METHOD AND APPARATUS FOR ION MANIPULATION USING MESH IN A RADIO FREQUENCY FIELD

• US 20110192969A1
• Filed: 07/28/2008
• Published: 08/11/2011
• Est. Priority Date: 07/28/2008
• Status: Active Grant

• Current Assignee: LECO Corporation
• Original Assignee: LECO Corporation
• Inventors: Verentchikov, Anatoli N.
• Granted Patent: US 8,373,120 B2
• Time in Patent Office: Days
• US Class Current: 250/282
• CPC Class Codes: H01J 49/062 Ion guides linear ion traps performing mass selection H01J49/4225, mass filters H01J49/421

Abstract

Ion manipulation systems include ion repulsion by an RF field penetrating through a mesh. Another comprises trapping ions in a symmetric RF field around a mesh. The system uses macroscopic parts, or readily available fine meshes, or miniaturized devices made by MEMS, or flexible PCB methods. One application is ion transfer from gaseous ion sources with focusing at intermediate and elevated gas pressures. Another application is the formation of pulsed ion packets for TOF MS within trap array. Such trapping is preferably accompanied by pulsed switching of RF field and by gas pulses, preferably formed by pulsed vapor desorption. Ion guidance, ion flow manipulation, trapping, preparation of pulsed ion packets, confining ions during fragmentation or exposure to ion to particle reactions and for mass separation are disclosed. Ion chromatography employs an ion passage within a gas flow and through a set of multiple traps with a mass dependent well depth.

Claims

1. In a mass spectrometer, an guide comprising:

a mesh electrode having cells of a size ranging from 10 μ

m to 1 mm;

a space above said mesh electrode for transporting ions from an external ion source into the mass spectrometer;

a second electrode positioned behind said mesh electrode at a distance comparable to a cell size of said mesh electrode; and

a radio frequency voltage supply coupled between said mesh and second electrodes to provide a radio frequency field above the mesh electrode for repelling the ions.

2. The ion guide of claim 1 and further including a third electrode located above said mesh electrode to form a substantially symmetric RF field around said mesh electrode.

3. The ion guide of claim 2 and further including a gas supply for supplying a flow of gas through said mesh electrode for collisional dampening of the ions, said supply comprising one of a continuous gas supply, a pulsed gas valve, and a cold surface exposed to a pulsed particle beam.

4. The ion guide of claim 1 and further including at least one DC voltage supply coupled to at least one of said mesh and second electrodes.

5. The ion guide of claim 1 wherein said mesh defines mesh cells and wherein the average density of ions is adjusted below single ion per mesh cell.

6. The ion guide of claim 1 wherein said radio frequency voltage supply includes a secondary coil and is switched off either by disconnecting two parts of said secondary coil or by clamping outputs of said secondary coil by employing FTMOS transistors, said transistors being coupled by one of:

(i) low capacitance diodes; and

(ii) linear RF amplifier.

7. The ion guide of claim 1 wherein said mesh defines mesh cells and the geometrical scale of said mesh cells and distance between said mesh and said second electrode is below 3 mm and wherein the RF frequency is adjusted in the range from 100 KHz up to 1 GHz and in reverse proportion to said mesh cell size.

8. The ion guide of claim 1 wherein said mesh defines mesh cells and the geometrical scale of said mesh cells and distance between said mesh and said second electrode is below 1 mm;

below 0.33 mm;

below 0.1 mm;

below 30 μ

m;

below 10 μ

m;

below 3 μ

m;

below 1 μ

m; and

wherein the RF frequency is adjusted in the range from 2 MHz up to 1 GHz and in reverse proportion to said mesh cell size.

9. The ion guide of claim 3 wherein said gas supply provides a gas pressure range expanded proportionally to the frequency of said RF voltage source is in the range from about 1 Torr to about ambient atmospheric gas pressure.

10. The ion guide of claim 1 wherein said mesh electrode is supported and aligned using a dielectric material and wherein said dielectric material is a layer which has a shape of one of:

a sheet between mesh and electrode;

a bridge under mesh wires;

islands under mesh wires; and

a bridge between two mesh wires.

11. The ion guide of claim 10 wherein said mesh and dielectric layer form a sandwich and is made using one of PCB technology on rigid or flexible sheets;

MEMS technology;

controlled particle deposition; and

oxidation of said mesh to form an insulating layer.

12. The ion guide of claim 11 wherein said mesh electrode is a repelling RF mesh electrode wherein an ion channel is formed by said repelling RF mesh electrode with a penetrating RF field and one of:

a same repelling RF mesh wrapped into a cylinder or a box of arbitrary shape;

another repelling RF mesh;

a DC repelling electrode;

a set of electrodes forming a moving wave of electrostatic field; and

an RF trapping mesh.

