JP5293562B2 - Ion trap mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high mass accuracy, in a structure for performing capture of ion or ion discharge by resonance excitation by applying a rectangular wave voltage to a ring electrode and an end cap electrode, by removing the effect of ripple derived from a commercial AC voltage which is superimposed on DC voltage for forming the rectangular wave voltage. <P>SOLUTION: In this device, the start time of mass scanning can be synchronized with a specific phase of commercial AC voltage, and measurement for the same calibration sample is performed with this phase being set to 0, (2/3)&pi;, and -(2/3)&pi; (S1-S9). A function for correcting an error derived from mechanical error or the like of ion trap and a function for correcting an error of AC component are determined from the measurement values and true values of m/z for a plurality of calibration samples, and stored as correction information (S10-S12). In measurement of a target sample, the start time of mass scanning is fixed to 0, and error correction processing is performed to mass data obtained in this state by use of the correction information. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a mass spectrometer having an ion trap that traps ions or sorts ions by the action of a high-frequency electric field. More specifically, the present invention relates to an ion that uses a rectangular wave voltage as a high-frequency voltage applied to an electrode constituting the ion trap. The present invention relates to a trap mass spectrometer.

  In a mass spectrometer, an ion trap captures and confines ions by the action of a high-frequency electric field, selects ions with a specific mass-to-charge ratio m / z, and cleaves the selected ions. Used for. As will be described later, a typical ion trap has a single ring electrode whose inner surface is a rotating one-leaf hyperboloid shape, and an inner surface disposed opposite to the ring electrode is a rotating two-leaf hyperboloid shape. Although it is a three-dimensional quadrupole ion trap composed of a pair of end cap electrodes, a linear ion trap composed of four rod electrodes arranged in parallel is 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 capturing ions is usually formed in a space surrounded by the ring electrode and the end cap electrode by applying a sinusoidal high frequency high voltage to the ring electrode. To confine ions while vibrating. On the other hand, in recent years, ion traps that confine ions by applying a rectangular wave high voltage to the ring electrode instead of a sinusoidal high frequency high voltage have been developed (Patent Document 1, Patent Document 2, Non-Patent Document). 1 etc.). This type of ion trap is usually called a digital ion trap because a rectangular wave voltage having binary voltage levels of high and low is used.

  A conventional ion trap driven by a sine wave high voltage (hereinafter referred to as an “analog ion trap”) uses an LC resonator to generate a sine wave high frequency high voltage, and the amplitude of the sine wave voltage is reduced. The mass range of ions that can be captured is controlled by changing the mass. On the other hand, a digital ion trap generates a rectangular high-frequency voltage by switching two DC voltages with different voltage levels at high speed, and usually changes the frequency while keeping the amplitude of the rectangular wave voltage constant. To control the mass range of ions that can be trapped. Therefore, since the amplitude of the high voltage applied to the ring electrode is smaller than that of the analog ion trap, the high frequency voltage generation circuit can be configured at low cost. In addition, there is an advantage that generation of undesired discharge between the electrodes can be avoided.

  In the digital ion trap, the voltage level of the rectangular wave voltage applied to the ring electrode is as high as about ± several hundreds V to ± several kV, and the frequency is as wide as several tens of kHz to several MHz. In order to generate such a rectangular wave voltage, the high-frequency voltage generation circuit employs a configuration in which a positive high voltage and a negative high voltage are switched by a high-speed semiconductor switching element such as a power MOSFET (Patent Document). 2, see Non-Patent Document 1). In addition, the stability of the voltage level is important for positive and negative high voltages, so the commercial AC voltage supplied from outside is boosted, and the output voltage is AC / DC converted to stabilize the voltage level. A stabilized DC power supply device having such a configuration is used. However, even if a high-accuracy power supply device is used, it is inevitable that a ripple (AC component) derived from the commercial AC voltage is superimposed on the output voltage to some extent.

