JP5146411B2 - Ion trap mass spectrometer - Google Patents

Description

  The present invention relates to an ion trap mass spectrometer having an ion trap that traps ions by the action of a high-frequency electric field, and more particularly to an ion trap mass spectrometer that uses a digitally driven ion trap as an ion trap.

  In a mass spectrometer, an ion trap captures and confines ions by the action of a high-frequency electric field, sorts out ions with a specific mass (strictly, mass-to-charge ratio m / z), and so on. It is used to cleave ions. As shown in FIG. 3A, a typical ion trap has one ring electrode 21 whose inner surface is a rotating single-leaf hyperboloid shape, and an inner surface disposed opposite to this ring electrode 21. Although it is a three-dimensional quadrupole ion trap composed of a pair of end cap electrodes 22 and 24 having a rotating two-leaf hyperboloid shape, in addition to this, a linear type composed of four rod electrodes arranged in parallel Ion traps are also known. In this specification, for the sake of convenience, the ion trap will be described by taking “three-dimensional quadrupole type” as an example.

  In a conventional general ion trap, a high frequency electric field for ion trapping is usually formed in a space surrounded by the ring electrode 21 and the end cap electrodes 22, 24 by applying a sinusoidal high frequency voltage to the ring electrode 21. The high-frequency electric field confines ions while vibrating them. On the other hand, in recent years, ion traps that confine ions by applying a rectangular wave voltage to the ring electrode 21 instead of a sinusoidal high-frequency voltage have been developed (Patent Document 1, Patent Document 2, Non-Patent Document). 1 etc.). This type of ion trap is generally called a digital ion trap (DIT = Digital Ion Trap) because a rectangular wave voltage having binary voltage levels of high and low is used.

  In an ion trap mass spectrometer (hereinafter abbreviated as “DIT-MS”) using a digital ion trap, as described in Non-Patent Document 1, a rectangular high voltage having a predetermined frequency corresponding to the mass range of ions to be captured. Is applied to the ring electrode 21 as a high frequency voltage for trapping, thereby confining ions in a target mass range in the ion trap 2. The ions thus confined are sequentially ejected from the ion emission port 25 in accordance with the mass, and the resonance excitation of the ions is used when the ions are detected by the detector provided outside the ions. That is, a rectangular wave high voltage (usually having an amplitude of several hundreds V or more) applied to the ring electrode 21 is divided by a predetermined frequency dividing ratio, and a rectangular wave low voltage (usually having an amplitude of several volts) is applied to the end cap electrode 22; 24, and simultaneously scan the frequency of the rectangular wave high voltage and the rectangular wave low voltage. As a result, the ions trapped in the ion trap 2 are resonantly excited in the order of their mass, discharged to the outside of the ion trap 2 through the ion emission port 25, and sequentially detected by the detector to create a mass spectrum.

FIG. 4 is a diagram illustrating an example of the timing of the capture rectangular wave voltage applied to the ring electrode 21 and the resonance excitation rectangular wave voltage applied to the end cap electrodes 22 and 24. The rectangular wave voltage for capture is usually two voltages (with a duty ratio of 0.5 (= 50%), ± 500 [V], ± 1 [kV] and the same absolute value but different polarities ( (V _H , V _L ) alternately appear in a rectangular wave shape. On the other hand, the resonance excitation rectangular wave voltage has a rectangular wave shape whose frequency is 1 / n (n is an integer of 2 or more) of the capturing high frequency voltage and a DC low voltage of about several volts appears for an arbitrary time. is there.

  In the example shown in FIG. 4, the resonance excitation rectangular wave voltage is obtained by dividing the capturing rectangular wave voltage by a quarter (that is, the frequency is ¼). In this case, the stable solution of the Matthew equation is used. Ion ejection by resonance excitation can be performed at a capture parameter β = 0.5 based on conditions. Further, the polarity of the rectangular wave voltage for resonance excitation applied between the inlet end cap electrode 22 and the outlet end cap electrode 24 is reversed. For example, in the case of resonance excitation discharge of positive ions, A rectangular wave pulse having a voltage of about a positive number V of the same polarity as the ions is applied to the end cap electrode 22 and a voltage of a negative number V of the opposite polarity to the ions is applied to the outlet end cap electrode 24 at the same timing. ing.

