JP2011216494A - Mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of a signal intensity of MS/MS spectrum due to a secondary dissociation of primary fragment ions generated by photodissociation.SOLUTION: An exciting laser beam for bringing about photodissociation is irradiated on a position away from a center of a capturing region A in an ion trap 1 and simultaneously an excitation signal for exciting precursor ions selectively is impressed on end cap electrodes 12, 13. Due to an action of an excited electric field thus formed, the precursor ions vibrate greatly and go out of the capturing region A and cross an excitation light irradiating region B and thereby dissociation is brought about when irradiated with the exciting laser beam. Meanwhile, since fragment ions generated by the dissociation receive hardly any action of the excitation electric field and remain in the capturing region A and do not enter the excitation light irradiating region B. As a result, the fragment ions hardly receive the exciting laser beam and a secondary dissociation is hardly caused.

Description

  The present invention relates to a mass spectrometer equipped with an ion trap that traps ions by an electric field, and more particularly to a mass spectrometer that uses photodissociation to cleave ions trapped in the ion trap.

  In mass spectrometry, an ion having a specific mass is selected as a precursor ion, followed by promoting the cleavage (fragmentation) of the precursor ion, and mass analysis of various product ions (fragment ions) generated thereby. Methods of analysis (also called tandem analysis) are well known. One of the most widely used methods for cleaving precursor ions is Collision Induced Dissociation (CID) in which the precursor ions collide with gas atoms (or molecules).

On the other hand, there is also a method called photodissociation in which ions are cleaved by irradiating the ions with excitation light to increase internal energy. Photodissociation involves irradiating an ion with ultraviolet light as excitation light, irradiating the ion with strong infrared light as the excitation light, or irradiating the ion with strong infrared light as excitation light to excite the electronic state of the ion and causing cleavage. Infrared multiphoton dissociation (IRMPD), which promotes cleavage by absorbing the photon in the ion and exciting the vibrational state of the ion, is known (see Non-Patent Document 1, etc.). In a mass spectrometer using a three-dimensional quadrupole ion trap or the like, ions can be confined and held in a relatively narrow space, so that the same ion can be irradiated with excitation light for a relatively long time. Easy. Therefore, often the ion trap mass spectrometer MS / MS analysis in the apparatus (or multi-stage MS ⁿ analysis cause cleavage), the photodissociation (primarily infrared multiphoton dissociation) is utilized.

  When collision-induced dissociation is performed inside an ion trap, the frequency of the resonance excitation signal in the ion trap is generally matched to the mass of the precursor ion for analysis, and only the precursor ion is selectively excited to collide with gas atom molecules. This promotes cleavage (primary dissociation). In this case, the fragment ions having a smaller mass generated by the primary dissociation are not excited and do not collide with gas atom molecules vigorously, and the secondary dissociation phenomenon in which the fragment ions are further cleaved does not occur.

  On the other hand, when photodissociation is performed inside the ion trap, fragment ions generated by the dissociation (primary dissociation) of precursor ions by light absorption are irradiated with excitation light in the same manner as the precursor ions. Therefore, secondary dissociation in which fragment ions further photodissociate easily occurs. When such secondary dissociation occurs, the signal intensity of fragment ions (primary fragment ions) due to primary dissociation decreases on the MS / MS spectrum as shown in FIG. There is a problem that it drops significantly.

L. Sleno and one other, "Ion activation methods for tandem mass spectrometry", Journal of Mass Spectrometry ), 39 (2004), pp.1091-1112

  The present invention has been made in order to solve the above-mentioned problems. The object of the present invention is to prevent precursor ion while suppressing secondary dissociation as much as possible when photodissociation is performed inside an ion trap that traps ions. An object of the present invention is to provide a mass spectrometer capable of improving the S / N of an MS / MS spectrum by improving the efficiency of primary dissociation.

