JP6107594B2 - Mass spectrometry method and mass spectrometer - Google Patents

Description

  The present invention relates to a mass spectrometry method using a mass spectrometer including a matrix-assisted laser desorption ionization (MALDI) ion source and an ion trap, and a mass spectrometer used in the method.

  In recent years, mass spectrometric techniques involving ion dissociation operations have been actively used for identification and structural analysis of macromolecular compounds derived from living bodies such as proteins, peptides, sugar chains, and nucleic acids. As a technique for dissociating ions, collision-induced dissociation (CID = Collision Induced Dissociation) using an ion trap or a collision cell is often used. However, depending on the type of ion source, in-source decomposition (ISD = In-Source Decay) may be used. In-source decomposition is cleavage occurring in the ionization chamber or the like simultaneously with ionization or immediately after ionization, and well-known is the cleavage of molecular ions during ionization by electron ionization (EI).

Ionization by the MALDI method is generally said to be soft ionization, and originally it is difficult to cause cleavage at the time of ionization. However, it was generated by increasing the energy at the time of ionization, for example, by increasing the intensity of laser light applied to the sample. It is known that ion cleavage is promoted. In the in-source decomposition of a MALDI ion source particularly for proteins and peptides, the cleavage of N-Cα bond of the peptide main chain is induced by hydrogen radicals generated from the matrix by laser light irradiation, mainly c-series ions and this. It is known that z-series ions that are paired with each other are generated (see Non-Patent Document 1). Using such a phenomenon, an analysis of estimating an amino acid sequence of a peptide by analyzing a mass spectrum obtained by in-source decomposition in a MALDI time-of-flight mass spectrometer has been performed.
In the following description, a mass spectrometry method using in-source decomposition in a MALDI ion source is referred to as “MALDI-ISD analysis”.

By the way, in an ion trap mass spectrometer such as a MALDI ion trap mass spectrometer or a MALDI ion trap-time-of-flight mass spectrometer, in order to improve the analysis sensitivity and mass resolution, the ion trapping mass spectrometer can be used. Cooling is often performed (see Patent Document 1, Non-Patent Document 2, etc.). When performing cooling, an inert gas such as He or Ar or a rare gas such as He or Ar or N ₂ gas (cooling gas) is introduced into the ion trap, and ions trapped in the ion trap by the action of an electric field are introduced. Collide with these gases. Since the kinetic energy possessed by the ions is lost by this collision, the free motion range of the ions is narrowed, and the ions gather near the center of the trapping space in the ion trap. As a result, for example, variations in initial positions of ions when ions are ejected from an ion trap are reduced, and variations in initial energy of ions are also reduced. This improves analytical sensitivity and mass resolution.

  However, in the cooling operation described above, ions and cooling gas collide with each other, so that unintentional ion fragmentation (fragmentation) may occur. When performing MALDI-ISD analysis in an ion trap mass spectrometer, fragment ions derived from the target compound and generated by in-source decomposition are introduced into the ion trap in addition to the molecular ion derived from the target compound in the sample. , Temporarily trapped in the ion trap. If cooling is performed at this time, molecular ions derived from the target compound may collide with the cooling gas and be cleaved. As a result, fragment ions generated by in-source decomposition and unintentional fragment ions resulting from collisions with the cooling gas are mixed in the ion trap, and the ions of fragment ions generated by in-source decomposition that are the targets of analysis There was a problem that it became difficult to belong to a series.

JP 2005-78810 A

Mitsuo Takayama, “Characteristics of In-Source Decomposition in Various Mass Spectrometry Decomposition Methods—Hydrogen-Attachment Dissociation (HAD)”, Journal of the Japan Society for Mass Spectrometry, Vol. 50, No. 6, 2002, pp.337-349 Koichi Tanaka and one other, "Trial of top-down proteomics analysis method using MALDI-QIT-TOF MSn", Shimadzu review, published on October 30, 2004, 61, No. 1, No. 2, p.3- Ten

In general, various ion peaks derived from the target compound appear in the mass spectrum obtained by MALDI-ISD analysis (hereinafter referred to as “ISD mass spectrum”) and MS ⁿ spectrum using CID. If the sequence of ions is determined even with only a part of fragment ions, that is, if fragment ions are assigned, the accuracy of peptide sequence determination and structural analysis using an analysis technique such as database search is improved. In other words, if the assignment of fragment ions observed in the ISD mass spectrum becomes difficult as described above, the identification and structural analysis of peptides and proteins become difficult, and the accuracy and reliability thereof are lowered.

