JP2006134893A - Tandem mass spectrometry - Google Patents

Abstract

An ion source (10), primary time-of-flight means (20, 80), a collision cell (40) for generating fragment ions and a secondary time-of-flight analyzer (50) are included. Providing a tandem mass spectrometer.
The secondary time-of-flight analyzer includes ion mirrors 51, 52 arranged to produce a secondary field along or relative to the optical axis of the device. The primary time-of-flight analyzer includes a sequential S configuration of toroidal or cylindrical electrostatic analyzer 70, two electrostatic lenses 80 and 96 on either side of the ion mirror, or static An electrolens 80 may be included. Spatial convergence coexisting with temporal convergence is an essential requirement for secondary field mirrors to produce high resolution.
[Selection] Figure 1

Description

  The present invention relates to a tandem mass spectrometer.

  With the expansion of the areas of biotechnology and bioscience, with regard to the structural analysis from mass spectrometry, especially complex mixtures and small and medium-sized biomolecules (100-100000 Da) used in sub-picomolar amounts, so to speak. The demand for sensitivity has increased. The same demand for structural information arises for synthetic polymers.

  Traditional mass spectrometry of such biomolecules and macromolecules has been performed with tandem instruments consisting of twin sectors, twin dipoles or some hybrid combinations, for example sectors + quadrupoles. In such a system, the molecules are ionized by some technique, such as fast electron impact (FAB), mass / energy selected by a primary mass spectrometer (MS1), and then the selected ions are several It undergoes collision activation by passing through a cell containing neutral gas. The fragment ions thus obtained are then analyzed with a secondary mass spectrometer (MS2).

  According to the present invention, a tandem mass comprising an ion source, a primary time-of-flight analyzer, means for dissociating ions from the primary analyzer to generate fragment ions, and a sequential arrangement of secondary time-of-flight analyzers. An analytical device is provided. Secondary time-of-flight analyzers consist of ion mirrors arranged to properly reflect the secondary field, and primary time-of-flight analyzers focus the ions spatially at or near the entrance of the secondary field ion mirror. Includes electrostatic field means to provide.

  The inventor has recognized that a tandem time-of-flight mass spectrometer provides significant increases in specificity and sensitivity. Nevertheless, conventional time-of-flight analyzers produce a spatial expansion of ions, so using two such analyzers in series is impractical for the resolution level required for structure determination. A secondary time-of-flight analyzer that includes an ion mirror that is arranged to produce a secondary field (along or at the same angle as the optical axis of the device), and the spatial flow of ions near or near the ion mirror. The use of a primary time-of-flight analyzer that includes electrostatic field means to provide focusing provides an effective ion tandem time-of-flight mass spectrometer that provides a high level of resolution as well as a direct increase in sensitivity. The

  The ion mirror takes the appropriate form and is arranged to produce a parabolic field along the optical axis of the device. The ion mirror approximates the secondary field and allows the action of fringing the field at the entrance, exit and other places.

  The ion source provides a pulsed beam or continuous beam of ions. Pulsing can be achieved by pulsing a continuous source such as electrospray or using an intrinsic pulsing method such as matrix-related laser desorption / ionization (MALDI), for example in the mass range 100-100000 Da. This can be achieved by providing molecular ions. Means are provided for compressing or focusing the ions into a pulse of ions. The focusing means compresses the pulse of ions into shorter duration ion pulses or converts the continuous beam into a pulsed beam. Focusing occurs before the primary mass spectrometer, after the primary mass spectrometer, or both.

  This type of ion mirror, used in combination with an ion “focuser”, greatly improves mass resolution compared to that obtained by known tandem mass spectrometry systems based on time-of-flight. If an ion mirror is used, the mass spectrum can be detected without any reversal, and the mass spectrum can be easily calibrated with absolute accuracy.

  The time of flight of an ion through an ion mirror depends on its mass-to-charge ratio and is completely independent of its energy, so it is due to the action of the ion “focuser” on the ion and as part of fragmentation A high degree of mass spectrometry is obtained even when undergoing a very substantial spread of that energy due to the distribution of energy.

