JP2005251594A - Ion trap / time-of-flight mass spectrometer - Google Patents

Abstract

【Task】
In the ion trap / TOF-MS, the trapping parameter of the ion trap can be calibrated.
[Solution]
After trapping ions with the ion trap, the main high-frequency voltage applied to the ring electrode is swept in steps, and a plurality of mass spectra are acquired with the TOF during the one step, and with the TOF during the one step. The integrated mass spectrum is obtained by integrating the ionic current values in the obtained mass spectrum, and further, the integrated mass spectrum of all the steps of the main high-frequency voltage is integrated to obtain a pseudo mass spectrum. Then, it compares with a standard pseudo mass spectrum.
【effect】
Even in a mass spectrometer that combines an ion trap and a TOF, the ion trap can be efficiently calibrated.
[Selection] Figure 1

Description

  The present invention relates to an ion trap / time-of-flight mass spectrometer.

Recently, mass spectrometry has been recognized as a major analytical technique in the fields of biotechnology and biochemistry. This is mainly due to the continuous development and improvement of ionization technology and mass spectrometer for the bio field. As ionization techniques for the bio field, there are two ionization techniques that are thermally unstable and can directly and stably ionize high molecular weight biomolecules. One ionization technique is electro spray ionization (ESI) in which biomolecules dissolved in a solution can be taken out directly into the atmosphere as ions. Another ionization technique is the matrix-assisted laser desorption ionization method, which ionizes sample molecules by irradiating the sample molecules with laser light.
desorption ionization, MALDI).

  These two ionization methods are both soft ionization methods, but the forms of ion beams generated by the respective methods are completely different. In ESI, a continuous ion beam is generated, whereas in MALDI, ions are generated in pulses. Therefore, mass spectrometers that are optimal for each ionization method are prepared. Specifically, ESI is often used in combination with a quadrupole mass spectrometer (QMS) or ion trap mass spectrometer, and MALDI is a time-of-flight (TOF). Often used in combination.

  Recently, a mass spectrometer of a type that can be combined with both ESI and MALDI has been studied.

  Mass spectrometers combining soft ionization techniques such as ESI and MALDI as described above and TOF have begun to spread rapidly in the bio field. Various devices have been proposed in the process.

For example, two quadrupole MS (Quadrupole Mass) between an ESI ion source or a MALDI ion source and a TOF as disclosed in Japanese Patent Application Laid-Open No. 11-154486 (Patent Document 1) and USP 6,331,702 (Patent Document 2). Spectrometer, QMS) is a Q-TOF. However, with this Q-TOF, even MS / MS is possible, but MS ³ and MS ⁴ that repeat MS / MS for obtaining further structural information cannot be achieved.

An apparatus capable of MS ³ or MS ⁴ is an ion trap / TOF in which an ion trap composed of a ring electrode and a pair of end cap electrodes and a TOF are combined.
It is disclosed in International Journal of Mass Spectrometry, 213 (2002), 45-62 (Non-patent Document 1) and Japanese Patent Application Laid-Open No. 2003-123865 (Patent Document 3). Ion trap /
In the TOF, ions generated by an ion source are once trapped in an ion trap, and the generated ions are sent to the TOF through a process such as MS / MS for mass analysis.

However, this ion trap / TOF has a new problem. That is, since mass analysis is performed by TOF after accumulating once in the ion trap, the mass range that can be analyzed by TOF is determined by the accumulation capability of the ion trap that can accumulate ions at one time. In other words, the mass number range that can be measured with one acceleration is reduced by TOF,
The wide range of the measured mass number range, which is an excellent feature of TOF, can hardly be used.

  In order to solve this problem, a new ion trap / TOF having a collision damping region for reducing the kinetic energy of ions ejected from the ion trap between the ion trap and the TOF has been proposed. The collision damping region is formed by arranging a multipole ion guide in a region where neutral gas is supplied between the ion trap and the TOF.

JP-A-11-154486 USP 6,331,702 Japanese Patent Laid-Open No. 2003-123865 International Journal of Mass Spectrometry, 213 (2002), 45-62

In the ion trap / TOF having the collision damping region, the ion trap plays the following role.
(A) Receives ions from the ion source and accumulates them in the ion trap. Unnecessary ions can be removed while ions are trapped. Thereafter, the trapped ions are ejected from the ion trap, thermalized by a multipole ion guide in the collision damping region, and then sent to the TOF to give a mass spectrum by the TOF.

    Here, thermalization means that ions introduced into the multipole ion guide collide with neutral gas molecules in the multipole ion guide, rapidly lose their kinetic energy, and gather near the central axis of the multipole ion guide. Eventually, the kinetic energy of ions drops to the same level of thermal motion as the surrounding gas molecules. Ions gather on the central axis of the ion guide and diffuse and move on the axis due to thermal motion.

(B) Receives ions from the ion source and accumulates them in the ion trap. Only the precursor ions with a specific mass remain in the trapped ions, and all other mass ions are excluded from the ion trap (precursor ion isolation). An auxiliary alternating current with a frequency ω _{supp that} is the same as the natural frequency ω of the precursor ion or _{close to} the pole is applied between the end cap electrodes to excite and dissociate the precursor ion (Collision-induced Dissociation, CID). The product ions generated by this CID are later ejected from the ion trap and are thermalized with a multipole ion guide. Subsequently, the ions are sent to TOF for mass analysis.

