JP3946162B2 - Ion trap mass spectrometry method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion trap mass spectrometry method and apparatus.
[0002]
[Prior art]
A mass spectrometer is an instrument that performs ionization by adding a charge to a sample molecule, separates the generated ions into a mass-to-charge ratio by an electric field or a magnetic field, and measures the amount as a current value by a detector.
[0003]
This mass spectrometer has high sensitivity, and is superior in quantification and identification ability compared to general analyzers.
[0004]
In recent years, in the life science field, peptide analysis as an alternative to genome analysis has attracted attention, and the effectiveness of mass spectrometers with high sensitivity and excellent identification ability has been reevaluated.
[0005]
When a sample is measured with a mass spectrometer, a current value in units of mass to charge ratio is obtained. This is called a mass spectrum. This mass spectrum varies depending on the structure of the sample to be measured, and information on the structure of the sample can be obtained from the pattern of the mass spectrum.
[0006]
However, the constituent components in the sample may be complex, or the obtained mass spectrum information may be insufficient for specifying the components. In particular, in a mass spectrometer, molecular ions are separated based on a mass-to-charge ratio. Therefore, even if they have different structures, it is difficult to distinguish molecular ions when the mass-to-charge ratio is the same.
[0007]
To solve this, MS ⁿ analysis was devised. In this MS ⁿ analysis, molecular ions are taken into a mass spectrometer, ions other than a specific mass number are excluded, and collision between a selected molecular ion and a neutral molecule causes a partial binding of the molecular ion. This is a method for measuring broken ions and broken ions.
[0008]
Collision with the neutral molecule to break the bond between the selected molecular ions is called collision induced dissociation (CID). Depending on the number of repetitions of a series of operations of ion uptake, ion selection, and collision induced dissociation, MS ² and MS ³ and so on.
[0009]
Since bonds between atoms in a molecule have different bond energies depending on their structures and bond types, the lower the bond energy, the more broken by collision-induced dissociation.
[0010]
When a molecular ion collides with a neutral molecule, by giving the molecular ion the kinetic energy necessary to break the molecular ion bond, a fragment ion unique to the molecular ion is generated, and the molecular ion structure can be known. it can.
[0011]
Furthermore, as the number of repetitions of MS ⁿ analysis increases, more structural information can be obtained.
[0012]
There are various types of mass spectrometers depending on the operation and configuration for separating ions, and one configuration suitable for performing MS ⁿ analysis is an ion trap mass spectrometer.
[0013]
An ion trap mass spectrometer can perform ion selection and collision-induced dissociation by forming a quadrupole electric field in which ions with a specific mass-to-charge ratio stay in the ion trap and changing the quadrupole electric field. it can.
[0014]
Then, after performing collision-induced dissociation, if the ions generated by collision-induced dissociation are subjected to ion selection and collision-induced dissociation again without guiding the ions to the detector, a plurality of MS ⁿ analyzes can be performed. It becomes possible.
[0015]
Known techniques of ion trap mass spectrometers include those described in Patent Document 1 and Patent Document 2.
[0016]
In the technique described in Patent Document 1, the ionization chamber is partitioned by a partition wall into a second space in which an ion trap is disposed and a first space in which no ion trap is disposed. The partition wall is formed with a slit for communicating the first space and the second space.
[0017]
By forming the partition wall, increasing the gas pressure in the first space, increasing the irradiation volume of the ultraviolet light to the sample gas, increasing the amount of ions generated, and improving the measurement sensitivity of the mass spectrometer It is configured.
[0018]
In the technique described in Patent Document 2, a plurality of ion trap mass spectrometers having different measurement mass number ranges are arranged in one analyzer. Then, the ions are guided by the ion lens and the ion guide, introduced into the deflector, and introduced into one of the two mass spectrometers according to the electric field generated by the deflector due to the difference in mass number. .
[0019]
In each mass spectrometer, a gate electrode is disposed in the previous stage of ion introduction, and a lens electrode is disposed in the subsequent stage. The voltage applied to the gate electrode and the lens electrode permits introduction of ions from the outside during ion accumulation, and permits the derivation of ions from the ion trap mass spectrometer to the outside during ion detection.
[0020]
[Patent Document 1]
JP 2002-181790 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 11-144675
[Problems to be solved by the invention]
However, when MS ⁿ analysis is performed with an ion trap mass spectrometer in the prior art, there are the following problems.