  The ion “focuser” includes an electrostatic means that limits the “focuser” area, thereby allowing an ion pulse selected by the primary mass spectrometer to enter the “focuser” area and thereby the pulse. Has an exit to the “focus” area. The electrostatic means acts to apply electrostatic acceleration forces to the ions in the pulse that have entered the “focus” area, thereby proportional to their distance from the exit of the “focus” area. Accelerate to high energy.

  Preferably, the primary mass spectrometer can provide convergence of isobaric ion packets with respect to diffusion perpendicular to the optical axis, diffusion along the mechanical optical axis, ion energy diffusion within the packet and time convergence. Includes time-of-flight (TOF) analysis means.

  Preferably, the primary analyzer includes a plurality of toroidal or cylindrical electrostatic analyzers in sequential S configuration. This device provides a focused isobaric ion packet to a specific point that will eventually depart from the case of ions of different mass at some point in the space converged to the dissociation cell. Furthermore, it has the advantage of triple isochronous convergence.

  In another embodiment, the primary time-of-flight means includes an ion mirror after the electrostatic lens. Preferably, the primary time-of-flight means further includes a secondary electrostatic lens after the ion mirror. An ion mirror is a non-grid plane mirror with a substantial optical intensity of zero. In yet another embodiment, the primary time-of-flight means includes an electrostatic lens. The ion source then contains electrostatic means for accelerating the ions in the electrostatic lens. This arrangement contains only a few components and is relatively easy to set up. The electrostatic lens may include an axial symmetry body when the potential is increased. The structure described for the primary time-of-flight means allows for spatial convergence resulting in a significant improvement in resolution. The concept of spatial convergence is a significant advance in this field.

  Three embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.

Referring to FIG. 1, the tandem mass spectrometry system includes a “focuser” 10, a time-of-flight analyzer 20, an ion lens L and a deflector plate D ₁ , an ion “focuser” 30, a cell 40 in which ions are dissociated, and a deflector plate. Includes a continuous array of pulsed ion sources or continuous sources equipped with D ₂ as well as secondary field ion mirrors for TOF (time-of-flight) analysis.

  Ions generated by the ion source 10 are entered into the mass spectrometer 20 in short pulses, typically with a duration of less than 300-500 ns.

  The specimen under examination can be ionized using a laser beam or ion beam, both of which can be generated in a pulsed mode. The pulses that generate the ionization beam have a relatively short duration, and the resulting ions are extracted from the source for entry into the time-of-flight analyzer 20 using an electrostatic extraction field. Alternatively, longer ionization pulses can be used, but in this case the extraction field is pulsed. The analyzer 20 is directed to select only ions having a selected mass to charge ratio.

In the example of the laser pulse, the pulse ionizes and volatilizes the target material, and starts time measurement on the primary time-of-flight stage 20. The primary time-of-flight mass spectrometer 20 includes four toroidal electrostatic analyzers in an “S” configuration that feeds the next in a wavy path as shown in FIG. The deflector D ₁ refocuses the beam with a primary detector, ie an ion multiplier in front of the end of the primary mass spectrometer and in front of the collision cell 40. Next, the preliminary time-of-flight spectrum is recorded. The time measurement from this preliminary experiment is used to time the deactivation of the baffle plate D _{1 that} causes an ion packet of a desired mass to enter the dissociation cell 40. Alternatively, all ions of the entire mass are entered into the dissociation cell. After collision activation, the fragment ions are advanced to the secondary time-of-flight mass analyzer 50, followed by mass separation and detection with a channel plate or other detector assembly.

Using two sets of electrostatic deflecting plates D ₁ and D ₂ , the angle of incidence at the entrance of the ion mirror 50 is controlled to optimize the sensitivity.

It is known that the optimal mass resolution R of a TOF mass spectrometer is related to the duration or duration of an ion pulse ΔT as well as the time of flight T of ions passing through the analyzer, which are expressed as follows:

  Therefore, the mass resolution R is improved when the time width ΔT of the ion pulse is as short as possible. For example, ions entering the flight path of the TOF mass spectrometer 50 typically have an energy on the order of 10 keV, and if the flight path is 1 m 2, the resolution of 5000 at mass 5000 is Only achieved if the pulse width ΔT has an order of 14 ns or less.

