[0001] The present invention relates to mass spectrometers.
[0002] Time of flight mass analysers are discontinuous devices in that they receive a packet
of ions which is then injected into the drift region of the time of flight mass analyser
by energising a pusher/puller electrode. Once injected into the drift regions, the
ions become temporally separated according to their mass to charge ratio and the time
taken for an ion to reach a detector can be used to give an accurate determination
of the mass to charge ratio of the ion in question.
[0003] Many commonly used ion sources are continuous ion sources such as Electrospray or
Atmospheric Pressure Chemical Ionisation ("APCI"). In order to couple a continuous
ion source to a discontinuous time of flight mass analyser an ion trap may be used.
The ion trap may continuously accumulate ions from the ion source and periodically
release ions in a pulsed manner so as to ensure a high duty cycle when coupled to
a time of flight mass analyser.
[0004] A commonly used ion trap is a 3D quadrupole ion trap. 3D quadrupole ion traps comprise
a central doughnut shaped electrode together with two generally concave endcap electrodes
with hyperbolic surfaces. 3D quadrupole ion traps are relatively small devices and
the internal diameter of the central doughnut shaped electrode may be less than 1
cm with the two generally concave endcap electrodes being spaced by a similar amount.
Once appropriate confining electric fields have been applied to the ion trap, then
the ion containment volume (and hence the number of ions which may be trapped) is
relatively small. The maximum density of ions which can be confined in a particular
volume is limited by space charge effects since at high densities ions begin to electrostatically
repel one another.
[0005] It is desired to provide an improved ion trap, particularly one which is suitable
for use with a time of flight mass analyser.
[0006] According to a first aspect of the present invention, there is provided a mass spectrometer
comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use; and
a time of flight mass analyser.
[0007] In all embodiments of the present invention ions are not substantially fragmented
within the ion tunnel ion trap i.e. the ion tunnel ion trap is not used as a fragmentation
cell. Furthermore, an ion tunnel ion trap should not be construed as covering either
a linear 2D rod set ion trap or a 3D quadrupole ion trap. An ion tunnel ion trap is
different from other forms of ion optical devices such as multipole rod set ion guides
because the electrodes forming the main body of the ion trap comprise ring, annular,
plate or substantially closed loop electrodes. Ions therefore travel within an aperture
within the electrode which is not the case with multipole rod set ion guides.
[0008] The ion tunnel ion trap is advantageous compared with a 3D quadrupole ion trap since
it may have a much larger ion confinement volume. For example, the ion confinement
volume of the ion tunnel ion trap may be selected from the group consisting: (i) ≥
20 mm
3; (ii) ≥ 50 mm
3; (iii) ≥ 100 mm
3; (iv) ≥ 200 mm
3; (v) ≥ 500 mm
3; (vi) ≥ 1000 mm
3; (vii) ≥ 1500 mm
3; (viii) ≥ 2000 mm
3; (ix) ≥ 2500 mm
3; (x) ≥ 3000 mm
3; and (xi) ≥ 3500 mm
3. The increase in the volume available for ion storage may be at least a factor x2,
x3, x4, x5, x6, x7, x8, x9, x10, or more than x10 compared with a conventional 3D
quadrupole ion trap.
[0009] The time of flight analyser comprises a pusher and/or puller electrode for ejecting
packets of ions into a substantially field free or drift region wherein ions contained
in a packet of ions are temporally separated according to their mass to charge ratio.
Ions are preferably arranged to be released from the ion tunnel ion trap at a predetermined
time before or at substantially the same time that the pusher and/or puller electrode
ejects a packet of ions into the field free or drift region.
[0010] Most if not all of the electrodes forming the ion tunnel ion trap are connected to
an AC or RF voltage supply which acts to confine ions with the ion tunnel ion trap.
According to less preferred embodiments, the voltage supply may not necessarily output
a sinusoidal waveform, and according to some embodiments a non-sinusoidal waveform
such as a square wave may be provided.
[0011] The ion tunnel ion trap is arranged to accumulate and periodically release ions without
substantially fragmenting ions. According to a particularly preferred embodiment,
an axial DC voltage gradient may be maintained in use along at least a portion of
the length of the ion tunnel ion trap. An axial DC voltage gradient may be particularly
beneficial in that it can be arranged so as to urge ions within the ion trap towards
the downstream exit region of the ion trap. When the trapping potential at the exit
of the ion trap is then removed, ions are urged out of the ion tunnel ion trap by
the axial DC voltage gradient. This represents a significant improvement over other
forms of ion traps which do not have axial DC voltage gradients.
