JPH08129001A - Chromatograph mass spectrometer using sim method - Google Patents

Abstract

PURPOSE: To automatically perform the grouping of an objective compd. (monitor ion) before the SIM (selective ion monitor) analysis. CONSTITUTION: At first, the mass spectrometric analysis of a sample is performed in a scanning mode and a total ion chromatogram (TIC) is formed from a collected mass spectrum. Next, the respective peaks of the TIC are detected in a predetermined standard and a place where a peak interval is a predetermined value or more is set to a boundary to divide the TIC into a plurality of sections (grouping). A monitor ion is changed over at every divided section to perform SIM analysis.

Description

Detailed Description of the Invention

[0001]

This invention relates to a selective ion monitor (Se
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromatograph mass spectrometer that performs analysis by the lected ion monitoring (SIM) method, and particularly to an apparatus that automatically performs grouping for grouping all ions monitored in the SIM method according to retention time.

[0002]

2. Description of the Related Art A gas chromatograph mass spectrometer (GC
/ MS) is widely used for component analysis in the fields of environment, pharmacy, general engineering, natural product chemistry and the like, and the SIM method is used especially for quantitative analysis of trace organic compounds.

In a usual analysis method (mass scanning method) using a gas chromatograph mass spectrometer, as shown in FIG.
First, a sample is injected into a carrier gas by an injector (injector) 11 and each component in the sample is temporally separated by a gas chromatograph (GC) 12. When the gas discharged from the gas chromatograph section 12 is continuously measured in time focusing on appropriate characteristics, a chromatogram 2 as shown in FIG.
1 is obtained. Next, the gas thus separated into components is introduced into the mass spectrometric analysis unit (MS) 13, and mass scanning is repeatedly performed at short time intervals by the scanning pattern 22 shown in the lower part of FIG. Accordingly, in each peak portion of the chromatogram 21, a mass spectrum 23 (relative intensity) representing the ion intensity (relative intensity) at each mass number (actually, the value m / z obtained by dividing the mass number m by the charge z) is obtained (see FIG. )) Is obtained. By comparing the pattern of this mass spectrum 23 with each compound data of a predetermined database, the chromatogram 21
The compound of each peak is identified. Normally, for the convenience of later data processing, after removing the background from the continuous mass spectrum 23 as shown in FIG. 9A, the centroid of the graph subdivided for each mass number is taken. Convert to data expressed as relative intensity ratio. The mass spectrum at this time becomes a graph (called centroid display) as shown in FIG. 9B, and the comparison with the database is performed by this pattern.

However, the mass scanning method has a problem that the absolute detection intensity at each mass number (m / z) is low and the S / N ratio is poor because the scanning speed in the mass spectrometric section 13 is high. Therefore, when attempting to perform quantitative analysis of trace components, it is necessary to qualitatively confirm in advance what components are present in the sample by the mass scanning method, and then when performing gas chromatography-mass analysis again. The SIM method is used in which only the mass numbers of the components (monitor ions) whose existence is confirmed by qualitative analysis are detected (monitored) in the mass analysis unit 13. In addition, although the gas chromatograph was mentioned as the example above, the same mass spectrometry can be performed also in a liquid chromatograph.

[0005]

In a chromatographic mass spectrometer capable of performing the SIM method, the number of ions that can be simultaneously monitored is limited.
Therefore, when there are many compounds contained in the sample,
It is not possible to monitor the ions of all compounds. For example, a device that can simultaneously monitor 10 types of ions, one target ion (the ion that is the basis of quantification) and one reference ion (the ion for confirming the type of compound) for each compound, a total of 2 When monitoring individual ions, 1
Only 5 compounds can be quantified in one measurement.

Further, in order to increase the sensitivity of analysis and to be able to quantify a very small amount of compound, it is necessary to take a sufficiently long ion detection time (called dwell time) in mass spectrometry. However, since the peak duration (peak width) of the chromatogram is limited, the cycle time (tc in Fig. 5) is sufficiently short in order to perform mass spectrometry as close to the peak top as possible. You need to do it. In order to meet these conflicting problems, only a small number of ions should be monitored in one cycle.