  When using an ion focuser at an early stage, the mass selective ion packet is compressed using a preliminary time-of-flight spectrum to compress the spatially or temporally diffused ions at the focal point in the dissociation cell 40. A pulse having a gradient across the active concentrator 10 is timed.

Alternatively, the time of flight of all (parent and product) ions can be timed from the source. In this case, not used deflector D _1. After a satisfactory spectrum is obtained, the kinetic energy imparted to the parent ion is changed in small portions for another time-of-flight experiment. In this secondary experiment, the parent ion flight time is changed by the time associated with the energy shift, but the flight time of the fragment ion remains fixed in relation to its respective parent ion. This allows all parent ion fragmentation to be analyzed simultaneously since each set of fragments associated with an individual parent ion can be identified.

  An ion focuser 30 is provided between the ion lens L and the TOF mass spectrometer 50 in order to compress the ion pulses generated by the source 10 into shorter duration pulses.

As shown in FIG. 3, the ion “focuser” 30 includes a pair of electrodes P ₁ , P ₂ that are normally held at the ground potential. In order to compress the pulse of the mass-selective parent ion into a shorter pulse, the _one closer to the electrode P _{1, the} mass spectrometer 20, when the pulse is completely located in the “focuser” area S ₁ between the electrodes. The electrode is quickly ramped up to a positive voltage V ₁ (relative to positive ions).

This voltage applies an electrostatic acceleration force in the direction of the ion mirror 50 to each ion in the pulse, accelerating the ion to high energy by an amount proportional to its separation from the basing electrode P ₁ . The ions in the pulse that first enter the concentrator area and are closer to the electrode P ₁ spend less time in the acceleration field than ions that later enter the “focuser” area. Therefore, “late ions” tend to catch “early ions”. The distance s separating the two electrode plates, the distance d separating the downstream plate and the TOF mass spectrometer 50, and the electrode plate so that all ions in the pulse reach the entrance of the TOF mass spectrometer substantially simultaneously. Select the voltage V ₁ applied to P ₁ .

The significant result of applying the acceleration voltage V ₁ to the mass-selected ions in each pulse is to introduce significant diffusion of their energy. For example, when an ion pulse generated by the ion source 10 is diffused to an area spanning 50 mm so as to reach the electrodes P ₁ and P ₂ of the ion concentrator, the energy of the parent ions reaching the ion mirror 50 is 10 keV (when this is the energy of the leading ion in a pulse that does not receive any energy from the acceleration field) to 14 keV (the energy of the trailing ion in the pulse receiving a maximum energy of 4 keV from the acceleration field) .

  A compressed ion pulse (typically having a duration of 10 ns or less) passes through a cell 40 located at the entrance of the TOF mass spectrometer 50. One possibility is to break up the ions by gas collisions. Another possibility is to use a laser pulse to dissociate the mass selective parent ions that make up the compressed pulse. Since compressed ion pulses are sufficiently limited in both time and space, the laser pulse can be synchronized to coincide with the arrival of each ion pulse at the time focus.

Fragment ions generated by dissociation of the mass-selective parent ion are on the same trajectory as the parent ion, so there is little time diffusion introduced before entering the ion mirror 50. The undissociated precursor ions and fragment ions introduced into the ion mirror 50 exhibit substantial energy diffusion for two reasons. Ions of the same mass exhibit large energy diffusion due to the action of the ion concentrator as in the previous period. Different mass ions have different energies (each fragment ion of mass M _F has the fraction M _P / M _F energy of the precursor ions to which it is obtained (mass M _P)).

  The secondary field E of the ion mirror 50 allows high mass resolution to be obtained even when ions introduced into the flight path of the analyzer have different energies. Ions are exposed to electrostatic reflectivity F that increases linearly as a function of the depth of ion penetration into the field region. This force acts in the X direction (FIG. 4) and has a magnitude directly proportional to the separation x of ions from the Z axis.

（式中、ｋは定数であり、ｑは電荷である）。 The electrostatic reflection force F is expressed as follows:

(Where k is a constant and q is a charge).

The equation for ion motion in the field region is similar to that related to simple harmonic motion decay, and the time interval t during which the ion mass m travels from the point of entry 1 to the point of reflection 2 is Shown by the formula:

Thus, the ions occupy the field area for the total time interval t ′ given by:

  As this result shows, ions occupy a field region E for a time interval that depends only on its mass-to-charge ratio (m / q), so that, as in this example, they have different energies Even the ions are distinguished from each other as a function of their mass-to-charge ratio.

