JP7816004B2 - Mass spectrometry method and mass spectrometry program - Google Patents

Description

The present invention relates to a mass spectrometry method and a mass spectrometry program that causes a computer to execute the method.

In mass spectrometry, molecules (sample molecules) from a gaseous or liquid sample are generally ionized, and then the ions are separated and detected using electrical and magnetic forces according to their mass-to-charge ratio (m/z), which is determined by their mass and charge, to obtain a mass spectrum that shows the relationship between m/z and detection intensity. Various methods are used to ionize molecules, including electron ionization (EI) and chemical ionization (CI).

EI is a method for ionizing sample molecules by colliding them with thermoelectrons emitted from a heated filament. In this method, electrons from the sample molecules are knocked out, generating ions with approximately the same mass as the sample molecules. In many cases, fragmentation also occurs, producing fragment ions with masses smaller than the sample molecules. Because the types of fragment ions generated depend on the type of sample molecule, the detected fragment ions provide useful information for identifying the type of sample molecule from among multiple candidate molecules with the same molecular weight. However, mass spectra obtained with EI contain a mixture of peaks due to the sample molecule (which has been ionized without fragmentation) and peaks due to fragment ions, making it difficult to identify the peaks due to the sample molecules. In particular, sample molecules that are prone to fragmentation may be fragmented by the thermoelectron collisions. In such cases, it is difficult to determine the molecular weight of the sample molecule from the peak detection results, and ultimately, it is also difficult to identify the type of sample molecule.

In contrast, CI generates reactant gas ions by colliding thermal electrons with molecules of a reactant gas separate from the sample molecules, and then brings the reactant gas ions into contact with the sample molecules to cause an ion-molecule reaction, thereby generating protonated molecules in which one proton (H ⁺ ) is added to the sample molecule (see, for example, Patent Document 1; note that the reactant gas ions are usually ions other than protons). The protonated molecules behave as monovalent cations overall. While peaks due to the protonated molecules appear in mass spectra obtained by CI, peaks due to fragment ions are rarely observed because fragmentation is difficult to occur in CI. Therefore, the m/z value of the protonated molecule can be easily determined, and the molecular weight of the sample molecule can also be easily determined by subtracting 1 from the m/z value.

Conventionally, mass spectra have been obtained from the same sample using both CI and EI methods, and the type of sample molecule has been identified based on the molecular weight of the sample molecule determined from the mass spectrum obtained using CI and the m/z value of the fragment ion determined from the mass spectrum obtained using EI (Patent Document 1).

Japanese Patent Application Publication No. 11-064285

Ideally, mass spectra obtained using CI should show almost no peaks other than those due to protonated molecules. However, in reality, reactant gas ions can directly attach to sample molecules, resulting in the generation of ion-adduct molecules other than protonated molecules (note that protonated molecules are also a type of ion-adduct molecule), which can result in peaks in the mass spectrum with m/z values greater than those due to protonated molecules. This can lead to analysts mistakenly identifying ion-adduct molecules to which reactant gas ions have been attached as peaks due to protonated molecules, resulting in an incorrect molecular weight determination of the sample molecule. If the molecular weight of the sample molecule determined is incorrect, even if the m/z values of the fragment ions are obtained using EI, the type of sample molecule cannot be identified, or may be identified incorrectly.

The problem that this invention aims to solve is to provide a mass spectrometry method and a mass spectrometry program that can accurately determine the molecular weight of sample molecules.

In order to solve the above problems, the mass spectrometry method according to the present invention comprises:
a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step.

The mass spectrometry program according to the present invention is installed on a computer.
a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step.

In this invention, as with conventional CI methods, molecules of a specified reactant gas are first ionized to generate adduct molecules, and then the sample molecules are contacted with the reactant gas ions to generate adduct ions (which, as described below, are not necessarily the same as the reactant gas ions) attached to the sample molecules. A mass spectrum is then acquired. The m/z value is then obtained for each of the multiple peaks that appear in this mass spectrum. Each of the multiple m/z values obtained from the mass spectrum is the sum of the molecular weight of the sample molecule and the m/z value of each of the multiple adduct ions generated by contact between the reactant gas ions and the sample molecules. Therefore, if the m/z value of each of the multiple adduct ions is known, the molecular weight of the sample molecule can be determined based on the m/z value obtained from the mass spectrum and the m/z value of the adduct ions. Therefore, an adduct ion database is created in advance, in which the m/z values of multiple adduct ions for each reactive gas are recorded. By obtaining the m/z values of each of the multiple adduct ions corresponding to the reactive gas used in the analysis (the specified reactive gas) from this adduct ion database, the molecular weight of the sample molecule can be determined based on the m/z values of each of the peaks in the mass spectrum and the m/z values of each of the adduct ions.

