JPH08129002A - Chromatograph mass spectrometer using SIM method - Google Patents

Abstract

(57) [Summary] [Purpose] Automatically set the optimum dwell time and cycle time according to the analysis target. [Constitution] A mass chromatogram of each target compound ion is prepared from the mass spectrum obtained by the scan mode analysis, and the target ion and the reference ion are determined based on the S / N ratio of the peak. Further, the dwell time of both ions is calculated based on the ratio of the peak intensity of the target ions of all the target compounds and the ratio of the detection limit.

Description

Detailed Description of the Invention

[0001]

This invention relates to a selective ion monitor (Se
The present invention relates to a chromatograph mass spectrometer that performs analysis by the lected ion monitoring (SIM) method, and particularly, the detection time (dwell time dwell) of each monitor ion in the SIM method.
time) and the cycle for detecting all monitor ions (cycle time)
cycle time) related device to set automatically.

[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 a sample injection section (injector) 11, and each component in the sample is temporally separated by a gas chromatograph section (GC) 12. When the gas discharged from the gas chromatograph section 12 is continuously measured in time focusing on appropriate characteristics, a chromatogram 21 as shown in FIG. 4 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 as shown in the lower part of FIG. As a result, at each peak portion of the chromatogram 21, a mass spectrum 23 (FIG. 6 (a) showing the ion intensity (relative intensity) at each mass number (actually, the mass number m divided by the charge z). )) Is obtained. The compound of each peak of the chromatogram 21 is specified by collating the pattern of the mass spectrum 23 with each compound data of a predetermined database. Normally, for the convenience of data processing later, after removing the background from the continuous mass spectrum 23 as shown in FIG. 6A, 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. 6B, 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]

When analytical values are important in the fields of medicine, environment, etc., in addition to the peak (target peak) that is the basis of quantification, other peaks of the compound (see Peak), it may be required to confirm that the peak is indeed of the target compound. In this case, high-sensitivity analysis cannot be performed unless an appropriate target peak is selected, and it cannot be surely confirmed that the target compound is an appropriate reference peak. Therefore, conventionally, it has been difficult for beginners to select these peaks.

Next, in the SIM method, the detection conditions are changed stepwise in the mass spectrometric section as shown in FIG. 7, and predetermined dwell times td1, td2, ... Are provided for each monitor ion for detection. In order to increase the sensitivity and to be able to quantify a very small amount of compound, it is desirable that the dwell times td1, td2, ... Of the monitor ions be sufficiently long. However, as shown in FIG. 5, since the duration (peak width) of the peak in the chromatogram is limited, in order to perform mass spectrometry as close to the peak top as possible, the cycle time tc ( = Σtdi + α) cannot be made too long. For this reason, conventionally, an expert has determined the optimal dwell time for each compound to be analyzed by experience. Therefore, the present invention provides a chromatograph mass spectrometer capable of automatically setting the optimum dwell time and cycle time according to the analysis target, and enabling anyone to perform highly sensitive SIM analysis.

[0007]

Means for Solving the Problems The present invention, which has been made to solve the above-mentioned problems, provides a target ion as a basis for quantitative calculation and a reference ion for confirming a compound for each analyte compound in a sample. Quantitative analysis is performed by detecting each ion in the mass spectrometer for the dwell time set for each target ion and reference ion for the sample separated by the chromatograph. In a chromatograph mass spectrometer using the SIM method, a) A mass for collecting a mass spectrum for each short time by repeatedly performing mass scanning on the sample that has passed through the chromatograph device in the mass spectrometer for each short time. Create a mass chromatogram of the ion of the target compound from the spectrum sampling means and b) mass spectrum data. Mass chromatogram generating means for determining the target ion and reference ion based on the S / N ratio of the peak of the mass chromatogram of that ion for each target compound, and d) all target compounds Dwell time determining means for calculating the dwell time of the target ion and the reference ion based on the ratio of the peak intensity of the target ion and the ratio of the detection limit.

The mass spectrum collected by the mass spectrum collecting means includes a selected ion spectrum obtained by performing SIM analysis with monitor ions equal to or more than the number of target monitor ions to be finally obtained.

[0009]

The mass chromatogram creating means creates a mass chromatogram of all target compound ions (molecular ions and fragment ions) based on the data of all mass spectra. At this time, the number of ions forming a mass chromatogram is set to be larger than the number of monitor ions (the number of target ions + the number of reference ions) to be determined later.
The monitor ion determination means determines the target peak and the reference peak based on the S / N ratio of each peak of these mass chromatograms. Then, the dwell time determining means calculates the dwell time of each target ion and the reference ion based on the ratio of the peak intensity (height, area, etc.) of the target ion of each target compound and the detection limit ratio of each target compound. To do. Since the dwell time determined by this reflects the peak intensity and detection limit value of each target compound, the sensitivity analysis of each target compound is well balanced in the subsequent SIM analysis, and the highly sensitive quantitative analysis as a whole. Is performed.

