U.S. patent application number 16/878722 was filed with the patent office on 2020-11-26 for ion trap with elongated electrodes.
The applicant listed for this patent is Thermo Fisher Scientific (Bremen) GmbH. Invention is credited to Eduard V. Dennisov, Dmitry Grinfeld, Jan-Peter Hauschild, Alexander Kholomeev, Alexander A. Makarov, Amelia Corinne Peterson.
Application Number | 20200373146 16/878722 |
Document ID | / |
Family ID | 1000004989091 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200373146 |
Kind Code |
A1 |
Hauschild; Jan-Peter ; et
al. |
November 26, 2020 |
Ion Trap with Elongated Electrodes
Abstract
An ion trap 1 comprises one ejection electrode 2 for ion
trapping having an opening 4, through which ions in the ion trap 1
can be ejected in an ejection direction E and further electrodes 3
for ion trapping, wherein the ejection electrode 2 and the further
electrodes 3 are elongated in a longitudinal direction L. The angle
.alpha. between the longitudinal direction L and the ejection
direction E is nearly 90.degree.. The ion trap 1 comprises a
primary winding 5 connected to an RF power supply 6, a secondary
winding 7 coupling with the primary winding 5 for transforming the
RF voltage of the RF power supply 6 supplying the transformed RF
signals to the ejection electrode 2 and secondary windings 7'
coupling with the primary winding 5 for transforming the RF voltage
of the RF power supply 6 supplying the transformed RF signals to
the further electrodes 3. The ion trap 1 comprises a first DC
supply 8, a second DC supply 9 and a controller 50, which is
applying in a time period a first DC voltage provided by first DC
supply 8 via the secondary winding 7 to the ejection electrode 2 to
pull ions in the ion trap to the opening 4 of the ejection
electrode 2 and a second DC voltage provided by the second DC
supply 9 via the secondary windings 7' to the at least 70% of the
further electrodes 3 to push ions in the ion trap to the opening 4
of the ejection electrode 2.
Inventors: |
Hauschild; Jan-Peter;
(Weyhe, DE) ; Makarov; Alexander A.; (Bremen,
DE) ; Kholomeev; Alexander; (Bremen, DE) ;
Grinfeld; Dmitry; (Bremen, DE) ; Dennisov; Eduard
V.; (Bremen, DE) ; Peterson; Amelia Corinne;
(Bremen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thermo Fisher Scientific (Bremen) GmbH |
Bremen |
|
DE |
|
|
Family ID: |
1000004989091 |
Appl. No.: |
16/878722 |
Filed: |
May 20, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 49/067 20130101;
H01J 49/427 20130101; H01J 49/4225 20130101 |
International
Class: |
H01J 49/42 20060101
H01J049/42; H01J 49/06 20060101 H01J049/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2019 |
GB |
1907235.4 |
Claims
1. An ion trap comprising: an ejection electrode for ion trapping
having an opening, through which ions in the ion trap can be
ejected in an ejection direction E; electrodes for ion trapping a
primary winding connected to an RF power supply; a secondary
winding coupling with the primary winding for transforming the RF
voltage of the RF power supply and supplying the transformed RF
signals to the ejection electrode; secondary windings coupling with
the primary winding for transforming the RF voltage of the RF power
supply and supplying the transformed RF signals to the further
electrodes; a first DC supply; a second DC supply; and a
controller, wherein the ejection electrode and the further
electrodes are elongated in a longitudinal direction L, the angle
.alpha. between the longitudinal direction L and the ejection
direction E deviates from 90.degree. not more than 15.degree., the
controller is configured for applying in a time period a first DC
voltage provided by first DC supply via the secondary winding to
the ejection electrode to pull ions in the ion trap to the opening
of the ejection electrode and a second DC voltage provided by the
second DC supply via the secondary windings to the at least 70% of
the further electrodes to push ions in the ion trap to the opening
of the ejection electrode.
2. The ion trap according to claim 1, wherein the ion trap is
comprising 3 further electrodes.
3. The ion trap according to claim 1, wherein the ion trap is
comprising 5 further electrodes.
4. The ion trap according to claim 1, wherein the ion trap is
comprising 7 further electrodes.
5. The ion trap according to claim 1, wherein the ion trap is a
curved ion trap.
6. The ion trap according to claim 1, wherein the angle .alpha.
between the longitudinal direction L and the ejection direction E
deviates from 90.degree. not more than 7.degree., preferably not
more than 3.degree..
7. The ion trap according to claim 1, wherein the controller is
applying in the time period the second DC voltage provided by the
second DC supply via the secondary windings to the at least 80% of
the further electrodes to push ions in the ion trap to the opening
of the ejection electrode.
8. The ion trap according to claim 7, wherein the controller is
applying in the time period the second DC voltage provided by the
second DC supply via the secondary windings to all further
electrodes to push ions in the ion trap to the opening of the
ejection electrode.
9. The ion trap according to claim 1, wherein the control is
applying at the same time a first DC voltage provided by first DC
supply via the secondary winding to the ejection electrode to pull
ions in the ion trap to the opening of the ejection electrode and a
second DC voltage provided the second DC supply via the secondary
windings to the at least 70% of the further electrodes to push ions
in the ion trap to the opening of the ejection electrode
10. The ion trap according to claim 1, wherein voltage difference
between the first DC voltage applied to the ejection electrode and
the second DC voltage applied to the further electrodes is between
50 V and 800 V, preferably between 100 V and 600 V and particular
preferably between 200 V and 400 V.
