DE20308577U1 - mass spectrometry - Google Patents

Description

Micromass Limited F173 007 U-DE

GB-Manchester M22 5PP 08/25/2003/sc/tk

mass spectrometry

The present invention relates to a mass spectrometer.

Multipole rod set RF ion guides are known and used for transporting ions at relatively low pressures (e.g. < 10" mbar) where ion collisions with background gas molecules are unlikely, and also for transporting ions at intermediate pressures (e.g. 10" - 10 mbar) where ion-molecule collisions can be expected. Multipole rod set RF ion guides are used at intermediate pressures for a wide range of applications. For example, multipole rod set RF ion guides are used as collision cells where ion-molecule collisions are intended to induce ion fragmentation, and as reaction cells where ion-molecule collisions are intended to produce ion-molecule reactions. Multipole rod set RF ion guides are also used as cooling devices where ion-molecule collisions lead to an equalization of the ion and gas molecule temperatures or their kinetic energies. Known multipole rod set RF ion guides have a straight central axis with a single ion entrance and a single ion exit.

It is desirable to provide a mass spectrometer with improved RF ion guidance.

According to one aspect of the present invention, a mass spectrometer is provided with an ion guide. The ion guide has a plurality of plate electrodes and an entrance for receiving ions along a first axis and an exit from which ions exit the ion guide along a second axis. The second axis is at an angle θ to the first axis, where θ > 0°. An ion guide region is provided between the entrance opening and the exit opening of the ion guide. According to the preferred embodiment, the angle θ is preferably < 10°, 10 - 20°, 20 30°, 30 - 40°, 40 - 50°, 50 - 60°, 60 - 70°, 70 - 80°, 80 90°, 90 - 100°, 100 - 110°, 110 - 120°, 120 - 130°, 130 140°, 140 - 150°, 150 - 160°, 160 - 170° or 170 - 180°. Angles > 180° are also considered, where the ion guide has a spiral ion guide region. An angle of 0° corresponds to a state in which the second axis is parallel to the first axis. An angle of 180° corresponds to an embodiment in which a U-shaped ion guide region has been provided within the ion guide so that ions entering the ion guide are deflected by 180° before exiting the ion guide in the opposite direction to that in which the ions entered the ion guide.

In another aspect, the present invention provides a mass spectrometer comprising an ion guide having a plurality of plate electrodes, an entrance for receiving ions along a first axis, and an exit from which ions exit along a second axis. The ion guide further comprises a curved ion guide region between the entrance and the exit. The

The curved ion guide region preferably comprises a single continuous, preferably smoothly continuous, ion guide region through which ions are guided from the entrance to the exit. According to the preferred embodiment, the ion guide region is substantially "S"-shaped and/or has a single diffraction point. According to this particular embodiment, the term "curved ion guide region" should not be construed as a labyrinthine ion guide region or a labyrinthine ion guide region with one or more dead ends. The first axis may be substantially parallel to the second axis and preferably laterally offset from it.

In another aspect, the present invention provides a mass spectrometer having an ion guide with a plurality of plate electrodes, an entrance for receiving ions along a first axis, a curved ion guide region, and an exit from which ions exit. In this ion guide, the second axis is coaxial with the first axis.

An ion guide having a curved ion guide region and a coaxial first and second axis provides a longer ion guide region without requiring the distance between the ion guide entrance and the ion guide exit to be increased. This is particularly advantageous when the ion guide is used as a collision, fragmentation or reaction cell because the increased path length through the gas increases the likelihood that collisions, fragmentations or reactions will occur. According to the preferred embodiment, the ion guide further comprises a

device in the form of a baffle, a plate or an electrode, which is arranged at least partially outside the ion guide region, to block neutral particles or photons that pass directly from the entrance of the ion guide to its exit.

In another aspect, the present invention provides a mass spectrometer comprising a first ion guide having a plurality of plate electrodes, an inlet for receiving ions, and an outlet from which ions exit. The mass spectrometer further comprises a second ion guide having a plurality of plate electrodes, an inlet for receiving ions, and an outlet from which ions exit.

According to the preferred embodiment, the mass spectrometer further comprises a third ion guide having a plurality of plate electrodes, an inlet for receiving ions and an outlet from which ions exit. The mass spectrometer may also comprise a fourth ion guide having a plurality of plate electrodes, an inlet for receiving ions and an outlet from which ions exit. According to other embodiments, five, six, seven, eight, nine, ten or more than ten ion guides may be provided.

In one mode of operation, the first ion guide and the second ion guide can be maintained at different DC potentials during use, so that ions exiting the first ion guide are forced into the second ion guide. The second and third ion guides can be maintained at different DC potentials during use, so that

I ₁₁₁ H ·· t · &diams;· **

that ions emerging from the second ion guide are forced into the third ion guide. The third and fourth ion guides can also be maintained at different DC potentials during use so that ions emerging from the third ion guide are forced into the fourth ion guide. Embodiments are also contemplated in which ions are forced from the first into the second ion guide and/or from the second into the third ion guide and/or from the third into the fourth ion guide and/or from the fourth ion guide.

In another or further mode of operation, the second ion guide may be maintained at a different DC potential than the first ion guide so that ions are trapped in the first ion guide. The third ion guide may be maintained at a different DC potential than the second ion guide so that ions are trapped in the second ion guide. The fourth ion guide may be maintained at a different DC potential than the third ion guide so that ions are trapped in the third ion guide. Embodiments are also contemplated in which, for example, ions are trapped in the first, second and third ion guides or in the second and third ion guides.

It is also to be understood that the embodiments discussed above relating to forcing ions from an ion guide may be combined with embodiments discussed above relating to trapping ions within an ion guide.

According to a preferred embodiment, either the first and/or the second and/or the third and/or the fourth ion guide may comprise ion storage regions. In a first mode of operation, these ion storage regions may receive ions through a single opening, and in a second mode of operation, ions are allowed to exit the ion storage region through the same opening.

In another aspect, the present invention provides a mass spectrometer having an ion guide with a plurality of plate electrodes, two or more inlets for receiving ions, and one or more outlets from which ions exit.

According to a preferred embodiment, the ion guide preferably has two entrances for receiving ions and one exit from which ions exit. According to another embodiment, the ion guide has three entrances for receiving ions and one exit from which ions exit. The plate electrodes can have any shape so that ion beams can be received by the ion guide at any angle or from any direction or can exit the ion guide at any angle or in any direction.

Further embodiments are contemplated in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more than 10 ion inputs are provided and in which 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more than 10 ion outputs are provided. For example, the ion guide may have three inputs and three

&bull; : : ·: &idigr; J- &idigr;7* '

have outputs.

Preferably, the mass spectrometer further comprises at least two identical or different ion sources. The ion sources are preferably at least one of an electrospray ion source ("ESI ion source"), an atmospheric pressure chemical ionization ion source ("APCI ion source"), an atmospheric pressure photoionization ion source ("APPI ion source"), a matrix assisted laser desorption ionization ion source ("MALDI ion source"), a laser desorption ionization ion source ("LDI ion source"), an inductively coupled plasma ion source ("ICP ion source"), an electron impact ion source ("EI ion source"), a chemical ionization ion source ("CI ion source"), a fast atom bombardment ion source ("FAB ion source"), and a liquid secondary ion mass spectrometry ion source ( ^" LSIMS ion source").

Embodiments are contemplated in which, for example, two ion sources are provided. One ion source may be a continuous ion source such as an APCI or electrospray ion source, and the other ion source may be a pulsed ion source such as a MALDI ion source.

Embodiments are also contemplated in which more than two ion sources are provided. For example, according to one embodiment, at least 3, 4, 5, 6, ₁ 8, 9 or 10 APCI ion sources, electrospray ion sources or any of the other ion sources mentioned above may be provided. The preferred ion guide may allow ions from one or

sampled from several selected ion sources and then mass analyzed.

In another aspect, the present invention provides a mass spectrometer having an ion guide with a plurality of plate electrodes, one or more inputs for receiving ions, and two or more outputs from which ions exit.

According to the preferred embodiment, the ion guide has an entrance for receiving ions and two exits from which ions exit. According to another embodiment, the ion beam entering an entrance of the ion guide is split into three or more beams, the third beam exiting the ion guide via a third exit. According to a further preferred embodiment, the ion guide has two entrances for receiving ions and two exits from which ions exit. The mass spectrometer can further comprise at least two ion sources. An ion beam entering an entrance of the ion guide can be split into two or more beams, a first beam exiting the ion guide via a first exit and a second beam exiting via a second exit. Preferably, the ions entering an entrance of the ion guide are split into two or more beams by one or more electrodes arranged adjacent to the entrance, one or more electrodes arranged within the ion guide, or one or more electrodes arranged adjacent to an exit of the ion guide.

An ion beam entering the ion guide can be

ti·· ··· , I I

a desired ratio into two or more beams. Preferably, at least one beam has a percentage of ions entering the ion guide that is 0-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90% or greater than 90%.

According to the preferred embodiment, at least a portion of an ion beam entering the ion guide is switchable to or between one of a plurality of exits. At least one electrode may be disposed adjacent to one or more of the exits to either cause ions to exit the ion guide via that exit or to substantially prevent ions from exiting the ion guide via that exit. One or more electrodes may be provided adjacent to the entrance or within the ion guide. According to one embodiment, an ion beam may be switched between exits by applying and then removing a blocking DC potential to an electrode disposed adjacent to an exit of the ion guide.

The mass spectrometer may further comprise a first ion detector arranged to receive ions exiting a first output and a second ion detector arranged to receive ions exiting a second ion output. The mass spectrometer may further comprise a first mass analyzer arranged to receive ions exiting the first output and a second mass analyzer arranged to receive ions exiting the second ion output.

&Ggr;&Ugr;"·

The mass spectrometer may comprise one or more mass analyzers arranged to receive ions exiting the ion guide via at least a first outlet and one or more ion detectors arranged to receive ions exiting the ion guide via at least a second ion outlet.

According to another embodiment, the mass spectrometer comprises a first and/or a second ion storage device, each comprising a plurality of plate electrodes. In a first mode of operation, an ion beam enters an ion storage device via an opening, and in a second mode of operation, an ion beam exits the ion storage device via the same opening.

An embodiment is also contemplated wherein the ion guide has two exits, with an ion storage device disposed downstream of one exit and a mass analyzer disposed downstream of the other exit.