Now, the rectangular wave voltage applied to the inlet end cap electrode 22 at the time of ion resonance excitation discharge is a period T seconds (where T is sufficiently smaller than 1 second) as shown in FIG. Suppose that the baseline is 0 [V], the voltage value is + V _E , and the pulse width is d seconds. In this case, the time average potential of this rectangular wave voltage is + (dV _E ) / T. As shown in FIG. 4B-2, a pulse voltage having a reverse polarity is applied to the exit-side end cap electrode 24, so that the time average potential of the rectangular wave voltage is − (dV _E ) / T. . Therefore, as shown in FIG. 3B, in the space inside the ion trap 2, in the axial direction of the central axis C of both end cap electrodes 22, 24, the difference 2 in time-average potential between both end cap electrodes 22, 24 ( Due to dV _E ) / T, a potential gradient is always generated.

  Thereby, the center Q of the trajectory of the ions trapped in the ion trap 2 is shifted to the exit side end cap electrode 24 side from the geometric center P of the ion trap space. When such a shift of the center Q of the ion trajectory occurs, a deviation from the ideal resonance excitation condition occurs, so that the spatial expansion of ions ejected from the ion trap 2 is an ideal resonance excitation condition. Compared to this, it becomes larger and contributes to lowering the mass resolution.

Special Table 2007-527002 JP 2008-282594 A

Furuhashi, Takeshita, Ogawa, Iwamoto, Din, Gills, Smirnov, “Development of Digital Ion Trap Mass Spectrometer”, Shimazu Review, Shimazu Review Editorial Department, March 31, 2006, Vol. 62, No. 3, No. 4, pp.141-151

  The present invention has been made to solve the above-mentioned problems, and its object is to improve the mass resolution by bringing the resonance excitation conditions close to the ideal state when ions are ejected from the ion trap by resonance excitation. An object of the present invention is to provide an ion trap mass spectrometer capable of performing the above.

The present invention made to solve the above problems has an ion trap that traps ions in a space surrounded by three or more electrodes, and applies a rectangular wave voltage for ion trapping to at least one electrode, An ion trap mass spectrometer that selectively discharges ions having a specific mass-to-charge ratio from the ion trap by applying a rectangular wave voltage for resonance excitation to each of a pair of electrodes arranged opposite to each other. In
a) Adjustment amount calculation means for calculating an adjustment amount of at least one of the resonance excitation rectangular wave voltages so that the time average potentials of the resonance excitation rectangular wave voltages applied to the pair of electrodes during ion ejection are the same. When,
b) voltage generating means for receiving the adjustment amount calculated by the adjustment amount calculating means and generating a rectangular wave voltage for resonance excitation in which at least one DC potential is adjusted, which is applied to each of the pair of electrodes;
It is characterized by having.

  In the ion trap mass spectrometer according to the present invention, the ion trap is a three-dimensional quadrupole ion trap or a linear ion trap. In the case of a three-dimensional quadrupole ion trap, the ion trap is usually composed of an annular ring electrode and a pair of end cap electrodes arranged opposite to each other with the ring electrode interposed therebetween. A resonance excitation rectangular wave voltage is applied. On the other hand, in the case of a linear ion trap, the ion trap is usually composed of four rod electrodes arranged in parallel to each other so as to surround the central axis, and the two rod electrodes opposed across the central axis are the ring Instead of the electrodes, the other two rod electrodes replace the pair of end cap electrodes.

  In the ion trap mass spectrometer according to the present invention, the adjustment amount calculation means is based on parameters that determine the pulse waveform of the resonance excitation rectangular wave voltage, that is, the period or frequency, the pulse width, and the pulse height (voltage). The time average potential can be calculated, and the adjustment amount can be obtained so that the time average potential becomes a target value. More specifically, a boundary line is drawn at a certain potential between the low level and the high level of the pulse waveform of the rectangular wave voltage, and the pulse waveform on the positive polarity side of the boundary line in the pulse waveform of one cycle. The potential of the boundary line that makes the area surrounded by the boundary line equal to the pulse waveform on the negative polarity side of the boundary line and the area surrounded by the boundary line may be the time average potential.

  According to the ion trap mass spectrometer of the present invention, for example, ions having a specific mass in ions confined in the space inside the three-dimensional quadrupole ion trap are resonant with both end cap electrodes so as to be resonantly excited and discharged. When the excitation rectangular wave voltage is applied, the time average potentials at the end cap electrodes are equal, so that no gradient of the DC potential occurs in the direction of the axis connecting the centers of the electrodes. For this reason, the center of the orbit of the ions trapped in the vibration state and the geometric center of the ion trap substantially coincide, and the resonance excitation under the resonance excitation condition is performed in a state close to ideal according to the theory. As a result, ions having a mass corresponding to the frequency of the resonant excitation rectangular wave voltage are selected and ejected with high resolution.