  In the digital ion trap, a rectangular wave voltage divided signal applied to the ring electrode is applied to the end cap electrode, and only ions having a specific mass-to-charge ratio according to the frequency of the rectangular wave voltage at that time are resonantly excited. Can be discharged from the ion trap. When acquiring the mass spectrum, the resonance excitation discharge described above is used to scan the frequency of the rectangular wave voltage, thereby scanning the mass-to-charge ratio of the ions discharged from the ion trap and detecting the discharged ions. Detect with. The mass-to-charge ratio of ions ejected by resonance excitation is inversely proportional to the square of the frequency of the rectangular wave voltage, while being proportional to the amplitude of the rectangular wave voltage. Therefore, if the amplitude of the rectangular wave voltage fluctuates during mass scanning, there will be a shift in the mass-to-charge ratio of the ejected ions. As described above, the ripple superimposed on the rectangular wave voltage is one of the fluctuation factors of the amplitude, so that the mass-to-charge ratio shifts.

  In a conventional ion trap mass spectrometer, an approximate correction equation is created so that the error characteristics of the apparatus can be corrected by measuring in advance a calibration sample (calibrant) whose true value of mass-to-charge ratio is known. In addition, when the target sample is measured, a process for correcting the mass error using the correction formula is performed. However, as described above, the influence of the ripple derived from the commercial AC voltage and superimposed on the rectangular wave voltage cannot be corrected by the correction equation as described above. Therefore, when the influence of ripple becomes large, there arises a problem that the mass accuracy and mass resolution of the mass spectrum are lowered.

International Publication No. 01/029871 Pamphlet International Publication No. 2005/083743 Pamphlet

Furuhashi, Takeshita, Ogawa, Iwamoto, “Development of Digital Ion Trap Mass Spectrometer”, Shimazu Review, Shimazu Review Editorial Department, March 31, 2006, Vol. 62, No. 3.4, pp. 141-151

  The present invention has been made to solve the above-described problems, and in an ion trap mass spectrometer that performs mass analysis using the digital ion trap as described above, it is superimposed on a rectangular wave voltage applied to a ring electrode. The main purpose is to eliminate the influence of ripples derived from commercial AC voltage and increase the mass accuracy and mass resolution of the acquired mass spectrum.

In order to solve the above-mentioned problems, the present invention is designed to temporarily capture various ions in an ion trap composed of a plurality of electrodes, scan the mass-to-charge ratio of ions discharged from the ion trap, and discharge the ions. In an ion trap mass spectrometer that performs mass scanning by detecting generated ions,
a) a DC voltage source for generating a DC voltage from a commercial AC voltage to apply a rectangular wave voltage to at least one of the electrodes in order to discharge some ions while holding the ions in the ion trap; A rectangular wave voltage generating means including switching means for switching a DC voltage from a voltage source into a rectangular wave;
b) phase detection means for detecting the phase of the commercial AC voltage;
c) mass scanning control means for controlling the rectangular wave voltage generating means to start mass scanning when the phase of the AC voltage detected by the phase detecting means is a specific phase;
d) For a calibration sample with a known mass-to-charge ratio, a plurality of specific phases are set by the mass scanning control means, mass scanning is performed, mass errors are respectively obtained from the results, and the mass errors are used. Correction information acquisition means for creating and storing error correction information with the mass-to-charge ratio as a variable;
e) At the time of measuring the target sample, the mass scanning control unit sets one specific phase and executes mass scanning, and the error correction information stored in the correction information acquiring unit is used for the result. Correction processing means for performing correction and obtaining a mass spectrum;
It is characterized by having.

  In the ion trap mass spectrometer according to the present invention, the ion trap may be either a three-dimensional quadrupole ion trap or a linear ion trap. In the case of a three-dimensional quadrupole ion trap, a rectangular wave high voltage is applied to the ring electrode in order to capture ions, and when ions having a specific mass-to-charge ratio are ejected in mass scanning, the end is further increased. A rectangular wave low voltage having a frequency obtained by dividing the rectangular wave voltage and having an appropriately set amplitude is applied to the cap electrode.

  In the ion trap mass spectrometer according to the present invention, the specific phase when measuring the calibration sample is preferably 3 or more, and in particular, three of 0, + (2/3) π, and − (2/3) π. It is good to set and execute mass scanning respectively.

