GB2378572A

GB2378572A - Mass spectrometer comprising mass separating means which utilises forces produced by radial motion of sample

Info

Publication number: GB2378572A
Application number: GB0223904A
Authority: GB
Inventors: Robert Harold Bateman; Stuart Jarvis
Original assignee: Micromass UK Ltd
Current assignee: Micromass UK Ltd
Priority date: 2000-10-12
Filing date: 2001-10-12
Publication date: 2003-02-12
Anticipated expiration: 2021-10-12
Also published as: GB2378572B; GB0223904D0; GB2378571A; GB2378571B; GB0223903D0

Abstract

The present invention relates to a mass spectrometer comprising a cyclonic mass separator including a conical chamber 14, and a mass analyser up or down stream of the mass separator 14. The sample is injected into the chamber through a tangential inlet 15 forming a vortex within the chamber 14. Centrifugal forces force the heavier particles away from the axis or rotation, while the lighter material will remain closer to the axis. The sample accelerates as it is forced down the reducing cross section with the heavier fractions selectively pushed towards the wall of the cyclonic chamber. The height of the particles within the chamber will therefore be determined according to the mass of the particle. Ions are sampled either axially 18 or radially 17 from the conical chamber 14.

Description

74127002.353

MAS S S PE CTROMETER

The present invention relates to a mass 5 spectrometer.

It is known to separate particles prior to analysis by a mass spectrometer to remove unwanted particles from the fluid to be analyzed. The unwanted particles may, for example, be solvent particles or ions having a mass 10 to charge ratio outside of a range of interest.

Mass filtering of ions prior to mass analysis is conventionally performed using a quadrupole mass filter or other ion optical device disposed in a vacuum chamber. However, quadrupole mass filters and other ion 15 optical devices normally require very low pressures (high vacuum) for operation.

WO00/19484 discloses a vortex gas flow interface for removing large solvent droplets from an electrosprayed sample.

20 According to a first aspect of the present invention, there is provided a mass spectrometer as claimed in claim 1.

An important advantage of the preferred mass separator is that it preferably operates at much higher 25 pressures than ion optical devices, and indeed operation at pressures up to or even above atmospheric pressure are contemplated. Particularly advantageously, the preferred embodiment can be easily coupled to an atmospheric pressure ionization source.

30 Preferably, the chamber further comprises an inlet for a drying gas.

Preferably, the sample inlet and/or the inlet for a drying gas are arranged so as to generally or substantially tangentially inject a sample or drying gas 35 into the chamber.

Preferably, the shaft comprises one ore more holes.

Preferably, the pressure reducing means comprises a vacuum pump.

Preferably, the chamber comprises an outlet through

which, in use, particles are extracted, preferably for subsequent analysis in the mass analyses.

Preferably, the outlet is arranged to preferentially extract either: (i) heavier particles 5 which have been forced towards the wall of the chamber; or (ii) lighter particles which have been forced towards the centre of the chamber.

According to a second aspect of the present invention, there is provided a mass spectrometer as 10 claimed in claim S. Preferably, the chamber comprises an outlet through which, in use, particles are extracted, preferably for subsequent analysis in the mass analyzer.

Preferably, the outlet is arranged to 15 preferentially extract either: (i) heavier particles which have been forced towards the wall of the chamber; or (ii) lighter particles which have been forced towards the centre of the chamber.

According to a third aspect of the present 20 invention, there is provided a mass spectrometer as claimed in claim 11.

Preferably, the chamber comprises an outlet through which, in use, particles are extracted, preferably for subsequent analysis in the mass analyser.

25 Preferably, the outlet is arranged to preferentially extract either: (i) heavier particles which have been forced towards the wall of the chamber; or (ii) lighter particles which have been forced towards the centre of the chamber.

30 According to a fourth aspect of the present invention, there is provided a mass spectrometer as claimed in claim 14.

Preferably, the cyclonic mass separator comprises a conical chamber.

35 Preferably, in use a sample is arranged to enter the conical chamber tangentially so as to create a centrifugal force.

- 3 Preferably, heavier particles are forced towards the thinner end of the conical chamber and/or lighter particles are forced towards the thicker end of the conical chamber.

5 Preferably, particles are arranged to be sampled from the thicker end of the conical chamber.

Preferably, particles are arranged to be sampled axially and/or tangentially from the conical chamber.

Preferably, particles are arranged to be sampled 10 from the thinner end of the conical chamber.

An advantage of the preferred embodiment is that the vortex, centrifuge and cyclonic mass separators allow for the analysis of high flows of fluid into a mass spectrometer. The mass separator according to the 15 preferred embodiment efficiently removes solvent molecules from the fluid and allows a higher concentration of analyses to be injected into the mass spectrometer. As a result, the sensitivity of the mass analyser is significantly improved.

