JP2001210269A - Ion trap type mass spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ion introduction efficiently for introducing ions from the outside to the ion trap. SOLUTION: Voltages having the prescribed phase contrasts and the same frequency as the RF voltage applied by the ring electrode 2 at the time of ion introduction, are to be applied to the first and second end-cap electrodes 3 and 4. This enables not only the introduction of the ion reflected duet to the quadrupole field caused by the ring electrode 2 but retaining of the ion inside the internal space 1a by decelerating the ion which is suddenly accelerated and emitted from the opening 6 after it is incident to the internal space 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion trap mass spectrometer, and more particularly, to an ion trap mass spectrometer which introduces ions generated outside an ion trap into the ion trap and captures the ions.

[0002]

2. Description of the Related Art FIG. 4 is a structural view of a main part of a general ion trap type mass spectrometer. The ion trap 1 has a single annular ring electrode 2 having an inner surface having a rotating one-leaf hyperboloidal shape, and a pair of second ring electrodes having an inner surface having a rotating two-leafed hyperboloidal shape provided to face each other. An RF main voltage generator 11 is connected to the ring electrode 2, and an auxiliary voltage generator 12 is connected to the end cap electrodes 3, 4. You.
A thermoelectron generator 7 is provided outside the opening 5 formed in the center of the first end cap electrode 3, and electrons emitted from the thermoelectron generator 7 pass through the opening 5 to form ions. The sample molecules are introduced into the internal space 1a of the trap 1 and come into contact with the sample molecules introduced from the sample introduction section 8 to be ionized. On the other hand, a detector 9 is provided outside the opening 6 provided substantially in line with the opening 5 in the second end cap electrode 4, and emitted from the internal space 1 a of the ion trap 1 through the opening 6. The detected ions are detected and a detection signal is sent to the data processing unit 10.

A ring electrode 2 and end cap electrodes 3 and 4 are generated by an RF main voltage generator 11 and an auxiliary voltage generator 12.
When an appropriate voltage is applied to the internal space 1a, a quadrupole electric field is formed in the internal space 1a surrounded by these electrodes.
The ions generated in a can be confined. At the time of such ion trapping, the ring electrode 2 usually has 1 M
A high-frequency AC voltage having a frequency of about Hz (an applied voltage to the ring electrode 2 is hereinafter referred to as an “RF main voltage”) is applied,
The end cap electrodes 3, 4 are kept at almost zero potential.
If the RF main voltage is appropriately scanned after the ions are captured in the internal space 1a of the ion trap 1 in this manner, ions having different mass numbers are sequentially emitted from the opening 6, so that
These ions are detected by the detector 9 and the detection signal is subjected to arithmetic processing in the data processing unit 10, whereby a mass spectrum can be created.

After capturing ions in the internal space 1a of the ion trap 1, two end cap electrodes 3,
4 when an auxiliary AC voltage having an opposite phase is applied to the internal space 1a.
Produces a dipole electric field. Then, ions having an oscillation frequency corresponding to the frequency of the applied voltage resonate and are discharged from the internal space 1 a through the opening 6. This allows
Unwanted ions can be eliminated from the internal space 1a of the ion trap 1, or only ions having a specific mass number can be extracted.

When this mass spectrometer is used as a detector for a liquid chromatograph, for example, a special interface is required for ionization, so that ionization is not performed inside the ion trap 1 as described above. Then, ions generated by an external ion source are introduced into the internal space 1 a of the ion trap 1 through the opening 5 provided in the first end cap electrode 3. In a conventional general ion trap type mass spectrometer, a predetermined RF main voltage is applied to the ring electrode 2 even when such external ions are introduced, so that the end cap electrodes 3 and 4 are maintained at, for example, zero potential. Controlling.

[0006]

However, unlike the case where the sample molecules are introduced, the ions have electric charges. Therefore, when the ions are introduced into the ion trap 1, the ions are affected by the electric field formed by the RF main voltage. Receive. FIG. 6 is a schematic diagram showing the behavior of ions transported through the ion guide 22 provided outside the opening 5.

FIG. 6A shows a case where an electric field is formed near the entrance of the opening 5 such that a force (arrow A) acts in a direction to push ions that pass through the opening 5 back. Therefore, as shown in the drawing, most of the ions take a reflected trajectory without entering the internal space 1a of the ion trap 1. On the other hand, in FIG. 6B, an electric field is formed such that a force (arrow B) acts on the ions passing through the opening 5 and entering the internal space 1a of the ion trap 1 in the direction of accelerating the ions. At this time, the ions are rapidly accelerated and proceed straight as they are, and are ejected to the outside through the opening 6, or they collide with the second end cap electrode 4 at high speed and disappear. In any of the above cases, ions are not captured in the internal space 1a of the ion trap 1. That is, FIG.
As shown in (c), ions are introduced from the opening 5 into the internal space 1a of the ion trap 1, and do not collide with the second end cap electrode 4 on the outlet side but again in the direction of the first end cap electrode 3 on the inlet side. Only a small portion of the ions with a circular orbit that is pulled back to can be captured.