Ions introduced and accumulated in the ion trap are sent to the TOF through the process (a) or (b) to give a mass spectrum. In order to reliably select, excite, and dissociate ions having a specific mass within the ion trap, it is necessary that the correlation between the ion mass and the trap parameters be strictly determined. That is, for the isolation of precursor ions and the resonance excitation and dissociation of precursor ions, the correlation between the mass-to-charge ratio m / z of the precursor ions and the frequency ω _{supp of the} main high-frequency voltage V and auxiliary AC voltage is strictly determined. I have to keep it. If an accurate correlation between V, ω _supp , and m / z is recorded in the controller, V, ω _supp can be freely controlled to isolate, excite, and dissociate any ions. These parameters V and ω _supp are called trap parameters, and theoretical and empirical formulas are shown in the literature and the like regarding the correlation between them and ion mass m / z. However, in an actual ion trap, changes in room temperature, changes in pressure in the ion trap, changes in voltage, variations in electrode mechanical processing, variations in assembly of the ion trap electrode, contamination of the ion trap electrode, contamination in the ion trap Due to various causes such as space charge, the correlation between the trap parameter and m / z deviates from the theoretical formula and the experimental formula. Calibration corrects this deviation.

This calibration is performed as follows.
(A) A standard substance (for example, polyethylene glycol Polyglycol (PEG)) that gives ions with known masses at almost equal intervals in a wide mass range is ionized and introduced into an ion trap.
(B) Next, fix one of the trap parameters (V or ω _supp ) and sweep the other one to obtain a mass spectrum.
(C) From the relationship between the known mass of the ions appearing on the acquired mass spectrum and V, ω _supp , the deviation from the calculated mass is obtained to correct the correlation.
(D) Create a calibration curve m = f (V) or m = g (ω _supp ).

If a calibration curve is created in the CPU, conversion from V or ω _supp to mass m, or conversely, conversion from mass m to V or ω _supp becomes possible. In particular, in order to eliminate unnecessary ions from ions trapped in the ion trap or perform MS / MS processing, it is necessary to apply V or ω _supp and to sweep. Therefore, accurate conversion from m to V or ω _supp is essential.

However, in the case of an apparatus in which an ion trap, a multipole ion guide, and a TOF are coupled in series, a mass spectrum can be obtained even if the main high-frequency voltage V or auxiliary AC frequency ω _supp of the trap parameter of the ion trap is swept independently. I can't. In a normal ion trap mass spectrometer, a detector is disposed after the ion trap electrode. When the main high-frequency voltage V applied to the ion trap is swept, ions are released out of the ion trap in order of mass. The detector detects the emitted ions to obtain a mass spectrum. However, in the ion trap / TOF, since the detector is in the TOF section, ions emitted from the ion trap cannot be directly detected by the TOF detector.

  On the other hand, the sweep time of the main high-frequency voltage V for mass spectrum acquisition is approximately 0.1 second to several seconds / total mass region. On the other hand, the time required for acquiring the mass spectrum of TOF is 100 μsec or less. From this, the following estimation is possible.

  A standard sample solution is introduced into an ESI ion source and ionized. The generated ions are introduced into the orthogonal ion trap / TOF. A standard sample is a mixture of a plurality of known components. When measured with a normal LC / MS apparatus, a large number of ions with known masses can be obtained over a wide mass region as shown in FIGS. 7 and 8A. An appearing mass spectrum 100 is obtained. Mass spectrum collection is repeatedly performed by TOF while slowly sweeping the main high-frequency voltage V applied to the ion trap (for example, 1 second / total mass region). TOF can repeatedly acquire mass spectra at intervals of 100 μsec or less. If mass spectra are acquired continuously for one second by TOF, about 10,000 mass spectra (FIG. 7, 101 to 104) can be collected after the end of the sweep (after one second). When the sweeping of the main high-frequency voltage V is completed, 10,000 mass spectra are integrated. That is, when the ion intensity I of the same m / z is integrated, one integrated mass spectrum 105 is obtained. Since TOF repeatedly collects ions emitted from the ion trap, if the obtained mass spectrum (101 to 104) is integrated, the integrated mass spectrum 105 should be the same as the mass spectrum 100 of the standard sample. It is.

  However, the integrated mass spectrum actually obtained by this method was contrary to expectations. The actual integrated mass spectrum (FIG. 8 (b), 110) acquired by TOF is a mass spectrum that is completely different from the mass spectrum of the standard sample (FIG. 8 (a), 100). On the obtained integrated mass spectrum 110, ions appear only in the low-mass region, and there are almost no ions of known mass derived from the standard substance that should appear in the middle and high-mass regions. That is, as shown in FIG. 9, the mass spectrum (101 to 104) obtained by TOF has only low-mass ions remarkably, and even if these are simply integrated and averaged, the mass spectrum 110 has a high mass. No ions appear. With this, even if a mass spectrum is obtained, calibration over a wide mass region cannot be performed.

  The reason why ions appear in this low mass region is explained as follows.

  It is known that when one of the trap parameters (for example, V) is swept to release ions from the ion trap, the kinetic energy of the released ions expands from 0 to several keV (see, for example, Japanese Patent Laid-Open No. Hei 9- 161719).

  Ions dissociated from ions whose kinetic energy exceeds 100 eV still have sufficient kinetic energy, so they diffuse without being thermalized in the ion guide, or go straight through the multipole ion guide at high speed and are captured by slits, etc. The Therefore, a small number of ions reach the TOF pulsar part. Even when ions reach the pulsar part of the TOF, the probability that the arrival timing coincides with the pulse timing of the TOF is small, so the possibility of giving ions on the mass spectrum of the TOF is extremely small.

  Ions whose kinetic energy is about 100 eV to 10 eV repeatedly collide with the inert gas in the ion guide, and are excited to dissociate. Among the dissociated ions, ions that still have excessive kinetic energy further collide with the inert gas to generate next-generation product ions. The product ions whose mass is reduced by dissociation are thermalized and sent to the pulsar part of the TOF, and an ion signal is given only to the low mass part by the TOF.

  Ions whose kinetic energy is 10 eV or less are thermalized without being dissociated even when they repeatedly collide with inert gas molecules in the multipole ion guide. The thermalized ions are sent to the pulsar part of the TOF and give ions on the mass spectrum of the TOF. However, the higher the mass of ions, the smaller the proportion of ions with a kinetic energy of 10 eV or less.