[0012] Preferably, the axial DC voltage difference maintained along a portion of the ion
tunnel ion trap is selected from the group consisting of: (i) 0.1-0.5 V; (ii) 0.5-1.0
V; (iii) 1.0-1.5 V; (iv) 1.5-2.0 V; (v) 2.0-2.5 V; (vi) 2.5-3.0 V; (vii) 3.0-3.5 V;
(viii) 3.5-4.0 V; (ix) 4.0-4.5 V; (x) 4.5-5.0 V; (xi) 5.0-5.5 V; (xii) 5.5-6.0 V;
(xiii) 6.0-6.5 V; (xiv) 6.5-7.0 V; (xv) 7.0-7.5 V; (xvi) 7.5-8.0 V; (xvii) 8.0-8.5
V; (xviii) 8.5-9.0 V; (xix) 9.0-9.5 V; (xx) 9.5-10.0 V; and (xxi) > 10V. Preferably,
an axial DC voltage gradient is maintained along at least a portion of ion tunnel
ion trap selected from the group consisting of: (i) 0.01-0.05 V/cm; (ii) 0.05-0.10
V/cm; (iii) 0.10-0.15 V/cm; (iv) 0.15-0.20 V/cm; (v) 0.20-0.25 V/cm; (vi) 0.25-0.30
V/cm; (vii) 0.30-0.35 V/cm; (viii) 0.35-0.40 V/cm; (ix) 0.40-0.45 V/cm; (x) 0.45-0.50
V/cm; (xi) 0.50-0.60 V/cm; (xii) 0.60-0.70 V/cm; (xiii) 0.70-0.80 V/cm; (xiv) 0.80-0.90
V/cm; (xv) 0.90-1.0 V/cm; (xvi) 1.0-1.5 V/cm; (xvii) 1.5-2.0 V/cm; (xviii) 2.0-2.5
V/cm; (xix) 2.5-3.0 V/cm; and (xx) > 3.0 V/cm.
[0013] In a preferred form, the ion tunnel ion trap comprises a plurality of segments, each
segment comprising a plurality of electrodes having apertures through which ions are
transmitted and wherein all the electrodes in a segment are maintained at substantially
the same DC potential and wherein adjacent electrodes in a segment are supplied with
different phases of an AC or RF voltage. A segmented design simplifies the electronics
associated with the ion tunnel ion trap.
[0014] The ion tunnel ion trap preferably consists of: (i) 10-20 electrodes; (ii) 20-30
electrodes; (iii) 30-40 electrodes; (iv) 40-50 electrodes; (v) 50-60 electrodes; (vi)
60-70 electrodes; (vii) 70-80 electrodes; (viii) 80-90 electrodes; (ix) 90-100 electrodes;
(x) 100-110 electrodes; (xi) 110-120 electrodes; (xii) 120-130 electrodes; (xiii)
130-140 electrodes; (xiv) 140-150 electrodes; (xv) > 150 electrodes; (xvi) ≥ 5 electrodes;
and (xvii) ≥ 10 electrodes.
[0015] The diameter of the apertures of at least 50% of the electrodes forming the ion tunnel
ion trap is preferably selected from the group consisting of: (i) ≤ 10 mm; (ii) ≤
9 mm; (iii) ≤ 8 mm; (iv) ≤ 7 mm; (v) ≤ 6 mm; (vi) ≤ 5 mm; (vii) ≤ 4 mm; (viii) ≤ 3
mm; (ix) ≤ 2 mm; and (x) ≤ 1 mm. At least 50%, 60%, 70%, 80%, 90% or 95% of the electrodes
forming the ion tunnel ion trap may have apertures which are substantially the same
size or area in contrast to an ion funnel arrangement. The thickness of at least 50%
of the electrodes farming the ion tunnel ion trap may be selected from the group consisting
of: (i) ≤ 3 mm; (ii) ≤ 2.5 mm; (iii) ≤ 2.0 mm; (iv) ≤ 1.5 mm; (v) ≤ 1.0 mm; and (vi)
≤ 0.5 mm. Preferably, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%
of the electrodes are connected to both a DC and an AC or RF voltage supply. Preferably,
the ion tunnel ion trap has a length selected from the group consisting of: (i) <
5 cm; (ii) 5-10 cm; (iii) 10-15 cm; (iv) 15-20 cm; (v) 20-25 cm; (vi) 25-30 cm; and
(vii) > 30 cm.