In another aspect, the present invention provides a mass spectrometer having an ion guide having a plurality of plate electrodes, one or more inputs for receiving ions, and one or more outputs from which ions exit. In a first mode of operation, an ion beam enters the ion guide through a first opening and exits the ion guide through a second opening, and in a second mode of operation, an ion beam enters the ion guide through the second opening

According to the preferred embodiment, an ion beam exits the ion guide via the first opening in the second operating mode. Alternatively, the ion beam can exit the ion guide via a third opening different from the first and second openings in a second operating mode.

In another aspect, the present invention provides a mass spectrometer having an ion storage device having a plurality of plate electrodes, wherein in a first mode of operation an ion beam enters the ion storage device via an opening and in a second mode of operation an ion beam exits the ion storage device via the same opening.

Other embodiments are contemplated in which the ion storage device has two openings, namely a first opening for receiving ions and a second opening from which ions exit the ion storage device.

In another aspect, the present invention provides a mass spectrometer having an ion guide having a plurality of plate electrodes, an entrance for receiving ions, and an exit from which ions exit. The entrance has a first cross-sectional profile and a first cross-sectional area, and the exit has a second cross-sectional profile and a second cross-sectional area. The first cross-sectional profile is different from the second cross-sectional profile, and/or the first cross-sectional area is different from the second cross-sectional area.

ji . ..

The first and/or second cross-sectional profiles may be substantially circular, oval, rectangular or square. An ion beam received by the ion guide has a third cross-sectional profile and a third cross-sectional area. Preferably, the first cross-sectional profile and/or the first cross-sectional area are substantially equal to the third cross-sectional profile and/or the third cross-sectional area. The mass spectrometer may comprise an ion optical device having a fourth cross-sectional profile and a fourth cross-sectional area further downstream of the ion guide. The second cross-sectional profile and/or the second cross-sectional area may be substantially equal to the fourth cross-sectional profile and/or the fourth cross-sectional area. The ion optical device may comprise an ion guide or a quadrupole mass filter/analyzer having substantially circular cross-sectional profiles. The ion guide may comprise a quadrupole, hexapole, octopole or higher order rod set, an ion tunnel with multiple electrodes having apertures of substantially the same size, or an ion funnel with multiple electrodes having progressively smaller apertures. The ion optical device may comprise a transverse acceleration time-of-flight mass analyzer or a magnetic sector analyzer having substantially square or rectangular cross-sectional profiles.

According to other embodiments, the ion optical device may comprise a Fourier transform ion cyclotron resonance mass analyzer ("FTICR mass analyzer") having a substantially circular cross-sectional profile, a two-dimensional (linear) quadrupole ion trap having

« · ·
9 · · · ·· 9 &bull; &bull; &bull; · &bull; t · ·· ···· ···· ···· &bull; · ·
· ·
I · 4 &bull; &bull;
> · · · · · &bull;
&bull;
&bull; ·
· · · · · ··· · &bull;

a substantially circular cross-sectional profile or

a three-dimensional (Paul) quadrupole ion trap with

have a substantially circular cross-sectional profile.

Mention has been made above of "cross-sectional area" and "cross-sectional profile". Although these are intended to include the physical cross-sectional area and profile of a device or ion beam, the terms should also be understood to include the practical acceptance range or profile of the device or ion beam analogous to the numerical aperture of an optical device.

According to a preferred embodiment, the ion guide region has a length between at least one of the inlets and the outlets of the ion guide that changes in size and/or shape. The ion guide region can also have a length, a width or a height that progressively decreases in size or whose shape changes continuously.

Preferably, the ion guide further comprises a second inlet for receiving ions and/or a second outlet via which ions exit the ion guide, wherein the second inlet has a fifth cross-sectional profile and a fifth cross-sectional area and the second outlet has a sixth cross-sectional profile and a sixth cross-sectional area, wherein the fifth cross-sectional profile is different from the sixth cross-sectional profile and/or the fifth cross-sectional area is different from the sixth cross-sectional area.

Preferably, the first cross-sectional profile and the first cross-sectional area and/or the second cross-sectional profile and the second cross-sectional area and/or the fifth cross-sectional profile and the fifth cross-sectional area and/or the sixth cross-sectional profile and the sixth cross-sectional area are different.

According to the embodiments described above, at least 50%, 60%, 70%, 80%, 90% or 95% of the plate electrodes may be substantially parallel. According to the preferred embodiment, the plate electrodes are arranged in a first (e.g. horizontal) plane and the ion guide is similarly curved in the first (e.g. horizontal) plane. However, embodiments are also contemplated in which the plate electrodes are not flat but curved. In these embodiments, the plates may initially be arranged in a first (e.g. horizontal) plane, but the plate electrodes are then curved in a second orthogonal (e.g. vertical) plane. According to this embodiment, the plate electrodes may therefore act more like a periscope and transfer ions from one (vertical) plane to another.

The plate electrodes are preferably arranged at substantially equal distances from one another. However, according to less preferred embodiments, the distance between the electrodes can change along the ion guide. For example, the distance between the electrodes can progressively decrease (increase) so that ions are funneled from a relatively large (small) inlet opening to a relatively small (large) outlet opening. Other

Embodiments are considered in which the distance between the electrodes changes nonlinearly along the ion guide.

The plurality of plate electrodes preferably comprise 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more than 20 plate electrodes. The plate electrodes of the preferred ion guide can have a thickness of less than or equal to 5 mm, less than or equal to 4.5 mm, less than or equal to 4 mm, less than or equal to 3.5 mm, less than or equal to 3 mm, less than or equal to 2.5 mm, less than or equal to 2 mm, less than or equal to 1.5 mm, less than or equal to 1 mm, less than or equal to 0.8 mm, less than or equal to 0.6 mm, less than or equal to 0.4 mm, less than or equal to 0.2 mm, less than or equal to 0.1 mm or less than or equal to 0.25 mm.

According to one embodiment, the plate electrodes may be formed by applying a conductive paint or other substance to a substrate. In these embodiments, the typical thickness of the applied conductive layer (electrode layer) is about 250 μηι (0.25 mm).

The plate electrodes of the preferred ion guide can be spaced apart by a distance of less than or equal to 5 mm, less than or equal to 4.5 mm, less than or equal to 4 mm, less than or equal to 3.5 mm, less than or equal to 3 mm, less than or equal to 2.5 mm, less than or equal to 2 mm, less than or equal to 1.5 mm, less than or equal to 1 mm, less than or equal to 0.8 mm, less than or equal to 0.6 mm, less than or equal to 0.4 mm, less than or equal to 0.2 mm, less than or equal to 0.1 mm or less than or equal to 0.25 mm.

·

·

·

be spaced apart.

According to the preferred embodiment, AC or RF voltage is supplied to the plate electrodes. Adjacent plate electrodes can be supplied with opposite phases of the AC or RF voltage. The alternating or HF voltage preferably has a frequency of < 100 kHz, 100 - 200 kHz, 200 - 300 kHz, 300 - 400 kHz, 400 500 kHz, 0.5 - 1.0 MHz, 1.0 - 1.5 MHz, 1.5 - 2.0 MHz, 2.0 2.5 MHz, 2.5 - 3.0 MHz, 3.0 - 3.5 MHz, 3.5 - 4.0 MHz, 4.0 4.5 MHz, 4.5 - 5.0 MHz, 5.0 - 5.5 MHz, 5.5 - 6.0 MHz, 6.0 6.5 MHz, 6.5 - 7.0 MHz, 7.0 - 7.5 MHz, 7.5 - 8.0 MHz, 8.0-8.5 MHz, 8.5 - 9.0 MHz, 9.0 - 9.5 MHz, 9.5 - 10.0 MHz or > 10.0 MHz.

The AC or RF voltage is preferably < 50 V peak to peak, 50 - 100 V peak to peak, 100 - 150 V peak to peak, 150 - 200 V peak to peak, 200 - 250 V peak to peak, 250 - 300 V peak to peak, 300 - 350 V peak to peak, 350 400 V peak to peak, 400 - 450 V peak to peak, 450 - 500 V peak to peak or > 500 V peak to peak.

Preferably, in use, the ion guide is maintained at a pressure selected from the group consisting of: (i) greater than or equal to 0.0001 mbar, (ii) greater than or equal to 0.0005 mbar, (iii) greater than or equal to 0.001 mbar, (iv) greater than or equal to 0.005 mbar, (v) greater than or equal to 0.01 mbar, (vi) greater than or equal to 0.05 mbar, (vii) greater than or equal to 0.1 mbar, (viii) greater than or equal to 0.5 mbar, (ix) greater than or equal to 1 mbar, (x) greater than or equal to 5 mbar, and (xi) greater than or equal to 10 mbar.

Preferably, in use, the ion guide is maintained at a pressure selected from the group consisting of: (i) less than or equal to 10 mbar, (ii) less than or equal to 5 mbar, (iii) less than or equal to 1 mbar, (iv) less than or equal to 0.5 mbar, (v) less than or equal to 0.1 mbar, (vi) less than or equal to 0.05 mbar, (vii) less than or equal to 0.01 mbar, (viii) less than or equal to 0.005 mbar, (ix) less than or equal to 0.001 mbar, (x) less than or equal to 0.0005 mbar, and (xi) less than or equal to 0.0001 mbar.

Preferably, the ion guide is maintained in use at a pressure selected from the following group: (i) between 0.0001 and 10 mbar, (ii) between 0.0001 and 1 mbar, (iii) between 0.0001 and 0.1 mbar, (iv) between 0.0001 and 0.01 mbar, (v) between 0.0001 and 0.001 mbar, (vi) between 0.001 and 10 mbar, (vii) between 0.001 and 1 mbar, (viii) between 0.001 and 0.1 mbar, (ix) between 0.001 and 0.01 mbar, (x) between 0.01 and 10 mbar, (xi) between 0.01 and 1 mbar, (xii) between 0.01 and 0.1 mbar, (xiii) between 0.1 and 10 mbar, (xiv) between 0.1 and 1 mbar and (xv) between 1 and 10 mbar.

Preferably, in use, the ion guide is maintained at a pressure selected from the group consisting of: (i) greater than or equal to 1 × 10" mbar, (ii) greater than or equal to 5 × 10" mbar, (iii) greater than or equal to 1 × 10" mbar, (iv) greater than or equal to 5 × 10" mbar, (v) greater than or equal to 1 × 10 mbar, and (vi) greater than or equal to 5 × 10" ⁵ mbar.

