The disclosure relates to the field of mass spectroscopic analysis, such as multi-reflecting time-of-flight mass spectrometry apparatuses and a method for using multi-reflecting time-of-flight mass spectrometry apparatuses.
Time-of-flight mass spectrometry is a widely used tool of analytical chemistry, characterized by a high speed of analysis in a wide mass range. Multi-reflecting time-of-flight mass spectrometers (MR-TOF MS) enable substantial increases in resolving power due to the flight path extension. Such flight path extension requires the folding of ion path trajectories. Reflecting the ions in mirrors is one method for accomplishing the folding of ion paths. UK Patent No. GB2080021, by inventor H. Wollnikas, appears to have disclosed the potential for utilizing mirrors to reflect ions. The deflection of ions in sector fields provides a second method for accomplishing the folding of ion paths. This second method appears to have been disclosed in a 2003 scholarly article attributed to Japan's Osaka University. See Michisato Toyoda et al., Multi-Turn Time-of-Flight Mass Spectrometers with Electrostatic Sectors, 38 J. Mass Spectrometry 38 1125 (2003). Of these two methods for folding ion paths, mirror-type MR-TOF MS, due to their high-order time per energy focusing, allow for larger energy acceptance, which is an important advantage.
As far back as 1989, an advanced scheme of folded-path MR-TOF MS using two-dimensional (planar) gridless mirrors was known. The Russian Patent No. SU 1725289, by Nazarenko et. al., appears to have utilized this scheme, which is illustrated in the present
The present inventors, in Publication No. WO2005001878, appear to have disclosed a set of periodic lenses in the field-free region between the planar ion mirrors to confine ion packets in the drift z-direction. The present
The present inventors, in UK Publication No. GB2476964, appear to have disclosed curved ion mirrors in the drift z-direction forming a hollow cylindrical electrostatic ion trap, further extending the ion flight path within a MR-TOF MS.
Increasing the flight path length in the MR-TOF MS causes three distortions (aberrations) to the flight time (TOF), each of which limit the mass resolving power. The three aberrations are: (i) ion energy spread, (ii) spatial spread of ion packets in the y-direction, and (iii) spatial spread of ion packets in the z-direction. The z-directional spatial spread aberrations are primarily the second order TOF aberrations (“T|zz”) referred as the “spherical” aberration. A spherical aberration is created by periodic lenses confining the ion beam in the z-direction and is always positive (T|zz>0).
The present inventors, in Publication No. WO2013063587, appear to disclose an improvement to the ion mirror isochronicity with respect to energy and y-spread. Thus, T|zz aberrations caused by the periodic lenses remain the major remaining TOF aberration limiting the mass resolving power of the MR-TOF MS.
To reduce those T|zz aberrations, the present inventors, in U.S. Patent Application No. 2011186729, appear to disclose a quasi-planar ion mirror comprising, in essence, a spatially and periodically modulated ion mirror field as illustrated in
Even so, numerical simulations of MR-TOF MS with quasi-planar ion mirrors show that such mirrors achieve efficient elimination of TOF aberrations only if the period of the electrostatic field inhomogeneity in the z-direction equals or exceeds the y-height of the mirror window. Hence, in the field of MR-TOF MS, practical analyzer sizes continue to limit the density of ion trajectory folding and the flight path extension. What is more, the fact that periodic modulation affects y-components of the field and complicates the analyzer tuning presents another limitation.
Accordingly, a need exists in the art to provide an alternative way of reducing the spherical TOF aberrations T|zz, which can be used in planar or hollow cylindrical MR-TOF MS with densely folded ion trajectories and can provide for technical simplicity and decoupling of tuning of ion-optical properties in y- and z-directions.
One aspect of the disclosure provides a multi-reflecting time-of-flight mass spectrometer. The spectrometer includes two electrostatic ion mirrors, a set of periodic lenses, a pulsed ion source or pulsed ion converter, an ion receiver, and at least one electrode structure. The ion mirrors extend along a drift direction. The set of periodic lenses is disposed between the mirrors. The pulsed ion source or pulsed ion converter forms ion bunches, which travel along ion trajectories. The ion receiver receives the ion bunches. At least one electrode structure is disposed in the pathway of the ion trajectories and forms at least one of an accelerating electrostatic fields or a reflecting electrostatic field. The accelerating or reflecting electrostatic field provides local negative flight time aberration in the drift direction. The ion trajectories form multiple reflections between the ion mirrors and pass through said set of period lenses.