The present invention prevents analysts from mistaking ion-adduct molecules with adduct ions having a larger m/z value than the peak due to the protonated molecule for peaks due to the protonated molecule, thereby enabling accurate determination of the molecular weight of the sample molecule.

1 is a schematic diagram showing an example of a mass spectrometer used when carrying out a mass spectrometry method according to the present invention. 1 is a flowchart showing the operation of an embodiment of a mass analysis method and an embodiment of a mass analysis program according to the present invention. FIG. 2 is a diagram showing an example of data contained in an adduct ion database used in the mass analysis method and mass analysis program of the present embodiment. FIG. 2 is a diagram showing an example of a CI mass spectrum obtained by the mass spectrometry method of the present embodiment. FIG. 2 is a diagram showing an example of data contained in a fragment ion database used in the mass analysis method and mass analysis program of the present embodiment. FIG. 2 is a diagram showing an example of an EI mass spectrum obtained by the mass spectrometry method of the present embodiment. FIG. 10 is a diagram showing another example of a CI mass spectrum obtained by the mass spectrometry method of the present embodiment.

An embodiment of a mass analysis method and a mass analysis program according to the present invention will be described using Figures 1 to 7.

(1) An Example of a Mass Spectrometer Before describing the mass analysis method and mass analysis program of this embodiment, we will explain an example of a mass analysis device, namely, a gas chromatograph mass spectrometer (GC-MS) 1. This GC-MS 1 is used to implement the mass analysis method of this embodiment, and part of the operation of this device is executed by the mass analysis program of this embodiment.

Figure 1 shows the schematic configuration of the GC-MS1. The GC-MS1 has a gas chromatograph (GC) unit 10, a mass spectrometry (MS) unit 20, a data processing unit 30, and a database 40.

The GC section 10 has an injector 11, a sample vaporization chamber 12, a capillary column 13, and a column oven 14. The injector 11 drips a liquid sample into the sample vaporization chamber 12. The sample vaporization chamber 12 vaporizes the liquid sample and is connected to the inlet end of the capillary column 13. The capillary column 13 separates the gaseous sample introduced from the sample vaporization chamber 12 into individual components in the time direction as it passes through. The capillary column 13 is housed in the column oven 14 and is heated by the column oven 14.

The MS section 20 has an ion source 21, a lens electrode 22, a quadrupole mass filter 23, and an ion detector 24. These are housed in a vacuum chamber 25.

The ion source 21 is a dual-purpose CI/EI ion source and includes an ionization chamber 211 into which a sample gas containing sample molecules to be analyzed is introduced, a filament 212 that generates thermoelectrons, a reaction gas flow path 213 with a valve 214 installed midway, and a filament power supply unit 215. When a predetermined current is supplied from the filament power supply unit 215 to the filament 212, the filament 212 is heated and thermoelectrons are generated.

When ionization is performed using the CI method, current is supplied to the filament 212 with the valve 214 open (ON). This allows reactant gas to be supplied into the ionization chamber 211 through the reactant gas flow path 213, and reactant gas ions are generated when thermoelectrons collide with the reactant gas molecules. These reactant gas ions react with sample molecules in the sample gas, generating ion-adduct molecules in which adduct ions are attached to the sample molecules. On the other hand, when ionization is performed using the EI method, current is supplied to the filament 212 with the valve 214 closed (OFF). The thermoelectrons are accelerated by an electric field formed by DC voltages applied to electrodes (not shown), the ionization chamber 211, the filament 212 itself, etc., and enter the ionization chamber 211. These thermoelectrons then collide with sample molecules introduced into the ionization chamber 211, ionizing the sample molecules, and further fragmenting the ions to generate fragment ions. In both the CI and EI methods, ions (ion adduct molecules or fragment ions) generated in the ionization chamber 211 are ejected from the ionization chamber 211 by the action of the electric field formed by the repeller electrode placed in the ionization chamber 211.