11. The ion trap according to claim 1, wherein the ion trap is
comprising a focusing lens, which is arranged for the ejected ions
downstream of the of the opening of the ejection electrode and is
focusing the ejected ions.
12. The ion trap according to claim 11, wherein the focusing lens
has an opening into which the ejected ions are directed which is
larger than the opening of the ejection electrode.
13. The ion trap according to claim 11, wherein the focusing lens
is an electrostatic lens to which a DC voltage is applied, so that
the voltage difference between the DC voltage of the focusing lens
and the first DC voltage of the ejection electrode is between 250 V
and 1,500 V, preferably between 400 V and 1,000 V and particular
preferably between 600 V and 800 V.
14. The ion trap according to claim 11, wherein the focusing lens
is an electrostatic lens to which a DC voltage is applied and the
ratio of the voltage difference between the DC voltage of the
focusing lens and the first DC voltage of the ejection electrode
and the voltage difference between the DC voltage applied to the
ejection electrode and the DC voltage applied to the further
electrodes is between 1.5 and 6, preferably between 2.0 and 4 and
particular preferably between 2.2 and 3.
15. The ion trap according to claim 11, wherein the ion trap is
comprising an acceleration lens, which is arranged for the ejected
ions downstream of the focusing lens.
16. The ion trap according to claim 15, wherein the acceleration
lens has an opening into which the ejected ions are directed which
is smaller than the opening of focusing lens.
17. The ion trap according to claim 15, wherein the acceleration
lens is an electrostatic lens to which a DC voltage is applied, so
that the voltage difference between the DC voltage of the
acceleration lens and the DC voltage of the focusing lens is
between 800 V and 5,000 V, preferably between 1,500 V and 3,500 V
and particular preferably between 2,000 V and 2,700 V.
18. The ion trap according to claim 15, wherein the acceleration
lens is an electrostatic lens to which a DC voltage is applied, and
ratio of the voltage difference between the voltage difference
between the DC voltage of the acceleration lens and the first DC
voltage of the ejection electrode and the voltage difference
between the first DC voltage applied to the ejection electrode and
the second DC voltage applied to the further electrodes is between
2 and 12, preferably between 4 and 9 and particular preferably
between 5 and 7.
19. The ion trap according to claim 15, wherein the acceleration
lens is an electrostatic lens to which a DC voltage is applied, and
ratio of the voltage difference between the first DC voltage
applied to the ejection electrode and the second DC voltage applied
to the further electrodes and the voltage difference between the
voltage difference between the DC voltage of the acceleration lens
and the second DC voltage applied to the further electrodes and is
between 0.05 and 0.4, preferably between 0.1 and 0.25 and
particular preferably between 0.12 and 0.2.
20. The ion trap according to claim 1, wherein the secondary
winding supplying the transformed signal to the ejection electrode
and the secondary winding supplying the transformed signal to one
of the further electrodes are a pair of secondary windings
connected in series.
21. The ion trap according to claim 1, wherein the secondary
windings supplying the transformed signal to two of the further
electrodes are a pair of secondary windings connected in
series.
22. The ion trap according to claim 1 at least one of claims 1 to
21, wherein by tapping RF signals from the RF supply of the
ejection electrode and further electrodes of the ion trap further
components of a mass spectrometer, in particular a HCD cell or a
transport multipole, are supplied with a RF voltage, wherein
preferably an inductance divider is used.
23. Method of ejecting ions from an ion trap, which is comprising
one ejection electrode and further electrodes elongated in a
longitudinal direction L for ion trapping, wherein the ejection
electrode comprising an opening, through which ions in the ion trap
can be ejected in an ejection direction E, wherein an angle .alpha.
between the longitudinal direction L and the ejection direction E
deviates from 90.degree. not more than 15.degree., wherein RF
voltage is supplied to the ion trap by a primary winding connected
to an RF power supply, a secondary winding coupling with the
primary winding transforming the RF voltage of the RF power supply
and supplying the transformed RF voltages to the ejection electrode
and secondary windings coupling with the primary winding
transforming the RF voltage of the RF power supply and supplying
the transformed RF voltages to the further electrodes, a first DC
supply and a second DC supply, comprising the steps: switching off
the RF voltage supplied to the one ejection electrode and the
further electrodes of the ion trap; and applying in a time period a
first DC voltage via secondary winding provided by the first DC
supply to the ejection electrode to pull ions in the ion trap to
the opening of the ejection electrode and a second DC voltage
provided by the second DC supply via the secondary windings to the
at least 70% of the further electrodes to push ions in the ion trap
to the opening of the ejection electrode.
Description
PRIORITY
[0001] This application claims priority to UK Patent Application
1907235.4, filed on May 22, 2019, and titled "Ion Trap with
Elongated Electrodes," by Jan Peter Hauschild et al, which is
hereby incorporated herein by reference in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to an ion trap and to a method of
ejecting ions from an ion trap, wherein the ions are ejected in an
ejection direction E which is perpendicular or substantially
perpendicular to the longitudinal direction L of the ion trap.
BACKGROUND OF THE INVENTION
[0003] Ion traps could be used in order to provide a buffer for the
incoming stream of ions and to prepare a packet with spatial,
angular and temporal characteristics adequate for the specific mass
analyser. Examples of pulsed mass analysers include time-of-flight
(TOF), Fourier transform ion cyclotron resonance (FT ICR),
Orbitrap.RTM. types (i.e. those using electrostatic only trapping),
or a further ion trap.