  For example, in a configuration using a three-dimensional quadrupole ion trap, as described above, if a ripple derived from the commercial AC voltage is superimposed on the rectangular wave voltage applied to the ring electrode, the frequency of the commercial AC voltage is superimposed. (Usually 50Hz or 60Hz) and mass error synchronized to the phase. If the phase of the commercial AC voltage at the start of mass scanning over a predetermined mass range is always the same and the mass scanning is at a constant speed (if the change in mass-to-charge ratio is linear with respect to the time axis), then The sinusoidal component of the mass error derived from ripples such as can be written as W · sin (m / z · L) (where m / z is the mass-to-charge ratio, L is a constant, and W is the amplitude) . The amplitude W can be expressed by a function having a mass-to-charge ratio as a variable.

  The mass error includes an error derived from a mechanical dimensional error of the apparatus and an AC component error derived from ripple as described above, and the sum of both can be regarded as a mass error. Any error can be expressed by a function having a mass-to-charge ratio as a variable, and measurement of a plurality of calibration samples having a known mass-to-charge ratio (or a calibration sample including a plurality of components having a known mass-to-charge ratio). Based on the result, that is, the difference between the true mass-to-charge ratio and the measured value, the function can be determined approximately. Therefore, in the ion trap mass spectrometer according to the present invention, the correction information acquisition means performs mass scanning with the AC voltage phase at the starting point of mass scanning determined for one or more calibration samples, and the respective masses are obtained from the results. An error is obtained, and error correction information including the above function having the mass-to-charge ratio as a variable is created and stored using the mass error. This error correction information does not reflect a mass error due to a mechanical dimensional error of the apparatus as in the prior art, but also reflects an AC component mass error due to a ripple.

  When mass scanning is performed on the target sample, the mass scanning is always started in synchronization with a specific phase (for example, 0) of the commercial AC voltage. As a result, the mass error due to ripple is also in a reproducible state, that is, the same state as when the error correction information is acquired, so that the correction processing means can obtain the result obtained by performing the mass scan of the target sample. On the other hand, correction using the error correction information stored in the correction information acquisition unit is executed to obtain a mass spectrum from which the above-described mass error is removed.

  The ion trap mass spectrometer according to the present invention corrects a mass error caused by a dimensional error of the ion trap and the like, and also causes a mass deviation due to the influence of an AC component derived from a commercial AC voltage that has not been considered in the past. It can be corrected. Thereby, a mass spectrum with high mass accuracy and mass resolution can be obtained. In addition, since the mass error derived from the commercial AC voltage can be removed by electrical control and signal processing as described above, a circuit for generating a rectangular wave voltage for driving the ion trap (rectangular wave voltage generating means) ), The circuit for smoothing the DC voltage (removing the ripple) can be simplified to some extent, and the cost of such a circuit can be reduced.

The block diagram of the principal part of the ion trap mass spectrometer which is one Example of this invention. 7 is a control / processing flowchart when creating correction information using a calibration sample in the ion trap mass spectrometer of the present embodiment. The flowchart at the time of the mass error correction | amendment process using correction | amendment information in the ion trap mass spectrometer of a present Example. The figure explaining the principle of the mass error correction | amendment in the ion trap mass spectrometer of a present Example. The figure explaining the principle of the mass error correction | amendment in the ion trap mass spectrometer of a present Example. The figure explaining the principle of the mass error correction | amendment in the ion trap mass spectrometer of a present Example.

  Hereinafter, an ion trap mass spectrometer according to an embodiment of 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 ion trap mass spectrometer of the present embodiment.

  The ion trap mass spectrometer includes an ionization unit 1 that ionizes a sample, a three-dimensional quadrupole ion trap 2, and a detection unit 3 that detects ions. Here, the ionization unit 1 is a matrix-assisted laser desorption ion source (MALDI), and the sample S placed on the sample plate 12 is irradiated with laser light emitted from the laser irradiation unit 11. The sample component in the sample S is ionized by this laser light irradiation, and the generated ions are extracted by the extraction electrode 13 and transported through the ion transport optical system 14.