[0022]
(A) Ions given at the time of collision-induced dissociation with more kinetic energy than can stably exist in the quadrupole electric field cannot be confined in the ion trap and are discharged out of the ion trap. Therefore, when MS ⁿ is repeated, the detection sensitivity decreases.
[0023]
(B) When the time spent for collision-induced dissociation is short, sufficient energy for the dissociation reaction cannot be given to the molecular ions, and the generation efficiency of cleavage ions is lowered. Therefore, it is necessary to give a sufficient time to the collision-induced dissociation. However, the time for one sequence becomes longer, and the detection sensitivity per unit time becomes lower.
[0024]
The ion trap mass spectrometer cannot capture new ions during ion separation or collision-induced dissociation, and ions transported from the ion source during that time are not used for measurement.
[0025]
That is, as the number of repetitions of MS ⁿ increases, and as the time spent for ion separation and collision-induced dissociation increases, the loss of ions shown in (a) and the ions generated in the ion source shown in (b) are measured. A reduction in efficiency is encouraged.
[0026]
An object of the present invention is to realize an ion trap mass spectrometry method and apparatus capable of improving the sensitivity of MS ⁿ analysis of an ion trap mass spectrometer.
[0027]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0028]
(1) In the ion trap mass spectrometry method, the sample is subjected to first ion separation in units of components, the separated sample is ionized, the ionized sample is subjected to first collision-induced dissociation and guided to the ion trap, and the ion trap After performing the second ion separation in the inside, a second collision-induced dissociation is performed, and mass separation is performed to detect ions.
Alternatively, after performing the second ion separation in the ion trap, the second collision-induced dissociation is performed, and the ions are mass-separated by the mass-to-charge ratio in the mass separation unit arranged at the subsequent stage of the ion trap, and the ions are separated. To detect.
[0034]
According to the present invention, performing a first ion separation is MS ^2, then rapidly accelerated ions by ion guide for taking ions into the ion trap performs a collision induced dissociation, MS ³ in the ion trap Is configured to do only.
[0035]
Therefore, an ion trap mass spectrometry method and apparatus capable of improving the sensitivity of MS ⁿ analysis of the ion trap mass spectrometer can be realized.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0037]
FIG. 1 is a schematic configuration diagram of a mass spectrometer that is an embodiment of the present invention. In FIG. 1, the mobile phase 1 is introduced into the flow path by a liquid feed pump 2. Then, the sample is introduced from the sample injector 3 and introduced into the separation column 4.
[0038]
The sample introduced into the separation column 4 is separated into component units by the separation column 4 and sent to the ion source 5.
[0039]
The ion source 5 has a capillary shape, and electrostatic spraying is performed by applying a high voltage of several kV to its tip. Ions generated by the electrostatic spray are attracted to the first pore 11 charged to several hundred volts, introduced into the vacuum chamber 51, and sent to the first ion guide 21 through the second pore 12. .
[0040]
The inside of the vacuum chamber 51 is maintained at a degree of vacuum of about 10 ⁻³ Torr by evacuation by the turbo molecular pumps 61 and 62 and the rotary pump 65 and natural suction from the first pores 11.
[0041]
An octupole is used for the first ion guide 21, and a high frequency electric field is formed by applying a high frequency voltage to the first ion guide 21, and ions are converged.
[0042]
Here, in one embodiment of the present invention, the slit electrode 22 and the second ion guide 23 are arranged at the subsequent stage of the first ion guide 21, and a potential gradient described later is formed between them, thereby preventing collision-induced dissociation. The induced ions are transported to the ion trap 31 by breaking the molecular bond.
[0043]
An Einzel lens is used for the slit electrode 22 and an octupole similar to the first ion guide 11 is used for the second ion guide 23 to form a high-frequency electric field.
[0044]
The slit electrode 22 is disposed in the vacuum chamber 51, and the second ion guide 23 is disposed in the vacuum chamber 52.
[0045]
Here, as shown in FIG. 2, in order to cause collision-induced dissociation in the vicinity of the slit electrode 22, the offset voltage Vg1 of the first ion guide 21, the voltage Vs of the slit electrode 22, and the offset voltage Vg2 of the second ion guide 23 are set. , Vs>Vg1> Vg2.