[0016] Preferably, means is provided for introducing a gas into the ion tunnel ion trap
for collisional cooling without fragmentation of ions. Ions emerging from the ion
tunnel ion trap will therefore have a narrower spread of energies which is beneficial
when coupling the ion trap to a time of flight mass analyser. The ions may be arranged
to enter the ion tunnel ion trap with a majority of the ions having an energy ≤ 5
eV for a singly charged ion so as to cause collisional cooling of the ions. The ion
tunnel ion trap may be maintained, in use, at a pressure selected from the group consisting
of: (i) > 1.0 x 10
-3 mbar; (ii) > 5.0 x 10
-3 mbar; (iii) > 1.0 x 10
-2 mbar; (iv) 10
-3-10
-2 mbar; and (v) 10
-4-10
-1 mbar.
[0017] Although the ion tunnel ion trap is envisaged to be used primarily with a continuous
ion source other embodiments of the present invention are contemplated wherein a pulsed
ion source may nonetheless be used. The ion source may comprise an Electrospray ("ESI"),
Atmospheric Pressure Chemical Ionisation ("APCI"), Atmospheric Pressure Photo Ionisation
("APPI"), Matrix Assisted Laser Desorption Ionisation ("MALDI"), Laser Desorption
Ionisation ion source, Inductively Coupled Plasma ("ICP"), Electron Impact ("EI")
or Chemical Ionisation ("CI") ion source.
[0018] Preferred ion sources such as Electrospray or APCI ion sources are continuous ion
sources whereas a time of flight analyser is a discontinuous device in that it requires
a packet of ions. The ions are then injected with substantially the same energy into
a drift region. Ions become temporally separated in the drift region accordingly to
their differing masses, and the transit time of the ion through the drift region is
measured giving an indication of the mass of the ion. The ion tunnel ion trap according
to the preferred embodiment is effective in essentially coupling a continuous ion
source with a discontinuous mass analyser such as a time of flight mass analyser.
[0019] Preferably, the ion tunnel ion trap comprises an entrance and/or exit electrode for
trapping ions within the ion tunnel ion trap.
[0020] According to a second aspect of the present invention, there is provided a mass spectrometer
comprising:
an ion tunnel ion trap comprising ≥ 10 ring or plate electrodes having substantially
similar internal apertures between 2-10 mm in diameter and wherein a DC potential
gradient is maintained, in use, along a portion of the ion tunnel ion trap and two
or more axial potential wells are formed along the length of the ion trap
[0021] The DC potential gradient can urge ions out of the ion trap once a trapping potential
has been removed.
[0022] According to a third aspect of the present invention, there is provided:
an ion tunnel ion trap comprising at least three segments, each segment comprising
at least four electrodes having substantially similar sized apertures through which
ions are transmitted in use;
wherein in a mode of operation:
electrodes in a first segment are maintained at substantially the same first DC potential
but adjacent electrodes are supplied with different phases of an AC or RF voltage
supply;
electrodes in a second segment are maintained at substantially the same second DC
potential but adjacent electrodes are supplied with different phases of an AC or RF
voltage supply;
electrodes in a third segment are maintained at substantially the same third DC potential
but adjacent electrodes are supplied with different phases of an AC or RF voltage
supply;
wherein the first, second and third DC potentials are all different.
[0023] The ability to be able to individually control multiple segments of an ion trap affords
significant versatility which is not an option with conventional ion traps. For example,
multiple discrete trapping regions can be provided.
[0024] According to a fourth aspect of the present invention, there is provided a mass spectrometer
comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, wherein the transit time of ions through the ion
tunnel ion trap is selected from the group comprising: (i) ≤ 0.5 ms; (ii) ≤ 1.0 ms;
(iii) ≤ 5 ms; (iv) ≤ 10 ms; (v) ≤ 20 ms; (vi) 0.01-0.5 ms; (vii) 0.5-1 ms; (viii)
1-5 ms; (ix) 5-10 ms; and (x) 10-20 ms.