  The present invention has been made in view of these problems, and the object of the present invention is from among various ion peaks observed on a mass spectrum obtained by MALDI-ISD analysis for compounds such as peptides and proteins. It is to provide a mass spectrometric method and a mass spectroscope capable of easily identifying fragment ions by in-source decomposition and improving the accuracy of peptide amino acid sequence estimation and protein identification using the results. .

  The amount of fragment ions generated by ion cleavage due to collision between ions and a cooling gas in the ion trap increases as the internal energy of the ions increases. This is because the higher the internal energy of ions, the greater the collision energy with the cooling gas. The easiest way to increase the internal energy of ions in the MALDI ion source is to increase the energy of the laser beam irradiated to the sample for ionization. In addition, ion cleavage by collision with a cooling gas is generally similar to low-energy collision-induced dissociation used in MS / MS analysis using an ion trap, and is similar to low-energy collision-induced dissociation of peptides. In addition, it has been empirically found that b-series and y-series ions are mainly generated, and as described above, c-series and z-series ions mainly generated by MALDI-ISD analysis are hardly generated.

  Based on these facts, the inventor of the present application repeated experiments on MALDI-ISD analysis. As a result, when the laser light energy is increased in the MALDI ion source, both in-source decomposition and ion cleavage due to cooling in the ion trap are promoted, but fragment ions resulting from in-source decomposition (mainly c series, It has been found that the degree of increase in the amount of (z-series ions) produced is significantly different from the degree of increase in the amount of fragment ions (mainly b-series and y-series ions) derived from collision with the cooling gas in the ion trap. It was. The inventor of the present application has reached the present invention based on such experimental findings.

That is, a mass spectrometry method according to the present invention for solving the above-mentioned problems includes a matrix-assisted laser desorption ionization (MALDI) ion source and an ion trap that temporarily holds ions, and the MALDI Mass separation provided by the ion trap or separately from the ion trap after cooling the ion trap generated by an ion source and trapped by the action of a high-frequency electric field with a predetermined cooling gas. A mass spectrometry method using a mass spectrometer that separates and detects ions according to a mass-to-charge ratio,
a) Mass spectrum acquisition step for performing mass analysis on the same sample using in-source decomposition while changing the power of laser light irradiated to the sample in a MALDI ion source in a plurality of stages, and acquiring a mass spectrum respectively;
b) Using the signal intensity of any peak observed in the plurality of mass spectra as a reference, obtain the relative intensity of other peaks in each mass spectrum, and peaks having the same mass-to-charge ratio among the plurality of mass spectra A fragment ion identification step that identifies the ion series of fragment ions corresponding to the peak by comparing the relative intensities of
It is characterized by performing.

A mass spectrometer according to the present invention is an apparatus for carrying out the mass spectrometry method according to the present invention, and is a matrix-assisted laser desorption ionization (MALDI) ion source and ions generated by the ion source. An ion trap that temporarily holds the ion trap, and after the ion generated by the MALDI ion source and trapped in the ion trap by the action of a high-frequency electric field collides with a predetermined cooling gas, In a mass spectrometer that separates and detects ions according to a mass to charge ratio by the ion trap or by a mass separator provided separately from the ion trap,
a) For the same sample, perform mass analysis using in-source decomposition while changing the power of the laser beam irradiated to the sample in multiple steps in the MALDI ion source, and control each part to acquire each mass spectrum An execution control unit;
b) Using the signal intensity of an arbitrary peak observed in a plurality of mass spectra obtained under the control of the measurement execution control unit as a reference, the relative intensity of other peaks in each mass spectrum is obtained, and a plurality of masses are obtained. A data processing unit for identifying the ion series of fragment ions corresponding to the peaks by comparing the relative intensities of the peaks having the same mass-to-charge ratio between the spectra;
It is characterized by having.