  Further, as a preferred aspect of the ion trap mass spectrometer according to the present invention, the adjustment amount calculating means is configured so that the time-average potentials of the resonance excitation rectangular wave voltages applied to the pair of electrodes are each zero. The adjustment amount of each rectangular wave voltage may be calculated, and the voltage generation unit may generate a resonance excitation rectangular wave voltage in which the DC potential is adjusted by the adjustment amount calculated by the adjustment amount calculation unit.

  That is, according to this configuration, for example, in a three-dimensional quadrupole ion trap, a direct current potential gradient does not occur in the direction of an axis connecting the centers of both end cap electrodes, and the direct current potential becomes zero. As a result, regardless of whether the ions are positive or negative, a DC electric field hardly acts on the ions trapped in the vibration state, and the vibration conditions and resonance excitation conditions become even more ideal.

  According to the ion trap mass spectrometer of the present invention, when the ions trapped in the space inside the ion trap are ejected to the outside by resonance excitation, the resonance excitation condition becomes close to the ideal state. Therefore, ions having a target mass-to-charge ratio can be discharged from the ion trap with high resolution and detected by, for example, a detector disposed outside the ion trap. For example, a mass spectrum with high mass resolution and high mass accuracy can be acquired by performing the resonance excitation discharge as described above while performing frequency scanning of a rectangular wave voltage.

The schematic block diagram of the principal part of DIT-MS which is one Example of this invention. Explanatory drawing of characteristic resonance excitation voltage control in DIT-MS of a present Example. The schematic diagram which shows the electric potential state of the space in the ion trap in a present Example and conventional DIT-MS. The timing diagram which shows an example of the rectangular wave voltage waveform at the time of the resonance excitation discharge | emission in DIT-MS.

  A DIT-MS which is an embodiment of an ion trap mass spectrometer according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a main part of the DIT-MS ion trap of this embodiment.

  The DIT-MS according to this embodiment includes an ionization unit 1 that ionizes a target sample, a three-dimensional quadrupole ion trap 2 that separates ions according to mass (strictly, mass to charge ratio m / z), And a detector 3 for detecting ions.

  The ionization unit 1 uses a matrix-assisted laser desorption ionization method (MALDI), a laser irradiation unit 11 that emits pulsed laser light, a sample plate 12 to which a sample S including a target sample component is attached, a laser It includes an aperture 13 for extracting ions emitted from the sample S by light irradiation and limiting the extraction direction, an ion lens 14 for guiding the extracted ions, and the like. Of course, other laser ionization methods other than MALDI and ionization methods that do not use laser light may be used.

  The ion trap 2 includes a ring-shaped ring electrode 21 and an inlet end cap electrode 22 and an outlet end cap electrode 24 which are arranged to face each other so as to sandwich the ring electrode 21. A space surrounded by the electrodes 21, 22, and 24 is an ion trapping region. An ion incident port 23 is bored substantially at the center of the entrance-side end cap electrode 22, and ions emitted from the ionization unit 1 pass through the ion incident port 23 and are introduced into the ion trap 2. On the other hand, an ion emission port 25 is formed substantially at the center of the exit-side end cap electrode 24, and ions discharged from the ion trap 2 through the ion emission port 25 reach the detection unit 3 and are detected.

  The detection unit 3 includes a conversion dynode 31 that converts ions into electrons and a secondary electron multiplier 32 that multiplies and detects electrons arriving from the conversion dynode 31, and detects according to the amount of incident ions. The signal is sent to the data processing unit 8. The data processing unit 8 has a function of creating a mass spectrum based on detection signals obtained by the detection unit 3 for ions that are sequentially ejected while being mass-separated in the ion trap 2.

The main power supply unit 4 applies a rectangular high voltage to the ring electrode 21 of the ion trap 2, and includes a first voltage source 41 that generates a first voltage V _H , and a second voltage V _L (V _L <V _H ), A first switching element 43 and a second switching element 44 connected in series between the output terminal of the first voltage source 41 and the output terminal of the second voltage source 42; including. The auxiliary power supply unit 5 corresponding to the voltage generation means in the present invention applies different rectangular wave low voltages to the end cap electrodes 22 and 24 of the ion trap 2, and includes a pulse voltage generation unit 51, variable DC voltage generation, and the like. Part 52 and voltage superposition parts 53 and 54.