The lens electrode 22 focuses the ions emitted from the ionization chamber 211 by the action of the electric field it forms. The quadrupole mass filter 23 has four rod-shaped electrodes, each of which is applied with a predetermined voltage consisting of a superimposed DC voltage and a radio frequency voltage. The quadrupole mass filter 23 selectively passes only ions having an m/z value corresponding to this voltage among the ions focused by the lens electrode 22. By varying this voltage within a predetermined range, the m/z values of the ions passing through the quadrupole mass filter 23 can be scanned within a predetermined range. The ion detector 24 outputs a detection signal corresponding to the amount of incident ions.

The data processing unit 30 has a mass spectrum acquisition unit 31, an m/z value acquisition unit 32, a sample molecular weight identification unit 33, a sample molecule candidate data acquisition unit 34, and a sample molecule identification unit 35. The data processing unit 30 is actually hardware such as a CPU and memory, and the mass analysis program (software) of this embodiment. Furthermore, the database 40 is a combination of an adduct ion database (adduct ion DB) 41 and a fragment ion database (fragment ion DB) 42, and is composed of a storage device such as a hard disk (HD) or solid state drive (SSD), or a storage medium such as a CD or DVD. Details of the data processing unit 30 and database 40 will be described later, along with an explanation of the mass analysis method and mass analysis program of this embodiment.

The GC-MS 1 also includes an analysis control unit 50 that controls the operation of the GC unit 10 and MS unit 20, a display unit 51 that displays analysis results, etc., and an input unit 52 that includes a keyboard, mouse, etc. for user input. The display unit 51 and input unit 52 may be integrated using a touch panel. The data processing unit 30, database 40, analysis control unit 50, display unit 51, and input unit 52 are embodied in a computer such as a PC.

(2) Mass spectrometry method of this embodiment and operation of the mass spectrometry program of this embodiment The mass spectrometry method of this embodiment will be described with reference to the flowchart of Figure 2. In the following description, the operations performed by each unit of the data processing unit 30 are controlled by the mass spectrometry program of this embodiment.

First, under the control of the analysis control unit 50, GC/MS measurement is performed using the CI method to acquire a mass spectrum (Step 1: Mass spectrum acquisition step). GC/MS measurement using the CI method is performed as follows:

In the GC section 10, a liquid sample is dropped from the injector 11 into the sample vaporization chamber 12. The liquid sample vaporizes in a short time, becoming a sample gas that is then carried into the capillary column 13 by a flow of carrier gas, such as He gas, supplied from a carrier gas source (not shown) into the sample vaporization chamber 12. The various molecules (sample molecules) contained in the sample gas sent into the capillary column 13 are separated in the time direction as they pass through the capillary column 13, and are sequentially introduced into the ion source 21 of the MS section 20.

As described above, in the ion source 21, thermoelectrons generated by the filament 212 collide with molecules of the reaction gas supplied into the ionization chamber 211 (CI method), generating ion-adduct molecules in which adduct ions are attached to sample molecules. The generated ion-adduct molecules are emitted from the ionization chamber 211, focused by the lens electrode 22, and incident on the quadrupole mass filter 23. They pass through the quadrupole mass filter 23 and are detected by the ion detector 24 only when the voltage applied to the rod-shaped electrodes of the quadrupole mass filter 23 is a predetermined value corresponding to the m/z of the ions. Here, the type of ions incident on the ion detector 24 changes depending on their m/z value as the voltage applied to the rod-shaped electrodes of the quadrupole mass filter 23 changes over time within a predetermined range. Therefore, the mass spectrum acquisition unit 31 receives the detection signal sent by the ion detector 24 and acquires a mass spectrum indicating the relationship between the m/z of the ions and their detection intensity based on the change in the intensity of the detection signal over time.

In the following, the mass spectrum obtained when ionization is performed using the CI method, as in step 1, will be referred to as the "CI mass spectrum," and the mass spectrum obtained when ionization is performed using the EI method, as in step 7 described below, will be referred to as the "EI mass spectrum."

Next, the m/z value acquisition unit 32 detects peaks from the CI mass spectrum acquired by the mass spectrum acquisition unit 31 (step 2) and acquires the m/z values of those peaks (step 3: ion-adduct molecule m/z value acquisition step). These peak detections and m/z value acquisitions can be performed using conventional methods.

