JPH0328775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superimposed field mass spectrometer equipped with electric field generating means that can arbitrarily change electric field distribution.

In a superimposed field mass spectrometer, for example, as shown in FIG. 1, concentric cylindrical electrodes 2 and 2' are installed in a uniform magnetic field formed between magnetic poles 1 and 1', and a toroidal electric field perpendicular to the magnetic field is installed. is generated as a superimposed field. If an attempt is made to sweep the mass by electric field sweeping in a mass spectrometer that uses such a superimposed field as an analysis field, the ion beam focusing device will change, and in order to cancel the position change, the constants C and C of the toroidal electric field are changed. ′ must be changed in conjunction with the electric field sweep. However, as shown in Fig. 1, in the conventional device using concentric cylindrical electrodes, the electric field distribution is uniquely determined by the electrode shape.
C and C' cannot be changed. 3 and 3' are correction electrodes called Matsuda plates used for this purpose, and by changing the DC voltage applied to the electrodes 3 and 3', the constant C of the toroidal electric field,
By changing C′, we can do this.

In general, for mass spectrometers, it is desirable for the magnetic field strength to be high in terms of resolution or measurement range.
For this purpose, it is necessary to make the magnetic pole spacing as narrow as possible. However, in the conventional device described above, there is a limit to how narrow the space can be because the electrodes 2, 2' and the correction electrodes 3, 3' must be installed between the magnetic poles. Furthermore, although it is possible to change the constants C and C' using correction electrodes, the further away from the center of the field, the greater the deviation from the ideal toroidal electric field, which also has the disadvantage of increasing higher-order aberrations. .

The present invention has been made in view of the above points, and provides a superimposed field mass spectrometer that can be installed even in a narrow gap and is equipped with an electric field generating means that can arbitrarily change the electric field distribution. It is intended to.

The present invention provides a superimposed field mass spectrometer comprising a means for generating a uniform magnetic field and an electric field generating means for generating an electric field in a direction orthogonal to the uniform magnetic field by superimposing it on the uniform magnetic field. The means includes a plurality of pairs of concentric arc-shaped linear electrode groups provided vertically symmetrically across the center plane on a pair of parallel planes that are at equal distances across the center plane that is perpendicular to the uniform magnetic field; It is composed of a storage means for storing information regarding the potential applied to each pair of linear electrodes, and a power supply means for applying a predetermined potential to each electrode pair based on the information read from the storage means. It is characterized by An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 2 shows the structure of an embodiment of the present invention, in which reference numerals 1 and 1' are magnetic poles similar to those in FIG. 1. Between the magnetic poles, thin substrates 4 and 4' made of an insulator are placed in parallel at equal distances from each other from the central plane L through which ions pass. The substrate is given an arcuate shape along the central path O of ions as shown in FIG.
Seven concentric arc-shaped electrodes A ₁ to An (substrate 4) and B ₁ to Bn (substrate 4') each having a width of 0.5 mm are arranged at a pitch of 0.5 mm. This electrode pattern can be created, for example, by pattern exposure and etching techniques similar to printed circuit boards used in ordinary electronic devices. The patterns of the two substrates should be symmetrical across the center plane, in other words, A ₁ and B ₁ ,
An and Bn are arranged so as to face each other across the center plane, and the lead wires drawn out from each electrode of each substrate are connected to each pair of directly facing electrodes as a set, and each set is connected to a power source. 5. 6
is a memory in which voltages to be applied for n groups are stored, and the information stored in the memory 6 is read out by a read control circuit 7 and supplied to the power source 5 as voltage information for each group.

In the above configuration, when a voltage is applied to n sets of electrodes, an electric field is generated in the space between the electrodes. Within the electric field, there is an equipotential surface connecting each pair of electrodes to which the same potential is applied, but the equipotential surface is influenced by the potentials applied to the adjacent electrodes. Therefore, by finding out what kind of electric field is formed when what kind of voltage is applied to each electrode, it is possible to generate an electric field with an arbitrary distribution in the space between these electrodes. be.

Here, when a certain electric field φ is formed in the space between the electrodes, the potentials of the n sets of electrodes are as follows:
Consider using Figure 4.

Now, consider the electric field φ to be a toroidal electric field that is axially symmetrical with respect to the central axis of rotation q of the ion, and the electric potential at any position within the electric field is expressed as the fourth
If we write φ(x, y) using the x-y coordinates shown in the figure, the following equation holds true.

△φ (x, y) = 0 ......(1) 1/(ρ ₀ +x)〓/〓x [(ρ ₀ +x)〓Φ/〓x] +〓 ² Φ/〓y ₂ = 0 ...( 2) Here, ρ ₀ is the rotation radius of the ion center path, and φ is the potential at an arbitrary point (x, y).

From the above equation, the following equation is obtained as a general form of φ(x, y).

φ(x, y) = −E ₀ ρ ₀ Σaij/i〓j〓(x/ρ ₀ ) ⁱ (y/ρ ₀ ) ^j
...(3) where aij is the coefficient and E ₀ is the central orbit of the ion x=
This is the electric field strength at y=0.

If the distance between electrodes is 2h, each electrode is y=±
Since it exists in the plane of h, it is understood that by setting y=h in equation (3) and substituting the value of x according to the position of each electrode, the potential at each electrode position can be obtained. Conversely, if the potential determined in this way is applied to each electrode, a toroidal electric field will be generated in the space between the electrodes.
Incidentally, field disturbance occurs in the edge field of the electric field, but if the electrode distance 2h is made sufficiently larger than the electrode width w, the field disturbance near the ion center path can be ignored.

