JP2008190898A - Quadruple mass spectrometer and mass calibration method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quadruple mass spectrometer capable of performing high-precision mass spectrometry, even with respect to a high-frequency power supply that is not equipped with high linearity of precision. <P>SOLUTION: In a mass calibration method for the quadruple electrode type mass analyzer that has a mass separation part equipped with a DC bias and quadruple electrodes to which a high frequency is applied, processes are carried out that includes an ion source for ionizing a measuring sample to generate ions and a detection part for detecting the ions separated in the mass separation part, the measured mass range of ions to be detected is divided into a plurality of sections and the errors between the mass index value of a mass number to be detected, with respect to the respective sections and the actually detected mass number is calculated; and the mass index value of the mass number is calibrated on the basis of the error calculated at each section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a quadrupole mass spectrometer and a mass calibration method for a quadrupole mass spectrometer, and relates to a mass calibration method for a mass spectrometer capable of performing mass scanning by changing a high-frequency potential applied to a mass separation unit. It is.

  A mass spectrometer capable of mass scanning by changing the applied high-frequency voltage generates a quadrupole electric field in the mass separator and detects ions by vibrating the ions in the electric field. What is called a type is common.

  This quadrupole mass spectrometer is described, for example, in Japanese Patent Laid-Open No. 7-296766 (Patent Document 1).

  The ions measured by the mass spectrometer can be given by the following relational expression (1).

M = 0.14 × V / f ² r0 ² (1)
M: Mass number of ions to be observed V: High frequency voltage (V) applied to the electrode
f: High frequency applied to the electrode (MHz)
r0: Electric field radius (cm)
In a normal apparatus, f and r0 in the above formula (1) are fixed values, and V is varied to measure the target mass. That is, the observed mass number M of ions and the high-frequency voltage (V) applied to the electrode are proportional to each other, and the magnitude of the observed mass number can be determined by linearly changing the voltage applied to the quadrupole electric field. I can go home.

  However, an error occurs due to an error in the output voltage, a working error in the electrodes constituting the quadrupole electric field, and the like. Therefore, at the time of actual measurement, a standard sample that is known to be observed near the target mass number is measured in advance, and the relationship between the voltage V and the observed mass M is corrected with a straight line.

JP-A-7-296766

  As described above, high-accuracy mass analysis requires high-precision linearity in the high-frequency power source applied to the mass separation unit.

  The present invention addresses the above problems and provides a quadrupole mass spectrometer capable of performing high-accuracy mass analysis even with a high-frequency power supply that does not have high-accuracy linearity, and a mass calibration method for the quadrupole mass spectrometer The purpose is to do.

  The present invention includes a mass separation unit including a quadrupole electrode to which a DC bias and a high frequency are applied, an ion source that ionizes a measurement sample to generate ions, and a detection unit that detects ions separated by the mass separation unit In the mass calibration method of the quadrupole mass spectrometer having the above, the measurement mass range of ions to be detected is divided into a plurality of sections, and the indicated mass value of the mass number to be detected for each of the sections is actually detected. An error with respect to the mass number calculated is calculated, and the indicated mass value of the mass number is calibrated based on the error calculated for each section.

  The present invention also provides a mass separator having a quadrupole electrode to which a DC bias and a high frequency are applied, an ion source that ionizes a measurement sample to generate ions, and detects ions separated by the mass separator. In a quadrupole mass spectrometer having a detection unit, a function of dividing a measurement mass range of ions to be detected into a plurality of sections, and an indicated mass value of a mass number to be detected for each of the sections are actually detected. A function of calculating an error function indicating an error from the mass number, and a function of calibrating the indicated mass value of the mass number over the plurality of sections based on the error function calculated for each section. And

  According to the present invention, it is possible to provide a quadrupole mass spectrometer and a mass calibration method for the quadrupole mass spectrometer that can perform high-accuracy mass analysis even if the high-frequency power source does not have highly accurate linearity.

  Examples of the present invention will be described below.

