JPH0354830B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a mass spectrometer that has a wide measurement mass range, is excellent in sensitivity and resolution, and can be miniaturized. [Prior art] Recently, there has been a strong demand for analyzing high-mass molecules in applied fields such as biochemistry, and in response to this demand, methods have been developed to ionize samples by bombarding them with high-speed primary ions or neutral particles. The ionization method is attracting attention. According to this ionization method, m/z
It has become possible to create ions of high-mass molecules of approximately 2,000 to 5,000 with relative ease. At present, such high-mass molecular ions can only be analyzed using large-scale mass spectrometers, but large-scale mass spectrometers are extremely expensive and cannot be easily used by anyone. Therefore, there is a demand for a small or medium-sized mass spectrometer that can analyze up to a high mass range, and for example, the following measures have been taken. That is, the electric field E and uniform fan-shaped magnetic field H of a conventional small to medium-sized mass spectrometer as shown in Fig. 1a are used as they are, and the ion rotation angle φm in the magnetic field is reduced as shown in Fig. 1b. , is a method to expand the measurement mass range. In FIG. 1, S is an ion source and D is an ion detector. However, in this method, as φm becomes smaller, the ion trajectory becomes longer, and the ion beam spreads in the vertical direction, which deteriorates the ion transmission (passage efficiency) and lowers the sensitivity. A major drawback is that the expansion increases second- and third-order high-order aberrations and reduces resolution. By the way, the present inventor has previously proposed a mass spectrometer that is excellent in sensitivity and resolution. This mass spectrometer was developed in Japanese Patent Application No. 56-118645 (Japanese Unexamined Patent Publication No. 58-19848).
The ion source S consists of an ion source S, a uniform fan-shaped magnetic field H, and a toroidal electric field E.
and a uniform fan-shaped electric field H, there are two electrostatic quadrupole lenses Q1 and Q2 that provide focusing properties in the direction perpendicular to the orbital plane of the passing ion beam and provide divergence properties in the radial direction of the ion beam. It is characterized by the placement of [Object of the Invention] The present invention relates to an improvement of this proposed device, and while retaining the excellent points of sensitivity and resolution,
In response to the above-mentioned demands, it is an object of the present invention to provide a mass spectrometer that can have a wide measurement mass range so as to be able to analyze high-mass molecular ions, and can also be miniaturized. [Configuration of the Invention] The present invention provides an ion source, an ion detector that detects ions emitted from the ion source, a uniform magnetic field disposed between the ion source and the ion detector,
An electric field is placed between the magnetic field and the ion detector, and an electric field is placed between the ion source and the magnetic field to provide focusing property in the direction perpendicular to the orbital plane of the ion beam and divergent property in the radial direction of the ion beam. two electrostatic quadrupole lenses spaced apart from each other; and an electrostatic quadrupole positioned between the magnetic field and the electric field to provide focusing in a direction perpendicular to the orbital plane of the ion beam. When the rotation angle and rotation radius of the ion beam in the magnetic field are φm and rm, respectively, and the rotation angle and rotation radius of the ion beam in the electric field are φe and re, respectively, 79°≦φe≦83°36 It is characterized by satisfying ゜≦φm≦38゜0.68≦re/rm≦0.72. Hereinafter, the present invention will be explained in detail using the drawings. [Embodiment] FIG. 3 is an apparatus configuration diagram showing an embodiment of the present invention. An ion source 1 includes an ionization chamber 2 and a plurality of electrodes 3
The accelerated ion beam IB is taken out from the slit 4. This IB passes through two electrostatic quadrupole lenses 5 and 6 and enters a uniform fan-shaped magnetic field 7. Ions are dispersed in this magnetic field 7 according to their mass-to-charge ratio, and those with a specific mass-to-charge ratio enter the ion detector 10 via an electrostatic quadrupole lens 8 and a cylindrical electric field 9 and are detected. . The magnetic field 7 is configured so that its magnetic field strength can be repeatedly swept at high speed by a power source (not shown). Therefore, with the sweep, the mass-to-charge ratio of ions passing through the magnetic field 7 changes, and the ions captured by the detector 10 have different masses, and a mass spectrum signal is obtained from the detector 10. Incidentally, angles ε ₁ and ε ₂ are set on the entrance and exit surfaces of the magnetic field 7 so that the ion beam enters and exits obliquely, and the entrance end surface is given a radius of curvature Rm1. FIG. 4 shows the A of the electrostatic quadrupole lenses 5, 6, and 8.
It is a diagram showing a -A cross-sectional structure and the configuration of a power source 11 for applying a potential thereto. electrostatic quadrupole lens 5,
6 and 8 each consist of four cylindrical electrodes, which are arranged symmetrically at 90° intervals around the ion beam path 0, and when analyzing positive ions, A positive potential is applied to the electrodes Py that face each other in the radial direction (x direction) of the ion beam, and a negative potential is applied to the electrodes Px that face each other in the radial direction (x direction) of the ion beam. Therefore, positive ions receive a force in the focusing direction in the y direction, and a force in the divergent direction in the x direction. In the case of the electrostatic quadrupole lens 8, since the lens 8 is arranged at the focal point in the x direction, the effect on the x direction is small, and only the focusing property in the y direction is provided. FIG. 5 is an explanatory diagram showing the flow of the ion beam IB within the above-mentioned ion optical system. Figure a shows the change in the beam width in the x direction. A directional dispersion angle α′ greater than α is given.
Therefore, the ion beam enters the magnetic field 7 as if it were emitted starting from point F. The image magnification X at this point F is α/α', and the image is reduced, so it can be seen from the equation below that gives the resolution R of the magnetic field mass spectrometer that high resolution can be obtained. R=γ・rm/(X・S+Δ+d) In the above equation, S and d are the slit widths in the ion source and ion detector, respectively, γ is the mass dispersion coefficient,
Δ is the spread of the image due to aberration. The beam width of the ion beam incident on the magnetic field 7 gradually decreases due to the focusing effect of the magnetic field 7, and after it is once focused to a point near the output end of the electrostatic quadrupole lens 8, it is combined with the magnetic field 7. The light enters the electric field 9 arranged so as to satisfy the double focusing condition, and is focused again on the detector 10 by the focusing action of the electric field 9. FIG. 5b shows an ion trajectory diagram in the y direction, and it can be seen from the figure that the height of the ion beam is kept extremely small within the magnetic field 7 due to the focusing action of the electrostatic quadrupole lenses 5 and 6 in the y direction. Ru. Therefore, it is possible to increase the magnetic field strength by reducing the distance between the magnetic poles, and if the distance between the magnetic poles is the same, a large amount of ions can be effectively passed through, and the sensitivity can be improved. In the present invention, in the ion optical system shown in FIG. 3 which has excellent characteristics of high resolution and high sensitivity, 79°≦φe≦83°, 36°≦φm≦38°, 0.68≦
It is characterized by setting re/rm≦0.72.