[0004] Ion traps are storage devices that use RF fields for
transporting or storing ions. Typically, they include a RF signal
generator that provides a RF signal to the primary winding of a
transformer. A secondary winding of the transformer is connected to
the electrodes (typically four) of the storage device. Typically
they comprise elongate electrodes extended in a longitudinal
direction L and the electrodes are paired along axes perpendicular
to the longitudinal direction. In a ion trap having e.g. 4
electrodes the electrodes are shaped to create a quadrupolar RF
field with hyperbolic equi-potentials that contain ions entering or
created in the ion trap. Trapping within the ion trap can be
assisted by the use of a DC field. As can be seen from FIG. 2a,
each of the four elongate electrodes is split into three along the
z axis. Elevated DC voltages can be applied to the front and back
sections of each electrode relative to the larger central section,
thereby superimposing a potential well on the trapping field of the
ion trap that results from the superposition of RF and DC field
components. RF voltages may also be applied to the electrodes to
create an RF field component that assists in ion selection.
[0005] In particular there are two types of ion traps having
elongated electrodes: Linear ion traps comprise straight linear
electrodes. Curved linear ion traps called C-trap comprise curved
electrodes. An ion trap can have various number of of electrodes.
In particular an ion trap has pairs of electrodes. Preferably on
ion trap has 4 electrodes (quadrupole ion trap), 6 or 8
electrodes.
[0006] This invention is now to related to such ion traps, which
are ejected ions which are trapped in the ion trap in an ejection
direction E which is perpendicular or substantially perpendicular
to the longitudinal direction L of the ion trap. Therefore the ion
trap comprises one electrode, an ejection electrode, which has an
opening in the ejection direction E. Preferably the opening is
positioned in the middle of the ejection electrode or at least
close to the middle of the electrode. The opening is in particular
positioned in the middle of the ejection electrode in its
longitudinal direction L or at least close to the middle of the
ejection electrode in its longitudinal direction L.
[0007] To eject ions from the ion trap in the ejection direction E
different approachs are known to apply a DC voltages to the
electrodes, preferably after the RF voltage trapping the ions in
the ion trap has been switched off or at least reduced.
[0008] Chien et al. are proposing in "Enhancement of resolution in
Matrix-assisted Laser Desorption Using an Ion-trap
Storage/Reflectron Tim-of-flight Mass Spectrometer", Rapid. Comm.
Mass Spectrom. Vol. 7, 837-844 (1993) to apply to an electrode,
through which the ions are leaving the ion trap a DC voltage which
is pulling the ions to the this ejection electrode. On the other
hand Fountain et al. "Mass-selective Analysis of Ions in
Time-of-flight Mass spectrometry Using an Ion-trap Storage Device",
Rapid. Comm. Mass Spectrom. Vol. 8, 487-494 (1994) to apply to
electrode, which is opposite of the electrode, through which the
ions are leaving the ion trap a DC voltage which is pushing the
ions to the electrode, through which the ions are leaving the ion
trap.
[0009] In U.S. Pat. No. 5,569,917 is disclosed to apply at the same
time to apply to an electrode, through which the ions are leaving
the ion trap a DC voltage which is pulling the ions to the this
ejection electrode and to the electrode, which is opposite of this
electrode, a DC voltage of opposite polarity which is pushing the
ions to the electrode, through which the ions are leaving the ion
trap.
[0010] A similar approach is also decribed in US 2011/0315873 A1
for an ion trap having elongated electrodes. The details, how to
apply DC voltages to the electrodes to eject ions from the ion
trap, are illustrated below. Also in this approach voltage
difference is applied to the ejection electrodes and the electrode
opposite of the ejection electrode. This approach requires a
specific DC voltage supply for these two electrodes.
[0011] The effeciency of the ejection of the ions from ion trap
using this approaches is limited. Not all ions stored in the ion
trap can be extracted and transferred e.g. by the accelartion lens
to a mass analyser. In particular the efficiency depends on the
occurrence of space charges in an ion trap and the mass
distribution of the stored ion population.
[0012] Further a lot of ions pushed to the ejection electrode get
lost because they hit the edge of the opening of the ejection
electrode. This results in an increased contamination of the edge
which might further influence the behaviour of the ion trap, in
particular during ion ejection.
[0013] Due to the mentined problems further the dynamic range and
linearity of mass analysers to which the ejected ions are
transferred, is limited.
[0014] Another disadvantage of the known approachs to eject ions
from ion traps is that to each electrode of a the ion trap a
specific DC voltage has to be applied which is requiring a lot of
DC supply devices and a detailed control of the application of
different DC voltages to each DC electrode. It is an object of the
invention to provide an improved ion trap having a higher
efficiency of ion ejection.
[0015] It is an object of the invention to provide an improved ion
trap, wherein the dependence of the efficiency of ion ejection on
space charge is reduced.
[0016] It is an object of the invention to provide an improved ion
trap, wherein the dependence of the efficiency of ion ejection on
the mass distribution within the stored ion population is
reduced.
[0017] It is an object of the invention to provide an improved ion
trap, wherein during the ion ejection the contamination of the
opening, through which the ions are ejected is reduced in
comparison to ion traps of the prior art.
[0018] It is an object of the invention to provide an improved ion
trap, by which the dynamic range of a mass analyser can increased,
to which the ion trap is supplying the ejected ions.
[0019] It is an object of the invention to provide an improved ion
trap, by which the linearity of a mass analyser can increased, to
which the ion trap is supplying the ejected ions.
[0020] Another object of the invention is to provide an improved
ion trap with a simplified voltage supply.
SUMMARY OF THE INVENTION
[0021] At least one and preferably all of the objects are solved by
an ion trap of claim 1.
