JP5747839B2 - Data processing equipment for chromatographic mass spectrometry - Google Patents

Description

The present invention relates to a gas chromatograph mass spectrometer (GC / MS), a liquid comprising a combination of a chromatograph such as a gas chromatograph (GC) or a liquid chromatograph (LC) and a mass spectrometer including an MS ^n- type mass spectrometer. The present invention relates to a data processing apparatus that processes data collected by a chromatograph mass spectrometer such as a chromatograph mass spectrometer (LC / MS).

  When performing qualitative analysis or quantitative analysis of each component in a sample containing a plurality of components (compounds), GC / MS or LC / MS is often used. In qualitative analysis using GC / MS or LC / MS, generally, scan measurement is performed in a mass spectrometer, and mass spectra over a predetermined mass-to-charge ratio range are repeatedly acquired. By comparing this mass spectrum pattern with a mass spectrum pattern stored in advance in a spectrum database (library), a compound having a high pattern similarity is extracted, and a compound corresponding to a peak on a chromatogram is specified. When a sharp peak with a narrow time width appears on the chromatogram, qualitative analysis may be performed using the mass spectrum of the measurement point (measurement time) giving the peak top.

  However, since the peak of the chromatogram is dull or deformed due to various factors, it is often difficult to determine the measurement point that gives the peak top strictly. In preparation for such cases, conventional GC / MS and LC / MS data processing apparatuses use mass spectra at a plurality of measurement points (generally about 3 to 5 points) near the peak top of the chromatogram. Has a function of calculating an average mass spectrum obtained by averaging (see Non-Patent Document 1).

  By the way, in GC / MS / MS and LC / MS / MS using a tandem quadrupole mass spectrometer as a mass spectrometer, multiple reaction monitoring (MRM = Multiple Reaction Monitoring) is performed in order to perform quantitative analysis of the target compound. Analysis by measurement mode is often used. The MRM measurement mode is a mode in which only ions having a specific mass-to-charge ratio are passed through the front-stage quadrupole mass filter and the rear-stage quadrupole mass filter to detect ions that finally reach the detector, There is an advantage that ions derived from impurities that could not be separated by the chromatograph and ions derived from the target component can be separated to detect only the latter. On the other hand, in the MRM measurement mode, since qualitative information cannot be obtained except for the holding time, it is difficult to identify even if an unknown component is included in the sample. Therefore, in the conventional GC / MS / MS and LC / MS / MS, the MRM measurement and the scan measurement are alternately repeated at short time intervals that can be considered to be substantially the same, so that the quantitative information by the MRM measurement can be obtained. Qualitative information from scan measurement can be acquired in parallel.

  However, when MRM measurement and scan measurement are repeated alternately at short time intervals, there are the following problems.

  That is, in the MRM measurement, since ion selection is performed by a two-stage quadrupole mass filter, the amount of ions reaching the detector is relatively smaller than the simple scan measurement in which ions pass through one quadrupole mass filter. Considerably less. On the other hand, high sensitivity is required for MRM measurement for quantitative analysis. Therefore, in general, when the MRM measurement and the scan measurement are performed at the same time (strictly speaking, it is time-division as described above, but is substantially the same in a long time), the relative values obtained by the MRM measurement Thus, the gain of the detector is set high so that a sufficient detection signal can be obtained even with a small amount of ions. However, when the gain of the detector is high in this way, the detection signal obtained by the scan measurement exceeds the input range of the A / D converter, and data saturation often occurs.

  When signal intensity data of a certain mass-to-charge ratio is saturated in scan measurement, the pattern of the mass spectrum at that time is destroyed. When the average mass spectrum is calculated in the predetermined time range near the top of the chromatogram peak and a mass spectrum with a corrupted pattern is included, the resulting average mass spectrum also accurately represents the characteristics of the target compound. There is a risk of not being. In this case, an incorrect compound hits during database search and causes misidentification, or a correct compound does not hit and causes identification failure.

