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An ion trap mass spectrometer uses electrospray ionization to introduce multiply-charged positive ions in an axial direction into a quadrupole ion trap and glow discharge ionization to introduce singly-charged negative ions in a radial direction into the ion trap. Methods of controlling ion-to-ion c

An ion trap mass spectrometer uses electrospray ionization to introduce multiply-charged positive ions in an axial direction into a quadrupole ion trap and glow discharge ionization to introduce singly-charged negative ions in a radial direction into the ion trap. Methods of controlling ion-to-ion charge transfer reactions include applying a combination of a dipolar DC voltage and a dipolar RF voltage across endcap electrodes to allow partial charge state neutralization reactions to occur between the positive and negative ions and then control suspension and resumption of further charge state neutralization reactions. The remaining ions can be further processed and transformed and a mass spectrum created by scanning a quadrupolar RF field.

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An ion trap mass spectrometer uses electrospray ionization to introduce multiply-charged positive ions in an axial direction into a quadrupole ion trap and glow discharge ionization to introduce singly-charged negative ions in a radial direction into the ion trap. Methods of controlling ion-to-ion c

An ion trap mass spectrometer uses electrospray ionization to introduce multiply-charged positive ions in an axial direction into a quadrupole ion trap and glow discharge ionization to introduce singly-charged negative ions in a radial direction into the ion trap. Methods of controlling ion-to-ion charge transfer reactions include applying a combination of a dipolar DC voltage and a dipolar RF voltage across endcap electrodes to allow partial charge state neutralization reactions to occur between the positive and negative ions and then control suspension and resumption of further charge state neutralization reactions. The remaining ions can be further processed and transformed and a mass spectrum created by scanning a quadrupolar RF field. means for focusing electrons emitted by said photocathode onto said electron sensor. 16. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator a reflective mode photocathode positioned at said second end of said light concentrator; and means for focusing electrons emitted by said photocathode onto said electron sensor; wherein said means comprises first and second annular electrodes interior to said light concentrator and separated by a gap. 17. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator; a reflective mode photocathode positioned at said second end of said light concentrator; and means for focusing electrons emitted by said photocathode onto said electron sensor; wherein said light concentrator comprises an evacuated chamber enclosing said electron sensor and said photocathode. 18. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator; a reflective mode photocathode positioned at said second end of said light concentrator; and means for focusing electrons emitted by said photocathode onto said electron sensor; wherein said light concentrator comprises a Winston cone. 19. A photosensor as recited in claims 15, 16, 17, 18, further comprising an entrance window at said first end of said light concentrator. 20. A photosensor as recited in claim 19, wherein said entrance window is hexagonal-shaped. 21. A photosensor as recited in claim 19, wherein said electron sensor is attached to and positioned central to said entrance window. 22. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator; an entrance window at said first end of said light concentrator; wherein said electron sensor is attached to and positioned central to said entrance window; a reflective mode photocathode positioned at said second end of said light concentrator; and means for focusing electrons emitted by said photocathode onto said electron sensor. 23. A photosensor as recited in claim 15, 16, 17, 18 or 22, wherein said photocathode comprises a type III-V material. 24. A photosensor as recited in claim 23, if wherein said type III-V material comprises GaAsP. 25. A photosensor as recited in claims 16, 17, 18, 22, further comprising a positive-ion feedback protection electrode adjacent said electron sensor. 26. A photosensor as recited in claims 15, 16, 17, 18, 22, wherein said light concentrator includes an interior reflective coating. 27. A photosensor as recited in claims 15, 16, 17, 18, 22, wherein said electron sensor is selected from the group consisting essentially of a P-I-N diode, an avalanche photo diode, and a scintillator. 28. A photosensor as recited in claim 22, wherein said entrance window is hexagonal-shaped. 29. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator; a reflective mode photocathode positioned at said second end of said light concentrator; and first and second annular electrodes interior to said light concentrator and separated by a gap, said electrodes configured for focusing photoelectrons emitted by said photocathode onto said electron sensor. 30. A photosensor as recited in claim 29, wherein said light concentrator comprises an evacuated chamber enclosing said electron sensor and said photocathode. 31. A photosensor as recited in claim 29, wherein said light concentrator comprises a Winston cone. 32. A photosensor as recited in claim 29, wherein said photocathode comprises a type III-V material. 33. A photosensor as recited in claim 32, wherein said type III-V material comprises GaAsP. 34. A photosensor as recited in claim 29, further comprising a positive-ion feedback protection electrode adjacent said electron sensor. 35. A photosensor as recited in claim 29, wherein said light concentrator includes an interior reflective coating. 36. A photosensor as recited in claim 29, wherein said electron sensor is selected from the group consisting essentially of a P-I-N diode, an avalanche photo diode, and a scintillator. 37. A photosensor as recited in claim 29, further comprising an entrance window at said first end of said light concentrator. 38. A photosensor as recited in claim 37, wherein said entrance window is hexagonal-shaped. 39. A photosensor as recited in claim 37, wherein said electron sensor is attached to and positioned central to said entrance window. 40. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an electron sensor positioned at said first end of said light concentrator; a positive-ion feedback protection electrode adjacent said electron sensor; a reflective mode photocathode positioned at said second end of said light concentrator; and first and second annular electrodes interior to said light concentrator and separated by a gap, said electrodes configured for focusing photoelectrons emitted by said photocathode onto said electron sensor. 41. A photosensor as recited in claim 40, wherein said light concentrator comprises an evacuated chamber enclosing said electron sensor and said photocathode. 42. A photosensor as recited in claims 40, wherein said light concentrator comprises a Winston cone. 43. A photosensor as recited in claim 40, wherein said photocathode comprises a type III-V material. 44. A photosensor as recited in claim 43, wherein said type III-V material comprises GaAsP. 45. A photosensor as recited in claim 40, wherein said light concentrator includes an interior reflective coating. 46. A photosensor as recited in claim 40, wherein said electron sensor is selected from the group consisting essentially of a P-I-N diode, an avalanche photo diode, and a scintillator. 47. A photosensor as recited in claim 40, further comprising an entrance window at said first end of said light concentrator. 48. A photosensor as recited in claim 47, wherein said entrance window is hexagonal-shaped. 49. A photosensor as recited in claim 47, wherein said electron sensor is attached to and positioned central to said entrance window. 50. A photosensor, comprising: a compound parabolic light concentrator having first and second ends; an entrance window positioned at said first end of said light concentrator; an electron sensor positioned at said first end of said light concentrator central to said entrance window; a positive-ion feedback protection electrode adjacent said electron sensor; a reflective mode photocathode positioned at said second end of said light concentrator; and first and second annular electrodes interior to said light concentrator and separated by a gap, said electrodes configured for focusing photoelectrons emitted by said photocathode onto said electron sensor. 51. A photosensor as recited in claim 50, wherein said light concentrator comprises an evacuated chamber enclosing said electron sensor and said photocathode. 52. A photosensor as recited in claim 50, wherein said light concentrator comprises a Winston cone. 53. A photosensor as recited in claim 50, wherein said photocathode comprises a type III-V material. 54. A photosensor as recited in claim 53, wherein said type III-V material comprises GaAsP. 55. A photosensor as recited in claim 50, wherein said light concentrator includes an interior reflective coating. 56. A photosensor as recited in claim 50, wherein said electron sensor is selected from the group consisting essentially of a P-I-N diode, an avalanche photo diode, and a scintillator. 57. A photosensor as recited