In order to solve the above-mentioned problems, the present invention includes an ion trap that traps ions in a space surrounded by a plurality of electrodes, dissociates the ions in the ion trap, and mass analysis is performed on the ions generated thereby. In the mass spectrometer to
a) excitation light irradiation means for irradiating excitation light for causing photodissociation in a region deviating from the center of the trapping region of the ion trap;
b) A desired precursor ion is selectively resonantly oscillated in the ion trap to reach the irradiation region of the excitation light, and fragment ions generated by photodissociation have a predetermined frequency component so as not to oscillate resonantly. Excitation signal generating means for generating an excitation signal and applying it to at least one electrode constituting the ion trap;
It is characterized by having.

  In the mass spectrometer according to the present invention, first, ions for analysis are captured as precursor ions in an ion trap. The selection of precursor ions may be performed either inside or outside the ion trap. In any case, the precursor ions are concentrated near the center of the trapping region of the ion trap. The excitation light irradiating means irradiates excitation light to a part of the area around the center of the trapping region, that is, while irradiating the excitation light to the excitation signal generating means. An excitation signal having a frequency component to be excited is generated and applied to at least one electrode constituting the ion trap. For example, when the ion trap is a three-dimensional quadrupole ion trap composed of one ring electrode and two end cap electrodes, an excitation signal may be applied between both end cap electrodes.

  Since the precursor ions are excited by the action of an electric field formed inside the ion trap by the excitation signal, the precursor ions do not fall within the center of the trapping region and enter the irradiation region of the excitation light outside the region. Then, the precursor ion is irradiated with excitation light and cleaved by photodissociation (primary dissociation) to generate fragment ions. On the other hand, since the generated fragment ions are not excited by the action of the excitation electric field, they are concentrated in the vicinity of the center of the trapping region under the influence of the trapping electric field. Therefore, fragment ions are difficult to be irradiated with excitation light, and fragment ions can be prevented from secondary dissociation due to photodissociation.

  As a preferred aspect of the present invention, the excitation light irradiation means may be configured to irradiate excitation light so as to surround the center of the trapping region of the ion trap. Specifically, the irradiation position of the excitation light may be set so that the irradiation area of the excitation light has an annular shape and the central portion where the excitation light does not hit is the center of the capture area.

  According to this configuration, the probability that the selectively excited precursor ions are irradiated with the excitation light when they deviate from the center of the trapping region is increased, and the dissociation efficiency of the precursor ions can be improved.

  In the mass spectrometer according to the present invention, the ion trap may be, for example, a three-dimensional quadrupole ion trap including one ring electrode and two end cap electrodes, or a plurality of rods whose inner surface is a curved surface. In any case, the size of the region where ions exist with a high probability near the center of the trapping region of the ion trap is approximately the ratio to the distance between the electrodes. It has been decided.

  Therefore, in order to prevent the excitation light from being applied to the fragment ions generated by the primary dissociation, in the case of a three-dimensional quadrupole ion trap, the excitation light irradiation region by the excitation light irradiation means is an ion trap. The distance between the end cap electrodes may be 2.5% or more away from the center of the capture region. Further, in the case of a linear ion trap, the excitation light irradiation region by the excitation light irradiation means is separated from the center of the trapping region of the ion trap by 2.5% or more of the interval between the curved surfaces of the two opposing rod electrodes. Good.

  According to the mass spectrometer of the present invention, it is possible to prevent fragment ions generated by the cleavage of the precursor ion by photodissociation upon irradiation with excitation light from being further dissociated due to secondary dissociation. . Therefore, when the MS / MS spectrum is created, the signal intensity of the peak of the fragment ion does not have to be lowered, and a high S / N can be ensured.