20 According to a fifth aspect of the present invention, there is provided a mass spectrometer as claimed in claim 22.

According to a sixth aspect of the present invention, there is provided a mass spectrometer as 25 claimed in claim 23.

According to a seventh aspect of the present invention, there is provided a mass spectrometer as claimed in claim 24.

Preferably, the mass separator is arranged and 30 adapted to be operated at a pressure selected from the group comprising: (i) 2 1 mbar; (ii) 2 2 mbar; (iii) 2 5 mbar; (iv) 2 10 mbar; (v) 2 20 mbar; (vi) 2 50 mbar; (Vii) 2 TOO mbar; (viii) 2 150 mbar; (ix) 2 200 mbar; (X) 2 250 mbar; (xi) 2 300 mbar; (xii) 2 350 mbar; 35 (xiii) 2 400 mbar; (xiv) 2 450 mbar; (xv) 2 500 mbar; (XVI) 2 550 mbar; (xvii) 2 600 mbar; (xviii) 2 650 mbar; (XIX) 2 700 mbar; (xx) 2 750 mbar; (xxi) 2 800 mbar;

- 4 - (xxTi) > 850 mbar; (xxiii) > 900 mbar; (xxiv) 950 mbar; (xxv) 2 1000 mbar; (xxvi) approximately atmospheric pressure; and (xxvii) above atmospheric pressure. 5 According to an eighth aspect of the present invention, there is provided a mass spectrometer as claimed in claim 26.

According to a ninth aspect of the present invention, there is provided a mass spectrometer as 10 claimed in claim 27.

According to a tenth aspect of the present invention, there is provided a method of mass spectrometry as claimed in claim 28.

According to a eleventh aspect of the present 15 invention, there is provided a method of mass spectrometry as claimed in claim 29.

According to a twelfth aspect of the present invention, there is provided a method of mass spectrometry as claimed in claim 30.

20 According to a thirteenth aspect of the present invention, there is provided a method of mass spectrometry as claimed in claim 31.

According to a fourteenth aspect of the present invention, there is provided a mass spectrometer as 25 claimed in claim 32.

According to a fifteenth aspect of the present invention, there is provided a mass spectrometer as claimed in claim 33.

Various embodiments of the present invention will 30 now be described, by way of example only, and with reference to the accompanying drawings in which: Fig. l shows a vortex mass separator according to a first embodiment of the present invention; Fig. 2 shows a centrifugal mass separator according 35 to a second embodiment of the present invention; Fig. 3 shows a cyclonic mass separator according to a third embodiment of the present invention;

- 5 Fig. 4 shows another centrifugal mass separator; Fig. 5 is a cross sectional view of Fig. 4; Fig. 6 shows another vortex mass separator; and Fig. 7 shows a cross sectional view of Fig. 6.

5 According to the preferred embodiment, sample ions in a gaseous atmosphere are separated and concentrated into a region from which ions are drawn into a mass spectrometer for analysis by the action of the centrifugal force established in a vortex, centrifuge or 10 cyclonic device.

Sample ions, solvent ions, spray nebulising gas and drying gas may, in one embodiment, be sprayed into a chamber from an atmospheric pressure ion source such as an electrospray source. The chamber is preferably a 15 cylindrical chamber for a vortex or centrifuge device.

The various particles are induced to rotate, and centrifugal force causes the sample ions with higher mass to migrate towards the perimeter of the chamber.

Ions are drawn into the mass spectrometer, which is 20 under vacuum, through an orifice in the outer wall of the chamber. The atmosphere sampled by the mass spectrometer is therefore preferably enriched in sample ions due to the mass separation.

A vortex is preferably generated by rotating a 25 hollow shaft at the centre of the cylindrical chamber.

The hollow shaft includes one or more holes in its wall which allow fluid to flow from within the cylindrical chamber through these holes and out along the central axis of the hollow shaft. One end of the hollow shaft 30 is connected to a pump or other pressure reducing means while the other end is either blanked off or connected to another pump.

In an alternative embodiment, the hollow shaft is fixed and a vortex is created by the generally or 35 substantially tangentially injecting the sample fluid (preferably a gas) and/or drying gas.

