JPS63168960A - Scanning method of quadruple mass spectrometer - Google Patents

Abstract

PURPOSE:To prevent a strong current from flowing in a detector and to protect the detector from deterioration, by making either a high-frequency voltage or a DC voltage deviate from a specific relation, and avoiding to detect a background peak, at the point where the background peak exists. CONSTITUTION:In a scanning method of a quadruple mass spectrometer, either a DC voltage or a high-frequency voltage which is applied to a rod is made to deviate from a specific scanning condition at the point where a background peak exists. And the scanning line is made to detour and deviate from the stable area of the background component ions with a strong peak, and the detection of the peak current is avoided. Therefore, the deterioration of a detector such as a secondary electron multiplier owing to a large ion current of an unnecessary background component can be prevented, and the service life of the detector is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a mass spectrum measurement technique using a quadrupole mass spectrometer.

(Prior Art) When measuring the mass spectrum of a sample, a strong background peak may exist in the spectrum. For example, in a gas chromatograph mass spectrometer, there is a strong solvent peak in which the sample is dissolved, in the case of CI ionization, there is a reaction ion peak, and in an apparatus that uses discharge plasma as an ion source, there is a strong peak due to ions of gas components forming the bulk plasma. Appears as a background peak.

The presence of strong peaks in the mass spectrum means that a strong ion current has flowed into the detector. There was a problem with accelerating the

(Problems to be Solved by the Invention) The present invention prevents strong ion current originating from background components from flowing into the detector when measuring a mass spectrum using a quadrupole mass spectrometer. The purpose is to prevent deterioration.

(Means for Solving the Problems) In order to achieve the above object, the scanning method of the quadrupole mass spectrometer according to the present invention is such that the scanning method of the quadrupole mass spectrometer according to the present invention maintains the direct current voltage and the high frequency voltage applied to the rods in a constant relationship with each other. In a quadrupole mass spectrometer that scans the mass spectrum of a sample by changing the frequency, the background peak can be removed by changing either the high frequency voltage or the DC voltage from the above relationship at the location where the background peak exists. This is to avoid detection.

(Operation) Quadrupole mass spectrometers utilize the fact that the stability of ion trajectories varies depending on the mass number of ions when ions pass through a four-electrode field formed in an area surrounded by four rods. When the DC voltage applied to the rod is U1 and the high frequency voltage is V, the stability of ions in the four-electrode field is determined by the parameters a and q defined by the following equation. Given as shown.

a = 4 e U/mω'r o' (
1) q = 2e V / mω'ra"
(2) However, U: DC voltage V: High frequency voltage m: Ion mass ω: High frequency angular frequency ro: Radius of the inscribed circle of the four rods The part surrounded by A, B, and C in the diagram has a certain mass. This is the stable region of ions, and now the point (a, q) on the a-q plane
When U and V are scanned so as to draw a straight line DE, the line segment F
Ions with the above mass number draw a stable trajectory between G and reach the detector, and their condensation mass spectrum is obtained.

The relational expression between U and V corresponding to this scanning line DE can be expressed as U=α+βv(3) from equations (1) and (2).
When deviates from this relational expression and detours the scanning line in the direction of U>α+βv(4) as shown by the broken line HIJK in the figure, ions with the mass number on the line segment FG will no longer reach the detector.

(Example) Figure 2 shows the DC type pressure U (
3) This shows an example in which the scanning line is detoured by deviating from the conditions of the equation.The horizontal axis represents mass, and the values of U and V that give the scanning line in Figure 1 are expressed as a function of mass. It is something. In the same figure, ions with mass numbers MI and M3 reach the detector, but ions with mass number M,
Since the scanning line passes through an unstable region as shown by the broken line in the figure, it does not reach the detector.

Therefore, if the mass number of the strong peak of the background component, which is known in advance, is made to correspond to M in FIG. 2, it is possible to prevent a strong peak current from flowing into the detector.

Note that FIG. 3 shows an example in which the scanning line is detoured by changing the high frequency voltage V.

(Effects of the Invention) As described above, in the scanning method of a quadrupole mass spectrometer, the present invention maintains either the DC voltage or the high frequency voltage applied to the rod at a constant level at a location where a background peak exists. By deviating from the scanning conditions and bypassing the scanning line out of the stable region of background component ions with strong peaks, we avoided detection of peak currents, which makes it difficult to detect detectors such as secondary electron multipliers. This has the advantage of preventing deterioration of the detector due to large ion current due to unnecessary background components and improving the lifetime of the detector.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is an explanatory diagram of the operation of one embodiment of the same, and FIG. 3 is an explanatory diagram of the operation of another embodiment of the same.

Claims (1)

[Claims] (1) In a quadrupole mass spectrometer that scans the mass spectrum of a sample by changing the DC voltage and high-frequency voltage applied to the rod while maintaining a constant relationship with each other, the high-frequency voltage is By making either of the and the DC voltage deviate from the above relationship,
A scanning method for a quadrupole mass spectrometer, characterized in that it avoids the detection of background peaks.