Mass spectrometer

• US 20040094709A1
• Filed: 09/04/2003
• Published: 05/20/2004
• Est. Priority Date: 09/04/2002
• Status: Active Grant

• Current Assignee: Micromass UK Ltd (Waters Corporation)
• Original Assignee: Micromass UK Ltd (Waters Corporation)
• Inventors: Bateman, Robert Harold
• Granted Patent: US 6,835,928 B2
• Time in Patent Office: Days
• US Class Current: 250/292
• CPC Class Codes: H01J 49/004 Combinations of spectrometers, tandem spectrometers, e.g. MS/MS, MSn

Abstract

A mass spectrometer is disclosed comprising a multi-mode quadrupole rod set. In a first mode of operation, the quadrupole rod set is operated as a mass filter to selectively transmit ions having desired mass to charge ratios to an ion detector. In a second mode of operation, the quadrupole rod set operates as a drift or time of flight region in which ions which have been pulsed into the drift or time of flight region become temporally separated according to their mass to charge ratios. In the second mode of operation, the ion detector determines the time of flight of ions passing through the quadrupole rod set.

Claims

1. A mass spectrometer comprising:

a multi-mode quadrupole rod set; and

an ion detector;

wherein in a first mode of operation said quadrupole rod set acts as a mass filter and wherein in a second mode of operation said quadrupole rod set forms a time of flight region of a Time of Flight mass analyser.

2. A mass spectrometer as claimed in claim 1, wherein in said first mode of operation ions having mass to charge ratios within a first range are transmitted by said quadrupole rod set and ions having mass to charge ratios outside of said first range are substantially attenuated by said quadrupole rod set.

3. A mass spectrometer as claimed in claim 2, wherein in said first mode of operation AC or RF voltages are applied to the rods of said quadrupole rod set and a DC potential difference is maintained between adjacent rods.

4. A mass spectrometer as claimed in claim 1, wherein in said second mode of operation ions are pulsed into said time of flight region.

5. A mass spectrometer as claimed in claim 1, wherein in said second mode of operation ions are transmitted through said quadrupole rod set without being substantially mass filtered and become temporally separated according to their mass to charge ratio, and wherein said ion detector determines the time of flight of said ions through said time of flight region.

6. A mass spectrometer as claimed in claim 5, wherein in said second mode of operation AC or RF voltages are applied to the rods of said quadrupole rod set and all the rods of said quadrupole rod set are maintained at substantially the same DC potential.

7. A mass spectrometer as claimed in claim 1, wherein in said first and/or said second mode of operation said quadrupole rod set is maintained at a pressure selected from the group consisting of:

(i) greater than or equal to 1×

10<sup>−

7</sup> mbar;

(ii) greater than or equal to 5×

10<sup>−

7</sup> mbar;

(iii) greater than or equal to 1×

10<sup>−

6</sup> mbar;

(iv) greater than or equal to 5×

10<sup>−

6</sup> mbar;

(v) greater than or equal to 1×

10<sup>−

5</sup> mbar; and

(vi) greater than or equal to 5×

10<sup>−

5</sup> mbar.

8. A mass spectrometer as claimed in claim 1, wherein in said first and/or said second mode of operation said quadrupole rod set is maintained at a pressure selected from the group consisting of:

(i) less than or equal to 1×

10<sup>−

4</sup> mbar;

(ii) less than or equal to 5×

10<sup>−

5</sup> mbar;

(iii) less than or equal to 1×

10<sup>−

5</sup> mbar;

(iv) less than or equal to 5×

10<sup>−

6</sup> mbar;

(v) less than or equal to 1×

10<sup>−

6</sup> mbar;

(vi) less than or equal to 5×

10<sup>−

7</sup> mbar; and

(vii) less than or equal to 1×

10<sup>−

7</sup> mbar.