In a vortex, the tangential velocity v of the fluid

- 6 at a particular radius is inversely proportional to the radius r, and the angular velocity is inversely proportional to the square of the radius. Therefore, the centrifugal force Fc on a particle of mass m at 5 radius r is proportional to the product mar, and hence is proportional to m/r3. If the central rotating shaft has a radius rat, and a rotational frequency f1, then the shaft tangential velocity v1 is given by: 10 v1 = Infirm and the tangential velocity v of a particle at a radius r is given by: 15 v = 2nf1r 2/r The fluid angular velocity is given by: = 2nf r /r and the centripetal force Fc is given by: Fc = m(2nf1rl2)2/r3 25 A centrifuge effect may be generated by a rotating central solid shaft with attached paddles. The paddles which rotate with the central shaft extend to the outer wall of the cylindrical chamber preferably without actually touching it. Here, the angular velocity of 30 the fluid is constant. The tangential velocity v of the fluid at a particular radius r is given by: v = or 35 and hence the tangential velocity v is proportional to the radius r since is constant. Likewise, the centripetal force Fc on a particle of mass m at radius r

- 7 - is given by: Fc = mrm2 5 and hence is proportional to mr.

A further preferred embodiment uses a cyclonic mass separator. The cyclonic mass separator has the advantage of having no moving parts and operates by a fluid stream entering the wide end of a conical vessel 10 tangentially, forming a vortex within the vessel.

Centrifugal force forces the heavier particles away from the axis of rotation, while the lighter material will remain closer to the axis. The fluid accelerates as it is forced down the reducing cross section, with the 15 heavier fractions selectively pushed towards the wall of the cyclonic device. The height within the chamber will therefore be determined according to the mass of the particle. Ions may be sampled either axially or radially from the conical vessel.

20 The mass separators described above may be arranged downstream of an ionization source and upstream of a mass analyser, or alternatively the mass separators may be arranged upstream of the ionization source.

A vortex mass separator will now be described in 25 more detail with reference to Fig. 1. Further assistance in creating the vortex may be provided by causing the fluid to enter the chamber in a generally or substantially tangential direction. Due to centrifugal force, heavier particles are forced away from the axis 30 of rotation, while the lighter particles are drawn towards the central axis. The distance of a particle from the axis of rotation will therefore be determined by its mass. It is therefore possible to extract high mass particles by extracting particles from near the 35 wall of the chamber.

The vortex mass separator according to the preferred embodiment comprises a chamber 5, at the

- 8 centre of which is a rotatable hollow central shaft 6.

The hollow shaft 6 has at least one hole 7 preferably towards the base of the chamber 5. At least one end of the central shaft 6 has a pump attached to it in order 5 to reduce the pressure within the shaft 6 and to aspirate fluid from the chamber 5 via the hollow central shaft 6. The other end of the shaft 6 may either be blanked off or connected to another pump. An aperture 8 in the wall of the chamber 5 may be used to extract the 10 separated sample (enriched in high mass particles) for subsequent analysis in a mass analyser, and/or low mass particles may be extracted via shaft 6.

In an alternative embodiment the shaft 6 is fixed and a vortex is generated by the tangential injection of 15 sample fluid and/or drying gas.

Fig. 2 shows a preferred centrifugal mass separator. The centrifugal mass separator comprises a chamber 9, at the centre of which is a central shaft 10 having one or more paddles 11 attached thereto. When 20 the central shaft 10 and paddle(s) 11 rotate, a centrifuge effect is generated within the chamber 9.

Centrifugal force causes heavier particles to move towards the wall 12 of the chamber 9. An aperture 13 in the wall 12 of the chamber 9 may be used to extract the 25 separated sample for analysis in a mass analyzer.

Fig. 3 shows a preferred cyclonic mass separator.

The cyclonic mass separator comprises a conical vessel 14 in which a fluid is preferably added at the wide end of the vessel 15 in a generally or substantially 30 tangential direction. Centrifugal force causes lighter particles to remain nearer the thicker end of the conical vessel 14 whilst heavier particles are forced towards the thinner end of the conical vessel 14.

Sampling can occur at either end of the vessel 14, 35 either radially via an aperture (e.g. aperture 17) in the wall of the conical vessel 14 or axially from either end of conical vessel 14 as shown by arrows 18.

- 9 Fig. 4 shows another centrifugal mass separator.

According to this embodiment, a cylindrical chamber 19 is provided having two inlet apertures 20,21 which generally or substantially tangentially inject fluid 5 into the chamber 19 so as to create a rotational effect within the chamber 19. Centrifugal force forces heavier particles towards the outside of the chamber 19. In contrast to the embodiment described in relation to Fig. 2, neither a rotating shaft nor paddles are provided.

10 The top of the chamber is preferably blanked off 22.

One or more outlet apertures 23 may be provided in the wall of the chamber 19 through which the sample (preferably enriched in high mass particles) can exit the chamber 19. Drying gas is preferably injected via 15 the upper inlet aperture 20 and a fluid containing the sample is preferably injected via the lower inlet aperture 21, although this arrangement could be reversed. The apertures 23 in the outside wall of the chamber are used to extract the separated high mass 20 sample for subsequent analysis in a mass analyzer.