13. The ion guide of claim 12 wherein said ion channel is formed into one of a bent channel;

a loop channel;

parallel channels of co-flows and counter-flows;

a smooth or stepped funnel;

merging channels;

splitting channels;

a channel with a free drain;

a capped channel;

a channel with a valve switch;

an ion reservoir;

a pulse damper; and

an ion pump.

14. The ion guide of claim 12 wherein the ion flow within said ion channel is induced by one of:

a gas flow;

an axial electrostatic field;

a moving wave of electrostatic field; and

a moving magnetic field.

15. The ion guide of claim 1 wherein the ion guide serves as one of the following devices:

an ion beam guide;

an ion beam guide with collisional dampening;

an array of parallel ion guides;

an array of ion traps;

an ion fragmentation cell;

an ion storing reactor with particles;

a cell for ion spectroscopy;

an ion source for continuous injection into a mass spectrometer;

an ion source for pulsed injection into a mass spectrometer;

an ion packet pulsed source for injection into a time-of-flight mass-spectrometer;

a mass filter; and

a mass analyzer.

16. An interface for transporting ions from gaseous ion sources into a mass spectrometer comprising at least an ion guide of claim 1.

17. The interface of claim 16 wherein said ion guide operates as an ion guide in a wide mass range of gas pressures from 1 mtorr and up to 1 atmosphere and wherein in order to ensure RF confinement, the mesh scale L and RF frequencies F are adjusted as:

L(mm)<

1/P(Torr) and F(MHz)>

1*P(Torr).

18. The interface of claim 16 and including multiple nozzles employed to sample a higher gas flow from said gaseous ion source.

19. The interface of claim 16 wherein said ion guide extends through multiple stages of differential pumping.

20. The interface of claim 16 wherein said ion guide is used to merge ion flows from multiple ion sources for one of:

(i) alternative operation of individual ion sources, such as ESI, APCI, APPI, CI, EI, etc.;

(ii) periodic switching between main ion source and an ion source with mass calibrating compound; and

(iii) simultaneous operation for mixing ion flows either for their reaction, for mass calibration or sensitivity calibration.

21. The interface of claim 16 wherein said ion guide is used to excite ions for the purposes of (i) breaking ion clusters;

(ii) ion fragmentation; and

(iii) inducing or inhibiting ion to particle reactions.

22. The interface of claim 16 wherein said ion guide is used for ion introduction into the mass spectrometer by one of (i) direct and continuous introduction into continuously operating mass spectrometer (MS), such as quadrupole, magnet sector MS, or TOF MS with orthogonal accelerator;

(ii) pulsed axial introduction into periodically operating MS, such as ITMS, FTMS, orbitrap and TOF MS with a synchronized orthogonal accelerator; and

(iii) orthogonal pulsed acceleration into a periodically operating MS.

23. A pulsed ion converter, comprising an ion guide of claim 1 wherein the mass spectrometer is a time-of-flight mass spectrometer, wherein ions are injected into the converter from an external ion source and ion packets are directly ejected by a pulse of electric field out of said ion guide and into the time-of-flight mass spectrometer.

24. The pulsed ion converter of claim 23 wherein said mesh electrode is a repelling RF mesh electrode wherein an ion channel is formed by said repelling RF mesh electrode with a penetrating RF field and one of:

a same repelling RF mesh wrapped into a cylinder or a box of arbitrary shape;

another repelling RF mesh;

a DC repelling electrode;

a set of electrodes forming a moving wave of electrostatic field; and

an RF trapping mesh.

25. The pulsed ion converter of claim 23 wherein said ion guide comprises an array of ion guides.

26. The pulsed ion converter of claim 23 wherein both gas pressure and RF frequency are adjusted reverse proportional to mesh cell size.

27. The pulsed ion converter of claim 23 wherein said radio frequency voltage supply includes a secondary coil and is switched off either by disconnecting two parts of said secondary coil or by clamping outputs of said secondary coil by employing FTMOS transistors, said transistors being coupled by one of:

(i) low capacitance diodes; and

(ii) a linear RF amplifier, wherein the delay between RF signal switching and the application of electric pulses is adjusted to improve time focusing in said time-of-flight mass spectrometer.

28. The pulsed ion converter of claim 33 wherein the strength of said pulsed electric field is adjusted in reverse proportion to reduced mesh geometrical scale.

29. The pulsed ion converter of claim 23 wherein said ion guide protrudes through multiple stages of differential pumping, wherein gas pressure varies substantially along said ion guide and wherein ion injection into the ion guide occurs at substantially higher gas pressure compared to the region of ion ejection.

30. A mass selective storage device comprising an ion guide of claim 1.

31. A mass selective storage device comprising an ion guide of claim 16.

32. An ion chromatograph comprising an ion guide of claim 2 wherein ions are driven between individual traps by gas flow and wherein ion trapping within cells varies in time by adjusting RF and DC signals.