The timing signal generation unit 6 is a hardware logic circuit, and the first switching element 43 and the second switching element 44 are alternately turned on under the control of the control unit 7 (however, at least at the same time may be turned on). Drive pulses having a predetermined frequency are generated and supplied to the switching elements 43 and 44. Since the first voltage V _H is output when the first switching element 43 is turned on and the second voltage V _L is output when the second switching element 44 is turned on, the output voltage V _OUT is ideally high. A rectangular wave voltage having a predetermined frequency f (period t) having a level of V _H and a low level of V _L is obtained (see FIG. 4A). In general, V _H and V _L are high voltages having the same absolute value and opposite polarities. For example, the absolute value is about several hundred V to 1 kV. The frequency f is usually in the range of several tens of kHz to several MHz.

The timing signal generator 6 gives a pulse signal obtained by dividing the drive pulse supplied to the main power supply 4 by an appropriate ratio (1/4 in this example) to the pulse voltage generator 51 of the auxiliary power supply 5. Based on the signal obtained from the timing signal generator 6, the pulse voltage generator 51 is a rectangular wave low having a frequency of f / 4, a low level of 0 [V], a high level of + V _E , and a pulse width of d. A voltage and a rectangular wave low voltage having a polarity opposite to that of the voltage are generated. Conventionally, these rectangular wave low voltages are applied to the end cap electrodes 22 and 24 as they are. However, in the DIT-MS of this embodiment, the DC voltage generated by the variable DC voltage generator 52 is converted to the voltage superimposing unit 53. , 54 are superimposed on the respective rectangular wave low voltages (that is, the DC level is shifted or offset) and applied to the end cap electrodes 22, 24. Normally, the voltage value V _E of the rectangular wave low voltage is much lower than the voltage values V _H and V _L of the rectangular wave high voltage, and is about several volts, for example.

  The control unit 7 is mainly composed of a personal computer, and its function is achieved by executing a control / processing program preinstalled in the personal computer. The control unit 7 includes an excitation resonance voltage DC potential calculation unit 71 corresponding to the adjustment amount calculation means in the present invention as a characteristic functional block.

The mass spectrometry operation in the DIT-MS of the present embodiment will be described.
In the ionization unit 1, a laser beam is emitted from the laser irradiation unit 11 for a short time and applied to the sample S under the control of the control unit 7. The matrix in the sample S is rapidly heated by laser light irradiation, and vaporizes with the target component. At this time, the target component is ionized. The generated ions are converged by an electrostatic field formed by the ion lens 14, introduced into the ion trap 2 through the ion incident port 23, and captured. Then, cooling is performed by bringing ions into contact with the cooling gas introduced into the ion trap 2 prior to ion introduction.

  The mass range of ions stably trapped in the ion trap 2 depends on the frequency of the rectangular wave high voltage applied to the ring electrode 21. Therefore, when the ions are confined in the ion trap 2 as described above, the timing signal generator 6 supplies a drive pulse of a predetermined frequency to the switching elements 43 and 44 in accordance with an instruction from the controller 7, and according to this. A rectangular high voltage having a frequency is generated by the main power supply unit 4 and applied to the ring electrode 21. At this time, the voltage applied to the end cap electrodes 22 and 24 is maintained at the ground potential.

  After cooling for a predetermined time, ions having a specific mass are selectively vibrated by resonance excitation, discharged from the ion trap 2 through the ion emission port 25, and detected by the detection unit 3. At this time, a rectangular wave high voltage for ion trapping is applied from the main power supply unit 4 to the ring electrode 21, while a rectangular wave low voltage for resonance excitation is applied from the auxiliary power supply unit 5 to the end cap electrodes 22 and 24, respectively. Specifically, the voltage is applied by executing the following control.

  That is, the excitation resonance voltage DC potential calculation unit 71 in the control unit 7 calculates the time average potential of the rectangular wave low voltage waveform generated by the pulse voltage generation unit 51 prior to the execution of resonance excitation discharge, and the time average The DC potential shift amount is calculated so that the potential becomes zero.