  Therefore, high-mass ions disappear from the mass spectrum, and low-mass fragment ions (product ions) become conspicuous. In this state, it is impossible to calibrate the trap parameters of the ion trap.

  An object of the present invention is to solve such a problem, even when a collision damping region is provided between the ion trap and the TOF, the ion trap / time of flight which can perform the ion trap calibration. A type mass spectrometer is provided.

  In order to achieve the above object, the present invention includes an ionization section that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap section that traps ions from the ionization section, and a plurality of poles. And a multipole ion guide part to which ions discharged from the ion trap part are guided, and a time-of-flight mass spectrometer (hereinafter referred to as TOF) for mass-analyzing ions discharged from the multipole ion guide part. After trapping ions with the ion trap using an ion trap / time-of-flight mass spectrometer, the main high-frequency voltage applied to the ring electrode is swept stepwise, and a plurality of masses are generated with the TOF during the one step. The spectrum is acquired, and the integrated mass spectrum is obtained by integrating the ion current values in the mass spectrum obtained by the TOF in one step. The resulting, further, so as to obtain a pseudo mass spectrum by integrating each integrated mass spectrum of all the steps of the main RF voltage.

  Alternatively, the frequency of the auxiliary AC voltage is swept in place of the main high frequency voltage.

  Furthermore, the same analysis as described above is performed for the standard sample to obtain a pseudo mass spectrum in advance, and at the time of calibration, the pseudo mass spectrum of the standard sample and the pseudo mass spectrum of the unknown sample are compared and corrected by taking the difference. A value can be obtained.

In addition, a detector that detects the ion intensity is arranged on the extension line of the axis of the multipole ion guide and after the ion pulser part or in the direction opposite to the direction in which the ion pulser part normally accelerates ions on the TOF side. During calibration, detection is performed by the above-described detector, and during normal analysis, detection is performed by TOF. By arranging other detectors near the ion pulser part,
It is possible to detect ions emitted from the ion trap without being affected by mass dispersion caused by TOF, and the calibration process is simplified.

  Even in a mass spectrometer that combines an ion trap and a TOF, the ion trap can be efficiently calibrated.

  Examples of the present invention are shown below.

  The apparatus according to the present invention includes a soft ionization means such as ESI, a system for guiding ions generated by the ionization means from an atmospheric pressure to an ion trap under vacuum, an ion trap, and ions discharged from the ion trap for analysis. It consists of a system that leads to the pulsar part of the TOF, and the TOF. A multipole ion guide is used for the part that transfers ions from the ion source to the ion trap and from the ion trap to the pulsar section of the TOF.

  A first embodiment according to the present invention is shown in FIG.

  The sample solution sent from the liquid chromatograph (LC) 1 is sent to the spray probe 2 of the ESI ion source, and sprayed into the atmospheric pressure ionization chamber 4 as ionized fine droplets to be ionized. The generated ions 3 are introduced into a vacuum chamber 9 evacuated by a turbo molecular pump (TMP) 30 through an intermediate pressure chamber 6 evacuated by an oil rotary pump (RP) 7. The ions are accelerated by the DC voltage applied to the ion accelerating electrode 10 and introduced into the ion transport space 29 from the pores of the ion transport casing 26 disposed in the vacuum chamber 9. A first multipole ion guide 12, an ion trap 20, and a second multipole ion guide 22 are arranged in series in an ion transfer casing 26 that is a metal shield tube. In the first and second multipole ion guides 12 and 22, a plurality of poles serving as electrodes are arranged in parallel to form a multipole. The ion trap 20 includes a donut-shaped ring electrode 16 and two end cap electrodes 14 and 19.

Here, the first multipole ion guide 12 has a role of efficiently transferring ions generated by the atmospheric pressure ion source to the ion trap 20. On the other hand, the second multipole ion guide 22 is an ion guide for receiving and thermalizing ions emitted from the ion trap and transferring them to the TOF. A high frequency voltage is applied to the first and second multipole ion guides 12 and 22 from high frequency power sources 43 and 45, respectively. An inert gas such as He, Ne, Ar, Xe or nitrogen gas is introduced into the ion transfer casing 26 from the gas introduction system 31 through a pipe 32 as a single gas or a mixed gas thereof. Gas is supplied from the gas introduction system 31 so that the pressure in the ion transfer space 29 is 10 ⁻¹ to 10 ⁻³ Torr (100 mTorr to ¹ mTorr).

  The ions introduced into the ion transport space 29 are thermally normalized in the first multipole ion guide 12, and then are efficiently transferred from the pore 15 opened at the center of the end cap electrode 14 of the ion trap 20 to the ion trap space 17. Well introduced. A main high frequency voltage V (˜1 MHz, about several kV) supplied from the main high frequency power supply 44 is applied to the ring electrode 16. As a result, a quadrupole high-frequency electric field is generated in the ion trap space 17, and ions introduced by this electric field are stably trapped.

  The trapped ions are ejected from the ion trap space 17 through the pores 18 after removal of unnecessary ions and MS / MS processing, and enter the second multipole ion guide 22. Here, the low kinetic energy ions repeatedly collide with the introduced inert gas molecules and dissociate or lose their kinetic energy and are thermalized. These ions are converged on the central axis of the ion guide by a high-frequency electric field generated by a high-frequency voltage applied to the second multipole ion guide 22 from the high-frequency power supply 45. The thermalized ions are diffused little by little and released from the ion transfer housing 26.

Next, ions are introduced into the TOF space 53 evacuated to a high vacuum (about 10 ⁻⁷ to 10 ⁻⁸ Torr) by a turbo molecular pump (TMP) 33. In the TOF space 53, an ion pulsar unit 59, an ion reflector 54, and a detector 55 that perform ion packet generation and ion acceleration are arranged. The ions travel between the ion extrusion electrode 50 and the ion extraction electrode 51 of the pulsar unit 59. The ions are deflected in the direction perpendicular to the ion entrance direction, that is, in the direction of the TOF flight axis by the positive and negative pulse voltages applied simultaneously to the ion extrusion electrode 50 and the ion extraction electrode 51, and enter the ion acceleration electrode 52. Finally, the ions are accelerated and released into the TOF space 53. The ions fly through the TOF space 53, pass through the ion reflector 54, and return to the detector 55. As a result, the ion intensity corresponding to the arrival time of ions is measured and a mass spectrum is given by the data processing device 40.

