JP3683749B2 - Mass spectrometry method - Google Patents

Description

このような重み付け係数を用いることにより、ｎ番目のマススペクトルにとって時間的により近い位置にあるマススペクトルの中の内部標準物質の位置情報を重視した形で、内部標準物質由来の信号の平均的位置を計算させることができる。
【００２４】
また、マススペクトルがバーグラフの形で記録されている場合に、前述した２つの変形例を併用した形で、内部標準物質由来のピークに重み付けを行なっても良いことは言うまでもない。
【００２５】
【発明の効果】
以上述べたごとく、本発明の質量分析方法によれば、精密質量マスクロマトグラムを測定するに際して、そのマススペクトルの前後に測定した複数枚のマススペクトルの内部標準物質に関する情報を用いて質量校正、あるいは質量校正の補正を行なうようにしたので、測定時の内部標準物質の導入量を減らしても従来と同じ精度の質量校正、あるいは質量校正の補正が行なえ、結果的に、内部標準物質に由来するケミカルノイズや目的成分のイオン化の抑制現象を低減することができるので、実質的な感度の向上が図れる。
【図面の簡単な説明】
【図１】従来の質量分析装置を示す図である。
【図２】本発明の質量分析装置による測定例を示す図である。
【符号の説明】
１・・・成分分析装置、２・・・質量分析計、３・・・システム、４・・・トータルイオンクロマトグラム（ＴＩＣ）、５・・・マススペクトル。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mass spectrometry method, and more particularly, to a mass spectrometry method that can suitably perform accurate mass measurement of sample components separated by chromatography or the like.
[0002]
[Prior art]
Component analysis means that separates various components in a sample as a function of time, such as gas chromatography, liquid chromatography, electrophoresis, etc., and a mass that repeatedly ionizes the separated sample components and repeatedly measures the mass spectrum Mass spectrometry combined with an analyzer is widely known as an excellent analytical technique.
[0003]
FIG. 1 schematically shows an apparatus configuration for carrying out this analysis method. In the figure, reference numeral 1 denotes a sample component analyzer such as a gas chromatograph device, a liquid chromatograph device, an electrophoresis device or the like. Various sample components separated in 1 are introduced into the mass spectrometer 2 through an interface unit (not shown). The result of ionization and mass analysis performed by the mass spectrometer 2 is taken into the data system 3 and analyzed.
[0004]
In such a configuration, a mass chromatogram is usually used to confirm how various sample components flow out of the sample component separation apparatus 1, that is, the chromatographic behavior of various sample components. The mass chromatogram is continuously observed by repeatedly scanning the mass spectrometer 2 while the sample component flows out from the sample component analyzer 1 such as a gas chromatograph device, a liquid chromatograph device, or an electrophoresis device. Mass spectra are stored one after another in the data system 3, and after the measurement is completed, only the intensities of ions belonging to an arbitrary mass range are extracted from the stored mass spectra, and temporal changes in the ion intensities are reproduced as chromatograms. Obtained by configuring. And generally the width of the arbitrary mass range said here is 1u in many cases.
[0005]
When the elemental composition of the target ion is known in advance, the observational mass range is specified by specifying a very narrow range around the theoretical mass number calculated from the elemental composition. It is theoretically possible to obtain a mass chromatogram of only ions. To make this happen,
1. The resolution of the mass spectrometer is high enough to separate the ions of interest from other contaminant ions.
[0006]
2. The mass measurement accuracy of each mass spectrum is high enough not to confuse the target ion with other contaminant ions.
is required. Such a mass chromatogram is called a high-resolution mass chromatogram or an accurate mass chromatogram. In order to obtain this mass chromatogram, an appropriate internal standard substance is continuously introduced into the ion source, and the internal standard substance is converted into the internal standard substance. It is common to ensure the necessary mass measurement accuracy by performing mass calibration or correction of mass calibration for each mass spectrum using ions having a known mass number.
[0007]
[Problems to be solved by the invention]
In such a configuration, it is necessary to introduce a sufficient amount of an internal standard substance into the mass spectrometer in order to keep the mass calibration of each mass spectrum or the accuracy of correction of the mass calibration high. However, when a large amount of an internal standard substance is introduced into the mass spectrometer, ionization of the target component to be observed is suppressed, or ions derived from the internal standard substance are scattered inside the mass spectrometer to be the observation object. It was difficult to achieve both sufficient mass accuracy and detection sensitivity, because it became chemical noise in the accurate mass mass chromatogram of the target ion.
[0008]
In view of the above points, an object of the present invention is to provide a mass spectrometry method capable of measuring an accurate mass mass chromatogram with high sensitivity even if the amount of an internal standard substance required for accurate mass measurement is reduced. .
[0009]
[Means for Solving the Problems]
In order to achieve this object, a mass spectrometry method according to the present invention comprises a component analysis means for separating components in a sample as a function of time, and sequentially ionizing the separated sample components and measuring their mass spectra repeatedly. In a mass spectrometry method combined with a mass spectrometer, a standard substance having a known mass number is ionized together with the sample components to measure a mass spectrum, and the mass spectrum is calibrated based on a signal derived from the standard substance. The method is characterized in that mass calibration is performed with reference to signals derived from standard substances observed in a plurality of mass spectra obtained close to each other in time.
[0010]
In addition, the method of referring to the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in time, averages the position of the signal among the plurality of mass spectra, and the average position and the standard It is characterized in that mass calibration of the mass spectrum is performed from the known mass number of the substance.
[0011]
In addition, the method for referring to the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in time is weighted in relation to the intensity of the signal, and then the position of the signal is plural. The mass spectrum is averaged, and mass calibration of the mass spectrum is performed from the average position and the known mass number of the standard substance.
