JP5141505B2 - Ion guide and mass spectrometer equipped with the same - Google Patents

Description

  The present invention relates to an ion guide for transporting ions to a subsequent stage while converging ion trajectories, and a mass spectrometer including the ion guide.

  FIG. 7 is a schematic configuration diagram of a tandem mass spectrometer that performs measurement by the MS / MS method using two quadrupole mass filters. In this apparatus, a first-stage quadrupole mass filter 30, a collision cell 31, a second-stage quadrupole mass filter 33, and a detector 34 are arranged along an ion passage path. Inside the collision cell 31, an ion guide 40 for controlling the trajectory of flying ions by an electric field is disposed.

  When ions are introduced from the left side in FIG. 7, only ions having a specific mass-to-charge ratio are selected by the first-stage quadrupole mass filter 30 and introduced into the ion guide 40 in the collision cell 31. Collision-induced dissociation (CID) gas is introduced into the collision cell 31, and the ions selected in the previous stage collide with the CID gas and dissociate, and various product ions generated according to the dissociation mode are the first. It is introduced into a two-stage quadrupole mass filter 33. Product ions having a specific mass-to-charge ratio are selected by the second-stage quadrupole mass filter 33 and reach the detector 34 to be detected.

  FIG. 8 shows an example of the configuration of the ion guide. The ion guide 40 is a multipole type in which eight rods 41 in the form of cylindrical rods are arranged around the ion optical axis C in a rotationally symmetrical manner. A voltage obtained by superimposing a high frequency voltage having the same amplitude and the inverted phase on the same DC voltage is applied to the two adjacent rod electrodes 41. As a result, a high-frequency electric field is generated in a space surrounded by the rod electrodes 41, and ions introduced therein travel while vibrating at a predetermined cycle. At this time, it is desirable that the shape of the electric field coincides with a predetermined curve theoretically derived from an equipotential line in a plane orthogonal to the ion optical axis C.

  In the ion guide, the rod electrode is generally arranged parallel to the ion optical axis, but may be arranged slightly inclined. For example, if the rod electrode is inclined by a slight angle (for example, 0.5 °) so as to approach the ion optical axis on the ion exit side, ions can be accelerated toward the exit side. On the contrary, if it is slightly tilted away from the ion optical axis on the exit side, the flying ions can be decelerated.

JP 2007-128694

  In recent years, the types of analysis target substances have been diversified and complicated, and in order to cope with this, there has been a demand for higher sensitivity and higher accuracy of mass spectrometers. In order to meet these requirements, it is necessary to improve the performance of ion guides such as ion acceptability and ion permeability. For that purpose, it is desirable to make the shape of the high-frequency electric field in the ion guide as close as possible to the theoretical curve.

  In order to bring the electric field in the ion guide closer to the ideal state, it is necessary to increase the accuracy of the arrangement of the electrodes. One of the methods is a method of holding the rod electrode with a non-conductive holder. However, in this method, since the non-conductive holder is in the immediate vicinity of the rod electrode, the electric field in the ion guide is disturbed by the holder charged by the collision of flying ions.

  In view of this, a method has been proposed in which a metal connecting material is welded to the back portion of the rod electrode (opposite the ion optical axis) and the connecting material is fixed by a holder to move the holder away from the ion optical axis. However, in this method, the rod electrode is deformed by thermal strain at the welded portion, and its straightness is easily lost. Therefore, the electric field is also distorted, and it is difficult to take such a method particularly in the case of accelerating / decelerating ions by tilting the rod electrode by a slight angle with respect to the ion optical axis.

  On the other hand, an ion guide that uses a metal plate electrode instead of the rod electrode and surrounds the ion optical axis at its end face has been proposed mainly in order to simplify the assembly structure and reduce the cost (see Patent Document 1). However, in this configuration, since the electric field formed in the ion guide is away from the ideal state, it is difficult to improve the ion convergence.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress the disturbance of the electric field in the ion guide and to form an ion guide that can form an electric field close to an ideal state. It is to provide a mass spectrometer provided.

