GB2504416A - Damping the movement of a solenoid actuated component within a mass spectrometer by the induction of eddy currents - Google Patents

Abstract

A device for damping oscillations of a component, e.g. the variable slit 1 of a magnetic sector mass spectrometer, is disclosed comprising: one or more inserts (not shown) arranged to be inserted between a solenoid coil 5 and a permanent magnet 4 to which the component is attached; wherein relative movement 7 between the permanent magnet 4 and the solenoid coil 5 induces eddy currents within the one or more inserts which result in the generation of an electromagnetic damping force. The insert preferably comprises a non-ferritic, non-magnetic, electrically conductive metal, alloy, ceramic or composite material, e.g. copper or a copper alloy. The component preferably comprises a mass-resolving slit, but may alternatively be a corona pin, electrostatic plate, or a gas or liquid nozzle.

Description

Intellectual Property Office Applicacion Nc,. (lB 1312526.3 RTM Dacc:2% Dircinbcr 2013 The following terms are registered trade marks and should he rcad as such wherever they occur in this document: Orbitrap Inlelleclual Property Office is an operaling name of the Pateni Office www.ipo.gov.uk

METHOD OF DAMPING THE MOVEMENT OF A SOLENOID ACTUATED SLIT WITHIN A

MASS SPECTROMETER BY THE INDUCTION OF EDDY CURRENTS

CROSS-REFERENCE TO RELATED APPLICATION None.

BACKGROUND TO THE PRESENT INVENTION

The present invention relates to a magnetic sector mass spectrometer.

Magnetic sector mass spectrometers are known which utilise variable slits in order to attenuate and define an ion beam at specific focal points within the instrument.

It is known to provide a slit which uses a magnet within a solenoid coil in order to provide the motive force necessary to vary the width of the slit.

However, one problem with such known magnetic sector mass spectrometers is that the process of changing the width of the slits using the solenoid can cause the position of the slits to oscillate. Furthermore, even if the position of the slits of the magnetic sector mass spectrometer are not deliberately varied then the slits may still oscillate due to environmental vibrations.

It will be apparent, therefore, that the slits of known magnetic sector mass spectrometers are prone to unwanted oscillations which can adversely affect the resolution of the mass spectrometer.

It is known to attempt to dampen unwanted oscillations of the slit blades of a magnetic sector mass spectrometer by applying a small amount of frictional force to a slit carriage by pressing a thin strip of semi-rigid plastic material against the slit cairiage.

However, this known approach is generally problematic for a number of reasons as will be discussed in more detail below.

Firstly, the amount of force applied by the strip has to be set very precisely such that the slit is neither over-damped nor under-damped. If too much force is applied then the movement of the slit will become discontinuous and will be prone to being irreproducible.

Conversely, if too little force is applied then the slit will oscillate too much when the position of the slit is varied and the slit will be susceptible to environmental vibrations.

Secondly, the amount of frictional force which is applied to the slit using a strip of plastic has been found to vary during operation. For example, it has been found that on occasions the strip may have subtlety shifted which will result in the slit having too much or too little damping effect.

Thirdly, the quality of the dampening strip can have a critical effect on the damping of the slit. For example, it has been observed that on a microscopic level the dampening strip may have a rough edge or a non-smooth contact surface with the result that the slit movement is discontinuous or irreproducible.

It is therefore desired to provide an improved magnetic sector mass spectrometer and an improved damping mechanism.

SUMMARY OF THE PRESENT INVENTION

According to an aspect of the present invention there is provided a device for damping oscillations of a slit of a magnetic sector mass spectrometer comprising: one or more inserts arranged to be inserted, in use, between a solenoid coil and a permanent magnet of a magnetic sector mass spectrometer, wherein relative movement between the permanent magnet and the solenoid coil induces, in use, eddy currents within the insert which results in the generation of an electromagnetic damping force.

The insert preferably comprises a non-ferritic metal, alloy, ceramic or composite material.