[0012]
In addition, the reference method of the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in terms of time, after performing weighting based on a predetermined rule specified in advance for each mass spectrum, The signal position is averaged among a plurality of mass spectra, and mass calibration of the mass spectrum is performed from the average position and the known mass number of the standard substance.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of the mass spectrometric method according to the present invention. In the figure, reference numeral 4 denotes a total ion chromatogram (TIC) when mass analysis is performed on a sample component separated and outflowed as a function of time from a sample component analyzer such as a gas chromatograph device, a liquid chromatograph device or an electrophoresis device. ). This is the sample component that was separated in time by the sample component analyzer and observed as a total ion amount by the mass spectrometer. The horizontal axis is the time until the sample component flows out from the sample component analyzer, and the vertical axis Indicates the ionic strength derived from the sample components.
[0014]
Reference numeral 5 denotes individual mass spectra constituting the TIC. The horizontal axis represents ion mass-to-charge ratio (m / z), and the vertical axis represents ion intensity. In these, mass spectra obtained by repeatedly scanning the mass of sample components flowing out from the sample component analyzer with a mass spectrometer are arranged according to the passage of time. In the figure, the peak marked with an asterisk (*) is a mass spectrum signal derived from the added internal standard substance.
[0015]
By calibrating the m / z value with reference to the signal position of the internal standard substance, accurate mass measurement can be performed. Normally, m / z is accurately calibrated by interpolating between the signals using a plurality of mass spectrum signals derived from the internal standard substance. Further, after calibration, an ion peak having a predetermined m / z value is extracted from each mass spectrum and connected with a line as time passes, whereby a precise mass mass chromatogram of the target ion can be obtained.
[0016]
In such a configuration, in order to generate an accurate mass mass chromatogram, conventionally, calibration of m / z was performed based only on signal position information derived from an internal standard substance observed in each mass spectrum. . In the present invention, when mass calibration of each mass spectrum or correction of mass calibration is performed, not only information of the mass spectrum but also mass calibration using information of a plurality of mass spectra measured before and after the mass spectrum, Alternatively, correction of mass calibration is performed.
[0017]
For example, when trying to perform mass calibration of the nth mass spectrum in the mass spectrum group measured by the gas chromatograph mass spectrometer, (n−m) th, (n−m + 1) th, (N−m + 2) th,..., (N−2) th, (n−1) th, nth, (n + 1) th, (n + 2) th,..., (N + m−2) th, ( The information on the internal standard substance contained in each of the total (2m + 1) mass spectra of the (n + m−1) th and (n + m) th is used.
[0018]
That is, when the mass spectrum has already been peak-determined and recorded in the form of a bar graph, the signal position derived from the internal standard substance contained in each (2m + 1) mass spectrum is averaged, and the average is obtained. Calibration of the mass number of the measurement sample or correction of the calibration of the mass number is performed from the position and the known mass number of the internal standard substance. The signal position mentioned here means the time from the start of scanning until the mass spectrum appears in the case of a magnetic mass spectrometer, and the time of flight of the mass spectrum peak in the case of a time-of-flight mass spectrometer. To do.
[0019]
If the mass spectrum is not yet peak-determined and is recorded in the form of a profile, after adding all (2m + 1) mass spectra, the peak derived from the internal standard is determined to determine the position, From the position information and the known mass number, mass calibration of each mass spectrum or correction of mass calibration is performed.
[0020]
This enables accurate mass calibration even when the S / N ratio of the signal derived from the internal standard substance is somewhat poor, thereby reducing the amount of internal standard substance introduced into the mass spectrometer. The ionization of the analysis component to be suppressed, or ions derived from the internal standard substance are scattered inside the mass spectrometer and become chemical noise on the accurate mass mass chromatogram of the target ion in advance. It can be avoided.
[0021]
Note that various variations are possible in averaging the signal derived from the internal standard substance among a plurality of mass spectra. For example, when the mass spectrum is recorded in the form of a bar graph, it is simply added when averaging the positions of the peaks derived from each internal standard substance contained in each (2m + 1) mass spectrum. Rather than performing weighting in proportion to the intensity of each internal standard substance-derived peak in each mass spectrum, the average position is obtained, and mass calibration or mass calibration is performed from the average position and the known mass number. You may make it correct | amend. By weighting in this way, m / z can be calibrated with emphasis on information of a mass spectrum with a good S / N ratio.
[0022]
As another modification, when the mass spectrum is recorded in the form of a profile, the positions of the peaks derived from the internal standard substances contained in each of the (2m + 1) mass spectra are averaged. At this time, instead of simply adding, the peaks may be weighted based on a predetermined weighting factor designated in advance and then added. For example, when m = 2, the following weighting is performed.
[0023]