Fig. 5 is a cross sectional view of the chamber 19 shown in Fig. 4 and shows how inlets 20,21 inject a sample in a generally or substantially tangential direction so as to cause a circulating flow of fluid 25 thereby generating a centrifugal force for mass separation of the sample particles. The outlet 23 is shown at the opposite side of the chamber 19 from the inlets 20,21.

Fig. 6 shows another preferred vortex mass 30 separator. A chamber 28 surrounds a central tube 29 to which a vacuum pump is connected at one end 30. The other end of the tube is preferably blanked off 31.

Along the length of the tube 29 a plurality of holes 32 are provided that create a suction effect within the 35 chamber 28. Inlets 33,34 feed into the chamber 28 in a generally tangential direction to the centre of the chamber so as to help create a rotating effect within

the chamber 28. The top of the chamber is preferably blanked off 35. One or more exit apertures 36 are provided to allow a sample (preferably enriched in high mass particles) to exit the chamber 28 for subsequent 5 mass analysis. Drying gas is preferably injected into the chamber via upper inlet 33 and the sample is preferably injected via the lower inlet 34, although this arrangement could be reversed. Tangential injection of the sample and/or drying gas together with 10 the central suction effect helps to create a vortex within the chamber 28, which forces the heavier particles towards the outside of the chamber 28.

The shaft may rotate or more preferably it is fixed and a vortex is generated by the tangential injection of 15 sample fluid and/or drying gas.

Fig. 7 shows a cross-sectional view of the preferred embodiment shown in Fig. 6. In this view the chamber 28 is shown with the sample inlets 33,34 injecting the sample in a generally or substantially 20 tangential direction to the centre of the chamber. In the centre of the chamber tube 29 is shown. Along the length of the tube 28 holes 32 are arranged at regular intervals. Preferably, three evenly spaced holes 32 are arranged around the circumference of the tube 29 at each 25 axial location where holes are provided. On the wall at the far side of the chamber 28 from the inlet 34 is the exit aperture 36.

Claims

74127003.351

Claims

5 1. A mass spectrometer comprising: an ion source; a cyclonic mass separator comprising a conical chamber, said cyclonic mass separator being arranged downstream of said ion source; and 10 a mass analyser, said mass analyser being arranged downstream of said ion source and said cyclonic mass separator.
2. A mass spectrometer comprising: 15 an ion source; a cyclonic mass separator comprising a conical chamber, said cyclonic mass separator being arranged upstream of said ion source; and a mass analyzer, said mass analyser being arranged 20 downstream of said ion source and said cyclonic mass separator.
3. A mass spectrometer as claimed in claim 1 or 2, wherein in use a sample is arranged to enter said 25 conical chamber tangentially.
4. A mass spectrometer as claimed in claim 1, 2 or 3, wherein heavier particles are forced towards a thinner end of said conical chamber and/or lighter particles are 30 forced towards a thicker end of said conical chamber.
5. A mass spectrometer as claimed in claim 4, wherein particles are arranged to be sampled from said thicker end of said conical chamber.
6. A mass spectrometer as claimed in claim 5, wherein said particles are arranged to be sampled axially and/or tangentially from said conical chamber.

- 12
7. A mass spectrometer as claimed in claim 4, 5 or 6, wherein particles are arranged to be sampled from said thinner end of said conical chamber.

5
8. A mass spectrometer as claimed in claim 7, wherein said particles are arranged to be sampled axially and/or tangentially from said conical chamber.
9. A mass spectrometer as claimed in any preceding 10 claim, wherein said ion source comprises an atmospheric pressure Ion source.
10. A mass spectrometer as claimed in claim 9, wherein said ion source comprises an electrospray ion source.
11. A mass spectrometer as claimed in any preceding claim, wherein said mass separator is arranged and adapted to be operated at a pressure selected from the group comprising: (i) 2 1 mbar; (ii) > 2 mbar; (iii) > 5 20 mbar; (iv) 2 TO mbar; (v) 2 20 mbar; (vi) 2 50 mbar; (Vii) 2 TOO mbar; (viii) 2 150 mbar; (ix) 2 200 mbar; (X) 2 250 mbar; (xi) 2 300 mbar; (xii) 2 350 mbar; (Xiii) 2 400 mbar; (xiv) 2 450 mbar; (xv) 2 500 mbar; (XVI) 2 550 mbar; (xvii) 2 600 mbar; (xviii) 2 650 mbar; 25 (xix) 2 700 mbar; (xx) 2 750 mbar; (xxi) 2 800 mbar; (XXii) 2 850 mbar; (xxTii) 2 900 mbar; (xxiv) 2 950 mbar; (xxv) 2 1 0 0 0 mbar; (xxvi) approximately atmospheric pressure; and (xxvii) above atmospheric pressure.