  It has been found that the flight time of ions passing through the ion mirror is independent of angular deviations in the XY plane over a relatively large angular range when measured by a flat detector in the YZ plane.

Hereinafter, the flight path in the system of FIG. 4 will be considered. Thereafter, non-dissociated precursor ions [I _P ] and masses [M _D (1), M _D (2), respectively, where M _D (1)> M _D (2). The two daughter ions [I _D (1), I _D (2)] having the above are also considered. In this example, it is assumed that all the ions have the same charge.

The heaviest non-dissociated precursor ion I _P has the longest flight time through the field region, and they travel along the outermost path, while the light daughter ion I _D (2) has the shortest flight time , They take the innermost path to have low energy.

  Ions with different masses are present in the field region at different locations. Ions can be detected using, for example, a multichannel plate detector attached to the time-focal plane.

As described above, the incident angle の of ions entering the TOF mass spectrometer can be controlled using the _two baffle plates D ₁ and D ₂ . Special features of the second set of deflector D ₂ is to reduce the spatial spread of ions at the detector, thereby all ions are detected. To that end, baffle plate D ₂ applies all ions to electrostatically deflected ions received by the detector. In principle, all non-dissociated precursor ions and fragment ions that make up the entire mass spectrum can be collected.

  A feature of this form of energy independent ion mirror is that the dissociation cell 40 can be held at the ground potential, eliminating the need for ion beam lag and subsequent spatial defocusing, and any energy dependent extraction. Avoid the need for optics.

  In yet another embodiment, the secondary field has rotational symmetry about an axis, eg, the X axis. Such a field is generated by an electrode structure consisting of one electrode having a conical electrode surface and a second electrode having a hyperbolic or spherical electrode surface facing the conical electrode surface. The second electrode is held at a delayed potential with respect to the first electrode.

  Tandem mass spectrometry systems such as those described above find particular use in the structural analysis of large molecules, such as biological and polymer specimens. Since the time of flight of the ion mirror through the ion mirror depends on its mass-to-charge ratio, and is completely independent of their energy, the energy of the ion due to the action of the ion focuser on the precursor counter-ion is substantial. High mass resolution is obtained even when subjected to diffusion.

  A second embodiment of the present invention will now be described, which is similar to the first embodiment. Only the differences from the first embodiment are described, and the same reference numbers are used for equivalent features.

  The second embodiment is the same as the first embodiment except that the primary time-of-flight analyzer takes a further different form. The same reference numbers are used for equivalent features. The first part of the primary time-of-flight mass spectrometer of the second embodiment includes an electrostatic lens 80, after which a planar ion mirror is provided, which exhibits an optical intensity of zero. This takes the form of two parallel planar charged grids 92, one provided on the other. Each grid element 94 is provided at a small angle perpendicular to the optical path of ions from the electrostatic lens 80. The ions are reflected by the mirror 93 and pass through yet another electrostatic lens 96 that is identical to the primary electrostatic lens 80. The ions then go to the dissociation cell 40. Electrostatic lenses 80 and 96 help to achieve the required spatial convergence.

  The third embodiment is similar to the first embodiment, except that the primary tandem mass spectrometer 20 does not take the form of four toroidal electrostatic analyzers, instead a single electrostatic lens 80 is used. Includes. The lens is in the form of a cylindrical tube, which exists with an ascending potential of a few kV and has a surrounding tubular enclosure or shield 82 connected to the ground. In use, an approximately short duration laser pulse is focused through the lens 86 and directed to the target material 88. A part of the target substance 88 on the surface is volatilized. Two closely spaced plates 90 adjacent to the laser focus point on the target material 88 are sequentially warped so that the target material ion firing “cloud” is directed to the electrostatic lens 80 and the rest of the device. It is homogenized with the target substance at the potential.

  The primary time-of-flight mass spectrometer in each embodiment is capable of spatial convergence at or near the entrance of the secondary mass spectrometer 50. Time convergence is also provided, and these features allow the three embodiment devices to provide significant improvements in resolution over existing devices.

