JP3053832B2 - Scanning mass spectrometer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a scanning mass spectrometer.
In this case, at least one magnetic sector with a variable magnetic field strength and an electro-optical detector are provided, said magnetic sector having an exit surface and an ion beam of a limited range of ion mass being provided. Directed to the electro-optic detector and focused on a predetermined focal plane, the electro-optic detector comprising a channel plate with an image plate, a fiber optic window, and a photodiode detector co-planar with the exit face. Has an assembly,
The electron multiplier assembly is provided in a means forming a vacuum vessel, wherein the image plate is located at a focal plane where a limited range of ion masses impinges;
The fiber optic window has an entrance end coplanar with the image plate and an exit end coplanar with the photodiode detector.

Prior Art FIG. 1 depicts a prior art dual focus scanning mass spectrometer 10 having a sample inlet 12 and an ion source including an ionization region 16.
14 is provided, and an ion beam 22 is provided in that region.
The sample gas molecules are exposed to the electron beam 20 to form Ion beam 22 is directed through electrostatic sector 24 and magnetic sector 26. The ions travel through the magnetic sector and are scanned as indicated by reference numeral 30 and their selected masses are focused at the focal point 32 and pass through a narrow slit 34 to an electron multiplier 36. It is configured as follows.

FIG. 1 also illustrates how compact the mass spectrometer can be made by bending the ion path and using magnetic scanning to limit the required dimensions of the magnetic sector. Is a turbo pump 40
It also illustrates how the pressure is reduced in this instrument by the ion pump 42.

In this instrument, slightly higher or lower mass ions are focused along a nearly linear trajectory, the focal plane 44, which passes through the axial focal point 32, which is It is inclined at an angle with respect to 34, ie 37.4 degrees. This focal plane 44, which is tilted by an angle, is hereafter referred to as the angled focal plane and is shown in FIGS. 1a and 1b.
In the figure, it is drawn by a dotted line. The angular accuracy of this angled focal plane is a function of the geometry of the instrument,
That is, it is a function of the 90 degree electrostatic sector and the 90 degree magnetic sector. The effect of these sectors on ions of different masses is described in Mainz, pages 52-91 of The Methods and Applications in Mass Spectroscopy, published by Werlheim / Bergstrasse, Ferragheme GmbH, 1953. In a paper entitled "Ion Optics" by Dr. Heinz Ewald and Dr. Heinrich Hintenberger of the Max Planck Institute for Chemistry, and in the ACS Symposium Series 102: 291-318,
It is described in part in a paper by Boettgar, Giffin and Norris entitled "Electro-optical detectors in mass spectrometry with simultaneous monitoring of all ions over a wide mass range".

As is known in FIG. 1b, depending on the geometry of the instrument, ions with slightly higher or lower masses, such as here identified by way of example as 32a, 32b, 32c and 32d, are usually Are not detected because they are blocked from entering electron multiplier 36, and further increase or decrease the strength of the magnetic field (also referred to as a step or adjustment) to put those ions into focus, Until they are directed to electron multiplier 36, they continue to be blocked, and thus remain undetected. When the field strength is changed, time is required for this change and for subsequent stabilization to a new value.
Typically, for toxic gas monitoring, the step and stabilization time increase the cycle time, and the total measurement (capture) time for 50 ports can be as high as 3 hours. This is because standard equipment requires measuring nearly 40 different gases, each requiring 15 individual field strengths, and those measurements need to be repeated for 50 ports for each. is there.

The present invention is basically a limited range of ion mass,
But with an intensifier plate of a channel-type electron multiplier assembly provided at an angled focal plane that can provide simultaneous analysis, which can be switched to some range for detection over a wide mass range An apparatus for detecting ions along this angled focal plane utilizing an electro-optic ion detector is provided. Thus, little change in magnetic field is required even for detection of a wide range of ion masses. For example, if the mass spectrometer does not utilize an electro-optic detector, it can be as many as 600 times, while using the present invention, the mass can be as high as 40 to 40.
Detecting a 0 simply requires six readjustments of the magnetic field.