Preferably, the ion guide is used on

a pressure selected from the following group: (i) less than or equal to 1 × 10" ⁴ mbar, (ii) less than or equal to 5 × 10" ⁵ mbar, (iii) less than or equal to 1 × 10" mbar, (iv) less than or equal to 5 × 10" ⁶ mbar, (v) less than or equal to 1 × 10" ⁶ mbar, (vi) less than or equal to 5 × 10" mbar and (vii) less than or equal to 1 × 10" ⁷ mbar.

Preferably, the ion guide is maintained in use at a pressure selected from the following group: (i) between 1 × 10" ⁷ and 1 × 10~ ⁴ mbar, (ii) between 1 × 10~ ⁷ and 5 × 10" ⁵ mbar, (iii) between 1 × 10~ ⁷ and 1 × 10" ⁵ mbar, (iv) between 1 × 10" ⁷ and 5 × 10" ⁶ mbar,

-7 &mdash; 6

(v) between 1 &khgr; 10 and 1 &khgr; 10" mbar, (vi) between

-7 - 7 - 7

1 x 10 and 5 x 10 mbar, (vii) between 5 x 10 and 1 x 10" ⁴ mbar, (viii) between 5 x 10" ⁷ and 5 x 10" ⁵ mbar, (ix)

-7 - R - 7

between 5 &khgr; 10 and 1 &khgr; 10 mbar, (x) between 5 &khgr; 10 and 5 &khgr;10" mbar, (xi) between 5 &khgr;10" and 1 &khgr;10" mbar, (xii) between 1 &khgr; 10 and 1 &khgr; 10 mbar, (xiii) between 1 &khgr; 10 and 5 &khgr; 10 mbar, (xiv) between 1 &khgr; 10 and 1 &khgr;10" mbar, (xv) between 1 &khgr;10" and 5 &khgr;10" mbar, (xvi) between 5 &khgr;10" and 1 &khgr;10" ⁴ mbar, (xvii) between 5 &khgr;10" and 5 &khgr; 10 mbar, (xviii) between 5 &khgr;10" and 1 &khgr;10" mbar, (xix) between 1 &khgr;10" and 1 &khgr;�Igr;&Ogr; ⁴ mbar, (xx) between 1 &khgr;10" and 5 &khgr;10" mbar and (xxi) between 5 &khgr;10" ⁵ and 1 &khgr;10" ⁴ mbar.

The ion guide preferably further comprises a first outer (for example upper) plate electrode arranged on a first side of the ion guide and a second (for example lower) outer plate electrode arranged on a second side of the ion guide. According to less preferred embodiments, no

upper or lower plate electrode. In these embodiments, ions can be prevented from escaping from the top or bottom of the ion guide by AC or RF confinement provided by other means such as an adjacent rod set arrangement.

According to another embodiment, the plate electrodes remote from the center of the ion guide may be maintained at continuously increasing positive or negative DC potentials so that ions moving away from the central region of the ion guide are increasingly forced back toward the center of the ion guide. According to this embodiment, no external plate electrodes enclosing the ion guide may be provided.

It may be arranged that the first outer plate electrode and/or the second outer plate electrode are biased to a DC bias voltage with respect to the average voltage of the plate electrodes to which an AC or RF voltage is applied.

This bias voltage is preferably less than -10 V, -9 to -8 V, -8 to -7 V, -7 to -6 V, -6 to -5 V, -5 to -4 V, -4 to -3 V, -3 to -2 V, -2 to -1 V, -1 to 0 V, 0 to 1 V, 1 to 2 V, 2 to 3 V, 3 to 4 V, 4 to 5 V, 5 to 6 V, 6 to 7 V, 7 to 8 V, 8 to 9 V, 9 to 10 V or more than 10 V.

According to one embodiment, the upper and/or lower plate, i.e. the outer electrodes, are supplied with a pure DC voltage (i.e. no AC or RF voltage is applied to them). According to another

2S-0S-U3

According to one embodiment, the upper and/or lower plate is supplied with a pure AC or RF voltage (i.e. the plates are not biased with a DC voltage with respect to the other plate electrodes). According to another embodiment, the upper and/or lower plate is supplied with both a DC voltage and an AC or RF voltage (i.e. the outer electrodes are biased with respect to the other electrodes by a DC voltage and they are also supplied with an AC or RF voltage).

According to the embodiments described above, the ion guide may further comprise an opening arranged in the upper and/or lower plate. The opening may be used to allow ions and/or a gas and/or a laser beam to enter and/or exit the ion guide.

According to one embodiment, one or more of the plate electrodes are maintained in use at a different DC potential from that of the other plate electrodes, so that a plurality of discrete ion guide regions are formed within the ion guide. For example, one or more of the plate electrodes may be maintained at a DC potential towards the center of the stack of plate electrodes, so that they form a potential wall. According to such an arrangement, two parallel and longitudinally extending ion guide regions may then be formed within the ion guide, for example forming an upper ion guide region and a lower ion guide region. According to other embodiments, more than two parallel ion guide regions

be formed.

According to another embodiment, a plurality of plate electrodes are maintained at substantially different DC potentials. According to these embodiments, a DC potential profile can be maintained between the plates. For example, a V-shaped DC potential profile can be maintained between the plate electrodes so that ions are forced toward the central region of the ion guide. According to this embodiment, upper and lower plate electrodes that effectively enclose the ion guide may not need to be provided so that the ion guide can appear substantially open from the top and bottom.

Preferably, the ion guide comprises a first outer portion, a second outer portion and an intermediate portion between the first and second outer portions, the DC potential at which the plate electrodes are maintained being increased in the first and/or second outer portions with respect to the intermediate portion so that ions are directed back to a central region of the ion guide.

Further embodiments are contemplated in which the DC potentials applied to the plate electrodes may vary over time. Preferably, one or more transient DC potentials or one or more DC potential waveforms are applied to the plate electrodes. This may preferably cause ions to flow from one region (e.g. an upper region) of the ion guide to

another area (e.g. a lower area) of the ion guide.

According to another aspect of the present invention, there is provided a mass spectrometer with an ion guide, the ion guide comprising:

several electrode layers and

several insulator layers interspersed or nested between the electrode layers.

Preferably, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the electrode layers are arranged on or deposited on the insulator layers.

According to another aspect of the present invention, there is provided a mass spectrometer having an AC or RF ion guide, the ion guide comprising:

several electrodes and

several insulators that are interspersed, inserted or nested between the electrodes,

wherein the electrodes are mounted on or deposited on the insulators.

Preferably, the ion guide has an ion inlet and an ion outlet, whereby gas molecules within the ion guide are substantially prevented from exiting at any point other than through the ion inlet or the ion outlet.

&Igr; *· ·&diams;

the ion guide. A gas opening may be provided for introducing gas into the ion guide, but preferably gas can be substantially prevented from escaping from the ion guide via this gas opening.

In another aspect, the present invention provides a mass spectrometer having a first ion guide, a gas collision/reaction cell, and a second ion guide. The second ion guide has a plurality of plate electrodes, an entrance for receiving ions, an ion guide region extending through the ion guide, and an exit from which ions exit. There is preferably no direct line of sight from the entrance to the exit of the second ion guide.

According to the preferred embodiment, the mass spectrometer further comprises an electrospray ion source ("ESI ion source"), an atmospheric pressure chemical ionization ion source ("APCI ion source"), an atmospheric pressure photoionization ion source ("APPI ion source"), a matrix assisted laser desorption ionization ion source ("MALDI ion source"), a laser desorption ionization ion source ("LDI ion source"), an inductively coupled plasma ion source ("ICP ion source"), an electron impact ion source ("EI ion source"), a chemical ionization ion source ("CI ion source"), a fast atom bombardment ion source ("FAB ion source"), or a liquid secondary ion mass spectrometry ion source

( ¹¹ LSIMS ion source") .

The mass spectrometer may also include a mass analyzer located downstream of the second ion guide

rr:\

The mass analyzer may comprise a time-of-flight mass analyzer, a quadrupole mass analyzer, a Fourier transform ion cyclotron resonance mass analyzer ("FTICR mass analyzer"), a two-dimensional (linear) quadrupole ion trap, a three-dimensional (Paul) quadrupole ion trap, or a magnetic sector mass analyzer.

Ion guides according to the preferred embodiment may advantageously comprise an ion guide region having at least one curved or non-linear section, and may comprise more than one ion entrance and/or ion exit. It would be very difficult and prohibitively expensive to attempt to manufacture and construct equivalent ion guides from conventional multi-pole rod set RF ion guides.

The ion guide according to the preferred embodiment is constructed from a series of shaped plates or plate electrodes. The plates need not be straight and they may have more than one ion input and/or ion output. The preferred ion guides are relatively simple to manufacture and are considerably less expensive than conventional multi-pole rod set ion guides. Ion guides with complicated shapes can also be easily manufactured. For example, several identical plates with complicated shapes can be easily and inexpensively manufactured from thin sections of sheet metal by die cutting or stamping, photochemical etching, laser cutting, wire EDM, spark EDM, etc. Furthermore, the plates can be stacked in an assembly or multiple array with the plates spaced apart and insulated and with

alternating plates are electrically connected to each other so that adjacent plates are kept 180° out of phase with each other.

According to a preferred embodiment, the RF ion guide is constructed from a series of shaped plates arranged in a stack with suitable DC potentials applied to a top or upper plate electrode and to a bottom or lower flat plate electrode. This is a particularly simple and inexpensive way of constructing a complex RF ion guide. The top and bottom plates can be operated with an AC or RF voltage applied to them, or a combination of AC or RF and DC voltages.

According to the preferred embodiment, the plates can be made with an entrance and an exit that are not aligned so that there is no line of sight through the ion guide, so that neutral particles, large particles or droplets, or radiation such as visible light or UV light do not pass straight through the ion guide.

The present invention provides a method for mass spectroscopy comprising the following steps:

Generating ions from an atmospheric ion source and

Leading the ions through an ion guide, whereby the ion guide has several plate electrodes, an entrance to the

Receiving ions and an exit through which ions exit the ion guide, wherein an ion guide channel is formed in the plate electrodes and extends substantially along the length of the ion guide and wherein the plate electrodes are arranged in the plane of ion movement.

The present invention further provides a method for producing a young guide for a mass spectrometer, in which a plurality of electrodes are interspersed or nested with a plurality of insulators to form an ion guide with a plurality of electrodes arranged on the insulators, so that an ion guide stack is formed.

