1. Field of the Invention
The present invention relates to a mass spectrometer and a method of mass spectrometry.
2. Discussion of the Prior Art
A known collision cell comprises a plurality of electrodes with an RF voltage applied between neighbouring electrodes so that ions are radially confined within the collision cell. Ions are arranged to enter the collision cell with energies typically in the range 10-1000 eV and undergo multiple collisions with gas molecules within the collision cell. These collisions cause the ions to fragment or decompose.
Gas reaction cells are also similarly known wherein ions are arranged to enter the reaction cell with energies typically in the range 0.1-10 eV. The ions undergo collisions with gas molecules but instead of fragmenting the ions tend to react with the gas molecules forming product ions.
When an ion collides with a gas molecule it may get scattered and lose kinetic energy. However, the ion is not lost from the collision cell since it is radially confined within the collision cell by the applied RF voltage. If an ion undergoes a large number of collisions, perhaps more than 100 collisions, then the ion will effectively lose all its forward kinetic energy. Such ions will now have a mean energy substantially equal to that of the surrounding gas molecules i.e. they will have become thermalized. The thermalized ions will now appear to move randomly within the gas due to continuing random collisions with gas molecules. Some ions may therefore be expected to remain within the collision cell for a relatively long period of time.
In practice ions are nonetheless observed to exit the collision cell after some delay. It is generally thought that ions continue to move relatively slowly forwards through the collision cell due to the bulk movement of gas which effectively forces ions through the collision cell. It is also thought that space charge effects caused by the continual ingress of ions into the collision cell also act to force ions through the collision cell. Ions within the collision cell therefore experience electrostatic repulsion from ions arriving from behind and this effectively pushes the ions through the collision cell.
As will be appreciated from the above, ion transit times through known RF collision and reaction cells can be relatively long due to ions losing their forward kinetic energy through multiple collisions with the collision gas. The continued presence or absence of an incoming ion beam and any surface charging leading to axial potential barriers can further adversely affect the transit time.
A relatively long ion transit time through a collision cell can significantly affect the performance of a mass spectrometer. For example, ions are required to have a relatively fast transit time through a collision cell when performing Multiple Reaction Monitoring (MRM) experiments using a triple quadrupole mass spectrometer. A fast transit time is also required when rapidly switching to different product ion spectra acquisitions using a hybrid quadrupolexe2x80x94Time of Flight mass spectrometer. When a mass spectrometer switches rapidly between various different parent ions, then if the resultant fragment ions formed within the collision cell exit the collision cell relatively slowly then significant quantities of fragment ions may still be present in the subsequent acquisition. This therefore causes a memory effect or crosstalk.
A known method of reducing crosstalk is to reduce the RF voltage to a low enough level in the period between measurements so that ions are no longer confined within the collision cell and consequently leak away. However, it takes a certain amount of time for the collision cell to re-fill with ions after the RF voltage has been reduced and hence if short inter-acquisition times are desired then the collision cell may not be sufficiently full before the next acquisition commences. This has the effect of reducing sensitivity which becomes more acute at shorter acquisition times.
Another situation where ions need to be rapidly transmitted through the collision cell is when a mass spectrometer is operated in a parent ion scanning mode. According to this made of operation only a specific fragment ion is set to be transmitted by a mass filter downstream of a collision cell of a tandem mass spectrometer (e.g. a triple quadrupole mass spectrometer) whilst a mass analyser upstream of the collision cell is scanned. When a specific fragment ion is observed, the parent ion which was fragmented to produce the specific fragment ion can then be determined. In theory a large number of parent ions admitted to the collision cell could have given rise to the specific fragment ion. The aim of such experiments is to screen for all components belonging to a particular class of compounds that may be recognised by a common fragment ion or to discover all parent ions that may contain a particular sub-component such as the phosphate functional group in phosphorylated peptides. However, if the transit time of ions through the collision cell is relatively long then the parent ions appear to become smeared across a number of masses and consequently resolution is reduced together with sensitivity. This effect is particularly exacerbated when the mass analyser upstream of the collision cell is scanned at a relatively high scan rate when sensitivity may be completely lost.