  Calibration of ion trap parameters is performed according to the following steps.

  FIG. 2 shows a calibration flowchart. Further, FIG. 3 shows a schematic operation diagram in which the calibration is repeated twice.

(Step 201)
First, a standard sample solution is introduced into an ion source and ionized.

(Step 202)
The generated ions are introduced into the vacuum chamber 9 through the intermediate pressure chamber 6. An acceleration voltage of about −100 V is applied to the ion acceleration electrode 10 from an ion acceleration power source (not shown) (when positive ions are introduced). The introduced ions are accelerated and introduced into the ion transport space 29 through the pores opened in the center of the ion acceleration electrode 10. Ions are introduced into the first multipole ion guide 12. A high frequency voltage (1 to 2 MHz, 1 to 2 kV) is applied from a high frequency power supply 43 to the electrodes constituting the first multipole ion guide 12. An inert gas is introduced into the ion transfer space 29 from the gas introduction system 31, and the pressure is maintained at about 10 ⁻¹ to 10 ⁻³ Torr. The ions are thermalized in the first multipole ion guide 12 and gradually converge on the central axis of the ion guide. Ions that have lost most of their kinetic energy are accelerated by the ion gate voltage of about −100 V applied to the ion gate electrode 13 and are ionized from the pores 15 opened at the center of the end cap electrode 14 of the ion trap 20. It is introduced into the trap space 17. That is, the ion gate electrode 13 is in an open state. A main high frequency voltage V is applied to the ring electrode 16 from a main high frequency power supply 44. The ions are trapped and accumulated in the ion trap space 17 by the quadrupole high-frequency electric field generated in the ion trap space 17 by the main high-frequency voltage V. When the voltage +100 V having the same polarity as the ions is applied to the ion gate electrode 13 at time t1, the ion gate is turned off and the introduction and accumulation of ions is completed. Ions continuously introduced during the period (t0-t1) are accumulated in the ion trap space 17. During this period, unnecessary ions can be excluded from the ion trap by applying an auxiliary AC voltage from the auxiliary AC power source 42 to the end cap electrodes 14 and 19 (reference: USP 5,134,286).

  Steps 201 to 202 are steps for introducing and accumulating ions in the ion trap and eliminating unnecessary ions, and in FIG. 3, the periods of t0 to t1 and t4 to t5 correspond.

(Step 203)
Next, in order to calibrate the main high frequency voltage V and the mass, first, the main high frequency voltage V is set to an initial value V0 (V = V0). A counter m that sweeps the main high-frequency voltage stepwise is set to an initial value 0 (m = 0).

(Step 204)
The main high frequency voltage V is applied according to the equation V = V0 + ΔV × m. Here, ΔV is an increment per step of the stepped sweep.

(Step 205)
The ions of the standard substance trapped in the ion trap space 17 resonate in the order of mass by the step-like sweep of the main high-frequency voltage V, and are discharged outside the ion trap. As shown in the mass spectrum 111 of FIGS. 10 (a) and 11 (a), as the main high-frequency voltage V is swept, a mass window m _IT having a narrow mass of 0.1 to 1 is formed on the mass axis of the ion trap. Can be considered moving along. Here, the mass window m _IT refers to a mass range that resonates and discharges when a certain main high-frequency voltage V is applied.

  At the same time as the sweep of the main high-frequency voltage V of the ion trap is started, the TOF starts collecting mass spectra at high speed.

(Step 206)
In the case where the main high-frequency voltage V is swept stepwise, in this embodiment, the dwell time of one step is set to 10 milliseconds (0.01 seconds), for example. The reason why the stay time of one step is set as long as 10 milliseconds is that the time required until the ions introduced into the second multipole ion guide 22 are discharged is as long as 10 to 30 milliseconds (details). Later). During this dwell time, TOF can acquire mass spectra at intervals of 10 kHz, so that a maximum of 100 mass spectra can be obtained with a dwell time of 10 msec. In this embodiment, all mass spectra obtained during one step are integrated. That is, when one step is 10 milliseconds, an integrated mass spectrum Mm obtained by integrating 100 mass spectra is obtained.

(Step 207)
Therefore, if the integration of the mass spectrum is repeated up to n times in one step (the upper limit number of mass spectra that can be acquired in one step or the number of times set by the measurer below the upper limit number), the result is In one step of the stepped sweep, one integrated mass spectrum Mm is acquired.

(Step 208)
Next, the mass window m _IT of the ion trap is obtained from the applied main high frequency voltage V. This is because the calibration curve m _IT = f (V) of the main high-frequency voltage V and the ion trap mass window m _IT recorded in advance in the data processor 40 or a dedicated controller (not shown) for controlling the apparatus. Can be obtained from An example of the calibration curve is a state where two data of “main high-frequency voltage V” and “mass window m _IT ” in Table 1 below are stored in association with each other.

(Step 209)
After the main high-frequency voltage V, the mass window m _IT and the integrated mass spectrum Mm are stored in the memory of the data processor 40, the sweep counter m is incremented by 1 (m = m + 1).

(Step 210)
If the counter m has not reached the preset value (the upper limit of the main high frequency voltage V), the process returns to step 204, and the sweeping of the main high frequency voltage V and the collection of the mass spectrum are continued. When the counter m reaches a preset value, the sweep of V ends. At this time, the m integrated mass spectra Mm are stored in the memory of the data processing device 40 in the state shown in Table 1 below.