[0025] By providing an axial DC potential ions can be urged through the ion trap much faster
than conventional ion traps.
[0026] According to a fifth aspect of the present invention, there is provided a mass spectrometer
comprising:
an ion tunnel ion trap, the ion tunnel ion trap comprising a plurality of electrodes
having apertures through which ions are transmitted in use, and wherein in a mode
of operation trapping DC voltages are supplied to some of the electrodes so that ions
are confined in two or more axial DC potential wells.
[0027] The ability to provide two or more trapping regions in a single ion trap is particularly
advantageous.
[0028] According to a sixth aspect of the present invention, there is provided a mass spectrometer
comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, and wherein in a mode of operation a V-shaped,
W-shaped, U-shaped, sinusoidal, curved, stepped or linear axial DC potential profile
is maintained along at least a portion of the ion tunnel ion trap.
[0029] Since preferably the DC potential applied to individual electrodes or groups of electrodes
can be individually controlled, numerous different desired axial DC potential profiles
can be generated.
[0030] According to a seventh aspect of the present invention, there is provided a mass
spectrometer comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, and wherein in a mode of operation an upstream
portion of the ion tunnel ion trap continues to receive ions into the ion tunnel ion
trap whilst a downstream portion of the ion tunnel ion trap separated from the upstream
portion by a potential barrier stores and periodically releases ions. According to
this arrangement, no ions are lost as the ion trap substantially stores all the ions
it receives.
[0031] Preferably, the upstream portion of the ion tunnel ion trap has a length which is
at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the total length of the
ion tunnel ion trap. Preferably, the downstream portion of the ion tunnel ion trap
has a length which is less than or equal to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,
or 90% of the total length of the ion tunnel ion trap. Preferably, the downstream
portion of the ion tunnel ion trap is shorter than the upstream portion of the ion
tunnel ion trap.
[0032] According to an eighth aspect of the present invention, there is provided a mass
spectrometer comprising:
a continuous ion source for emitting a beam of ions;
an ion trap arranged downstream of the ion source, the ion trap comprising ≥ 5 electrodes
having apertures through which ions are transmitted in use, wherein the electrodes
are arranged to radially confine ions within the apertures, and wherein ions are accumulated
and periodically released from the ion trap without substantial fragmentation of the
ions; and
a discontinuous mass analyser arranged to receive ions released from the ion trap.
[0033] Preferably, an axial DC voltage gradient is maintained along at least 5%, 10%, 15%,
20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% of
the length of the ion trap.
[0034] Preferably, the continuous ion source comprises an Electrospray or Atmospheric Pressure
Chemical Ionisation ion source.
[0035] Preferably, the discontinuous mass analyser comprises a time of flight mass analyser.
[0036] According to a ninth aspect of the present invention, there is provided a method
of mass spectrometry, comprising:
trapping ions in an ion tunnel ion trap comprising a plurality of electrodes having
apertures through which ions are transmitted in use; and
releasing ions from the ion tunnel ion trap to a time of flight mass analyser.
[0037] Preferably, an axial DC voltage gradient is maintained along at least a portion of
the length of the ion trap.
[0038] Various embodiments of the present invention will now be described, by way of example
only, and with reference to the accompanying drawings in which:
Fig. 1 shows a preferred ion tunnel ion trap;
Fig. 2 shows another ion tunnel ion trap wherein the DC voltage supply to each ion
tunnel segment is individually controllable;
Fig. 3(a) shows a front view of an ion tunnel segment, Fig. 3(b) shows a side view
of an upper ion tunnel section, and Fig. 3(c) shows a plan view of an ion tunnel segment;
Fig. 4 shows an axial DC potential profile as a function of distance at a central
portion of an ion tunnel ion trap;
Fig. 5 shows a potential energy surface across a number of ion tunnel segments at
a central portion of an ion tunnel ion trap;
Fig. 6 shows a portion of an axial DC potential profile for an ion tunnel ion trap
being operated in an trapping mode without an accelerating axial DC potential gradient
being applied along the length of the ion tunnel ion trap; and
Fig. 7(a) shows an axial DC potential profile for an ion tunnel ion trap operated
in a "fill" mode of operation, Fig. 7(b) shows a corresponding "closed" mode of operation,
and Fig. 7(c) shows a corresponding "empty" mode of operation.