Therefore, a method called grouping is used in which the chromatogram 21 is divided at appropriate points and a different ion set is used for each portion. That is, as shown in FIG. 7, until the time td, the ions of the compound having the retention time up to that time are set as monitor ions (group I), and thereafter, the ions of the compound having the retention time at that time td or more are monitored. By making it an ion (group II), it becomes possible to perform mass spectrometry for a larger number of compounds with a longer dwell time. Note that in FIG. 7, an example of two divisions is given for simplicity, but
It may be further divided into a large number.

For such grouping, conventionally, an analyst views the chromatogram 21 and designates an appropriate division position while considering that the number of monitor ions does not exceed the limit number of the apparatus. Was there. Therefore, the SI
Before performing the M analysis, the analyst had to perform various instruction work using a keyboard, a mouse or the like, and the grouping work was one obstacle to complete automation of SIM analysis. Therefore, the present invention provides a chromatograph mass spectrometer that automatically performs grouping in the SIM method.

[0009]

SUMMARY OF THE INVENTION The present invention, which has been made to solve the above-mentioned problems, provides a SIM in which a sample separated into components by a chromatographic device is analyzed by a mass spectrometer for predetermined monitor ions. In the chromatograph mass spectrometer using the method, a) Collect a mass spectrum for each short time by repeatedly performing mass scanning on the sample that has passed through the chromatograph in the mass spectrometer every short time. And b) Create an all-ion chromatogram from the collected mass spectra, and divide the total-ion chromatogram into multiple sections with the location where the interval between each peak of the total-ion chromatogram is equal to or greater than a predetermined value as a boundary. And c) switching the monitor ion for each divided section
And SIM control means for performing M analysis.

[0010]

The dividing means is a total ion chromatogram (TI
The TIC is divided with a boundary at a position where the interval between the peaks in C) is a predetermined value or more. As a result, the target compound contained in the sample is divided into a plurality of groups according to the retention time. At this time, since the peaks that are close to each other are not divided, clear grouping is possible, and a decrease in analysis sensitivity is prevented. Within each group, the SIM control means monitors only the ions of the target compound contained in that group, and when the boundary is reached, the monitored ion is switched to the ion of the target compound of the next group for SIM analysis. As a result, monitor ions can be detected within a long dwell time within each group.

[0011]

EXAMPLE A gas chromatograph mass spectrometer (GC / MS) which is an example of the present invention will be described with reference to FIGS. The gas chromatograph mass spectrometer of this embodiment is shown in FIG.
As shown in FIG. 2, it is composed of an injector (injector) 11, a gas chromatograph section (GC) 12, a mass spectrometric section (MS) 13, a data processing / control section 14, and the like. Data processing·
The control unit 14 includes an external storage device 15 and a display 1.
6 is connected.

A procedure for determining monitor ions by this gas chromatograph mass spectrometer, performing automatic grouping, and then performing SIM analysis will be described with reference to FIGS. First, a method will be described in which the analyst first specifies the target compound before performing the analysis in the scan mode (the mode in which the mass is continuously scanned to obtain a continuous mass spectrum).

First, the analyst inputs the name of the target compound to be analyzed from the keyboard (step S).
1). On the other hand, the data processing / control unit 14 refers to the database stored in the external storage device 15 connected to the data processing / control unit 14 to refer to the mass spectrum of the input compound (specifically, the molecular ion M of the compound). The mass number (m / z) of the ⁺ and fragment ions [MA] ⁺ and the base peak (= ion having a relative intensity of 100% and the data of the intensity ratio) are read (step S2).

Next, when the analyst injects the sample from the injector 11 according to the instruction from the data processing / control unit 14, the data processing / control unit 14 performs mass spectrometry in the scan mode (step S3). This analysis will be performed later
Preparatory for analysis. Data processing / control unit 1
Among the mass spectra obtained at each time point in this scan mode analysis, the search unit 4 searches for one that matches the mass spectrum read in step S2 (step S4). Next, a TIC (total ion chromatogram) is created from all the mass spectra, and the retention time tr of the target compound is detected from the position of this matching mass spectrum in the TIC (step S5). Then, the monitor ion of each target compound is automatically determined (step S
6). The details of the method for automatically determining the monitor ions by the data processing / control unit 14 are described in the specification of Japanese Patent Application No. 6-194924 filed by the applicant of the present application. In this way, after the retention time tr and the monitor ion for SIM analysis are determined for all the target compounds input in step S1, the SI as shown in FIG.
Create M table.