  Steps 203 to 210 are steps for sweeping ion trap parameters (main high frequency voltage V) and collecting mass spectra by TOF, and correspond to the periods t1 to t3 and t5 to t6 in FIG.

The upper limit value of the counter m is determined by the entire mass range and the size of the mass window. If the mass range is swept up to the mass range of 0.1 mass unit, the total number of steps is 2,000 / 0.1 =
20,000 steps are required. In this case, 20,000 is set in the counter m. The set value of the counter m represents the resolution.

Further, the sweep time of the main high-frequency voltage V (time from t1 to t3, t5 to t6 in FIG. 3) is determined by the entire mass range and the stay time of one step. If the counter m is 20,000 and the TOF data collection rate is 10 kHz and the TOF data collection frequency per step is one, the sweep time is 20,000 / 10,000 = 2 seconds. Become. However, the ions ejected into the second multipole ion guide 22 are not immediately passed through the ion guide after being thermalized in the second multipole ion guide 22, but about 10 to 30 milliseconds. stay. Therefore, if the ions of the next mass window are introduced into the second multipole ion guide 22 before the ions are excluded from the second multipole ion guide 22, crosstalk occurs between adjacent mass windows. Will get up. That is, in the apparatus configuration of this embodiment, high-speed main high-frequency voltage V sweep is not possible. Therefore, the staying time for one step is 10 to 30 milliseconds. If the stay time for one step is set to 30 milliseconds, the overall sweep time is
20,000 × 0.03 = 600 (seconds) = about 10 minutes. When the stay time of one step is 10 milliseconds, 200 (seconds) is required as described above. Therefore, the entire sweep time in this embodiment requires about 3 to 10 minutes.

  Further, the residence time of ions in the second multipole ion guide 22 depends on the pressure of the second multipole ion guide 22. Therefore, in order to reduce the measurement time and improve the S / N ratio, the TOF measurement count (n) per step may be set to be input from the outside.

Assuming that one integrated mass spectrum is generated at 0.01 seconds per step and is swept in the range of mass 1 to 2000 in 200 seconds, while the main high-frequency voltage V is being swept, the TOF is used as shown in FIG. , 20,000 integrated mass spectra as shown in FIG. 11B are collected (200 seconds / 0.01 seconds). The individual integrated mass spectra obtained only show low mass product ions, as indicated in the column of problems to be solved by the invention.

(Step 211)
Therefore, the main high-frequency voltage V0, the integrated mass spectrum M0, and the mass window m _IT = m0 of the counter m = 0 are read out from the data stored in step 209. The horizontal axis of the integrated mass spectrum M0 is the TOF mass axis m _TOF , and the vertical axis is the ion intensity I. From the integrated mass spectrum M0, an ion _mTOF that falls within the mass window m0 range (lower limit ml, upper limit mu) is selected. The ion intensity Im _TOF of ions satisfying ml <m _TOF <mu is integrated to obtain the integrated intensity SI. As a result, a pseudo mass spectrum with m _{IT on} the horizontal axis and SI on the vertical axis is obtained. This processing is expressed by an equation: SI = Σ (Im _TOF ). The integrated intensity SI of the pseudo mass spectrum is associated with the counter m = 0 and recorded in the data processor 40 or a memory in a dedicated controller for controlling the apparatus.

  The counter m is updated, the integrated mass spectrum M1 when m = 1 is read, and the same processing as in the above step 211 is repeated to obtain a pseudo mass spectrum.

(Step 212)
When the processing for obtaining the pseudo mass spectrum as described above is completed for the m accumulated mass spectra recorded, the information shown in Table 2 is stored in the data processing device 40 or the memory in the dedicated controller for controlling the device. It will be recorded.

  Here, FIG. 12A shows an example of the integrated mass spectrum read in step 211. An example of the integrated mass spectrum at m1 in FIG. 10 is 112, and an example of the integrated mass spectrum at m2 in FIG. FIG. 12B shows pseudo mass spectra 117 and 118 created from these integrated mass spectra.

(Step 213)
If this data is output as a mass spectrum, a pseudo mass spectrum 119 in which the horizontal axis is the ion trap mass window m _IT and the vertical axis is the integrated intensity SI as shown in FIG.

  The processing from step 211 to step 213 can be performed at the end of the sweep of the main high-frequency voltage V (t3 or t6 in FIG. 3). On the other hand, a method of immediately processing the acquired mass spectrum while sweeping the main high-frequency voltage V is also possible.

By making it possible to set the range (ml-mu) of the mass window m _IT for integrating the ion intensity from the data processing device 40, it becomes possible to remove different solvent ions, background noise, and the like depending on the sample and analysis.

  Further, the completed pseudo mass spectrum is appropriately displayed as a bar graph (mass spectrum) as shown in FIG. 4A or as a table as shown in Table 2 by a data processing device 40 on a display device such as a display. can do. Thereby, the measurer can confirm that the measurement has been performed smoothly. The bar graph to be displayed may be a main high-frequency voltage V and a corresponding SI table (mass spectrum as shown in FIG. 4B).

(Step 214)
A difference (mass shift) Δ = mr−m _IT between the mass mr (Table 3) of the standard material stored in advance and the mass m _IT on the pseudo mass spectrum is obtained. The mass mr of the standard sample is acquired by analyzing a sample with a known mass by the same method as the above steps, and is recorded in advance in the data processor 40 or a memory in a dedicated controller for controlling the device. Yes.

(Step 215)
M _IT , V, Δ are obtained for the standard substance on the pseudo mass spectrum, and Table 4 is created.

This reveals the mass window m _IT of the ion trap, that is, the deviation Δ of the mass-to-charge ratio (m / z) from the original mass, and calibration of the main high-frequency voltage V and the mass-to-charge ratio (m / z). Is complete.