[0010]

EXAMPLE A gas chromatograph mass spectrometer (GC / MS) will be described as an example of the present invention. As shown in FIG. 3, the gas chromatograph mass spectrometer of the present embodiment has an injector (injector) 11, a gas chromatograph section (G).
C) 12, a mass spectrometric unit (MS) 13, a data processing / control unit 14, and the like. The procedure for performing SIM analysis with this gas chromatograph mass spectrometer will be described with reference to FIGS. 1 and 2. It is assumed that the name of the target compound has been known from the information on the sample, the qualitative analysis, etc. before the following processing.

First, the operator uses an input device (keyboard, mouse, etc.) to determine various parameters (measurement parameters) relating to the measurement conditions in the gas chromatograph section 12 and the mass spectrometric section 13, and the dwell time and cycle time described later. The parameter (analysis parameter) used when performing is given to the data processing / control part 14 (step S1).

The analysis parameters set in step S1 include the following. n: maximum number of compounds included in one ion set (default = 5) α: number of ions monitored by one compound (default = 2) γ: number of measurement points per peak of chromatogram (default = 20) Note) If the operator does not specify these analysis parameters, the default values in parentheses are used.

Next, a standard solution containing the target compound is injected from the injector 11, and measurement is performed in a scan mode (a mode in which a continuous mass spectrum is obtained by continuously scanning the mass) (step S2). . Rough SIM (for example, the dwell time of each monitor ion is constant) in which detailed parameters to be determined later are not set by the monitor ions more than the number of monitor ions to be SIM-measured later, not in the scan mode. The measurement may be performed in the mode. In addition, it is convenient for subsequent calculations to keep each target compound contained in the standard solution at the same concentration.

Next, a chromatogram of each monitor ion is created from the data obtained in the scan mode or rough SIM measurement (step S3). Then, peaks are detected from this chromatogram, and the S / N ratio and peak width of each peak are measured (step S4). Then, the monitor ion corresponding to the one having the highest S / N ratio among the peaks of each compound is set as the target ion, and the other (α-1) monitor ions are set as the reference ions (step S5).
As described above, the target ion and the reference ion are determined.

Next, make sure that the number of compounds in each group does not exceed the analysis parameter n set in step S1.
All target compounds are grouped (grouped) according to the retention time (step S6). The grouping may be performed by the operator himself or may be automatically performed by a method separately filed by the applicant of the present application. Then, for each grouped ion set, the following steps S7 to S18 are performed.
Is processed. Alternatively, the following treatment may be performed with all the target compounds as one group without performing the grouping. In the following description, for convenience of notation, the number of target compounds in each group is n.

First, the average value β [sec] of the peak widths of the peaks corresponding to the target ions and the reference ions included in the group is calculated (step S7). The average value β may be calculated only from the peaks of the target ions. Next, the intensity of the highest intensity target ion in the group is set to 1, and the reciprocal a of the ratio of the intensity of the other target ions (TI) to the intensity a
k (k = 1, ..., N) is calculated (step S8). According to this definition, ak ≧ 1.

Next, it is checked whether or not the detection limit value [ppm] is required for each target compound, and if there is a required one, the maximum detection limit value is set to 1 and the The reciprocal bk (k = 1, ..., N) of the ratio of the detection limit values of other target ions (TI) is calculated (step S9). From this definition, bk ≧ 1. BK = 1 for target compounds for which detection limits are not required
And

On the other hand, the SIM measurement cycle time tc is calculated by tc = β / γ (1) (step S10). Then, the basic unit time t0 is calculated by the following equation (step S11). However, in the following equation, Σ (k = 1, n) represents the total sum from k = 1 to k = n. tc = Σ (k = 1, n) (ak ・ bk ・ t0) + (α-1) ・ n ・ t0 (2) In the above equation, the first term on the right side [Σ (k = 1, n) (ak・ Bk ・ t
0)] corresponds to the dwell time of the target ion, and the second term [(α-1) · n · t0] corresponds to the dwell time of the reference ion.

