to the ring electrode;
An auxiliary RF power supply that applies a high-frequency voltage to at least one of the end cap electrodes, a control circuit that controls the power supply, a detector that detects ions emitted from a through hole of one of the end cap electrodes, An ion trap mass spectrometer comprising a measuring device for obtaining a mass spectrum based on the number and the amplitude V, wherein an auxiliary electrode is provided on at least one end cap electrode on the side opposite to the ring electrode, and the auxiliary electrode is provided with an end cap electrode. And a voltage is applied between them.

According to the ion trap mass spectrometer of the present invention, a trapping electric field by the ring electrode and an auxiliary high-frequency electric field by the end cap electrode are formed inside the ion trap electrode, and these electric fields cause ions to enter the ion trap electrode. Be trapped. At this time, when a DC or high-frequency voltage is applied between the end cap electrode and the auxiliary electrode provided on the opposite side to the ring electrode of at least one end cap electrode, the ion trap electrode is formed through the through hole provided in the end cap electrode. An electric field different from the trapping electric field and the auxiliary high-frequency electric field is formed therein. The electric field formed by the auxiliary electrode acts in a direction of taking out ions from the inside of the ion trap electrode to the outside depending on the polarity of the electric field, or acts in a direction of suppressing the ions.
Therefore, the amount of ions detected by the detector can be increased, and the detection sensitivity can be improved.

Since the electric field formed by the auxiliary electrode remains near the end cap electrode, the electric field near the center of the ion trap electrode does not have asymmetry. Since the electric field formed by the auxiliary electrode used in the present invention is a seeping electric field, an asymmetric electric field is formed only near the end cap electrode. Therefore, of the ions oscillating inside the ion trap electrode, only ions oscillating up to the vicinity of the end cap electrode are extracted to the outside under the influence of the asymmetric electric field formed by the auxiliary electrode. On the other hand, since the electric field by the auxiliary electrode does not reach near the center of the ion trap electrode, ions oscillating near the center of the ion trap electrode are not affected by the auxiliary electrode, and the original ion trap mass spectrometer has It does not affect the detection characteristics.

According to the first embodiment of the present invention, the voltage applied to the auxiliary electrode is a DC voltage, whereby an asymmetric electric field can be formed near the end cap electrode where the auxiliary electrode is provided. Further, a second embodiment of the present invention provides
The voltage applied to the auxiliary electrode is a high-frequency voltage synchronized with the high-frequency voltage applied to the end cap electrode, whereby the asymmetrical voltage synchronized with the electric field change generated inside the ion trap electrode near the end cap electrode where the auxiliary electrode is installed By forming an electric field, ions vibrated by the internal electric field are easily affected by the asymmetric electric field, and the efficiency of extracting ions to the outside can be increased.

According to a third embodiment of the present invention, the end cap electrode is provided with a plurality of through holes, and the electric field formed by the auxiliary electrode is impregnated into the inside of the ion trap electrode through the through holes. An asymmetric electric field can be formed in the vicinity of the electrode. According to a fourth embodiment of the present invention, the auxiliary electrode is formed by a plurality of electrodes corresponding to the through holes formed in the end cap electrode, and a voltage can be independently applied to each electrode. Accordingly, an arbitrary asymmetric electric field can be formed near the end cap electrode. Further, in the fifth embodiment of the present invention, a plurality of electrodes forming an auxiliary electrode are connected via a resistor to apply a divided voltage, whereby an arbitrary voltage is applied to each electrode. Thus, it is possible to easily form an arbitrary asymmetric electric field near the end cap electrode.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. An embodiment of the present invention will be described with reference to the schematic perspective views of the ion trap mass spectrometer of the present invention shown in FIGS. FIG. 1 is a diagram for explaining an ion extracting operation, and FIG. 2 is a diagram for explaining an ion trapping operation.

In FIG. 1, an ion trap electrode 1 is
A ring electrode 2 having a hyperboloid of revolution and first and second end cap electrodes 3 and 4 provided at both open ends of the ring electrode 2 are connected to a main RF power source 5.
An auxiliary RF power source 6 is connected to the two end cap electrodes 3 and 4 via a transformer 8. Main RF power supply 5 has RF frequency ω
, An AC voltage having an amplitude V is generated, a trapping electric field is formed in the ion trap electrode 10 by the ring electrode 2, the auxiliary RF power source 6 generates a high-frequency voltage, and the ion trap electrode 10 is An auxiliary high-frequency electric field is formed therein. Main RF power supply 5 and auxiliary R
The control circuit 7 controls the voltage and timing generated by the F power supply 6.

Through holes are formed in the end cap electrodes 3 and 4, and ions trapped in the ion trap electrode 10 are taken out through the through holes or ions generated in a sample ionization chamber (not shown) through the through holes. Is introduced into an ion trap or an electron beam for ionization is introduced. A detector 9 such as a secondary electron multiplier is provided outside the end cap electrode 4 on the side from which ions are extracted.
To detect ions selectively extracted from the ion trap electrode 10. Measuring device 19
Calculates a mass spectrum based on the number of detected ions and the amplitude V of the main RF power supply 5.

