JP2005078810A - Ion trap tof mass spectroscope and ion trap method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion trap device in which a sufficient cooling effect is secured while ion cleavage can be suppressed to the minimum in acceleration for a next-stage TOF (Time Of Flight) mass analysis. <P>SOLUTION: In the ion trap 12 provided with a ring electrode 23 and an opposing pair of end cap electrodes 21, 22 pinching it, and retaining ions inside an ion trap space 24 surrounded by those electrodes by applying an appropriate voltage to those electrodes 21, 22, 23, inert gas (Ne, Ar, Kr, Xe, N<SB>2</SB>) with a molecular weight of not less than 10 is used as gas to be introduced into the ion trap space 24, instead of conventional helium gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion trap TOF mass spectrometer having an ion trap used for mass spectrometry and ion selection and an operation method thereof.
[0002]
[Prior art]
An ion trap TOF mass spectrometer will be described with reference to FIG. As shown in FIG. 1, in the ion trap TOF mass spectrometer 10, an ion trap 12 is provided at an ion inlet of a TOF (Time Of Flight) type mass spectrometer 11, where ion isolation (selection) is performed. ) And cleavage. Although the ion trap 12 itself has a function of mass separation, in the ion trap TOF mass spectrometer 10, the ion trap 12 is used only for isolating and cleaving ions, and mass analysis of ions is performed by the TOF 11 in the next stage. Is called. As a result, as compared with the case where the ion trap 12 is not provided, the TOF 11 can perform mass analysis with higher mass resolution, and more information can be obtained about ions having a large molecular weight.
[0003]
In the ion trap 12, as shown in FIG. 2, 1 × 10 ⁻³ Torr (about 0) in an ion trap space 24 surrounded by both the end cap electrodes 21 and 22 at the inlet and the outlet and the ring electrode 23 positioned therebetween. . Helium (He) gas of about 1 Pa) is constantly introduced. For one thing, the ion and helium gas collide to collect ions in the vicinity of the center of the ion trap space 24, thereby improving the sensitivity and mass resolution. This is called a cooling action. Further, when a waveform including the same frequency as the ion resonance frequency is applied to both end cap electrodes 21 and 22 of the ion trap 12, this increases the kinetic energy of the ions, and the ions collide with helium molecules in this state. By doing so, it also has the effect that ion cleavage is performed. This is called a CID (Collision Induced Dissociation) action.
[0004]
[Patent Document 1]
JP 2002-184349 A [Patent Document 2]
Japanese translation of PCT publication No. 2002-518810
[Problems to be solved by the invention]
The ions need to be accelerated to the potential of TOF 11 (for example, -10 kV for positive ions) when fed into TOF 11. This is performed by momentarily applying a high voltage between the end cap electrodes 21 and 22 of the ion trap 12, but when ions accelerated in this way collide with helium gas existing in the ion trap space. The phenomenon of ion cleavage is observed. According to the experiment, when a sufficient amount of helium gas was introduced to cool the ions, a phenomenon was observed in which the base portion of the peak was lifted by ion cleavage. Although this is caused by cleavage, it also leads to a decrease in the signal intensity of ions that should be originally obtained. Such a phenomenon is particularly remarkable in cluster ions and multicharge ions.
[0006]
For example, FIG. 3A is an insulin mass spectrum when helium is introduced in an amount such that the degree of vacuum in the ion trap is 1 × 10 ⁻³ Torr, and the base is lifted by cleaved ions. This shows that the resolution of mass spectrometry is deteriorated, and hexavalent ions are not sufficiently separated.
[0007]
When the amount of cooling gas introduced is reduced, such cleavage is reduced and separation is improved, but cooling is not sufficiently performed, and sensitivity and mass resolution are lowered.
[0008]
The present invention has been made in order to solve such problems, and the object of the present invention is to perform ion cleavage during acceleration for the next TOF mass analysis while ensuring a sufficient cooling effect. An object of the present invention is to provide an ion trap apparatus that can be minimized.
[0009]
[Means for Solving the Problems]