Next, these monitor ions are subjected to automatic grouping described later (step S7). After the grouping is completed, the sample is injected again from the injection part 11 and the SIM analysis is started (step S8). On this occasion,
In the mass spectrometric section 13, the SI created as a result of grouping
Based on the M table (FIG. 2B), the set of monitor ions is switched for each partial section of the retention time, and SIM analysis is performed.

Next, the automatic grouping in step S7 will be described in detail. The apparatus of this embodiment can perform automatic grouping by two methods, and the analyst can select either mode in advance. One is a mode that emphasizes sensitivity and tries to quantify each compound as accurately as possible (sensitivity-oriented mode), and the other emphasizes that analysis is performed quickly. This is a mode (overall observation mode) in which it is only necessary to compare different concentration ratios.

First, the case where the sensitivity priority mode is selected will be described with reference to the flowchart of FIG. First, the data processing / control unit 14 takes a predetermined time width a (for example, 1 minute) before and after the peak top of each target compound in TIC to determine a section centered on one peak (this section is a peak section). Is called) (step S21). After determining the peak intervals for all the target compounds, the gap length (time) b between the adjacent peak intervals is calculated in order from the shorter retention time tr (step S
22), which is a predetermined reference value b0 (for example, 0.5 minutes)
It is determined whether or not the above (step S23). When the length of the gap between adjacent peak sections is less than b0 (including the case where adjacent peak sections overlap)
Cannot be divided between the peaks, the process returns to step S22 and the same determination is performed for the next adjacent peak section. When there is a gap of b0 or more between the adjacent peak sections, it is set as a division point of the grouping, and a group is set by the monitor ions of the compound of the peak before that point (step S24). Then, it is determined whether or not the check of the gap length has been completed for all the peaks (step S25), and if there are still peaks, the process returns to step S22. In this way, it is determined whether or not each adjacent peak section of the TIC can be sequentially divided, and the division is performed at the dividable portions, so that all monitor ions are grouped. The result of grouping is
The SIM table as shown in FIG.
It is referred to later when performing SIM analysis (step S8). As a result, in the sensitivity-oriented mode, grouping is performed so that the number of compounds included in one group is as small as possible, and high-sensitivity SIM analysis can be performed.

In the above mode, it is also possible to adjust the purpose of analysis by changing the interval b0 that serves as a reference for dividing. That is, by setting the interval b0, which is the criterion for division, to be small, the number of divisions increases, and higher sensitivity analysis becomes possible. On the contrary, by setting the reference interval b0 large, it is possible to reduce the number of divisions and to approximate the whole observation mode described below.

Next, the case where the sensitivity priority mode is selected will be described with reference to the flowchart of FIG. First, the data processing / control unit 14 displays the SIM table (see FIG.
The number N of all monitor ions written in (a)) is counted (step S31). Then, it is determined whether or not the number N of all monitor ions is equal to or less than the number β of ions that can be simultaneously detected by the gas chromatograph mass spectrometer (step S32). If N ≦ β, all monitor ions are grouped (step S33). Thereby, the quantitative ratio of the entire target compound can be measured quickly.

On the other hand, if N> β in step S32, it is not possible to measure all the target compounds by one SIM analysis due to the limitation of the apparatus. Therefore, it is assumed that all monitor ions are divided into NG = [INT (N / β) +1] (INT (x) represents the maximum integer not exceeding x) groups. Then, at this time, the compounds in the SIM table are divided so that the number of compounds is as equal as possible in each group (the number of monitor ions may be equal). Specifically, monitor ions are counted in order from the one with the shortest retention time in the SIM table, and INT
If the (N / NG) -th item coincides with the break of the compound, it is set as the temporary boundary, and if not, the break of the compound immediately before that is set as the temporary boundary (step S34). Next, the difference Δtr between the retention times tr of the peaks on both sides of the temporary boundary thus determined is compared with a predetermined lower limit value Δtrmin (step S35). If Δtr ≧ Δtrmin, the temporary boundary is determined as As a boundary, the monitor ions up to that point are grouped (step S36). When Δtr <Δtrmin, the break of the compound immediately before that is set as the boundary (step S37). Even at the break immediately before that, Δtr <Δ
In the case of trmin, the break immediately before that is set as the boundary (same). After deciding the first group in this way, NG
It is determined whether the boundaries have been determined for all the groups (step S38). If the number of confirmed groups has not yet reached NG, the process returns to step S34, counting of monitor ions is started again immediately after the confirmed group, and the temporary boundary and the main boundary are set at the INT (N / NG) th position in the same manner as above. decide.