[0046]
Since the voltage Vs is higher than the voltage Vg1, ions are decelerated immediately before the slit electrode 22. The voltage Vg2 is smaller than the voltage Vg1, and has a large potential gradient with the voltage Vs. Ions are rapidly accelerated by this steep potential gradient. The rapidly accelerated ions repeatedly collide with neutral molecules such as air entering the vacuum chamber 51 from the first pore 11, and collision-induced dissociation occurs.
[0047]
According to the inventors' experiment, for example, collision-induced dissociation occurred when the voltage Vs was set to 45V, the voltage Vg1 was set to 50V, and the voltage Vg2 was set to 35V. By adjusting the voltage Vs of the slit electrode 22, the degree of collision-induced dissociation can be changed.
[0048]
Ions whose molecular bonds are cut by this collision-induced dissociation are converged by the second ion guide 23 and transported to the ion trap 31. Then, MS ³ is performed in the ion trap 31, the light is converged by the focus electrode 32, and the ion is detected by the detector 41.
[0049]
In one embodiment of the present invention, since only MS ³ is performed in the ion trap 31, the operating time of the ion trap 31 can be shortened, and the sensitivity can be improved by increasing the number of operations per unit time.
[0050]
FIG. 3 is an explanatory diagram using a mass spectrum for the operation of the ion trap mass spectrometer by collision-induced dissociation of the slit electrode 22 in one embodiment of the present invention.
[0051]
Also, FIG. 4 is an explanatory diagram using a mass spectrum for the operation of an ion trap mass spectrometer in which collision-induced dissociation is performed only in an ion trap without the slit electrode, unlike the present invention.
[0052]
3 and 4, the horizontal axis of the mass spectrum is the mass-to-charge ratio, and the vertical axis is the current value of the detector. Each mass spectrum in FIGS. 3 and 4 is a mass spectrum predicted when ions are detected in each step of ion separation and collision-induced dissociation.
[0053]
First, the sample of the mass spectrum shown in (1) of FIG. 3 is ionized by the ion source 5 after MS ² component separation is performed by the separation column 4 ((2) of FIG. 3). Then, after passing through the first ion guide 21, collision-induced dissociation is performed by the slit electrode 22 and the second ion guide 23 ((3) in FIG. 3).
[0054]
Then, the ions are taken into the ion trap 31 ((4) in FIG. 3), and in order to perform the MS ³ , the ions are separated so as to leave the target ions from the trapped ions ((5) in FIG. 3). ). The separated ions are collision-induced dissociated to generate ions ((6) in FIG. 4), mass-separated and discharged, and detected by the detector 41.
[0055]
On the other hand, in the case of the example shown in FIG. 4, the sample of the mass spectrum shown in (1) of FIG. 4 is subjected to component separation by the separation column ((2) of FIG. 4), and then the ion source. Ionized. Then, after passing through the ion guide, it is taken into the ion trap ((3) in FIG. 4).
[0056]
Ions are separated so as to leave the target ions from the trapped ions ((4) in FIG. 4). Then, the separated ions are collision-induced dissociated to generate daughter ions ((5) in FIG. 4) and confined in the ion trap.
[0057]
Furthermore, in order to perform MS ³ , the target daughter ions are separated from the mass spectrum shown in (5) of FIG. 4 ((6) of FIG. 4), and collision-induced dissociation is performed to generate grandchild ions ( (7) of FIG. And mass separation discharge is performed and it detects with a detector.
[0058]
Thus, in the example of performing collision induced dissociation only in the ion trap as in the example of FIG. 4, in order to perform MS ³ , two ion separations and two collision induced dissociation are performed inside the ion trap. There is a need to do.
[0059]
In the case of the ion trap mass spectrometer of the example shown in FIG. 4, since the operations from the mass spectra (3) to (7) shown in FIG. 4 are performed in the ion trap, the voltage sweep time and the ion trajectory Depending on the sample including the stabilization time, approximately 140 msec was required for one sequence.
[0060]
In contrast, in the case of the embodiment of the present invention shown in FIG. 3, MS ² ion separation is continuously performed by the separation column 4 and collision-induced dissociation is performed by the slit electrode 22. ³ is performed, and the time for ion separation and collision-induced dissociation of MS ² can be eliminated.
[0061]
As a result, in one embodiment of the present invention, the time required for one sequence can be reduced to about 80 msec, the number of operations of the ion trap 31 per unit time is increased, the S / N ratio is improved, and detection is performed. Sensitivity can be increased. In particular, in the case of a molecular ion having a large binding energy, a long time is required for collision-induced dissociation, and thus the effect of the present invention is great.