  The ion trap 2 includes one ring electrode 21 and a pair of end cap electrodes 22 and 24 arranged to face each other. A space surrounded by the electrodes 21, 22 and 24 is an ion trapping region. An ion incident port 23 is formed in the center of the inlet end cap electrode 22, and ions emitted from the ionization unit 1 are introduced into the ion trap 2 through the ion incident port 23 as described above. On the other hand, an ion exit port 25 is formed in the exit-side end cap electrode 24 substantially in line with the ion entrance port 23. Ions discharged from the ion trap 2 through the ion emission port 25 reach the detector 3 and are detected. The detection unit 3 includes a conversion dynode 31 that converts ions to electrons and a secondary electron multiplier 32, and sends a detection signal corresponding to the amount of incident ions to the data processing unit 8.

A main power supply unit 4 is connected to the ring electrode 21, and an auxiliary power supply unit 5 is connected to the end cap electrodes 22 and 24. The main power supply unit 4 uses the first switch 43 and the second switch 44 to switch the positive voltage V _H generated by the first voltage source 41 and the negative voltage V _L generated by the second voltage source 42 to generate a rectangular wave. A voltage V _OUT is generated. The first switch 43 and the second switch 44 are semiconductor switching elements such as power MOSFETs. The first and second voltage sources 41 and 42 are DC voltage source devices that generate a DC voltage from a commercial AC voltage supplied from an external commercial AC power supply 100. The positive voltage V _H and the negative voltage V _L , that is, the high level and low level of the rectangular wave voltage can be, for example, ± 250V, ± 500V, ± 750V, ± 1000V, and the like. However, the amplitude of the rectangular wave voltage V _OUT is not limited to this. The frequency of the rectangular wave voltage is generally in the range of several tens of kHz to several MHz.

  The control unit 6 includes a CPU, a digital circuit, and the like, and supplies a pulse signal for turning on and off the switches 43 and 44 to the main power supply unit 4 and controls the auxiliary power supply unit 5. As a result, ions in a predetermined mass range are trapped in the ion trap 2, and ions having a specific mass-to-charge ratio among the accumulated ions are selectively ejected from the ion trap 2 through the ion emission port 25. A detection signal for ions is acquired. The AC voltage phase detection unit 7 detects the timing at which the phase of the sine wave commercial AC voltage becomes 0 (zero crossing in the negative direction), and sends a detection signal corresponding to the timing to the control unit 6. The correction information creation unit 9 receives data from the data processing unit 8 under the control of the control unit 6, creates and stores correction information for correcting a mass error as described later, and if necessary, The correction information is read out and provided to the data processing unit 8.

In the ion trap mass spectrometer of the present embodiment, a frequency-divided signal of the rectangular wave voltage is applied to the end cap electrodes 22 and 24 in a state where a predetermined rectangular wave high voltage is applied to the ring electrode 21 from the main power supply unit 4. As a result, ions having a specific mass-to-charge ratio among the ions held in the ion trap 2 are selectively resonantly excited, and the ions are ejected through the ion emission port 25. At this time, the frequency Ω and amplitude E of the rectangular wave voltage applied to the ring electrode 21 and the mass-to-charge ratio M of ions ejected from the ion trap 2 are:
M∝E / Ω ²
There is a relationship. Based on this relationship, the control unit 6 scans the mass-to-charge ratio of ions ejected from the ion trap 2 by changing the frequency Ω of the rectangular wave voltage within a predetermined range. The data processing unit 8 creates a mass spectrum over a predetermined mass range based on the detection signal obtained from the detection unit 3 with such mass scanning.

Due to mechanical dimensional errors of each electrode 21, 22, 24 of the ion trap 2, displacement of the relative arrangement, etc., a mass error occurs in the actually measured mass spectrum. Since such errors have measurement reproducibility, an error function Fd with the mass-to-charge ratio M as a variable can be obtained in advance and used to correct the error. FIG. 4 is a diagram illustrating an example of the relationship between the mass-to-charge ratio M and the mass error D during mass scanning. As shown in this figure, the error D with respect to the mass-to-charge ratio M is
D = Fd (M) (1)
It becomes. Usually, the error function Fd is approximately obtained using a plurality of calibration samples (calibrants) whose true value of the mass-to-charge ratio M is known. The greater the number of calibration samples (the number of mass-to-charge ratio points to be calibrated), the higher the accuracy of approximation of the error function Fd.