1 is a schematic configuration diagram of an ion trap time-of-flight mass spectrometer according to a reference example related to the present invention. In the mass spectrometer of the above reference example, a schematic diagram (a) spatially showing the relationship between the ion trapping region and the excitation light irradiation region in the ion trap, and the ion trapping region and excitation based on the existence probability of the ion The figure which shows the relationship with a light irradiation area | region (b). The figure which shows an example of the frequency characteristic of an excitation signal in the mass spectrometer of the said reference example. The figure which shows the result of having measured the peak intensity change of the precursor ion at the time of changing the irradiation time of infrared laser light as excitation laser light, and four types of fragment ions. 1 is a schematic configuration diagram of an ion trap time-of-flight mass spectrometer according to an embodiment of the present invention. Schematic which shows spatially the relationship between the ion capture | acquisition area | region and excitation light irradiation area | region in an ion trap in the mass spectrometer of the said Example. The schematic block diagram of the ion trap of the mass spectrometer by the other Example of this invention. The schematic block diagram of the ion trap of the mass spectrometer by the other Example of this invention. The figure for demonstrating the fall of the signal strength by secondary dissociation.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an embodiment of a mass spectrometer according to the present invention, a reference example of a mass spectrometer that is not included in the present invention but is related to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an ion trap time-of-flight mass spectrometer (IT-TOFMS) according to a reference example.
Inside a vacuum chamber (not shown) to be evacuated, an annular ring electrode 11 whose inner surface has a rotating one-leaf hyperboloid shape is opposed to and sandwiched between them (in FIG. 1, left and right). The three-dimensional quadrupole ion trap 1 is provided, which is composed of a pair of end cap electrodes 12 and 13 whose inner surface has a rotating two-leaf hyperboloid shape. A trapping region A for trapping ions by a trapping electric field is formed in a space surrounded by these electrodes 11, 12, and 23.

  An ion source 2 made of, for example, MALDI or the like is disposed outside the entrance 14 formed in the entrance end cap electrode 12 of the ion trap 1, while it is provided in the exit end cap electrode 13. A time-of-flight mass spectrometer 3 including a flight space 4 and an ion detector 5 for separating ions according to mass (strictly, mass to charge ratio m / z) is disposed outside the emission port 15. ing. However, the ion source 2 is not limited to MALDI, and can be replaced with various known forms of ion sources. On the other hand, a mass spectrometer of another form may be used instead of the time-of-flight mass spectrometer 3, and the ion trap 1 itself is used as a mass analyzer and only the ion detector is arranged outside the emission port 15. You can also.

  A laser irradiation hole 16 is formed in the center of the ring electrode 11 along the axis (R axis) direction of the ring electrode 11, and laser as excitation light emitted from the excitation laser irradiation source 22 through the laser irradiation hole 16. Light is irradiated so as to pass through the center of the ion trap 1 (the center of the trapping region A). In addition, a buffer gas is supplied from the gas introduction unit 23 into the ion trap 1.

  A high frequency voltage generator 20 is connected to the ring electrode 11, and an excitation signal generator 21 is connected to both end cap electrodes 12 and 13. The high frequency voltage generator 20 and the excitation signal generator 21 are controlled by a control signal supplied from the controller 24 so as to generate an alternating voltage having a predetermined frequency and a predetermined amplitude, respectively. However, a DC voltage may be superimposed on the AC voltage and applied as necessary. The control unit 24 includes a CPU, a ROM, a RAM, and the like, and controls the high-frequency voltage generation unit 20 and the excitation signal generation unit 21 according to a preset control program, as well as the ion source 2 and the excitation laser irradiation source. 22, the operation of the gas introduction unit 23 and the like are also controlled.

  In this IT-TOFMS, an operation when acquiring an MS / MS spectrum of ions having a specific mass will be described.

  First, under the control of the control unit 24, a buffer gas such as He is introduced from the gas introduction unit 23 into the ion trap 1 in a pulsed manner, and a predetermined high frequency voltage is applied to the ring electrode 11 from the high frequency voltage generation unit 20. By applying this, a quadrupole electric field for trapping ions is formed in the space inside the ion trap 1. In this state, when various ions generated from the sample to be analyzed in the ion source 2 are introduced into the ion trap 1 through the incident port 14, the ions collide with the buffer gas and lose kinetic energy, that is, are cooled, It is trapped by the quadrupole electric field and gathers near the center of the trapping region A.