“GCMSsolution Operation Q & A Q: I want to average mass spectrum (Inquiry No. 0620)”, Shimadzu Corporation, [Search February 6, 2012], Internet <URL: http://www.an. shimadzu.co.jp/gcms/support/faq/gcmssol/faq6.htm#0620>

  The present invention has been made to solve the above-mentioned problems, and its object is to improve the accuracy of qualitative analysis by obtaining an average mass spectrum that accurately represents the characteristics of the target compound. It is an object of the present invention to provide a data processing apparatus for chromatographic mass spectrometry capable of performing

The present invention made to solve the above problems is a data processing device for processing data obtained by a chromatograph mass spectrometer that analyzes a component in a sample temporally separated by a chromatograph by a mass spectrometer. In the chromatograph mass spectrometry data processing apparatus for processing mass spectrum data repeatedly obtained by carrying out scan measurement in the mass spectrometer,
a) Mass spectrum data obtained during the period when the target component is introduced into the mass spectrometer and a signal at the time of measurement among mass spectrum data of a plurality of measurement points included in a predetermined time range or measurement point range. Saturation data identification means for identifying mass spectral data including data where saturation has occurred or is likely to occur;
b) Among the mass spectrum data of the plurality of measurement points, only the mass spectrum data that has not been determined to include data that has been or may have been signal saturated by the saturation data identifying means, An average mass spectrum creating means for creating a mass spectrum;
It is characterized by having.

As one aspect of the data processing apparatus for chromatographic mass spectrometry according to the present invention,
Flag storage means for determining whether or not signal saturation has occurred or is likely to be included for each mass spectrum data during measurement and storing a saturation identification flag indicating the determination result in association with the data Prepared,
The saturation data identification unit is configured to identify mass spectrum data including data in which signal saturation has occurred or is likely to occur at the time of measurement based on a saturation identification flag stored in association with mass spectrum data. be able to.

The chromatograph here includes both a gas chromatograph and a liquid chromatograph. The mass spectrometer includes not only a general mass spectrometer but also an MS ⁿ type mass spectrometer such as a tandem quadrupole mass spectrometer. Therefore, the scan measurement here includes not only simple scan measurement but also precursor ion scan measurement, product ion scan measurement, and neutral loss scan measurement in MS / MS analysis. Mass spectral data can be obtained by these various scan measurements. Includes MS ² spectral data.

In the data processing apparatus for chromatographic mass spectrometry according to the present invention, for example, there is a time range or measurement point range in which a target component to be analyzed is designated by a user and the averaging process is performed on a chromatogram corresponding to the target component. When specified by the user, the saturation data identifying means may or may have caused signal saturation during measurement in the mass spectrum data of a plurality of measurement points included in the specified time range or measurement point range. Identify mass spectral data, including data. The average mass spectrum creation means excludes mass spectrum data determined to include data in which signal saturation has occurred or is likely to occur, and uses the remaining mass spectrum data in the time direction for each mass to charge ratio. An average mass spectrum is created by averaging the signal strength data. Therefore, since a mass spectrum that does not accurately show the characteristics of the target component is not reflected in the average mass spectrum, an accurate average mass spectrum can be calculated even when the gain of the detector is high.

  According to the chromatograph mass spectrometry data processing apparatus of the present invention, for example, even when the gain of the detector of the mass spectrometer is excessive and data saturation occurs, a plurality of measurements near the chromatogram peak top are performed. From the point, it is possible to create and display an average mass spectrum that is accurate, that is, exhibits a pattern that accurately represents the characteristics of the target component. Thereby, the accuracy of the qualitative analysis using the average mass spectrum can be ensured.

The whole block diagram of one Example of GC / MS / MS to which the chromatograph mass spectrometry data processing apparatus concerning this invention is applied. The flowchart which shows the control and processing operation at the time of measurement data collection in GC / MS / MS of a present Example. The flowchart which shows the control and processing operation at the time of preparation of the average mass spectrum in GC / MS / MS of a present Example. The schematic diagram for demonstrating the average mass spectrum preparation operation | movement in GC / MS / MS of a present Example.

  Hereinafter, the chromatograph mass spectrometry data processing apparatus according to the present invention will be described in detail with an example. FIG. 1 is an overall configuration diagram of an embodiment of GC / MS / MS to which a chromatographic mass spectrometry data processing apparatus according to the present invention is applied.

  The GC / MS / MS includes a gas chromatograph (GC) 1 and a tandem quadrupole mass spectrometer 2 in order to perform analysis on a sample and collect data. In GC1, a carrier gas such as helium is supplied to the column 12 through the sample vaporizing chamber 10 at a constant flow rate. The column 12 is built in the column oven 11 and is temperature-controlled so as to be maintained at a constant temperature or according to a predetermined temperature profile. When a small amount of sample liquid is injected into the sample vaporizing chamber 10 at a predetermined timing, the sample liquid is vaporized in a short time and is introduced into the column 12 along with a carrier gas flow. Various components contained in the sample are separated while passing through the column 12 and flow out from the outlet of the column 12 with a time lag.