When ripples (AC components) resulting from the commercial AC voltage V _ac are superimposed on the DC voltages V _H and V _L that are the outputs of the first voltage source 41 and the second voltage source 42, as shown in FIG. An AC component error synchronized with the commercial AC voltage is superimposed on the error function Fd. In general, the change in mass to charge ratio during mass scanning is linear with respect to the measurement time axis. Therefore, the alternating current (sine wave) component of the mass error can be described as W · sin (ML). Here, L is a constant and W is an amplitude. Since the frequency of the AC component is determined, if the phase of the AC component is synchronized with mass scanning, the amplitude W can be expressed by a function Fa (M) with the mass-to-charge ratio M as a variable. That is, the AC component Dac of the mass error is expressed by the following equation (2) as shown in FIG.
Dac = Fa (M) · sin (ML) (2)
Therefore, when this AC component Dac is taken into consideration, the mass error D shown in the equation (1) is
D = Fd (M) + Fa (M) · sin (ML) (3)
It becomes. The second term on the right side of equation (3) is due to the ripple caused by the commercial AC voltage that has not been considered in the past.

  In the ion trap mass spectrometer of this embodiment, in order to synchronize the phase of the AC component of the mass error and the mass scanning, the AC voltage phase detector 7 detects the timing when the phase of the commercial AC voltage becomes 0, The start point of mass scanning is synchronized with a specific phase determined by the detection result. By such synchronous control, the AC component of the mass error also has measurement reproducibility, and the mass error can be corrected by a correction formula based on the formula (3).

  As a specific example, correction information generation processing for correcting a mass error and mass data correction processing based on the correction information will be described. FIG. 2 is a flowchart showing a correction information creation process for correcting a mass error, and FIG. 3 is a flowchart showing a mass data correction process using the correction information.

For example, when the correction information creation process is started in response to an instruction to execute a calibration operation, first, among the plurality of calibration samples (in particular, the number is not limited, but it is more preferable), the first calibration sample is set at the measurement position. (Step S1). The controller 6 sets the mass scanning start timing to phase 0 of the commercial AC voltage (step S2), and executes mass scanning in a predetermined mass range a plurality of times under the conditions. That is, based on the detection signal given from the AC voltage phase detector 7, the measurement sequence is determined so that mass scanning is started at the timing when the phase of the commercial AC voltage V _ac is 0, and the operation of each unit is controlled.

The data processing unit 8 integrates the spectrum data obtained by the plurality of mass scans, performs peak detection on the mass spectrum obtained thereby, and obtains a measured value of the mass-to-charge ratio m / z corresponding to the peak top. . Thereby, a measured value when the mass scanning start point is the AC voltage phase 0 is obtained (step S3). The measured values of mass-to-charge ratio at this time is Mc _1.

Next, for the same calibration sample, the mass scanning start timing is set to the commercial AC voltage phase (2/3) π (step S4), and a plurality of mass scans are performed under the same conditions as in step S3. The measurement is repeatedly executed, and the corresponding measurement value of the mass to charge ratio is acquired from the result (step S5). The measured values of mass-to-charge ratio at this time is Mc _2.

Furthermore, for the same calibration sample, the mass scanning start timing is set to commercial AC voltage phase − (2/3) π (step S6), and mass analysis is performed a plurality of times under the same conditions as in step S3. Are repeatedly executed, and the corresponding measurement value of the mass-to-charge ratio is obtained from the result (step S7). The measured value of the mass-to-charge ratio at this time is Mc ₃ .

When the measured values Mc ₁ , Mc ₂ , and Mc ₃ of the mass-to-charge ratio in which the phase of the commercial AC voltage at the start of mass scanning is 0, (2/3) π, and − (2/3) π are obtained, The correction information creation unit 9 that has received this from the data processing unit 8 calculates an average value from the three measurement values (step S8). If the true value of the mass-to-charge ratio of the calibration sample is Mc ₀ , the measured values Mc ₁ , Mc ₂ , Mc ₃ can be described as follows:
_{Mc 1 = Mc 0 + Fd (} Mc 0) + Fa (Mc 0) · sin (Mc 0 · L) ... (4)
Mc ₂ = Mc ₀ + Fd (Mc ₀ ) + Fa (Mc ₀ ) · sin (Mc ₀ · L + 2π / 3) (5)
Mc ₃ = Mc ₀ + Fd (Mc ₀ ) + Fa (Mc ₀ ) · sin (Mc ₀ · L−2π / 3) (6)
The average value Mc _s of these mass-to-charge ratios is
Mc _s = (Mc ₁ + Mc ₂ + Mc ₃ ) / 3 = Mc ₀ + Fd (Mc ₀ ) (7)
Thus, the sin term, that is, the AC component, existing in the equations (4) to (6) is removed.