[0022] The inventive ion trap comprises for ion trapping one
ejection electrode and further electrodes. The ejection electrode
and the further electrodes are elongated in a longitudinal
direction L. The ion trap may be a straight linear ion trap or a
curved linear ion trap (C-trap). Also the ion trap might comprise
electrodes with linear and curved portions. The ion trap may be a
linear quadrupole ion trap, i.e. having four elongate electrodes.
However, the invention may be applied in ion traps having more than
four electrodes (e.g. six or eight electrodes). The electrodes of
the ion trap, the ejection electrode and further electrodes, have
preferably the same shape along the longitudinal direction L of the
ion trap. So the longitudinal direction can be (the same direction
along the whole ion trap) a straight line or a curved line or a
partially straight and curved line.
[0023] In a specific embodiment, different electrodes of the ion
trap can be used as ejection electrode at different instants of
time.
[0024] The ejection electrode of the ion trap has an opening,
through which ions in the ion trap 1 can be ejected in an ejection
direction E. The ejection direction E of a package of ejected ions
is defined as the average direction in which the ions of the
package fly when leaving the opening of the ejection electrode. So
for an ejected package of ions the ejection direction is typically
defining the direction of the central ion beam of the ion package.
The width of the ion beam perpendicular to the ejection direction E
might still depend on experimental conditions. The ejection
direction E of the ejected ions is at least nearly perpendicular to
the longitudinal direction L of the electrodes. The angle .alpha.
between the longitudinal direction L and the ejection direction E
deviates from 90.degree. typically not more than 15.degree.,
preferably not more than 10.degree. and particularly preferably not
more than 5.degree..
[0025] For the ion trapping in the ion trap the electrodes of the
ion trap, the ejection electrode and the further electrodes, are
supplied with a RF voltage. Some or all electrodes may be during
ion trapping also supplied with a DC voltage e.g. to create
potential walls.
[0026] The RF voltage applied to the electrodes is generated by
transforming the RF voltage provided by a RF power supply. This RF
power supply is providing the generated RF signal to a primary
winding. Then is primary winding is inductively coupled with a
secondary winding. The RF signal generated by transformation in
this winding is then supplied to the ejection electrode. Futher the
primary winding is also inductively coupled with other secondary
windings. The signal generated by transformation in these other
windings is then supplied to the other electrodes of the ion
trap.
[0027] The power supply of the ion trap is controlled by a
controller, which may comprise various control means, for example:
a processor, switches, and/or software to be executed by the
processor and other software and hardware components.
[0028] With the RF voltages applied to the electrodes, the ions can
be trapped in the ion trap. Optionally, the trapped ions are cooled
or thermalised in the ion trap prior to ejection. For the ejection
of the ions from the ion trap according to the invention also DC
voltages have to be applied to the electrodes of the ion trap.
Typically, they are applied, after the RF voltage provided to the
electrodes has been switched off. The the inventive ion trap is
comprising at least two DC supplies, providing DC voltages to the
electrodes of the ion trap. The application of the DC voltages is
controlled by the control of the ion trap.
[0029] For ejection of ions from the ion trap, a first DC voltage
provided by first DC supply is applied to the ejection electrode.
The first DC voltage is provided to the ejection electrode via the
secondary winding, which is also supplying the RF signal to the
ejection electrode. The first DC voltage is applied to the ejection
electrode to pull the ions in the ion trap to the opening of the
ejection electrode.
[0030] A second DC voltage is provided by second DC supply. The
second DC voltage is provided to at least 70% of the further
electrodes via the secondary windings which are also supplying the
RF signal to the further electrodes. The second DC voltage pushes
ions in the ion trap to the opening of the ejection electrode.
Therefore, the DC voltage provided by second DC supply to the at
least 70% of the further electrodes has the same polarity as most
ions in the ion trap.
[0031] Preferably the number of further electrodes is 3, so that
the ion trap is a quadrupole. But the number of the further
electrodes could be also in other embodiments 5 (heaxpole) or 7
(octopole).
[0032] In a preferred embodiment the ion trap comprises curved
electrodes. In particular the inventive ion trap can be a curved
ion trap.
[0033] In preferred embodiments of the inventive ion trap the angle
.alpha. between the longitudinal direction L and the ejection
direction E deviates from 90.degree. not more than 7.degree.,
preferably not more than 3.degree..
[0034] In other preferred embodiment of the inventive ion trap the
controller is applying in the time period the second DC voltage
provided by the second DC supply via the secondary windings to the
at least 80% of the further electrodes to push ions in the ion trap
to the opening of the ejection electrode. In a more preferred
embodiment of the inventive ion trap the controller is applying in
the time period the second DC voltage provided by the second DC
supply via the secondary windings to all further electrodes 3 to
push ions in the ion trap to the opening of the ejection
electrode.
[0035] The time period in which the controller is applying the
first DC voltage to the ejection electrode and second DC voltage to
the furtherr electrodes, can be between 5 ms and 5000 ms,
preferably between 10 ms and 2000 ms and particular preferably
between 50 ms and 500 ms. In particular both DC voltages can be
applied at the same time, but there might be a delay up to 5000 ns,
preferably up 500 ns and in particular preferably up to 100 ns.
Preferably the second voltage is at first applied to the further
electrodes.
[0036] Typically, is voltage difference between the first DC
voltage applied to the ejection electrode 2 and the second DC
voltage applied to the further electrodes 3 between 50 V and 800 V,
preferably between 100 V and 600 V and particular preferably
between 200 V and 400 V.