The first ion guide according to the present invention, which has been made to solve the above problems,
A plate-like metal that extends in the direction of the ion optical axis and has a length in the radial direction from the ion optical axis, n (n is an even number of 4 or more) sheets whose end faces surround the ion optical axis An ion guide provided with a plate as an electrode,
In the plane orthogonal to the ion optical axis, the edge of the metal plate on the ion optical axis side has a convex arc shape or hyperbolic shape toward the optical axis.

The second ion guide according to the present invention, which has been made to solve the above problems,
A plate-like metal that extends in the direction of the ion optical axis and has a length in the radial direction from the ion optical axis, n (n is an even number of 4 or more) sheets whose end faces surround the ion optical axis The board,
An electrode fixed along the end surface on the ion optical axis side of the metal plate, and having an ion optical axis side edge convex toward the optical axis in a plane orthogonal to the ion optical axis. With a stick,
It is characterized by providing.

  A mass spectrometer according to the present invention, which has been made to solve the above problems, includes the ion guide.

According to the ion guide and the mass spectrometer including the ion guide according to the present invention, the ion optical axis side edge of the metal plate or electrode rod as an electrode protrudes toward the optical axis in a plane orthogonal to the ion optical axis. Therefore, an electric field close to an ideal state can be formed in the space surrounded by each electrode.
Moreover, since a metal plate having one end faced in the direction of the ion optical axis or a metal plate having an electrode rod fixed to the end surface is used as the electrode, the electrode (metal plate) is separated from the ion optical axis by a non-conductive holder. Can be held. Thereby, a nonelectroconductive holder can be arrange | positioned away from an ion optical axis, and disturbance of the electric field in an ion guide by charging of a nonelectroconductive holder can be suppressed.

  According to the second ion guide of the present invention, particularly when the edge shape is an arc shape, the electrode rod can be formed into a columnar shape, which makes it very easy to manufacture. Even when the edge shape is a hyperbolic shape, it is easier to process the rod-like member into such a shape than to process the edge of the plate. In the second ion guide, it is necessary to fix the electrode rod to another member (metal plate). However, since the electrode rod is fixed to the end face of the metal plate over its entire length, Deformation can be minimized.

  An embodiment of an ion guide according to the present invention will be described with reference to the drawings. Fig.1 (a) is a side view of the ion guide unit 10 which equips the inside with the ion guide which concerns on a present Example, FIG.1 (b), (c) is an AA arrow cross section of Fig.1 (a), respectively. It is a figure and a BB arrow sectional drawing. The ion guide unit 10 of the present embodiment is disposed in the collision cell 31 of the tandem mass spectrometer that performs MS / MS analysis as shown in FIG. 7 and extends in the direction of the ion optical axis C. An ion guide 11 having eight metal plates as electrodes and a cylindrical case 14 surrounding them are provided.

  Each electrode of the ion guide 11 is arranged in a rotationally symmetrical manner with the end surface on the long side thereof directed toward the ion optical axis C and maintaining an angle of 45 ° around the ion optical axis C. Four electrodes arranged every other one of the eight electrodes are referred to as a first electrode 11A, and the four electrodes adjacent thereto are referred to as a second electrode 11B. Here, the configuration is an octupole composed of eight electrodes. However, when a multipole electric field is formed, the number of electrodes may be an even number of 4 or more, such as a quadrupole or a hexapole.

FIG. 2A shows a perspective view of one first electrode 11A. The first electrode 11A has a circular arc shape or a hyperbolic shape in which the edge on the ion optical axis C side is convex toward the optical axis in a plane orthogonal to the ion optical axis C. Further, the end surface on the ion optical axis C side is inclined so as to be slightly away from the ion optical axis C as it goes in the direction of ion travel (the right direction in FIGS. 1C and 2A). By this inclination, the strength of the multipole electric field can be reduced toward the exit side of the ion guide 11, and the flying ions can be decelerated. The other three first electrodes 11A other than the first electrode 11A and the four second electrodes 11B adjacent to them have the same shape.
As shown in FIG. 2B, the first electrode 11A and the second electrode 11B are fixed by welding or the like with an electrode rod 112 having a predetermined cross-sectional shape on the end surface of the metal plate 111 that has not been subjected to end surface processing. It may be a thing. This electrode bar 112 is not limited to a round bar and has a semicircular cross section as long as at least the edge on the side of the ion optical axis C is a convex arcuate or hyperbolic shape toward the optical axis in a plane orthogonal to the ion optical axis C. It may be a shape.