  The present invention relates to a quadrupole mass spectrometer and a mass calibration method for the quadrupole mass spectrometer.

  The quadrupole mass spectrometer includes a Q filter type, an ion trap type, and the like. Here, the Q filter type will be mainly described.

  First, the mass separation unit will be described with reference to FIG.

  The mass separation unit 12 is composed of four electrodes 1.

  The opposing surface of the electrode 1 has a hyperboloid. The four electrodes 1 are placed so that the hyperboloid faces each other, and a DC bias and a high frequency are applied. A DC bias having the same polarity is applied to the opposing electrode 1.

  The four electrodes 1 are required to have a hyperboloid with extremely high accuracy, and the gap between the opposing surfaces is also required to have high uniformity accuracy. If the accuracy of the hyperboloid and the gap between the opposing surfaces are not good, a measurement error occurs.

  The ion gas of the measurement sample flows in from one of the opposing spaces of the mass separator 12, flows in the mass separator 1 along the longitudinal direction, and ions of a specific mass flow out from the other. The ions that flow out are detected by the detection unit.

  An outline of the quadrupole mass spectrometer will be described with reference to FIG.

  The ion source 11 ionizes the measurement sample to produce ions. The produced ions are introduced into the mass separation unit 12 evacuated by the evacuation unit 15.

  A voltage (DC bias and high frequency) set by the control unit 14 is applied to the electrode 1 of the mass separation unit 12 from the high frequency power supply unit 16, and mass separation is performed from the supplied ion gas.

  Further, the mass-separated ions are detected as an ion amount by the detection unit 13 to obtain a mass spectrum. The detected mass spectrum is stored in the data processing unit 17.

  In order to actually start using the mass spectrometer of this configuration, a standard sample known to be observed near the target mass number is measured in advance as described in the prior art, and the voltage V is observed. The mass number calibration for correcting the relationship of the mass M to be performed is required.

  Hereinafter, the procedure of mass number calibration in the present embodiment will be described with reference to FIG.

  In step 21 of FIG. 3, first, a standard sample to be measured is determined, and a mixed sample is prepared. (Example) Component A: M / Z200 (M1), Component B: M / Z500 (M2), Component C: M / Z1000 (M3), component D: M / Z1500 (M4)).

  Subsequently, in step 22, the M / z (correction mass number) is registered in the data processing unit 17. About this process, you may have the function implemented after the scanning of the mass spectrometer of step 24 shown below.

  In step 23, the sample prepared in step 21 is introduced into the ion source 11, ionized, and introduced into the mass separation unit 12.

  In step 24, the mass separator 12 is scanned with a predetermined high-frequency voltage, and ions are mass-separated.

  In step 25, the error (Merr) between the measured mass number (Mc) (maximum value of the mass spectrum) and the registered mass number (Mi) in step 22 is calculated.

Mass error (Merr) = (Mi) − (Mc) (2)
Calculate the above mass error for all the components registered in step 22.

  The data processing unit calculates the error obtained at this time as Merr (1), Merr (2), Merr (3), Merr (4),... Register with.

  However, the mass error is measured in the range corresponding to Merr (1) from the mass number 0 (or the minimum mass number in the scanning range of the mass spectrometer); the range exceeding Merr (0) and Merr (n); Since it is not possible, it is registered as Merr (0) = Merr (1) and Merr (n + 1) = Merr (n) for convenience.

  Next, a mass error function in an arbitrary mass range is obtained from the obtained array Merr (i) (I = 1, 2,..., N). At this time, the error function is performed using a cubic spline function capable of estimating the error in consideration of the relationship between the areas before and after.

  In step 26, the data processing unit 17 divides the mass range into (M0−M1), (M1−M2),... (Mn−Mn + 1) based on the error array obtained in step 25. To do.

  In the above, M0 and Mn + 1 are as follows.

