Multi-reflecting ion optical device
A multi-reflecting ion optical device includes electrostatic field generating means configured to generate electrostatic field defined by a superposition of first and second distributions of electrostatic potential Φ EF , Φ LS . The first distribution Φ EF subjects ions to energy focusing in a flight direction and the second distribution Φ LS subjects ions to stability in one lateral direction, to stability in another lateral direction for the duration of at least a finite number of oscillations in the one lateral direction and to subject ions to energy focusing in the one lateral direction for a predetermined energy range.
1. A multi-reflecting ion optical device comprising electrostatic field generating means configured to generate electrostatic field defined by a superposition of first and second mutually independent distributions of electrostatic potential (Φ EF , Φ LS , whereby ion motion in a flight direction is decoupled from ion motion in lateral directions, orthogonal to the flight direction, said first distribution of electrostatic potential (Φ EF being effective to subject ions having the same mass-to-charge ratio to energy focusing with respect to the flight direction and said second distribution of electrostatic potential Φ LS being effective to subject ions to stability in one said lateral direction, to stability in another said lateral direction for the duration of at least a finite number of oscillations in said one lateral direction and to subject ions having the same mass-to-charge ratio to energy focusing with respect to said one lateral direction for a predetermined energy range.
2. An ion optical device as claimed in claim 1 wherein said first distribution of electrostatic potential Φ EF is effective to subject ions having the same mass-to-charge ratio to ideal energy focusing with respect to the flight direction.
3. An ion optical device as claimed in claim 1 wherein said second distribution of electrostatic potential Φ LS has the form:
Φ
LS
=
ϕ
(
x
)
-
y
2
ϕ
″
(
x
)
+
y
4
24
ϕ
(
4
)
(
x
)
-
y
6
720
ϕ
(
6
)
(
x
)
+
…
wherein x and y respectively represent distance along mutually orthogonal X- and Y-axis lateral directions, φ(x) represents the distribution of electrostatic potential as a function of distance x along the X-axis direction and φ″(x), φ (4) (x) and φ (6) (x) are respectively the second, fourth and sixth derivatives of φ(x) with respect to distance x.
4. An ion optical device as claimed in claim 1 wherein said second distribution of electrostatic potential Φ LS has the form defined by equations 14 and 15 described herein.
5. An ion optical device as claimed in claim 1 having the form of a multi-reflecting time-of-flight mass analyser.
6. A time-of-flight mass spectrometer including an ion source for supplying ions, a multi-reflecting time-of-flight mass analyser as claimed in claim 5 for analysing ions supplied by said ion source, and a detector for receiving ions having the same mass-to-charge ratio and different energies at substantially the same time after ions have been separated according to mass-to-charge ratio by the multi-reflecting time-of-flight mass analyser.
7. An ion optical device as claimed in claim 1 having the form of an ion trap.
8. An ion optical device as claimed in claim 7 wherein said ion trap includes image current detection means effective to generate a mass spectrum responsive to ion motion in the ion trap.
9. An ion optical device as claimed in claim 7 wherein said ion trap is arranged to carry out mass-selective ejection of ions to generate a mass spectrum.
10. An ion optical device is claimed in claim 7 wherein said ion trap is an ion trap storage device.
11. An ion optical device as claimed in claim 1 including an ion source mounted on and enclosed by an electrode structure of said electrostatic field generating means.
12. As ion optical device as claimed in claim 11 wherein said ion source is a MALDI ion source.
13. An ion optical device as claimed in claim 11 including means for irradiating the ion source with pulses of laser radiation introduced via an opening in an electrode of the electrode structure.
14. An ion optical device as claimed in claim 2 wherein said second distribution of electrostatic potential Φ LS has the form:
Φ
LS
=
ϕ
(
x
)
-
y
2
ϕ
″
(
x
)
+
y
4
24
ϕ
(
4
)
(
x
)
-
y
6
720
ϕ
(
6
)
(
x
)
+
…
wherein x and y respectively represent distance along mutually orthogonal X- and Y-axis lateral directions, φ(x) represents the distribution of electrostatic potential as a function of distance x along the X-axis direction and φ″(x), φ (4) (x) and φ (6) (x) are respectively the second, fourth and sixth derivatives of φ(x) with respect to distance x.
15. An ion optical device as claimed in claim 2 wherein said second distribution of electrostatic potential Φ LS has the form defined by equations 14 and 15 described herein.
16. An ion optical device as claimed claim 2 having the form of a multi-reflecting time-of-flight mass analyser.