  After these various ions are trapped in the trapping region A in the ion trap 1, an excitation signal is generated so as to greatly excite ions other than the precursor ions in order to leave only the desired precursor ions in the ion trap 1. It is generated by the unit 21 and applied to the end cap electrodes 12 and 13. Thereby, undesired ions other than the target precursor ion are discharged to the outside of the ion trap 1 through the entrance port 14 and the exit port 15.

  After selecting the precursor ions in this way, in order to photodissociate the ions, the excitation laser irradiation source 22 is driven, and the excitation laser light is emitted to the center of the trapping region A (excitation light irradiation region B) in the ion trap 1. Irradiate. At the same time, the excitation signal generator 21 generates an excitation signal having a frequency component that does not excite the precursor ions but excites the fragment ions generated by the primary dissociation of the precursor ions. 12 and 13. This excitation signal will be specifically described later.

  2A is a schematic diagram spatially showing the relationship between the ion trapping region A and the excitation light irradiation region B in the ion trap, and FIG. 2B is an ion trapping region based on the existence probability of the ions. It is a figure which shows the relationship between A and the excitation light irradiation area | region B. FIG. As shown in FIG. 2 (b), most of the unexcited ions are present in the trapping region A, particularly at the center with a high probability. Since this region is irradiated with the excitation laser light, the precursor ions that are not excited are efficiently irradiated with the laser light and photodissociation is promoted. As a result, the precursor ions are cleaved and fragment ions having a smaller mass are generated.

  Although fragment ions are also trapped by the trapping electric field, they begin to oscillate greatly in the Z-axis direction under the influence of the electric field formed by the excitation signal. Therefore, as shown in FIG. 2 (a), the fragment ions have a longer time outside the excitation light irradiation region B, and secondary dissociation due to photodissociation hardly occurs. That is, while the precursor ions are photodissociated with high efficiency, the primary fragment ions generated thereby can be prevented from further photodissociating.

  However, since photo-dissociation of the precursor ions occurs in the excitation light irradiation region, secondary dissociation may occur if it takes a long time for the generated fragment ions to vibrate with a large amplitude so as to deviate from the excitation light irradiation region. is there. The photodissociation reaction rate differs depending on the ion species, and secondary dissociation is likely to occur particularly in fragment ions having a high reaction rate. Therefore, in general, when irradiating the excitation laser light to promote photodissociation, it is desirable to keep the inside of the ion trap 1 in a high vacuum state, but intentionally suppressing secondary dissociation of fragment ions. In addition, a small amount of buffer gas may be introduced into the ion trap 1 when the laser beam is irradiated.

  When a buffer gas is introduced into the ion trap 1, ions whose photons are absorbed and whose internal energy is increased collide with the buffer gas, and the relaxation of the excited state is likely to occur, so that the photodissociation reaction rate is reduced. Therefore, although the efficiency of primary dissociation of the precursor ion itself decreases, secondary dissociation of the primary fragment ions is further suppressed. Such an effect is exhibited even by ultraviolet photodissociation, but is particularly effective because it is more prominent in infrared multiphoton dissociation.

  After applying photodissociation for a predetermined time as described above to cleave the precursor ions, a voltage is applied to the end cap electrodes 12 and 13 to discharge the fragment ions trapped in the ion trap 1. Initial kinetic energy is applied, and the kinetic energy is emitted from the emission port 15 and introduced into the time-of-flight mass spectrometer 3 for mass analysis. Then, an MS / MS spectrum is created by processing a detection signal from the ion detector 5 with a data processing unit (not shown).

