JP4470505B2 - Data processing equipment for chromatographic mass spectrometry - Google Patents

Description

  The present invention relates to a chromatograph mass spectrometer that uses a mass spectrometer as a chromatograph detector such as a liquid chromatograph, a gas chromatograph, a supercritical chromatograph, and more specifically, processes data collected by chromatograph mass spectrometry. The present invention relates to a data processing apparatus.

In gas chromatograph mass spectrometer (GC / MS), liquid chromatograph mass spectrometer (LC / MS), or supercritical chromatograph mass spectrometer (SFC / MS), sample components are separated in the time axis direction by chromatograph. , and detecting the separated according to mass in each ionization mass spectrometry unit each of the separated components (strictly mass-to-charge ratio). Based on the thus obtained data, it is possible to create a mass spectrum of mass on the horizontal axis, the vertical axis and relative intensity (ionic strength). Ideally, it is desirable that only peaks of ionic species generated from the measurement object appear in this mass spectrum. However, undesired peaks actually appear due to various factors. For example, in LC / MS, peaks derived from compounds other than the measurement target such as free substances from the separation column liquid phase, sample solvent, mobile phase solvent, or impurities contained in the sample are often mixed. In addition, a peak due to noise in the detector may be included.

  If such noise is mistakenly recognized as a peak derived from the target substance, it will interfere with qualitative analysis and quantitative analysis. Therefore, such noise (collectively referred to as background) must be removed by data processing. Has been done. As one of methods for removing such unnecessary peaks in the mass spectrum, for example, there is a background removal process described in Patent Document 1. In this method, the mass spectrum acquired in the time zone without the peak of the measurement target component is regarded as background noise, and the background noise is subtracted from the mass spectrum acquired in the time zone where the peak of the measurement target appears. , Try to reduce the influence of the background.

  However, in some cases, the background level that overlaps the peak portion of the measurement object may differ from the background noise level measured in a time zone in which there is no peak of the measurement target component. In such a case, the background noise is multiplied by an appropriate increase or decrease rate, and then the mass spectrum is subtracted. However, it is difficult to accurately determine the increase or decrease rate. It is very difficult to completely eliminate background noise by processing.

  As another method for removing unnecessary peaks, processing for deleting peaks below a certain signal intensity from the mass spectrum is also performed. In the background erasing process, noise that does not appear when background noise is acquired cannot be removed. However, this technique can also remove a non-reproducible peak due to detector noise or the like. However, it is difficult to determine the signal level for identifying the peak to be removed, and it is impossible to sufficiently eliminate the peak that is noise, or conversely, the peak of the measurement object is erroneously determined to be noise. And sometimes erased.

JP 2000-206103 A

  As described above, in the conventional background / noise removal method, it is not always possible to sufficiently remove unnecessary peaks, or necessary peaks due to the measurement object may be erroneously removed. The present invention has been made in view of these points, and the object of the present invention is to appropriately erase only peaks due to unnecessary background / noise, and to obtain a good mass spectrum including peaks due to an object to be measured. An object is to provide a data processing apparatus for chromatographic mass spectrometry that can be obtained.

In order to solve the above problems, the present invention provides a data processing apparatus for chromatographic mass spectrometry that processes data collected by chromatographic mass analysis of a measurement object, and a) a mass spectrum at a predetermined elapsed time. B) a mass chromatogram acquisition means for acquiring a mass chromatogram of each mass for each peak appearing in the mass spectrum; and c) the predetermined spectrum in each mass chromatogram. A peak detecting means for detecting a chromatogram peak in a range near the elapsed time; d) an S / N ratio calculating means for calculating an S / N ratio of each detected chromatogram peak; and e) a calculated S / N. Peak discriminating means for judging whether or not the peak is a significant chromatogram peak by comparing the ratio with a predetermined threshold value, and f) judged to be significant A mass spectrum reconstructing means for selecting a mass having a romatogram peak and creating a mass spectrum including only the peak of the mass; g) a threshold setting means for setting a plurality of the threshold values; and h) each set threshold value. On the other hand, executing the processing of the peak discriminating means and the mass spectrum reconstructing means, creating mass spectra of different shapes in parallel , and a plurality of mass spectrum creating means for displaying each generated mass spectrum on a display unit , It is characterized by providing.