[0062]
Here, the example shown in FIG. 4 is a case where the collision-induced dissociation is performed only in the ion trap and the separation column is used, but a case where the separation column is not used is also conceivable.
[0063]
FIG. 5 is an explanatory diagram using a mass spectrum for the operation of the ion trap mass spectrometer when the collision-induced dissociation is performed only in the ion trap and the separation column is not used.
[0064]
In the case of the example of FIG. 5, after the sample of the mass spectrum shown in (1) is taken into the ion trap, ion separation → collision induced dissociation → ion separation → collision induced dissociation is performed, and both MS ² and MS ³ Performed in an ion trap.
[0065]
Therefore, in the case of the example of FIG. 5 as well, about 140 msec is required for one sequence as in the example of FIG.
[0066]
As described above, according to one embodiment of the present invention, ion separation that is MS ² is performed by a separation column, and then ions are rapidly accelerated by an ion guide for taking ions into the ion trap, thereby causing collision-induced dissociation. Since the configuration is such that only MS ³ is performed in the ion trap, an ion trap mass spectrometry method and apparatus capable of improving the sensitivity of MS ⁿ analysis of the ion trap mass spectrometer can be realized.
[0067]
Note that in the embodiment described above, collision-induced dissociation to near offset voltage of the voltage of the slit electrode 22 first ion guide 21 is not performed, operation of the ion trap becomes MS ^2.
[0068]
In the above-described embodiment, the ion guide is described as an octupole. However, a multipole such as a quadrupole or a hexapole may be used. If the mass separation operation is performed in the first ion guide 21 in the previous stage of the slit electrode 22, the accuracy of ion separation can be increased.
[0069]
In addition, if a mass separation unit such as a time-of-flight mass spectrometer is arranged after the ion trap 31, the discharge from the ion trap 31 can be operated without mass separation, so the time required for one sequence Can be further shortened.
[0070]
【The invention's effect】
According to the present invention, since MS ² is performed before the ion trap, only MS ³ needs to be performed in the ion trap. Therefore, the operation time of the ion trap at MS ³ is shortened, and ions per unit time are reduced. The number of trap operations is increased, the S / N ratio is improved, and the detection sensitivity can be increased.
[0071]
Therefore, an ion trap mass spectrometry method and apparatus capable of improving the sensitivity of MS ⁿ analysis of the ion trap mass spectrometer can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a mass spectrometer according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram of a potential gradient applied to a first ion guide, a second ion guide, and a slit electrode.
FIG. 3 is an operation explanatory diagram of an ion trap mass spectrometer according to an embodiment of the present invention.
FIG. 4 is an operation explanatory diagram of an ion trap mass spectrometer in an example in which collision-induced dissociation is performed only in an ion trap, unlike the present invention.
FIG. 5 is an operation explanatory view of an ion trap mass spectrometer in another example in which collision-induced dissociation is performed only in an ion trap, unlike the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Mobile phase 2 Liquid feed pump 3 Sample injector 4 Separation column 5 Ion source 11 1st pore 12 2nd pore 21 1st ion guide 22 Slit electrode 23 2nd ion guide 31 Ion trap 32 Focus electrode 41 Ion detector 51 , 52 Vacuum chamber 61, 62 Turbo molecular pump 65 Rotary pump

Claims (1)

A sample introduction unit for introducing a sample, a sample separation unit for performing first ion separation on a component basis of the introduced sample,
An ionization unit for ionizing the separated sample;
An electrically pile-on guide section to the ion trap performs a first collision-induced dissociation of the ionized sample,
An ion trap that confines the introduced ions and performs second ion separation and second collision-induced dissociation;
A mass separation unit for separating ions by mass-to-charge ratio;
A detector for detecting mass-separated ions;
In an ion trap mass spectrometer comprising:
Upper heard on the guide portion includes a first ion guide electrode of the first voltage is applied, and the second ion guide electrode of the first voltage less than the second voltage is applied, the first An ionized sample is provided between the ion guide electrode and the second ion guide electrode and has a slit electrode to which a third voltage higher than the first voltage is applied. An ion trap mass spectrometer characterized in that the electrode passes through the slit electrode and the second ion guide electrode.

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