  The case 14 is attached to one end of the cylindrical portion 141 surrounding the first electrode 11A and the second electrode 11B, and is attached to one end of the cylindrical portion 141 to support a first end surface of each electrode (left end surface in FIG. 1 (c)). A plate for fixing the plate spring 13 as shown in FIG. 3 between the support portion 142, the second support portion 143 attached to the other end of the cylindrical portion 141, and the second support portion 143. A spring fixing portion 144. The 1st support part 142 and the 2nd support part 143 consist of insulators, such as ceramics and a plastics, and the opening for allowing ion to pass through in the center is provided. Further, the second support portion 143 is provided with a cylindrical through hole at a position corresponding to each electrode.

  The plate spring 13 shown in FIG. 3 includes a metal ring-shaped frame portion 131 and eight spring portions 132 that are cantilever springs protruding inward from the frame portion 131. The spring part 132 is T-shaped so that the left and right ends of adjacent spring parts 132 are close to each other. Such a leaf spring 13 can be manufactured at low cost by pressing a metal plate. The spring part 132 may be configured to protrude outward from the frame part 131.

  A metal thin plate 15 is disposed on the surface of the first support portion 142 that supports the electrode. FIG. 4 shows a plan view of the thin plate 15. The thin plate 15 includes a ring-shaped frame portion 151 and four metal contacts 152 protruding inward from the frame portion 151. The thin plate 15 can also be manufactured at low cost by pressing. In the thin plate 15 disposed on the first support portion 142, the position of the metal contact 152 corresponds to the position of the first electrode 11A. Thereby, the thin plate 15 contacts only the first electrode 11A and does not contact the second electrode 11B.

  FIG. 5 shows an end view of the ion guide unit 10 with the leaf spring 13 and the leaf spring fixing portion 144 removed from the end portion on the second support portion 143 side. Insulating spacers 121 made of an insulator are inserted into four holes corresponding to the first electrode 11A among the eight through holes provided in the second support portion 143, and four holes corresponding to the second electrode 11B are inserted. A conductive spacer 122 made of a conductive material is inserted into the hole. Each spacer has a cylindrical shape having the same length, and the length is set such that the other end slightly protrudes from the surface of the second support part 143 with one end contacting the electrode.

  FIG. 6 is a partial end view showing a state where the leaf spring 13 and the leaf spring fixing portion 144 are attached to the ion guide unit 10 shown in FIG. The leaf springs 13 are arranged such that adjacent left and right ends of adjacent spring portions 132 hold down the protruding portions of one insulating spacer 121 or one conductive spacer 122. Accordingly, the leaf spring 13 is insulated from the first electrode 11A by the insulating spacer 121, and is electrically connected to the second electrode 11B via the conductive spacer 122. At this time, since each conductive spacer 122 is in contact with the two spring portions 132, compared to the case where each conductive spacer is in contact with one spring portion, contact failure caused by dirt, dust, or the like at those contact points occurs. Probability decreases.

  With the above configuration, the spring portion 132 of the leaf spring 13 presses the first electrode 11A and the second electrode 11B toward the first support portion 142 via the insulating spacer 121 or the conductive spacer 122. Accordingly, each electrode is sandwiched and fixed from both sides by the leaf spring 13 and the first support portion 142. At this time, the end face of the first electrode 11A is in contact with the insulating spacer 121 or the metal thin plate 15, and the end face of the second electrode 11B is in contact with the conductive spacer 122 or the second support portion 143 made of an insulator. A voltage V + v · cos ωt obtained by superimposing the high frequency voltage v · cos ωt on the DC voltage V is applied to the first electrode 11A through the thin plate 15 from a voltage application circuit (not shown), and the leaf spring 13 is applied to the second electrode 11B. The voltage Vv · cosωt on which the high frequency voltage whose phase is inverted (that is, shifted by 180 °) is superimposed is applied to the same DC voltage via the conductive spacer 122. As a result, a multipole electric field is formed in a space surrounded by the edge surfaces of the eight electrodes, and ions introduced therein are converged.