9. A mass spectrometer as claimed in claim 1, wherein in said first and/or said second mode of operation said quadrupole rod set is maintained at a pressure selected from the group consisting of:

(i) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

4</sup> mbar;

(ii) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

5</sup> mbar;

(iii) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

5</sup> mbar;

(iv) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

6</sup> mbar;

(v) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

6</sup> mbar;

(vi) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

7</sup> mbar;

(vii) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

4</sup> mbar;

(viii) between 5×

10<sup>−

7</sup> and 5×

10<sup>−

5</sup> mbar;

(ix) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

5</sup> mbar;

(x) between 5×

10<sup>−

7</sup> and 5×

10<sup>−

6</sup> mbar;

(xi) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

6</sup> mbar;

(xii) between 1×

10<sup>−

6</sup> mbar and 1×

10<sup>−

4</sup> mbar;

(xiii) between 1×

10<sup>−

6</sup> and 5×

10<sup>−

5</sup> mbar;

(xiv) between 1×

10<sup>−

6</sup> and 1×

10<sup>−

5</sup> mbar;

(xv) between 1×

10<sup>−

6</sup> and 5×

10<sup>−

6</sup> mbar;

(xvi) between 5×

10<sup>−

6</sup> mbar and 1×

10<sup>−

4</sup> mbar;

(xvii) between 5×

10<sup>−

6</sup> and 5×

10<sup>−

5</sup> mbar;

(xviii) between 5×

10<sup>−

6</sup> and 1×

10<sup>−

5</sup> mbar;

(xix) between 1×

10<sup>−

5</sup> mbar and 1×

10<sup>−

4</sup> mbar;

(xx) between 1×

10<sup>−

5</sup> and 5×

10<sup>−

5</sup> mbar; and

(xxi) between 5×

10<sup>−

5</sup> and 1×

10<sup>−

4</sup> mbar.

10. A mass spectrometer as claimed in claim 1, further comprising:

a collision cell; and

a further quadrupole rod set arranged upstream of said collision cell;

wherein said multi-mode quadrupole rod set is arranged downstream of said collision cell.

11. A mass spectrometer as claimed in claim 10, wherein in a MS mode of operation said further quadrupole rod set acts as a mass filter to mass filter parent ions.

12. A mass spectrometer as claimed in claim 10, wherein in a MS mode of operation parent ions are collisionally cooled within said collision cell.

13. A mass spectrometer as claimed in claim 10, wherein in a MS mode of operation parent ions exit said collision cell in a substantially non-pulsed manner.

14. A mass spectrometer as claimed in claim 10, wherein in a MS mode of operation said multi-mode quadrupole rod set is operated in a third mode of operation so as to transmit parent ions without substantially mass filtering said parent ions.

15. A mass spectrometer as claimed in claim 10, wherein in a MS/MS mode of operation said further quadrupole rod set acts as a mass filter to mass filter parent ions.

16. A mass spectrometer as claimed in claim 10, wherein in a MS/MS mode of operation at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of parent ions entering or within said collision cell are fragmented upon entering or within said collision cell to form fragment ions.

17. A mass spectrometer as claimed in claim 10, wherein in a MS/MS mode of operation fragment ions are collisionally cooled within said collision cell.

18. A mass spectrometer as claimed in claim 10, wherein in a MS/MS mode of operation fragment ions exit said collision cell in a substantially non-pulsed manner.

19. A mass spectrometer as claimed in claim 10, wherein in a MS/MS mode of operation said multi-mode quadrupole rod set is operated in said first mode of operation so as to mass filter fragment ions.

20. A mass spectrometer as claimed in claim 19, wherein said multi-mode quadrupole rod set is scanned so as to act as a mass analyser.

21. A mass spectrometer as claimed in claim 10, wherein in a MS-TOF mode of operation said further quadrupole rod set acts as an ion guide to transmit parent ions without substantially mass filtering said parent ions.

22. A mass spectrometer as claimed in claim 10, wherein in a MS-TOF mode of operation parent ions are collisionally cooled and/or trapped within said collision cell.

23. A mass spectrometer as claimed in claim 10, wherein in a MS-TOF mode of operation parent ions are pulsed out of said collision cell.

24. A mass spectrometer as claimed in claim 10, wherein in a MS-TOF mode of operation said multi-mode quadrupole rod set is operated in said second mode of operation so that parent ions become temporally separated as they pass through the time of flight region formed by said multi-mode quadrupole rod set.

25. A mass spectrometer as claimed in claim 10, wherein in a MS/MS-TOF mode of operation said further quadrupole rod set acts as a mass filter to mass filter parent ions.

26. A mass spectrometer as claimed in claim 10, wherein in a MS/MS-TOF mode of operation at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of parent ions entering or within said collision cell are fragmented upon entering or within said collision cell to form fragment ions.