After the monitor ions are grouped in this way to form monitor ion sets of NG groups, if monitor ions remain in the SIM table, the number of groups is set to [NG + 1] and the same processing as above is performed. Is repeated (steps S39 → S40 → S3
4). As a result, the grouping of all monitor ions in the overall observation mode is completed.

In the above, the target compound was designated first, and then the mass spectrometry was performed in the scan mode.
It is also possible to first perform mass spectrometry in scan mode, create a TIC, and then specify a target compound. This will be described with reference to the flowchart of FIG.
First, a sample is injected from the injection part and mass spectrometry is performed in scan mode (step S51). A TIC is created from the mass chromatogram obtained at each time point (step S52), and all peaks appearing in the TIC are detected according to a predetermined standard (step S53). With respect to each of these peaks, a database (DB) stored in the external storage device 15 is referred to search for a compound that matches the mass spectrum. And like above
Monitor ions are determined in advance by the method described in Japanese Patent Application No. 6-194924 (step S54). On the other hand, a TIC graph in which a compound name is added to each peak is displayed on the display 16 and the analyzer waits for designation of the target compound. The analyst specifies the peak of the target compound for SIM analysis by operating the mouse or keyboard while looking at the TIC curve displayed on the display 16 (step S55). When the target compound is designated, the data processing / control unit 14 creates a SIM table as shown in FIG. 2A (step S56). The above-described automatic grouping is performed on each monitor ion in the SIM table (step S57). Then, when the analyst again injects the sample from the injecting unit 11 and performs a predetermined analysis start key operation, the data processing / control unit 14 performs SIM analysis based on the SIM table (FIG. 2B) in which the grouping is performed. Is performed (step S58).

[0023]

In the chromatograph mass spectrometer according to the present invention, grouping is automatically performed without requiring a troublesome operation by an analyst. Therefore, in combination with automation of other operations, SIM analysis can be fully automated, and anyone can easily perform highly sensitive analysis. Further, in the present apparatus, by varying the time of the peak interval serving as a reference of division, it is possible to arbitrarily select subdivided grouping or rough grouping as much as possible. Therefore, for example, if you want to perform analysis with the highest sensitivity possible, reduce the reference time interval to perform subdivision grouping, and conversely, if you want to analyze as quickly as possible and observe the overall composition ratio, increase the reference time interval. Optimal grouping can be performed according to the purpose, such as performing rough grouping.

[Brief description of drawings]

FIG. 1 is a flowchart showing one procedure of SIM analysis in a gas chromatograph mass spectrometer which is an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the contents of a SIM table created before SIM analysis.

FIG. 3 is a flowchart showing a procedure of automatic grouping processing in the sensitivity-oriented mode.

FIG. 4 is a flowchart showing a procedure of automatic grouping processing in the whole observation mode.

FIG. 5 is a flowchart showing a procedure of another SIM analysis method in the gas chromatograph mass spectrometer of the embodiment.

FIG. 6 is a schematic configuration diagram of a gas chromatograph mass spectrometer according to an example.

FIG. 7 is a graph showing an example of a total ion chromatogram.

FIG. 8 is a graph showing a relationship between a chromatogram and a mass scanning pattern.

FIG. 9 is a graph showing an example of a mass spectrum and its centroid display.

[Explanation of symbols]

 11 ... Injector 12 ... Gas chromatograph part 13 ... Mass spectrometric part 14 ... Data processing / control part 15 ... External storage device 16 ... Display

Claims (1)

[Claims] 1. A chromatograph mass spectrometer using the SIM method, wherein a sample separated into components by a chromatograph is analyzed by a mass spectrometer with respect to predetermined monitor ions. A mass spectrum sampling means for collecting mass spectra for each short time by repeatedly performing mass scanning for each sample in the mass spectrometer for the sample thus prepared, and b) creating an all-ion chromatogram from the collected mass spectra. , A dividing means for dividing the total ion chromatogram into a plurality of sections with a position where the interval of each peak of the total ion chromatogram is equal to or more than a predetermined value as a boundary, and c) switching monitor ions for each of the divided sections, and SI
A chromatograph mass spectrometer using the SIM method, comprising: SIM control means for performing M analysis.