[0037] The inventive ion trap comprises in a preferred embodiment a
focusing lens, which is arranged for the ejected ions downstream of
the of the opening of the ejection electrode and is focusing the
ejected ions. Preferably the focusing lens has an opening into
which the ejected ions are directed which is larger than the
opening of the ejection electrode. The focusing lens 10 may be an
electrostatic lens to which a DC voltage is applied. Typically is
the voltage difference between the DC voltage of the focusing lens
and the first DC voltage of the ejection electrode is between 250 V
and 1,500 V, preferably between 400 V and 1,000 V and particular
preferably between 600 V and 800 V. Typically the ratio of the
voltage difference between the DC voltage of the focusing lens and
the first DC voltage of the ejection electrode and the voltage
difference between the first DC voltage applied to the ejection
electrode and the second DC voltage applied to the further
electrodes 3 is between 1.5 and 6, preferably between 2.0 and 4 and
particular preferably between 2.2 and 3.
[0038] The inventive ion trap comprises in a preferred embodiment
an acceleration lens, which is arranged for the ejected ions
downstream of the focusing lens. The acceleration lens 12 has
preferably an opening 13 into which the ejected ions are directed
which is smaller than the opening of focusing lens. the
acceleration lens 12 Preferably is the acceleration lens an
electrostatic lens to which a DC voltage is applied. Typically the
voltage difference between the DC voltage of the acceleration lens
and the DC voltage of the focusing lens is between 800 V and 5,000
V, preferably between 1,500 V and 3,500 V and particular preferably
between 2,000 V and 2,700 V. Typically is the ratio of the voltage
difference between the voltage difference between the DC voltage of
the acceleration lens and the first DC voltage of the ejection
electrode and the voltage difference between the first DC voltage
applied to the ejection electrode and the second DC voltage applied
to the further electrodes between 2 and 12, preferably between 4
and 9 and particular preferably between 5 and 7. Typically is the
ratio of the voltage difference between the first DC voltage
applied to the ejection electrode and the second DC voltage applied
to the further electrodes and the voltage difference between the
voltage difference between the DC voltage of the acceleration lens
and the second DC voltage applied to the further electrodes and is
between 0.05 and 0.4, preferably between 0.1 and 0.25 and
particular preferably between 0.12 and 0.2.
[0039] In a preferred embodiment of the ion trap the secondary
winding supplying the transformed RF voltage to the ejection
electrode and the secondary winding supplying the transformed RF
voltage to one of the further electrodes are a pair of secondary
windings connected in series.
[0040] In a preferred embodiment of the ion trap the secondary
windings supplying the transformed RF voltage to two of the further
electrodes 3 are a pair of secondary windings connected in
series.
[0041] In preferred embodiment of the inventive ion trap further
components of a mass spectrometer, in particular a HCD cell or a
transport multipole, are supplied with a RF voltage, by tapping RF
voltages from the RF supply of the ejection electrode 2 and further
electrodes 3 of the ion trap. Preferably an inductance divider is
used for tapping the RF voltage.
[0042] At least one and preferably all of the objects are solved by
a method of electing ions from an ion trap of claim 23.
[0043] The ion trap comprises one ejection electrode and further
electrodes elongated in a longitudinal direction L for ion
trapping, wherein the ejection electrode comprises an opening,
through which ions in the ion trap can be ejected in an ejection
direction E, wherein an angle .alpha. between the longitudinal
direction L and the ejection direction E deviates from 90.degree.
not more than 15.degree., wherein RF voltage is supplied to the ion
trap by a primary winding connected to an RF power supply, a
secondary winding coupling with the primary winding transforming
the RF voltage of the RF power supply 6 and supplying the
transformed RF voltages to the ejection electrode and secondary
windings coupling with the primary winding transforming the RF
voltage of the RF power supply and supplying the transformed RF
voltages to the further electrodes, a first DC supply 8 and a
second DC supply 9.
[0044] The methods comprises the first step of switching off the RF
voltage supplied to the one ejection electrode and the further
electrodes of the ion trap and then in a second step applying in a
time period a first DC voltage via secondary winding provided by
the first DC supply to the ejection electrode to pull ions in the
ion trap to the opening of the ejection electrode and a second DC
voltage provided by the second DC supply via the secondary windings
to the at least 70% of the further electrodes to push ions in the
ion trap to the opening 4 of the ejection electrode.
[0045] Further details of the inventive method can be derived from
this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 shows the ejection of ions from an ion trap according
to the prior art.
[0047] FIG. 2 shows the ejection electrode of an ion trap with
elongated electrodes.
[0048] FIG. 3 shows more detailed electrical circuit of the voltage
supply of another ion trap according to the prior art, which is a
linear ion trap.
[0049] FIG. 4 shows more detailed electrical circuit of the voltage
supply of another ion trap according to the prior art, which is a
curved ion trap.
[0050] FIG. 5 shows detailed electrical circuit of the voltage
supply of a first embodiment of an inventive ion trap.
[0051] FIG. 6 shows the ejection of ions from a second embodiment
of an inventive ion trap.
[0052] FIG. 7 shows the detailed electrical circuit of the voltage
supply of a first embodiment of an inventive ion trap shown in FIG.
5 including also an RF voltage supply for HCD cell and transport
multipole.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0053] FIG. 1 shows the ejection of ions from an ion trap according
to the prior arthaving elongated electrodes in the longitudinal
direction L. A cross section of the ion trap perpendicular to the
longitudinal direction L is shown. The ion trap is comprising an
elongate ejection electrode 2 and three further elongate electrodes
3. The ejection electrode 2 has an opening 4 through which ions
stored in the ion trap 1 can be ejected in an ejection direction E.