27. A mass spectrometer as claimed in claim 10, wherein in a MS/MS-TOF mode of operation fragment ions are collisionally cooled and/or trapped within said collision cell.

28. A mass spectrometer as claimed in claim 10, wherein in a MS/MS-TOF mode of operation fragment ions are pulsed out of said collision cell.

29. A mass spectrometer as claimed in claim 10, wherein in a MS/MS-TOF mode of operation said multi-mode quadrupole rod set is operated in said second mode of operation so that fragment ions become temporally separated as they pass through the time of flight region formed by said multi-mode quadrupole rod set.

30. A mass spectrometer as claimed in claim 10, wherein said collision cell comprises a segmented rod set.

31. A mass spectrometer as claimed in claim 10, wherein said collision cell comprises a stacked ring set comprising a plurality of electrodes having apertures wherein ions are transmitted, in use, through said apertures.

32. A mass spectrometer as claimed in claim 10, wherein an axial DC voltage gradient is maintained in use along at least a portion of the length of said collision cell.

33. A mass spectrometer as claimed in claim 32, wherein in a mode of operation an axial DC voltage difference is maintained, in use, along at least a first portion of said collision cell and is selected from the group consisting of:

(i) 0.1-50 V;

(ii) 50-100 V;

(iii) 100-200 V;

(iv) 200-500 V;

(v) 500-1000 V;

(vi) 1000-2000 V;

(vii) 2000-3000 V;

(viii) 3000-4000 V;

(ix) 4000-5000 V;

(x) 5000-6000 V;

(xi) 6000-7000 V;

(xii) 7000-8000 V;

(xiii) 8000-9000 V;

(xiv) 9000-10000 V; and

(xv) >

10 kV.

34. A mass spectrometer as claimed in claim 32, wherein in a mode of operation an axial DC voltage gradient is maintained, in use, along at least a first portion of said collision cell selected from the group consisting of:

(i) 0.1-5 V/mm;

(ii) 5-10 V/mm;

(iii) 10-20 V/mm;

(iv) 20-30 V/mm;

(v) 30-40 V/mm;

(vi) 40-50 V/mm;

(vii) 50-60 V/mm;

(viii) 60-70 V/mm;

(ix) 70-80 V/mm;

(x) 80-90 V/mm;

(xi) 90-100 V/mm;

(xii) 100-150 V/mm;

(xiii) 150-200 V/mm;

(xiv) 200-250 V/mm;

(xv) 250-300 V/mm;

(xvi) 300-350 V/mm;

(xvii) 350-400 V/mm;

(xviii) 400-450 V/mm;

(xix) 450-500 V/mm; and

(xx) >

500 V/mm.

35. A mass spectrometer as claimed in claim 33, wherein said first portion is located within a region located 0-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the length of said collision cell measured from an ion entrance of said collision cell to an ion exit of said collision cell.

36. A mass spectrometer as claimed in claim 33, wherein said first portion is located in the rearmost 10%, 20%, 30%, 40% or 50% of said collision cell.

37. A mass spectrometer as claimed in claim 10, wherein said collision cell 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; and

(xv) >

150 electrodes.

38. A mass spectrometer as claimed in claim 10, wherein said collision cell is maintained, in use, at a pressure selected from the group consisting of:

(i) >

1.0×

10<sup>−

3</sup> mbar;

(ii) >

5.0×

10<sup>−

3</sup> mbar;

(iii) >

1.0×

10<sup>−

2</sup> mbar;

(iv) 10<sup>−

3</sup>−

10<sup>−

2</sup> mbar; and

(v) 10<sup>−

4</sup>−

10<sup>−

1</sup> mbar.

39. A mass spectrometer as claimed in claim 10, wherein in a mode of operation ions are trapped but are not substantially fragmented within said collision cell.

40. A mass spectrometer as claimed in claim 10, wherein in a mode of operation ions are trapped and are substantially fragmented within said collision cell.

41. A mass spectrometer as claimed in claim 10, wherein in a mode of operation ions are trapped within said collision cell and are progressively moved towards an exit of said collision cell.

42. A mass spectrometer as claimed in claim 10, wherein in a mode of operation ions are stored or trapped within said collision cell near the exit of said collision cell.