Previously, electro-optical detectors were used in mass spectrometers, but the image intensifier plate was either normally placed at the magnetic sector exit port or was placed at a very small angle . These prior art instruments were designed with a long focal plane, a large image intensifier, and a correspondingly long fiber optic assembly (window).

These channel electron multiplier assemblies also
Also called a microchannel plate assembly, and the image intensifier plate is also a microchannel electron multiplier microchannel plate,
It is also called a photocathode plate or simply an image plate.

FIGS. 2a and 2b are examples of such prior art detectors, which are fully described in the aforementioned Boettger et al. Article.

In FIG. 2a, a channel type electron multiplier assembly
50 is connected to the output of a magnetic sector 26a of a non-scanning mass spectrometer, which is also called a spectrographic mass spectrometer, and an image plate 52 is connected to a fiber optic window 54 and to a photodiode array 56. Are combined. An image plate 52 is provided along the focal plane of the magnetic sector 26, as in FIG. 1, and a phosphor coating 60 on the entrance end of the fiber optic window 54 converts electron energy from the image plate 52 to light energy. In addition, the light energy is transmitted to a photodiode array 56 outside the vacuum vessel defined by a vacuum flange 62. Image plate 52 has a linear array of fourteen one inch long microchannel electron multipliers, and photodiode array 56 has fourteen one inch long photodiode detectors (each of which is a linear array of 1024 diodes). (Including arrays). This prior art photodiode array 56 has several difficulties and limitations, including: 1) The detector to cover a wide mass range is quite large, which means that the components and the associated fiber optics 2) large vacuum vessels reflect cost accordingly, and 3) very large photodiode arrays can also be a significant cost increase.

FIG. 2b shows an image plate 72 aligned with a focal plane 74 at an angle with respect to the exit axis 76 of the ion beam 80.
An optical fiber window 70 is shown coupled to FIG. The maximum angle between the focal plane 74 and the image plate 72 is limited by the fiber's ability in the fiber optic window 70 to receive light incident on the end of the fiber. If the angle is too large, the light transmission will be very low. The fibers in the fiber optic window 70 should be fused together into one single piece of glass; otherwise, an attempt was made to create a high vacuum inside the analyzer, such as by plugging the glass between the fibers with glass. Sometimes they should be extremely difficult to move.

A diagram illustrating another prior art is shown in FIGS. 3a to 3c, which are described in the 1979 edition of the Nuclear Instrument and Methods Magazine, Vol. 162, pp. 587-601, by the visor Microchannel Plate. This is fully explained in the article entitled "Detector". As seen in FIG. 3a,
The microchannel or image plate 80 is a circular glass structure having a plurality of channels 82 in which are provided a linear channel electron multiplier 84 as shown in FIG. 86 (the ends of which are covered with phosphorus to form a screen 90 as shown in FIG. 3c) are optically coupled. The components shown in FIG. 3c are suitably tightened together by bolts 92 to form a channel electron multiplier assembly 94 that operates similarly to the channel electron multiplier set assembly of FIG. 2a. Assembly 4 is commercially available and is also used in the present invention, as described in more detail below.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a channel electron multiplier assembly of the type described having a channel electron multiplier plate image surface located along an angled focal plane, a photodiode array. And a dual focus mass spectrometer with an electro-optic ion detector having a specially shaped fiber optic assembly, whereby essentially a limited range of ion mass is detected simultaneously, so that the magnetic field is more Step adjustment is performed a small number of times, and thus the measurement speed is greatly increased.

According to the invention, the object is achieved in that the image plate is arranged at a predetermined angle with respect to the exit surface such that a limited range of detection lines is at an angle with respect to the exit surface. The simultaneous detection of a limited range of mass greatly increases the speed of mass determination, reduces the number of field adjustments required over a wide range of mass, and the fiber optic window has a flat ribbon-like shape. A special shape consisting of a plurality of fiber optic windows arranged at a distance from one another, which is solved by the fact that the entrance and exit sides of the optical image of the ion mass are at right angles to the axis of the fiber.

