Tandem collision/reaction cell for inductively coupled plasma-mass spectrometry (ICP-MS)

10290,482

15/920081

March 13, 2018

A tandem collision/reaction cell for an inductively coupled plasma-mass spectrometry (ICP-MS) system includes a first ion guide, a second ion guide, and an intermediate electrode in the vicinity of an exit end of the first ion guide. A DC potential barrier is applied to the intermediate electrode. The cell may provide two or more stages of an ion-molecule collision process.

Agilent Technologies, Inc. (Santa Clara, CA, US)

Agilent Technologies, Inc. (Santa Clara, CA, US)

1. A tandem collision/reaction cell, comprising: a housing comprising a cell entrance, a cell exit spaced from the cell entrance along a longitudinal axis of the collision/reaction cell, and a gas supply port communicating with an interior of the housing; a first ion guide positioned in the housing and comprising a first ion guide entrance and a first ion guide exit, the first ion guide configured to generate a first RF confining field effective to confine ions in a radial direction orthogonal to the longitudinal axis; a second ion guide positioned in the housing and comprising a second ion guide entrance and a second ion guide exit, the second ion guide configured to generate a second RF confining field effective to confine ions in a radial direction orthogonal to the longitudinal axis; and an intermediate electrode configured to generate an on-axis DC potential barrier in a vicinity of the first ion guide exit, wherein the on-axis DC potential barrier is effective to prevent at least some interfering ions from exiting the first ion guide and low enough to allow analyte ions of smaller cross-section than the interfering ions to exit the first ion guide.

2. The tandem collision/reaction cell of claim 1 , wherein the on-axis DC potential barrier has a magnitude in a range from 0.1 V to 10 V.

3. The tandem collision/reaction cell of claim 1 , wherein the first ion guide and the second ion guide are multipole ion guides.

4. The tandem collision/reaction cell of claim 3 , wherein: the first ion guide comprises a plurality of elongated first ion guide electrodes positioned at a radial distance orthogonal to the longitudinal axis and circumferentially spaced from each other about the longitudinal axis, and defining the first ion guide entrance and the first ion guide exit; and the second ion guide comprises a plurality of elongated second ion guide electrodes positioned at a radial distance orthogonal to the longitudinal axis and circumferentially spaced from each other about the longitudinal axis, and defining the second ion guide entrance and the second ion guide exit, the second ion guide entrance being spaced from the first ion guide exit by an axial gap.

5. The tandem collision/reaction cell of claim 1 , comprising a voltage source configured to apply a first RF potential superimposed on a first DC bias potential to electrodes of the first ion guide to generate the first RF confining field, apply a second RF potential superimposed on a second DC bias potential to electrodes of the second ion guide to generate the second RF confining field, and apply a third DC potential to the intermediate electrode to generate the on-axis DC potential barrier.

6. The tandem collision/reaction cell of claim 5 , wherein the voltage source has a configuration selected from the group consisting of: the voltage source is configured to apply the first DC bias potential in a range from −50 V to −10 V; the voltage source is configured to apply the second DC bias potential in a range from −100 V to −20 V; the voltage source is configured to apply the third DC potential in a range from −50 V to +500 V; and a combination of two or more of the foregoing.

7. The tandem collision/reaction cell of claim 5 , comprising an ion optics component positioned downstream from the second ion guide exit, wherein the voltage source is configured to apply a fourth DC potential to the ion optics component, and the fourth DC potential has a magnitude that produces an on-axis potential more positive than the second DC bias potential.

8. The tandem collision/reaction cell of claim 7 , wherein the fourth DC potential is in a range from −90 V to 0 V.

9. The tandem collision/reaction cell of claim 1 , wherein the intermediate electrode has a configuration selected from the group consisting of: the intermediate electrode is a plate having an aperture surrounding the first ion guide at the first ion guide exit; the intermediate electrode is a plate comprising an inside surface defining an aperture surrounding the first ion guide at the first ion guide exit, wherein the first ion guide comprises a plurality of first ion guide electrodes arranged in a multipole configuration, and the inside surface protrudes between the first ion guide electrodes; the intermediate electrode is a plate having an aperture between the first ion guide exit and the second ion guide entrance; the intermediate electrode is an ion guide positioned between the first ion guide exit and the second ion guide entrance, and is configured to generate a third RF confining field; the intermediate electrode is a multipole ion guide positioned between the first ion guide exit and the second ion guide entrance, and is configured to generate a third RF confining field; the intermediate electrode, the first ion guide, and the second ion guide are multipole ion guides, the intermediate electrode is positioned between the first ion guide exit and the second ion guide entrance, and the intermediate electrode has a shorter axial length than the first ion guide and the second ion guide; and the intermediate electrode, the first ion guide, and the second ion guide are multipole ion guides, the intermediate electrode is positioned between the first ion guide exit and the second ion guide entrance, and the intermediate electrode has an axial length in a range of 10% to 60% of an axial length of the first ion guide and an axial length of the second ion guide.