M0: Mass number 0 (or the minimum mass number in the scanning range of the mass spectrometer)
Mn + 1: Maximum mass number in the scanning range of the mass spectrometer Next, in step 28, the following tertiary is provided for each section (M0-M1), (M1-M2),... (Mn-Mn + 1). The coefficients Ai, Bi, Ci, Di are calculated so that the polynomial (3) satisfies the following equations (4-1) to (4-6).

  Sdi (M) and Sddi (M) are the first and second derivatives of Si (M), respectively.

Si (M) = Ai + BiM + CiM2 + DiM3 (3)
Si (Mi) = Merr (i) ... (4-1)
Si (Mi + 1) = Merr (i + 1) ... (4-2)
Sdi (Mi) = Sd (i-1) (Mi) (4-3)
Sdi (Mi + 1) = Sd (i + 1) (Mi + 1) (4-4)
Sddi (Mi) = Sdd (i-1) (Mi) (4-5)
Sddi (Mi + 1) = Sdd (i + 1) (Mi + 1) (4-6)
However, when i = 0 and i = N (when there is data on only one side), in the section [Mi, Mi + 1], Si (M) is set to the following first order polynomial (5), and the following equation (6-1) ) And (6-2), the coefficients Ai and Bi are calculated.

Si (M) = Ai + BiM (5)
Si (Mi) = Merr (i) (6-1)
Si (Mi + 1) = Merr (i + 1) (6-2)
Using the above formula, separate error functions Si (M) are calculated for each section [Mi, Mi + 1] (i = 0, 1,... N).

  Next, in step 28, the error function obtained in step 27 is stored in the data processing unit 17.

  This completes the flow of mass calibration. In the subsequent measurement, the error function Si (M) (i = 0,... An error in mass can be estimated.

  FIG. 4 is a flow for measurement using the above-described mass calibration method.

  First, in step 31, set the lower limit (Mmin) and upper limit (Mmax) of the mass range scanned.

  Subsequently, in step 32, the corresponding section (Mn−Mn + 1) of Mmin and Mmax is specified, and mass axes Mmin (C) and Mmax (C) corresponding to Mmin and Mmax are calculated from the corresponding error functions, respectively. The voltage range minimum value (Vmin) and maximum value (Vmax) to be scanned are determined by 1).

  In step 33, the mass range determined in step 32 is scanned and measured.

  In step 34, the obtained mass spectrum is corrected using the error function described above and stored in the data processing unit. The above is the flow during measurement.

  According to the mass spectrometer and the mass calibration method of the mass spectrometer according to the above embodiments, the measurement mass range to be used is divided into a plurality of sections, and an optimal error function is calculated and stored for each section. Then, for the mass M to be detected, the indicated mass value Md is calculated and measured based on the optimum error function among the stored error functions.

  By using the calibration method and the functions related to calibration, the high-frequency power supply unit 16 used for scanning the mass separation unit 12 can perform mass analysis with high accuracy even if the output voltage linearity is not necessarily high.

  Further, in the four electrodes 1 constituting the mass separation unit 12, extremely high accuracy is required for the accuracy of the hyperboloid and the accuracy of the gap between the opposing surfaces. By using the calibration method and the functions related to calibration, high-accuracy mass spectrometry can be performed even if the accuracy of the hyperboloid and the accuracy of the gap between the opposing surfaces are not necessarily high. For this reason, since high processing accuracy and high assembly accuracy are not required, manufacture is easy.

  In addition, when recalibrating the main calibration to improve the workability at the time of mass calibration, the data processing unit 17 performs mass calibration based on the previous mass error or initializes the mass axis, etc. It may have a selection function.

  In the present embodiment, the mass separation unit is described as a Q filter type, but the present invention can also be applied to an ion trap type or the like.

  In the case of the ion trap type described above, the step of guiding and trapping both the sample to be measured and the ions of the standard substance into the ion trap, and selecting precursor ions from the ions of the sample to be measured, Leaving the precursor ions and standard ions in the substrate, excluding other ions, exciting and cleaving the precursor ions to generate product ions, and the precursor ions trapped in the ion trap In addition, it is possible to set a mass calibration function independently for each step of ejecting the product ions and standard ions from the ion trap and guiding them to the detection unit, but the present invention is also applicable to each calibration. Is possible.