In the vicinity of the end cap electrodes 3 and 4 on the side opposite to the ion trap electrode 2, first and second auxiliary electrodes 11 and
12 are provided. The first and second auxiliary electrodes 11 and 12
Can be installed on both sides of the end cap electrode or only on one side of the detector 9. Hereinafter, a case where the electrodes are provided on both sides of the end cap electrodes 3 and 4 will be described. A first auxiliary power supply 13 and a second auxiliary power supply 14 are connected to the first and second auxiliary electrodes 11 and 12, respectively, and a DC voltage, a high-frequency voltage, or a voltage obtained by superposing both of them is applied. The first auxiliary power supply 13 and the second auxiliary power supply 14 can be controlled by the control circuit 7 in FIG. 1 or another control circuit (not shown), and applies a high-frequency voltage synchronized with a high-frequency voltage applied to the end cap electrode. It can also be configured.

Next, the operation of trapping ions by the ion trap electrode will be described with reference to FIG. 2, and the operation of extracting ions from the inside of the ion trap electrode will be described with reference to FIG. The sign in which the + sign in FIGS. 1 and 2 is circled is
Represents positively charged ions. Note that the configuration shown in FIG. 2 is the same as that of FIG. 1 described above, and thus the description of the configuration in FIG. 2 will be omitted.

The ion trapping operation is performed as follows. In FIG. 2, ions generated in a sample ionization chamber (not shown) are introduced into the ion trap electrode 10 through a through hole formed in the end cap electrode 3 or an electron beam for ionization is introduced. 10 to generate ions inside. The generated ions are stably trapped in the ion trap electrode 10 under certain conditions regarding the mass / charge, the minimum radius of the ring electrode, the DC voltage U, the amplitude V of the AC voltage, and the frequency ω, and the angular frequency of the AC electric field While oscillating at ω, it oscillates harmonically with a period slower than ω in the radial direction and the major axis direction of the ion trap electrode 10, and slowly vibrates in the vicinity of the center of the cell of the electrode in a 小 -shape with a small period at ω. Vibration of amplitude. Thereby, other ions that selectively confine only predetermined ions in the ion trap electrode 10 can be removed.

At the time of introducing ions into the ion trap electrode 10 or introducing an ionizing electron beam, the second
A positive voltage is applied to the auxiliary electrode 12 with respect to the second end cap electrode 4. As a result, the electric field generated by the second auxiliary electrode 12 penetrates through the through-hole, generates a positive electric field near the second end cap electrode 4, and generates a local asymmetric electric field near the second end cap electrode 4. Form. This asymmetric electric field prevents ions in the ion trap electrode 10 from being emitted toward the detector 9 and assists in trapping ions in the ion trap electrode 10.

Next, the operation of extracting ions is performed as follows. In FIG. 1, the second auxiliary electrode 12
Then, a negative voltage is applied to the second end cap electrode 4. As a result, the electric field generated by the second auxiliary electrode 12 penetrates through the through-hole to generate a negative electric field near the second end cap electrode 4, and a local asymmetric electric field near the second end cap electrode 4. To form The asymmetric electric field has a function of promoting the emission of ions in the ion trap electrode 10 to the detector 9, thereby improving the efficiency of detection of ions by the detector 9. At this time, the second auxiliary electrode 1
The asymmetric electric field detected by the second end cap electrode 4
And does not affect the electric field near the center of the ion trap electrode 10. Also, the second auxiliary electrode 12
Alternatively, a configuration in which a high-frequency voltage synchronized with a high-frequency voltage applied to the end cap electrode 4 may be applied.

Further, a positive voltage is applied to the first auxiliary electrode 11 with respect to the first end cap electrode 3. As a result, the electric field generated by the first auxiliary electrode 11 penetrates through the through-hole, generates a positive electric field near the first end cap electrode 3, and generates a local asymmetric electric field near the first end cap electrode 3. Form. This asymmetric electric field causes the ions in the ion trap electrode 10
Is prevented from being released to the outside through the through hole, and the detection efficiency of ions by the detector 9 is improved.

Next, a configuration example of the ion trap electrode will be described with reference to FIGS.

FIG. 3 is a partially cutaway perspective view for explaining a first configuration example of the ion trap electrode. In FIG. 3, the ion trap electrode 10 includes a ring electrode 2 and first and second end cap electrodes 3 and 4, and has a configuration in which the end cap electrode and the auxiliary electrode are formed concentrically.

A through hole is formed in the center of the first and second end cap electrodes 3 and 4 in the axial direction, and the first and second auxiliary electrodes 11 and 1 are formed through insulators 15 and 16 penetrating in the axial direction.
2 is attached. The first and second auxiliary electrodes 11, 12
Through holes are also formed in the axial direction, and ions or electron beams are introduced or ions are extracted through the through holes. A first auxiliary power supply 13 is connected to the first auxiliary electrode 11, and a first auxiliary power supply 14 is connected to the second auxiliary electrode 12. With the above configuration, the electric field generated by the first and second auxiliary electrodes 11 and 12 penetrates into the inside of the ion trap electrode 10 through the central through-hole to form an asymmetric electric field.