The present invention further provides a method for producing a young guide for a mass spectrometer, in which a plurality of electrode layers are deposited on a plurality of insulator layers to form an ion guide stack with a plurality of electrode layers arranged on the insulator layers.

The term "plate electrode" as used in the present application should be interpreted broadly. According to a preferred embodiment, the plate electrodes comprise thin metal sheets. However, according to other embodiments, the plate electrodes may comprise wire meshes or grids and therefore have openings. The term is also intended to include electrodes that have been applied to a substrate in the manner of an insulator.

■·· ·■■&diams;

Electrodes forming an ion guide are arranged in the plane of ion movement, in contrast to an ion tunnel or ion funnel ion guide, in which the ring electrodes are arranged in a plane perpendicular to the direction of ion movement.

The ion guides described above can be used either as an ion guide per se, or they can form a fragmentation, collision, reaction or collision cooling cell.

Various embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure IA shows a plan view of an AC or RF ion guide according to an embodiment, and Figure IB shows a sectional view of the ion guide of Figure IA along a cross section A-A,

Figure 2 shows an embodiment in which the plates have a C-shaped ion path so that the ions are rotated by 90° from the entrance to the exit,

Figure 3 shows an embodiment in which the plates have an S-shaped ion path so that ions are displaced laterally from the entrance to the exit,

Figure 4 shows an embodiment in which the plates have a Ω-shaped ion path so that there is no line of sight between the entrance and the exit, but the ions are not displaced laterally or obliquely when they exit the ion guide,

r te· »

t '-

Figure 5 shows an embodiment in which an S-shaped ion path is formed from two plate stacks with C-shaped ion paths,

Figure 6 shows an embodiment in which a Ω-shaped ion path is formed from two plate stacks with S-shaped ion paths,

Figure 7 shows an embodiment in which a Ω-shaped ion path is formed from two plate stacks with C-shaped ion paths,

Figure 8 shows an embodiment in which the ion guide has two inlets and one outlet,

Figure 9 shows another embodiment in which the ion guide has two inputs and one output,

Figure 10 shows another embodiment in which the ion guide has two inputs and one output,

Figure 11 shows another embodiment in which the ion guide has two inputs and one output,

Figure 12 shows an embodiment in which the ion guide has three inputs and one output,

Figure 13 shows an embodiment in which the ion guide has one input and two outputs,

Figure 14 shows an embodiment in which the ion guide has one input and three outputs,

&bull;t

Figure 15 shows an embodiment in which the ion guide has two inlets and two outlets,

Figure 16A shows an embodiment in which the ion guide has three openings that can be selectively used as inputs and outputs, and Figure 16B shows the same ion guide used in a different operating mode,

Figure 17 shows an embodiment of a three-aperture ion guide combined with a single-aperture RF ion guide and an ion capture region,

Figure 18A shows an embodiment of an ion guide with three ion paths of different size and shape and Figure 18B shows a cross-section of an ion guide with a non-rectangular cross-sectional profile,

Figure 19A shows an embodiment in which an ion guide has a total of six openings, and Figure 19B shows another embodiment in which an ion guide has a total of six openings,

Figure 2 0 shows a mass spectrometer having a preferred ion guide,

Figure 21A shows an embodiment of an ion guide that is operated with a DC voltage applied to the top and bottom plates, Figure 2IB shows an embodiment of an ion guide that is operated with an AC or RF voltage applied to the top and bottom plates, and Figure 2IC shows a

/ i to'&igr; :: :·:

embodiment of an ion guide that is operated with both a DC voltage and an AC or RF voltage applied to the top and bottom plates, and

Figure 22 shows an ion guide consisting of a stack of electrodes mounted or deposited on insulators.

Several different embodiments of the present invention are described. However, a common feature of the various embodiments is that an AC or RF ion guide is provided which has a plurality of plate electrodes. The plate electrodes are preferably relatively thin and may be made of metal sheets. Alternatively, the plate electrodes may be made of a non-conductive plate, for example of glass or ceramic, which is then at least partially covered with an electrically conductive coating. The glass or ceramic plate may be shaped in the same way as the metal sheets to provide an ion guiding region.

The glass or ceramic plates are preferably continuous and areas of their surface may be coated with a conductive coating to provide shaped electrodes for guiding the ions.

The preferred plate electrodes differ from conventional rod set electrodes, which have a circular cross-sectional profile and whose length is usually much larger than their width. In contrast, the plate electrodes, which provide ion guidance according to the preferred

4 ::

preferred embodiment, preferably have a rectangular cross-sectional profile, and the width of the electrodes may be comparable to (or even greater than) the length of the electrodes.

Figure 1A shows a plan view of an AC or RF ion guide la constructed from a stack of plate electrodes such that an S-shaped ion path is formed within the AC or RF ion guide la. The AC or RF ion guide la preferably consists of a series of identical plates, each approximately 0.7 mm thick and preferably spaced 1.0 mm apart.

Figure IB is a sectional view along A-A of the ion guide shown in Figure IA and therein is shown an AC or RF ion guide la comprising a stack of six plate electrodes 2 having an upper plate electrode 3 and a lower plate electrode 4. The internal opening or ion guide region 5 within the ion guide la is preferably 11.2 mm high and 5 mm wide. The length of the ion path passing through the ion guide la shown in Figure IA may be about 60 mm. The frequency of the RF supply applied to the plates 2, 3, 4 forming the ion guide la may be 6 MHz and the RF voltage may be 200 V peak to peak. The uppermost or upper plate electrode 3 and the lowermost or lower plate electrode 4 may, according to one embodiment, be biased at +3 V relative to the average voltage of the shaped plate electrodes 2 to which the AC or RF voltage was applied.

· ■··*

The preferred AC or RF ion guide la preferably comprises a plurality of plate electrodes 2 arranged in a stack or array. The ion guide la preferably comprises an upper plate electrode 3 and a lower plate electrode 4. The electrodes 2 other than the upper plate electrode 3 and the lower plate electrode 4 preferably comprise a channel provided in the plates substantially along their entire length. In the example shown in Figure 1A, the plate electrodes 2 and the upper plate electrode 3 and the lower plate electrode 4 are S-shaped. The channel provided in each of the plate electrodes 2 results in an ion guiding region 5 being provided in the ion guide la.

Having described the basic arrangement of the ion guide la, various embodiments will now be described in more detail.

A first main embodiment of the present invention will now be described with reference to Figures 2-4, in which various arrangements of an AC or RF ion guide la are shown. Curved or otherwise non-linear channels are provided in the plate electrodes 2 except for the upper plate electrode 3 and the lower plate electrode 4. The ion guide la has an entrance 6 and an exit 7, and the ion guide region 5 is arranged such that there is no line of sight between the ion entrance opening 6 and the ion exit opening 7. This is advantageous in that radiation, neutral particles or droplets entering the ion guide la at the entrance 6 are not obliquely or laterally displaced from the ion guide la.

and therefore do not exit the ion guide la through the outlet 7 in the embodiments shown in Figures 2 and 3. In the embodiment shown in Figure 4, a device can be arranged outside the ion guide region 5 to block radiation, neutral particles or droplets that run directly from the inlet 6 to the outlet 7. This device can comprise a baffle, a plate or an electrode.

The ion guide la can preferably be operated at medium pressures of, for example, between 0.0001 and 10 mbar. Due to the presence of gas, frequent collisions between ions and molecules occur, which can lead to ions being slowed down and possibly even coming to a standstill within the ion guide la.

A second main embodiment of the present invention will now be described with reference to Figures 5-7. According to the second main embodiment, two or more AC or RF ion guides la, Ib are provided, each ion guide la, Ib comprising a stack of plate electrodes. Each plate electrode 2 is shaped to provide a path for the ions to pass therethrough. A DC potential may be applied to the region where the ions leave one ion guide la and then enter an adjacent ion guide Ib. The DC potential may create an axial field which helps to keep ions moving as they traverse the ion guides la, Ib in the presence of a gas.

In the embodiment shown in Figure 7, a potential well can be created along the ion beam axis. Ions can be trapped, for example, within the second ion guide Ib or the third ion guide Ic. The potential applied in the region between the exit of the first ion guide la and the entrance of the second ion guide Ib and the potential applied in the region between the exit of the second ion guide Ib and the entrance of the third ion guide Ic can be selected so that, in a first operating mode, ions are trapped within the second ion guide Ib. In a similar way, ions could be arranged to be trapped in the third ion guide Ic. Other embodiments are contemplated in which ions are trapped within the second ion guide Ib and the third ion guide Ic. Ions can be trapped within a particular ion guide la, Ib, Ic by maintaining the downstream ion guide Ib, Ic, Id at a different DC potential.

A third main embodiment of the present invention will now be described with reference to Figures 8-12. According to the third main embodiment, two or more entrances can be provided to the ion guide la, which has one or more exits. Alternatively, the ion guide la can have one or more entrances and two or more exits. In contrast, conventional multipole rod set ion guides have only a single ion entrance and a single ion exit.

Figures 8-11 show embodiments in which the ion guide la has two entrances 6a, 6b and wherein

. &igr;131;j · · ;

it is possible to switch between receiving ions from one input 6a to receiving ions from another input 6b. Alternatively, two or more ion beams can be merged. The ion inputs can be arranged at angles in the range of 0 - 10°, 10 - 20°, 20 30°, 30 - 40% 40 - 50°, 50 - 60°, 60 - 70°, 70 - 80°, 80 90% 90 - 100°, 100 - 110°, 110 - 120°, 120 - 130°, 130 140°, 140 - 150°, 150 - 160°, 160 - 170° or 170 - 180° to each other.

The ion guide 1a can be used with a first ion source (not shown) for analyzing analyte ions and a second ion source (not shown) for generating reference ions. Alternatively, the ion guide can be used with two different types of ion sources and can be used, for example, in conjunction with an atmospheric pressure ionization ion source ("API ion source") and a matrix-assisted laser desorption ionization ion source ("MALDI ion source"). The plate electrodes can be made with any shape so that ion beams can be received by the ion guide at any angle or from any direction or can exit the ion guide at any angle or in any direction.