The insert preferably comprises a non-magnetic metal, alloy, ceramic or composite material.

The insert preferably comprises an electrically conductive metal, alloy, ceramic or composite material.

The insert preferably comprises copper or a copper alloy.

According to another aspect of the present invention there is provided a magnetic sector mass spectrometer comprising: a first solenoid coil; a first permanent magnet; and a first device for damping oscillations as described above, wherein the tirst device for damping oscillations is arranged between the first solenoid coil and the first permanent magnet.

The mass spectrometer preferably further comprises a first slidable carriage aftached to a first slit blade and to the first permanent magnet so that movement of the first permanent magnet induced by applying a current to the first solenoid coil causes the first slidable carriage to translate the first slit blade in a first direction.

The mass spectrometer preferably further comprises: a second solenoid coil; a second permanent magnet; and a second device for damping oscillations as described above, wherein the second device for damping oscillations is arranged between the second solenoid coil and the second permanent magnet.

The mass spectrometer preferably further comprises a second slidable carriage attached to a second slit blade and to the second permanent magnet so that movement of the second permanent magnet induced by applying a current to the second solenoid coil causes the second slidable carriage to translate the second slit blade in a second direction.

The second direction is preferably substantially opposed to the first direction.

According to another aspect of the present invention there is provided a method of damping oscillations of a slit of a magnetic sector mass spectrometer comprising: inserting one or more inserts between a solenoid coil and a permanent magnet of a magnetic sector mass spectrometer, wherein relative movement between the permanent magnet and the solenoid coil induces eddy currents within the insert which results in the generation of an electromagnetic damping force.

According to another aspect of the present invention there is provided a method of mass spectrometry comprising a method of damping oscillations as described above.

According to another aspect of the present invention there is provided a mass spectrometer comprising: a first component attached to a magnet; a solenoid; and a non-magnetic second component arranged between the solenoid and the magnet; wherein relative movement between the magnet and the solenoid induces an eddy current within the second component which results in the generation of an electromagnetic damping force.

The first component preferably comprises a slit, an aperture plate, a corona pin, an electiostatic plate or a gas or liquid nozzle.

According to another aspect of the present invention there is provided a method of mass spectrometry comprising: providing a first component attached to a magnet, a solenoid and a non-magnetic second component arranged between the solenoid and the magnet; wherein relative movement between the magnet and the solenoid induces an eddy current within the second component thereby resulting in the generation of an electromagnetic damping force.

The first component preferably comprises a slit, an aperture plate, a coiona pin, an electrostatic plate or a gas or liquid nozzle.

The preferred embodiment relates to a technique for applying a damping or dampening force to the movement of one or more slits of a magnetic sector mass spectrometer.

It is known to mount a slit blade to a carriage which is connected to a permanent magnet disposed within a cylindrical solenoid coil. Activation of the solenoid coil causing translation of the magnet, carriage and slit blade and hence increases or decreases the spacing between two slit blades.

According to a preferred embodiment of the present invention a cylindrical copper (or other non-ferrous metallic) insert is preferably placed within the solenoid coil. When the solenoid is activated in order to move or translate the slit, eddy currents which are induced by the movement of the permanent magnet within the solenoid coil result in a back electiomotive force which opposes the movement of the permanent magnet and the slit connected thereto. As a result a dampening force is generated which acts to dampen any undesired oscillations of the slit or slit blade.

The dampening mechanism according to the preferred embodiment allows the position of each slit or slit blade to be moved or translated and then stabilised very quickly without the slit or slit blade oscillating.

The slits or slit blades are preferably mounted to a carriage which is preferably arranged so that very little force is required in order to adjust the position of the slit or slit blade. As a result, the position of the slit or slit blade can be varied very rapidly and in a precise manner without requiring the use of strong electrical currents or magnetic fields.

This does, however, mean that the slits are potentially susceptible to environmental vibrations.