The present invention includes a scanning mass spectrometer coupled to an electro-optic detector. This electro-optic detector optically communicates between the image surface of the image plate provided along the angled ion focal plane at the exit plane of the magnetic sector, and between the angled image plate and the photodiode detector array. And a specially shaped fiber optic window to be coupled. This fiber optic window allows the fiber entrance end (entrance plane) to be parallel to the angled image plate and the fiber exit end (exit or second image plane) to be parallel to the photodiode image plane. It has such a shape. The channel electron multiplier assembly is housed in a vacuum vessel, and the photodiode array is provided outside the vacuum vessel.

By reading the following detailed description together with the drawings,
Those skilled in the art will appreciate that the electro-optic detector is smaller and therefore less expensive, that the magnetic field strength does not need to be adjusted for all masses, but only once for each range of masses. Thus, the adjustment and stabilization time required when adjusting the magnetic field for each mass can be reduced, greatly increasing the speed of analysis, forming a fused fiber optic window, and forming an exit image. The minimization of fiber compression and expansion to maintain low distortion, and the special shape of the fiber optic window, reduce the volume of the vacuum vessel and reduce photodetector electronics from physical interference with other components. Protect and reduce excessive pump run time and / or excessive high volume pump use;
It will be appreciated that the input and output of an optical image perpendicular to the axis of the fiber is possible.

Also, instead of detecting the entire range of mass simultaneously, the ability to simultaneously detect a limited range of mass and to detect the entire range of mass incrementally makes the present invention a single The advantages of a focused (scanning) mass spectrometer can be tied to a spectrographic (non-scanning) mass spectrometer, which is smaller, less expensive, and more expensive than currently used scanning mass spectrometers. It will also be apparent that a fast scanning mass spectrometer can be provided.

Examples FIGS. 1a-1b, 2a-2b and 3a-3c
The figures have already been described considerably in the context of the present invention and need not be described again here.

4 and 5a and 5b show the magnetic sector 26 of the scanning mass spectrometer 10 as described above.
1 schematically illustrates an electro-optical detector 100 of the present invention, coupled at an outlet plate 102 of the present invention. Magnetic sector 2
The exit plate 102 of FIG. 6 is shown schematically and this is an exit surface 106 provided at the magnetic center of the bend 110.
And the top of the vacuum vessel 104 in a centered manner, thus being directed toward the surface of the image plate 80 of the channel electron multiplier assembly 94 in the ion vacuum vessel 104. The image plate 80 of the channel electron multiplier assembly 94 corresponds to the apparatus described in FIGS. 3a to 3c, and for simplicity the same reference numbers have been used in this figure. The high and low mass ions 32a and 32c, located outside the central ion beam 32b, are focused and impact the surface of the image plate 80 as described in FIGS. 1a and 1b. Is shown.

The image plate 80 is also received at an angle with respect to the exit surface 106, corresponding to the angled focal plane 44, and is supported by suitable means such as a support plate 112, itself a table 114. , Supported by.
See FIGS. 5a and 5b for this. The vacuum vessel 104 is composed of two body members 116 and 120 and one flexible coupling 122, and the degree of vacuum in the vacuum vessel 104 is maintained by a vacuum pump 124. The two body members 116 and 120 can be moved relative to each other by a plurality of adjustment screws 126 so that the position of the image plate 80 with respect to the exit surface 106 can be changed, and Member 120
It is understandable that when coupled to a, it may be referred to as a vacuum flange. The transducer 130 provides a means of accurately measuring the position of the lower body member 120 relative to the upper body member 116 from which the position of the image plate 80 is determined.

The support plate 112 has a central rectangular opening 132 through which the stiffened fiber optic window 134 optically couples to the fiber optic window 86 containing the phosphor coating 90 and extends through the opening 136 in the vacuum flange 120, Connected to photodiode detector array 140. The photodiode array 140 is a suitable electronic circuit 142
To provide the required signal generated by the detected ions. Photodiode detector 140 is exit surface 1
Provided parallel to 06.