In the embodiment shown in Figure 8, the plate electrodes of the ion guide are shaped so that the two entrances are on opposite sides of the plates and the exit is on a third side. The plate electrodes can be substantially rectangular or square. Figure 9 shows an embodiment in which the plates are shaped so that

the entrances are at right angles to each other so that, in use, the ion beams received by the entrances are both oblique to the ion beam emerging from the ion guide. Alternatively, the entrances may be on the same side of the plate with the exit on a second side as shown in Figure 10. Figure 11 shows another embodiment in which one of the entrances and the exit are on opposite sides of the plate, directly opposite each other, and a second entrance is on a third side.

Figure 12 shows an embodiment in which the AC or RF ion guide la has three inputs 6a, 6b, 6c. Other embodiments are contemplated in which four or more inputs may be provided. The ion guide la shown in Figure 12 can be used to switch between or merge ion beams, for example from two different ion sources for analyzing analyte ions and a third ion beam for generating reference ions.

An AC or RF ion guide la with multiple ion inlets 6a, 6b, 6c can be used to multiplex between different ion sources within a multiple array of ion sources. Such an arrangement enables parallel analysis of a large number of sample streams, for example four to eight different liquid or gas streams from four to eight different liquid or gas chromatography columns.

A fourth main embodiment of the present invention

will now be described with reference to Figures 13-16. Ion guides la of the type shown in Figure 13 are contemplated which have more than one output 7a, 7b so that an ion stream can be split between or switched between two or more outputs. Such an embodiment can be used, for example, to split or switch ions between two detectors. Ions can be split or switched between, for example, a Faraday cup detector and an ion counting detector to provide a detection system which has a very wide dynamic range and yet is capable of detecting and counting individual ions.

Alternatively, such an ion guide la can be used to split or switch ions between a detector and another analyzer, such as a mass analyzer. For example, ions can be split so that part of the ion signal is monitored on a detector while the remainder is passed on to a device for further analysis, for example a collision cell and a mass analyzer for ion structure studies or for more specific ion monitoring.

Alternatively, such an ion guide la can be used to split or switch ions between two mass analyzers. For example, ions can be split between two mass analyzers operating at different resolutions or between two mass analyzers tuned for different masses.

The embodiment shown in Figure 13 can be used to split an ion beam into two ion beams to be directed to two or more different mass analyzers and can provide a means for measuring isotope ratios. Two mass analyzers can be tuned to the appropriate masses to measure any desired isotope ratio. This embodiment is the inverse of the embodiment shown in Figure 8 in which an AC or RF ion guide 1a is provided with two inputs 6a, 6b and a single output 7.

All of the embodiments shown in Figures 8-12 can be reversed to have a single input and two (or more) outputs.

Figure 14 shows an embodiment in which an AC or RF ion guide la has three outputs 7a, 7b, 7c. Other embodiments are contemplated in which more than three outputs are provided. The embodiment shown in Figure 14 with three outputs 7a, 7b, 7c enables an ion stream to be switched or split between different detectors and/or mass analyzers in any combination.

Embodiments are considered in which the AC or RF ion guide la has several inputs and several outputs. For example, Figure 15 shows an embodiment in which an ion guide la is provided with two inputs 6a, 6b and two outputs 7a, 7b. According to this embodiment, the ion guide la can

guide la Ions can be received from two different ion sources, such as a thermionization ion source and an inductively coupled plasma ion source ("ICP ion source"). The ions can then be directed to two different mass analyzers, each tuned to two different isotope mass-to-charge ratios.

Embodiments are contemplated in which the AC or RF ion guide la may be used with multiple entrances and/or exits, with ions taking one path in one mode of operation and taking the other path in another mode of operation. For example, in the embodiment illustrated in Figures 16A and 16B, the aperture 7 illustrated in Figure 16A acts as an exit aperture in the mode of operation illustrated in Figure 16A, but the same aperture (now designated 6') may act as an entrance aperture in a subsequent mode of operation as illustrated in Figure 16B. In the subsequent mode of operation, ions exit the ion guide la via a third aperture 7'.

Ion guides la are contemplated in which ion streams can be directed back and forth within an overall arrangement of ion sources, analyzers and detectors. For example, an AC or RF ion guide la may, in one mode of operation, allow ions to pass from an ionization source to a mass analyzer, and the ion guide la may, in another mode of operation, receive ions from the mass analyzer or an ion trap and direct them through a third aperture to a detector. Ions may be allowed to pass through one aperture or they may be prevented from

through an aperture by applying a suitable potential to an element adjacent to a particular aperture. An AC or RF ion guide la with multiple apertures can be used to direct an ion stream in multiple directions.

Figure 17 shows a further embodiment with a first AC or RF ion guide la with three openings 6, 7, 8 and a second AC or RF ion guide 1b with a single opening 9. Ions enter the first AC or RF ion guide la through the entrance opening 6 and are directed by 90° to the opening 8. The ions then pass through the opening 9 into the second AC or RF ion guide 1b. The second AC or RF ion guide 1b has a single opening 9 and an ion storage region 10 for receiving and storing ions. In one operating mode, it can be ensured that ions which have been stored or captured in the capture or storage area 10 exit the second AC or RF ion guide 1b via the opening 9 and re-enter the first AC or RF ion guide 1a via the opening 8 through which the ions previously exited. The ions are then guided through 90° to the exit opening 7 through which the ions exit the first ion guide 1a.

The ions may be induced or assisted to move through a particular aperture 6, I ₁ 8, 9 by applying appropriate voltages to elements immediately adjacent to the aperture, or this may not be the case. For example, ions may be induced to move into the second AC or RF

to enter or exit the ion guide Ib by reducing or increasing the DC potential applied to the second AC or RF ion guide with respect to the DC potential applied to the first AC or RF ion guide la.

Figure 18A shows further embodiments in which an AC or RF ion guide la is used to change the cross-sectional beam profile of an ion beam or to change the cross-sectional area of the ion beam. According to one embodiment, the input aperture 6 can preferably be adapted to the incoming ion beam in both size and cross-sectional shape. Similarly, the output apertures 7a, 7b can also be adapted in size and cross-sectional profile to match the optimal size and cross-sectional profile of the ion optical devices located downstream of the AC or RF ion guide la and intended to receive the ion stream exiting the ion guide la. One input aperture 6 and the two output apertures 7a, 7b can all have different cross-sectional areas and/or cross-sectional profiles. Preferably, the cross-sectional area of the input aperture(s) is substantially equal to the sum of the cross-sectional areas of the output apertures. The guide areas between the openings 6, 7a, 7b can also have lengths whose size and/or shape changes continuously.

Figure 18B shows an embodiment of an AC or RF ion guide la, in which the plate electrodes 2, which carry the AC or RF voltage,

have a channel whose width changes increasingly from an upper section of the ion guide la to the lower section of the ion guide la. According to the embodiment shown in Figure 18B, the width of the channel in the plate electrodes 2 is such that an ion beam passing through the ion guide la has a substantially circular cross-sectional profile.

Other embodiments are contemplated in which the shape and size of each aperture or ion path may be different from those of the others: such AC or RF ion guides la may also be manufactured with cross-sectional shapes or profiles other than rectangular or circular.

Figures 19A and 19B show further embodiments in which ions are provided for entering and/or exiting the AC or RF ion guide la through the upper plate electrode 3 and/or through the lower plate electrode 4. The embodiment shown in Figures 19A and 19B is similar to the embodiments shown in Figures 12, 14 and 15, but with an additional opening 11 provided in the upper plate electrode 3 and an additional opening 12 provided in the lower plate electrode 4. The additional openings 11, 12 can be used to allow ions (or gas or a laser beam) to be introduced into the AC or RF ion guide la or to allow ions (or gas or a laser beam) to exit the AC or RF ion guide la. In the example shown in Figures 19A and 19B, the AC or RF ion guide la has a total of six openings.

Figure 20 shows a plan view of a preferred embodiment in which an AC or RF ion guide 1a is provided downstream of a collision cell 34 in a mass spectrometer 30. For ease of illustration, several horizontally extending vacuum openings are shown, whereas in the preferred embodiment the vacuum openings preferably extend vertically below the mass spectrometer 30. The mass spectrometer 30 preferably comprises an inductively coupled plasma ion source ("ICP ion source") (not shown). A number of sampling cones 31 and vacuum pumps may be provided to allow a portion of the ions emitted by the ion source to enter a vacuum chamber 32. The ions are then caused to enter an RF hexapole ion guide 33 which preferably has an enclosed section 34. Gas is preferably introduced into the enclosed section 34 so that ions passing through the enclosed section 34 collide with the gas introduced into the enclosed section 34. These collisions cause the ions to lose energy. Argon ions and other ions from the plasma can be substantially attenuated preferably by charge exchange with the collision gas in the ion beam. The remaining analyte ions then exit the hexapole ion guide 33 and enter an S-shaped AC or RF ion guide 1a which displaces ions laterally. These ions then exit the S-shaped AC or RF ion guide 1a and pass through an intermediate chamber opening 36 into the next vacuum chamber (analyzer vacuum chamber) 35. The ions pass

then through a quadrupole mass filter 37 with a pre-filter 38 and a post-filter 39 for mass analysis and then to a detector 40 which is preferably cylindrically shaped and arranged along the horizontal axis.

ICP ion sources typically produce high levels of fast neutral atoms and molecules and an intense beam of visible and UV radiation. The collision/reaction cell 34 may also result in a background of fast neutral atoms and molecules. The visible and UV radiation and the fast particles result in a continuum of background noise if they are allowed to reach the detector. This noise interferes with the measurement of analyte signals and limits their detection. The S-shaped RF ion guide 1a advantageously eliminates any line-of-sight path, thereby preventing fast neutral particles and radiation from reaching the detector 40 while still guiding ions for subsequent mass analysis and detection by the mass spectrometer 30.

The ion signal for uranium ions (m/z 238) was measured using the embodiment shown in Figure 20. An ICP torch provided the source of the ions to be analyzed by an analyzer with a low mass resolution of 12.6 and a high mass resolution of 15.6. The ICP torch was set so that the x-axis was at 2.54, the y-axis was at -0.69, and the z-axis was at 1.10. The pressure in the analyzer was maintained at 5.1 x 10 mbar and a collision gas of hydrogen and helium was present in the collision cell 34.