  Spatial convergence coexisting with time convergence is an essential requirement for secondary field mirrors to show high resolution.

FIG. 1 is a diagram of a tandem mass spectrometer according to a first embodiment of the present invention. FIG. 2 is a cross-sectional plan view of the primary mass spectrometer of the embodiment of FIG. FIG. 3 is a schematic diagram of an ion “focuser” used in the tandem mass spectrometer of FIG. FIG. 4 shows a transverse cross-sectional view and a perspective view, respectively, of a type 1 ion mirror with a two-dimensional secondary field. FIG. 5 is a diagram of a tandem mass spectrometer according to the second embodiment of the present invention. FIG. 6 is a diagram of a tandem mass spectrometer according to the third embodiment of the present invention.

Claims (16)

  Ion source, primary time-of-flight means having the property of providing spatial collection with temporal convergence, means for dissociating ions from the primary time-of-flight means to generate fragment ions, and secondary time-of-flight A tandem mass spectrometer comprising a sequential arrangement of means, wherein the secondary time-of-flight means is arranged to reflect along the optical axis of the apparatus to be arranged to produce a substantially secondary field The primary time-of-flight means includes electrostatic field means for providing spatial focusing as well as temporal focusing of ions near or near the entrance of the ion mirror, and the time of the secondary time-of-flight means The apparatus, wherein a detector is disposed in the convergence plane, and the time convergence plane is perpendicular to the optical axis of the apparatus.   The tandem mass spectrometer of claim 1, wherein the ion mirror is arranged to produce a parabolic field along the optical axis of the device.   The tandem mass spectrometer according to claim 1 or 2, wherein the ion source is arranged to emit a pulsed beam of ions.   4. A tandem mass spectrometer according to claim 1, 2 or 3, wherein the device comprises means for compressing or focusing ions into pulses of ions.   5. A tandem mass spectrometer according to claim 4, wherein the ion source and / or the primary time-of-flight means comprises means for compressing or focusing the ions into a pulse of ions.   Means for compressing or focusing the ions into a pulse of ions includes an entrance where a pulse of ions selected by the primary time-of-flight means enters the focus area, and where the pulse exits the focus area. Define a concentrator area having an exit and apply electrostatic acceleration or deceleration forces to the ions in the pulse when entering the concentrator area, thereby proportionally separating them from the exit of the concentrator area 6. A tandem mass spectrometer according to claim 4 or 5, comprising electrostatic means operable to accelerate or decelerate the ions to high or low energy.   7. A tandem mass spectrometer as claimed in claim 6, wherein the electrostatic means of the means for compressing or focusing the ions into a pulse of ions includes a corresponding electrode plate at the entrance to or exit from the concentrator area. .   The primary time-of-flight means is adapted for the isobaric ion packet with respect to diffusion perpendicular to the optical axis of the device, diffusion along the optical axis of the device, energy diffusion of ions in the packet, and temporal convergence. 8. A tandem mass spectrometer according to any one of claims 1 to 7, arranged to provide convergence.   The tandem mass spectrometer according to any one of claims 1 to 8, wherein the primary time-of-flight means includes a sequential S-shaped configuration of a plurality of toroidal or cylindrical electrostatic devices.   The tandem mass spectrometer according to claim 9, wherein the primary time-of-flight means includes two, three or four of the electrostatic devices.   The tandem mass spectrometer according to any one of claims 1 to 8, wherein the primary time-of-flight means includes an electrostatic lens.   The tandem mass spectrometer according to claim 11, wherein the ion source includes electrostatic means for accelerating ions into the electrostatic lens.   The tandem mass spectrometer according to claim 11 or 12, wherein the electrostatic lens includes an axisymmetric body with a potential raised with respect to the ground.   The tandem mass spectrometer according to claim 11, wherein the primary time-of-flight means further includes a primary time-of-flight ion mirror after the electrostatic lens.   The tandem mass spectrometer according to claim 14, wherein the primary time-of-flight means further includes a secondary electrostatic lens after the primary time-of-flight ion mirror.   The tandem mass spectrometer according to claim 14 or 15, wherein the primary time-of-flight ion mirror is a plane mirror having an optical intensity of substantially zero.

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