Method and apparatus for generation of reagent ions in a mass spectrometer

1. A reagent ion source for a mass spectrometer, comprising:

a reagent vapor source for supplying reagent vapor to a reagent ionization volume;

the reagent ionization volume being located within a chamber of the mass spectrometer and having, during operation of the mass spectrometer, an interior region maintained at a low vacuum pressure;

a set of electrodes disposed within the reagent ionization volume;

a voltage source for controllably applying a discharge potential across the set of electrodes to generate an electrical discharge that ionizes the reagent vapor to produce reagent ions;

a reagent ion outlet extending from the interior region of the reagent ionization volume to the chamber of the mass spectrometer; and

at least one ion optical element for transporting the reagent ions to a succeeding chamber of the mass spectrometer, the at least one ion optical element being positioned along an analyte ion path;

wherein the reagent ionization volume includes a discharge region extending between the set of electrodes, an ionization region communicating with the reagent ion outlet, and a partition dividing the discharge region from the ionization region, the partition having a conductance limited aperture formed therein such that the ionization region and the discharge region are held at substantially different pressures during device operation.

2. The reagent ion source of claim 1 , wherein the reagent vapor source includes an evaporation chamber for holding a quantity of reagent substance in condensed-phase form, and a heater for controlling the temperature of the reagent substance to regulate the production of reagent vapor.

3. The reagent ion source of claim 1 , wherein the reagent vapor source further includes a first inlet for receiving a flow of carrier gas, the carrier gas assisting to transport the reagent vapor to the reagent ionization volume.

4. The reagent ion source of claim 1 , wherein the reagent substance is a polyaromatic hydrocarbon.

5. The reagent ion source of claim 1 , wherein an axis defined between the set of electrodes in the discharge region is generally transverse to a primary flow axis in the ionization region.

6. The reagent ion source of claim 1 , wherein the location within the interior region in which the electrical discharge occurs is maintained at a pressure between 0.5 and 10 Torr.

7. The reagent ion source of claim 1 , wherein the voltage source pulses the discharge potential to selectively switch on or off production of reagent ions.

8. The reagent ion source of claim 1 , wherein the reagent vapor source comprises:

a first evaporation chamber for holding a quantity of a first reagent substance in condensed-phase form; and

a second evaporation chamber for holding a quantity of a second reagent substance in condensed-phase form.

9. The reagent ion source of claim 8 , wherein the at least one ion optical element is configured to selectively transmit a first reagent ion species formed from the first reagent substance or a second reagent ion species formed from the second reagent substance.

10. The reagent ion source of claim 8 , further comprising a flow switch for selectively directing vapor from the first or second reagent substance to the reagent ionization volume.

11. The reagent ion source of claim 1 , wherein a potential applied to the at least one ion optical element is varied to selectively transmit the reagent ions or the analyte ions.

12. The reagent ion source of claim 1 , wherein the electrical discharge is a low-current electrical discharge.

13. The reagent ion source of claim 12 , wherein the low-current electrical discharge is a glow discharge.

14. Apparatus for supplying analyte ions and reagent ions in a mass spectrometer, comprising:

an analyte ionization chamber maintained, during operation of the mass spectrometer, at a generally atmospheric pressure;

a first passageway for transporting analyte ions formed in the analyte ionization chamber to a first chamber maintained at reduced pressure relative to the analyte ionization chamber;

a reagent vapor source for supplying reagent vapor to a reagent ionization volume, the reagent ionization volume having, during operation of the mass spectrometer, an interior region maintained at a low vacuum pressure;

a set of electrodes disposed within the reagent ionization volume;

a voltage source for controllably applying a discharge potential across the set of electrodes to generate an electrical discharge that ionizes the reagent vapor to produce reagent ions;

a reagent ion outlet extending from the interior region of the reagent ionization volume to the first chamber; and

at least one ion optical element for transporting both the analyte ions and the reagent ions from the first chamber to a second chamber having a pressure lower than the first chamber;

wherein the reagent ionization volume includes a discharge region extending between the set of electrodes, an ionization region communicating with the reagent ion outlet, and a partition dividing the discharge region from the ionization region, the partition having a conductance limited aperture formed therein such that the ionization region and the discharge region are held at substantially different pressures during device operation.

15. The apparatus of claim 14 , wherein the reagent vapor source includes an evaporation chamber for holding a quantity of reagent substance in condensed-phase form, and a heater for controlling the temperature of the reagent substance to regulate the production of reagent vapor.

16. The apparatus of claim 14 , wherein the reagent vapor source further includes a first inlet for receiving a flow of carrier gas, the carrier gas assisting to transport the reagent vapor to the reagent ionization volume.

17. The apparatus of claim 14 , wherein the reagent substance is a polyaromatic hydrocarbon.

18. The apparatus of claim 14 , wherein an axis extending between the set of electrodes in the discharge region is generally transverse to a primary gas flow axis in the ionization region.

19. The apparatus of claim 14 , wherein the location within the interior region in which the electrical discharge occurs is maintained at a pressure between 0.5 and 10 Ton.

20. The apparatus of claim 14 , wherein the voltage source pulses the discharge potential to selectively switch on or off production of reagent ions.

21. The apparatus of claim 14 , wherein the reagent vapor source comprises:

a first evaporation chamber for holding a quantity of a first reagent substance in condensed-phase form; and

a second evaporation chamber for holding a quantity of a second reagent substance in condensed-phase form.

22. The apparatus of claim 21 , wherein the at least one ion optical element is configured to selectively transmit a first reagent ion species formed from the first reagent substance or a second reagent ion species formed from the second reagent substance.

23. The apparatus of claim 21 , further comprising a flow switch for selectively directing vapor from the first or second reagent substance to the reagent ionization volume.

24. The apparatus of claim 14 , further comprising an electrospray probe for introducing charged droplets containing the analyte into the analyte ionization chamber.

25. The apparatus of claim 14 , wherein a potential applied to the ion optic element is varied to selectively transmit the reagent or analyte ions.

26. The apparatus of claim 14 , wherein the at least one ion optical element comprises a plurality of spaced ring electrodes to which RF voltages are applied.

27. The apparatus of claim 14 , wherein the at least one ion optical element comprises a skimmer.

28. The apparatus of claim 14 , wherein the electrical discharge is a low-current electrical discharge.

29. The apparatus of claim 28 , wherein the low-current electrical discharge is a glow discharge.