JPH0432149A - Qudrupole mass spectrometer - Google Patents

Abstract

PURPOSE:To facilitate drastically high resolution by determining the dc voltage and high frequency voltage to be applied to a qudrupole mass spectrometer based on a second stable region of a Mathieu chart. CONSTITUTION:A ratio lambda of dc voltage U and a maximum amplitude E of high frequency voltage is determined as lambda<lambda0=0.4877, as shown in a line (b), based on a second stable region II in a Mathieu chart, and this level is maintained, while the dc voltage U and the maximum amplitude E of high frequency voltage are increased. Since the shape of the second stable region II of the Mathieu chart is longitudinal, and it is very narrow in its width, the value of DELTAm is very small compared with a case where a first stable region I is used. The value of DELTAm is not almost changed regardless of the value of lambda. Even when the dc voltage U and the maximum amplitude E of high frequency voltage are varied, and the ratio thereof lambda are varied, it is possible to maintain the initial value of DELTAm almost constantly. The value DELTAm can thus be reduced to a very small value in a stable manner, while resolution can be easily and drastically increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to a quadrupole mass spectrometer. More specifically, the present invention relates to a quadrupole mass spectrometer that allows high resolution to be easily obtained.

(Prior Art) A quadrupole mass spectrometer is a mass spectrometer that can be suitably used for measuring gas components in a vacuum container of 10-''Pa or less.

A conceptual diagram of the quadrupole electrode section of a quadrupole mass spectrometer is shown in FIG. As shown in the figure, a quadrupole mass spectrometer has four electrodes (quadrupole) in its analysis tube, and the facing electrodes are connected to each other and are connected to a DC voltage U. A high frequency voltage E cosωt (ω is angular velocity, t is time) is applied at the same time.

When ions enter from the tip of such a quadrupole electrode section, the ions move in the direction along the electrode (Z direction) and vibrate in the XY force direction. Only ions with m/e value) pass through the analysis tube,
Other ions diverge in the XY force directions and collide with the electrode. This makes it possible to select ions.

When selecting ions, mass scanning uses the DC voltage U and the maximum amplitude E of the high-frequency voltage as their ratio (U/E=λ).
Conventionally, when setting this ratio λ, the first part of the Matthew diagram based on the Mathieu function as shown in Figure 2 is used to set the ratio λ.
The stable region (hatched region (I) in Figure 2) is used (“Special Functions” by Morikazu Toda, Asakura Shoten, p.96-100).
, 1981). FIG. 3 is an enlarged view of the vicinity of the first stable region of the Matthew diagram shown in FIG. 2.

That is, as shown in the straight line a in FIG. 3, the ratio λ between the DC voltage U and the maximum amplitude E of the high-frequency voltage (that is, the slope of the straight line a) is λ times λ. = 0.1678 and the maximum amplitude E of the high-frequency voltage is increased, when the straight line a passes through the first stability region (I), Δm with the mass m as the center
A singly charged ion having a mass width of , will pass through the analysis tube. For this reason, conventionally the desired resolution (m/Δm
), the ratio λ between the DC voltage U and the maximum amplitude E of the high-frequency voltage was determined so that Δm based on the first stability region (I) of the Matthew diagram becomes a predetermined value. For example, when trying to increase the resolution (m/Δm), the ratio λ between the DC voltage U and the maximum amplitude E of the high-frequency voltage should be set to λO=
0.1678, thereby reducing the mass width Δm of ions passing through the analysis tube.

(Problem to be Solved by the Invention) However, the ratio λ between the DC voltage U and the maximum amplitude E of the high frequency voltage is λ. Even if we try to approach = 0.1678 and reduce Δm, if we use the first stable region (I) of the Matthew diagram as described above, the shape of the region (I) will become significantly wider downward. Therefore, the value of λ becomes slightly smaller, and λ. ∆
Therefore, if the maximum amplitude E of the DC voltage U or high-frequency voltage fluctuates even slightly and λ becomes small, Δm becomes significantly larger than the predetermined value, making it difficult to achieve high resolution. It cannot be obtained stably.In order to obtain stable resolution, it is necessary to stabilize the DC voltage or high-frequency voltage power supply, but there is a limit to this.For this reason, the first stability of the conventional Matthew diagram A quadrupole mass spectrometer using region (I) has a problem in that it is not possible to increase the resolution.