When the above calibration process is summarized, the process as shown in FIG. 4 is performed. That is, the pseudo mass spectrum obtained by the sweep of the main RF voltage V shown in FIG. 4 (a), the horizontal axis shown in FIG. 4 (b) is converted to a pseudo-mass spectrum of the mass m _IT, on the pseudo mass spectrum From the apparent mass m _IT (corresponding to the mass window of the ion trap) and the mass mr of the standard material recorded in advance in the data processor 40 or a dedicated controller for controlling the device, a mass deviation Δ = m _IT − FIG. 4C is obtained by obtaining mr over the entire mass range. As a result, a new mass m _IT for calibration and the correlation between the main high-frequency voltage V can be constructed.

In the present embodiment, the ions emitted from the ion trap 20 in the order of mass are discharged from the ion trap regardless of the mass of the ions by collision and dissociation by the second multipole ion guide 22 or the like. The mass of ions and the intensity of ions can be determined. Actually, the mass of ions is the ion trap sweep mass window m _IT (or V), and the ion intensity is an integrated value SI of a plurality of ion intensities detected by TOF. That is, the entire TOF is regarded as an ion trap detector.

Similar to the main high-frequency voltage V, the calibration of the auxiliary AC frequency ω _supp and the mass m can be performed in the same procedure. While applying the main high frequency voltage of frequency Ω and voltage V to the ring electrode 16, the auxiliary AC frequency ω _supp starts sweeping stepwise from the frequency Ω / 2 toward the direction of _decreasing frequency over time. Meanwhile, the TOF repeats high-speed data collection of about 10 kHz. Then, SI is calculated by integrating the ion intensity of the mass spectrum Mm obtained by TOF during one step of the auxiliary AC frequency ω _supp to obtain a table (in Table 2, the main high frequency voltage V is replaced with the auxiliary AC frequency ω _supp . Table is obtained). When the sweeping of the auxiliary AC frequency ω _supp is completed, a pseudo mass with the horizontal axis representing the auxiliary AC frequency ω _supp and the vertical axis representing the accumulated ion intensity SI is stored on the memory in the data processor 40 or a dedicated controller for controlling the device. A spectrum is created. By obtaining a deviation from the known mass mr of the standard substance, the frequency ω _supp of the auxiliary AC voltage and the mass can be calibrated.

  Next, a second embodiment of the present invention will be shown.

  In the present embodiment, a second detector for calibration is newly provided in the ion trap orthogonal TOF having substantially the same configuration as that of the first embodiment. The feature of the present embodiment is that a mass spectrum for calibration is directly obtained by detecting the total amount of ions before mass analysis by TOF with the second detector.

  FIG. 5 shows the configuration of this embodiment.

  A basic configuration and a method of giving a mass spectrum by TOF are the same as those in FIG. In the present embodiment, a second detector 56 is provided in the TOF space 53. The location of the second detector 56 may be between the end cap electrode 19 of the ion trap 20 and the vicinity of the ion pulser portion 59 of the TOF. However, here, in terms of the actual configuration of the apparatus, an example in which a detector is arranged adjacent to the TOF ion pulser unit 59 that can be arranged most simply and on the opposite side to the ion acceleration direction when performing mass analysis using TOF. Indicates.

  FIG. 13 shows a flowchart of this embodiment. The calibration of the ion trap parameters proceeds according to the following procedure.

(Step 301)
A solution in which a standard substance such as Polyethylene Glycol (PEG) that gives a mass peak of known mass in a wide mass range is dissolved is introduced into the spray probe 2 of the ESI ion source.

(Step 302)
The generated ions are introduced into the ion trap space 17 and trapped to eliminate unnecessary ions.

(Step 303)
After applying a DC voltage having the same polarity as the ions to the ion gate electrode 13 to close the ion gate, the main high frequency voltage V is set to the initial value V0 (V = V0). A counter m that sweeps the main high-frequency voltage stepwise is set to an initial value 0 (m = 0).

(Step 304)
The main high frequency voltage V is applied according to the equation V = V0 + ΔV × m. Here, ΔV is an increment per step of the stepped sweep.

  Steps 301 to 304 are the same as steps 201 to 203 in the first embodiment shown in FIG.

(Step 305)
When the main high-frequency voltage V is swept, the ions become unstable in order from the lowest mass and are ejected from the ion trap 20. The released ions are introduced into the second multipole ion guide 22. The ions collide with the inert gas in the second multipole ion guide 22 and are cleaved and finally thermalized. Ions are further introduced into the TOF space 53 evacuated to a high vacuum. The ions travel between the extrusion electrode 50 and the extraction electrode 51 of the ion pulser unit 59. A DC voltage having a polarity opposite to that of ions is applied to the extrusion electrode 50 of the ion pulser unit 59, and a DC voltage having the same polarity as that of ions is applied to the extraction electrode 51. Therefore, the ions that have reached the pulsar section 59 are deflected in the direction of the extrusion electrode 50. The ions pass through the mesh-shaped extrusion electrode 50 and reach the second detector 56, and the ion intensity is detected. As a feature of the present embodiment, the integrated mass spectrum Mm in the first embodiment is measured at a time by the second detector 56 in order to detect the mass before the TOF is mass analyzed by the second detector 56.

(Step 306)
The ion intensity detected by the second detector 56 is sent to the data processor 40 and stored in the memory together with the value of the main high-frequency voltage V being swept. As a result, a mass spectrum in which the horizontal axis indicates the main high-frequency voltage V and the vertical axis indicates the ion intensity I is obtained. From pre-recorded main RF voltage V and an ion trap mass window m _IT calibration curve m _IT = f (V), determine the mass window m _IT.

(Step 307)
After the main high-frequency voltage V, the mass window m _IT and the integrated mass spectrum Mm are stored in the memory of the data processing device 40, the sweep counter m is incremented by 1 (m = m + 1).

(Step 308)
If the counter m has not reached the preset value (the upper limit of the main high-frequency voltage V), the process returns to step 305, and the sweep of the main high-frequency voltage V and the collection of the mass spectrum are continued. When the counter m reaches a preset value, the sweep of V ends.