It is a figure which concerns on the Example of this invention and shows the mass separation part of a quadrupole-type mass spectrometer. It is a figure concerning the Example of this invention, and is a figure which shows the outline of a quadrupole-type mass spectrometer. FIG. 5 is an operation flowchart of the mass number calibration method according to the embodiment of the present invention. It is an operation | movement flowchart regarding the Example of this invention, and shows a measuring method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrode, 11 ... Ion source part, 12 ... Mass separation part, 13 ... Detection part, 14 ... Control part, 15 ... Vacuum exhaust apparatus, 16 ... High frequency power supply part, 17 ... Data processing part

Claims (9)

A mass separation unit comprising a quadrupole electrode to which a DC bias and a high frequency are applied;
An ion source that ionizes the measurement sample to produce ions,
In a mass calibration method of a quadrupole mass spectrometer having a detection unit that detects ions separated by the mass separation unit,
The measured mass range of ions to be detected is divided into a plurality of sections, and an error between the indicated mass value of the mass number to be detected and the actually detected mass number is calculated for each section, and calculated for each section. A mass calibration method for a quadrupole mass spectrometer, wherein the indicated mass value of the mass number is calibrated based on the error. A mass separation unit comprising a quadrupole electrode to which a DC bias and a high frequency are applied;
An ion source that ionizes the measurement sample to produce ions,
In a mass calibration method of a quadrupole mass spectrometer having a detection unit that detects ions separated by the mass separation unit,
The measurement mass range of ions to be detected is divided into a plurality of sections, and an error function indicating an error between the indicated mass value of the mass number to be detected and the actually detected mass number is calculated for each of the sections. A mass calibration method for a quadrupole mass spectrometer, wherein the indicated mass value of the mass number is calibrated based on the error function calculated every time. In the mass calibration method of the quadrupole mass spectrometer according to claim 2,
The measurement mass range is divided by a plurality of reference mass divisional areas of 3 or more, and a spline function is calculated based on an error corresponding to the reference mass divisional areas adjacent to each other, and the calculated spline function is used as the error function. A mass calibration method for a quadrupole mass spectrometer characterized by A mass separation unit comprising a quadrupole electrode to which a DC bias and a high frequency are applied;
An ion source that ionizes the measurement sample to produce ions,
In a quadrupole mass spectrometer having a detection unit that detects ions separated by the mass separation unit,
A function for dividing the measured mass range of ions to be detected into a plurality of sections, and a function for calculating an error function indicating an error between the indicated mass value of the mass number to be detected and the actually detected mass number for each of the sections. And a function of calibrating the indicated mass value of the mass number over the plurality of sections based on the error function calculated for each section. The quadrupole mass spectrometer according to claim 4,
A quadrupole mass spectrometer having a function of storing the error function. In the quadrupole mass spectrometer according to claim 5,
A quadrupole mass spectrometer having a function of selecting whether a calibrated value or a value before calibration is used as a reference value when mass recalibration is performed. In the quadrupole mass spectrometer according to claim 4,
A quadrupole mass spectrometer having an ion trap type mass separation unit in the mass separation unit. In the quadrupole mass spectrometer according to any one of claims 4 to 7,
A quadrupole mass spectrometer comprising a division setting input unit that divides into a plurality of sections and calibrates over a plurality of sections. In the mass calibration method of the quadrupole mass spectrometer according to claim 1,
The mass separator has an ion trap type mass separator,
Guiding and trapping both the measurement sample and the standard substance ions in the ion trap;
Selecting precursor ions from the ions of the measurement sample, leaving the precursor ions and standard ions in the ion trap, and excluding other ions;
Exciting and cleaving the precursor ions to generate product ions;
A quadrupole mass capable of performing mass calibration independently for each step of ejecting the precursor ions and their product ions trapped in the ion trap and ions of a standard substance from the ion trap and guiding them to the detection unit. Mass calibration method for analyzers.

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