  The tandem quadrupole mass spectrometer 2 includes a collision cell in which an ion source 21 using an electron ionization (EI) method or a chemical ionization (CI) method, a front quadrupole mass filter 22, and a multipole ion guide 24 are incorporated. 23, a post-stage quadrupole mass filter 25 and a detector 26 are provided in the vacuum chamber 20. As the detector 26, for example, a combination of a conversion dynode and an electron multiplier is used.

  When performing MS / MS analysis, collision-induced dissociation (CID) gas is supplied into the collision cell 23. The sample gas flowing out from the outlet of the column 12 of GC1 is introduced into the ion source 21, and the component molecules in the sample gas are ionized. Of the various ions generated, only ions having a specific mass-to-charge ratio pass through the front quadrupole mass filter 22 and are introduced into the collision cell 23. The ions come into contact with the CID gas in the collision cell 23 to promote dissociation, and various product ions are generated. Only product ions having a specific mass-to-charge ratio pass through the subsequent quadrupole mass filter 25 and reach the detector 26 to be detected.

  In the tandem quadrupole mass spectrometer 2, ions are passed through either the front quadrupole mass filter 22 or the rear quadrupole mass filter 25 without introducing CID gas into the collision cell 23 (ion selection). In this case, it is possible to execute normal mass spectrometry without ion dissociation, that is, measurement in the selected ion monitoring (SIM) measurement mode or scan measurement mode.

  The detector 26 outputs a detection signal corresponding to the amount of ions that have reached, and the detection signal is converted into digital data by the A / D converter 27 and input to the data processing unit 30. The data processing unit 30 includes a data collection processing unit 31 as a functional block, and stores data in the data storage unit 33 through the data collection processing unit 31. The data processing unit 30 also includes an average mass spectrum creation processing unit 32 that performs operations characteristic of the present embodiment. Each unit of the GC 1 and the tandem quadrupole mass spectrometer 2 is controlled by the analysis control unit 40, and the operations of the analysis control unit 40 and the data processing unit 30 are comprehensively controlled by the central control unit 41. An input unit 42 and a display unit 43 are connected to the central control unit 41 as a user interface.

  All or a part of the data processing unit 30, the analysis control unit 40, and the central control unit 41 use a personal computer as a hardware resource and execute dedicated control / processing software installed in the computer in advance. Thus, each function can be realized.

  The tandem quadrupole mass spectrometer 2 can perform various modes of measurement. The above-described MRM measurement mode is generally used when performing quantitative analysis of a known target component. In the MRM measurement mode, the applied voltage to each is selected so that ions having a predetermined mass-to-charge ratio are selected by the front-stage quadrupole mass filter 22 and the rear-stage quadrupole mass filter 25, respectively. Detect specific fragment ions. In this measurement mode, ions derived from contaminants introduced into the ion source 21 at the same time as the target component can be excluded, so that noise caused by such undesired ions can be removed. However, since the unknown component included in the sample is not detected in the simple MRM measurement mode, the MRM measurement mode and the scan measurement mode are short when it is desired to know in parallel what components are included in the sample. Often, a measurement technique is used that is performed alternately at time intervals.

  In the MRM measurement mode, since ion selection is performed by both the front-stage quadrupole mass filter 22 and the rear-stage quadrupole mass filter 25, the amount of ions derived from the target component finally reaching the detector 26 is the ion source 21. Is considerably less than the amount of the same ions produced in On the other hand, in scan measurement without ion dissociation, ion selection is performed by only one quadrupole mass filter 22 or 25, so that the amount of ions derived from the target component reaching the detector 26 is larger than that in MRM measurement. Become. For this reason, if the gain of the detector 26 is increased so that ions can be detected with high sensitivity during MRM measurement, the detection signal is too large during scan measurement and the input range of the A / D converter 27 is exceeded and output. Data may be digitally saturated. Therefore, in the GC / MS / MS of this embodiment, even when the data collected by measurement is saturated, characteristic data processing is performed to avoid adversely affecting the results of processing such data. Like to do.

  Next, characteristic data processing operations executed in the GC / MS / MS of this embodiment will be described. First, processing operations executed mainly by the data collection processing unit 31 when collecting mass spectrum data in the scan measurement mode will be described with reference to FIG. FIG. 2 is a flowchart showing control and processing operations during data collection in the scan measurement mode. When the MRM measurement and the scan measurement are alternately repeated as described above, the processing shown in FIG. 2 is executed only during the scan measurement period, and data is collected during the MRM measurement period as in the conventional case. Good.