FIG. 4 is a partially cutaway perspective view for explaining a second configuration example of the ion trap electrode. 4, the ion trap electrode 10 includes a ring electrode 2 and first and second end cap electrodes 3 and 4, and has a configuration in which a plurality of through holes are formed in the end cap electrode.

The first and second end cap electrodes 3 and 4 include:
Through holes 18 are formed at a plurality of locations in the central portion and the peripheral portion, and the first and second auxiliary electrodes 11 and 12 are attached with the insulator 17 interposed therebetween. Through holes are formed in the first and second auxiliary electrodes 11 and 12 at central portions thereof. The introduction of ions or electron beams or the extraction of ions is performed through through holes formed in the center portions of the end cap electrode and the auxiliary electrode. A first auxiliary power supply 13 is connected to the first auxiliary electrode 11, and a first auxiliary power supply 14 is connected to the second auxiliary electrode 12.

With the above configuration, the first and second auxiliary electrodes 11,
The electric field generated by the electrode 12 penetrates the inside of the ion trap electrode 10 through a through hole formed in the center portion of the end caps 3 and 4 and a plurality of through holes formed in the peripheral portion, thereby forming an asymmetric electric field.

The sectional view shown in FIG. 5 is a third configuration example.
In the second configuration example shown in FIG.
This is an example in which 1 and 12 are constituted by a plurality of electrodes divided corresponding to a plurality of through holes formed in the first and second end cap electrodes 3 and 4. In FIG. 5, the second auxiliary electrode 12
And only the second end cap electrode 4 is shown. The divided electrodes are arranged at positions corresponding to the through holes formed in the end cap 4 so that an electric field generated by the electrodes penetrates into the ion trap electrode through the through holes.

Each of the divided electrodes is configured to be capable of independently applying a voltage, whereby an electric field pattern can be made arbitrary. In the example shown in FIG.
A divided voltage is applied to each electrode by connecting each divided electrode via a resistor.

According to the above embodiment, by applying a DC voltage to the auxiliary electrode, an asymmetric electric field can be formed near the end cap electrode where the auxiliary electrode is provided. By applying a high-frequency voltage synchronized with the high-frequency voltage to be applied, it is easy to be affected by the asymmetric electric field of ions vibrated by the internal electric field, and the efficiency of extracting ions to the outside can be increased.

According to the embodiment of the present invention, an asymmetric electric field can be formed near the end cap electrode by using the end cap electrode having a plurality of through holes. Further, by forming the auxiliary electrode with a plurality of electrodes corresponding to the through holes and applying a voltage to each electrode independently, an arbitrary asymmetric electric field can be formed near the end cap electrode.

[0036]

As described above, according to the ion trap mass spectrometer of the present invention, the ion detection sensitivity can be improved without imparting asymmetry to the electric field near the center of the ion trap electrode. The sensitivity of the mass spectrometer can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an ion trap mass spectrometer according to the present invention, for explaining ion extraction.

FIG. 2 is a schematic perspective view of the ion trap mass spectrometer of the present invention, which is a view for explaining the ion trap.

FIG. 3 is a partially cutaway perspective view for explaining a first configuration example of the ion trap electrode.

FIG. 4 is a partially cutaway perspective view for explaining a second configuration example of the ion trap electrode.

FIG. 5 is a partially cutaway perspective view for explaining a third configuration example of the ion trap electrode.

FIG. 6 is a schematic view of a conventionally known ion trap electrode.

FIG. 7 is a diagram illustrating a trappable voltage condition.

FIG. 8 is a view for explaining a conventional ion trap mass spectrometer using an ion trap electrode.

[Explanation of symbols]

1 ... Ion trap mass spectrometer, 2 ... Ring electrode,
3, 4 end cap electrode, 5 main RF power supply, 6 auxiliary RF power supply, 7 control circuit, 8 transformer, 9 detector, 10 ion trap electrode, 11, 12 auxiliary electrode, 13, 14 ... Auxiliary power supply, 15, 16, 17 ... Insulator, 18 ... Through hole, 19 ... Measuring device.

Claims (1)

[Claims] A ring electrode; a pair of end cap electrodes having through holes provided at both open ends of the ring electrode;
A main RF power source for applying an AC voltage having an amplitude V at an F frequency ω to the ring electrode, an auxiliary power source for applying a high-frequency voltage to at least one of the end cap electrodes, a control circuit for controlling the power source, and one end cap electrode At least one end cap electrode in an ion trap mass spectrometer comprising a detector for detecting ions emitted from the through-holes of the target and a measuring device for obtaining a mass spectrum based on the number and amplitude V of the detected ions. An ion trap mass spectrometer, wherein an auxiliary electrode to which a voltage is applied between the ring electrode and the end cap electrode is provided.