A &igr; conical lens 31 was placed at a potential of 50 V, ·· ·.·. ««^ _t *» _t · ·· ···· ; ; .;

»· · &bull; ·· _s ta r &bull; * * -&iacgr; ·
·« *
ti « ^e ·« % ·
-· * »

a hexapole output lens was set at a potential of 190 V and the hexapole 33 was biased by 0 V. The ions had an energy of 2 eV in the quadrupole mass analyzer 3 7 and were detected by a photomultiplier with a gain set at 450. The measurements indicated that the transmittance of ions through the S-shaped AC or RF ion guide la was between 50% and 100%, while the transmission of fast neutral particles, visible radiation and UV radiation was essentially eliminated.

Figures 21A-C show three different configurations in which an AC or RF ion guide 1a is operated with either a DC bias, an AC or RF voltage, or a combination of a DC bias and an AC or RF voltage applied to the upper plate electrode 3 and the lower plate electrode 4, respectively. When an AC or RF voltage is applied to the upper plate electrode 3 and the lower plate electrode 4, as shown in Figures 21B and 21C, the upper plate electrode 3 and the lower plate electrode 4 can either be coupled directly to the next plate electrode 2 or coupled via a capacitor to another plate electrode 2 so that a 180° phase shift is maintained between adjacent electrodes 2, 3, 4.

The atomic ion transmission for beryllium, cobalt, indium and uranium for the three different configurations shown in Figures 21A, 21B and 21C respectively and for different DC voltages was tested and the results are presented in the table below.

· · f

· ■

V Mass sensitivity Co In (cps) (Volt) Be 59 There 115 There U 2 9 There 1100000 1600000 238 There Configuration 1 5 5000 550000 1300000 1500000 (Figure 21A) 0 500 900000 1800000 1800000 Configuration 2 15000 1700000 (Figure 21B) -5 0 0 Configuration 3 0 20000 1200000 2500000 0 (Figure 21C) 1 20000 1200000 2700000 1900000 10 15000 50000 1000000 2500000 0 3400000

It is evident from the above table of relative sensitivity measurements for the four elements that it is advantageous to apply an AC or RF voltage to the plates 3, 4 instead of or in addition to
a DC bias. It appears that applying primarily an AC or RF voltage, as in Figure 2IB, gives the best overall transmission over a wide mass range. However, it appears that applying a combination of an AC or RF voltage and a DC bias increases the transmission over a more limited mass range. The combination of an AC or RF voltage and a 10 V DC voltage, as in Figure 2IC, gave a transmission for uranium approximately twice that previously recorded for the mass spectrometer shown in Figure 20 when the output of the RF hexapole ion guide 33 was placed adjacent to the quadrupole mass analyzer 37.

Intermediate chamber opening 36 was arranged.

Figure 22 shows an embodiment in which the electrodes 2 are attached to or on insulators 2'. According to one embodiment, the insulators 2' may comprise Bakellite (RTM), a ceramic or a plastic such as PTFE, polyethylene, PEEK or Kapton (RTM). The electrodes 2 may be interspersed or nested between the insulators 2'. According to one embodiment, the electrodes 2 may be applied to the insulators 2' and may comprise, for example, electrically conductive paint. According to this embodiment, the electrode layers preferably have a thickness of approximately 250 μιγ. A particularly advantageous feature of the embodiment shown in Figure 22 is that there are preferably no air gaps between the electrodes 2 and the insulators 2'. Accordingly, gas within the ion guide 1a is advantageously prevented from escaping from the ion guide except at the inlet and outlet of the ion guide. The ion guide la shown in Figure 22 is therefore particularly suitable for use as a collision or reaction cell, wherein gas is introduced into the ion guide la. A gas inlet opening can be provided in an upper plate electrode 3 or a lower plate electrode 4, but the gas preferably does not exit the ion guide la via this opening. Because the ion guide la shown in Figure 22 is considerably less prone to leakage than embodiments in which an air gap is present between electrodes, the gas introduced into the ion guide la can be maintained at a relatively high pressure without the need to use larger vacuum pumps. Similarly, compared with other embodiments, a larger pressure difference along the ion guide la can be achieved.

leadership la be maintained.

While 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 details may be made without departing from the scope of the invention as set forth in the appended claims.

Claims (88)