As noted earlier, standard channel electron multiplier assemblies, such as 94, are commercially available and can be purchased from Galileo, located in Sturbridge, Minnesota, or from Hamamatsu, Japan. The microchannel plate assembly 94 is commonly assigned a fiber optic window 86 covered by a phosphor coating 90 that converts the secondary electron energy guided through the fiber optic window 86 into a visible light image.

A standard photodiode array, such as the photodiode detector 140, is formed on an integrated circuit, perhaps 10
Includes an array of 24 photodiodes, which are packaged with the fiber optic windows on the array. One such array is the Hamamatsu S2304-1
024F and the others are EG & G Reticon RL 1024SF. These exemplified arrays are 1 inch long and 0.
100 inches. Thus, a standard fiber optic window is one inch wide and 0.125 inch thick, and has a length of three to four inches depending on the distance from the channel electron multiplier assembly 94 to the vacuum flange 120.

As shown in FIG. 4, the fused optical fiber window 114 is shaped so that the fiber entry end is parallel to the angled image plate 80. 6a to 6g show how the optical fiber window 114 is formed. As shown in FIG. 6a, the fibers 114a are drawn into a bundle 114b of rectangular cross section and melted, and then several matched bundles
114b is drawn through the die 150 under controlled heating conditions as shown in FIG. 6b, forming a molten glass ribbon 114c, as shown in FIG. Is cut off. The width of the ribbon is equal to the desired focal plane length, and the thickness is reduced so that the exit image can be dependent on the thickness of the image plate 80 and the photodiode detector array 140. As shown, after the fiber is melted into a ribbon shape,
The ribbon is cooled. After being cut to length, the ribbon is again heated and first twisted by 90 degrees, as shown at 152 in FIG.6d, and then as shown as 154 in FIGS.6f and 6g. , Bent beyond the torsional portion 152. To form this latter angle beyond the torsional portion 152, minimal compression and expansion of the fiber is performed to minimize distortion of the exit image. The end of the fiber is polished perpendicular to the axis of the fiber for maximum light receiving efficiency.

The exit side or second image surface 146 is the image plate 8
If it lies parallel to 0 and the exit surface 146 is aligned with the center of the image plate 80, no special fiber shape need be taken. Special shape is 1) Vacuum container 10
It must contain a minimal volume inside 4 and 2) is needed to protect the photodetector electronics from physical interference with other components of the analyzer. The minimum volume inside the vacuum vessel 104 is important to avoid excessive pumping time and / or the use of excessively large vacuum pumps.

As mentioned earlier, the analysis speed is greatly increased, and even though the electro-optic detector 100 does not completely cover the mass range, the magnetic field strength does not need to be adjusted for each mass, just the mass of the mass. Since only one time is required for each range, the adjustment and stabilization time required when adjusting the magnetic field strength for each mass can be reduced.

The standard mass range that can actually be measured over a one inch focal plane at a given constant magnetic field strength is on the order of about 1.5 to 1 and therefore the electro-optical detector 1
Assuming that the total mass range to be measured by 00 is between 40 and 400, the standard range would be:

Thus, if electro-optical detectors are not used, 60
The magnetic field only needs to be adjusted six times from mass 40 to 400, as opposed to zero.

Effects of the Invention It is possible to provide a double-weight mass spectrometer with a significantly improved measurement speed.