It will be appreciated by those skilled in the art that an undesired movement of a slit or slit blade of 1 pm can be critical in terms of defining an ion beam within a magnetic mass spectrometer.

It will be apparent, therefore, that not only can environmental vibrations be unavoidable but they can also seriously destabilise the operation of a magnetic sector mass spectrometer.

The device for dampening oscillations of a slit of a magnetic sector mass spectrometer according to the preferred embodiment is particularly advantageous in that the dampening mechanism is able to dampen unwanted oscillations which result from translation of the slit or slit blade and/or unwanted oscillations which result from environmental vibrations.

A magnetic sector mass spectrometer which incorporates the dampening mechanism according to the present invention is particularly advantageous and has significantly improved operational performance relative to a conventional magnetic sector mass spectrometer.

The stabilising effect of the dampening mechanism according to the preferred embodiment is particularly advantageous when it is desired to operate the magnetic sector mass spectrometer for a prolonged period of time at a relatively high resolving power.

It will be appreciated that during normal operation of the magnetic sector mass spectrometer the widths of the slits will be frequently varied during the process of optiniising transmission i.e. obtaining the highest sensitivity at the desired resolving power.

The dampening effect of the eddy currents induced within the preferred insert preferably results in fast stabilisation of the width of the slits when the width of the slits are deliberately varied.

Some analytical techniques require that the resolving power and hence the width of the slits need to be varied at certain points during an analysis. For example, an experimental protocol may require that two separate experiments are conducted sequentially at different resolving powers or that the resolving power is varied during a single experiment. The stabilisation time of the slits will play an important role in the ability of the mass spectrometer to perform such experiments.

Another important performance criterion of a mass spectrometer is the reproducibility of experimental results.

In order to illustrate the issue of reproducibility it should be understood that the width of the slits is preferably set by passing an electric current through each of the solenoid coils which surround a permanent magnet to which a slit is connected.

The current applied to the solenoid(s) is preferably directly related to the intended width of the slits and hence the resolving power and transmission of the mass spectrometer.

Once the optimum values of the slit width (and hence current) have been determined for a given experiment the values are then preferably stored or saved e.g. in a computer memory.

The stored values are then preferably recalled and implemented when the experiment is subsequently run.

Furthermore, a batch of experiments may be performed over the course of several days after the optimum values have been established. In such circumstances it is vital to the utility of the mass spectrometer that the predetermined current results in exactly the same slit widths being achieved as during the optimisation process.

As will be understood by those skilled in the art, any deviation in resolving power or transmission can result in the invalidation of the data acquired by the mass spectrometer.