In this drawing further is shown the DC voltage supply to the
electrodes of the ion trap when ions shall be ejected. The ejected
ions are accelerated from the opening 4 of the ion trap to an
acceleration lens 12 having an opening 13. At least an RF voltage
is applied to the four electrodes 2,3 of the ion trap, when ions
are trapped. It is further possible to apply a small DC voltage to
at least one of the electrodes 2,3 of the ion trap to improve the
trapping by potential wells. Axial trapping is enabled by applying
DC voltages to the end apertures of the trap (not shown).
[0054] When the trapped ions are to be ejected, the RF voltage and
if present also the small DC voltage is switched off. Then an
offset voltage V.sub.acc is applied via an offset DC source which
is positioned between the lower further electrode 3 and the
acceleration lens 12, which is grounded. The same offset voltage
V.sub.acc (now shown) is also supplied to the upper further
electrode 3. A typical value for the applied offset voltage is
2,200 V. Via a first DC supply 8 a first DC voltage V.sub.eject is
applied to ejection electrode 2. This first DC voltage V.sub.eject
is applied between the lower further electrode 3 and the ejection
electrode 2 by the first DC supply 8. A typical value for the first
DC voltage V.sub.eject is 300V, wherein the negative polarity is
applied to the ejection electrode 2. Due to the ejection electrode
2 also being connected to the offset DC source that supplies
voltage V.sub.acc, relative to ground a voltage of 1,900 V is
applied to the ejection electrode 2. Via a second DC supply 9 a
second DC voltage is applied to left further electrode 3, which is
arranged opposite to the ejection electrode 2 in the ion trap. In
the shown example second DC voltage has the same value V.sub.eject
as the first DC voltage. This second DC voltage is applied between
the lower further electrode 3 and the left further electrode 3' by
the first DC supply 9. Then the value of the second DC voltage is
also 300V, wherein the positive polarity is applied to the left
further electrode 3'. Due to the ejection electrode 2 also being
connected to the offset DC source that supplies voltage V.sub.acc,
relative to ground a voltage of 2,500 V is applied to the left
further electrode 3. When these voltages are applied to the
electrodes 2,3 of the ion trap, positively charged ions are pushed
by the voltage applied to the left further electrode 3 in the
direction of the ejection electrode 2 and pulled by the voltage
applied to the ejection electrode 2 to the ejection electrode 2.
This effect on the positively charged ions is created by the
electric field in the ion trap, which is provided by the voltage
difference between the left further electrode 3 and the ejection
electrode 2. This electric field has in particular a component
directed to the ejection electrode 2 and as shown by the ion beam
32 of the ions in the ion trap is directed to the opening 4 of the
ejection electrode 2. But not all ions are ejected through the
opening and are further accelerated by the acceleration lens 12. A
portion of ions strike the edge of the opening 4. This leads to a
reduced efficiency of the ion ejection and to a contamination of
the ejection electrode 2 at the edge of its opening. Further, a
small dotted circle shows the central region from which ions are
ejected from the ion trap 1, when the DC voltages are applied as
described before.
[0055] FIG. 2 shows the ejection electrode 2 of an ion trap with
elongated electrodes. The ejection electrode in elongated in the
longitudinal direction L. Also shown is opening 4 provided in the
ejection electrode. Through this aperture 4 ions trapped in the ion
trap 1 can be ejected by applying the DC voltages to the ejection
electrode 2 and also further electrodes 3 of the ion trap 1. It is
shown that the ions are ejected from the ion through the opening 4
into an ejection direction E. It is shown, that the ejection
direction E of the ejected ions is substantially perpendicular to
the longitudinal direction L of the electrodes. In general, the
ejection direction E of the ejected ions is at least nearly
perpendicular to the longitudinal direction L of the electrodes.
The angle .alpha. between the longitudinal direction L and the
ejection direction E deviates from 90.degree. typically not more
than 15.degree., preferably not more than 10.degree. and particular
preferably not more than 5.degree..
[0056] FIG. 3 shows in more detail an electrical circuit of the
voltage supply of the ion trap 1 according to the prior art
disclosed in US 2011/0315873 A1. In this Figure is the voltage
supply for a linear ion trap shown.
[0057] It is shown the ejection of ions stored in the ion trap 1 in
ejection direction E. The ion trap is comprising an ejection
electrode 2 and the further electrodes 3, 3'. To facilitate
ejection, a opening 4 is provided in the ejection electrode 2.
[0058] A RF power supply 6 is shown which is connected with a
primary winding 5. Further three pairs of symmetrical secondary
windings 7,7' are shown, which are coupled with the primary winding
5. A RF switch 20 is shown to switch off the RF power supplied to
secondary windings explained below. A first pair of secondary
symmetrical windings 21 is shown which are connected to the
full-wave rectifier 42 to rapidly reduce the RF voltage in the
further secondary winding after the switch of the supplied RF
voltage.
[0059] A first and a second winding 7' of a second pair of
secondary windings supplies the further electrodes 3, of the ion
trap, which are above the middle and at the right side of the ion
trap 1. A first winding 7' of a third pair of secondary windings
supplies the other further electrode 3 of the ion trap below the
middle of the ion trap. The second winding 7 of a third pair of
secondary windings supplies the other ejection electrode 2 of the
ion trap. As can be seen from FIG. 3, all of the first windings of
the first, second and third pair of secondary windings are
connected together at the central tap 22 of the first pair of
windings. However, only the second winding of the first pair is
also connected to the central tap 22. The ends of the second of the
windings 7' and 7 of the second and third pairs of secondary
windings close to the central tap 22 are instead connected to a DC
offset supply.