In the data processing apparatus according to the present invention, in order to remove peaks derived from the noise and background in the mass spectrum, rather than determining the peak appearing in the mass spectrum, the mass of the spectral peak is present Using the chromatogram peak appearing on the mass chromatogram, it is judged whether it is the original target substance, or noise or background.

That is, when the mass spectrum creation means creates a mass spectrum at a predetermined elapsed time according to an operator's instruction or automatic selection in light of a predetermined condition, the mass chromatogram acquisition means, each appearing in the mass spectrum It acquires mass chromatogram of each mass for the peak. Thereafter, the peak detecting means detects a chromatogram peak in the vicinity of the elapsed time corresponding to the mass spectrum in each mass chromatogram in light of predetermined peak detection conditions. For example, if there is free matter from the separation column liquid phase, the background level will change over time, but in such a case, it appears as a peak in the mass spectrum but does not appear as a clear peak in the mass chromatogram. . On the other hand, for example, noise that jumps into an electric system such as a detector often has a spike shape, and such noise can be identified by appropriately setting the peak detection condition. Therefore, the mass having a peak mass spectrum at these factors, removal of substantially peak is made at this point.

Next, the S / N ratio calculating means calculates the S / N ratio of each detected chromatogram peak, and the peak discriminating means compares the calculated S / N ratio with a predetermined threshold, and the S / N ratio is calculated. A significant chromatogram peak is determined when the threshold is greater than or equal to the threshold, and noise or background is determined when the threshold is less than the threshold. Since the signal-to-noise ratio is determined not simply the signal intensity, the significance of the peak is determined with high accuracy by excluding the influence of these factors even when the background and noise are relatively high, for example. be able to. Thus, mass spectrum reconstructing means, thus selecting the mass with a chromatogram peak is determined that a significant, again creating a mass spectrum containing only the peak of its mass. In the mass spectrum created in this way, an undesired peak due to noise or background is removed.

  The threshold for determining the S / N ratio can be set from the outside by the operator, but a plurality of types of thresholds can be set, and the result of determining the S / N ratio of the peak with each threshold You may make it produce the mass spectrum of a different shape based on this in parallel. Accordingly, even when it is difficult to determine the threshold value, the mass spectrum corresponding to the plurality of threshold values can be presented to the operator so that the best mass spectrum can be easily selected.

  According to the data processor for chromatographic mass spectrometry according to the present invention, the peak derived from the background and noise included in the mass spectrum can be accurately removed, and the target substance to be analyzed in the removal process It is possible to reduce the erroneous removal of the peak derived from. Therefore, it is possible to easily obtain a good mass spectrum including only a peak derived from the target substance to be analyzed, thereby improving the accuracy of identification and structural analysis of the target substance.

  Hereinafter, GC / MS will be described with reference to the drawings as an embodiment of a chromatograph mass spectrometer equipped with a data processing apparatus according to the present invention.

  FIG. 1 is a block diagram of the main part of the GC / MS according to this embodiment. The GC / MS performs a gas chromatograph (GC) analysis on a sample to be analyzed to separate various sample components in the time axis direction, and sequentially performs mass analysis on the separated sample components. The MS unit 2 that acquires the detection signal, the data processing unit 3 that receives the detection signal and executes predetermined data processing, the control unit 4 that controls the operations of the GC unit 1 and the MS unit 2, and the MS unit 2 And a storage unit 5 for storing the acquired data. The data processing unit 3 and the control unit 4 are embodied by a general-purpose personal computer (PC) 6, and the functions as the data processing unit 3 and the control unit 4 are achieved by executing a predetermined control program installed in the PC 6. Is done. Connected to the PC 6 are an operation unit 7 which is a pointing device such as a keyboard and a mouse, and a display unit 8 for displaying various graphs to be described later.