[0039] A preferred ion tunnel ion trap will now be described in relation to Figs. 1 and
2. The ion tunnel ion trap 1 comprises a housing having an entrance aperture 2 and
an exit aperture 3. The entrance and exit apertures 2,3 are preferably substantially
circular apertures. The plates forming the entrance and/or exit apertures 2,3 may
be connected to independent programmable DC voltage supplies (not shown).
[0040] Between the plate forming the entrance aperture 2 and the plate forming the exit
aperture 3 are arranged a number of electrically isolated ion tunnel segments 4a,4b,4c.
In one embodiment fifteen segments 4a,4b,4c are provided. Each ion tunnel segment
4a;4b;4c comprises two interleaved and electrically isolated sections i.e. an upper
and lower section. The ion tunnel segment 4a closest to the entrance aperture 2 preferably
comprises ten electrodes (with five electrodes in each section) and the remaining
ion tunnel segments 4b,4c preferably each comprise eight electrodes (with four electrodes
in each section). All the electrodes are preferably substantially similar in that
they have a central substantially circular aperture (preferably 5 mm in diameter)
through which ions are transmitted. The entrance and exit apertures 2,3 may be smaller
e.g. 2.2 mm in diameter than the apertures in the electrodes or the same size.
[0041] All the ion tunnel segments 4a,4b,4c are preferably connected to the same AC or RF
voltage supply, but different segments 4a;4b;4c may be provided with different DC
voltages. The two sections forming an ion tunnel segment 4a;4b;4c are connected to
different, preferably opposite, phases of the AC or RF voltage supply.
[0042] A single ion tunnel section is shown in greater detail in Figs. 3(a)-(c). The ion
tunnel section has four (or five) electrodes 5, each electrode 5 having a 5 mm diameter
central aperture 6. The four (or five) electrodes 5 depend or extend from a common
bar or spine 7 and are preferably truncated at the opposite end to the bar 7 as shown
in Fig. 3(a). Each electrode 5 is typically 0.5 mm thick. Two ion tunnel sections
are interlocked or interleaved to provide a total of eight (or ten) electrodes 5 in
an ion tunnel segment 4a;4b;4c with a 1 mm inter-electrode spacing once the two sections
have been interleaved. All the eight (or ten) electrodes 5 in an ion tunnel segment
4a;4b;4c comprised of two separate sections are preferably maintained at substantially
the same DC voltage. Adjacent electrodes in an ion tunnel segment 4a;4b;4c comprised
of two interleaved sections are connected to different, preferably opposite, phases
of an AC or RF voltage supply i.e. one section of an ion tunnel segment 4a;4b;4c is
connected to one phase (RF+) and the other section of the ion tunnel segment 4a;4b;4c
is connected to another phase (RF-).
[0043] Each ion tunnel segment 4a;4b;4c is mounted on a machined PEEK support that acts
as the support for the entire assembly. Individual ion tunnel sections are located
and fixed to the PEEK support by means of a dowel and a screw. The screw is also used
to provide the electrical connection to the ion tunnel section. The PEEK supports
are held in the correct orientation by two stainless steel plates attached to the
PEEK supports using screws and located correctly using dowels. These plates are electrically
isolated and have a voltage applied to them.
[0044] Gas for collisionally cooling ions without substantially fragmenting ions may be
supplied to the ion tunnel ion trap 1 via a 4.5 mm ID tube.
[0045] The electrical connections shown in Fig. 1 are such that a substantially regular
stepped axial accelerating DC electric field is provided along the length of the ion
tunnel ion trap 1 using two programmable DC power supplies DC1 and DC2 and a resistor
potential divider network of 1 MΩ resistors. An AC or RF voltage supply provides phase
(RF+) and anti-phase (RF-) voltages at a frequency of preferably 1.75 MHz and is coupled
to the ion tunnel sections 4a,4b,4c via capacitors which are preferably identical
in value (100pF). According to other embodiments the frequency may be in the range
of 0.1-3.0 MHz. Four 10 µH inductors are provided in the DC supply rails to reduce
any RF feedback onto the DC supplies. A regular stepped axial DC voltage gradient
is provided if all the resistors are of the same value. Similarly, the same AC or
RF voltage is supplied to all the electrodes if all the capacitors are the same value.