  When the measurement is started, the analysis control unit 40 applies a voltage to the preceding or succeeding quadrupole mass filter 22 or 25 so as to repeat mass scanning over a predetermined mass-to-charge ratio range. During one mass scanning period, the detection signal obtained by the detector 26 is converted into a digital value by the A / D converter 27 and sent to the data collection processing unit 31. Data obtained by one mass scan is mass spectrum data at a certain measurement point (measurement time). When the mass spectrum data of a certain measurement point is obtained (step S1), the data collection processing unit 31 determines whether or not there is data whose signal intensity exceeds the threshold value (step S2). .

  As described above, if the detection signal output from the detector 26 is excessive, the input range of the A / D converter 27 may be exceeded. If the output data is saturated beyond the input range, the data value will be equal to or greater than the predetermined value.Therefore, the threshold value should be determined accordingly, that is, to detect whether saturation has occurred or is likely to occur. That's fine. When there is data in which the signal intensity exceeds the threshold value in the mass spectrum data, the saturation identification flag F for the mass spectrum data is set to “1” (step S3), and the data whose signal intensity exceeds the threshold value. If not, the saturation identification flag F is set to “0” (step S4). Then, the acquired mass spectrum data and the saturation identification flag F are stored in the data storage unit 33 in association with each other (step S5). The mass spectrum data stored in the data storage unit 33 may be profile data corresponding to a predetermined mass-to-charge ratio, or may be mass spectrum data obtained by performing centroid processing on the profile data.

  Then, for example, it is determined whether or not the measurement is completed by determining that a predetermined measurement time has elapsed since the start of measurement (step S6). If the measurement is not yet completed, the process returns to step S1 and obtained by scan measurement. Continue collecting data. By repeating the above steps S1 to S5, the mass spectrum data is stored in the data storage unit 33 together with the saturation identification flag F for each mass scan from the measurement start time to the measurement end time.

  Some A / D converters have an input range overflow detection function. When such an A / D converter is available, signal intensity saturation occurs in the mass spectrum data. Whether there is data can be determined based on the overflow detection output. Further, by detecting the level of the analog detection signal input to the A / D converter 27, it may be determined whether the data after A / D conversion is saturated.

  Next, processing operations when creating and displaying an average mass spectrum in a state where the mass spectrum data is stored in the data storage unit 33 as described above will be described with reference to FIGS. FIG. 3 is a flowchart showing the average mass spectrum creation processing operation, and FIG. 4 is a schematic diagram for explaining the average mass spectrum creation operation.

  The user performs a predetermined operation on the input unit 42 to display a total ion chromatogram (TIC) created based on the data collected in the scan measurement mode performed on the target sample on the screen of the display unit 43. Display above. The user designates a chromatogram peak to be averaged on the total ion chromatogram, and sets parameters (processing conditions) necessary for the averaging process (step S11). This parameter includes, for example, the number of measurement points used for averaging or a time range. By performing a graphical operation such as dragging on the chromatogram, a time range for performing the averaging process may be designated.

  When a process execution instruction is issued by the user (step S12), the average mass spectrum creation processing unit 32 receives this, and the data storage unit 33 stores the mass spectrum data of the measurement point range instructed by the above parameters together with the saturation identification flag. (Step S13). As an example, let us consider a case where the number of measurement points to be averaged is “5” with respect to the chromatogram peak as shown in FIG. At this time, since the measurement points to be averaged are A1 to A5 near the peak top, the mass spectrum data obtained at these measurement points A1 to A5 are read from the data storage unit 33 together with the saturation identification flag.

  Next, after setting the variable n to 1 (step S14), the average mass spectrum creation processing unit 32 acquires mass spectrum data at the nth measurement point (step S15). In the example of FIG. 4, first, mass spectrum data of the first measurement point A1 is acquired. Next, it is determined whether or not the saturation identification flag F associated with the mass spectrum data is 0 (step S16). If the saturation identification flag F is 0, it can be determined that the mass spectrum data at that time does not include data in which signal saturation has occurred, so the acquired mass spectrum data is set as an averaging process target (step S17). Proceed to step S18. On the other hand, if the saturation identification flag F is 1, there is a high possibility that the mass spectrum data at that time includes data that has caused signal saturation, so the process of step S17 is avoided and the process proceeds to step S18. That is, at this time, the mass spectrum data is not set as an averaging process target.