Neutral loss/gain scanning modes of operation are also used wherein both the mass analyser upstream of the collision cell and the mass filter/analyser downstream of the collision cell are scanned synchronously with a constant mass offset to identify those parent ions which fragment through loss of a specific functional group or react to form a specific product ion with a specific mass difference. A long transit time for ions through the collision cell may cause peak smearing but since the mass analyser downstream of the collision cell is scanning the smearing is not observed. The resultant effect is a loss of sensitivity and resolution (even though the loss of resolution may be obscured) which is again exacerbated at higher scan rates.
Long transit times are also a problem with reaction cells. Ions are typically injected into reaction cells with relatively low energies and RF confinement is used to cause the ions to interact with a background buffer gas and/or a reagent gas. Any axial velocity component above thermal levels is effectively lost and the ions can become effectively stranded within the reaction cell. In some situations, such as with short reaction cells, the ions may be deliberately trapped by application of trapping voltages at the entrance and exit of the reaction cell. This prolongs the ion-molecule interaction times but when the trapping voltages are removed the ions have no specific impetus towards the exit. Some ions will eventually diffuse to the exit but the duty cycle is poor and there is a risk of crosstalk with subsequent trapping cycles. It is therefore known to reduce the RF voltage applied to the reaction cell between experiments to a level such that ions are no longer confined within the reaction cell.
With pulsed ion sources such as Laser Desorption Ionisation (xe2x80x9cLDIxe2x80x9d) and Matrix Assisted Laser Desorption Ionization (xe2x80x9cMALDIxe2x80x9d) ion sources the impetus of ions being effectively pushed through the collision cell by the space charge repulsion from continual ingress of ions is either not effectively present or is severely reduced consequently, ions from one pulse, or laser shot, can become merged with those from the next pulse and so on. Pulsed ion sources can advantageously be coupled to a discontinuous mass analyser such as a Time of Flight mass spectrometer, an ion trap mass spectrometer or a Fourier Transform Ion Cyclotron Resonance (xe2x80x9cFTICRxe2x80x9d) mass spectrometer so that the operation of the mass analyzer can be synchronised with the pulses of ions emitted from the ion source. This enables the duty cycle for sampling ions and therefore sensitivity to be maximised. The smearing of each pulse of ions and the subsequent merging of one pulse with the next can compromise the opportunity to synchronise the mass analyser with the pulsed ion source. Hence it is no longer possible to maintain a high duty cycle and therefore sensitivity.
It is therefore desired to provide an improved fragmentation, collision, reaction or cooling cell for a mass spectrometer.
According to an aspect of the present invention there is provided a mass spectrometer comprising:
a fragmentation device comprising a plurality of electrodes wherein, in use, one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are urged along the fragmentation device.
An axial voltage gradient may be provided along at least a portion of the length of the fragmentation device which varies with time whilst ions are being transmitted through the fragmentation device.
The fragmentation device may comprise at least a first electrode held at a first reference potential, a second electrode held at a second reference potential, and a third electrode held at a third reference potential, wherein:
at a first time t1 a first DC voltage is supplied to the first electrode so that the first electrode is held at a first potential above or below the first reference potential;
at a second later time t2 a second DC voltage is supplied to the second electrode so that the second electrode is held at a second potential above or below the second reference potential; and
at a third later time t3 a third DC voltage is supplied to the third electrode so that the third electrode is held at a third potential above or below the third reference potential.
Preferably, at the first time t1 the second electrode is at the second reference potential and the third electrode is at the third reference potential;
at the second tire t2 the first electrode is at the first potential and the third electrode is at the third reference potential; and
at the third time t3 the first electrode is at the first potential and the second electrode is at the second potential.
Alternatively, at the first time t1 the second electrode is at the second reference potential and the third electrode is at the third reference potential;
at the second time t2 the first electrode is no longer supplied with the first DC voltage so that the first electrode is returned to the first reference potential and the third electrode is at the third reference potential; and
at the third time t3 the second electrode is no longer supplied with the second DC voltage so that the second electrode is returned to the second reference potential and the first electrode is at the first reference potential.
Preferably, the first, second and third reference potentials are substantially the sate. The first, second and third DC voltages are also preferably substantially the same. Preferably, the first, second and third potentials are substantially the same.
According to an embodiment the fragmentation device comprises 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30 segments, wherein each segment comprises 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30 electrodes and wherein the electrodes in a segment are maintained at substantially the same DC potential. Preferably, a plurality of segments are maintained at substantially the same DC potential. According to an embodiment each segment is maintained at substantially the same DC potential as the subsequent nth segment wherein n is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or  greater than 30.