According to an embodiment the mass spectrometer may further comprise: (a) an ion source selected from the group consisting of: (i) an Electrospray ionisation ("ESI") ion source; (ii) an Atmospheric Pressure Photo lonisation ("APPI") ion source; (iii) an Atmospheric Pressure Chemical lonisation ("APCI") ion source; (iv) a Matrix Assisted Laser Desorption lonisation ("MALDI") ion source; (v) a Laser Desorption lonisation ("LDI") ion source; (vi) an Atmospheric Pressure lonisation ("API") ion source; (vU) a Desorption lonisation on Silicon ("0105") ion source; (viii) an Electron Impact ("El") ion source; (ix) a Chemical lonisation ("Cl") ion source; (x) a Field lonisation ("Fl") ion source; (xi) a Field Desorption ("FD") ion source; (xii) an Inductively Coupled Plasma ("ICP") ion source; (xiU) a Fast Atom Bombardment ("FAB") ion source; (xiv) a Liquid Secondary Ion Mass Spectrometry ("LSIMS") ion source; (xv) a Desorption Electrospray lonisation ("DESI") ion source; (xvi) a Nickel-63 radioactive ion source; (xvU) an Atmospheric Pressure Matrix Assisted Laser Desorption lonisation ion source; (xvUi) a Thermospray ion source; (xix) an Atmospheric Sampling Glow Discharge lonisation ("ASGDI") ion source; (xx) a Glow Discharge ("GD") ion source; (xxi) an Impactor ion source; (xxii) a Direct Analysis in Real Time ("DART") ion source; (xxiii) a Laserspray lonisation ("LSI") ion source; (xxiv) a Sonicspray lonisation ("SSI") ion source; (xxv) a Matrix Assisted Inlet lonisation ("MAIl") ion source; and (xxvi) a Solvent Assisted Inlet lonisation ("SAIl") ion source; and/or (b) one or more continuous or pulsed ion sources; and/or (c) one or more ion guides; and/or (d) one or more ion mobility separation devices and/or one or more Field Asymmetric Ion Mobility Spectrometer devices; and/or (e) one or more ion traps or one or more ion trapping regions; and/or (f) one or more collision, fragmentation or reaction cells selected from the group consisting of: (i) a Collisional Induced Dissociation ("CID") fragmentation device; (U) a Surface Induced Dissociation ("SID") fragmentation device; (Ui) an Electron Transfer Dissociation ("ETD") fragmentation device; (iv) an Electron Capture Dissociation ("ECD") fragmentation device; (v) an Election Collision or Impact Dissociation fragmentation device; (vi) a Photo Induced Dissociation ("PID") fragmentation device; (vii) a Laser Induced Dissociation fragmentation device; (vUi) an infrared radiation induced dissociation device; (ix) an ultraviolet radiation induced dissociation device; (x) a nozzle-skimmer interface fragmentation device; (xi) an in-source fragmentation device; (xD) an in-source Collision Induced Dissociation fragmentation device; (xiU) a thermal or temperature source fragmentation device; (xiv) an electnc field induced fragmentation device; (xv) a magnetic field induced fragmentation device; (xvi) an enzyme digestion or enzyme degradation fragmentation device; (xvii) an ion-ion reaction fragmentation device; (xvhi) an ion-molecule reaction fragmentation device; (xix) an ion-atom reaction fragmentation device; (xx) an ion-metastable ion reaction fragmentation device; (xxi) an ion-metastable molecule reaction fragmentation device; (xxii) an ion-metastable atom reaction fragmentation device; (xxiii) an ion-ion reaction device for reacting ions to form adduct or product ions; (xxiv) an ion-molecule reaction device for reacting ions to form adduct or product ions; (xxv) an ion-atom reaction device for reacting ions to form adduct or product ions; (xxvi) an ion-metastable ion reaction device for reacting ions to form adduct or product ions; (xxvii) an ion-metastable molecule reaction device for reacting ions to form adduct or product ions; (xxviU) an ion-metastable atom reaction device for reacting ions to form adduct or product ions; and (xxix) an Electron lonisation Dissociation ElD") fragmentation device; and/or (g) a mass analyser selected from the group consisting of: (i) a quadrupole mass analyser; (ii) a 2D or linear quadrupole mass analyser; (iii) a Paul or 3D quadrupole mass analyser; (iv) a Penning trap mass analyser; (v) an ion trap mass analyser; (vi) a magnetic sector mass analyser; (vii) Ion Cyclotron Resonance ("ICR") mass analyser; (vUi) a Fourier Transform Ion Cyclotron Resonance ("FTICR") mass analyser; (ix) an electrostatic or orbitrap mass analyser; (x) a Fourier Transform electrostatic or orbitrap mass analyser; (xi) a Fourier Transform mass analyser; (xU) a Time of Flight mass analyser; (xDi) an orthogonal acceleration Time of Flight mass analyser; and (xiv) a linear acceleration Time of Flight mass analyser; and/or (h) one or more energy analysers or electrostatic energy analysers; and/or (i) one or more ion detectors; and/or C) one or more mass filters selected from the group consisting of: (i) a quadrupole mass filter; (U) a 2D or linear quadrupole ion trap; (Hi) a Paul or 3D quadrupole ion trap; (iv) a Penning ion trap; (v) an ion trap; (vi) a magnetic sector mass filter; (vii) a Time of Flight mass filter; and (viii) a Wien filter; and/or (k) a device or ion gate for pulsing ions; and/or (I) a device for converting a substantially continuous ion beam into a pulsed ion beam.