  In step S18, it is determined whether or not the variable n is the final point within the measurement point range. If it is not the final point, the variable n is incremented (step S19), and the process returns to step S15. In the example of FIG. 4, since the measurement point A5 is the final point within the measurement point range, Steps S15 to S19 are repeated four times, and when Step S18 is reached, the final point is determined and the process proceeds to Step S20. . By repeating these steps S15 to S19, the respective mass spectrum data of the measurement points A1 to A5 are acquired, but it is assumed that the saturation identification flag F given at the time of measurement is 1 for the measurement points A3 and A4. The two mass spectrum data of the measurement points A3 and A4 are not set as the averaging process target. In other words, only the mass spectrum data of the three measurement points A1, A2, and A5 are subjected to the averaging process.

  The average mass spectrum creation processing unit 32 calculates the average value of the intensity data for each mass-to-charge ratio by using only the mass spectrum data at the measurement point selected according to the saturation identification flag, and creates the average mass spectrum (step) S20). And while drawing the created average mass spectrum on the screen of the display part 43, the measurement point (A1, A2, A5 in the said example) utilized for the averaging process, and the measurement point excluded from the averaging process (A3, A4 in the above example) are displayed in an identifiable manner (step S21). The latter display may be performed with text information as shown in FIG. 4, or may be graphically displayed, for example, a mark indicating a measurement point on the chromatogram curve may be displayed with a different display color.

  As described above, in the GC / MS / MS according to the present embodiment, when an average mass spectrum for a certain component is created and displayed, mass spectrum data including data whose signal intensity may be saturated is excluded. The accuracy of the average mass spectrum is improved.

  In the above embodiment, the characteristic processing is performed on the mass spectrum data obtained in the simple scan measurement. However, the measurement mode for collecting the mass spectrum data, that is, the precursor ion scan measurement in the MS / MS analysis. The above-described processing can be applied to the mode, the product ion scan measurement mode, the neutral loss scan measurement mode, and the like.

  Moreover, although the said Example is GC / MS / MS, LC / MS / MS may be sufficient, and it is clear that GC / MS and LC / MS may be sufficient. Further, the above-described embodiment is an example of the present invention, and it is obvious that other than the above-described modified examples, any appropriate modification, correction, or addition within the spirit of the present invention is included in the scope of the claims of the present application. It is.

1. Gas chromatograph (GC)
DESCRIPTION OF SYMBOLS 10 ... Sample vaporization chamber 11 ... Column oven 12 ... Column 2 ... Tandem quadrupole mass spectrometer 20 ... Vacuum chamber 21 ... Ion source 22 ... Pre-stage quadrupole mass filter 23 ... Collision cell 24 ... Multipole ion guide 25 ... latter-stage quadrupole mass filter 26 ... detector 27 ... A / D converter 30 ... data processing unit 31 ... data collection processing unit 32 ... average mass spectrum creation processing unit 33 ... data storage unit 40 ... analysis control unit 41 ... center Control unit 42 ... input unit 43 ... display unit

Claims (2)

A data processing device for processing data obtained by a chromatograph mass spectrometer for analyzing components in a sample separated in time by a chromatograph by a mass spectrometer, and performing a scan measurement in the mass spectrometer In the chromatograph mass spectrometry data processing apparatus that processes the mass spectrum data obtained repeatedly,
a) Mass spectrum data obtained during the period when the target component is introduced into the mass spectrometer and a signal at the time of measurement among mass spectrum data of a plurality of measurement points included in a predetermined time range or measurement point range. Saturation data identification means for identifying mass spectral data including data where saturation has occurred or is likely to occur;
b) Among the mass spectrum data of the plurality of measurement points, only the mass spectrum data that has not been determined to include data that has been or may have been signal saturated by the saturation data identifying means, An average mass spectrum creating means for creating a mass spectrum;
A chromatographic mass spectrometry data processing apparatus comprising: A chromatograph mass spectrometry data processing apparatus according to claim 1,
Flag storage means for determining whether or not signal saturation has occurred or is likely to be included for each mass spectrum data during measurement and storing a saturation identification flag indicating the determination result in association with the data Prepared,
The saturation data identification means identifies mass spectrum data including data in which signal saturation has occurred or is likely to occur during measurement based on a saturation identification flag stored in association with mass spectrum data. A chromatograph mass spectrometry data processing apparatus.

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