43. A mass spectrometer as claimed in claim 10, wherein in a mode of operation ions are collisionally cooled within said collision cell in an ion trapping region located near the exit of said collision cell.

44. A mass spectrometer as claimed in claim 10, wherein in a mode of operation electrodes forming said collision cell are maintained at different DC potentials so that at least a first and a second different stage axial acceleration electric field regions are provided to accelerate ions out of said collision cell.

45. A mass spectrometer as claimed in claim 44, wherein in use prior to accelerating ions out of said collision cell the pressure within said collision cell is reduced.

46. A mass spectrometer as claimed in claim 44, wherein the ratio of the axial electric field strength in said second stage axial acceleration electric field region to the axial electric field strength in said first stage axial acceleration electric field region is selected from the group consisting of:

(i) ≧

2;

(ii) ≧

3;

(iii) ≧

4;

(iv) ≧

5;

(v) ≧

6;

(vi) ≧

7;

(vii) ≧

8;

(viii) ≧

9; and

(ix) ≧

10.

47. A mass spectrometer as claimed in claim 44, wherein said collision cell further comprises one or more grid electrodes arranged between electrodes forming said collision cell, wherein one or more DC voltages are applied to said one or more grid electrodes in order to provide said first and/or said second stage axial acceleration electric field region.

48. A mass spectrometer as claimed in claim 10, wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are initially provided at a first axial position and are then subsequently provided at second, then third different axial positions along said collision cell.

49. A mass spectrometer as claimed in claim 10, wherein one or more transient DC voltages or one or more transient DC voltage waveforms move in use from one end of said collision cell to another end of said collision cell so that ions are urged along said collision cell.

50. A mass spectrometer as claimed in claim 48, wherein said one or more transient DC voltages 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.

51. A mass spectrometer as claimed in claim 48, wherein said one or more transient DC voltage waveforms comprise a repeating waveform.

52. A mass spectrometer as claimed in claim 51, wherein said one or more transient DC voltage waveforms comprise a square wave.

53. A mass spectrometer as claimed in claim 10, wherein said collision cell comprises a quadrupole rod set.

54. A mass spectrometer as claimed in claim 10, further comprising an AC or RF ion guide arranged upstream of said further quadrupole rod set, said AC or RF ion guide comprising a plurality of electrodes.

55. A mass spectrometer as claimed in claim 1, further comprising an AC or RF ion guide arranged upstream of said multi-mode quadrupole rod set, said AC or RF ion guide comprising a plurality of electrodes.

56. A mass spectrometer as claimed in claim 54, wherein said AC or RF ion guide comprises a quadrupole, hexapole, octapole or higher order multipole rod set.

57. A mass spectrometer as claimed in claim 54, wherein said AC or RF ion guide comprises a segmented rod set.

58. A mass spectrometer as claimed in claim 54, wherein said AC or RF ion guide comprise an ion tunnel ion guide comprising a plurality of electrodes having apertures through which ions are transmitted.

59. A mass spectrometer as claimed in claim 54, wherein said AC or RF ion guide is supplied with an AC or RF voltage having a frequency selected from the group consisting of:

(i) <

100 kHz;

(ii) 100-200 kHz;

(iii) 200-300 kHz;

(iv) 300-400 kHz;

(v) 400-500 kHz;

(vi) 0.5-1.0 MHz;

(vii) 1.0-1.5 MHz;

(viii) 1.5-2.0 MHz;

(ix) 2.0-2.5 MHz;

(x) 2.5-3.0 MHz;

(xi) 3.0-3.5 MHz;

(xii) 3.5-4.0 MHz;

(xiii) 4.0-4.5 MHz;

(xiv) 4.5-5.0 MHz;

(xv) 5.0-5.5 MHz;

(xvi) 5.5-6.0 MHz;

(xvii) 6.0-6.5 MHz;

(xviii) 6.5-7.0 MHz;

(xix) 7.0-7.5 MHz;

(xx) 7.5-8.0 MHz;

(xxi) 8.0-8.5 MHz;

(xxii) 8.5-9.0 MHz;

(xxiii) 9.0-9.5 MHz;

(xxiv) 9.5-10.0 MHz; and

(xxv) >

10.0 MHz.

60. A mass spectrometer as claimed in claim 54, wherein said AC or RF ion guide is supplied with an AC or RF voltage having an amplitude selected from the group consisting of:

(i) <

50V peak to peak;

(ii) 50-100V peak to peak;

(iii) 100-150V peak to peak;

(iv) 150-200V peak to peak;

(v) 200-250V peak to peak;

(vi) 250-300V peak to peak;

(vii) 300-350V peak to peak;

(viii) 350-400V peak to peak;

(ix) 400-450V peak to peak;

(x) 450-500V peak to peak; and

(xi) >

500V peak to peak.