The control unit 4 in accordance with the scan interval set by the operation unit 7, and controls the MS unit 2 to scan repeatedly a predetermined quality Ryohan circumference. For example, when the scan interval is 0.3 seconds, the mass spectral data of a predetermined quality Ryohan circumference every 0.3 seconds is stored in the storage unit 5. The data processing unit 3 is thus based on the obtained data, total ion chromatogram of the horizontal axis a time axis, the vertical axis and the signal intensity without limiting the mass, paying attention to a single mass ion mass chromatogram in which the horizontal axis represents time axis, the vertical axis and the signal intensity Te, or can create horizontal axis mass, mass spectrum vertical axis and signal strength, the at some point.

  Next, regarding the data processing unit 3 corresponding to the data processing apparatus according to the present invention, refer to the flowchart of FIG. 2 and each of the diagrams of FIGS. To explain. Here, a substance whose position at which a peak appears in the total ion chromatogram is known is an analysis target.

  When processing is started, first, a mass spectrum to be subjected to background / noise removal processing is determined (step S1). Specifically, for example, when the operator performs a predetermined operation with the operation unit 7, the data processing unit 3 displays a total ion chromatogram as shown in FIG. 3 on the screen of the display unit 8. The operator selects a peak corresponding to the target substance from a plurality of peaks P1 to P5 appearing in the chromatogram while viewing the display, and designates it with the operation unit 7. Alternatively, the data processing unit 3 may automatically detect peaks and search for peaks that satisfy a predetermined condition. When the peak of the target substance is determined in this way, the data processing unit 3 acquires the mass spectrum data at the peak top retention time t1 of the selected peak from the storage unit 5, creates a mass spectrum, and displays it on the display unit 8. indicate.

This mass spectrum is, for example, as shown in FIG. In the example of FIG. 4, but six of the peaks of mass 9 8,99,100,207,300,301 has appeared, not all these are peaks due to the target substance, actually unnecessary peaks due to noise and background Is included. Therefore, in order to remove the peak by such noise or background, the data processing unit 3 collects the data constituting the mass chromatogram with the mass of all the peaks that appear in the mass spectrum from the storage unit 5, A mass chromatogram as shown in FIG. 5 is created (step S2). Here, mass chromatogram against the mass of the six is obtained.

Next, the data processing unit 3 sets a time range near the position of the original chromatogram peak for each mass chromatogram and executes peak detection (step S3). Here, a time width of ± Δt is set with respect to the retention time t1 of the peak top of the chromatogram peak, and peak detection is executed within the time range. This time width Δt is preferably determined in consideration of the half-value width of the chromatogram peak and the like. In general, a time width of several times the half-value width may be set. Specifically, here, Δt is set to 0.5 minutes, and peak detection is performed in the range of the time width 2Δt with the holding time t1 as the center. The peak detection method may be a conventional general chromatogram peak detection method. For example, follow the chromatogram curve sequentially from the left end to the right end of the time range, the point where the slope of the curve becomes a predetermined value or more is taken as the peak start point, and the slope changes from zero to a more negative value. A peak can be detected by setting a point at which the absolute value is equal to or less than a predetermined value as an end point of the peak. Therefore, a peak derived from the target substance is detected by such peak detection, but when a peak due to noise or the like exists within this time range, such a peak is also detected at the same time. On the other hand, for example, as in the case of the mass chromatogram of the mass 2 07, the level of the signal strength will be that no peak is when no clear peak is present in the time range of what is rising. In this example, the result of such peak detection chromatogram peak for Mass 9 8,99,100,300 as shown in FIG. 6 is detected.

Next, the S / N ratio is calculated for each chromatogram peak thus detected in each mass chromatogram (step S4). As a method for calculating the S / N ratio, a method generally used in the past can be used. Here, it is assumed that for example the S / N ratio of the peak definitive in Kakushitsu amount as shown in FIG. 7 is obtained. Thereafter, the calculated S / N ratio is compared with a determination threshold set in advance by an operator, and a peak having an S / N ratio equal to or higher than the determination threshold is determined to be a significant peak (that is, a signal). A peak having a / N ratio smaller than the determination threshold is determined to be a meaningless peak (that is, noise or background) (step S5). For example, if you set the determination threshold 5 and, three peaks of mass 9 8,99,300 is judged to be a signal, a peak of mass 1 00 is determined to be the background / noise (Fig. 7 reference). Here, since the significance of the peak is determined not by the signal intensity but by the S / N ratio, even if the peak signal intensity is apparently high due to the high background level, the peak The significance of can be accurately determined.