  The excitation signal applied to the end cap electrodes 12 and 13 at the time of photodissociation can be as follows, for example. When the mass of a fragment ion generated by cleavage of a precursor ion is known in advance, a sinusoidal signal having only a frequency component corresponding to the resonance frequency of the fragment ion is excited so as to selectively excite only the fragment ion. It may be a signal. For example, when there is one kind of fragment ion, as shown in FIG. 3A, a sine wave signal (or a rectangular wave signal or the like) having a single frequency component may be used as an excitation signal, and a plurality of fragment ions may be used. In the case of a seed, it is only necessary to combine sinusoidal signals having different single frequencies into an excitation signal.

  On the other hand, when the mass of fragment ions is unknown or the number is large, as shown in FIG. 3B, the frequency component corresponding to the resonance frequency of the precursor ion (actually, a predetermined frequency width above and below it). A broadband signal that does not have () may be used as the excitation signal. Generation of such a broadband signal can be performed using a known method disclosed in, for example, Japanese Patent No. 3470671.

Next, the results of experiments conducted to verify the effects of the mass spectrometer according to the above reference example will be described.
In this experiment, reserpine (molecular weight 608) was used as a sample, and an ESI (electrospray) ion source was used as an ion source. The proton-added ions (m / z 609) generated by this ion source are left as precursor ions in the ion trap, and are irradiated with infrared laser light as excitation laser light to cause infrared multiphoton dissociation. It is known that when reserpine is cleaved by collision-induced dissociation, fragment ions having mass-to-charge ratios m / z of 236, 397, and 448 are generated. In addition, in infrared multiphoton dissociation, a peak is also observed at m / z363.

  Fig. 4 shows the results of measuring peak intensity changes of precursor ions (m / z 609) and four types of fragment ions (m / z 236, 363, 397, 448) when the irradiation time of infrared laser light is changed. (A) is a case where there is no excitation signal at the time of infrared multiphoton dissociation, that is, the case of the conventional method. As the laser irradiation time is increased, the internal energy of the precursor ion increases accordingly, and infrared multiphoton dissociation starts to occur, so that the peak intensity decreases. Contrary to this decrease, the peak intensity of fragment ions (m / z 236, 397, 448) generated by the primary dissociation increases in the laser irradiation time in a certain range or less, but further laser irradiation time. When the length is increased, the peak intensity of the primary fragment ions decreases due to the effect of secondary dissociation. On the other hand, it can be seen that the peak intensity of the fragment ion of m / z 363 is increased in place of the peak intensity of the other fragment ions after decreasing. Therefore, it can be assumed that this is a secondary fragment ion generated by secondary dissociation.

  In order to maximize the peak intensity of fragment ions due to primary dissociation, it can be seen that in this example, the laser irradiation time needs to be about 8 ms. However, at this time, about half of the precursor ions remain, and the dissociation efficiency of the precursor ions is not so high.

  In FIG. 4B, infrared laser light was irradiated while applying a sine wave signal having a frequency of 74 kHz between the end cap electrodes as an excitation signal so that fragment ions having a mass to charge ratio of m / z 448 were selectively excited. Is the result of the case. Changes in the peak intensity of fragment ions (m / z 236, 397) other than m / z 448 can be regarded as within the range of signal intensity fluctuation, and are the same as those in FIG. On the other hand, since fragment ions of m / z 448 are selectively excited and deviate from the infrared irradiation region, they are not easily affected by secondary dissociation. Therefore, the peak intensity increases almost monotonously even when the laser irradiation time is increased, and intensity saturation is observed when the laser irradiation time is longer than 10 ms. Therefore, it can be said that the peak intensity of the fragment ion at m / z448 does not decrease due to secondary dissociation.

  In FIG. 4C, infrared laser light was irradiated while applying a sine wave signal having a frequency of 149 kHz as an excitation signal between the end cap electrodes so that fragment ions having a mass to charge ratio of m / z 236 were selectively excited. Is the result of the case. In this case, it can be seen that only the fragment ion of m / z 236 is not affected by the secondary dissociation, and the signal intensity monotonously increases even when the laser irradiation time is increased.