[Table] In Table 1, a indicates the conventional device shown in FIG. 1 b, b indicates the proposed device shown in FIG. A list of second-order and third-order aberration coefficients calculated for each example of a, b, and c in Table 1 is shown below. The lengths in Table 1 are normalized by setting the radius of curvature rm of the ion beam in the magnetic field to 1. φm: Angle of rotation of the ion beam due to the magnetic field (degrees) φe: Angle of rotation of the ion beam due to the electric field rm: Radius of rotation of the ion beam within the magnetic field re: Radius of rotation of the ion beam within the electric field Rm1: Radius of rotation of the ion beam at the input end of the magnetic field Radius of curvature QL: Length of electrostatic quadrupole lens QK1, QK2, QK3: Electrostatic quadrupole lens 5, 6,
8 intensities L1 to L5: Each distance Ax entered in Figure 1b, Figure 2, and Figure 3: Image magnification Aγ: Mass dispersion coefficient Ay, Aβ: Spreading of the beam in the height direction at the detector position Coefficients AA to BB: Second-order aberration coefficients XXX to DBB: Third-order aberration coefficients In Table 1, when comparing the three φm and re/rm, which contribute to the expansion of the measurement mass range and the size of the device, a is 35 °, 0.643, b is 72.5 °, 0.9, c
are 37° and 0.71, and it can be seen that a and c allow the mass range to be expanded without increasing the size of the device, while b is disadvantageous in this respect. On the other hand, when comparing Ay, Aβ (the smaller the transmission is, the better the transmission) and Aγ/Ax (=mass dispersion/ion beam width), which represent ion transmission (passage efficiency), a is 2.415, respectively. 10.678, 0.957, whereas b is 0.589, −0.805, 4.15, and c is 0.54, −1.08, respectively.
7.59, Ay and Aβ are smaller in b and c than in a, and Aγ/Ax is larger. Therefore, if you compare the same resolution or the same ion beam width, the transmission is better in b and c than in a. It can be seen that this is an order of magnitude better and that high sensitivity can be obtained.

