JP3600731B2 - Mass spectrometry system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mass spectrometry system for quantitatively analyzing compounds having a plurality of isomers having the same mass number.
[0002]
[Prior art]
A system that combines chromatography with a mass spectrometer (MS) is used for quantitative analysis of a substance having a small amount and a large amount of impurities (miscellaneous substances). According to this system, a compound to be quantified is temporally separated by chromatography, and only a specific ion of the quantified compound can be selectively observed by a mass spectrometer. Dioxins (PCDDs / PCDFs) have a large number of isomers (Isomers), and each isomer is separated in time by chromatography, and is obtained as a SIM (Selected Ion Monitoring) chromatogram of a specific ion measured by a mass spectrometer. Observed. In the case of a compound having such isomers (Compound), each isomer is almost temporally separated by chromatography, and the peak of each isomer is observed on one SIM chromatogram. However, some isomers are not separated by chromatography and cannot be separated by mass spectrometry because they have the same mass.
[0003]
The compound is quantified from the peak intensity of the SIM chromatogram. At this time, in order to remove the influence of the fluctuation of the apparatus, an internal standard compound is added to the sample, and the concentration calculation for measuring the SIM chromatogram includes the internal calculation. The ratio of the peak of the standard compound to the peak of the quantitative compound is used. This is called the internal standard method.
[0004]
Hereinafter, a description will be given using dioxin as an example.
For dioxin analysis, gas chromatography (GC) is used as chromatography. A high-resolution mass spectrometer with a resolution of, for example, 10,000 or more is used to remove the influence of foreign matter and obtain a SIM chromatogram of only the dioxin compound. In the measurement by the mass spectrometer, a highly sensitive SIM method is used, an internal standard method is used as a quantification method, and for example, a 13C compound is used as the internal standard substance.
[0005]
FIG. 6 is a diagram for explaining the flow of quantitative analysis of dioxin compounds, and FIG. 7 is a diagram showing an example of a SIM chromatogram of one compound T4CDF of dioxins. In order to shorten the time of the quantitative analysis operation, measurement and quantitative analysis of a plurality of compounds of dioxins are performed by one injection. The procedure of the quantitative analysis is as follows.
First, a SIM chromatogram of a dioxin compound is measured by GC / MS (step S21). Next, a peak of the SIM chromatogram is detected (step S22), and the detected peak is associated with an isomer of dioxin (assignment), and only the peak of the dioxin isomer is extracted (step S23). Then, quantitative calculation is performed using the extracted peak of the isomer, and the concentration is calculated (step S24).
[0006]
Compound T4CDF, one of the dioxins, has 38 isomers. Most of these isomers are temporally separated by gas chromatography (GC) and have the same mass. Therefore, as shown in FIG. 7, a mass spectrometer focuses on one ion on a SIM chromatogram. Appears as a peak separated into The quantitative analysis is performed using the peak intensity as described above.
[0007]
[Problems to be solved by the invention]
However, since dioxin is a trace analysis, and the detected peak includes a peak due to a foreign substance, it is necessary to extract only the dioxin isomer peak instead of the peak due to the foreign substance in the peak detection. In particular, in a sample having a low concentration, a peak due to a foreign substance may be mixed, and may be erroneously recognized as a dioxin peak. In order to prevent this misidentification, the following method is adopted.
[0008]
One is the method based on ratio shek. This involves first measuring the SIM chromatograms of two or more ions using the isotope of the quantitative compound, and calculating the peak ratio of the two SIM chromatograms. Since the abundance ratio of the isotope is known, it is determined whether or not the peak is the dioxin peak depending on whether or not the peak ratio is the same as the abundance ratio. The determination of the peak by the ratiosheck is widely used in the analysis using a mass spectrometer.
[0009]
The other is a method in which a peak is determined by an analyst. The time at which the peak appears (retention time) is determined by the GC column, and has already been reported in the literature as a relative retention time (eg, JJ Ryan, HBS Conacher, lg panopio). , BP-Y.Lau, ja hardy, Y. Masuda, J. Chromatogr. 541 (1991) 131-183). Also, there is a specific peak pattern depending on the type of sample (in the case of dioxin, exhaust gas, drainage, ash). Therefore, based on the peak retention time and the peak pattern, the analyst determines whether or not the peak is a dioxin peak.
[0010]
As described above, the isomer assignment of dioxins is performed based on the retention time of the SIM chromatogram and the intensity pattern. Usually, this operation is performed manually by an analyst with reference to the literature and data already measured. I have.