  The control unit 6 determines whether or not all the calibration samples have been measured (step S9), and returns to step S1 until it is determined that the measurement has been completed. If three mass-to-charge ratio measurement values and their average values with different AC voltage phases at the start of mass scanning are obtained for a plurality of calibration samples, the process proceeds from step S9 to S10.

The correction information creation unit 9 obtains a function for correcting the mass error using measurement results for a plurality of calibration samples. As described above, since the average value Mc _s of the mass-to-charge ratio is not affected by the AC component, first, the average value Mc corresponding to the true value Mc ₀ of the plurality of different mass-to-charge ratios obtained for the plurality of calibration samples. An approximate expression of the error function Fd is obtained using _s , and a correction function fd for obtaining a mass error due to factors such as a mechanical error of the apparatus is created.

In order to correct an error in the measured value of the mass-to-charge ratio, it is necessary to correct an error derived from the commercial AC voltage in addition to the correction function fd. Therefore, from the measured values Mc ₁ , Mc ₂ , Mc ₃ of the mass-to-charge ratio measured for the plurality of calibration samples as described above, Fa (M) in the equation (3), that is, the amplitude value of the AC component of the error is obtained. The function to obtain is derived as follows. That is, from the equations (4) to (6),
Mc ₁ −Mc _s = Fa (Mc ₀ ) · sin (Mc ₀ · L) = a ₁
Mc ₂ −Mc _s = Fa (Mc ₀ ) · sin (Mc ₀ · L + 2π / 3) = a ₂
Mc ₃ −Mc _s = Fa (Mc ₀ ) · sin (Mc ₀ · L−2π / 3) = a ₃
Can be written. Using these equations,
a ₁ ² + a ₂ ² + a ₃ ² = (3/2) · Fa (Mc ₀ ) ²
So,
Fa (Mc ₀ ) = √ {(2/3) · [(Mc ₁ −Mc _s ) ² + (Mc ₂ −Mc _s ) ² + (Mc ₃ −Mc _s ) ² ]} (8)
It becomes. Since the amplitude Fa (Mc ₀ ) can be obtained from the three measured values Mc ₁ , Mc ₂ , and Mc ₃ from the equation (8), the true value Mc _{0 of} a plurality of different mass-to-charge ratios obtained for a plurality of calibration samples. An approximate expression of the function Fa is obtained using the measured values Mc ₁ , Mc ₂ , and Mc ₃ corresponding to, and a function fa (M) for obtaining the amplitude of the AC component is created (step S11).

  The correction information creation unit 9 stores the functions fd and fa obtained from the measurement result of the calibration sample as described above in a built-in memory as data for correcting the mass error (step S12), and creates correction information. Exit.

When measuring a measurement target sample whose true value of mass-to-charge ratio is unknown, measurement and data processing are executed in the following procedure.
For example, when a measurement execution instruction is given, the measurement target sample is placed at the measurement position (step S21). The controller 6 sets the mass scanning start timing to phase 0 of the commercial AC voltage (step S22), and executes mass scanning in a predetermined mass range a plurality of times under the conditions. That is, based on the detection signal given from the AC voltage phase detector 7, the measurement sequence is determined so that mass scanning is started at the timing when the phase of the commercial AC voltage V _ac is 0, and the operation of each unit is controlled.