【table】

[Table] Further, in Table 2, the second-order and third-order aberration coefficients that determine the resolution are compared. If the practically required resolution is 50,000 and the width of the ion beam at the ion source is rm/(200-300), then it is desirable that the second-order aberration coefficient is at least smaller than 0.8-1, and the third-order aberration coefficient is at least 0.8-1. Aberration coefficient is at least 500
Preferably smaller than ~800. however
XXX, XXA, and XAA can be improved by adjusting the ion source slit, so up to about 1,000 is acceptable. If we take this value into account and look at the secondary aberration coefficients and tertiary aberration coefficients in Table 2, we can see that a has a relatively good tertiary aberration coefficient, but the secondary aberration coefficients of the liver and kidneys are all well outside the allowable range. The resolution is as
It is inevitable that it will be much worse than 50,000. Next, as for b, although the second-order aberration coefficient is within an acceptable range, the third-order aberration coefficient is large, and as a result, it is difficult to achieve a resolution of 50,000 with a margin. On the other hand, c according to the present invention, which is an improved version of b, is
Not only secondary aberrations but also tertiary aberrations are within the permissible range, making it possible to achieve a resolution of 50,000 with ease. To summarize the above, in c according to the present invention, even if the measurement mass range is expanded by reducing φm and re/rm, the aberration does not deteriorate as in the case of a, and the second-order The aberrations are the same as those in example b, and the third-order aberrations are much improved compared to example b. Moreover, the excellence of the transmission is inherited from that of b, and therefore it is an ideal mass spectrometer that can expand the measurement mass range without increasing the size of the device and also provides high sensitivity and high resolution. A device is realized.

【table】

【table】

【table】

【table】

【table】

[Table] Tables 3, 4, and 5 are related to the ion optical system of the present invention having such excellent characteristics.
φm, re/rm are the values in the example of c in Tables 1 and 2 above, that is, φe=80°, φm=37°, re/rm=
It shows how the second-order and third-order aberration coefficients change when changed around 0.71. Looking at the second-order aberration coefficients shown in Table 3, AD
It can be seen that in order to keep the value within the above-mentioned tolerance range, it is necessary to set φe in the range of 79° to 83°.
Within this range, the third-order aberration coefficient is also approximately within the permissible range. Looking at the second-order aberration coefficients shown in Table 4, AD
In order to keep the values of and BB within the above tolerance range,
It can be seen that φm needs to be set in the range of 36° to 38°. Within that range, the third-order aberration coefficient is also within the allowable range. Next, looking at Table 5, in order to keep the value of the second-order aberration coefficient BB within the above-mentioned tolerance range, re/rm must be
It is necessary to set it within the range of about 0.72 to 0.67, but if re/rm is 0.67, the third-order aberration coefficient will exceed the above-mentioned allowable range, so if we take into account the second-order and third-order aberration coefficients, we will end up setting the re/rm. Values must be in the range 0.72 to 0.68. As described above, according to the present invention, a mass spectrometer can be realized that has a wide measurement mass range, is excellent in sensitivity and resolution, and can be miniaturized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional device, FIG. 2 is a diagram showing the configuration of the proposed device, FIG. 3 is a device configuration diagram showing an embodiment of the present invention, and FIG. 4 is a cross-section of an electrostatic quadrupole lens. FIG. 5 is an explanatory diagram showing the flow of an ion beam within the ion optical system according to the present invention. 1: ion source, 4: slit, 5, 6, 8: electrostatic quadrupole lens, 7: uniform fan-shaped magnetic field, 9: cylindrical electric field, 10: ion detector.

Claims (1)

[Claims] 1. An ion source, an ion detector that detects ions emitted from the ion source, a uniform magnetic field disposed between the ion source and the ion detector, and a magnetic field and an ion detector. an electric field placed between the ion source and the magnetic field, and an interval between the ion source and the magnetic field to provide focusing properties in the direction perpendicular to the orbital plane of the ion beam and divergent properties in the radial direction of the ion beam. two electrostatic quadrupole lenses arranged with a gap between them, and an electrostatic quadrupole lens arranged between the magnetic field and the electric field to provide focusing in a direction perpendicular to the orbital plane of the ion beam, When the rotation angle and rotation radius of the ion beam in the magnetic field are φm and rm, respectively, and the rotation angle and rotation radius of the ion beam in the electric field are φe and re, respectively, 79°≦φe≦83°36°≦φm≦38 A mass spectrometer characterized by satisfying ゜0.68≦re/rm≦0.72.