The mass spectrometer may further comprise either: (i) a C-trap and a mass analyser comprising an outer barrel-like electrode and a coaxial inner spindle-like electrode that form an electrostatic field with a quadro-logarithmic potential distribution, wherein in a first mode of operation ions are transmifted to the C-trap and are then injected into the mass analyser and wherein in a second mode of operation ions are transmitted to the C-trap and then to a collision cell or Electron Transfer Dissociation device wherein at least some ions are fragmented into fragment ions, and wherein the fragment ions are then transmitted to the C-trap before being injected into the mass analyser; and/or (U) a stacked ring ion guide comprising a plurality of electrodes each having an aperture through which ions are transmitted in use and wherein the spacing of the electiodes increases along the length of the ion path, and wherein the apertures in the electrodes in an upstream section of the ion guide have a first diameter and wherein the apertures in the electrodes in a downstream section of the ion guide have a second diameter which is smaller than the first diameter, and wherein opposite phases of an AC or RE voltage are applied, in use, to successive electrodes.

According to an embodiment the mass spectrometer further comprises a device arranged and adapted to supply an AC or RF voltage to the electrodes. The AC or RF voltage preferably has an amplitude selected from the group consisting of: (i) C 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; (vih) 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.

The AC or RF voltage preferably has a frequency selected from the group consisting of: (i) C 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; (vUi) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xU) 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) 9.5-1 0.0 MHz; and (xxv)> 10.0 MHz.

BRIEE DESCRIPTION OE THE DRAWINGS

Various embodiments of the present invention together with an arrangement given for illustrative purposes only will now be described, by way of example only, and with reference to the accompanying drawings in which: Fig. 1 shows a schematic of a conventional mechanism for altering the width between two slit blades of a magnetic sector mass spectrometer comprising two slit blades each mounted to a separate carriage, wherein each carriage is connected to a permanent magnet located within a cylindrical solenoid wherein actuation of the solenoids causes displacement of the permanent magnets and associated carriage and slit blade; Fig. 2 illustrates the reproducibility of moving the source slit of a magnetic sector mass spectrometer when jumping the slits closed and compares the reproducibility for three different scenarios namely loose conventional damping, tight conventional damping and damping according to the preferred embodiment wherein the damping force results from the generation of eddy currents; Fig. 3 shows the reproducibility when moving the source slit by jumping open the slits tor conventional damping and damping according to the preferred embodiment of the present invention; Fig. 4 shows the reproducibility when moving the source slit by scrolling closed for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 5 shows the reproducibility when moving the source slit by scrolling open for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 6 shows the hysteresis of source slit movement when jumping for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 7 shows the hysteresis of source slit movement when scrolling for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 8 shows the reproducibility of collector slit movement when jumping closed for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 9 shows the reproducibility of collector slit movement when jumping open for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 10 shows the reproducibility of collector slit movement when scrolling closed for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 11 shows the reproducibility of collector slit movement when scrolling open for conventional damping and damping according to the preferred embodiment of the present invention; Fig. 12 shows the hysteresis of collector slit movement when jumping for conventional damping and damping according to the preferred embodiment of the present invention; and Fig. 13 shows the hysteresis of collector slit movement when scrolling for conventional damping and damping according to the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

A conventional arrangement will first be described before discussing a preferred embodiment of the present invention.

Conventional magnetic sector mass spectrometers are known which utilise variable slits to define an ion beam at various points along an optical axis. The width of the ion beam is restricted in the plane of mass dispersion in order to vary the resolving power of the instrument. There are two key positions at which the ion beam width is restricted namely at the entrance into the analyser (i.e. the source position) and immediately in front of the detector (i.e. the collector position).