Specifically, when positive ions are to be analyzed, a rectangular wave low voltage having a waveform as shown in FIG. 2A is applied to the inlet end cap electrode 22. At this time, the period T is determined by the frequency of the rectangular high voltage applied to the ring electrode 21, which is known because it is instructed by the control unit 7 itself. Further, the pulse width d and the voltage value V _E are also known because they are instructed by the control unit 7 itself or predetermined in circuit. The time average potential V _{av at} this time is V _av = + (dV _E ) / T as described above. As shown in FIG. 2B, the time average potential V _av at the time when the number of periods is sufficiently large is a boundary where the area of the area A and the area of the area B are equal within one period of the rectangular wave voltage. Is a line. When the time average potential V _{av is set} to zero, the DC potential shift amount x becomes equal to the time average potential V _av, and the DC potential shift amount is obtained by x = dV _E / T. Further, the rectangular wave low voltage applied to the outlet side end cap electrode 24 is obtained by inverting the polarity of the rectangular wave low voltage applied to the inlet side end cap electrode 22 as shown in FIG. Therefore, the DC potential shift amount for making the time average potential zero is also x (however, the shift direction is negative).

The excitation resonance voltage DC potential calculation unit 71 sends the DC potential shift amount obtained as described above to the variable DC voltage generation unit 52, and at the time of resonance excitation discharge, the variable DC voltage generation unit 52 generates a DC voltage corresponding to this. Occur. On the other hand, at the time of resonance excitation discharge, the pulse voltage generator 51 has a frequency of f / 4, a low level of 0 [V], a high level of + V _E , and a pulse width based on the signal obtained from the timing signal generator 6. A rectangular wave low voltage having a value of d and a rectangular wave low voltage having a polarity opposite to that of the rectangular wave low voltage is generated. The two rectangular wave low voltages having different polarities are shifted by a voltage corresponding to the DC potential shift amount in the voltage superimposing units 53 and 54, respectively, and applied to the end cap electrodes 22 and 24.

  Accordingly, since the time average potential of the rectangular wave low voltage applied to the end cap electrodes 22 and 24 at the time of resonance excitation discharge is substantially zero, as shown in FIG. There is no DC potential gradient in the opposite direction. Accordingly, the center of the trajectory of ions trapped in the space inside the ion trap 2 coincides with the geometric center of the ion trap 2.

  When scanning the mass of ions ejected from the ion trap 2, the frequency of the rectangular high voltage applied to the ring electrode 21 is scanned under the control of the control unit 7, and accordingly, the end cap electrodes 22, 24 are scanned. The frequency of the applied square wave low voltage is also scanned. That is, the period T of the rectangular wave low voltage is changed and the pulse width d is also changed at the same time. However, prior to the change, the excitation resonance voltage DC potential calculation unit 71 calculates the DC potential shift amount associated with the change. I can keep it. Therefore, the variable DC voltage generator 52 changes the DC voltage as the frequency and pulse width of the rectangular wave low voltage are sequentially changed, and the time average potential of the rectangular wave low voltage applied to the end cap electrodes 22 and 24 is changed. It can be maintained at almost zero.

  In the DIT-MS of the present embodiment, the resonance excitation condition is almost ideal because the center of the orbit of ions trapped in the ion trap 2 substantially coincides with the geometric center of the ion trap 2 at the time of resonance excitation discharge. Thus, ions having a mass corresponding to the frequency of the rectangular wave high voltage are discharged with high selectivity. The ions discharged from the ion trap 2 are sequentially detected by the detection unit 3, and the data processing unit 8 creates a mass spectrum corresponding to the mass scan. As described above, since the mass accuracy of ions ejected from the ion trap 2 is high and the resolution thereof is also high, a mass spectrum with high mass accuracy and mass resolution can be obtained.

  In the above embodiment, control is performed such that the time average potential of the rectangular wave low voltage applied to each of the end cap electrodes 22 and 24 is zero, but at the time of resonance excitation discharge, in the space inside the ion trap 2 In order to eliminate the DC potential gradient in the direction along the central axis C, it is sufficient if the time average potentials of the rectangular wave low voltages applied to both the end cap electrodes 22 and 24 are equal. For this purpose, the excitation resonance voltage DC potential calculation unit 71 may calculate the DC potential shift amount so that the time average potential obtained as described above is not zero but an arbitrary target potential.

  Next, a method and result of a computer simulation performed to verify the effect of the ion trap mass spectrometer according to the present invention will be described.