[0011]
Further, the holding time may be shifted due to the following factors.
Since the dioxin quantitative analysis is a trace analysis, various substances are mixed in the sample. Therefore, the retention time of the chromatogram may be shifted depending on the degree of contamination of the sample and over time. Further, after measuring a plurality of samples, the column may be cut out about 1 m from the sample introduction end of the column in order to remove dirt. This will slightly shorten the chromatogram retention time. Of course, when the columns are exchanged, even if the columns are of the same type, they do not always show exactly the same retention time.
[0012]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and it is an object of the present invention to calculate a retention time and perform isomer assignment using the calculated retention time, thereby preventing misassignment.
[0013]
Therefore, the present invention is a mass spectrometry system for quantitatively analyzing a compound having a plurality of isomers having the same mass number, a chromatography for temporally separating the compound, and a specific ion for selecting a specific ion and temporally performing the chromatography. A mass spectrometer that measures the separated SIM chromatogram, and a correction curve that corrects the retention time using a beauty standard compound that is not based on the measured SIM chromatogram are determined. From the correction curve, the calculated retention of each isomer of the quantitative compound is calculated. Data processing means for determining time, assigning isomer peaks, and performing quantitative calculation.
[0014]
Further, the data processing means is characterized in that a reference retention time is obtained based on a SIM chromatogram of a compound added as an internal standard compound, and further comprising an output means for outputting data, wherein the data processing means comprises: The measured SIM chromatogram and the chromatogram pattern of the calculated retention time of each isomer are output from the output means by adding information of assignment to each peak of the measured SIM chromatogram. .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of a mass spectrometry system according to the present invention, and FIG. 2 is a diagram showing an example of a correction curve and a SIM chromatogram. In the figure, 1 is a chromatography, 2 is a mass spectrometer, 3 is an analysis processing control device, 4 is a data storage device, 5 is an output device, 11 is an analysis control unit, 12 is a retention time table, 13 is a correction curve calculation unit, Reference numeral 14 denotes a retention time calculation unit, 15 denotes an assignment processing unit, and 16 denotes a quantitative calculation processing unit.
[0016]
In FIG. 1, chromatography 1 is, for example, gas chromatography (GC) in which an isomer of a quantitative compound is temporally separated using an analytical column having a length of several tens of meters (eg, 60 m). Is a method for measuring a mass chromatogram, that is, a SIM chromatogram, which captures a temporal change of an ion having a specific mass from a quantitative compound temporally separated by chromatography 1. The analysis processing control device 3 is a computer that controls the chromatography 1 and the mass spectrometer 2, processes the SIM chromatograms of various quantitative compounds measured by the mass spectrometer 2, and performs peak assignment, quantitative calculation, and the like. For example, it comprises an analysis control unit 11, a retention time table 12, a correction curve calculation unit 13, a retention time calculation unit 14, an assignment processing unit 15, a quantitative calculation processing unit 16, and the like. The data storage device 4 is an external storage device that stores the SIM chromatogram measured by the mass spectrometer 2 and various data processed by the analysis processing control device 3, and the output device 5 is a display that outputs the data. And a printer.
[0017]
Further, the analysis control unit 11 controls the chromatography 1 and the mass spectrometer 2 and takes in the SIM chromatograms of various compounds measured by the mass spectrometer 2. The retention time table 12 is a table having a standard retention time of a SIM chromatogram of an internal standard compound (Internal Standard) and a retention time of a SIM chromatogram of various compounds (quantitative compounds) to be analyzed. The correction curve calculation unit 13 refers to the reference retention time of the retention time table 12 from the measured retention time of the SIM chromatogram of the internal standard compound measured by the mass spectrometer 2, thereby obtaining various quantitative compounds QNT-A, QNT- This is to calculate a correction curve T = (1 + a) T ₀ + b for obtaining the retention time of B. For example, as shown in FIG. 2, the vertical axis T ₀ is plotted on the vertical axis T ₀ for the internal standard compounds IS-A and IS-B. The reference holding time of the table 12 is used, and the horizontal axis T is the corresponding measurement holding time. The retention time calculator 14 corrects the retention time of each isomer peak appearing in the SIM chromatogram of the quantitative compound based on the correction curve of the correction curve calculator 13, and calculates the calculated retention time of each isomer of the quantitative compound. Ask. The assignment processing unit 15 detects the peak of the measured SIM chromatogram of the quantitative compound, sets a retention time window based on the calculated retention time and its allowable range, and calculates the peaks existing in the retention time window as shown in FIG. The peak closest to the retention time is assigned to the isomer. The quantitative calculation processing unit 16 performs quantitative calculation by extracting, for example, only the peak of the dioxin isomer based on the assigned result, and calculating the concentration using the extracted peak of the isomer.