Ions are preferably confined radially within the fragmentation device by an AC or RF electric field. Ions are preferably radially confined within the fragmentation device in a pseudo-potential well and are constrained axially by a real potential barrier or well.
The transit time of ions through the fragmentation device is preferably selected from the group consisting of: (i) less than or equal to 20 ms; (ii) less than or equal to 10 ms; (iii) less than or equal to 5 ms; (iv) less than or equal to 1 ms; and (v) less than or equal to 0.5 Ms.
According to the preferred embodiment at least 50%, 60%, 70%, 80%, 90% or 95% of the ions entering the fragmentation device are arranged to have, in use, an energy greater than or equal to 10 eV for a singly charged ion or greater than or equal to 20 eV for a doubly charged ion such that the ions are caused to fragment. Preferably, at least 50%, 60%, 70%, 80%, 90% or 95% of the ions entering the fragmentation device are arranged to fragment upon colliding with collision gas within the fragmentation device.
Preferably, the fragmentation device 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, the fragmentation device 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 fragmentation device is maintained, in use, at a pressure selected prom 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.
The fragmentation device is preferably maintained, in use, at a pressure such that a viscous drag is imposed upon ions passing through the fragmentation device.
One or more transient DC voltages or one or more transient DC voltage waveforms are preferably initially provided at a first axial position and are then subsequently provided at second, then third different axial positions along the fragmentation device.
Preferably, the one or more transient DC voltages or the one or more transient DC voltage waveforms move in use from one end of the fragmentation device to another end of the fragmentation device so that ions are urged along the fragmentation device.
The one or more transient DC voltages preferably create: (i) a potential hill or barrier; (ii) a potential well; (iii) multiple potential hills or barriers; (iv) multiple potential wells; (v) a combination of a potential hill or barrier and a potential well; or (vi) a combination of multiple potential hills or barriers and multiple potential wells.
The one or more transient DC voltage waveforms preferably comprise a repeating waveform such as a square wave.
The amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms preferably remains substantially constant with time. Alternatively, the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms varies with time. For example, the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms may either; (i) increases with time; (ii) increases then decreases with time; (iii) decreases with time; or (iv) decreases then increases with time.
The fragmentation device preferably comprises an upstream entrance region, a downstream exit region and an intermediate region, wherein:
in the entrance region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a first amplitude;
in the intermediate region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a second amplitude; and
in the exit region the amplitude of the one or more transient DC voltages or the one or more transient DC voltage waveforms has a third amplitude.
Preferably, the entrance and/or exit region comprise a proportion of the total axial length of the fragmentation device selected from the group consisting of; (i)  less than 5%; (ii) 5-10%; (iii) 10-15%; (iv) 15-20%; (v) 20-25%; (vi) 25-30%; (vii) 30-35%; (viii) 35-40%; and (ix) 40-45%.
The first and/or third amplitudes are preferably substantially zero and the second amplitude is preferably substantially non-zero.
The second amplitude is preferably larger than the first amplitude and/or the second amplitude is larger than the third amplitude.
Preferably, one or more transient DC voltages or one or more transient DC voltage waveforms pass in use along the fragmentation device with a first velocity. The first velocity preferably either: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; (vi) decreases then increases; (vii) reduces to substantially zero; (viii) reverses direction; or (ix) reduces to substantially zero and then reverses direction.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably cause ions within the fragmentation device to pass along the fragmentation device with a second velocity.
The difference between the first velocity and the second velocity is preferably less than or equal to 100 m/s, 90 m/s, 80 m/s, 70 m/s, 60 m/s, 50 m/s, 40 m/s, 30 m/s, 20 m/s, 10 m/s, 5 m/s or 1 m/s.
The first velocity is preferably selected from the group consisting of: (i) 10-250 m/s; (ii) 250-500 m/s; (iii) 500-750 m/s; (iv) 750-1000 m/s; (v) 1000-1250 m/s; (vi) 1250-1500 m/s; (vii) 1500-1750 m/s; (viii) 1750-2000 m/s; (ix) 2000-2250 m/s; (x) 2250-2500 m/s; (xi) 2500-2750 m/s; (xii) 2750-3000 m/s; (Xiii) 3000-3250 m/s; (xiv) 3250-3500 m/s; (xv) 3500-3750 m/s; (xvi) 3750-4000 m/s; (xvii) 4000-4250 m/s; (xviii) 4250-4500 m/s; (xix) 4500-4750 m/s; (xx) 4750-5000 m/s; and (xxi)  greater than 5000 m/s.