It is also known to limit the maximum angular divergence of an ion beam in the plane of mass dispersion using an alpha slit located downstream of the ion source.

The precision, accuracy and stability of the position of each blade of each slit is critical to the performance of the mass spectrometer.

At normal operation and normal resolution of a conventional double focusing magnetic sector mass spectrometer (i.e. 10,000 resolving power ("RP"), 5% peak height definition) the source slit is typically about 38 pm wide and the collector slit is typically about 8 pm wide. A 1 pm error in the position of the source slit will have approximately a 2.5% effect on the recorded intensity of the ion beam.

More critically, a 1 pm error in the position of the collector slit blade will have a 12.5 ppm influence on the width of the ion beam causing the resolution to vary between 11,400 and 8,900 resolving power ("RP").

One known method which is employed to vary the position of the slit blades is shown in Fig. 1 and comprises having the slit blades 1 affixed to a leaf-spring 2 mounted carriage 3 which also supports a strong permanent magnet 4. The permanent magnet 4 is arranged so as to lie within a solenoid coil 5. Applying a current to the solenoid coil 5 causes the permanent magnet 4 to be deflected and hence vary the blade 1 position.

A mounting block 6 and the direction of slit blade movement 7 is also shown in Fig. 1.

It is known to attempt to apply a small amount of frictional damping to the movement of the slit blades 1 and associated carriage 3 by applying a damping strip made of KAFTON (RTM) so that the damping strip rests against the blade carriage 3. Setting the desired level of friction is, however, problematic. If too little force is applied then the slit blades 1 will oscillate too much. However, if too much force is applied then the slit blades 1 will experience discontinuous and irreproducible movement.

The preferred embodiment seeks to address this problem by utilising an alternative means of applying a damping force to the carriage 3 and associated slit blade 1.

According to the preferred embodiment a cylindrical copper insert (not shown in Fig. 1) is preferably placed within the centre of the solenoid bobbin 5 and is preferably arranged so as to be concentric to, but not touching the permanent magnet 4.

As the permanent magnet 4 moves it will preferably induce an eddy (or Foucault) current within the copper insert. The eddy current(s) preferably create an opposing magnetic, electromagnetic or electromotive force which preferably results in the position of the permanent magnet 4 and hence associated carriage 3 and slit blade 1 being stabilised in an optimal manner.

The preferred embodiment therefore relates to a non-contact method of applying a damping force to the movement of the slit blade 1 and advantageously such an approach is substantially more reliable than attempting to set an appropriate amount of frictional force using a damping strip.

Various alternative embodiments are contemplated. For example, the cylindrical insert may more generally comprise a non-ferritic or non-magnetic conductive metal or alloy to provide the dampening force. Copper is particularly preferred due to its high conductivity but other non-magnetic conductive metals or alloys may also be used.

Other alternative embodiments are also contemplated wherein different designs of cylindrical insert may be utilised. For example, according to an embodiment multiple layers of a thin sheet metal may be disposed as concentric tubes or a single thin sheet of metal may be rolled to form a tube with multiple layers. Alternatively, an insulating tube may be provided with metal wire wound around it. According to a yet further embodiment the bobbin of the solenoid coil 5 may itself be made of a suitable metal.

Although the preferred embodiment relates to a device for dampening the oscillations of one or more slits of a magnetic sector mass spectrometer, other embodiments are contemplated wherein the same method may be utilised to dampen to oscillation of other devices within a mass spectrometer which utilise a magnet and a solenoid coil in order to precisely position a device within the instrument. For example, the damping mechanism according to the preferred embodiment may also be utilised to dampen the oscillation of an aperture plate, a corona pin, an electrostatic plate or a gas or liquid nozzle.