1. A mass spectrometer comprising an ion guide, the ion guide having a plurality of plate electrodes, an entrance for receiving ions along a first axis, and an exit from which ions exit the ion guide along a second axis, the second axis being at an angle θ to the first axis and θ > 0°. 2. A mass spectrometer according to claim 1, wherein ? is within the following range: (i) < 10°, (ii) 10-20°, (iii) 20-30°, (iv) 30-40°, (v) 40-50°, (vi) 50-60°, (vii) 60-70°, (viii) 70-80°, (ix) 80-90°, (x) 90-100°, (xi) 1 00-110°, (xii) 110-120°, (xiii) 120-130°, (xiv) 130-140°, (xv) 140-150°, (xvi) 150-160°, (xvii) 160-170° and (xviii) 170-180°. 3. A mass spectrometer comprising an ion guide, the ion guide having a plurality of plate electrodes, an entrance for receiving ions along a first axis, and an exit from which ions exit the ion guide along a second axis, the ion guide further comprising a curved ion guide region between the entrance and the exit. 4. A mass spectrometer according to claim 3, wherein the ion guide region is substantially "S"-shaped and/or has a single inflection point. 5. A mass spectrometer according to claim 3 or 4, wherein the first axis is substantially parallel to the second axis. 6. A mass spectrometer according to claim 3, 4 or 5, wherein the second axis is laterally offset from the first axis. 7. A mass spectrometer comprising an ion guide, the ion guide having a plurality of plate electrodes, an entrance for receiving ions along a first axis, a curved ion guide region, and an exit from which ions exit the ion guide along a second axis, the second axis being substantially coaxial with the first axis. 8. A mass spectrometer according to claim 7, further comprising a device disposed at least partially outside the ion guide region for blocking particles and/or photons traveling directly from the entrance to the exit. 9. A mass spectrometer according to claim 8, wherein the device comprises a baffle, a plate or an electrode. 10. Mass spectrometer comprising:
a first ion guide having a plurality of plate electrodes, an input for receiving ions and an output from which ions exit from the first ion guide, and
a second ion guide having a plurality of plate electrodes, an input for receiving ions, and an output from which ions exit from the second ion guide. 11. The mass spectrometer of claim 10, further comprising a third ion guide having a plurality of plate electrodes, an input for receiving ions, and an output from which ions exit from the third ion guide. 12. The mass spectrometer of claim 11, further comprising a fourth ion guide having a plurality of plate electrodes, an input for receiving ions, and an output from which ions exit from the fourth ion guide. 13. A mass spectrometer according to claim 10, 11 or 12, wherein in one mode of operation the first ion guide and the second ion guide are maintained at different DC potentials in use so that ions exiting the first ion guide are forced into the second ion guide. 14. A mass spectrometer according to claim 11 or 12, wherein in one mode of operation the second ion guide and the third ion guide are maintained at different DC potentials in use so that ions emerging from the second ion guide are forced into the third ion guide. 15. A mass spectrometer according to claim 12, wherein in a mode of operation the third ion guide and the fourth ion guide are maintained at different DC potentials in use so that ions exiting the third ion guide are forced into the fourth ion guide. 16. A mass spectrometer according to claim 10, 11 or 12, wherein in a mode of operation the second ion guide is maintained at a different DC potential from that of the first ion guide so that ions are trapped in the first ion guide. 17. A mass spectrometer according to claim 11 or 12, wherein in one mode of operation the third ion guide is maintained at a different DC potential from that of the second ion guide so that ions are trapped in the second ion guide. 18. A mass spectrometer according to claim 12, wherein in a mode of operation the fourth ion guide is maintained at a different DC potential than that of the third ion guide so that ions are trapped in the third ion guide. 19. A mass spectrometer according to any one of claims 10 to 18, wherein either the first and/or the second and/or the third and/or the fourth ion guide has an ion storage region. 20. A mass spectrometer according to claim 19, wherein in a first mode of operation the ion storage region receives ions through a single aperture and in a second mode of operation ions exit the ion storage region through the single aperture. 21. A mass spectrometer comprising an ion guide, the ion guide having a plurality of plate electrodes, two or more inlets for receiving ions, and one or more outlets from which ions exit the ion guide. 22. A mass spectrometer according to claim 21, wherein the ion guide has two inputs for receiving ions and an output from which ions exit the ion guide. 23. A mass spectrometer according to claim 21, wherein the ion guide has three inputs for receiving ions and an output from which ions exit the ion guide. 24. A mass spectrometer according to claim 21, 22 or 23, further comprising at least two ion sources, wherein ions from a first ion source enter a first input and ions from a second ion source enter a second input, and wherein the first and/or second ion sources are selected from the group comprising: (i) an electrospray ion source ("ESI ion source"), (ii) an atmospheric pressure chemical ionization ion source ("APCI ion source"), (iii) an atmospheric pressure photoionization ion source ("APPI ion source"), (iv) a matrix assisted laser desorption ionization ion source ("MALDI ion source"), (v) a laser desorption ionization ion source ("LDI ion source"), (vi) an inductively coupled plasma ion source ("ICP ion source"), (vii) an electron impact ion source ("EI ion source"), (viii) a chemical ionization ion source ("CI ion source"), (ix) a fast atom bombardment ion source ("FAB ion source"), and (x) a liquid secondary ion mass spectrometry ion source ("LSIMS ion source"). 25. A mass spectrometer comprising an ion guide, the ion guide having a plurality of plate electrodes, one or more inlets for receiving ions, and two or more outlets from which ions exit the ion guide. 26. A mass spectrometer according to claim 25, wherein the ion guide has an input for receiving ions and two outputs from which ions exit the ion guide. 27. A mass spectrometer according to claim 25, wherein the ion guide has an input for receiving ions and three outputs from which ions exit the ion guide. 28. A mass spectrometer according to claim 21 or 25, wherein the ion guide has at least two inputs for receiving ions and at least two outputs from which ions exit the ion guide. 29. The mass spectrometer of claim 28, further comprising at least two ion sources, wherein ions from a first ion source enter a first input and ions from a second ion source enter a second input, and wherein the first and/or second ion sources are selected from the group comprising: (i) an electrospray ion source ("ESI ion source"), (ii) an atmospheric pressure chemical ionization ion source ("APCI ion source"), (iii) an atmospheric pressure photoionization ion source ("APPI ion source"), (iv) a matrix assisted laser desorption ionization ion source ("MALDI ion source"), (v) a laser desorption ionization ion source ("LDI ion source"), (vi) an inductively coupled plasma ion source ("ICP ion source"), (vii) an electron impact ion source ("EI ion source"), (viii) a chemical ionization ion source ("CI ion source"), (ix) a fast atom bombardment ion source ("FAB ion source"), and (x) a liquid secondary ion mass spectrometry ion source ("LSIMS ion source"). 30. A mass spectrometer according to any one of claims 21 to 29, wherein in use an ion beam entering the ion guide is split into two or more beams, the first beam exiting the ion guide via a first exit and the second beam exiting the ion guide via a second exit. 31. A mass spectrometer according to claim 30, wherein in use the ions entering an entrance of the ion guide are split into two or more beams by one or more electrodes arranged adjacent to the entrance, one or more electrodes arranged within the ion guide, or one or more electrodes arranged adjacent to an exit of the ion guide. 32. A mass spectrometer according to claim 30 or 31, wherein the first beam has a percentage of ions entering the ion guide selected from the group consisting of: (i) 0-10%, (ii) 10-20%, (iii) 20-30%, (iv) 30-40%, (v) 40-50%, (vi) 50-60%, (vii) 60-70%, (viii) 70-80%, (ix) 80-90%, and (x) greater than 90%. 33. A mass spectrometer according to any one of claims 21 to 32, wherein at least a portion of an ion beam entering the ion guide is switchable to or between one of a plurality of outputs. 34. A mass spectrometer according to claim 33, wherein, in use, the ions entering an entrance of the ion guide are switchable to or between one of a plurality of outputs by one or more electrodes arranged adjacent to the entrance, one or more electrodes arranged within the ion guide, or one or more electrodes arranged adjacent to an exit of the ion guide. 35. A mass spectrometer according to any one of claims 21 to 34, further comprising a first ion detector arranged to receive ions exiting a first output and a second ion detector arranged to receive ions exiting a second ion output. 36. A mass spectrometer according to any one of claims 21 to 35, further comprising a first mass analyzer arranged to receive ions exiting a first output and a second mass analyzer arranged to receive ions exiting a second ion output. 37. A mass spectrometer according to any one of claims 21 to 34, further comprising a mass analyzer arranged to receive ions exiting the ion guide via a first exit and an ion detector arranged to receive ions exiting the ion guide via a second exit. 38. A mass spectrometer according to any one of claims 21 to 34, further comprising:
an ion storage device arranged to receive ions exiting the ion guide via a first exit, the ion storage device having a plurality of plate electrodes, wherein in a first operating mode an ion beam enters the ion storage device via an opening and wherein in a second operating mode an ion beam exits the ion storage device via the opening, and
a mass analyzer arranged to receive ions exiting the ion guide via a second exit. 39. A mass spectrometer comprising an ion guide, the ion guide comprising a plurality of plate electrodes, one or more inlets for receiving ions, and one or more outlets through which ions exit the ion guide, wherein in a first operating mode an ion beam enters the ion guide via a first opening and exits the ion guide via a second opening, and wherein in a second operating mode an ion beam enters the ion guide via the second opening. 40. A mass spectrometer according to claim 39, wherein in the second mode of operation the ion beam exits the ion guide via the first opening. 41. A mass spectrometer according to claim 39, wherein in the second mode of operation the ion beam exits the ion guide via a third opening different from the first and second openings. 42. A mass spectrometer comprising an ion storage device, the ion storage device comprising a plurality of plate electrodes, wherein in a first operating mode an ion beam enters the ion storage device via an opening and wherein in a second operating mode an ion beam exits the ion storage device via the same opening. 43. A mass spectrometer comprising an ion guide, the ion guide comprising a plurality of plate electrodes, an inlet for receiving ions, and an outlet through which ions exit the ion guide, the inlet having a first cross-sectional profile and a first cross-sectional area, the outlet having a second cross-sectional profile and a second cross-sectional area, the first cross-sectional profile being different from the second cross-sectional profile and/or the first cross-sectional area being different from the second cross-sectional area. 44. A mass spectrometer according to claim 43, wherein the first cross-sectional profile and/or the second cross-sectional profile have a substantially circular or oval cross-section. 45. A mass spectrometer according to claim 43, wherein the first cross-sectional profile and/or the second cross-sectional profile have a substantially rectangular or square cross-section. 46. A mass spectrometer according to claim 43, 44 or 45, wherein in use an ion beam is received by the ion guide, the ion beam having a third cross-sectional profile and a third cross-sectional area, the first cross-sectional profile and/or the first cross-sectional area being substantially equal to or similar to the third cross-sectional profile and/or the third cross-sectional area. 47. A mass spectrometer according to any one of claims 43 to 46, further comprising an ion optical device downstream of the ion guide, the entrance of the ion optical device having a fourth cross-sectional profile and a fourth cross-sectional area, the second cross-sectional profile and/or the second cross-sectional area being substantially equal to the fourth cross-sectional profile and/or the fourth cross-sectional area. 48. The mass spectrometer of claim 47, wherein the ion optical device comprises a device selected from the group comprising: (i) an ion guide having a substantially circular cross-sectional profile, (ii) a quadrupole mass filter/analyzer having a substantially circular cross-sectional profile, (iii) a transverse acceleration time of flight mass analyzer having a substantially square or rectangular cross-sectional profile, (iv) a magnetic sector analyzer having a substantially rectangular cross-sectional profile, (v) a Fourier transform ion cyclotron resonance mass analyzer ("FTICR mass analyzer") having a substantially circular cross-sectional profile, (vi) a two-dimensional (linear) quadrupole ion trap having a substantially circular cross-sectional profile, and (vii) a three-dimensional (Paul) quadrupole ion trap having a substantially circular cross-sectional profile. 