61. A mass spectrometer as claimed in claim 54, wherein in a mode of operation parent ions are arranged to be trapped, stored or accumulated in said AC or RF ion guide whilst other ions are being collisionally cooled and/or fragmented in said collision cell and/or whilst ions are being transmitted through said multi-mode quadrupole ion trap operating in said second mode of operation.

62. A mass spectrometer as claimed in claim 54, wherein in a mode of operation ions are pulsed out of said AC or RF ion guide.

63. A mass spectrometer as claimed in claim 54, wherein one or more transient DC potentials or one or more DC potential waveforms are applied to said electrodes of said AC or RF ion guide.

64. A mass spectrometer as claimed in claim 63, wherein said one or more transient DC potentials or said one or more DC potential waveforms urge ions from one region of said AC or RF ion guide to another region of said AC or RF ion guide.

65. A mass spectrometer as claimed in claim 10, wherein an ion trap is arranged between said collision cell and said multi-mode quadrupole rod set.

66. A mass spectrometer as claimed in claim 1, further comprising a further drift or time of flight region arranged downstream of said multi-mode quadrupole rod set.

67. A mass spectrometer as claimed in claim 1, further comprising a reflectron arranged downstream of said multi-mode quadrupole rod set.

68. A method of mass spectrometry comprising:

providing a multi-mode quadrupole rod set and an ion detector;

operating said quadrupole rod set in a first mode of operation wherein said quadrupole rod set acts as a mass filter; and

operating said quadrupole rod set in a second mode of operation wherein said quadrupole rod set forms a time of flight region of a Time of Flight mass analyser.

69. A mass spectrometer comprising:

a first multi-mode AC or RF ion guide wherein in a first mode of operation said first AC or RF ion guide acts as an ion guide and wherein in a second mode of operation said first AC or RF ion guide forms a time of flight region.

70. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation ions are transmitted through said first AC or RF ion guide without being substantially mass filtered.

71. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation ions are not substantially fragmented within said first AC or RF ion guide.

72. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation ions are substantially continuously transmitted through said first AC or RF ion guide.

73. A mass spectrometer as claimed in claim 69, wherein in said second mode of operation ions are pulsed into said time of flight region.

74. A mass spectrometer as claimed in claim 69, wherein in said second mode of operation ions are transmitted through said first AC or RF ion guide without being substantially mass filtered and become temporally separated according to their mass to charge ratio.

75. A mass spectrometer as claimed in claim 74, further comprising an ion detector and wherein said ion detector determines the time of flight of said ions through said time of flight region.

76. A mass spectrometer as claimed in claim 69, further comprising a second AC or RF ion guide, wherein ions transmitted through said first multi-mode AC or RF ion guide are received by said second AC or RF ion guide.

77. A mass spectrometer as claimed in claim 76, wherein said second AC or RF ion guide comprises a segmented rod set.

78. A mass spectrometer as claimed in claim 76, wherein said second AC or RF ion guide comprise an ion tunnel ion guide comprising a plurality of electrodes having apertures through which ions are transmitted in use.

79. A mass spectrometer as claimed in claim 76, wherein in use one or more transient DC voltages or one or more transient DC voltage waveforms are initially provided at a first axial position and are then subsequently provided at second, then third different axial positions along said second AC or RF ion guide.

80. A mass spectrometer as claimed in claim 76, wherein one or more transient DC voltages or one or more transient DC voltage waveforms move in use from one end of said second AC or RF ion guide to another end of said second AC or RF ion guide so that ions are urged along said second AC or RF ion guide.

81. A mass spectrometer as claimed in claim 79, wherein said one or more transient DC voltages 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.

82. A mass spectrometer as claimed in claim 79, wherein said one or more transient DC voltage waveforms comprise a repeating waveform.

83. A mass spectrometer as claimed in claim 82, wherein said one or more transient DC voltage waveforms comprise a square wave.

