Ion focusing
The invention generally relates to apparatuses for focusing ions at or above ambient pressure and methods of use thereof. In certain embodiments, the invention provides an apparatus for focusing ions that includes an electrode having a cavity, at least one inlet within the electrode configured to operatively couple with an ionization source, such that discharge generated by the ionization source is injected into the cavity of the electrode, and an outlet. The cavity in the electrode is shaped such that upon application of voltage to the electrode, ions within the cavity are focused and directed to the outlet, which is positioned such that a proximal end of the outlet receives the focused ions and a distal end of the outlet is open to ambient pressure.
1. A method for analyzing a sample, the method comprising:
causing a discharge from a desorption electrospray ionization (DESI) source to impact a sample on a substrate in a manner that the sample is desorbed from the substrate to form droplets of the sample;
introducing the droplets of sample into a cavity in the presence of a turbulent gas flow within the cavity to produce sample ions that are focused in the cavity, wherein the focusing step comprises focusing the sample ions at ambient pressure;
directing the sample ions that have been focused into an inlet of a mass spectrometer; and
analyzing the sample ions.
2. The method according to claim 1 , wherein the method further comprises transferring the sample ions through an ion transfer member prior to the focusing step.
3. The method according to claim 1 , wherein the cavity is an electrode that is shaped to focus ions and focusing further comprises:
applying a voltage to the electrode, thereby focusing the sample ions; and
directing the sample ions to an outlet positioned with respect to the cavity to receive the sample ions that have been focused.
4. The method according to claim 3 , wherein the introducing step comprises introducing the sample ions into an ellipsoidal cavity of the electrode.
5. The method according to claim 3 , wherein the cavity further comprises:
at least one inlet within the electrode configured to operatively couple with the DESI source, such that discharge generated by the DESI source that has reflected from the substrate comprising the sample is injected into the cavity of the electrode; and
an outlet;
wherein the cavity in the electrode is shaped such that upon application of voltage to the electrode, ions within the cavity are focused and directed to the outlet, which is positioned such that a proximal end of the outlet receives the focused ions and a distal end of the outlet is open to ambient pressure.
6. The method according to claim 5 , wherein the cavity is an ellipsoidal cavity and the introducing step comprises introducing the sample ions into an ellipsoidal cavity of the electrode.
7. The method according to claim 5 , wherein the cavity is pressurized and the introducing step comprises introducing the sample ions into the pressurized cavity.
8. The method according to claim 5 , wherein the directing step comprises directing the sample ions to an outlet connected to the electrode.
9. The method according to claim 5 , wherein the directing step comprises directing the sample ions to an outlet spaced from the electrode.
10. The method according to claim 5 , wherein the directing step comprises directing the sample ions to a grounded outlet.
11. The method according to claim 5 , further comprising providing gas to the DESI source through a gas inlet.
12. The method according to claim 5 , further comprising a plurality of ring electrodes positioned within an interior portion of the cavity such that they are aligned with the outlet, wherein the electrodes are arranged in order of decreasing inner diameter with respect to the outlet, the method further comprising applying a potential to the plurality of ring electrodes.