[0060] With the circuit shown in FIG. 3, positive or negative
offsets (depending on the polarity of the ions trapped in the ion
trap) can be set from DC voltage supplies 24, 25 that are
selectable through a DC offset switch 23. However, rather than
simply supply these selected DC offset voltages directly to
secondary windings 7,7', they are routed through further high
voltage supply switches 26 and 27. These switches 26 and 27 that
preferably have low internal resistance may be set such that the DC
offsets are delivered direct to the secondary windings 7,7'. In an
alternative configuration, the switches may be set so that
independent HV offsets can be applied to the two secondary windings
7, 7' respectively supplying the ejection electrode 2 and the right
further electrode 3. In the case of positive ions in the ion trap,
a DC push voltage supply 9 supplies a large positive voltage
through push switch 27 that can be set on secondary winding 7'
thereby applying a large positive potential to the right further
electrode 3. This large positive potential repels ions stored in
the ion trap towards the aperture 4 provided in opposite ejection
electrode 2. A corresponding pull DC voltage supply 8 supplies a
large negative potential through pull switch 8 and onto secondary
winding 7, thereby applying a large negative potential on the
ejection electrode 2 that will attract ions towards its opening 4.
Accordingly, this arrangement allows either a small DC offset to be
applied to the electrodes 2 and 3 that may be used, for example, to
provide a potential well for trapping ions within the ion trap.
This potential may even, for example, be supplied at the same time
as the RF potential being supplied to the electrodes 2 and 3. When
the RF potential is switched off using switch 20, ions may be
ejected orthogonally from the ion trap by applying the DC push
voltage supply 9 and pull DC voltage supply 8 to the right further
electrode 3 and the ejection electrode 2 respectively in addition
to applying the DC offset voltage from 24 or 25 to all of the
electrodes.
[0061] FIG. 4. shows detailed electrical circuit of the voltage
supply of a curved ion trap 1 (C-trap) according to the prior art.
The electrical circuit for providing the RF voltages and DC
voltages is essentially the same as shown in FIG. 3. The ions are
now supplied to the C-trap 1 by a transport multipole 31 to which
ions are supplied from an ion source (not shown). The C-trap 1
ejects the trapped ions through the opening 4 of the ejection
electrode 2 into an Orbitrap.RTM. mass analyser.
[0062] FIG. 5 shows in detail an electrical circuit of the voltage
supply of a first embodiment of an inventive ion trap 1. The ion
trap 1 has elongated electrodes 2,3 in a longitudinal direction L
and can be a linear ion trap or a curved ion trap. A cross section
of the ion trap 1 perpendicular to the longitudinal direction L is
shown. The ion trap is comprising an ejection electrode 2 and three
further electrodes 3. The ejection electrode 2 has an opening 4
through which ions stored in the ion trap 1 can be ejected in an
ejection direction E.
[0063] In this drawing further is shown the RF voltage supply to
the electrodes 2,3 when ions are being trapped and the DC voltage
supply to the electrodes 2,3 of the ion trap when ions are being
ejected.
[0064] Normally at least an RF voltage of two opposite phases is
applied to the four electrodes 2,3 of the ion trap, when ions are
trapped. It is further possible to apply a small DC voltage to at
least one of the electrodes 2,3 of the ion trap to improve the
trapping by potential wells (supplied as the LO OFFSET voltage from
supply 9).
[0065] An RF generator is shown as RF power supply 6, which is
connected with a primary winding 5 of a transformer. This primary
winding 5 in the transformer arrangement is coupled with two pairs
of secondary windings 34, 35. The first pair of secondary windings
34 is supplying via the two windings 7' a transformed RF voltage to
the lower further electrode 3 and the left further electrode 3
arranged in the ion trap 1 opposite to the ejection electrode 2.
The second pair of secondary windings 35 is supplying via the
winding 7 a transformed RF voltage to the ejection electrode 2 and
via the winding 7' a transformed RF voltage to the upper further
electrode 3. Further a low offset DC voltage is optionally applied
to all electrodes 2, 3 when ions are trapped in the ion trap. In
this situation a pull switch 26 is opened (lower switch position)
and a push (offset) switch 27 is switched on to provide the low
offset voltage (OFFSET_LO).
[0066] When the controller 50 of the ion trap is switching the
voltage supply of the ion trap 1 to eject ions, the control is
switching the RF switch 36, the pull switch 26 and the push switch
27. At first the RF switch 36 is activated so as to switch off the
RF voltage supplied to all electrodes 2, 3 of the ion trap. Then
with a very short delay of 0-1000 ns the push switch 27 is
activated so as to provide a second DC voltage, a high push voltage
(OFFSET_HI) to the further electrodes 3 and the ejection electrode
2 via the opened pull switch 26. The value of the push voltage is
typically between 1,500 and 2,500 V, preferably between 1,800 V and
2,200 V. Then with a very short delay of 0-1000 ns the pull switch
26 is activated (upper switch position) so as to provide a first DC
voltage (PULL_DC) to the ejection electrode 2 in addition to the
high push voltage. Due to this DC voltage supply the ions in the
ion trap 1 are ejected through the opening 4 of the ejection
electrode. More details about the ion ejection are explained in
FIG. 6.