The mass spectrometer according to the present invention includes a mass spectrometer that discharges ions from the ion trap itself according to the mass-to-charge ratio and detects ions by an external ion detector, and an ion trap. And a mass spectrometer that detects ions by separating them according to the mass-to-charge ratio using a time-of-flight mass separator or a quadrupole mass filter.
The ion trap is generally a three-dimensional quadrupole ion trap, but may be a linear ion trap.

  Increasing the power of laser light applied to the sample in the MALDI ion source increases the signal intensity of c-series and z-series fragment ions mainly resulting from in-source decomposition. At the same time, the signal intensity of b-series and y-series fragment ions mainly derived from cooling in the ion trap also increases. However, as described above, the degree of increase in the signal intensity of these fragment ions is different. Therefore, in the mass spectrometry method according to the present invention, in the fragment ion identification step, each mass spectrum is based on the signal intensity of appropriate ions commonly observed in a plurality of mass spectra obtained by changing the laser beam power. The relative intensities of other peaks other than the standard are obtained. This makes it possible to compare the signal intensities between a plurality of mass spectra, and thus compares the relative intensities of peaks having the same mass-to-charge ratio among the plurality of mass spectra. Based on the result, fragment ions derived from in-source decomposition, that is, c-series ions and z-series ions are identified.

  According to the inventor's investigation, the signal intensity of the c-series and z-series fragment ions mainly derived from in-source decomposition is lower than that of the b-series and y-series fragment ions (however, in-source It is relatively high under a laser power that is higher than during normal analysis, where decomposition occurs. Therefore, in the mass spectrometry method according to the present invention, preferably, in the fragment ion identification step, the relative intensity of the peak on the mass spectrum obtained under a relatively high laser beam power is relatively low. It is preferable to search for ions having a high relative intensity ratio of peaks on the mass spectrum obtained under the laser light power, and to determine that the ions are fragment ions derived from in-source decomposition.

  More specifically, for example, a difference in relative intensity of peaks having the same mass-to-charge ratio in a plurality of mass spectra under different laser beam powers is obtained, and ions corresponding to peaks whose difference is equal to or greater than a predetermined threshold are obtained. It can be determined that it is a fragment ion derived from in-source decomposition.

  According to the mass spectrometry method and the mass spectrometer of the present invention, for example, fragment ions generated by in-source decomposition can be easily identified from mass spectra obtained by MALDI-ISD analysis for peptides and proteins. As a result, the assignment of some ion peaks in the ISD mass spectrum and the peak information can be used for analysis for protein identification or peptide amino acid sequencing. The accuracy can be further improved.

The schematic block diagram of one Example of the MALDI-IT-TOFMS system for enforcing the mass spectrometry method which concerns on this invention. The flowchart which shows an example of the characteristic analysis operation | movement in the MALDI-IT-TOFMS system of a present Example. The figure which shows an example of the ISD mass spectrum of Ang2 when changing laser beam power. The figure which shows an example of the ISD mass spectrum of Renin when changing a laser beam power. The figure which shows an example of the ISD mass spectrum (low mass to charge ratio range) of ACTH18-39 when changing laser beam power. The figure which shows an example of the ISD mass spectrum (high mass charge ratio range) of ACTH18-39 when changing laser beam power. The figure which shows the comparison result of the relative intensity | strength of the fragment ion derived from Ang2 shown in FIG. The figure which shows the comparison result of the relative intensity of the Renin origin fragment ion shown in FIG. The figure which shows the comparison result of the relative intensity | strength of the fragment ion derived from ACTH18-39 shown in FIG. The figure which shows the comparison result of the relative intensity | strength of the fragment ion derived from ACTH18-39 shown in FIG.