Next, the sample molecular weight identification unit 33 acquires information (reaction gas identification information) for identifying the reaction gas used when acquiring the CI mass spectrum (step 4). This information is typically the name of the reaction gas, but it may also be identified by the molecular formula of the molecules contained in the reaction gas. The operator may directly input the name of the reaction gas using the input unit 52 to identify the reaction gas, or candidates for reaction gas identification information may be displayed on the display unit 51 and the operator may select one using the input unit 52.

The sample molecular weight identification unit 33 then acquires the m/z values of each of the multiple adduct ions corresponding to the reactant gas identification information from the adduct ion DB 41 (Step 5: adduct ion m/z value acquisition step). Figure 3 shows an example of data stored in the adduct ion DB 41. In this example, the reactant gases recorded are methane ( _CH4 ), isobutane ( _C4H10 ), ammonia ( _NH3 ), methanol ( _CH4O ), and acetonitrile ( _C2H3N ) _, and the m _/ z values and ionic formulas of three adduct ions are recorded for each of these reactant gases. For example, if the reactant gas is methane, the adduct ion DB 41 stores the m/z values of the adduct ions: 1 (ionic formula H ⁺ ), 17 (ionic formula _CH5 ⁺ ), and 29 (ionic formula _{C2H5 +} ⁾ .

Here, we will explain the process of generating ion adduct molecules using methane as an example of the reactive gas. Methane molecules collide with thermal electrons and react according to the following formula (1):
CH ₄ +e ^- (thermoelectron) → CH ₄ ^+* +2e ^- …(1)
This CH ₄ ^+* reacts with a methane molecule to form CH ₄ ^+* (radical cation) according to the following formula (2):
CH ₄ ^+* +CH ₄ →CH ₅ ⁺ +CH ₃ ^* …(2)
By reacting with the sample molecule M, _CH5 ⁺ and _CH3 ^* (radicals) are generated. Of these, _CH5 ⁺ reacts with the sample molecule M,
M+ _CH5 ⁺ →MH ⁺ + _CH4 …(3)
As a result, an ion adduct molecule is generated in which the adduct ion, proton H ^+, is added to the sample molecule M. On the other hand, an ion adduct molecule is also generated in which the _CH5 ⁺ generated in equation (2) is added to the sample molecule M as an adduct ion.

Furthermore, from the CH ₄ ^+* produced in equation (1), the following equation (4)
CH ₄ ^+* +CH ₄ →CH ₃ ⁺ +CH ₅ ^* …(4)
However, CH ₃ ⁺ reacts with a methane molecule as shown in the following equation (5):
CH ₃ ⁺ +CH ₄ →C ₂ H ₅ ⁺ +H ₂
This C ₂ H ₅ ⁺ reacts with the sample molecule M as an adduct ion, producing C ₂ H ₅ ⁺ .

Next, the sample molecular weight identification unit 33 identifies the molecular weight of the sample molecule based on the m/z values of each of the multiple peaks that appear in the CI mass spectrum and the m/z values of each of the multiple adduct ions obtained in step 5 (step 6: sample molecular weight identification step).

Figure 4 shows an example of a CI mass spectrum obtained using methane as the reactant gas. The m/z values of the peaks appearing in this CI mass spectrum, obtained in step 3, are 343, 359, and 371. In contrast, the m/z values of the adduct ions obtained in step 5 when the reactant gas was methane are 1, 17, and 29. When the m/z values of the three peaks appearing in these CI mass spectra are aligned in ascending order with the m/z values of the adduct ions, the difference between the former and latter values for all three is 342. This allows us to identify the molecular weight of the sample molecule as 342 (step 6 above). It is also clear that the adduct ions H ⁺ , CH ₅ ⁺ , and C ₂ H ₅ ⁺ have been added to the sample molecule (note that it is not necessary to identify the type of adduct ion added to the sample molecule by CI in order to identify the type of sample molecule). However, at this point, the type of sample molecule (name, molecular formula, structural formula, etc.) has not yet been identified.

Next, under the control of the analysis control unit 50, GC/MS measurement is performed using the EI method, and the mass spectrum acquisition unit 31 acquires the EI mass spectrum (Step 7: EI mass spectrum acquisition step). In the EI method, the GC unit 10 introduces sample molecules into the ion source 21 of the MS unit 20 using the same operation as in the CI method. As described above, in the ion source 21, the sample molecules are ionized by thermal electrons colliding with them (EI method), and the ions are further fragmented to generate fragment ions. The generated fragment ions are focused by the lens electrode 22 and enter the quadrupole mass filter 23, and a mass spectrum is acquired using the same principle as in the CI method.