The second velocity is preferably selected from the group consisting of: (i) 10-250 m/s; (ii) 250-500 m/s; (iii) 500-750 m/s; (iv) 750-1000 m/s; (v) 1000-1250 m/s; (vi) 1250-1500 m/s; (vii) 1500-1750 m/s; (viii) 1750-2000 m/s; (ix) 2000-2250 m/s; (x) 2250-2500 m/s; (xi) 2500-2750 m/s; (xii) 2750-3000 m/s; (xiii) 3000-3250 m/s; (xiv) 3250-3500 m/s; (xv) 3500-3750 m/s; (xvi) 3750-4000 m/s; (xvii) 4000-4250 m/s; (xviii) 4250-4500 m/s; (xix) 4500-4750 m/s; (xx) 4750-5000 m/s; and (xxi)  greater than 5000 m/s.
Preferably, the second velocity is substantially the same as the first velocity.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably have a frequency, and wherein the frequency; (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
The one or more transient DC voltages or the one or more transient DC voltage waveforms preferably has a wavelength, and wherein the wavelength: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
According to an embodiment two or more transient DC voltages or two or more transient DC waveforms are arranged to pass simultaneously along the fragmentation device. The two or more transient DC voltages or the two or more transient DC waveforms may be arranged to move: (i) in the same direction; (ii) in opposite directions; (iii) towards each other; or (iv) away from each other.
The one or more transient DC voltages or the one or more transient DC waveforms may be repeatedly generated and passed in use along the fragmentation device. The frequency of generating the one or more transient DC voltages or the one or more transient DC voltage waveforms preferably: (i) remains substantially constant; (ii) varies; (iii) increases; (iv) increases then decreases; (v) decreases; or (vi) decreases then increases.
According to an embodiment a continuous beam of ions is received at an entrance to the fragmentation device. Alternatively, packets of ions are received at an entrance to the fragmentation device.
According to the preferred embodiment pulses of ions emerge from an exit of the fragmentation device.
The mass spectrometer preferably further comprises an ion detector, the ion detector being arranged to be substantially phase locked in use with the pulses of ions emerging from the exit of the fragmentation device.
The mass spectrometer preferably further comprises a Time of Flight mass analyser comprising an electrode for injecting ions into a drift region, the electrode being arranged to be energised in use in a substantially synchronised manner with the pulses of ions emerging from the exit of the fragmentation device.
Other embodiments are also contemplated wherein the mass spectrometer further comprises an ion trap arranged downstream of the ion guide, the ion trap being arranged to store and/or release ions from the ion trap in a substantially synchronised manner with the pulses of ions emerging from the exit of the ion guide.
Another embodiment is contemplated wherein the mass spectrometer further comprises an mass filter arranged downstream of the ion guide, wherein a mass to charge ratio transmission window of the mass filter is varied in a substantially synchronised manner with the pulses of ions emerging from the exit of the ion guide.
The fragmentation device may comprise an ion funnel comprising a plurality of electrodes having apertures therein through which ions are transmitted, wherein the diameter of the apertures becomes progressively smaller or larger. Alternatively, the fragmentation device may comprise an ion tunnel comprising a plurality of electrodes having apertures therein through which ions are transmitted, wherein the diameter of the apertures remains substantially constant. The fragmentation device may comprise a stack of plate, ring or wire loop electrodes.
The fragmentation device may comprise a plurality of electrodes, each electrode having an aperture through which ions are transmitted in use. Each electrode preferably has a substantially circular aperture. Preferably, each electrode has a single aperture through which ions are transmitted in use.
Preferably, the diameter of the apertures of at least 50%, 60%, 70%, 80%, 90% or 95% of the electrodes forming the fragmentation device is selected from the group consisting of: (i) less than or equal to 10 mm; (ii) less than or equal to 9 mm; (iii) less than or equal to 8 mm; (iv) less than or equal to 7 mm; (v) less than or equal to 6 mm; (vi) less than or equal to 5 mm; (vii) less than or equal to 4 mm; (viii) less than or equal to 3 mm; (ix) less than or equal to 2 mm; and (x) less than or equal to 1 mm.
At least 50%, 60%, 70%, 80%, 90% or 95% of the electrodes forming the fragmentation device preferably have apertures which are substantially the same size or area.