10. The tandem collision/reaction cell of claim 1 , comprising an ion optics component positioned downstream from the second ion guide exit and configured to generate a second DC potential barrier effective to prevent at least some interfering ions from passing through a mass analyzer downstream from the cell exit, and low enough to allow analyte ions to pass through the mass analyzer.

11. The tandem collision/reaction cell of claim 10 , wherein the ion optics component has a position selected from the group consisting of: the ion optics component is positioned at the cell exit; the ion optics component is positioned outside of the housing; the ion optics component is positioned between the cell exit and a mass analyzer; the ion optics component is positioned at an entrance of a mass analyzer; and the ion optics component is a mass analyzer.

12. An inductively coupled plasma-mass spectrometry (ICP-MS) system, comprising: the tandem collision/reaction cell of claim 1 ; and a mass analyzer communicating with the cell exit.

13. A method for operating a tandem collision/reaction cell in an inductively coupled plasma-mass spectrometry (ICP-MS) system, the method comprising: flowing a collision/reaction gas into the tandem collision/reaction cell, the tandem collision/reaction cell comprising a cell entrance, a cell exit spaced from the cell entrance along a longitudinal axis of the tandem collision/reaction cell, a first ion guide between the cell entrance and a second ion guide, and the second ion guide between the first ion guide and the cell exit; generating a first RF confining field in the first ion guide to confine ions in a radial direction orthogonal to the longitudinal axis; generating a second RF confining field in the second ion guide to confine ions in a radial direction orthogonal to the longitudinal axis; generating a first DC potential barrier in a vicinity of a first ion guide exit of the first ion guide; generating a second DC potential barrier downstream from a second ion guide exit of the second ion guide; transmitting analyte ions and interfering ions through the cell entrance and into the first ion guide, the analyte ions and the interfering ions having been produced from ionizing a sample under analysis, wherein the analyte ions and the interfering ions collide with the collision/reaction gas and lose kinetic energy, and the first DC potential barrier is high enough to prevent at least some of the interfering ions from exiting the first ion guide and low enough to allow the analyte ions to exit the first ion guide; and transmitting the analyte ions from the first ion guide into the second ion guide, wherein the analyte ions and any interfering ions in the second ion guide collide with the collision/reaction gas and lose kinetic energy, and the second DC potential barrier is high enough to prevent at least some of the interfering ions from passing through a mass analyzer downstream from the cell exit, and low enough to allow the analyte ions to pass through the mass analyzer.

14. The method of claim 13 , wherein the magnitudes of the first DC potential barrier and the second DC potential barrier are selected from the group consisting of: the magnitude of the first DC potential barrier is in a range from 0.1 V to 10 V; the magnitude of the second DC potential barrier is in a range from 0.1 V to 10 V; and both of the foregoing.

15. A method for analyzing a sample, the method comprising: producing analyte ions from the sample; transmitting the analyte ions into the tandem collision/reaction cell of claim 14 ; operating the tandem collision/reaction cell according to the method of claim 14 ; and transmitting the analyte ions into a mass analyzer.

16. The method of claim 13 , wherein the tandem collision/reaction cell comprises an intermediate electrode in a vicinity of the first ion guide exit, and generating the first DC potential barrier comprises applying a DC potential to the intermediate electrode.

17. The method of claim 13 , comprising applying a first RF potential superimposed on a first DC bias potential to the first ion guide to generate the first RF confining field, and a second RF potential superimposed on a second DC bias potential to the second ion guide to generate the second RF confining field.

18. The method of claim 17 , wherein the first DC bias potential and the second DC bias potential have magnitudes selected from the group consisting of: the first DC bias potential and the second DC bias potential have negative magnitudes; the first DC bias potential is in a range from −50 V to −10 V; the second DC bias potential is in a range from −100 V to −20 V; and the second DC bias potential is more negative than the first DC potential.

19. The method of claim 17 , wherein the first DC bias potential and the second DC bias potential have a configuration selected from the group consisting of: at least one of the first DC bias potential or the second DC bias potential is constant along a length of the first ion guide or the second ion guide; and at least one of the first DC bias potential or the second DC bias potential is an axial DC potential gradient along a length of the first ion guide or the second ion guide.

20. The method of claim 13 , comprising, before transmitting the analyte ions through the entrance and into the collision/reaction cell, performing an operation selected from the group consisting of: producing the analyte ions by exposing the sample to an inductively coupled plasma; producing the analyte ions by exposing the sample to an inductively coupled plasma produced by operating a plasma torch; and flowing the sample from a nebulizer or a spray chamber into a plasma torch, and producing the analyte ions by exposing the sample to an inductively coupled plasma produced by operating the plasma torch.

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