Next, the m/z value acquisition unit 32 detects peaks from the EI mass spectrum acquired by the mass spectrum acquisition unit 31 (step 8) and acquires the m/z values of those peaks (step 9: fragment ion m/z value acquisition step).

Next, the sample molecule candidate data acquisition unit 34 acquires, for each of the multiple molecules having the molecular weights identified in step 6, molecular identification information identifying each molecule and the m/z values of the fragment ions generated from the molecule from the fragment ion DB 42 (step 10: sample molecule candidate data acquisition step). Examples of molecular identification information include the name of the molecule, molecular formula (compositional formula), and structural formula of the molecule.

Figure 5 shows an example of data stored in the fragment ion DB 42. The top section of Figure 5 shows a table 421 in which a large number of compounds are assigned a serial number, and the compound names, molecular weights, and molecular formulas are recorded. Note that while eight compounds are shown in Figure 5, data for many more compounds is actually recorded, and data for other compounds can be displayed by sliding the scroll bar 422 displayed at the right end of the table. Figure 5 shows that there are multiple types of molecules with a molecular weight of 342, the example given in the explanation of step 6.

The fragment ion DB 42 also stores mass spectral data for each compound listed in the table, measured using fragment ions generated from the compound's molecules. The m/z values of the peaks in each mass spectral data are specified. When a data item is selected using the input unit 52 while the table 421 is displayed on the display unit 51, a highlight 423 (e.g., a different color from the surrounding area) is added behind the data item in the table 421 to indicate that the data item has been selected. Furthermore, the lower part of FIG. 5 displays a mass spectrum 424 obtained by measuring fragment ions generated from the compound's molecules highlighted by the highlight 423. The mass spectrum 424 contains peaks with m/z values of 69, 103, 115, 131, and 229, and these m/z values are also displayed within the mass spectrum 424. The peak with m/z value 342 is a peak resulting from an ion-adduct molecule that reached the ion detector 24 without fragmentation. The mass spectrum 424 further displays the serial number, molecular formula, structural formula (marked with a symbol 425), and molecular weight of the compound marked with a highlight 423.

Next, the sample molecule identification unit 35 extracts the m/z values of the fragment ions generated from each molecule obtained from the fragment ion DB 42 in step 10 that match the m/z values of the peaks in the EI mass spectrum obtained in step 9, and identifies the sample molecules for which these values match using the molecular identification information obtained in step 10 (step 11: sample molecule identification step).

For example, as shown in Figure 6, if the EI mass spectrum acquired in step 7 has peaks at m/z 69, 103, 115, ₁₃₁ , and ₂₂₉ , these match the m/z values of the fragment ions generated from _{C13H8F6O4 ,} the molecule highlighted ₄₂₃ in Figure _5. From this result, the sample molecule in this example can be identified as _{C13H8F6O4 .}

Note that if, due to measurement accuracy or other reasons, the m/z values stored in fragment ion DB 42 do not completely match the multiple m/z values in the measured EI mass spectrum for any of the molecules for which data was obtained in step 10 (molecules having molecular weights identified by the CI method), the molecule with the greatest degree of match calculated using a known method can be identified as the sample molecule.

After that, post-processing is performed, such as displaying information about the identified sample molecules on the display unit 51 or storing it in a data storage unit (not shown). At the same time, the CI mass spectrum and/or EI mass spectrum used in the analysis may be displayed on the display unit 51. This completes the series of operations in the mass spectrometry method according to this embodiment.

The present invention is not limited to the above embodiment and various modifications are possible.

For example, in the above embodiment, CI mass spectra and EI mass spectra were obtained using a GC-MS1. Alternatively, a liquid chromatograph mass spectrometer (LC-MS) may be used, with the liquid sample passing through the liquid chromatograph column and then vaporized in the ion source of the mass spectrometer. Alternatively, a mass spectrometer without a chromatograph may be used.