According to a less preferred embodiment the fragmentation device comprises a segmented rod set.
Preferably, the fragmentation device consists of; (i) 10-20 electrodes; (ii) 20-30 electrodes; (iii) 30-40 electrodes; (iv) 40-50 electrodes; (v) 50-60 electrodes; (vi) 60-70 electrodes; (vii) 70-80 electrodes; (viii) 80-90 electrodes; (ix) 90-100 electrodes; (x) 100-110 electrodes; (xi) 110-120 electrodes; (xii) 120-130 electrodes; (xiii) 130-140 electrodes; (xiv) 140-150 electrodes; or (xv) more than 150 electrodes.
The thickness of at least 50%, 60%, 70%, 80%, 90% or 95% of the electrodes is preferably selected from the group consisting of: (i) less than or equal to 3 mm; (ii) less than or equal to 2.5 mm; (iii) less than or equal to 2.0 mm; (iv) less than or equal to 1.5 mm; (v) less than or equal to 1.0 mm; and (vi) less than or equal to 0.5 mm.
The fragmentation device preferably has a length selected from the group consisting of: (i) less than 5 cm; (ii) 5-10 cm; (iii) 10-15 cm; (iv) 15-20 cm; (v) 20-25 cm; (vi) 25-30 cm; and (vii) greater than 30 cm.
The fragmentation device preferably comprises a housing having an upstream opening for allowing ions to enter the fragmentation device and a downstream opening for allowing ions to exit the fragmentation device.
The fragmentation device may further comprise an inlet port through which a collision gas is introduced. The collision gas may comprise air and/or one or more inert gases and/or one or more non-inert gases. Preferably, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the electrodes are connected to both a DC and an AC or RF voltage supply. Axially adjacent electrodes are preferably supplied with AC or RF voltages having a phase difference of 180xc2x0.
The mass spectrometer may comprise an ion source selected from the group consisting of: (i) Electrospray (xe2x80x9cESIxe2x80x9d) ion source; (ii) Atmospheric Pressure Chemical Ionisation (xe2x80x9cAPCIxe2x80x9d) ion source; (iii) Atmospheric Pressure Photo Ionisation (xe2x80x9cAAPPIxe2x80x9d) ion source; (iv) Matrix Assisted Laser Desorption Ionisation (xe2x80x9cMALDIxe2x80x9d) ion source; (v) Laser Desorption Ionisation (xe2x80x9cLDIxe2x80x9d) ion source; (vi) Inductively Coupled Plasma (xe2x80x9cICPxe2x80x9d) ion source; (vii) Electron Impact (xe2x80x9cEIxe2x80x9d) ion source; (viii) Chemical Ionisation (xe2x80x9cCIxe2x80x9d) ion source; (ix) a Fast Atom Bombardment (xe2x80x9cFABxe2x80x9d) ion source; and (x) a Liquid Secondary Ions Mass Spectrometry (xe2x80x9cLSIMSxe2x80x9d) ion source.
The ion source may comprise a continuous ion source or a pulsed ion source.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
a reaction cell wherein in use ions react and/or exchange charge with a gas in the reaction cell, the reaction cell comprising a plurality of electrodes wherein, in use, one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are urged along the reaction cell.
All the preferred features discussed above in relation to a collision cell are equally applicable to a reaction cell according to a preferred embodiment.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
a cell comprising a gas for damping, collisionally cooling, decelerating, axially focusing or otherwise thermalising ions without substantially fragmenting the ions, the cell comprising a plurality of electrodes wherein, in use, one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are urged along the cell.
All the preferred features discussed above in relation to a collision cell are equally applicable to a cell comprising a gas for damping, collisionally cooling, decelerating, axially focusing or otherwise thermalising ions according to a preferred embodiment.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
an ion source;
a mass filter;
a fragmentation device comprising a plurality of electrodes wherein, in use, one or more transient DC voltages or one or more transient DC voltage waveforms are progressively applied to the electrodes so that ions are urged along the fragmentation device; and
a mass analyser.
An ion guide may be arranged upstream of the mass filter. The ion guide preferably comprises a plurality of electrodes wherein at least some of the electrodes are connected to both a DC and an AC or RF voltage supply. One or more transient DC voltages or one or more transient DC voltage waveforms may be passed in use along at least a portion of the length of the ion guide to urge ions along the portion of the length of the ion guide.