(Step 309)
When sweeping is performed until the sweep of the main high-frequency voltage V reaches the upper limit, the ion intensity I and the mass window m _IT corresponding to the main high-frequency voltage V are obtained. The main high-frequency voltage V, ion intensity I, and mass window m _IT are stored in a table.

(Step 310)
From the above table, a mass spectrum having the horizontal axis m _{IT on} the horizontal axis and the ion intensity I on the vertical axis as shown in FIG.

(Step 311)
The mass spectrum of the mass window m _IT and the ion intensity I is compared with the mass spectrum of the standard material stored in advance, and the difference (mass deviation) Δ = mr−m _IT between the mass mr and the mass m _IT is obtained.

(Step 312)
The mass window m _IT , the main high-frequency voltage V, and the difference Δ are collected and stored in a table as calibration data. As a result, a table equivalent to Table 4 is obtained.

  The above is the calibration operation in the second embodiment.

  When the calibration is completed, the high voltage supplied to the second detector 56 is cut off, and the second detector 56 is turned off. Also, the DC voltage for ion deflection applied to the push-out electrode 50 and the extraction electrode 51 of the ion pulser unit 59 is cut off, and instead positive and negative pulse voltages are applied from a pulse power source (not shown) to extract ions. It is possible to accelerate the deflection in the direction of the electrode 51. Thereby, mass spectrometry by TOF becomes possible.

In the above steps, the calibration of the correlation between the main high-frequency voltage V and the mass m _IT is shown, but the auxiliary AC frequency ω _supp and the mass can be similarly calibrated. Specifically, the main RF voltage is fixed to a certain value V, while sweeping the auxiliary AC frequency omega _supp, by detecting the ionic strength in the second detector 56, the auxiliary AC frequency omega _supp and the mass m _IT This can be achieved by obtaining the mass spectrum of the standard sample and comparing it with the mass spectrum of the standard sample stored in advance, and obtaining the difference Δ for each mass m _IT .

The ions emitted from the ion trap are likely to be product ions having a low mass due to collision-induced dissociation (CID) in the second multipole ion guide 22. However, in the case of the present embodiment, the horizontal axis of the mass spectrum obtained by the second detector 56 is the mass window m _IT based on the sweep of the main frequency V of the ion trap or the auxiliary AC frequency ω _{supp to} the last. , Not the actual mass of ions detected by the TOF detector 55. Therefore, the ions in the ion trap can be accurately grasped no matter how the ions released from the ion trap are dissociated in the second multipole ion guide 22. That is, the pseudo-mass spectrum is obtained by a two-stage process in which the trap parameters (main high-frequency voltage V or auxiliary AC frequency ω _supp ) of the ion trap are integrated for each step and integration is performed for all steps in the swept range. Unlike the case of the first embodiment to be obtained, in this embodiment, the trap parameter does not need to be integrated step by step, and the normal mass spectrum 120 as shown in FIG. Can be obtained.

  As a modification of the present embodiment, as shown in FIG. 6, it is possible to place the second detector 56 in an extension part of the ion pulser part 59. In this case, in order to guide ions to the second detector 56 and detect the ion current, the potentials of the push-out electrode 50 and the extraction electrode 51 are kept at ground or at a low potential.

In the above Examples 1 and 2, after calibration of the trap parameters and mass is achieved, be done by setting these traps parameters to unwanted ions elimination or MS / MS and MS ⁿ and high accuracy in the ion trap it can. The product ions in the ion trap are sent to the TOF through the second multipole ion guide 22 and can give a highly sensitive and accurate mass spectrum.

  In the first embodiment, calibration of the trap parameters of the ion trap can be achieved with a simple configuration without requiring a special detector or detection switching means in the ion trap / TOF configuration.

  In Example 2, ions emitted from the ion trap can be detected by placing the second detector 56 in the ion pulser portion of the TOF. As in the first embodiment, calibration of the trap parameters of the ion trap can be achieved.

It is a schematic block diagram of the 1st Example of this invention. It is a flowchart of a 1st Example. It is an operation | movement sequence diagram of a 1st Example. It is explanatory drawing of the data conversion in a 1st Example. It is a schematic block diagram of the 2nd Example of this invention. It is a schematic block diagram of the modification of the 2nd Example of this invention. It is operation | movement explanatory drawing of a calibration. It is explanatory drawing of the data acquired by TOF. It is explanatory drawing of the data acquired by TOF. It is explanatory drawing of the data acquired by TOF at the time of the main high frequency voltage V sweep. It is explanatory drawing of the data acquired by TOF at the time of the main high frequency voltage V sweep. It is a figure explaining operation | movement of a 1st Example. It is a flowchart of a 2nd Example. It is explanatory drawing of the mass spectrum obtained in a 2nd Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid chromatograph (LC), 2 ... Spray probe, 4 ... Atmospheric pressure ionization chamber, 6 ... Intermediate pressure chamber, 7 ... Oil rotary pump (RP), 9 ... Vacuum chamber, 10 ... Ion acceleration electrode, 12 ... No. 1 multipole ion guide, 13, 21 ... ion gate electrode, 14, 19 ... end cap electrode, 15, 18 ... pore, 16 ... ring electrode, 17 ... ion trap space, 20 ... ion trap, 22 ... second Multi-polar ion guide, 26 ... Ion transfer housing, 29 ... Ion transfer space, 30 ... Turbo molecular pump, 31 ... Gas introduction system, 32 ... Pipe, 40 ... Data processing device, 42 ... Auxiliary AC power source, 43, 45 ... high frequency power supply, 44 ... main high frequency power supply, 50 ... ion extrusion electrode, 51 ... ion extraction electrode, 52 ... ion acceleration electrode, 53 ... TOF space, 54 ... ion reflector, 55 ... inspection Vessel, 56 ... second detector, 59 ... ion pulser unit.