  From the above results, it can be seen that fragment ions selectively excited at the time of infrared multiphoton dissociation are not affected by secondary dissociation and can secure a high peak intensity. In this experiment, in order to show the principle effect more clearly, a single frequency sine wave signal is applied to the end cap electrode as an excitation signal to suppress the secondary dissociation of a specific fragment ion. However, in order to suppress the influence of secondary dissociation for a plurality of or a large number of fragment ions and increase the signal intensity, a broadband signal as described above (with a broadband discrete frequency with the resonance frequency component of the precursor ion removed). It is clear that the composite waveform) may be applied to the end cap electrode as an excitation signal.

Next, an ion trap time-of-flight mass spectrometer according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 5 is a schematic configuration diagram of an ion trap time-of-flight mass spectrometer (IT-TOFMS) according to this embodiment. Constituent elements that are the same as or correspond to those in the reference example are given the same reference numerals.

  In this embodiment, one of the fundamental differences from the above reference example is that the excitation laser light is not irradiated at the center of the trapping region A of the ion trap 1 but at a position intentionally removed from the laser. The irradiation hole 17 is provided at a position shifted from the central axis of the ring electrode 11. The excitation signal generator 25 selectively excites a target precursor ion between the end cap electrodes 12 and 13 (no fragment ions are excited) when photodissociation is caused by laser light irradiation. An excitation signal having a frequency component is applied. In this case, since the excitation signal may be a single frequency sine wave signal or rectangular wave signal, the generation of the excitation signal is easier than in the case of the above reference example.

  FIG. 6 is a schematic diagram spatially showing the relationship between the ion trapping region A and the excitation light irradiation region B in the ion trap. When the excitation signal is applied to the end cap electrodes 12 and 13, the precursor ions vibrate greatly in the Z-axis direction due to the influence of the excitation electric field formed in the ion trap 1. If there is no excitation signal, the precursor ion does not enter the excitation light irradiation region B. However, when excited, the precursor ion crosses the excitation light irradiation region B and absorbs photons during that time, and eventually causes photodissociation. As a result, fragment ions are generated. Such fragment ions are not affected by the excitation electric field but do not vibrate greatly although they are affected by the trapped electric field due to the high-frequency voltage applied to the ring electrode 11. Therefore, fragment ions gather near the center of the trapping region A of the ion trap 1. That is, since the fragment ions deviate from the excitation light irradiation region B and are not irradiated with the excitation laser light, secondary dissociation hardly occurs. Therefore, the amount of primary fragment ions increases as the laser irradiation time is lengthened, and the S / N of the MS / MS spectrum can be increased.

  According to the simulation calculation by the present inventors, when the distance between the end cap electrodes 12 and 13 is 20 mm, the size of the spread of the ion cloud sufficiently cooled by the collision with the buffer gas is from the center of the ion trap 1. It was found that the range was about ± 0.5 mm or less. Therefore, by separating the irradiation position of the excitation laser light from the central portion of the ion trap 1 by 0.5 mm or more, it is possible to efficiently avoid the secondary dissociation due to the excitation laser light hitting the fragment ions. Since it is considered that the same model is established when the sizes of the ion trap 1 are different, the excitation light irradiation region B is separated from the center of the ion trap 1 by 2.5% or more of the interval between the end cap electrodes. The effect of suppressing secondary dissociation can be sufficiently exhibited.