The mass filter may comprise a quadrupole mass filter. The mass analyser may comprise a Time of Flight mass analyser, a quadrupole mass analyser or a Fourier Transform Ion Cyclotron Resonance (xe2x80x9cFTICRxe2x80x9d) mass analyser. The mass analyser may also comprise a 2D (linear) quadrupole ion trap or a 3D (Paul) quadrupole ion trap.
According to another aspect of the present invention there is provided a mass spectrometer comprising:
a fragmentation device comprising a plurality of electrodes having apertures, wherein ions are radially confined within the fragmentation device by an AC or RF voltage such that adjacent electrodes have a phase difference of 180xc2x0, and wherein one or more DC voltage pulses or one or more transient DC voltage waveforms are applied successively to a plurality of the electrodes so that ions are urged towards an exit of the fragmentation device and have a transit time of less than 20 ms through the fragmentation device.
According to another aspect of the present invention there is provided a mass spectrometer comprising a fragmentation device having a plurality of electrodes wherein one or more DC voltage pulses or one or more transient DC voltage waveforms are applied to successive electrodes.
According to another aspect of the present invention there is provided a method of mass spectrometry comprising:
providing a fragmentation device comprising a plurality of electrodes; and
progressively applying one or more transient DC voltages or one or more transient DC voltage waveforms to the electrodes so that ions are fragmented within the fragmentation device and are urged along the fragmentation device.
Preferably, the step of progressively applying one or more transient DC voltages or one or more transient DC voltage waveforms comprises maintaining an axial voltage gradient which varies with time whilst ions are being transmitted through the fragmentation device.
Preferably, the one or more transient DC voltages or the one or more transient DC voltage waveforms are passed along the fragmentation device with a first velocity.
The first velocity is preferably selected from the group consisting of: (i) 10-250 m/s; (ii) 250-500 m/s; (iii) 500-750 m/s; (iv) 750-1000 m/s; (v) 1000-1250 m/s; (vi) 1250-1500 m/s; (vii) 1500-1750 m/s; (viii) 1750-2000 m/s; (ix) 2000-2250 m/s; (x) 2250-2500 m/s; (xi) 2500-2750 m/s; (xii) 2750-3000 m/s; (xiii) 3000-3250 m/s; (xiv) 3250-3500 m/s; (xv) 3500-3750 m/s; (xvi) 3750-4000 m/s; (xvii) 4000-4250 m/s; (xviii) 4250-4500 m/s; (xix) 4500-4750 m/s; (xx) 4750-5000 m/s; and (xxi)  greater than 5000 m/s.
According to another aspect of the present invention there is provided a method of reacting ions and/or exchanging the charge of ions with a gas comprising:
providing a reaction cell comprising a plurality of electrodes; and
progressively applying one or more transient DC voltages or one or more transient DC voltage waveforms to the electrodes so that ions are urged along the reaction cell.
According to another aspect of the present invention there is provided a method of damping, collisionally cooling, decelerating, axially focusing or otherwise thermalizing ions without substantially fragmenting the ions comprising:
providing a cell comprising a plurality of electrodes; and
progressively applying one or more transient DC voltages to the electrodes so that ions are urged along the cell.
According to one embodiment a repeating pattern of DC electrical potentials is superimposed along the length of a collision, reaction or cooling cell so as to form a periodic DC potential waveform. The DC waveform may then be caused to effectively travel along the collision, reaction or cooling cell in the direction and at a velocity at which it is desired to move the ions.
The collision, reaction or cooling cell preferably comprises an AC or RF cell such as a multipole rod set or stacked ring set which is segmented in the axial direction so that independent transient DC potentials can be applied to each segment such transient DC potentials are preferably superimposed on top of the RF radially confining voltage and also on top of any constant DC offset voltage which may be applied to all the electrodes forming the cell. The transient DC potentials applied to the electrodes generate a travelling DC potential wave in the axial direction.
At any instant in time a voltage gradient is generated between segments which has the effect of pushing or pulling ions in a certain direction. As the ions move in the required direction the DC voltage gradient also moves. The individual DC voltages on each of the segments may be programmed to create a required waveform. Furthermore, the individual DC voltages on each of the segments may be programmed to change in synchronism so that a waveform is maintained but translated in the direction in which it is required to move the ions. No constant axial DC voltage gradient is required although less preferably one may be provided.