The present invention, which has been made to solve the above problems, comprises a ring electrode and a pair of end cap electrodes facing each other across the ring electrode, and is surrounded by these electrodes by applying an appropriate voltage to the electrodes. In an ion trap TOF mass spectrometer having an ion trap that holds ions in the ion trap space, the gas introduced into the ion trap space has an inert gas having a molecular weight of 10 or more (here, it has poor reactivity including N ₂ or the like). It is characterized by using gas).
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Conventionally, helium gas has been used as a gas to be introduced into the ion trap space. However, by replacing it with a heavy inert gas having a molecular weight of 10 or more, ions when ions collide with molecules of these gases are used. The change in the momentum on the side increases, and the cooling effect is further enhanced. Also, when ions are cleaved by applying a voltage at a resonance frequency to the end cap electrode (CID), the ion cleaving effect is enhanced.
[0011]
According to the experiment by the present inventor, it has been found that when the cooling gas is replaced with argon gas, an equivalent cooling effect can be obtained with 1/5 the amount of helium gas. The “cooling effect” here is evaluated based on the sensitivity of the ion trap apparatus. That is, when argon gas is used, it has been found that equivalent mass separation resolution and sensitivity can be obtained with 1/5 the amount of helium gas. Thereby, the cleavage of ions is greatly reduced, the lifting of the base and the reduction of the peak are prevented, and the resolution of mass spectrometry is improved.
[0012]
【Example】
In FIG. 3B, in the ion trap TOF mass spectrometer (FIGS. 1 and 2), an argon gas having an amount of vacuum of 1.8 × 10 ⁻⁴ Torr (0.023 Pa) is introduced into the ion trap space. The mass spectrum of the hexavalent ion of insulin when introduced is shown. Compared with the spectrum (a) in the case of introducing the helium gas described above, it can be seen that there is no lifting of the base and each peak is well separated.
[0013]
FIG. 4 is a comparative example of the mass spectrum of sodium trifluoroacetate (Trifluoroacetic acid = TFA). FIG. 4A shows the degree of vacuum in the ion trap of 1.8 × 10 ⁻⁴ Torr (0.023 Pa). When an amount of argon gas is introduced, (b) is a case where helium is introduced in an amount such that the degree of vacuum is 1 × 10 ⁻³ Torr (about 0.1 Pa). In this spectrum, the mass spectrum of the cluster ion of the sample is detected. As in the case of FIG. 3, the helium gas shows a lift of the base due to the cleavage, but the peak is clearly separated by using argon gas. ing.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an ion trap TOF mass spectrometer.
FIG. 2 is a schematic configuration diagram of an ion trap.
FIG. 3 shows insulin mass spectra when helium is used as the introduced gas (a) and when argon is used (b).
FIG. 4 is a mass spectrum of TFA when argon is used as the introduced gas (a) and when helium is used (b).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Ion trap TOF mass spectrometer 11 ... TOF type | mold mass spectrometer 12 ... Ion trap 21, 22 ... End cap electrode 23 ... Ring electrode 24 ... Ion trap space

Claims (4)

It has a ring electrode and a pair of end cap electrodes facing each other, and has an ion trap that holds ions in an ion trap space surrounded by these electrodes by applying an appropriate voltage to these electrodes. In the ion trap TOF mass spectrometer, an inert gas having a molecular weight of 10 or more is used as a gas introduced into the ion trap space. 2. The ion trap TOF mass spectrometer according to claim 1, wherein any one of Ne, Ar, Kr, Xe, and N ₂ or a mixed gas of two or more thereof is used as the gas. It has a ring electrode and a pair of end cap electrodes facing each other, and has an ion trap that holds ions in an ion trap space surrounded by these electrodes by applying an appropriate voltage to these electrodes. In the ion trap TOF mass spectrometer, an inert gas having a molecular weight of 10 or more is used as a gas introduced into the ion trap space. Ne to the gas, Ar, Kr, Xe, ion trap method according to claim 3, characterized in that use _either or their two or more mixture gas of N 2.

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