Mass spectrometer with an electrostatic ion trap

1. A mass spectrometer with an electrostatic ion trap connected to a voltage supply for applying electric potentials thereto, the mass spectrometer comprising:

an outer electrode having ion-repelling electric potentials applied thereto;

a plurality of inner electrodes, each having an ion-attracting electric potential applied thereto, wherein the outer electrode and the inner electrodes are shaped and arranged in such a way that the electric potential between the outer electrode and the inner electrodes corresponds to a superposition of partial electric potentials of following form:

U

⁢

(

x

,

y

,

z

)

=

U

o

+

U

C

·

ln

⁡

[

(

X

2

+

Y

2

)

2

-

2

·

b

2

·

(

X

2

-

Y

2

)

+

b

4

a

4

]

+

k

x

·

x

2

+

k

y

·

y

2

+

k

z

·

z

2

wherein x, y and z are Cartesian coordinates, X=(x+x o )·cos(α), Y=(y+y o )·sin(α) and x o , y o , α, U 0 , U C , a, b, k x , k y and k z are parameters where the sum over the parameters k x , k y and k z is equal to zero, the parameter k z is larger than zero and the parameter b is not equal to zero.

2. The mass spectrometer according to claim 1 , wherein each of the plurality of inner electrodes has a spindle shape, and the electric potential between the outer electrode and the plurality of spindle-shaped inner electrodes corresponds to an electric potential of following form:

U

⁢

(

x

,

y

,

z

)

=

U

o

+

U

C

·

ln

⁡

[

(

x

2

+

y

2

)

2

-

2

·

b

2

·

(

x

2

-

y

2

)

+

b

4

a

4

]

-

k

2

·

(

x

2

+

y

2

)

+

k

·

z

2

.

3. The mass spectrometer according to claim 2 , wherein the inner surface of the outer electrode and outer surfaces of the spindle-shaped inner electrodes correspond to equipotential surfaces of the electric potential U(x,y,z).

4. The mass spectrometer according to claim 2 , wherein the outer electrode has an opening therein, which opening is located in a plane of symmetry between the spindle-shaped inner electrodes.

5. The mass spectrometer according to claim 4 , wherein the aperture has one of a circular shape and a slit shape with a long dimension perpendicular to the plane of symmetry.

6. The mass spectrometer according to claim 4 , further comprising:

an ion source;

an ion optic; and

an ion guide system that transfers ions from the ion source to the ion optic, the ion optic being located between the ion guide system and the opening in the outer electrode and adapted to introduce ions through the opening into an interior of the electrostatic ion trap.

7. The mass spectrometer according to claim 4 , further comprising an ion source with a sample support and an ion optic, the ion optic being located between the sample support and the opening in the outer electrode.

8. The mass spectrometer according to claim 7 , wherein the ion source is a MALDI ion source.

9. The mass spectrometer according to claim 6 or 7 , wherein the ion optic comprises a power supply which generates temporally adjustable voltages so that ions are pulsed into the electrostatic ion trap.

10. The mass spectrometer according to claim 2 , wherein at least one of the electrodes of the electrostatic ion trap is segmented and the electrode system comprises additional, auxiliary electrodes.

11. The mass spectrometer according to claim 2 , wherein the voltage supply comprises a mechanism that generates temporally adjustable voltages that are applied to the electrodes.

12. The mass spectrometer according to claim 2 , wherein the electrostatic ion trap has a z-axis and comprises an ion detector which measures one of a motion of ions along the z-axis and a radial motion of ions as a function of time.

13. The mass spectrometer according to claim 12 , wherein the ion detector comprises detection elements in which ions induce electric signals due to their oscillations along the z-axis.

14. The mass spectrometer according to claim 13 , wherein the detection elements are segments of the electrodes of the electrostatic ion trap.

15. A method for the introduction of externally-generated ions into an electrostatic ion trap comprising:

(a) providing an outer electrode for the trap with ion-repelling electric potentials applied thereto;

(b) providing a plurality of inner electrodes for the trap, each inner electrode having a spindle shape and an ion attracting potential applied thereto, the outer electrode and the inner electrodes being shaped and arranged so that the electric potential between the outer electrode and the plurality of spindle-shaped inner electrodes corresponds to a harmonic electric potential of following form:

U

⁢

(

x

,

y

,

z

)

=

U

o

+

U

C

·

ln

⁡

[

(

X

2

+

Y

2

)

2

-

2

·

b

2

·

(

X

2

-

Y

2

)

+

b

4

a

4

]

+

k

x

·

x

2

+

k

y

·

y

2

+

k

z

·

z

2

;

and

(c) injecting the ions via an ion optic through an opening in the outer electrode, which opening is located in a plane of symmetry between the inner electrodes and outside a minimum of the harmonic electric potential.

16. The method according to claim 15 , wherein electric potentials applied to the electrodes of the electrostatic ion trap are reduced during the injection.

17. A method for the introduction of externally-generated ions into the electrostatic ion trap comprising:

(a) providing an outer electrode for the trap with ion-repelling electric potentials applied thereto;

providing a plurality of inner electrodes for the trap, each inner electrode having a spindle shape and an ion attracting potential applied thereto, the outer electrode and the inner electrodes being shaped and arranged so that the electric potential between the outer electrode and the plurality of spindle-shaped inner electrodes corresponds to a harmonic electric potential of following form:

U

⁢

(

x

,

y

,

z

)

=

U

o

+

U

C

·

ln

⁡

[

(

X

2

+

Y

2

)

2

-

2

·

b

2

·

(

X

2

-

Y

2

)

+

b

4

a

4

]

+

k

x

·

x

2

+

k

y

·

y

2

+

k

z

·

z

2

;

and

(c) injecting the ions via an ion optic through an opening in the outer electrode, which opening is located in a plane of symmetry between the inner electrodes and in a minimum of the harmonic electric potential.

18. The method according to claim 17 , wherein the electric potential applied to the inner electrodes is continuously reduced during the introduction of the ions.

19. The method according to claim 15 or 17 , wherein the ions have a kinetic energy of less than 1,000 electronvolts during the injection into the electrostatic ion trap.

20. The method according to claim 15 or 17 , wherein the ions have a kinetic energy of less than 100 electronvolts during the injection into the electrostatic ion trap.