Hereinafter, an embodiment of a mass spectrometry method according to the present invention and a MALDI-IT-TOFMS system for carrying out the method will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of a MALDI-IT-TOFMS system according to this embodiment. First, the configuration of this system and the basic analysis operation will be described.

  In FIG. 1, the MALDI ion source 1 includes a sample stage 11 on which a sample plate 10 is placed, an extraction electrode 13, an ion focusing electrode 14, a laser irradiation unit 15, and a reflecting mirror 16.

  On the sample plate 10, a sample 12 containing a target compound and prepared using a predetermined matrix is formed. The laser beam emitted from the laser irradiation unit 15 in a pulse shape is focused on a minute region on the sample 12 through the reflecting mirror 16. The target compound is vaporized together with the matrix from the sample 12 by the energy of the laser beam, and the target compound is ionized at that time. When performing a MALDI-ISD analysis, the intensity of the laser beam is increased compared to a normal analysis (that is, an analysis without in-source decomposition), and ion cleavage is performed simultaneously with or immediately after the target compound is ionized. Promote. Various ions generated in the vicinity of the sample plate 10 are extracted by the action of an electric field formed between the extraction electrode 13 and the sample plate 10, are accelerated and converged by the ion focusing electrode 14, and are in the direction of the white arrow. Proceed to

  The ion trap 2 has a three-dimensional quadrupole configuration including an annular ring electrode 20 and a pair of end cap electrodes 21 and 22 disposed with the ring electrode 20 interposed therebetween. Various ions sent from the MALDI ion source 1 as described above are once captured by the action of the quadrupole high-frequency electric field formed inside the ion trap 2 and collide with the cooling gas supplied from the gas supply unit 4. The energy is converged by utilizing the cooling action by. Thereafter, a predetermined initial energy is applied to each ion by a DC voltage applied between the end cap electrodes 21 and 22 at a predetermined timing, and these ions are discharged from the ion trap 2 all at once to the mass analysis unit 3. Sent. In addition, it is also possible to perform the ion cleavage operation by CID by supplying CID gas from the gas supply unit 4 into the ion trap 2, causing the trapped ions to be resonantly excited and brought into contact with the CID gas. However, intentional cleavage by CID is not performed here.

  The mass analyzer 3 includes a flight space 30 in which ions fly, a reflector 31 that forms an electric field that reflects the ions, and a detector 32 that detects the ions and outputs a detection signal corresponding to the amount of ions. . Various ions discharged from the ion trap 2 and sent to the mass analyzer 3 as described above fly freely in the flight space 30, are turned back by the action of the reflected electric field formed by the reflector 31, and fly again. It reaches the detector 32 via the space 30. At the time of introduction into the mass analyzer 3, each ion has a flight speed corresponding to its mass-to-charge ratio, and ions having a smaller mass-to-charge ratio reach the detector 32 earlier.

The signal output from the detector 32 is input to the data processing unit 6. The data processing unit 6 includes functional blocks such as a spectrum data storage unit 61, a fragment ion attribution processing unit 62, and a protein / peptide identification processing unit 63, which will be described later. The control unit 5 has a function of controlling each unit in order to execute mass spectrometry on the sample 12 and a function of a user interface through the input unit 7 and the display unit 8 attached thereto. Note that at least some of the functions of the control unit 5 and the data processing unit 6 can be realized by using a computer as hardware resources and executing dedicated software installed in the computer.

In the MALDI-IT-TOFMS system of this example, an ISD mass spectrum in which a peptide or protein is a target compound and in-source decomposition is promoted in the MALDI ion source 1 and peaks derived from fragment ions generated thereby are observed ( By analyzing the pseudo MS ² spectrum), the amino acid sequence of the peptide is estimated or the protein is identified. At that time, the fragment ions generated by the in-source decomposition are assigned by performing characteristic measurement operations and data processing obtained by the measurement.