FIG. 5 is a timing chart showing the relationship between the RF main voltage and the amount of trapped ions in the ion trap 1 in a conventional ion trap mass spectrometer. Even when a substantially constant amount of ions are transmitted through the ion guide 22 in the time direction, only the ions that have entered the predetermined phase range during one cycle of the RF main voltage are appropriately captured by the above-described phenomenon. Ions incident outside the phase range are not captured. According to our calculations, the optimal incident phase range to be captured is about 10% of one period
It turned out that the ion introduction efficiency was rather low on average.

In order to improve the sensitivity of the analysis, it is important to improve the efficiency of ion introduction into the ion trap. To this end, the optimum period (ie, the above-mentioned phase range) for incidence on the ion trap is extended. Is the challenge. The present invention has been made to solve such a problem, and an object of the present invention is to efficiently introduce ions into an ion trap by expanding an optimal phase range for ion incidence. It is an object of the present invention to provide an ion trap type mass spectrometer capable of performing the above.

[0010]

According to the present invention, there is provided an ion trap mass spectrometer comprising an ion trap formed by an annular ring electrode and a pair of end cap electrodes disposed so as to sandwich the ring electrode. In an ion trap mass spectrometer that introduces ions generated outside into the ion trap through an entrance opening provided in the end cap electrode, a high frequency AC voltage is applied to the ring electrode when the ions are incident on the ion trap. While applying a voltage having a period synchronized with the period of the high-frequency AC voltage and having a predetermined phase difference to at least one of the pair of end cap electrodes, It is characterized by increasing the introduction efficiency.

Here, the fact that the cycle of the high-frequency voltage applied to the end cap electrode is synchronized with the cycle of the voltage applied to the ring electrode means that the cycle has the same, that is, the same frequency, This means that the frequency of the former voltage is an integral multiple of the frequency of the latter voltage.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, for example, the frequency of an applied voltage to a ring electrode and the frequency of an applied voltage to an end cap voltage can be made the same to have a predetermined phase difference. . When an AC voltage having an appropriate phase difference with respect to the phase of the high-frequency AC voltage applied to the ring electrode is applied to the inlet end cap electrode, ions that enter the ion trap are reflected by the quadrupole electric field of the ring electrode. Timing (phase)
An electric field that attracts ions can be generated near the entrance aperture. Also, even if the timing (phase) is such that the ions entering the ion trap from the entrance aperture are rapidly accelerated by the quadrupole electric field, the ions once drawn are prevented from being excessively accelerated. Electric field can be generated. On the other hand, if a voltage having an appropriate phase difference is also applied to the exit side end cap electrode, the ions are decelerated and the entrance side is decelerated even at the timing (phase) at which the ions are excessively accelerated by the quadrupole electric field. An electric field can be generated that pushes the electric field back. Therefore,
Conventionally, ions that have not been captured due to reflection or ejection when a zero potential or a DC voltage is applied to the end cap electrode can also be captured.

[0013]

According to the ion trap mass spectrometer of the present invention, the efficiency of introduction of externally generated ions into the ion trap is greatly improved.
Therefore, the amount of ions when the once trapped ions are discharged from the ion trap and detected is increased, so that the detection sensitivity and the detection accuracy can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ion trap type mass spectrometer according to one embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a configuration diagram of a main part of the ion trap type mass spectrometer according to the present embodiment. Since the configuration around the ion trap 1 is the same as that of FIG. 4 already described, the same reference numerals are given and the description is omitted.

The ion source 21 ionizes sample molecules outside the ion trap 1, and is, for example, an ion source based on an atmospheric pressure chemical ionization method in which a liquid sample is sprayed into an atmospheric pressure atmosphere and ionized. The ions generated by the ion source 21 are transported through an ion guide (ion lens) 22 and are transported to the first end cap electrode 3.
To the opening 5. In addition, ion guide 2
The shape of 2 can be various configurations such as a configuration in which a plurality of annular bodies are juxtaposed. Independent first and second auxiliary voltage generators 121 and 122 are respectively connected to the first and second end cap electrodes 3 and 4 to apply AC voltages having different amplitudes and phases. The auxiliary voltage generators 121 and 122 and the RF main voltage generator 11 are controlled by the voltage controller 13.

In this mass spectrometer, the ions generated by the ion source 21 are incident (introduced) into the internal space 1a of the ion trap 1 within a predetermined period, are captured in the internal space 1a, and are captured in the subsequent period. Discharge after mass separation. The voltage control at the time of ion incidence will be described below.