By using such a weighting factor, the average position of the signal derived from the internal standard substance in a form that places importance on the positional information of the internal standard substance in the mass spectrum that is closer in time to the nth mass spectrum. Can be calculated.
[0024]
In addition, when the mass spectrum is recorded in the form of a bar graph, it goes without saying that the peak derived from the internal standard substance may be weighted in a form using the two modified examples described above in combination.
[0025]
【The invention's effect】
As described above, according to the mass spectrometry method of the present invention, when measuring an accurate mass mass chromatogram, mass calibration is performed using information on internal standard substances of a plurality of mass spectra measured before and after the mass spectrum, Or, since the calibration of mass calibration is performed, the mass calibration with the same accuracy as before or the calibration of mass calibration can be performed even if the amount of internal standard material introduced during measurement is reduced. Therefore, the chemical noise and the phenomenon of suppressing ionization of the target component can be reduced, so that the sensitivity can be substantially improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional mass spectrometer.
FIG. 2 is a diagram showing an example of measurement by the mass spectrometer of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Component analyzer, 2 ... Mass spectrometer, 3 ... System, 4 ... Total ion chromatogram (TIC), 5 ... Mass spectrum.

Claims (4)

A mass analysis method that combines a component analysis means for separating components in a sample as a function of time and a mass spectrometer that sequentially ionizes the separated sample components and repeatedly measures a mass spectrum thereof. When measuring a mass spectrum by ionizing a standard substance together with the sample components and performing mass calibration of the mass spectrum based on a signal derived from the standard substance, observation is made with a plurality of mass spectra obtained close in time A mass spectrometric method characterized in that mass calibration is performed with reference to a signal derived from a standard material. The reference method of the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in time is obtained by averaging the position of the signal among the plurality of mass spectra, and calculating the average position and the standard substance. 2. The mass spectrometric method according to claim 1, wherein mass calibration of the mass spectrum is performed based on the known mass number. The method of referring to the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in time is weighted in relation to the intensity of the signal, and then the position of the signal is set to the plurality of masses. 2. The mass spectrometric method according to claim 1, wherein the spectrum is averaged and the mass spectrum is calibrated from the average position and the known mass number of the standard substance. The reference method for the signal derived from the standard substance observed in the plurality of mass spectra obtained close to each other in time is obtained by performing weighting based on a predetermined rule specified in advance for each mass spectrum, and then the signal. 2. The mass spectrometric method according to claim 1, wherein the position of is averaged among a plurality of mass spectra, and mass calibration of the mass spectrum is performed from the average position and the known mass number of the standard substance.

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