  Here, the principle of fragment ion attribution processing in the MALDI-IT-TOFMS system of the present embodiment will be described using actual measurement results.

The actual measurement conditions are as follows.
(1) Sample (target compound)
(A) Angiotensin II, human [amino acid sequence: DRVYIHPF] (hereinafter referred to as “Ang2”)
(B) N-Acetyl-Renin Substrate Tetradecapeptide, porcine [amino acid sequence: Ac-DRVYIHPFHLLVYS] (hereinafter referred to as “Renin”)
(C) Adrenocorticotropic hormone fragment 18-39, human [amino acid sequence: RPVKVYPNGAEDESAEAFPLEF] (hereinafter referred to as “ACTH18-39”)
(2) Matrix: 2,5-dihydroxybenzoic acid
(3) Mass spectrometer: MALDI quadrupole ion trap time-of-flight mass spectrometer (AXIMA-Resonance, manufactured by Shimadzu Corporation)
(4) Sample plate: 2mm stainless steel plate

  FIG. 3 shows an example of Ang2 ISD mass spectrum obtained by changing the laser light power in three stages, FIG. 4 shows an example of ISD mass spectrum of Renin, and FIG. 5 shows an example of ISD mass spectrum of ACTH18-39. As shown in FIG. FIG. 5 and FIG. 6 differ only in the mass-to-charge ratio range. The laser light power is an arbitrary unit, that is, a relative value, and has three stages of “70”, “80”, and “90”. The laser light power during normal analysis without in-source decomposition is “60” or less in arbitrary units, and the laser light power used here is a condition where in-source decomposition easily occurs. 3 to 6, the fragment ion series and fragment number corresponding to the peak are described. However, if the compound to be measured is unknown, these are naturally unknown. .

  In order to compare the intensities of peaks of the same mass-to-charge ratio appearing in ISD mass spectra having different laser light powers, the intensity values are made relative (or normalized). FIG. 7 is a graph of relative intensities obtained by standardizing the peak intensities of other fragment ions with respect to one appropriately set reference ion in each ISD mass spectrum shown in FIG. Similarly, FIG. 8 shows each ISD mass spectrum shown in FIG. 4, FIG. 9 shows each ISD mass spectrum shown in FIG. 5, and FIG. 10 shows each ISD mass spectrum shown in FIG. It is a graph of the relative intensity | strength calculated | required by normalizing the peak intensity of another fragment ion with respect to one reference | standard ion. The reference ions can be appropriately determined among the commonly observed ions. In the examples of FIGS. 3 and 7, y7 ions, in the examples of FIGS. 4 and 8, y13 ions, FIGS. 5, 6, and 9 are used. In the example of FIG. 10, b13 ions are used as reference ions.

  7 to 10, the broken line corresponding to each laser beam power is the relative intensity with respect to the intensity of the reference ion. Therefore, by comparing the relative intensity with respect to the same ion under different laser beam powers, The laser light power dependency becomes clear. That is, in the graphs shown in FIGS. 7 to 10, any (three kinds) of compounds has a lower laser beam power than the fragment ion intensity obtained under a higher laser beam power in each fragment ion. It can be seen that there are ions in which the fragment ion intensity obtained below is relatively significantly higher. It can be seen that the majority of these ions are c-series ions, that is, fragment ions that are hardly generated in the course of cooling and are mainly generated by in-source decomposition. On the graph, these ions are indicated by a downward bold line arrow.

  From the above, the ISD mass spectrum is obtained by changing the laser light power stepwise within the range of the laser light power that promotes in-source decomposition, and the intensities of the same fragment ions in the obtained plurality of ISD mass spectra. It can be concluded that fragment ions (here, c-series ions) that can be estimated to be derived from ISD can be distinguished from among a large number of detected fragment ions. In the MALDI-IT-TOFMS of this example, fragment ions by in-source decomposition are assigned using the above principle. A specific analysis operation for this will be described with reference to the flowchart of FIG.