Next, it is judged whether or not the basic unit time t0 calculated in this way is longer than the minimum switching time tmin which is the limit of the hardware of the mass spectrometric section 13 (step S12). If t0 ≧ tmin, the basic unit time t0 calculated in step S11 is used to set the dwell time of each target ion to [akbkt0] (k = 1, ...,
n), and the dwell time of the reference ion is [t0] (uniform) (step S13).

If t0 is shorter than tmin, then tmi
Cycle time t calculated by substituting n for t0 in equation (2)
It is determined whether c (tmin) is shorter than β / 10 (step S14). That is, tc (tmin) =. SIGMA. (K = 1, n) (ak.bk.tmin) + (. Alpha.-1) .n.tmin≤.beta. / 10 (3). When the formula (3) is satisfied, the minimum switching time tmin is used, the dwell time of each target ion is set to [ak · bk · tmin] (k = 1, ..., N), and the dwell time of the reference ion is set to [ tmin] (uniform) (step S15). In this case, the number of SIM points included in the average peak width β is γ or less, but it is guaranteed by Expression (3) that it is 10 or more.

When it is determined in step S14 that the cycle time tc (tmin) calculated using tmin is still shorter than β / 10, the correction coefficient K is calculated by the following equation (step S16). Σ (k = 1, n) (K ・ ak ・ bk ・ tmin) + (α-1) ・ n ・ tmin = β / 10 (4) Formula (4) is a target extended by ak and bk. By shortening the ion dwell time with the correction coefficient K,
The cycle time is [β / 10]. However, when there is a target ion with ak = bk = 1, the dwell time of the ion cannot be further shortened, so that the dwell time of the ion is tmin of tmin as shown in the following equation (4 '). Leave and only for longer dwell times (Σ (k
= 2, n)) The correction coefficient K is multiplied. tmin + Σ (k = 2, n) (K · ak · bk · tmin) + (α-1) · n · tmin = β / 10 (4 ′) After the correction coefficient K is calculated in this way, its value and tmin The target ion dwell time using {tmin, K
.A2.b2.tmin, ..., K.an.bn.tmin}, and the reference ion dwell time is tmin (step S1).
7). In this case, the average number of SIM points in each peak will not be 10 or less, and it is guaranteed to measure the mass spectrum at a position sufficiently close to the peak top.

As described above, after determining the dwell time of the target ion and the reference ion for each case, these values are written in the SIM table (step S18). When the above processing is completed for all the ion groups divided into groups in step S6, SIM analysis is performed based on the values in this SIM table (steps S19 → S2).
0). As a result, the target ion and reference ion of each compound are detected at the optimum dwell time, and balanced and highly sensitive analysis is performed.

[0023]

In the chromatographic mass spectrometer according to the present invention, the target ion and the reference ion are automatically determined, and the optimum dwell times of them are automatically determined. SIM analysis can be performed. Since these automatically determined dwell times reflect the peak intensity and the detection limit value of each target compound, the sensitivity of each target compound is well balanced in SIM analysis, and the overall high sensitivity is obtained. Quantitative analysis is performed.

[Brief description of drawings]

FIG. 1 is a first half part of a flowchart showing a SIM analysis procedure in a gas chromatograph mass spectrometer according to an embodiment of the present invention.

FIG. 2 is the latter half of the flowchart.

FIG. 3 is a schematic configuration diagram of a gas chromatograph mass spectrometer according to an embodiment.

FIG. 4 is a graph showing an example of a total ion chromatogram.

FIG. 5 is a graph showing a relationship between a chromatogram and a mass scanning pattern.

FIG. 6 is a graph showing an example of a mass spectrum and its centroid display.

FIG. 7 is a graph showing the relationship between the dwell time and the cycle time during SIM analysis.

[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 target ion as a basis for quantitative calculation and a reference ion for compound confirmation are defined for each of the analysis target compounds in the sample, and for the sample separated into components by a chromatograph. In a chromatographic mass spectrometer using SIM method, a quantitative analysis is performed by detecting each ion only during a dwell time set for each target ion and reference ion in the mass spectrometer. Mass spectrum sampling means for collecting mass spectra for each short time by repeatedly performing mass scanning on the sample that has passed through the mass spectrometer at each short time, and b) From the mass spectrum data, the ion of the target compound Mass chromatogram creating means for creating a mass chromatogram, and c) For each target compound, A monitor ion determining means for determining the target ion and the reference ion based on the S / N ratio of the peak of the ion mass chromatogram, and d) the target based on the ratio of the peak intensity of the target ions of all the target compounds to the detection limit. A chromatograph mass spectrometer using the SIM method, comprising: dwell time determining means for calculating a dwell time of ions and reference ions.