Fig. 4 shows how, in one embodiment, the axial DC potential varies across a 10 cm
central portion of the ion tunnel ion trap 1. The inter-segment voltage step in this
particular embodiment is -1V. However, according to more preferred embodiments lower
voltage steps of e.g. approximately -0.2V may be used. Fig. 5 shows a potential energy
surface across several ion tunnel segments 4b at a central portion of the ion tunnel
ion trap 1. As can be seen, the potential energy profile is such that ions will cascade
from one ion tunnel segment to the next.
[0046] As will now be described in relation to Fig. 1, the ion tunnel ion trap 1 traps,
accumulates or otherwise confines ions within the ion tunnel ion trap 1. In the embodiment
shown in Fig. 1, the DC voltage applied to the final ion tunnel segment 4c (i.e. that
closest and adjacent to the exit aperture 3) is independently controllable and can
in one mode of operation be maintained at a relatively high DC blocking or trapping
potential (DC3) which is more positive for positively charged ions (and vice versa
for negatively charged ions) than the preceding ion tunnel segment(s) 4b. Other embodiments
are also contemplated wherein other ion tunnel segments 4a,4b may alternatively and/or
additionally be maintained at a relatively high trapping potential. When the final
ion tunnel segment 4c is being used to trap ions within the ion tunnel ion trap 1,
an AC or RF voltage may or may not be applied to the final ion tunnel segment 4c.
[0047] The DC voltage supplied to the plates forming the entrance and exit apertures 2,3
is also preferably independently controllable and preferably no AC or RF voltage is
supplied to these plates. Embodiments are also contemplated wherein a relatively high
DC trapping potential may be applied to the plates forming entrance and/or exit aperture
2,3 in addition to or instead of a trapping potential being supplied to one or more
ion tunnel segments such as at least the final ion tunnel segment 4c.
[0048] In order to release ions from confinement within the ion tunnel ion trap 1, the DC
trapping potential applied to e.g. the final ion tunnel segment 4c or to the plate
forming the exit aperture 3 is preferably momentarily dropped or varied, preferably
in a pulsed manner. In one embodiment the DC voltage may be dropped to approximately
the same DC voltage as is being applied to neighbouring ion tunnel segment(s) 4b.
Embodiments are also contemplated wherein the voltage may be dropped below that of
neighbouring ion tunnel segment(s) so as to help accelerate ions out of the ion tunnel
ion trap 1. In another embodiment a V-shaped trapping potential may be applied which
is then changed to a linear profile having a negative gradient in order to cause ions
to be accelerated out of the ion tunnel ion trap 1. The voltage on the plate forming
the exit aperture 3 can also be set to a DC potential such as to cause ions to be
accelerated out of the ion tunnel ion trap 1.
[0049] Other less preferred embodiments are contemplated wherein no axial DC voltage difference
or gradient is applied or maintained along the length of the ion tunnel ion trap 1.
Fig. 6, for example, shows how the DC potential may vary along a portion of the length
of the ion tunnel ion trap 1 when no axial DC field is applied and the ion tunnel
ion trap 1 is acting in a trapping or accumulation mode. In this figure, 0 mm corresponds
to the midpoint of the gap between the fourteenth 4b and fifteenth (and final) 4c
ion tunnel segments. In this particular example, the blocking potential was set to
+5V (for positive ions) and was applied to the last (fifteenth) ion tunnel segment
4c only. The preceding fourteen ion tunnel segments 4a,4b had a potential of - 1V
applied thereto. The plate forming the entrance aperture 2 was maintained at 0V DC
and the plate forming the exit aperture 3 was maintained at -1V.