  When the analysis is started, the control unit 5 controls the MALDI ion source 1 including the laser irradiation unit 15, the ion trap 2, the gas supply unit 4, and the mass analysis unit 3, and the same prepared on the sample plate 10. A MALDI-ISD analysis in which the laser beam power for ionization is switched to a plurality of stages is performed on the sample 12 (step S1). In the data processing unit 6, ISD mass spectrum data is obtained by converting the flight time of the flight time spectrum data obtained by sequentially converting the detection signals into digital data into the mass-to-charge ratio, and this is stored in the data storage unit 61. Store. For example, the laser light power may be switched in two stages of the laser light powers “70” and “90” shown in the actual measurement example, but the laser light power may be switched in more stages.

  If the ISD mass spectrum data under a plurality of stages of laser beam power is obtained, the fragment ion attribution processing unit 62 reads the ISD mass spectrum data from the spectrum data storage unit 61, and the ISD mass spectrum for different laser beam powers. Is created (step S2). Next, the fragment ion attribution processing unit 62 performs peak detection for each ISD mass spectrum and collects the mass-to-charge ratio and signal intensity of each detected peak as peak information (step S3).

  Subsequently, one peak is selected according to a predetermined criterion from among peaks commonly present in a plurality of ISD mass spectra (peaks having the same mass-to-charge ratio, strictly speaking, falling within a predetermined allowable mass error range). Then, an ion corresponding to the peak is set as a reference ion. Then, for each ISD mass spectrum, the intensity of the peak other than the reference ion is normalized with respect to the intensity of the reference ion to obtain the relative intensity (step S4). This corresponds to an operation for obtaining the graph shown in FIG. 7 from the ISD mass spectrum shown in FIG. 3, for example. However, as a matter of course, the sequence and fragment number of each fragment ion are unknown at this time, and the relative intensity of the peak at a certain mass-to-charge ratio is simply known in each ISD mass spectrum.

  The fragment ion assignment processing unit 62 is based on a graph of relative intensity with respect to the ISD mass spectrum obtained under different laser light powers, and the relative ratio of peaks having the same mass-to-charge ratio, strictly speaking, within a predetermined allowable mass error range. The intensities are sequentially compared (step S5). As described above, in the c-series ions, the relative intensity obtained under the condition where the laser light power is low tends to be larger than the relative intensity obtained under the condition where the laser light power is high. Therefore, for example, it is determined whether or not the difference in relative intensity of ions having the same mass-to-charge ratio is greater than or equal to a predetermined threshold, and it is determined that ions that are greater than or equal to the predetermined threshold are c-series ions. However, as is apparent from the results of the actual measurement example, the c-sequence ions cannot be identified without any error. Therefore, even when the c-sequence ions are automatically extracted, the process and processing For example, the result may be displayed on the display unit 8 so that the analyst can check the result and make corrections as appropriate.

  In any case, since c-series fragment ions can be identified with a high probability, the identified fragment ions are assigned as c-series ions generated by in-source decomposition (step S6). In addition, other fragment ions belong to ions of a series that is not at least the c series. Thus, the assignment of some peaks in the peak information obtained from the ISD mass spectrum is determined.

  Peak information including such attribution information is sent to the protein / peptide identification processing unit 63. The protein / peptide identification processing unit 63 performs, for example, a database search or a de novo sequence search based on such peak information, thereby estimating, for example, the amino acid sequence of the peptide or identifying the protein (step S7). Regardless of what algorithm is used in the protein / peptide identification processing unit 63, if it is completely unknown what kind of ions are derived from many peaks, the accuracy of amino acid sequence estimation and protein identification Becomes lower. On the other hand, in the system of the present embodiment, since at least the attribution information on the c-series ions is provided to the protein / peptide identification processing unit 63, it is possible to estimate the amino acid sequence and perform protein identification using this as one clue, Therefore, the accuracy of amino acid sequence estimation and protein identification can be improved.