In the above embodiment, we have described a chromatograph that uses a CI mass spectrum obtained at a single retention time, with only a peak due to one type of sample molecule appearing. However, the present invention can also be applied when peaks due to multiple types of sample molecules appear in a single CI mass spectrum. In the example shown in Figure 7, when methane, which produces three types of adduct ions, is used as the reaction gas, six peaks appear in the CI mass spectrum, suggesting the presence of 6/3 = two types of sample molecules. Assuming that the peak at m/z = 322, which has the smallest m/z value, is due to an ion adduct molecule formed by the addition of a proton to the first sample molecule, the molecular weight of the first sample molecule is M = 321. The m/z values of the ion adduct molecule formed by the addition of two types of adduct ions other than protons to the M = 321 sample molecule are m/z = 321 + 17 = 338 and m/z = 321 + 29 = 350, corresponding to the second and fourth peaks from the left in the CI mass spectrum in Figure 7. Furthermore, the remaining peaks in the CI mass spectrum, at m/z = 343, 359, and 371, can be explained as being due to a second sample molecule with a molecular weight of M = 342. The same applies when peaks due to three or more types of sample molecules appear in the CI mass spectrum.

In the above embodiment, the adduct ion DB 41 stores the ion formula of each adduct ion along with the m/z value of the adduct ion, but storing the ion formula is not essential. Similarly , the m/z values (and ion formulas) of adduct ions for reactive gases other than the five types listed in Fig . 3 can be stored in the adduct ion DB 41. Furthermore, although Fig. 3 lists three types of adduct ions for one type of reactive gas, two types or four or more types (if there are four or more types of adduct ions) may be listed.

In the above embodiment, it is described that a CI mass spectrum is acquired, the molecular weight of the sample molecule is determined, and then an EI mass spectrum is acquired. However, it is also possible to first acquire a CI mass spectrum and an EI mass spectrum, and then identify the molecular weight of the sample molecule based on the CI mass spectrum and the sample molecule based on the EI mass spectrum.

In the above embodiment, the mass spectrometry method according to the present invention identifies the molecular weight of the sample molecule based on the CI mass spectrum, and then identifies the name of the sample molecule based on this molecular weight and the EI mass spectrum. However, instead, it is also possible to only identify the molecular weight of the sample molecule based on the CI mass spectrum.

[Aspects]
It will be apparent to those skilled in the art that the above-described exemplary embodiments are examples of the following aspects.

(Item 1) A mass spectrometry method according to one aspect of the present invention comprises:
a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step.

(Item 4) A mass spectrometry program according to another aspect of the present invention is a program for executing the program on a computer,
a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step.

In the mass spectrometry method according to paragraph 1 and the mass spectrometry program according to paragraph 4, as in conventional CI methods, molecules of a specified reactant gas are first ionized to generate ions, and then the sample molecules are contacted with the reactant gas ions to generate ion adduct molecules in which adduct ions (which may not necessarily be the same as the reactant gas ions, as described below) are attached to the sample molecules. A mass spectrum is then acquired. The m/z value is then obtained for each of the multiple peaks that appear in this mass spectrum. Each of the multiple m/z values obtained from the mass spectrum is the sum of the molecular weight of the sample molecule and the m/z value of each of the multiple adduct ions generated by contact between the reactant gas ions and the sample molecules. Therefore, if the m/z value of each of the multiple adduct ions is known, the molecular weight of the sample molecule can be determined based on the m/z value obtained from the mass spectrum and the m/z value of the adduct ions. Therefore, an adduct ion database is created in advance, in which the m/z values of multiple adduct ions for each reactive gas are recorded. By obtaining the m/z values of each of the multiple adduct ions corresponding to the reactive gas used in the analysis (the specified reactive gas) from this adduct ion database, the molecular weight of the sample molecule can be determined based on the m/z values of each of the peaks in the mass spectrum and the m/z values of each of the adduct ions.

The mass spectrometry method according to paragraph 1 and the mass spectrometry program according to paragraph 4 prevent analysts from mistaking ion-adduct molecules with adduct ions having m/z values larger than those of peaks due to protonated molecules for peaks due to protonated molecules, thereby enabling accurate determination of the molecular weight of sample molecules.

As mentioned above, reactant gas ions and adduct ions are not necessarily the same. For example _, when the reactant gas is methane gas, the reactant gas ions _CH5 ⁺ and _C2H5 ⁺ are generated, and the adduct ions are H ⁺ (protons, which are different from reactant gas ions), _CH5 ⁺ _, and _C2H5 ⁺ . Here, the adduct ion H ⁺ is generated by the reaction of M (sample molecule) + _CH5 ⁺ → [M+H] ^{+ +} _CH4 .