[0067] FIG. 6 shows the ejection of ions from a second embodiment
of an inventive ion trap 1. The ion trap has elongated electrodes
2, 3 in the longitudinal direction L. A cross section of the ion
trap perpendicular to the longitudinal direction L is shown. The
ion trap comprises an ejection electrode 2 and three further
electrodes 3. The ejection electrode 2 has an opening 4 through
which ions stored in the ion trap 1 can be ejected in an ejection
direction E. In this drawing further is shown the DC voltage supply
to the electrodes of the ion trap when ions are ejected. The
ejected ions are accelerated to an acceleration lens 12 having an
opening 13. Further is shown a focusing lens 10 with an opening 11,
which is arranged between the opening of the ejection electrode 2
and the acceleration lens 12. Ejection electrode 2, focusing lens
10 and acceleration lens 12 are arranged along the ejection
direction E, wherein ejected ions first pass the opening 4 of the
ejection electrode 2, then the opening 11 of the focusing lens 10
and finally the opening 13 of the acceleration lens 12.
[0068] Normally at least an RF voltage is applied to the four
electrodes 2,3 of the ion trap, when ions are trapped, for example
in the manner shown in FIG. 5. It is further possible to apply a
small DC voltage to at least one of the electrodes 2,3 of the ion
trap to improve the trapping by potential wells.
[0069] When the trapped ions are to be ejected, the RF voltage and
if present also the small DC voltage is switched off. Then a second
DC voltage V.sub.acc is applied via second DC supply 9 which is
connected with the three further electrode 3 and the acceleration
lens 12, which is grounded. The three further electrode 3 are
connected with the second DC supply 9 via secondary windings 7' of
a transformer supplying the RF voltage to the three further
electrodes 3. A typical value for the applied second voltage is
2,000 V. The second DC supply 9 is also connected to the ejection
electrode 2 via a first DC supply 8, whereby a first DC voltage
V.sub.eject is applied to ejection electrode 2. This first DC
voltage V.sub.eject is applied between the further electrodes 3 and
the ejection electrode 2 by the first DC supply 8. A typical value
for the first DC voltage V.sub.eject is 300V, wherein the negative
polarity is applied to the ejection electrode 2. Due to this,
relative to ground, a voltage of 1,700 V is applied to the ejection
electrode 2. When these voltages are applied to the electrodes 2,3
of the ion trap, positively charged ions are pushed by the voltage
applied to the further electrodes 3 in direction of the ejection
electrode 2 and pulled by the voltage applied to the ejection
electrode 2 to the ejection electrode 2. This effect on the
positively charged ions is created by the electric field in the ion
trap, which is provided by the voltage difference between the
further electrode 3 and the ejection electrode 2. This electric
field has in particular an improved component directed to the
ejection electrode 2 and in particular an improved component
directed to the opening 4 of the ejection electrode 2. Providing
only the ejection electrode 2 with a different voltage to the
further electrodes 3 creates a more non-uniform electric field than
in the prior art. Thus by the curcature of the equi-potentials of
this electric field, stronger focusing of ions through the opening
4 of the ejection electrode 2 may be achieved. Such non-uniformity
of the electric field within the volume of the ion trap creates a
converging lens that may bring ions from a wide region (dashed
circle) through the narrow ejection opening 4. Thus, advantages are
that a higher amount of ions may be extracted from a region
substantially wider that the ejection opening and contamination of
the ejection electrode around the opening may be reduced.
Accordingly, as shown in the Figure, the ion beam 32 of the ions in
the ion trap is directed to the middle of opening 4 of the ejection
electrode 2. At least nearly all ions are passing the opening 4 and
are further accelerated by the grounded acceleration lens 12. In
the inventive ion trap 1, preferably ions do not strike the edge of
the opening 4 or only a small portion of ions do so. This leads to
an improved efficiency of the ion ejection: a contamination of the
ejection electrode 2 at the edge of its opening 4 can be avoided.
Further the dotted circle shows the region from which ions are
ejected from the ion trap 1, when the DC voltage is applied as
decribed before. In comparison to FIG. 1 the diameter of the circle
is bigger and therefore ions of a larger region in the ion trap are
ejected by the inventive ion trap. Further is shown that the ion
beam 32 leaving the opening 4 is strongly diverging. To reduce this
the focusing lens is positioned between the ejection electrode 2
and the acceleration lens 12. The focusing lens 10 has a wide
opening 11 with a diameter larger than the opening 13 of the
acceleration lens 12 and larger than the opening 4. Typically,
voltages Viens between 800 V and 5,000 V are applied to the
focusing lens 10 by a third DC voltage supply 40, wherein this
voltage is applied between the focusing lens 10 and the grounded
acceleration lens 12. In the shown embodiment a voltages V.sub.lens
of 2,400 V is applied. Preferably the voltages V.sub.lens is
between 1,500 V and 3,500 V. By the application of the voltage
V.sub.lens to the focusing lens a collinear ion beam 32 of the
ejected ions can be formed.
[0070] FIG. 7 shows the detailed electric circuit of voltage supply
shown in FIG. 5 wherin further RF voltages are tapped from the RF
voltage supply to provide RF voltages to further components of a
mass spectrometer, in this embodiment a transport multipole and a
HCD cell. Still other components of a mass spectrometer can be
supplied in the same way with a RF voltage. The common supply of
the electrodes of the ion trap and other components has the
advantage to reduce the number of RF sources and avoid
synchrosation problems between the ion trap and other components
which are influencing the performance of mass spectrometer. Several
of the processes of the inventive method can be supported or
implemented using one or more computers and processesors, being
stand alone or connected or in a cloud system, and by software to
execute the processes.
[0071] The embodiments described in this application represent
examples of the inventive ion traps and inventive methods.
Accordingly, the invention can be realised by each embodiment alone
or by a combination of several or all features of the described
embodiments without any limitations.
* * * * *