The only mass relative to the peak is determined to be a signal, i.e. in this example by selecting only three mass 9 8,99,300 to create again a mass spectrum of the holding time t1 (step S6). The resulting mass spectrum shown in FIG. 8 is a mass spectrum from which background and noise have been removed. As apparent from the comparison between FIG. 4 and FIG. 8, three peaks of mass 1 00,207,301 had appeared in the original mass spectrum has been removed. In this way, it is possible to obtain a mass spectrum from which unnecessary peaks other than the peak derived from the target substance as the original analysis target are removed.

In addition, when it is difficult to determine an appropriate determination threshold value due to, for example, a large number of peaks, a plurality of determination threshold values can be set from the operation unit 7, and a peak is selected by each determination threshold value. A plurality of mass spectra may be created in parallel using the result of performing. For example, when the selection of the peak sets the determination threshold to 15 in the above example, since the peak of the mass 3 00 is regarded as the background / noise, mass spectrum at that time is as shown in FIG. In this way, a plurality of mass spectra may be presented, and the operator may finally select which mass spectrum is appropriate.

  Note that the above embodiment is merely an example of the present invention, and it is obvious that changes and modifications can be made as appropriate within the scope of the present invention. For example, in the above embodiment, the data processing apparatus according to the present invention is applied to GC / MS, but the present invention is a variety of chromatographic mass spectrometers that combine other chromatographs such as LC and mass spectrometers. It can be easily conceived that it can be widely applied to. Further, the data processing apparatus may be a dedicated data processing apparatus even if the predetermined application software is not installed in the personal computer.

The block block diagram of the principal part of GC / MS by one Example of this invention. The flowchart which shows the procedure of the background / noise removal process of the mass spectrum by the data processor of a present Example. The figure which shows an example of a total ion chromatogram. The figure which shows an example of a mass spectrum. The figure which shows an example of a mass chromatogram. The figure which shows the peak detection result in the mass chromatogram of FIG. It shows the determination results and the S / N ratio of the peak obtained in the mass chromatogram for the mass peaks present in the mass chromatogram of FIG. The figure which shows the mass spectrum after a background / noise removal process was performed. The figure which shows the mass spectrum after the background / noise removal process at the time of changing the determination threshold value of S / N ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... GC part 2 ... MS part 3 ... Data processing part 4 ... Control part 5 ... Storage part 6 ... Personal computer (PC)
7 ... operation unit 8 ... display unit

Claims (1)

In a data processing apparatus for chromatographic mass spectrometry that processes data collected by chromatographic mass analysis of a measurement object,
a) Mass spectrum creating means for creating a mass spectrum at a predetermined elapsed time;
b) Mass chromatogram acquisition means for acquiring a mass chromatogram of each mass for each peak appearing in the mass spectrum;
c) peak detecting means for detecting a chromatogram peak in a range in the vicinity of the predetermined elapsed time in each mass chromatogram;
d) S / N ratio calculating means for calculating the S / N ratio of each detected chromatogram peak;
e) Peak discriminating means for judging whether or not it is a significant chromatogram peak by comparing the calculated S / N ratio with a predetermined threshold value;
f) Mass spectrum reconstruction means for selecting a mass having a chromatogram peak determined to be significant and creating a mass spectrum including only the peak of the mass;
g) threshold setting means for setting a plurality of the thresholds;
h) For each set threshold value, the processing of the peak discriminating means and the mass spectrum reconstructing means is executed, mass spectra having different shapes are created in parallel , and the generated mass spectra are displayed on the display unit . Multiple mass spectrum creation means;
A data processing apparatus for chromatographic mass spectrometry, comprising:

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