Here, in order to actually find the potential of each electrode, the coefficient a _ij must be found. How to obtain this will be explained below. By substituting equation (3) into equation (2), the following recursion formula for the coefficient a _ij is obtained.

(i+1)a _i,j+2 +a _i+1,j+2 +(i+2)a _i+2,j+a +a _i+3,j =0 ...(4) Here, i, j≦0 In this case, a _ij =0.

Also, since the potentials of directly facing electrodes are equal, the electric field is symmetrical with respect to the central plane L, so y
The coefficient of the odd term of the power is 0.

Putting these things together, the coefficient a _ij of the term that includes y representing a field outside the central plane where j = 0 is not equal to the coefficient a ij of the term that does not include y in the central plane (i _≧
1), and does not need to be calculated individually. An example of coefficients up to the fourth order is as shown in the following equation.

a ₀₂ ＝−a ₁₀ −a ₂₀ ……(5) a ₁₂ ＝a ₁₀ −a ₂₀ −a ₃₀ ……(6) a ₂₂ ＝−2a ₁₀ ＋2a ₂₀ −a ₃₀ −a ₄₀ ……(7) a ₀₄ =a ₁₀ −a ₂₀ +2a ₃₀ +a ₄₀ ...(8) In the calculation of the ion trajectory in the mass spectrometer,
Normally, it is sufficient to calculate the aberrations up to the 3rd order and keep the aberrations up to the 3rd order sufficiently small, and it is sufficient to consider up to the 4th order coefficients that affect the 3rd order aberrations.

Therefore, in order to find the voltage (potential) that should be applied to each electrode in order to generate a toroidal electric field with an arbitrary constant C, 4 of a ₁₀ , a ₂₀ , a ₃₀ , and a ₄₀ are required.
Then, determine all the coefficients up to the fourth order using equations (5) to (8), and use those coefficients.
According to equation (3), the voltage (potential) at each electrode position is
All you have to do is ask for it.

The four coefficients a ₁₀ , a ₂₀ , a ₃₀ , and a ₄₀ are determined, for example, as follows. That is, a program has been created to calculate the trajectory of ions flying in magnetic and electric fields, and in this program, a ₁₀ , a ₂₀ ,
The ion focusing performance in the ion optical system can be examined and evaluated based on the four coefficients a ₃₀ and a ₄₀ . Therefore, using the above program for a desired superimposed field optical system (for example, a superimposed field optical system including an electric field with a specific constant C ₁ ), we repeated the process of actually assigning numerical values to each coefficient and evaluating the aberrations, and finally By selecting a combination of coefficients that can reduce the aberrations overall, it is possible to determine the optimal coefficients a ₁₀ , a ₂₀ , a ₃₀ , and a ₄₀ for a specific optical system.

Then, as mentioned above, using the values of a ₁₀ , a ₂₀ , a ₃₀ , and a ₄₀ obtained in this way and the data on the position of each electrode, the equations (5) to (8) and (3) are calculated. ), information on the potential to be applied to each electrode A ₁ ~ An (including B ₁ ~ Bn connected to each other) V ₁₁ ~ V _1o is a superimposed field optical system containing an electric field with a specific constant C ₁ is calculated for the system. In exactly the same way, different constants C ₂ ,
Information on the potential applied to each electrode for a superimposed field optical system containing an electric field with C ₃ ...V ₂₁ ~V _2o , V ₃₁ ~
By determining V _3o , . . . and applying a voltage to each electrode based on the respective information, a superimposed field containing electric fields of each constant can be generated.

In the embodiment shown in FIG. 2, a plurality of pieces of information obtained as described above are stored in the memory 6, and when the readout control circuit 7 reads out any information from the information and supplies it to the power supply, the corresponding The power source 5 applies a voltage to each electrode based on the information. Therefore, an electric field is generated in the space between the electrodes in accordance with the information stored in the memory.

In the above example, a toroidal electric field was used as an example, but it goes without saying that any electric field can be generated as long as information regarding the electric field is obtained, as long as it is symmetrical with respect to the central plane.
Further, the substrates 4, 4' may be attached to the magnetic poles 1, 1', respectively.

As detailed above, according to the present invention, the electric field is generated by the linear electrodes installed on the two substrates, so the conventional electrodes 2 and 2' are not required, and they can be installed even in the gap between them. becomes possible. Furthermore, it is possible to arbitrarily change the distribution of the electric field to be generated.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining a conventional example, Fig. 2 is a diagram showing the configuration of an embodiment of the present invention, Fig. 3 is a diagram for explaining a substrate and a linear electrode, and Fig. 4 is a diagram for explaining a linear electrode. It is a figure showing the relationship between a shape electrode and xy coordinates. 4, 4': Board, 5: Power supply, 6: Memory, 7:
Readout control circuit, A, B: linear electrodes.

Claims (1)

[Claims] 1. A superimposed field mass spectrometer comprising a means for generating a uniform magnetic field and an electric field generating means for generating an electric field in a direction orthogonal to the uniform magnetic field by superimposing it on the uniform magnetic field, wherein the electric field generating means comprises: A plurality of pairs of concentric arc-shaped linear electrode groups provided vertically symmetrically across the center plane on a pair of parallel planes located at equal distances across the center plane perpendicular to the uniform magnetic field, and the plurality of pairs of wires. It is characterized by being comprised of a storage means for storing information regarding the potential applied to each pair of shaped electrodes, and a power supply means for applying a predetermined potential to each electrode pair based on the information read from the storage means. A superimposed field mass spectrometer.