Claims (11)

An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit In an analysis method using an ion trap / time-of-flight mass spectrometer, comprising: a multipole ion guide part to which a gas is guided; and a time-of-flight mass spectrometer (hereinafter referred to as TOF) for mass-analyzing ions discharged from the multipole ion guide part ,
After trapping ions with the ion trap, the main high-frequency voltage applied to the ring electrode is swept in steps, and a plurality of mass spectra are acquired by the TOF during the one step, and the TOF is captured during the one step. An ion current value in the obtained mass spectrum is integrated to obtain an integrated mass spectrum, and each integrated mass spectrum of all steps of the main high-frequency voltage is integrated to obtain a pseudo mass spectrum. Analysis method using trap / time-of-flight mass spectrometer. An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit In an analysis method using an ion trap / time-of-flight mass spectrometer, comprising: a multipole ion guide part to which a gas is guided; and a time-of-flight mass spectrometer (hereinafter referred to as TOF) for mass-analyzing ions discharged from the multipole ion guide part ,
After trapping ions with the ion trap, the frequency of the auxiliary alternating current applied to the end cap electrode is swept in steps, and a plurality of mass spectra are acquired with the TOF during the one step. An integrated mass spectrum is obtained by integrating ion current values in the mass spectrum obtained by TOF, and a pseudo mass spectrum is obtained by integrating each integrated mass spectrum of all steps of the auxiliary AC voltage. Analysis method using ion trap / time-of-flight mass spectrometer. In claims 1 and 2,
A standard sample pseudo-mass spectrum obtained by measuring a standard sample that gives ions of known mass and accumulating the integrated mass spectrum for each of the above steps is acquired and stored in advance.
An analysis method using an ion trap / time-of-flight mass spectrometer, wherein a difference in mass between a newly measured pseudo mass spectrum and the stored standard sample pseudo mass spectrum is calculated. An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit An ion trap having a multipole ion guide unit to which the gas is guided, a time-of-flight mass spectrometer (hereinafter referred to as TOF) for mass-analyzing ions discharged from the multipole ion guide unit, and a control unit for controlling the units. In a time-of-flight mass spectrometer,
After trapping ions with the ion trap, the main high-frequency voltage applied to the ring electrode is swept in steps, and a plurality of mass spectra are acquired by the TOF during the one step, and the TOF is captured during the one step. An ion current value in the obtained mass spectrum is integrated to obtain an integrated mass spectrum, and each integrated mass spectrum of all steps of the main high-frequency voltage is integrated to obtain a pseudo mass spectrum. Trap / time-of-flight mass spectrometer. An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit An ion trap having a multipole ion guide unit to which the gas is guided, a time-of-flight mass spectrometer (hereinafter referred to as TOF) for mass-analyzing ions discharged from the multipole ion guide unit, and a control unit for controlling the units. In a time-of-flight mass spectrometer,
After trapping ions with the ion trap, the frequency of the auxiliary alternating current applied to the end cap electrode is swept in steps, and a plurality of mass spectra are acquired with the TOF during the one step. An integrated mass spectrum is obtained by integrating ion current values in the mass spectrum obtained by TOF, and a pseudo mass spectrum is obtained by integrating each integrated mass spectrum of all steps of the auxiliary AC voltage. Ion trap / time-of-flight mass spectrometer. In claims 4 and 5,
A standard sample pseudo-mass spectrum obtained by measuring a standard sample that gives ions of known mass and accumulating the integrated mass spectrum for each of the above steps is acquired and stored in advance.
An ion trap / time-of-flight mass spectrometer that calculates a difference in mass between the pseudo mass spectrum and the standard sample pseudo mass spectrum. In claims 4 and 5,
It has a display device that displays the analysis results,
An ion trap / time-of-flight mass spectrometer characterized in that the unknown sample pseudo-mass spectrum is output to the display device with the horizontal axis representing the main high-frequency voltage or auxiliary AC frequency and the vertical axis representing the integrated ion intensity. In claims 4 and 5,
It has a display device that displays the analysis results,
An ion trap / time-of-flight mass spectrometer, wherein the unknown sample pseudo-mass spectrum is output to a display device as mass on the horizontal axis and integrated ion intensity on the vertical axis. In claims 4 and 5,
An ion trap / time-of-flight mass spectrometer characterized in that an ion mass range for integrating ion currents of a plurality of mass spectra acquired per step can be set from the outside. An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit , A multipole ion guide that guides ions, an ion pulser that accelerates ions in a direction perpendicular to the axis of the multipole ion guide, and time-of-flight mass spectrometry that performs mass analysis of ions accelerated by the ion pulser In an ion trap / time-of-flight mass spectrometer having a meter (hereinafter referred to as TOF) and a control unit for controlling the respective units,
A detector that is on an extension of the axis of the multipole ion guide and that detects the ion intensity after the ion pulser section;
At the time of the ion trap calibration, the ion pulsar is passed through, and the ion is detected by the detector.
An ion trap / time-of-flight mass spectrometer characterized in that, during normal analysis, ions are accelerated by the ion pulser unit and mass analysis is performed by the TOF. An ionization unit that ionizes a sample, a pair of end cap electrodes and a ring electrode, an ion trap unit that traps ions from the ionization unit, and a plurality of poles that are discharged from the ion trap unit , A multipole ion guide that guides ions, an ion pulser that accelerates ions in a direction perpendicular to the axis of the multipole ion guide, and time-of-flight mass spectrometry that performs mass analysis of ions accelerated by the ion pulser In an ion trap / time-of-flight mass spectrometer having a meter (hereinafter referred to as TOF) and a control unit for controlling the respective units,
A detector for detecting ion intensity is disposed on the opposite side to the direction in which the ion pulser unit accelerates ions with respect to the TOF,
During the ion trap calibration, the ion pulser accelerates ions toward the detector and performs ion detection with the detector.
During normal analysis, the ion trap / time-of-flight mass spectrometer is characterized in that ions are accelerated to the TOF side by the ion pulser unit and mass analysis is performed by the TOF.

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