84. A mass spectrometer as claimed in claim 79, wherein when said first multi-mode AC or RF ion guide is operated in said second mode of operation ions having mass to charge ratios within a first range are trapped in a first axial trapping region within said second AC or RF ion guide and ions having mass to charge ratios within a second different range are trapped in a second different axial trapping region within said second AC or RF ion guide.

85. A mass spectrometer as claimed in claim 84, wherein when said first multi-mode AC or RF ion guide is operated in said second mode of operation ions having mass to charge ratios within a third different range are trapped in a third axial trapping region within said second AC or RF ion guide and ions having mass to charge ratios within a fourth different range are trapped in a fourth different axial trapping region within said second AC or RF ion guide.

86. A mass spectrometer as claimed in claim 85, wherein when said first multi-mode AC or RF ion guide is operated in said second mode of operation ions having mass to charge ratios within a fifth range are trapped in a fifth axial trapping region within said second AC or RF ion guide and ions having mass to charge ratios within a sixth different range are trapped in a sixth different axial trapping region within said second AC or RF ion guide.

87. A mass spectrometer as claimed in claim 69, wherein in said first and/or second mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) greater than or equal to 1×

10<sup>−

7</sup> mbar;

(ii) greater than or equal to 5×

10<sup>−

7</sup> mbar;

(iii) greater than or equal to 1×

10<sup>−

6</sup> mbar;

(iv) greater than or equal to 5×

10<sup>−

6</sup> mbar;

(v) greater than or equal to 1×

10<sup>−

5</sup> mbar; and

(vi) greater than or equal to 5×

10<sup>−

5</sup> mbar.

88. A mass spectrometer as claimed in claim 69, wherein in said first and/or second mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) less than or equal to 1×

10<sup>−

4</sup> mbar;

(ii) less than or equal to 5×

10<sup>−

5</sup> mbar;

(iii) less than or equal to 1×

10<sup>−

5</sup> mbar;

(iv) less than or equal to 5×

10<sup>−

6</sup> mbar;

(v) less than or equal to 1×

10<sup>−

6</sup> mbar;

(vi) less than or equal to 5×

10<sup>−

7</sup> mbar; and

(vii) less than or equal to 1×

10<sup>−

7</sup> mbar.

89. A mass spectrometer as claimed in claim 69, wherein in said first and/or second mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

4</sup> mbar;

(ii) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

5</sup> mbar;

(iii) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

5</sup> mbar;

(iv) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

6</sup> mbar;

(v) between 1×

10<sup>−

7</sup> and 1×

10<sup>−

6</sup> mbar;

(vi) between 1×

10<sup>−

7</sup> and 5×

10<sup>−

7</sup> mbar;

(vii) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

4</sup> mbar;

(viii) between 5×

10<sup>−

7</sup> and 5×

10<sup>−

5</sup> mbar;

(ix) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

5</sup> mbar;

(x) between 5×

10<sup>−

7</sup> and 5×

10<sup>−

6</sup> mbar;

(xi) between 5×

10<sup>−

7</sup> and 1×

10<sup>−

6</sup> mbar;

(xii) between 1×

10<sup>−

6</sup> mbar and 1×

10<sup>−

4</sup> mbar;

(xiii) between 1×

10<sup>−

6</sup> and 5×

10<sup>−

5</sup> mbar;

(xiv) between 1×

10<sup>−

6</sup> and 1×

10<sup>−

6</sup> mbar;

(xv) between 1×

10<sup>−

6</sup> and 5×

10<sup>−

6</sup> mbar;

(xvi) between 5×

10<sup>−

6</sup> mbar and 1×

10<sup>−

4</sup> mbar;

(xvii) between 5×

10<sup>−

6</sup> and 5×

10<sup>−

5</sup> mbar;

(xviii) between 5×

10<sup>−

6</sup> and 1×

10<sup>−

5</sup> mbar;

(xix) between 1×

10⁵ mbar and 1×

10<sup>−

4</sup> mbar;

(xx) between 1×

10<sup>−

5</sup> and 5×

10<sup>−

5</sup> mbar; and

(xxi) between 5×

10<sup>−

5</sup> and 1×

10<sup>−

4</sup> mbar.

90. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) greater than or equal to 0.0001 mbar;

(ii) greater than or equal to 0.0005 mbar;

(iii) greater than or equal to 0.001 mbar;

(iv) greater than or equal to 0.005 mbar;

(v) greater than or equal to 0.01 mbar;

(vi) greater than or equal to 0.05 mbar;

(vii) greater than or equal to 0.1 mbar;

(viii) greater than or equal to 0.5 mbar;

(ix) greater than or equal to 1 mbar;

(x) greater than or equal to 5 mbar; and

(xi) greater than or equal to 10 mbar.

91. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) less than or equal to 10 mbar;

(ii) less than or equal to 5 mbar;

(iii) less than or equal to 1 mbar;

(iv) less than or equal to 0.5 mbar;

(v) less than or equal to 0.1 mbar;

(vi) less than or equal to 0.05 mbar;

(vii) less than or equal to 0.01 mbar;

(viii) less than or equal to 0.005 mbar;

(ix) less than or equal to 0.001 mbar;

(x) less than or equal to 0.0005 mbar; and

(xi) less than or equal to 0.0001 mbar.

92. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation said first AC or RF ion guide is maintained at a pressure selected from the group consisting of:

(i) between 0.0001 and 10 mbar;

(ii) between 0.0001 and 1 mbar;

(iii) between 0.0001 and 0.1 mbar;

(iv) between 0.0001 and 0.01 mbar;

(v) between 0.0001 and 0.001 mbar;

(vi) between 0.001 and 10 mbar;

(vii) between 0.001 and 1 mbar;

(viii) between 0.001 and 0.1 mbar;

(ix) between 0.001 and 0.01 mbar;

(x) between 0.01 and 10 mbar;

(xi) between 0.01 and 1 mbar;

(xii) between 0.01 and 0.1 mbar;

(xiii) between 0.1 and 10 mbar;

(xiv) between 0.1 and 1 mbar; and

(xv) between 1 and 10 mbar.

93. A mass spectrometer as claimed in claim 69, wherein said first multi-mode AC or RF ion guide comprises a quadrupole, hexapole, octapole or higher order multipole rod set.

94. A mass spectrometer as claimed in claim 69, wherein said first multi-mode AC or RF ion guide comprises a segmented rod set.

95. A mass spectrometer as claimed in claim 69, wherein said first multi-mode AC or RF ion guide comprise an ion tunnel ion guide comprising a plurality of electrodes having apertures through which ions are transmitted in use.

96. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation said first AC or RF ion guide is supplied with an AC or RF voltage having a frequency selected from the group consisting of:

(i) <

100 kHz;

(ii) 100-200 kHz;

(iii) 200-300 kHz;

(iv) 300-400 kHz;

(v) 400-500 kHz;

(vi) 0.5-1.0 MHz;

(vii) 1.0-1.5 MHz;

(viii) 1.5-2.0 MHz;

(ix) 2.0-2.5 MHz;

(x) 2.5-3.0 MHz;

(xi) 3.0-3.5 MHz;

(xii) 3.5-4.0 MHz;

(xiii) 4.0-4.5 MHz;

(xiv) 4.5-5.0 MHz;

(xv) 5.0-5.5 MHz;

(xvi) 5.5-6.0 MHz;

(xvii) 6.0-6.5 MHz;

(xviii) 6.5-7.0 MHz;

(xix) 7.0-7.5 MHz;

(xx) 7.5-8.0 MHz;

(xxi) 8.0-8.5 MHz;

(xxii) 8.5-9.0 MHz;

(xxiii) 9.0-9.5 MHz;

(xxiv) 9.5-10.0 MHz; and

(xxv) >

10.0 MHz.

97. A mass spectrometer as claimed in claim 69, wherein in said second mode of operation said first AC or RF ion guide is supplied with an AC or RF voltage having a frequency selected from the group consisting of:

(i) <

100 kHz;

(ii) 100-200 kHz;

(iii) 200-300 kHz;

(iv) 300-400 kHz;

(v) 400-500 kHz;

(vi) 0.5-1.0 MHz;

(vii) 1.0-1.5 MHz;

(viii) 1.5-2.0 MHz;

(ix) 2.0-2.5 MHz;

(x) 2.5-3.0 MHz;

(xi) 3.0-3.5 MHz;

(xii) 3.5-4.0 MHz;

(xiii) 4.0-4.5 MHz;