At the time of ion incidence, the voltage control unit 13 generates a high-frequency AC voltage having a predetermined frequency and a predetermined amplitude.
The F main voltage generator 11 is controlled. For example, if the voltage is a sine wave signal, an RF main voltage of V0 · cosωt is applied to the ring electrode 2 (see FIG. 2A). Due to this voltage, a quadrupole electric field is generated in the internal space 1a of the ion trap 1 for trapping ions incident through the opening 5. On the other hand, the voltage control unit 13 outputs the first auxiliary voltage V1 · cos (ωt + θ) having the same frequency as the RF main voltage, the phase advanced by θ1, and the predetermined amplitude V1.
In addition to controlling the first auxiliary voltage generation unit 121 to generate 1) (see FIG. 2B), the first auxiliary voltage generation unit 121 has the same frequency as the main RF voltage, a phase delayed by θ2, and a predetermined amplitude V2. The second auxiliary voltage generator 122 is controlled to generate the second auxiliary voltage V2 · cos (ωt−θ2) (FIG. 2)
(C)).

The amplitudes V1, V of the first and second auxiliary voltages
2. The phase lead θ1 and the phase delay θ2 are set as follows. That is, as shown in FIG.
At the time when a quadrupole electric field is generated that reflects ions that are emitted from the electrode and pass through the opening 5 of the first end cap electrode 3 (that is, the phase of the RF main voltage), A voltage is applied to 3 to generate an electric field that draws ions outside the opening 5 into the inside. Further, as shown in FIG. 6B, the timing when the quadrupole electric field is generated such that the ions introduced through the opening 5 and introduced into the inside 1a of the ion trap 1 are rapidly accelerated (RF main voltage Phase)
A voltage is applied to each of the first end cap electrode 3 and the second end cap electrodes 3, 4 so as to generate an electric field that hinders this acceleration.

As a result, as shown in FIG.
In one cycle of the F main voltage, the phase range in which ions can be trapped in the internal space 1a of the ion trap 1 is wider than in the past, and the ion introduction efficiency is significantly improved even when averaged. According to the result of the computer simulation by the inventor of the present application, it was confirmed that a sufficient pull-in effect was obtained when θ1 was around 60 °. Further, the effect can be obtained when θ2 is in the vicinity of 120 ° which is the opposite phase to θ1.

In the above embodiment, the first and second auxiliary voltages are R
Although the sine wave has the same frequency as the F main voltage, the sine wave does not need to have a sine wave shape as long as an electric field that satisfies the above conditions can be formed. Also, the frequencies need not be the same, and at least the first,
If the frequency of the second auxiliary voltage is set to be an integral multiple of the RF main voltage, the ion incident phase range can be expanded in each cycle of the RF main voltage.

When the gap between the exit side end of the ion guide 22 and the first end cap electrode 3 is large, a sufficient ion attraction effect can be obtained unless a large amplitude voltage is applied to the first end cap electrode 3. However, doing so may adversely affect the quadrupole electric field produced by the ring electrode 2 and impair the trapping action. Therefore, as shown in FIG. 3, a control electrode 24 is provided between the outlet end of the ion guide 22 and the first end cap electrode 3, and an appropriate DC voltage is applied to the control electrode 24. For example, the ions emitted from the ion guide 22 can be converged and guided to the opening 5 more efficiently.

The above embodiment is merely an example, and it is apparent that changes and modifications can be made as appropriate within the scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of an ion trap mass spectrometer according to one embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a temporal relationship between an RF main voltage, an auxiliary voltage, and an ion trapping amount in the ion trap mass spectrometer of the present embodiment.

FIG. 3 is a configuration diagram of a main part of an ion trap mass spectrometer according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a main part of a general ion trap type mass spectrometer.

FIG. 5 is a schematic diagram showing a temporal relationship between an RF main voltage, an auxiliary voltage, and an ion trap amount in a conventional ion trap mass spectrometer.

FIG. 6 is an explanatory diagram of the behavior of ions at the time of ion introduction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ion trap 2 ... Ring electrode 3, 4 ... End cap electrode 5, 6 ... Opening 7 ... Thermoelectron generation part 8 ... Detector 9 ... Sample introduction part 11 ... RF voltage generation part 121, 122 ... Auxiliary AC voltage generation part 13: Voltage control unit 21: Ion source 22: Ion guide

Claims (1)

[Claims] 1. An ion trap formed by an annular ring electrode and a pair of end cap electrodes disposed so as to sandwich the ring electrode, and an ion generated outside is provided on the end cap electrode. In an ion trap type mass spectrometer to be introduced into the ion trap through an opening, when applying ions to the ion trap, while applying a high-frequency AC voltage to the ring electrode, at least one of the pair of end cap electrodes, An ion trap mass spectrometer characterized by increasing the efficiency of introducing ions into the ion trap by applying a voltage having a period synchronized with the period of the high-frequency AC voltage and having a predetermined phase difference.