[0050] More complex modes of operation are contemplated wherein two or more trapping potentials
may be used to isolate one or more section(s) of the ion tunnel ion trap 1. For example,
Fig. 7(a) shows a portion of the axial DC potential profile for an ion tunnel ion
trap 1 according to one embodiment operated in a "fill" mode of operation, Fig. 7(b)
shows a corresponding "closed" mode of operation, and Fig. 7(c) shows a corresponding
"empty" mode of operation. By sequencing the potentials, the ion tunnel ion trap 1
may be opened, closed and then emptied in a short defined pulse. In the example shown
in the figures, 0 mm corresponds to the midpoint of the gap between the tenth and
eleventh ion tunnel segments 4b. The first nine segments 4a,4b are held at -1V, the
tenth and fifteenth segments 4b act as potential barriers and ions are trapped within
the eleventh, twelfth, thirteenth and fourteenth segments 4b. The trap segments are
held at a higher DC potential (+5V) than the other segments 4b. When closed the potential
barriers are held at +5V and when open they are held at -1V or -5V. This arrangement
allows ions to be continuously accumulated and stored, even during the period when
some ions are being released for subsequent mass analysis, since ions are free to
continually enter the first nine segments 4a,4b. A relatively long upstream length
of the ion tunnel ion trap 1 may be used for trapping and storing ions and a relatively
short downstream length may be used to hold and then release ions. By using a relatively
short downstream length, the pulse width of the packet of ions released from the ion
tunnel ion trap 1 may be constrained. In other embodiments multiple isolated storage
regions may be provided.
[0051] Although the present invention has been described with reference to preferred embodiments,
it will be understood by those skilled in the art that various changes in form and
detail may be made without departing from the scope of the invention as set forth
in the accompanying claims.
1. A mass spectrometer comprising:
an ion tunnel ion trap comprising ≥ 10 ring or plate electrodes having substantially
similar internal apertures between 2-10 mm in diameter and wherein a DC potential
gradient is maintained, in use, along a portion of the ion tunnel ion trap and two
or more axial potential wells are formed along the length of the ion trap.
2. A mass spectrometer comprising:
an ion tunnel ion trap comprising at least three segments, each segment comprising
at least four electrodes having substantially similar sized apertures through which
ions are transmitted in use;
wherein in a mode of operation:
electrodes in a first segment are maintained at substantially the same first DC potential
but adjacent electrodes are supplied with different phases of an AC or RF voltage
supply;
electrodes in a second segment are maintained at substantially the same second DC
potential but adjacent electrodes are supplied with different phases of an AC or RF
voltage supply;
electrodes in a third segment are maintained at substantially the same third DC potential
but adjacent electrodes are supplied with different phases of an AC or RF voltage
supply;
wherein said first, second and third DC potentials are all different.
3. A mass spectrometer comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, wherein the transit time of ions through the ion
tunnel ion trap is selected from the group comprising: (i) ≤ 0.5 ms; (ii) ≤ 1.0 ms;
(iii) ≤ 5 ms; (iv) ≤ 10 ms; (v) ≤ 20 ms; (vi) 0.01-0.5 ms; (vii) 0.5-1 ms; (viii)
1-5 ms; (ix) 5-10 ms; and (x) 10-20 ms.
4. A mass spectrometer comprising:
an ion tunnel ion trap, said ion tunnel ion trap comprising a plurality of electrodes
having apertures through which ions are transmitted in use, and wherein in a mode
of operation trapping DC voltages are supplied to some of said electrodes so that
ions are confined in two or more axial DC potential wells.
5. A mass spectrometer comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, and wherein in a mode of operation a V-shaped,
W-shaped, U-shaped, sinusoidal, curved, stepped or linear axial DC potential profile
is maintained along at least a portion of said ion tunnel ion trap.
6. A mass spectrometer comprising:
an ion tunnel ion trap comprising a plurality of electrodes having apertures through
which ions are transmitted in use, and wherein in a mode of operation an upstream
portion of the ion tunnel ion trap continues to receive ions into the ion tunnel ion
trap whilst a downstream portion of the ion tunnel ion trap separated from the upstream
portion by a potential barrier stores and periodically releases ions.
7. A mass spectrometer as claimed in claim 6, wherein said upstream portion of the ion
tunnel ion trap has a length which is at least 10%, 20%, 30%, 40%, 50%, 60%, 70%,
80%, or 90% of the total length of the ion tunnel ion trap.
8. A mass spectrometer as claimed in claim 6, wherein said downstream portion of the
ion tunnel ion trap has a length which is less than or equal to 10%, 20%, 30%, 40%,
50%, 60%, 70%, 80%, or 90% of the total length of the ion tunnel ion trap.
9. A mass spectrometer as claimed in claim 6, wherein the downstream portion of the ion
tunnel ion trap is shorter than the upstream portion of the ion tunnel ion trap.
10. A mass spectrometer as claimed in any preceding, wherein ions are substantially not
fragmented within said ion tunnel ion trap.