The technique of damping or dampening the movement of a solenoid actuated slit 1 accoiding to the preferred embodiment was tested in the two key focal positions of a magnetic sector double focussing mass spectrometer.

The dampening mechanism was constructed according to the preferred embodiment by utilising two cylindrical copper inserts. One copper insert was placed within the centre of each of two solenoid coils 5 which were responsible for controlling the separation of two adjacent slit blades 1. The copper inserts were arranged to be inserted so that they were concentric with but not touching the permanent magnets 4 which were aftached to a slit carriage 3 with a slit blade 1 attached to each slit carriage 3.

A key performance criteria of the slits 1 is the reproducibility with which the width of the slits 1 can be set. For the slit in the "source" location the figure of merit of interest was the intensity of the ion beam. For the slit in the "collector" location the figure of merit of interest was the resolution (i.e. peak width) of the ion beam.

A software application was written in order to test the performance of the slits 1.

The program was arranged to vary the width of the slits 1 and to record the respective figure of merit. The slit 1 of interest (either the "source" or "collector" slit) was initially set to a specific width which gave a desired ion beam intensity or resolution.

The width of the slit 1 was then varied using four methods which were intended to reproduce the expected movement of a slit 1 during normal operation. The four methods which were used to vary the width of the slit were: (i) from the initial slit width the width was increased to its maximum value (-700 pm) in a single step, then allowed to settle for 2 seconds and then set back to its initial value in a single step; (U) from the initial slit width the width was decreased to its minimum value (0 pm) in a single step, then allowed to settle for 2 seconds and then set back to its initial value in a single step; (Di) from the initial slit width the width was increased to its maximum value incrementally over the course of 2 seconds (using 1 OOx 20 ms increments), then allowed to settle for 0.4 seconds and then returned to its initial value incrementally over the course of 2 seconds; and (iv) from the initial slit width the width was decreased to its minimum value incrementally over the course of 2 seconds, then allowed to settle for 0.4 seconds and then returned to its initial value incrementally over the course of 2 seconds.

These methods were intended to reproduce modes of operation wherein a user varies the widths of the slits either by typing in a specified value (i.e. "jumping") or by using a continuously variable control and a pointing device (i.e. "scrolling"). When the software application was run each method was repeated five times. The software application allowed a variable delay time to be specified prior to the recording of the figure of merit so that the settling time of the slits could be evaluated.

The tests were conducted at the typical operating resolution of the mass spectrometer used with a peak width of 100 ppm i.e. ata resolution of 10,000 resolving power ("RP"). A typical mass spectrometer of this type will achieve this resolution with a source slit width of around 40 pm and a collector slit width of 8 pm. The intensity of the reference mass peak used at this resolution was high enough such that the statistical variation due to ion statistics was minimal but low enough so that no detector saturation occurred.

For the testing of the source slit, the new damping or dampening method was compared to the conventional damping or dampening method which relies upon a degree of friction being applied to the slits by a strip of stiff plastic. A comparison was made with the friction adjusted to two settings -one where the friction was low ("loose dampening") and one where the friction was high ("tight dampening"). The setting of the degree of friction is part of the setup process of a conventional magnetic sector mass spectrometer.

In order to test the collector slit, the comparison with the conventional slit dampening was made at one single friction setting deemed to be appropriate for use.

Figs. 2-7 show results from testing the source slit and Figs. 8-13 show results from the testing the collector slit.

Figs. 2-5 show the relative standard deviation of the recorded peak intensity from the five settings of the slit width using each of the four methods described above over a range of settling times from 100 ms to 3 s.

Figs. 8-11 show the equivalent data for the collector slit where the figure of merit is the peak width i.e. resolution.

Figs. 6-7 and 12-13 demonstrate the degree of hysteresis exhibited by the slit i.e. the difference in slit width that is observed dependent on the direction of travel i.e. whether the slit is moved in an opening or closing direction.

It will be appreciated that in all the data shown it is desired that the experimental results are as close to 0% as possible.