The data processing unit 8 integrates the spectrum data obtained by the plurality of times (for example, n times) of mass scanning, thereby acquiring the mass spectrum (step S23). This mass spectrum includes a mass error as described above. Therefore, next, the data processing unit 8 executes the correction process of the mass error using the functions fd and fa stored in the correction information creation unit 9. That is, since the measured value Mt of each mass-to-charge ratio is measured with the AC voltage phase 0 set at the start of mass scanning, the measured value Mt and the true value M have the following relationship.
Mt = M + Fd (M) + Fa (M) · sin (M · L) ≈M + fd (Mt) + fa (Mt) · sin (Mt · L)
Therefore, the true value M of a certain mass-to-charge ratio can be approximately obtained from the following equation (9).
M≈Mt−fd (Mt) −fa (Mt) · sin (Mt · L) (9)

When correcting the mass error for the entire mass spectrum, the calculation according to the equation (9) may be performed for each mass to charge ratio (step S24). This eliminates not only a mass error due to a mechanical error of the ion trap 2 or the like but also a mass error caused by superimposing the AC component of the commercial AC voltage on the DC voltages V _H and V _L , so that A highly accurate mass spectrum can be obtained.

  In the above description, the measurement was performed in a state in which the commercial AC voltage phase at the start of mass scanning was set to three types of 0, (2/3) π, and − (2/3) π for the calibration sample. However, the phase is not necessarily the above value. However, as is clear from the above description, it is desirable to determine the phase so that the AC component is removed when the average of a plurality of measured values for the same calibration sample is taken.

  Further, the above-described embodiment is merely an example, and it is obvious that modifications, corrections, and additions may be appropriately made within the scope of the present invention, and included in the scope of claims of the present application. For example, although the above embodiment is a three-dimensional quadrupole ion trap, the present invention can be applied to a linear ion trap using a multipole (for example, quadrupole) rod.

DESCRIPTION OF SYMBOLS 1 ... Ionization part 11 ... Laser irradiation part 12 ... Sample plate 13 ... Extraction electrode 14 ... Ion transport optical system 2 ... Ion trap 21 ... Ring electrode 22 ... Inlet end cap electrode 23 ... Ion entrance 24 ... Outlet end cap electrode 25 ... Ion exit 3 ... Detection unit 31 ... Conversion dynode 32 ... Secondary electron multiplier 4 ... Main power supply unit 41 ... First voltage source 42 ... Second voltage source 43 ... First switch 44 ... Second switch 5 ... Auxiliary power supply unit 6 ... control unit 7 ... AC voltage phase detection unit 8 ... data processing unit 9 ... correction information creation unit 100 ... commercial AC power supply

Claims (3)

Ions that once trap various ions inside an ion trap consisting of a plurality of electrodes, scan the mass-to-charge ratio of ions ejected from the ion trap, and perform mass scanning by detecting the ejected ions In the trap mass spectrometer,
a) a DC voltage source for generating a DC voltage from a commercial AC voltage to apply a rectangular wave voltage to at least one of the electrodes in order to discharge some ions while holding the ions in the ion trap; A rectangular wave voltage generating means including switching means for switching a DC voltage from a voltage source into a rectangular wave;
b) phase detection means for detecting the phase of the commercial AC voltage;
c) mass scanning control means for controlling the rectangular wave voltage generating means to start mass scanning when the phase of the AC voltage detected by the phase detecting means is a specific phase;
d) For a calibration sample with a known mass-to-charge ratio, a plurality of specific phases are set by the mass scanning control means, mass scanning is performed, mass errors are respectively obtained from the results, and the mass errors are used. Correction information acquisition means for creating and storing error correction information with the mass-to-charge ratio as a variable;
e) At the time of measuring the target sample, the mass scanning control unit sets one specific phase and executes mass scanning, and the error correction information stored in the correction information acquiring unit is used for the result. Correction processing means for performing correction and obtaining a mass spectrum;
An ion trap mass spectrometer comprising: The ion trap mass spectrometer according to claim 1,
The correction information acquisition means sets the specific phase by the mass scanning control means to 0, + (2/3) π, and − (2/3) π when the calibration sample is measured, and performs mass scanning respectively. An ion trap mass spectrometer characterized in that it is executed. The ion trap mass spectrometer according to claim 2,
The ion trap mass spectrometer is characterized in that the correction processing means performs correction processing on a result of mass scanning performed with the specific phase set to zero.

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