33. An ion chromatograph comprising an ion guide of claim 32 wherein the resolving power is improved by one of (i) by using resonant excitation of secular ion motion;

(ii) by adjusting a ratio of quadrupolar and higher order components of RF and DC fields; and

(iii) by multiple repetition of mass separation steps in a large array of sequential microscopic mass separating cells.

34. An ion source with internal ionization comprising RF repelling surface of claim 1 for one of (i) ion retention;

(ii) guidance;

(iii) excitation;

(iv) collisional dampening;

(v) cooling of internal energy in gas collisions;

(vi) converting pulsed ion flux into a continuous or quasi-continuous ion flux;

(vii) surface protection against charging and material deposition;

(viii) retaining charged particles of opposite polarities;

(ix) retaining ions in a wide mass range; and

(x) crude filtering ions by mass to charge ratio.

35. The ion source of claim 34 wherein internal ionization is made by one of (i) electrons of vapor samples;

(ii) photons of vapor samples;

(iii) reactant ions of vapor samples;

(iv) fast particles from surfaces;

(v) photons from surfaces; and

(vi) by photons from solid or liquid matrixes.

36. A fragmentation cell comprising an ion guide of claim 1 wherein ions are retained by radio frequency fields and ion fragmentation is induced by one of (i) ion injection into said ion guide at a sufficiently high kinetic energy;

(ii) ion impinging surface of the ion guide;

(iii) ion bombardment by fast atoms;

(iv) ion illumination by photons;

(v) ion exposure to fast electrons;

(vi) ion exposure to slow electrons for electron capture dissociation;

(vii) ion reactions with particles of opposite polarity; and

(viii) ion reactions with aggressive vapors.

37. A method of ion manipulation for use in a mass spectrometer, the method comprising:

providing a mesh electrode having cells of a size ranging from 10 μ

m to 1 mm;

providing a space above the mesh electrode for transporting ions from an external ion source into the mass spectrometer;

providing a second electrode behind the mesh electrode at a distance comparable to cell size of the mesh electrode; and

applying an RF field penetrating through the mesh electrode to repel the ions.

39. The method of claim 37 and further comprising a step of ion collisional dampening by one of providing a continuous gas flow;

providing a pulsed gas jet from a pulsed nozzle;

or providing a pulsed flux of desorbed vapors from a cold surface induced by pulsed particle beam.

40. The method of claim 37 and further comprising a step of applying a DC field to said mesh electrode to attract to said mesh electrode.

41. The method of claim 37 wherein the RF field is switched off for releasing the ions.

42. The method of claim 37 and further including the step of selecting the geometrical scale of said RF field to one of below 1 mm;

below 0.3 mm;

below 0.1 mm;

below 30 μ

m;

below 10 μ

m;

below 3 μ

m;

below 1 μ

m and wherein the RF frequency is adjusted in reverse proportion to the geometrical scale up to several GHz.

43. The method of claim 37 and further supplying a flow of gas and wherein the gas pressure range is proportional to the RF frequency and varies from 1 mtorr to atmospheric gas pressure.

44. The method of claim 37 and further including the step of inserting a dielectric into said RF field as a method of mesh support and alignment to a counter electrode.

45. The method of claim 37 and further including forming an ion channel and wherein the ion flow is guided within said ion channel, said ion channel being formed by a repelling RF field and one of:

a same repelling RF field wrapped into a cylinder or a box of arbitrary shape;

another repelling RF field;

a DC repelling field;

a moving wave of electrostatic field; and

RF trapping field.

46. The method of claim 45 wherein the guidance of the ion flow within said ion channel is used for transformation of said ion flow by one of the following methods:

bending;

looping;

arranging parallel channels for co-flows and counter-flows;

confining ion flows in a smooth or stepped funnel;

merging;

splitting;

free draining;

capping;

valve switching;

storing in ion reservoirs;

pulse damping;

modulating velocity of ion flow; and

pumping.

47. The method of claim 45 wherein ion flow is induced by one of the following methods by gas flow;

by axial electrostatic field;

by moving wave of electrostatic field; and

by moving magnetic field.

48. The method of claim 37 wherein said ion manipulation is used for one of the group of:

ion beam transfer;

ion beam confinement;

ion trapping;

ion fragmentation;

ion exposure to ion to particle reactions for a predetermined time;

ion continuous injection into a mass spectrometer;

ion pulsed injection into a mass spectrometer; and

ion packet injection into the time-of-flight mass-spectrometer.

38. A method of ion manipulation for use in a mass spectrometer, the method comprising:

providing a mesh electrode having cells of a size ranging from 10 μ

m to 1 mm;

providing a space above the mesh electrode for transporting ions from an external ion source into the mass spectrometer;

providing a second electrode behind the mesh electrode at a distance comparable to cell size of the mesh electrode; and

applying a radio frequency field substantially symmetrically around said mesh electrode for trapping ions.