In the mass spectrometry method according to paragraph 1, the ion adduct m/z value acquisition step must be performed after the mass spectrum acquisition step (because processing using the mass spectrum is performed), and the sample molecular weight determination step must be performed after each step (because the m/z values of the ion adduct molecule and adduct ion are used). On the other hand, the adduct ion m/z value acquisition step can be performed in any order as long as it is performed before the sample molecular weight determination step. The same applies to the mass spectrometry program according to paragraph 4.

(Item 2) The mass spectrometry method according to Item 2 further comprises the steps of:
an EI mass spectrum acquisition step of acquiring an EI mass spectrum, which is a mass spectrum obtained when the sample molecules are fragmented by electron ionization;
a fragment ion m/z value acquisition step of acquiring the m/z value of a peak appearing in the EI mass spectrum;
a sample molecule candidate data acquisition step of acquiring, for a plurality of molecules having the same molecular weight as the sample molecule identified in the sample molecular weight identification step, molecular identification information identifying the molecule and the m/z values of fragment ions generated from the molecule from a fragment ion database in which information identifying the molecule for each molecule, the molecular weight of the molecule, and the m/z values of fragment ions generated from the molecule by electron ionization method are recorded;
and a sample molecule identifying step of comparing, for each of the plurality of molecules, the m/z value of the fragment ion acquired in the sample molecule candidate data acquiring step with the m/z value acquired in the fragment ion m/z value acquiring step, and identifying the sample molecule based on molecular identification information of a molecule among the plurality of molecules for which the two m/z values match.

(5) The mass analysis program according to claim 5 is the mass analysis program according to claim 4, further comprising: an EI mass spectrum acquisition step of acquiring an EI mass spectrum, which is a mass spectrum obtained when the sample molecules are fragmented by electron ionization;
a fragment ion m/z value acquisition step of acquiring the m/z value of a peak appearing in the EI mass spectrum;
a sample molecule candidate data acquisition step of acquiring, for a plurality of molecules having the same molecular weight as the sample molecule identified in the sample molecular weight identification step, molecular identification information identifying the molecule and the m/z values of fragment ions generated from the molecule from a fragment ion database in which information identifying the molecule for each molecule, the molecular weight of the molecule, and the m/z values of fragment ions generated from the molecule by electron ionization method are recorded;
and a sample molecule identifying step of comparing, for each of the plurality of molecules, the m/z value of the fragment ion acquired in the sample molecule candidate data acquiring step with the m/z value acquired in the fragment ion m/z value acquiring step, and identifying the sample molecule based on molecular identification information of a molecule among the plurality of molecules for which the two m/z values match.

Here, molecular identification information includes the name of the molecule, molecular formula (compositional formula), molecular structural formula, etc.

The mass analysis method according to paragraph 2 and the mass analysis program according to paragraph 5 accurately determine the molecular weight of a sample molecule, and then identify the sample molecule using molecular identification information for the fragment ion m/z values obtained from a fragment ion database for each of multiple molecules having that molecular weight that match the m/z values determined from the EI mass spectrum of the sample molecule obtained using electron ionization. This makes it possible to accurately identify the sample molecule.

In the mass spectrometry method according to paragraph 2, the fragment ion m/z value acquisition step must be performed after the EI mass spectrum acquisition step (because processing using the EI mass spectrum is performed), and the sample molecule candidate data acquisition step must be performed after the sample molecular weight identification step (because processing using the sample molecular weight is performed). Furthermore, the sample molecule identification step must be performed after each step (because the m/z values acquired in the sample molecule candidate data acquisition step and the fragment ion m/z value acquisition step are used). On the other hand, the order of execution of the sample molecule candidate data acquisition step does not matter as long as it precedes the sample molecule identification step. Furthermore, the steps using the CI method described in paragraph 1 may be performed before the steps using the EI method described in paragraph 2, or the mass spectrum acquisition step (using the CI method) and the EI mass spectrum acquisition step may be performed first, followed by the remaining steps described in paragraphs 1 and 2. In the latter case, either the mass spectrum acquisition step (using the CI method) or the EI mass spectrum acquisition step may be performed first. In short, there are no restrictions on the order in which the steps may be performed, as long as it does not contradict the order in which the steps are performed in paragraphs 1 and 2. The same applies to the mass analysis program in paragraph 5.

(Clause 3) The mass spectrometry method according to paragraph 3 is the mass spectrometry method according to paragraph 1 or 2, wherein the sample molecules are molecules of components of a sample that has passed through a column of a gas chromatograph or liquid chromatograph.