Implementations of the disclosure may include one or more of the following features. In some implementations, the electrostatic ion mirrors may be planar. In other implementations, the electrostatic ion mirrors may be hollow cylindrical.
In some implementation, the multi-reflecting time-of-flight mass spectrometer includes an orthogonal accelerator with a curved accelerating field. Some examples may include an orthogonal accelerator that includes a lens that enlarges the size of the ion bunches as compared to the size of the incoming continuous ion beam. Other examples may include an orthogonal accelerator that includes a lens that focuses ion bunches in the drift direction to the turning point of the ion bunch at first reflection at the electrostatic ion mirrors.
Another aspect of the disclosure provides that the electrode structure is a single ion reflector or a single local distortion, which is disposed either at the location of ion mirrors' first reflection or at the location of the ion mirrors' final ion reflection. The multi-reflecting time-of-flight mass spectrometer may further include an ion mirror field curvature arranged by ion mirror edges in the drift direction.
In some implementations, the electrode structure includes a curved electrode that converts the ion bunches to secondary electrons. Additionally, the electrode structure may include a focusing field that redirects the ion trajectories. Or the electrode structure may be disposed within pulsed axial ion bunching of the ion trajectories to form an accelerating field in the drift direction. Additionally, the electrode structure may be arranged within an electrostatic sector of either the isochronous curved inlet or the energy filter. And the electrode structure may include an accelerator with static curved field.
Yet another aspect of the disclosure provides a method of mass spectrometric analysis. The method includes forming a pulsed ion packet within a pulsed ion source or a pulsed converter. The method also includes arranging multi-reflecting ion trajectories by reflecting ions between electrostatic fields of gridless ion mirrors. The ion mirrors are extended along a drift direction. The method also includes confining the ion packets along the multi-reflecting ion trajectories by spatially focusing fields of periodic lenses. The method also includes compensating for spherical time-of-flight aberrations created by the fields of periodic lenses utilizing local fields. The local fields are curved in the drift direction and are either accelerating or reflecting ions.
The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring to
The known MR-TOF MS 11 of
The known MR-TOF MS 11 of
Referring to
The known MR-TOF MS 21 of
The mean angle α is selected such that the z-directional advance between each reflection coincides with the period of the periodic lenses 25. These periodic lenses 25 focus ions in the z-direction, providing for spatial confinement of ion bunches along the prolonged flight paths.
Referring to
The known MR-TOF MS 31 of
Efficient elimination of TOF aberrations in the known MR-TOF MS 31 of
Referring to
In the local areas of spatially restricted electrode sets, the amplitudes of the induced flight time deviations sufficiently compensate for the TOF aberrations caused by the spatial z-spread of the ion packets.
As further illustrated in
Additionally, optimal compensation of the TOF aberrations caused by the spatial z-spread of the ion packets is optionally provided by implementing at least two of the local electrode sets between which the ion bunch phase space transforms in the z-direction.
Utilizing these design aspects,
Referring specifically to
The pulsed converter 42 comprises at least one z-curved electrode 45 creating an inhomogeneous accelerating field with the field curvature in the z-direction. The pulsed converter 42 preferably comprises electrodes creating electrostatic lens fields 46 which transform the space phase volume of the accelerated ions. The continuous ion beam 47 accelerates ions essentially perpendicular to the xz-plane. The ions flying in the inhomogeneous field created by the curved electrode 45 along the outer ion trajectories 48 reach the exit from the converter 42 faster than the ions flying along the central ion trajectory 49.
The electrostatic lens fields 46 enlarge the z-directional width of the ion bunch and, at the same time, reduce the angular spread in the accelerated bunch, which helps better coupling between the source emittance and the analyzer acceptance.