[0018]
Next, the overall processing flow will be described. FIG. 3 is a diagram for explaining the flow of the quantitative analysis process by the mass spectrometry system according to the present invention. FIG. 4 is a diagram showing a measured SIM chromatogram and a display example of bars showing patterns of the SIM chromatogram. FIG. 14 is a diagram illustrating a print output example of a display screen of No. 4;
[0019]
In the quantitative analysis process, as shown in FIG. 3, first, SIM chromatograms of the internal standard compounds IS-A and IS-B and the quantitative compounds QNT-A and QNT-B are measured (step S11), and the internal standard compound IS-A is measured. A, The measurement retention time of the SIM chromatogram of IS-B is obtained (step S12), and a correction curve T = (1 + a) T ₀ + b is calculated (step S13). Next, the calculated retention time of the quantitative compounds QNT-A and QNT-B is determined from the correction curve (step S14), and the isomer peak of the measured quantitative compound of the unknown sample is assigned from the calculated retention time (step S15). . Since the assigned peak corresponds to the dioxin isomer, the assigned peak and the other peaks are identified and displayed according to differences in color and other display modes as shown in FIG. 4 (step S16), and the intensity of the assigned peak is determined. The quantitative calculation is performed by calculating the concentration using the (area value) (step S17).
[0020]
The reference retention time must be determined in advance from a SIM chromatogram of a sample with high impurity concentration and low concentration (internal standard compound). The correction curve is for calculating the calculated retention time, and it has been found that when the deviation of the retention time is small, the approximation can be well approximated by linear correction as shown in FIG.
[0021]
The correction curve is calculated from the peaks of the SIM chromatogram of the internal standard compound. In the case of the linear equation, at least two peaks are required. In the case of dioxin, multiple compounds such as QNT-A and QNT-B are measured in a single injection as shown in FIG. 2 in order to increase the efficiency of the analysis operation. Therefore, two or more internal standard compounds IS-A and IS- B isomer peak is present. Since the internal standard compound is added, it always exists, has a certain intensity, and the number of peaks of the internal standard compound is small, so that isomer assignment can be easily performed. For example, there is a method of assigning in order of retention time from a strong peak. The coefficients a and b of the correction curve T = (1 + a) T ₀ + b are calculated by the least squares method from the measured retention time of the internal standard compound and the reference retention time.
[0022]
Once the correction curve is determined, the retention time of the quantitative compound can be calculated, and the range of the retention time can be calculated from the calculated value and the allowable time. By assigning the peak in the range as the corresponding isomer, the peak of the quantitative compound can be calculated. Assignments can be made. At this time, when there are a plurality of peaks in the range, the following method is available. One is to select the peak with the highest intensity, and the other is to select the peak closest to the calculated value. In the case of dioxin, the method of selecting the peak closest to the calculated value was good. The verification can determine whether the assignment is correct using the difference between the calculated retention time and the measured value. If the difference value is large, there is a possibility of misassignment.
[0023]
In order to clarify the correspondence between the peaks of the measured SIM chromatogram and the isomers, it is extremely effective to display a typical SIM chromatogram pattern together with the measured SIM chromatogram on the screen as shown in FIG. is there. In the display example shown in FIG. 4, the upper display is the measured SIM chromatogram, the middle display is the bar chromatogram showing the SIM chromatogram pattern and the calculated retention time, and the lower display is the SIM chromatogram of the internal standard compound. FIG. 5 shows a printout example of the screen. Here, by comparing the SIM chromatogram in the upper row and the bar display in the middle row, it is clearly understood that, for example, the peaks indicated by the crosses in FIG. 5 do not correspond to the peaks of the isomers of T4CDF. Some of these peaks have a ratio check of OK, indicating that determination by ratio check alone is not sufficient.
[0024]
The bar displaying the chromatogram pattern can be set as the intensity on the vertical axis and the retention time on the horizontal axis based on literature values or measured values. In addition, since the horizontal axis can be moved, reduced, and enlarged by a primary expression by manual operation, the peak of the measured SIM chromatogram and the pattern of the chromatogram can be matched as necessary. This is useful when the automatic isomer assignment was not performed correctly or when determining the reference retention time.