  However, in the case of the configuration shown in FIGS. 5 and 6, it is difficult to sufficiently increase the time during which the precursor ions oscillating with a large amplitude are in the excitation light irradiation region B. If the laser irradiation time is not lengthened, the dissociation efficiency is increased. Does not go up. Therefore, in order to ensure that the excited precursor ions enter the excitation light irradiation region B for a longer time, the configuration of the ion trap 1 may be modified as shown in FIG. That is, in this configuration, the excitation laser irradiation source 26 emits laser light whose cross-sectional shape in the irradiation range is an annular shape, and passes through the laser irradiation hole 18 provided in the ring electrode 11 in a large cylindrical shape, for example. In the trap 1, an excitation light irradiation region B having a shape in which the center is a non-irradiation region and the periphery surrounding it is an irradiation region is formed. Such a specially shaped laser beam can be generated by a method as disclosed in Japanese Utility Model Laid-Open No. 62-47959, for example.

  In this configuration, since the excitation light irradiation region B is widened, the opportunity for the precursor ions that are greatly oscillated by the excitation electric field to be irradiated with the excitation laser light is increased. Therefore, the precursor ion dissociation efficiency is improved accordingly. On the other hand, since the excitation laser light does not strike the fragment ions gathered near the center of the capture region A, secondary dissociation can be prevented.

  In the above embodiment, the excitation laser beam is irradiated into the ion trap 1 through the laser irradiation holes 16, 17, and 18 formed in the ring electrode 11. However, as shown in FIG. The excitation laser beam may be irradiated from an oblique direction through a gap between the cap electrode 12 (or 13). In this case, since it is not necessary to provide a laser irradiation hole in the ring electrode 11, the configuration is simple, and since the disturbance of the trapping electric field due to the provision of the laser irradiation hole in the ring electrode 11 does not occur, ion trapping efficiency is increased. Can do.

  The above-described embodiment is an example of the present invention, and it is a matter of course that changes, modifications, and additions within the scope of the present invention are included in the scope of the claims of the present application. For example, in the above embodiment, a three-dimensional quadrupole ion trap is used as the ion trap. For example, four (or more) rod electrodes whose inner surfaces are hyperboloids or cylindrical surfaces are arranged in parallel. The present invention can also be applied to a linear ion trap that forms a trapping region in a space surrounded by rod electrodes.

DESCRIPTION OF SYMBOLS 1 ... Ion trap 11 ... Ring electrode 12, 13 ... End cap electrode 14 ... Entrance 15 ... Outlet 16, 17, 18 ... Laser irradiation hole 2 ... Ion source 20 ... High frequency voltage generator 21, 25 ... Excitation signal generator 22, 26 ... Excitation laser irradiation source 23 ... Gas introduction part 24 ... Control part 3 ... Time-of-flight mass spectrometer 4 ... Flight space 5 ... Ion detector

Claims (4)

In a mass spectrometer that includes an ion trap that captures ions in a space surrounded by a plurality of electrodes, dissociates the ions in the ion trap, and mass-analyzes the ions generated thereby.
a) excitation light irradiation means for irradiating excitation light for causing photodissociation in a region deviating from the center of the trapping region of the ion trap;
b) A desired precursor ion is selectively resonantly oscillated in the ion trap to reach the irradiation region of the excitation light, and fragment ions generated by photodissociation have a predetermined frequency component so as not to oscillate resonantly. Excitation signal generating means for generating an excitation signal and applying it to at least one electrode constituting the ion trap;
A mass spectrometer comprising:   The mass spectrometer according to claim 1, wherein the excitation light irradiation unit irradiates excitation light so as to surround a center of a capture region of the ion trap.   The ion trap is a three-dimensional quadrupole ion trap composed of one ring electrode and two end cap electrodes, and the excitation light irradiation region by the excitation light irradiation means is the center of the trapping region of the ion trap. The mass spectrometer according to claim 1, wherein the distance between the two end cap electrodes is at least 2.5%.   The ion trap is a linear ion trap in which a plurality of rod electrodes whose inner surfaces are curved are arranged in parallel, and the excitation light irradiation area by the excitation light irradiation means is two opposite from the center of the trapping area of the ion trap. The mass spectrometer according to claim 1, wherein the distance between the inner curved surfaces of the rod electrodes is 2.5% or more apart.

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