[Brief description of the drawings]

FIG. 1a is a schematic diagram of a prior art scanning mass spectrometer with an electron multiplier at the detector portion of the instrument, and FIG. 1b is shown near the angled focal plane of FIG. 1a. FIG. 2a is a schematic view of an electro-optic ion detector for a spectral mass spectrometer, and FIG. 2b is an image aligned with a focal plane perpendicular to the exit normal. 3a to 3c show the components of a channel electron multiplier assembly, FIG. 4 shows the components of a channel electron multiplier assembly, FIG. 4 shows a specially shaped and specially positioned FIGS. 5a and 5b show an electro-optic detector of the present invention including a fused fiber optic assembly connected to an open channel electron multiplier assembly and to a photodiode array; A support plate for the Yan'neru electron multiplier assembly is a diagram showing a table for supporting the support plate, first 6g view from Figure 6a is a diagram showing a method of forming a fiber optic window. 10 …… Spectrometer, 12 …… Inlet, 14 ……
Ion source, 16 ... Ionization region, 20 ... Electron beam, 22
... Ion beam, 24 ... Electrostatic sector, 26 ... Magnetic sector, 32 ... Focal, 34 ... Slit, 36 ... Electron multiplier, 40 ... Turbo pump, 42 ... Ion pump, 44 ... …
Focal plane, 50: Electron multiplier assembly, 52: Image plate, 54: Fiber optic window, 56: Diode array, 60: Coating, 62: Vacuum flange, 70: Fiber optic window, 72 …… Image plate, 74… Focal plane, 76 …… Out side axis, 80 …… Image plate, 82 …… Channel, 86 …… Optical fiber window, 90 …… Screen, 92 …… Bottle, 94 …… Electronics Multiplier assembly, 100 …… Detector, 102 …… Exit plate,
104 Vacuum container 106 Outlet surface 112 Support plate 114 Base 116 and 120 Body member 126 Screw 130 Transducer 132 Opening 134
... Optical fiber window, 136 ... Aperture, 140 ... Detector array, 142 ... Electronic circuit, 150 ... Die

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 49/26

Claims (8)

(57) [Claims] At least one magnetic sector (26) having a variable magnetic field strength and an electro-optical detector (100) are provided, said magnetic sector (26) having an exit surface (106). An ion beam (32) of a limited range (32, 32a, 32c) of ion mass is directed to the electro-optical detector and focused on a predetermined focal plane, the electro-optical detector Plate (80), fiber optic window (134), and said exit surface (106)
A channel electron multiplier assembly (94) with a photodiode detector (140) co-planar with said electron multiplier assembly (94), wherein said electron multiplier assembly (94) is included in a means forming a vacuum vessel (104). Wherein the image plate (80) is located at a focal plane where a limited range of ion masses impinges; and the fiber optic window (134) is co-planar with the image plate (80) at the entrance end. And photodiode detector (14
0) and a coplanar exit end, in a scanning mass spectrometer, the image plate (80) has a limited range (32,32a, 3).
The detection line of 2c) is arranged at a predetermined angle with respect to the exit surface (106) so as to form an angle with respect to the exit surface (106), and the mass determination speed is determined by simultaneously detecting a limited range of mass. The fiber optic window (134) comprises a plurality of fiber optic windows (134c) arranged in a flat ribbon-like shape (134c). 134. A scanning mass spectrometer having a special shape (154) consisting of 134a), wherein the entrance and exit sides of the optical image of the ion mass are perpendicular to the axis of the fiber. 2. The spectrometer according to claim 1, further comprising means for step-adjusting the strength of the magnetic field in order to change the range of ion mass impinging on said image plate. 3. The spectrometer of claim 1, wherein said channel electron multiplier is movable relative to a magnetic sector. 4. A back support plate (112) and a support member (114) for positioning the image plate at an angle to a focal plane of a magnetic sector. The spectrometer described. 5. A spectrometer according to claim 4, wherein said means forming a vacuum vessel contains a portion of a fiber optic window (134). 6. The spectrometer according to claim 5, wherein the volume of said vacuum vessel is variable. 7. The means for forming a vacuum vessel comprises a first body member (116), a second body member (120) and a flexible connection (122), said connection being provided by said connection. 7. The spectrometer according to claim 6, wherein the first body member and the second body member are connected. 8. The spectrometer according to claim 7, wherein said photodiode detector (140) is arranged outside a vacuum vessel.