Ion guide

1. An ion guide for mass spectrometry comprising an electrode arrangement of at least two electrodes, at least one of which is an RF electrode, arranged adjacent to each other but spaced apart on a planar surface of a dielectric material, wherein the arrangement has been produced by separately providing the dielectric material and arranging the electrodes on it in a subsequent step, and wherein the electrodes are arranged at a distance from an ion flow path, wherein a portion of the dielectric surface is exposed between an adjacent pair of the spaced apart electrodes and wherein at least one electrode of said adjacent pair of electrodes is arranged to overhang the exposed portion of surface between them such that there is no direct line of sight from the ion flow path to the exposed portion of dielectric surface, ion-facing surfaces of said adjacent pair of electrodes are at different distances from the surface of the dielectric material and the electrode of the pair with the surface at a greater distance from the dielectric surface overhangs the exposed portion of dielectric surface and at least a part of the other electrode of the pair.

2. The ion guide according to claim 1 , wherein the dielectric material is glass, ceramic or printed circuit board.

3. The ion guide according to claim 1 , wherein the ion guide is a multipole.

4. The ion guide according to claim 1 , wherein there is a plurality of said pairs of adjacent electrodes having a portion of the dielectric surface exposed between them.

5. The ion guide according to claim 1 , wherein the electrode of said adjacent pair of electrodes that overhangs the exposed portion is an RF electrode.

6. The ion guide according to claim 1 , wherein the exposed portion of dielectric surface between electrodes is in the form of one or more grooves formed in the portion of dielectric surface between the adjacent electrodes.

7. The ion guide according to claim 1 , wherein the electrodes of the electrode arrangement comprise at least one DC electrode.

8. The ion guide according to claim 7 , wherein the electrodes comprise at least one DC electrode that provides an axial field.

9. The ion guide according to claim 8 , wherein the at least one DC electrode providing an axial field is segmented, wherein the size of gaps between segments of the DC electrode are <0.15 mm and/or such gaps are formed as grooves in the dielectric surface.

10. The ion guide according to claim 1 , wherein the electrodes are planar.

11. The ion guide according to claim 1 , wherein the electrode arrangement is a first such electrode arrangement and there is a second such electrode arrangement spaced apart from the first such electrode arrangement and parallel thereto and the first and second such electrode arrangements form a multipole wherein the ion optical axis is defined between the first and second such electrode arrangements.

12. The ion guide according to claim 11 , wherein the gap between the first and second such electrode arrangements is at least 1 mm.

13. The ion guide according to claim 11 , wherein the first and second such electrode arrangements each comprise N RF electrodes with alternating RF phases (N=2, 3, 4 . . . ), thereby forming a 2N polar multipole.

14. The ion guide according to claim 1 , wherein the ion guide forms one or more of the following: an ion trap, a mass analyser, a collision cell, a fragmentation cell, an ion mobility spectrometer, an ion transport multipole and an ion funnel.

15. The ion guide according to claim 1 , wherein the ion guide is a straight or bent ion guide.

16. The ion guide according to claim 11 , wherein the gap between the first and second such electrode arrangements is at least 3 mm.

17. The ion guide according to claim 11 , wherein the gap between the first and second such electrode arrangements is at least 5 mm.