Referring to
Referring to
A continuous ion beam 47 is injected into the pulsed converter 42 in the y-direction perpendicular to the plane of
The inhomogeneous accelerating field creates a certain correlation between the z-position of the ion and its final energy, but the additional energy spread created by this correlation is only about one percent of the total energy spread in the accelerated ion bunch.
Referring back to
Because the considered TOF aberration with respect to the spatial z-spread is proportional to the square of the amplitude of the oscillation of side trajectories with respect to the central one, the electrostatic lens fields 46 increases of the efficiency of compensation by increasing the spatial spread of outer ion trajectories 48 and by reducing the angular spread of outer ion trajectories 50. In this case the amplitude of oscillations of the outer ion trajectories 50 inside periodic lenses 44 is smaller than the amplitude of oscillations of the outer ion trajectories 48, and the pulsed converter 42 compensates for the major part of the TOF aberration with respect to the spatial z-spread of ions.
Referring to
The planar MR-TOF MS 61 of
The pulsed converter 42 preferably comprises electrodes creating one or more electrostatic lens fields 46 which provides for a weak focusing of a wide ion beam 48.
Referring to
The pulsed converter 42 comprises at least one electrode 45 creating a curved electrostatic field near the position of the continuous ion beam 47 and the focusing lens field 46. In operation, the lens field 46 focuses outer ion trajectories 48, maintaining the continuous ion beam 47 parallel to the central ion trajectory 49, to the position of the ion bunch turning point at first reflection from the mirror 43.
The inhomogeneous field created by electrode 45 is tuned to compensate the TOF aberration created by the spatial z-spread of ions in the outer ion trajectories 48, whereas the inhomogeneous field created by the local electrode 72 is tuned to compensate the TOF aberration due to the spatial z-spread of ions in the outer in trajectories 50. Thus, the planar MR TOF MS 71 achieves the full compensation of the TOF aberration with respect to the spatial z-spread of the ions.
In practical implementation, the local inhomogeneous field near the first ion bunch turning point in the mirror 43 can be created preferably by a local mask electrode or by the fringing field at the z-edge of the ion mirror nearest to the turning point.
Referring to
Ion bunches within the MR-TOF MS 81 of
In one example, to compensate for a positive flight time deviation of five nanoseconds for ions a mass of 1000 a.m.u. with the kinetic energy of 4000 eV and the offset from the central trajectory of two millimeters, the radius of the surface curvature should be 15.5 millimeters.
Preferably, to make the compensating TOF deviation tunable, a set of additional electrodes 89 can be arranged around the curved surface 84.
The considered curved surface 84 cannot compensate for the flight time aberration due to the spatial z-spread for offset trajectories 90 in
Referring to
In the planar MR-TOF MS 91, electrodes creating a focusing field 92 are implemented in front of the detector, and an additional local electrode is implemented in the mirror 82 near the turning points of the ions at their last reflection. The focusing system makes parallel the offset ion trajectories 87 coming from a single point at the turning point area.
In planar MR-TOF MS 91, the combination of the compensating means 84 and 93 can be tuned such that the curved electrode 84 compensates for the TOF aberration due to the spatial z-spread for offset ion trajectories 87, coming to the detector with different offsets from the central trajectory 88, and the compensating means 93 compensates the TOF aberrations for offset ion trajectories 90 coming to the same point at the detector under different angles.
Short ion bunches for flight time analysis in MR TOF MS can be created from a continuous ion beam by an axial dynamic bunching of ions in a continuous ion beam with a subsequent energy filtering of ion energy spread. Functionally similar the orthogonal pulsed ion converter shown in
To induce a negative flight time deviation for ions 105 flying off the central trajectory 106, at least one electrode (preferably the pulsed one 107) of the buncher is curved so that the equi-potentials 108 of the pulsed bunching field are also curved.
Similar to the orthogonal ion injection of
An additional negative flight time deviation for ions flying off the central trajectory 106 can be provided in the energy filter 104, because it is well known from the general ion-optical theory that both sector field and mirror-type devices can provide for a negative TOF aberration with respect to the spatial spread in the ion beam.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/US2014/061936 | 10/23/2014 | WO | 00 |