The basic configuration of the apparatus assumed in the simulation is almost the same as that shown in FIG. The rectangular wave high voltage applied to the ring electrode 21 at the time of resonance excitation discharge is V _H = 500 [V], V _L = −500 [V], and discharge start frequency f = 700 [kHz] (period t = 1.4286 [ μsec]). Further, as shown in FIG. 4B, the rectangular wave low voltage applied to the end cap electrode 22 is 3/4 period (3π / 2) from the rising edge of the voltage every 4 periods of the capturing rectangular wave high voltage. It has a pulse width corresponding to one period of rising with a delay, and a voltage value V _E = 2 [V]. The frequency scanning for mass separation and discharge of ions was set to the condition that the rectangular wave high voltage of the same cycle (t) was repeated 40 cycles while the cycle was increased by 2 [n seconds] from t. Under the above conditions, the DC potential shift amount for making the time average potential of the rectangular wave low voltage for resonance excitation zero is 0.5 [V].

  As a simulation method, 1000 positive ions each having 6 types of m / z in increments of 1 [Da] in the range of m / z = 1000 [Da] to 1005 [Da] are placed in the internal space of the ion trap 2. After being introduced and trapped and cooling the ions, resonance excitation was discharged from the ion trap 2 under the above conditions, and the number of detected ions with the passage of time from the start of discharge was counted every arbitrary sample time. As a result, a time distribution waveform of the number of detected ions was obtained, and the resolution was obtained therefrom. According to such a simulation calculation, the average resolution when the DC potential shift amount is not corrected is 1600 [FWHM] as in the conventional case, whereas the average resolution when the DC potential shift amount is corrected as described above. Was 2000 [FWHM]. Thus, by simulation, the improvement of mass resolution was confirmed as an effect of the present invention.

  It should be noted that the above embodiment is merely an example of the present invention, and it should be understood that modifications, additions, and modifications as appropriate within the spirit of the present invention are included in the scope of the claims of the present application.

DESCRIPTION OF SYMBOLS 1 ... Ionization part 11 ... Laser irradiation part 12 ... Sample plate 13 ... Aperture 14 ... Ion lens 2 ... Ion trap 21 ... Ring electrode 22 ... Inlet side end cap electrode 23 ... Ion entrance 24 ... Outlet side end cap electrode 25 ... Ion Outlet 3 ... Detection section 31 ... Conversion dynode 32 ... Secondary electron multiplier 4 ... Main power supply section 41 ... First voltage source 42 ... Second voltage sources 43 and 44 ... Switching element 5 ... Auxiliary power supply section 51 ... Pulse voltage Generating unit 52 ... variable DC voltage generating unit 53, 54 ... voltage superimposing unit 6 ... timing signal generating unit 7 ... control unit 71 ... excitation resonance voltage DC potential calculating unit 8 ... data processing unit

Claims (4)

Each of the pair of electrodes arranged opposite to each other has an ion trap that traps ions in a space surrounded by three or more electrodes, and applies a rectangular wave voltage for ion trapping to at least one electrode. In an ion trap mass spectrometer that selectively ejects ions having a specific m / z from the ion trap by applying a rectangular wave voltage for resonance excitation,
a) Adjustment amount calculation means for calculating an adjustment amount of at least one of the resonance excitation rectangular wave voltages so that the time average potentials of the resonance excitation rectangular wave voltages applied to the pair of electrodes during ion ejection are the same. When,
b) voltage generating means for receiving the adjustment amount calculated by the adjustment amount calculating means and generating a rectangular wave voltage for resonance excitation in which at least one DC potential is adjusted, which is applied to each of the pair of electrodes;
An ion trap mass spectrometer comprising: The ion trap mass spectrometer according to claim 1,
The adjustment amount calculation means calculates the adjustment amount of each rectangular wave voltage so that the time average potential of the resonance excitation rectangular wave voltage applied to each of the pair of electrodes becomes zero, and the voltage generation means An ion trap mass spectrometer for generating a resonance excitation rectangular wave voltage in which a direct current potential is adjusted by each adjustment amount calculated by the adjustment amount calculation means. The ion trap mass spectrometer according to claim 1 or 2,
The adjustment amount calculation means calculates a time average potential based on the period or frequency, pulse width, and pulse height of the resonance excitation rectangular wave voltage, and adjusts the adjustment amount so that the time average potential becomes a target value. An ion trap mass spectrometer characterized by: The ion trap mass spectrometer according to any one of claims 1 to 3,
The ion trap includes a ring electrode and a pair of end cap electrodes arranged to face each other across the ring electrode, and applies the resonance excitation rectangular wave voltage to the pair of end cap electrodes. Ion trap mass spectrometer.

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