49. A mass spectrometer according to any one of claims 43 to 48, wherein an ion guide region between the entrance and the exit (i) changes its size and/or its shape along the ion guide region or (ii) has a width and/or a height whose size progressively decreases. 50. A mass spectrometer according to any one of claims 43 to 49, wherein the ion guide further comprises a second entrance for receiving ions and/or a second exit via which ions exit the ion guide, wherein the second entrance has a fifth cross-sectional profile and a fifth cross-sectional area and the second exit has a sixth cross-sectional profile and a sixth cross-sectional area, wherein the fifth cross-sectional profile is different from the sixth cross-sectional profile and/or the fifth cross-sectional area is different from the sixth cross-sectional area. 51. A mass spectrometer according to claim 50, wherein the first cross-sectional profile and the first cross-sectional area and/or the second cross-sectional profile and the second cross-sectional area and/or the fifth cross-sectional profile and the fifth cross-sectional area and/or the sixth cross-sectional profile and the sixth cross-sectional area are different. 52. A mass spectrometer according to any preceding claim, wherein at least 50%, 60%, 70%, 80%, 90% or 95% of the plates are substantially parallel. 53. A mass spectrometer according to any preceding claim, wherein at least 50%, 60%, 70%, 80%, 90% or 95% of the plates are arranged in a first plane and the ion guide is curved in the first plane. 54. A mass spectrometer according to any preceding claim, wherein at least 50%, 60%, 70%, 80%, 90% or 95% of the plates are arranged at an entrance of the ion guide in a first plane and the ion guide is curved in a second plane orthogonal to the first plane. 55. A mass spectrometer according to any preceding claim, wherein at least 50%, 60%, 70%, 80%, 90% or 95% of the plates have substantially the same spacing. 56. A mass spectrometer according to any one of the preceding claims, wherein the plurality of plate electrodes comprise 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 or more than 20 plate electrodes. 57. A mass spectrometer according to any preceding claim, wherein the plate electrodes have a thickness selected from the following group: (i) less than or equal to 5 mm, (ii) less than or equal to 4.5 mm, (iii) less than or equal to 4 mm, (iv) less than or equal to 3.5 mm, (v) less than or equal to 3 mm, (vi) less than or equal to 2.5 mm, (vii) less than or equal to 2 mm, (viii) less than or equal to 1.5 mm, (ix) less than or equal to 1 mm, (x) less than or equal to 0.8 mm, (xi) less than or equal to 0.6 mm, (xii) less than or equal to 0.4 mm, (xiii) less than or equal to 0.2 mm, (xiv) less than or equal to 0.1 mm and (xv) less than or equal to 0.25 mm. 58. A mass spectrometer according to any one of the preceding claims, wherein the plate electrodes have a spacing selected from the following group: (i) less than or equal to 5 mm, (ii) less than or equal to 4.5 mm, (iii) less than or equal to 4 mm, (iv) less than or equal to 3.5 mm, (v) less than or equal to 3 mm, (vi) less than or equal to 2.5 mm, (vii) less than or equal to 2 mm, (viii) less than or equal to 1.5 mm, (ix) less than or equal to 1 mm, (x) less than or equal to 0.8 mm, (xi) less than or equal to 0.6 mm, (xii) less than or equal to 0.4 mm, (xiii) less than or equal to 0.2 mm, (xiv) less than or equal to 0.1 mm and (xv) less than or equal to 0.25 mm. 59. A mass spectrometer according to any one of the preceding claims, wherein an alternating or RF voltage is applied to the plate electrodes. 60. A mass spectrometer according to claim 59, wherein opposite phases of the AC or RF voltage are supplied to adjacent plate electrodes. 61. A mass spectrometer according to claim 59 or 60, wherein the AC or RF voltage has a frequency selected from the following group: (i) < 100 kHz, (ii) 100-200 kHz, (iii) 200-300 kHz, (iv) 300-400 kHz, (v) 400-500 kHz, (vi) 0.5-1.0 MHz, (vii) 1.0-1.5 MHz, (viii) 1.5-2.0 MHz, (ix) 2.0-2.5 MHz, (x) 2.5-3.0 MHz, (xi) 3.0-3.5 MHz, (xii) 3.5-4.0 MHz, (xiii) 4.0-4.5 MHz, (xiv) 4.5-5.0 MHz, (xv) 5.0-5.5 MHz, (xvi) 5.5-6.0 MHz, (xvii) 6.0-6.5 MHz, (xviii) 6.5-7.0 MHz, (xix) 7.0-7.5 MHz, (xx) 7.5-8.0 MHz, (xxi) 8.0-8.5 MHz, (xxii) 8.5-9.0 MHz, (xxiii) 9.0-9.5 MHz, (xxiv) 9.5-10.0 MHz and (xxv) > 10.0 MHz. 62. A mass spectrometer according to claim 59, 60 or 61, wherein the amplitude of the AC or RF voltage is selected from the group consisting of: (i) < 50 V peak to peak, (ii) 50-100 V peak to peak, (iii) 100-150 V peak to peak, (iv) 150-200 V peak to peak, (v) 200-250 V peak to peak, (vi) 250-300 V peak to peak, (vii) 300-350 V peak to peak, (viii) 350-400 V peak to peak, (ix) 400-450 V peak to peak, (x) 450-500 V peak to peak, and (xi) > 500 V peak to peak. 63. A mass spectrometer according to any preceding claim, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) greater than or equal to 0.0001 mbar, (ii) greater than or equal to 0.0005 mbar, (iii) greater than or equal to 0.001 mbar, (iv) greater than or equal to 0.005 mbar, (v) greater than or equal to 0.01 mbar, (vi) greater than or equal to 0.05 mbar, (vii) greater than or equal to 0.1 mbar, (viii) greater than or equal to 0.5 mbar, (ix) greater than or equal to 1 mbar, (x) greater than or equal to 5 mbar, and (xi) greater than or equal to 10 mbar. 64. A mass spectrometer according to any preceding claim, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) less than or equal to 10 mbar, (ii) less than or equal to 5 mbar, (iii) less than or equal to 1 mbar, (iv) less than or equal to 0.5 mbar, (v) less than or equal to 0.1 mbar, (vi) less than or equal to 0.05 mbar, (vii) less than or equal to 0.01 mbar, (viii) less than or equal to 0.005 mbar, (ix) less than or equal to 0.001 mbar, (x) less than or equal to 0.0005 mbar, and (xi) less than or equal to 0.0001 mbar. 65. A mass spectrometer according to any preceding claim, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) between 0.0001 and 10 mbar, (ii) between 0.0001 and 1 mbar, (iii) between 0.0001 and 0.1 mbar, (iv) between 0.0001 and 0.01 mbar, (v) between 0.0001 and 0.001 mbar, (vi) between 0.001 and 10 mbar, (vii) between 0.001 and 1 mbar, (viii) between 0.001 and 0.1 mbar, (ix) between 0.001 and 0.01 mbar, (x) between 0.01 and 10 mbar, (xi) between 0.01 and 1 mbar, (xii) between 0.01 and 0.1 mbar, (xiii) between 0.1 and 10 mbar, (xiv) between 0.1 and 1 mbar and (xv) between 1 and 10 mbar. 66. A mass spectrometer according to any one of claims 1 to 62, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) greater than or equal to 1 × 10 ^-7 mbar, (ii) greater than or equal to 5 × 10 ^-7 mbar, (iii) greater than or equal to 1 × 10 ^-6 mbar, (iv) greater than or equal to 5 × 10 ^-6 mbar, (v) greater than or equal to 1 × 10 ^-5 mbar, and (vi) greater than or equal to 5 × 10 ^-5 mbar. 67. A mass spectrometer according to any one of claims 1 to 62, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) less than or equal to 1 × 10 ^-4 mbar, (ii) less than or equal to 5 × 10 ^-5 mbar, (iii) less than or equal to 1 × 10 ^-5 mbar, (iv) less than or equal to 5 × 10 ^-6 mbar, (v) less than or equal to 1 × 10 ^-6 mbar, (vi) less than or equal to 5 × 10 ^-7 mbar, and (vii) less than or equal to 1 × 10 ^-7 mbar. 68. A mass spectrometer according to any one of claims 1 to 62, wherein the ion guide is maintained in use at a pressure selected from the group consisting of: (i) between 1 × 10 ^-7 and 1 × 10 ^-4 mbar, (ii) between 1 × 10 ^-7 and 5 × 10 ^-5 mbar, (iii) between 1 × 10 ^-7 and 1 × 10 ^-5 mbar, (iv) between 1 × 10 ^-7 and 5 × 10 ^-6 mbar, (v) between 1 × 10 ^-7 and 1 × 10 ^-6 mbar, (vi) between 1 × 10 ^-7 and 5 × 10 ^-7 mbar, (vii) between 5 × 10 ^-7 and 1 × 10 ^-4 mbar, (viii) between 5 × 10 ^-7 and 5 × 10 ^-5 mbar, (ix) between 5 × 10 ^-7 and 1 × 10 ^-5 mbar, (x) between 5 × 10 ^-7 and 5 × 10 ^-6 mbar, (xi) between 5 × 10 ^-7 and 1 × 10 ^-6 mbar, (xii) between 1 × 10 ^-6 and 1 × 10 ^-4 mbar, (xiii) between 1 × 10 ^-6 and 5 × 10 ^-5 mbar, (xiv) between 1 × 10 ^-6 and 1 × 10 ^-5 mbar, (xv) between 1 × 10 ^-6 and 5 × 10 ^-6 mbar, (xvi) between 5 × 10 ^-6 and 1 × 10 ^-4 mbar, (xvii) between 5 × 10 ^-6 and 5 × 10 ^-5 mbar, (xviii) between 5 × 10 ^-6 and 1 × 10 ^-5 mbar, (xix) between 1 × 10 ^-5 and 1 × 10 ^-4 mbar, (xx) between 1 × 10 ^-5 and 5 × 10 ^-5 mbar and (xxi) between 5 × 10 ^-5 and 1 × 10 ^-4 mbar. 69. A mass spectrometer according to any preceding claim, wherein the ion guide further comprises a first outer plate electrode disposed on a first side of the ion guide and a second outer plate electrode disposed on a second side of the ion guide. 70. A mass spectrometer according to claim 69, wherein the first outer plate electrode and/or the second outer plate electrode are biased to a DC bias with respect to the average voltage of the plate electrodes to which an AC or RF voltage is applied. 71. A mass spectrometer according to claim 70, wherein the bias voltage is selected from the following group: (i) less than -10 V, (ii) -9 to -8 V, (iii) -8 to -7 V, (iv) -7 to -6 V, (v) -6 to -5 V, (vi) -5 to -4 V, (vii) -4 to -3 V, (viii) -3 to -2 V, (ix) -2 to -1 V, (x) -1 to 0 V, (xi) 0 to 1 V, (xii) 1 to 2 V, (xiii) 2 to 3 V, (xiv) 3 to 4 V, (xv) 4 to 5 V, (xvi) 5 to 6 V, (xvii) 6 to 7 V, (xviii) 7 to 8 V, (xix) 8 to 9 V, (xx) 9 to 10 V and (xxi) more than 10 V. 72. A mass spectrometer according to claim 70, wherein a pure DC voltage is applied to the first outer plate electrode and/or the second outer plate electrode in use. 73. A mass spectrometer according to claim 70, wherein a pure AC or RF voltage is applied to the first outer plate electrode and/or the second outer plate electrode in use. 74. A mass spectrometer according to claim 70, wherein a DC voltage and an AC or RF voltage are applied to the first outer plate electrode and/or the second outer plate electrode in use. 75. A mass spectrometer according to any one of claims 69 to 74, further comprising an ion and/or gas and/or laser beam aperture disposed in the first outer plate electrode. 76. A mass spectrometer according to any one of claims 69 to 75, further comprising an ion and/or gas and/or laser aperture disposed in the second outer plate electrode. 77. A mass spectrometer according to any preceding claim, wherein one or more of the plate electrodes are maintained in use at a different DC potential from the other plate electrodes so that a plurality of discrete ion guide regions are formed within the ion guide. 78. A mass spectrometer according to any preceding claim, wherein a plurality of the plate electrodes are maintained at different DC potentials. 79. A mass spectrometer according to claim 78, wherein the ion guide comprises a first outer section, a second outer section and an intermediate section between the first and second outer sections, and wherein the DC potential at which the plate electrodes are maintained is increased in the first and/or second outer sections with respect to the intermediate section so that ions are directed back to a central region of the ion guide. 80. A mass spectrometer according to any preceding claim, wherein one or more transient DC potentials or one or more DC potential waveforms are applied to the plate electrodes. 81. A mass spectrometer according to claim 80, wherein the one or more transient DC potentials or the one or more DC potential waveforms force ions from one region of the ion guide to another region of the ion guide. 82. Mass spectrometer with an ion guide, which comprises:
several electrode layers and
several insulator layers interspersed or nested between the electrode layers. 83. A mass spectrometer according to claim 82, wherein at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of the electrode layers are disposed on or deposited on the insulator layers. 84. A mass spectrometer with an AC or RF ion guide, the ion guide comprising:
several electrodes and
several insulators interspersed or nested between the electrodes,
wherein the electrodes are mounted on or deposited on the insulators. 85. A mass spectrometer according to claim 82, 83 or 84, wherein the ion guide has an ion entrance and an ion exit and wherein gas molecules within the ion guide are substantially prevented from exiting the ion guide at a location other than through the ion entrance or the ion exit. 86. Mass spectrometer comprising:
a first ion guide,
a gas collision/reaction cell,
a second ion guide downstream of the gas collision/reaction cell, the second ion guide having a plurality of plate electrodes, an entrance for receiving ions, an ion guiding region through the second ion guide, and an exit through which ions exit the second ion guide, wherein there is no direct line of sight from the entrance to the exit. 87. The mass spectrometer of claim 86, further comprising an ion source selected from the group consisting of: (i) an electrospray ion source ("ESI ion source"), (ii) an atmospheric pressure chemical ionization ion source ("APCI ion source"), (iii) an atmospheric pressure photoionization ion source ("APPI ion source"), (iv) a matrix assisted laser desorption ionization ion source ("MALDI ion source"), (v) a laser desorption ionization ion source ("LDI ion source"), (vi) an inductively coupled plasma ion source ("ICP ion source"), (vii) an electron impact ion source ("EI ion source"), (viii) a chemical ionization ion source ("CI ion source"), (ix) a fast atom bombardment ion source ("FAB ion source"), and (x) a Liquid secondary ion mass spectrometry ion source ("LSIMS ion source"). 88. A mass spectrometer according to claim 86 or 87, further comprising a mass analyzer disposed downstream of the second ion guide, the mass analyzer being selected from the group comprising: (i) a time-of-flight mass analyzer, (ii) a quadrupole mass analyzer, (iii) a Fourier transform ion cyclotron resonance ("FTICR") mass analyzer, (iv) a two-dimensional (linear) quadrupole ion trap, (v) a three-dimensional (Paul) quadrupole ion trap, and (vi) a magnetic sector mass analyzer.