  The mass spectrometer according to the above embodiment was provided with a time-of-flight mass separator in addition to the ion trap, but the ion trap itself was sequentially discharged from the trap while being separated according to the mass-to-charge ratio. The ion may be detected by an ion detector disposed outside the trap. That is, in the mass spectrometer according to the present invention, the configuration other than the MALDI ion source and the ion trap can be changed as appropriate. The ion trap may be a linear ion trap instead of a three-dimensional quadrupole ion trap.

  Moreover, since the said Example is only an example of this invention, even if it corrects, changes, an addition etc. suitably in the range of the meaning of this invention in points other than the above-mentioned description, it is included in the claim of this application. Is clear.

DESCRIPTION OF SYMBOLS 1 ... MALDI ion source 10 ... Sample plate 11 ... Sample stage 12 ... Sample 13 ... Extraction electrode 14 ... Acceleration electrode 15 ... Laser irradiation part 16 ... Reflector 2 ... Ion trap 20 ... Ring electrode 21, 22 ... End cap electrode 3 ... Mass analysis section 30 ... Flight space 31 ... Reflector 32 ... Detector 4 ... Gas supply section 5 ... Control section 6 ... Data processing section 61 ... Spectral data storage section 62 ... Fragment ion attribution processing section 63 ... Protein / peptide identification processing section 7 ... Input unit 8 ... Display unit

Claims (4)

Ions having a matrix-assisted laser desorption ionization (MALDI) ion source and an ion trap that temporarily holds ions, and are generated by the MALDI ion source and trapped by the action of a high-frequency electric field inside the ion trap A mass spectrometer that separates and detects ions according to the mass-to-charge ratio by the ion trap or by a mass separator provided separately from the ion trap after cooling with a predetermined cooling gas . A mass spectrometry method,
a) Mass spectrum acquisition step for performing mass analysis on the same sample using in-source decomposition while changing the power of laser light irradiated to the sample in a MALDI ion source in a plurality of stages, and acquiring a mass spectrum respectively;
b) Using the signal intensity of any peak observed in the plurality of mass spectra as a reference, obtain the relative intensity of other peaks in each mass spectrum, and peaks having the same mass-to-charge ratio among the plurality of mass spectra A fragment ion identification step that identifies the ion series of fragment ions corresponding to the peak by comparing the relative intensities of
The mass spectrometry method characterized by performing.
The mass spectrometric method according to claim 1,
In the fragment ion identification step, the peak on the mass spectrum obtained under a relatively low laser light power compared to the relative intensity of the peak on the mass spectrum obtained under a relatively high laser light power. A mass spectrometric method characterized by searching for an ion having a higher relative intensity ratio and determining that the ion is a fragment ion derived from in-source decomposition. A matrix-assisted laser desorption ionization (MALDI) ion source and an ion trap that temporarily holds ions generated by the ion source, and a high-frequency electric field generated by the MALDI ion source inside the ion trap. After the ions trapped by the action of the above are collided with a predetermined cooling gas and cooled , the ions are separated according to the mass-to-charge ratio by the ion trap or by the mass separation unit provided separately from the ion trap. In the mass spectrometer to detect
a) For the same sample, perform mass analysis using in-source decomposition while changing the power of the laser beam irradiated to the sample in multiple steps in the MALDI ion source, and control each part to acquire each mass spectrum An execution control unit;
b) Using the signal intensity of an arbitrary peak observed in a plurality of mass spectra obtained under the control of the measurement execution control unit as a reference, the relative intensity of other peaks in each mass spectrum is obtained, and a plurality of masses are obtained. A data processing unit for identifying the ion series of fragment ions corresponding to the peaks by comparing the relative intensities of the peaks having the same mass-to-charge ratio between the spectra;
A mass spectrometer comprising:
The mass spectrometer according to claim 3,
The data processing unit is configured to detect a peak on a mass spectrum obtained under a relatively low laser light power as compared to a relative intensity of the peak on a mass spectrum obtained under a relatively high laser light power. A mass spectrometer characterized by searching for an ion having a high relative intensity ratio and determining that the ion is a fragment ion derived from in-source decomposition.

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