This invention was made to solve this problem, and its purpose is to obtain quadrupole mass spectrometry with dramatically high resolution.

(Means for Solving the Problem) In order to achieve the above-mentioned object, the quadrupole mass spectrometer of the present invention adjusts the direct current voltage and high frequency voltage applied to the quadrupole electrodes to the second stable value of the Matthew diagram. It is characterized by being determined based on the area.

The second stable region of the Matthew diagram used by the quadrupole mass spectrometer of the present invention is indicated by the shaded region (n) of the Matthew diagram shown in FIG. Further, FIG. 1 is an enlarged view of the vicinity of the second stable region of the Matthew diagram shown in FIG. 2.

In this invention, the ratio λ between the DC voltage U and the maximum amplitude E of the high frequency voltage is defined as the second stable region (If) of the Matthew diagram.
Based on the straight line shown in Figure 1, λo = 0.4
877, and the maximum amplitude E of the high frequency voltage is increased. In this case, the ions passing through the analysis tube become monovalent ions having a mass width of Δm centered on mass m, similar to the conventional example using the first stability region (I) of the Matthew diagram. However, as can be seen from Figure 1, the shape of the second stable region (n) of the Matthew diagram is elongated vertically and its width is very narrow, so the value of Δm is smaller than the first stable region (I). Significantly smaller than when used. Further, the value of Δm hardly changes regardless of the value of λ. Therefore, even if the DC voltage U or the maximum amplitude E of the high-frequency voltage fluctuates and the ratio λ changes, it is possible to keep Δm substantially constant at the initial value.

Therefore, according to the present invention based on the second stable region (n) of the Matthew diagram, Δm can be stably made very small, and the resolution can be easily and dramatically increased.

(Example) Hereinafter, this invention will be specifically explained based on examples.

Radius ro-4 inscribed in the four electrodes of the example quadrupole mass spectrometer
mll+, o-4 mark ll+, angular velocity of frequency voltage ω-2π
Regarding f, f = 2 MHz, the ratio λ between the DC voltage U and the maximum amplitude E of the high-frequency voltage based on the second stability region (II) of the Matthew diagram in Figure 1 (that is, the slope of the straight line) = 0.4
8628, the mass number M is 2.18.2
The DC voltage U and the maximum amplitude E of the high frequency voltage for the monovalent ions of 8.44 were calculated using the Matthew function. The results are shown in Table 1.

On the other hand, a quadrupole mass spectrometer was attached to a vacuum container, and the inside of the container was evacuated to 1×10"Pa or less. Then, mass spectra were measured under the conditions shown in Table 1. As a result, M
-18, the resolution was as high as 150 or more.

Table 1 For the case where the ratio λ of the DC voltage U and the maximum amplitude E of the high-frequency voltage based on the first stability region (1) of the Matthew diagram in Figure 3 (that is, the slope of the straight line a) = 0.16761, Similar to the example, the mass number M is 2.18.28.44
The DC voltage U and the maximum amplitude E of the high frequency voltage for the singly charged ions were calculated using the Matthew function. The results are shown in Table 2.

In addition, mass spectra were measured under the conditions shown in Table 2 in the same manner as in Examples. As a result, when M=18, the resolution was only about 50.

Table 2 Comparative Example (Effects of the Invention) According to this invention, the DC voltage and high frequency voltage applied to the quadrupole mass spectrometer are determined based on the second stability region of the Matthew diagram, resulting in dramatically higher resolution. can be easily realized.

[Brief explanation of drawings]

Figure 1 is an enlarged view of the Matthew diagram near the second stable region, Figure 2 is the Matthew diagram, Figure 3 is an enlarged view of the Matthew diagram near the first stability region, and Figure 4 is the quadrupole mass. FIG. 3 is a conceptual diagram of a quadrupole electrode section of the analyzer. ■...First stable region ■...Second stable region DC voltage U Fig. 1

Claims (1)

[Claims] (1) A quadrupole mass spectrometer, characterized in that the DC voltage and high frequency voltage applied to the quadrupole electrodes are determined based on the second stability region of the Matthew diagram.