In the mass spectrometry method according to paragraph 3, the sample molecules are molecules of components of the sample that have passed through the column. Therefore, even if the sample contains molecules of multiple components, the sample molecules are separated from the molecules of other components in the sample by passing through the column, and a mass spectrum is obtained by the CI method for the sample molecules alone, making it easier to identify the molecular weight.

1...Gas chromatograph mass spectrometer (GC-MS)
10...Gas chromatograph (GC) section 11...Injector 12...Sample vaporization chamber 13...Capillary column 14...Column oven 20...Mass spectrometry (MS) section 21...Ion source 211...Ionization chamber 212...Filament 213...Reaction gas flow path 214...Valve 215...Filament power supply section 22...Lens electrode 23...Quadrupole mass filter 24...Ion detector 25...Vacuum chamber 30...Data processing section 31...Mass spectrum acquisition section 32...m/z value acquisition section 33...Sample molecular weight identification section 34...Sample molecule candidate data acquisition section 35...Sample molecule identification section 40...Database 41...Adduct ion database (adduct ion DB)
42...Fragment ion database (fragment ion DB)
421...table 422...scroll bar 423...highlighted display 424...mass spectrum 425...structural formula of highlighted compound 50...analysis control unit 51...display unit 52...input unit

Claims (5)

a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step. moreover,
an EI mass spectrum acquisition step of acquiring an EI mass spectrum, which is a mass spectrum obtained when the sample molecules are fragmented by electron ionization;
a fragment ion m/z value acquisition step of acquiring the m/z value of a peak appearing in the EI mass spectrum;
a sample molecule candidate data acquisition step of acquiring, for a plurality of molecules having the same molecular weight as the sample molecule identified in the sample molecular weight identification step, molecular identification information identifying the molecule and the m/z values of fragment ions generated from the molecule from a fragment ion database in which information identifying the molecule for each molecule, the molecular weight of the molecule, and the m/z values of fragment ions generated from the molecule by electron ionization method are recorded;
a sample molecule identifying step of comparing, for each of the plurality of molecules, the m/z value of the fragment ion acquired in the sample molecule candidate data acquiring step with the m/z value acquired in the fragment ion m/z value acquiring step, and identifying the sample molecule based on molecular identification information of a molecule among the plurality of molecules for which the two m/z values match. The mass spectrometry method according to claim 1 or 2, wherein the sample molecules are molecules of components of a sample that has passed through a column of a gas chromatograph or liquid chromatograph. On the computer,
a mass spectrum acquisition step of acquiring a mass spectrum of ion-adduct molecules generated by ionizing a predetermined reaction gas molecule to generate reaction gas ions, and adding adduct ions to the sample molecule upon contact of the reaction gas ions with the sample molecule;
an ion adduct molecule m/z value acquisition step of acquiring an m/z value for each of a plurality of peaks appearing in the mass spectrum;
an adduct ion m/z value acquisition step of acquiring the m/z value of each of the plurality of adduct ions corresponding to the predetermined reaction gas from an adduct ion database in which the m/z values of the plurality of adduct ions that can be generated are recorded for each reaction gas;
and a sample molecular weight determination step of determining the molecular weight of the sample molecule based on the m/z value of each of the plurality of peaks and the m/z value of each of the plurality of adduct ions acquired in the m/z value acquisition step. Furthermore, an EI mass spectrum acquisition step is performed by a computer to acquire an EI mass spectrum, which is a mass spectrum obtained when the sample molecules are cleaved by electron ionization.
a fragment ion m/z value acquisition step of acquiring the m/z value of a peak appearing in the EI mass spectrum;
a sample molecule candidate data acquisition step of acquiring, for a plurality of molecules having the same molecular weight as the sample molecule identified in the sample molecular weight identification step, molecular identification information identifying the molecule and the m/z values of fragment ions generated from the molecule from a fragment ion database in which information identifying the molecule for each molecule, the molecular weight of the molecule, and the m/z values of fragment ions generated from the molecule by electron ionization method are recorded;
a sample molecule identifying step of comparing, for each of the plurality of molecules, the m/z value of the fragment ion acquired in the sample molecule candidate data acquiring step with the m/z value acquired in the fragment ion m/z value acquiring step, and identifying the sample molecule based on molecular identification information of a molecule among the plurality of molecules for which the two m/z values match.