The experimental data demonstrates that the damping or dampening device accoiding to the preferred embodiment results in a significant improvement in performance.

The oscillations associated with the movement of the slit are dampened significantly more quickly than with a conventional arrangement.

Furthermore, the hysteresis demonstrated with the preferred dampening device tends to 0% and demonstrates that setting of the slit width is highly reproducible and hence consistent performance of the mass spectrometer can be expected.

Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.

Claims (16)

1. Claims 1. A device for damping oscillations of a slit of a magnetic sector mass spectrometer comprising: one or more inserts arranged to be inserted, in use, between a solenoid coil and a permanent magnet of a magnetic sector mass spectrometer, wherein relative movement between said permanent magnet and said solenoid coil induces, in use, eddy currents within said insert which results in the generation of an electromagnetic damping force.
2. 2. A device as claimed in claim 1, wherein said insert comprises a non-ferritic metal, alloy, ceramic or composite material.
3. 3. A device as claimed in claim 1 or 2, wherein said insert comprises a non-magnetic metal, alloy, ceramic or composite material.
4. 4. A device as claimed in claim 1, 2 or 3, wherein said insert comprises an electrically conductive metal, alloy, ceramic or composite material.
5. 5. A device as claimed in any preceding claim wherein said insert comprises copper or a copper alloy.
6. 6. A magnetic sector mass spectrometer comprising: a first solenoid coil; a first permanent magnet; and a first device for damping oscillations as claimed in any preceding claim, wherein said first device for damping oscillations is arranged between said first solenoid coil and said first permanent magnet.
7. 7. A magnetic sector mass spectrometer as claimed in claim 6, further comprising: a first slidable carriage attached to a first slit blade and to said first permanent magnet so that movement of said first permanent magnet induced by applying a current to said first solenoid coil causes said first slidable carriage to translate said first slit blade in a first direction.
8. 8. A magnetic sector mass spectrometer as claimed in claim 6 or 7, further comprising: a second solenoid coil; a second permanent magnet; and a second device for damping oscillations as claimed in any of claims 1-5, wherein said second device for damping oscillations is arranged between said second solenoid coil and said second permanent magnet.
9. 9. A magnetic sector mass spectrometer as claimed in claim 8, further comprising: a second slidable carriage attached to a second slit blade and to said second permanent magnet so that movement of said second permanent magnet induced by applying a current to said second solenoid coil causes said second slidable carriage to translate said second slit blade in a second direction.
10. 10. A magnetic sector mass spectrometer as claimed in claim 9, wherein said second direction is substantially opposed to said first direction.
11. 11. A method of damping oscillations of a slit of a magnetic sector mass spectrometer comprising: inserting one or more inserts between a solenoid coil and a permanent magnet of a magnetic sector mass spectrometer, wherein relative movement between said permanent magnet and said solenoid coil induces eddy currents within said insert which results in the generation of an electromagnetic damping force.
12. 12. A method of mass spectrometry comprising a method of damping oscillations as claimed in claim 11.
13. 13. A mass spectrometer comprising: a first component attached to a magnet; a solenoid; and a non-magnetic second component arranged between said solenoid and said magnet; wherein relative movement between said magnet and said solenoid induces an eddy current within said second component which results in the generation of an electromagnetic damping force.
14. 14. A mass spectrometer as claimed in claim 13, wherein said first component comprises a slit, an aperture plate, a corona pin, an electrostatic plate or a gas or liquid nozzle.
15. 15. A method of mass spectrometry comprising: providing a first component attached to a magnet, a solenoid and a non-magnetic second component arranged between said solenoid and said magnet; wherein relative movement between said magnet and said solenoid induces an eddy current within said second component thereby resulting in the generation of an electromagnetic damping force.
16. 16. A method of mass spectrometry as claimed in claim 15, wherein said first component comprises a slit, an aperture plate, a corona pin, an electrostatic plate or a gas or liquid nozzle.