 At this time, in the plane orthogonal to the ion optical axis C, the edges of the eight electrodes on the side of the ion optical axis C are arcuate or hyperbolic convex toward the optical axis. An electric field having a shape along the line is generated. Thereby, the electric field close | similar to an ideal state can be formed in the space enclosed by the end surface of each electrode.

The ion guide unit according to the present embodiment also has the following effects. Since each electrode has a plate shape with one end surface having a length in the radial direction from the ion optical axis C, the electrodes can be held at a location away from the ion optical axis C. For this reason, it becomes difficult for ions to collide with the insulating first support part 142 which is the holding means, and the disturbance of the electric field in the ion guide due to the charging can be suppressed.
Since the electrode of this embodiment has no welded portion, the electrode is not deformed. Therefore, it is possible to arrange the electrodes with high accuracy. For example, the operation of accelerating / decelerating ions by inclining the end surface by a slight angle (for example, 0.5 °) with respect to the ion optical axis C side is also highly accurate. Can be done.

  The above-described ion guide unit 10 can be applied to various mass spectrometers having a function of transporting ions to the subsequent stage while converging the ion trajectory, and a plurality of ion guide units 10 such as a tandem mass spectrometer that performs MS / MS analysis. However, the present invention can be applied to a device having a single mass analyzer such as a liquid chromatograph mass spectrometer (LC / MS).

  The above embodiment is an example of the present invention, and appropriate modifications are allowed within the scope of the present invention.

It is a figure explaining the ion guide unit which is one Example of this invention, (a) is a side view, (b), (c) is AA arrow sectional drawing of (a), respectively, BB arrow FIG. It is a figure explaining an electrode, (a) is a perspective view of the electrode of a present Example, (b) is a perspective view of the electrode of a modification. The top view of a leaf | plate spring. The top view of a thin plate. The end view of an ion guide unit before attaching a leaf | plate spring and a leaf | plate spring fixing | fixed part. The enlarged end elevation of the ion guide unit after attaching a leaf | plate spring and a leaf | plate spring fixing | fixed part. 1 is a schematic configuration diagram of a tandem mass spectrometer. The schematic perspective view which shows an example of a structure of the conventional ion guide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ion guide unit 11, 40 ... Ion guide 111 ... Metal plate 112 ... Electrode rod 11A ... 1st electrode 11B ... 2nd electrode 121 ... Insulating spacer 122 ... Conductive spacer 13 ... Plate spring 131, 151 ... Frame part 132 ... Spring Part 14 ... Case 141 ... Tube part 142 ... First support part 143 ... Second support part 144 ... Plate spring fixing part 15 ... Thin plate 152 ... Metal contacts 30, 33 ... Quadrupole mass filter 31 ... Collision cell 34 ... Detector 41 ... Rod electrode

Claims (3)

A plate-like metal that extends in the direction of the ion optical axis and has a length in the radial direction from the ion optical axis, n (n is an even number of 4 or more) sheets whose end faces surround the ion optical axis An ion guide provided with a plate as an electrode,
An ion guide characterized in that, in a plane perpendicular to the ion optical axis, the ion optical axis side edge of the metal plate has a convex arc shape or hyperbolic shape toward the optical axis. A plate-like metal that extends in the direction of the ion optical axis and has a length in the radial direction from the ion optical axis, n (n is an even number of 4 or more) sheets whose end faces surround the ion optical axis The board,
An electrode fixed along the end surface on the ion optical axis side of the metal plate, and having an ion optical axis side edge convex toward the optical axis in a plane orthogonal to the ion optical axis. With a stick,
An ion guide comprising:   A mass spectrometer comprising the ion guide according to claim 1.

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