(xiv) 4.5-5.0 MHz;

(xv) 5.0-5.5 MHz;

(xvi) 5.5-6.0 MHz;

(xvii) 6.0-6.5 MHz;

(xviii) 6.5-7.0 MHz;

(xix) 7.0-7.5 MHz;

(xx) 7.5-8.0 MHz;

(xxi) 8.0-8.5 MHz;

(xxii) 8.5-9.0 MHz;

(xxiii) 9.0-9.5 MHz;

(xxiv) 9.5-10.0 MHz; and

(xxv) >

10.0 MHz.

98. A mass spectrometer as claimed in claim 69, wherein in said first mode of operation said first AC or RF ion guide is supplied with an AC or RF voltage having an amplitude selected from the group consisting of:

(i) <

50V peak to peak;

(ii) 50-100V peak to peak;

(iii) 100-150V peak to peak;

(iv) 150-200V peak to peak;

(v) 200-250V peak to peak;

(vi) 250-300V peak to peak;

(vii) 300-350V peak to peak;

(viii) 350-400V peak to peak;

(ix) 400-450V peak to peak;

(x) 450-500V peak to peak; and

(xi) >

500V peak to peak.

99. A mass spectrometer as claimed in claim 69, wherein in said second mode of operation said first AC or RF ion guide is supplied with an AC or RF voltage having an amplitude selected from the group consisting of:

(i) <

50V peak to peak;

(ii) 50-100V peak to peak;

(iii) 100-150V peak to peak;

(iv) 150-200V peak to peak;

(v) 200-250V peak to peak;

(vi) 250-300V peak to peak;

(vii) 300-350V peak to peak;

(viii) 350-400V peak to peak;

(ix) 400-450V peak to peak;

(x) 450-500V peak to peak; and

(xi) >

500V peak to peak.

100. A mass spectrometer as claimed in claim 69, further comprising an ion source selected from the group consisting of:

(i) an Electrospray (“

ESI”

) ion source;

(ii) an Atmospheric Pressure Chemical Ionisation (“

APCI”

) ion source;

(iii) an Atmospheric Pressure Photo Ionisation (“

APPI”

) ion source;

(iv) a Matrix Assisted Laser Desorption Ionisation (“

MALDI”

) ion source;

(v) a Laser Desorption Ionisation (“

LDI”

) ion source;

(vi) an Inductively Coupled Plasma (“

ICP”

) ion source;

(vii) an Electron Impact (“

EI”

) ion source;

(viii) a Chemical Ionisation (“

CI”

) ion source;

(ix) a Fast Atom Bombardment (“

FAB”

) ion source; and

(x) a Liquid Secondary Ions Mass Spectrometry (“

LSIMS”

) ion source.

101. A mass spectrometer as claimed in claim 69, further comprising a pulsed ion source.

102. A mass spectrometer as claimed in claim 69, further comprising a continuous ion source.

103. A method of mass spectrometry comprising:

providing a multi-mode AC or RF ion guide;

operating said AC or RF ion guide in a first mode of operation wherein said AC or RF ion guide acts as an ion guide; and

operating said AC or RF ion guide in a second mode of operation wherein said AC or RF ion guide forms a time of flight region.

104. A mass spectrometer comprising a collision cell, said collision cell comprising a plurality of electrodes wherein in a mode of operation a first stage axial acceleration electric field region and a second different stage axial field region are provided to accelerate ions out of said collision cell.

105. A mass spectrometer as claimed in claim 104, wherein the ratio of the axial electric field strength in said second stage axial acceleration electric field region to the electric field strength in said first stage axial acceleration electric field region is selected from the group consisting of:

(i) ≧

2;

(ii) ≧

3;

(iii) ≧

4;

(iv) ≧

5;

(v) ≧

6;

(vi) ≧

7;

(vii) ≧

8;

(viii) ≧

9; and

(ix) ≧

10.

106. A mass spectrometer as claimed in claim 104, wherein prior to accelerating ions out of said collision cell the pressure within said collision cell is reduced.

107. A method of mass spectrometry comprising:

providing a collision cell comprising a plurality of electrodes;

providing a first stage axial acceleration electric field across a first region of said collision cell; and

providing a second different stage axial field across a second different region of said collision cell;

wherein said first and second stage axial fields are provided to accelerate ions out of said collision cell.