[0025]
Since the bar display of the chromatogram pattern is used as the user interface as described above, for example, one of the bars is selected on the screen shown in FIG. 4 and isomers are assigned to the peaks of the measured SIM chromatogram by Drag & Drag. be able to. By such a device, the isomer assignment of the peak of the measured SIM chromatogram can be easily performed.
[0026]
The peaks of the measured SIM chromatogram shown in FIG. 4 are displayed in different colors, for example, as follows.
Blue: RetioCheck = NotOK Isomer = NotAssigned
Light blue: RetioCheck = OK Isomer = Not Assigned
Yellow: RetioCheck = NotOK Isomer = Assigned
Green: RetioCheck = OK Isomer = Assigned
As a result, the information of the peak ratio check and the isomer assignment becomes clear at a glance.
[0027]
In the display shown in FIG. 4, a SIM chromatogram of the 13C compound is also shown as an internal standard compound, but the 13C compound contains only an important isomer. It is the 2378 isomer. It can be considered that the retention time is almost the same between 13C and 12C. Therefore, the peak of the quantitative compound corresponding to the peak retention time of 2378 of 13C is the 2378 isomer, and the assignment can be verified.
[0028]
Note that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the embodiment, dioxin has been described as an object. However, other than dioxin, compounds having a plurality of similar isomers, for example, analysis using a standard internal standard method such as PCB analysis can be used. Although the correction curve uses a linear expression, a polynomial, a spline function, or the like may be used. Further, when there is no peak of the internal standard compound, that is, when the internal standard method is not used, a special compound may be added to correct the retention time. Although the chromatogram pattern is displayed in a bar format, it may be displayed as continuous data.
[0029]
【The invention's effect】
As is clear from the above description, according to the present invention, a correction curve is obtained from the retention time of the peak of the internal standard compound measured by the same injection, and the retention time of the peak of the quantitative compound is corrected using the correction curve. Therefore, it is possible to prevent misassignment of the peak of the quantitative compound due to contamination of the sample, a change with time, and a shift in the retention time due to partial cutting of the column. Moreover, since the internal standard compound has a small number of peaks and always has a certain level of intensity, the assignment can be performed easily and reliably, and the assignment is automated using the calculated retention time obtained from the correction curve. be able to. Furthermore, by displaying the calculated retention time and the chromatogram based on the measurement retention time together, the analysis result can be verified. In addition, by displaying a typical chromatogram pattern, it is easy for the analyst to understand the correspondence between peak retention time and peak pattern, and it is possible to correctly assign isomers of quantitative compounds, Erroneous recognition of peaks due to the above.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a mass spectrometry system according to the present invention.
FIG. 2 is a diagram showing an example of a correction curve and a SIM chromatogram.
FIG. 3 is a diagram illustrating a flow of a quantitative analysis process by the mass spectrometry system according to the present invention.
FIG. 4 is a diagram showing a display example of a bar showing a measured SIM chromatogram and a pattern of the SIM chromatogram.
FIG. 5 is a diagram showing a print output example of the display screen of FIG. 4;
FIG. 6 is a diagram for explaining the flow of quantitative analysis of a dioxin compound.
FIG. 7 is a diagram showing an example of a SIM chromatogram of one compound T4CDF of dioxins.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Chromatography, 2 ... Mass spectrometer, 3 ... Analysis processing control device, 4 ... Data storage device, 5 ... Output device, 11 ... Analysis control part, 12 ... Retention time table, 13 ... Correction curve calculation part, 14 ... Retention Time calculation unit, 15: Assignment processing unit, 16: Quantitative calculation processing unit

Claims (4)

A mass spectrometry system for quantitatively analyzing compounds having a plurality of isomers having the same mass number,
Chromatography to temporally separate compounds;
A mass spectrometer for selecting a specific ion and measuring a SIM chromatogram temporally separated by the chromatography;
A data for determining a correction curve for correcting the retention time using an internal standard compound based on the measured SIM chromatogram, calculating the calculated retention time of each isomer of the quantitative compound from the correction curve, assigning isomer peaks, and performing quantitative calculation. A mass spectrometry system comprising a processing unit. 2. The mass spectrometry system according to claim 1, wherein said data processing means obtains a reference retention time based on a SIM chromatogram of a compound added as an internal standard compound. 2. The data processing apparatus according to claim 1, further comprising an output unit that outputs data, wherein the data processing unit outputs the measured SIM chromatogram and a chromatogram pattern of a calculated retention time of each isomer from the output unit. Mass spectrometry system. 4. The mass spectrometry system according to claim 3, wherein the data processing means adds assignment information to each peak of the measured SIM chromatogram and outputs the result from the output means.

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