Multiple ion gate method and apparatus
A second gate in an Ion Mobility Spectrometer is used to select or block different time windows of the ion mobility spectrum. A second gate in the Ion Mobility Mass Spectrometer is used to modulate peak intensities in the IMS spectrum, allowing each peak in the IMS spectrum to be unambiguously matched with its set of fragment ions in a subsequent MS-MS mass spectrum.
1. A method for operating an ion mobility spectrometer, comprising:
(a) Opening a first ion gate to allow a packet of mixed ions into the ion mobility analyzer,
(b) Separating ions in the ion mobility analyzer,
(c) For each opening of the first gate, opening a second gate multiple times according to a waveform consisting of a series of time windows to allow ions with certain ion mobilities to pass through the second gate and/or to block the ions with other ion mobilities.
2. The method of claim 1 , wherein the series of time windows is predetermined by on-line or off-line ion mobility measurement of the mixed ions.
3. The method of claim 1 , wherein the series of time windows is predetermined by theoretical calculation of ion mobility of the mixed ions.
4. The method of claim 1 , wherein the series of time windows is chosen to select ions with certain collision cross section from the mixed ions.
5. The method of claim 1 , wherein the ions with certain ion mobilities are the ions of interest.
6. The method of claim 1 , wherein the time windows when the second gate is closed are chosen to selectively block ions with specific ion mobilities.
7. The method of claim 1 , further comprising: analyzing the ions that passed through the second gate with a mass spectrometer.
8. The method of claim 1 , further comprising:
(a) generating two or more waveforms, wherein the two or more waveforms have different combinations of opening times and widths;
(b) opening and closing the second ion gate according to the first waveform, while collecting a spectrum;
(c) opening and closing the second ion gate according to the second and subsequent waveforms, while collecting additional spectra;
(d) comparing the two or more spectra.
9. The method of claim 8 , further comprising:
(a) detecting a first ion mobility spectrum from a sample;
(b) generating two waveforms based on the ion mobility spectrum, wherein the two waveforms have different combinations of notch sizes for each of multiple ion mobility spectrum peaks;
(c) opening and closing the second ion gate according to the first waveform, while collecting fragment ion data from the ions that were allowed through the second ion gate, where the fragment ion data is collected in a mass spectrometer that is downstream of the IMS, and where the mass spectrometer has the ability to fragment ions;
(d) opening and closing the second ion gate according to the second waveform, while collecting fragment ion data in the mass spectrometer;
(e) comparing the two fragment ion mass spectra, and matching each fragment ion with its peak in the first IMS spectrum based on the ratios of the fragment peak intensities detected with the two waveforms, and the notch sizes of the two waveforms.
10. The method of claim 9 , wherein the first ion mobility spectrum is detected using a Faraday plate.
11. The method of claim 9 , wherein the first ion mobility spectrum is detected using the mass spectrometer.
12. The method of claim 1 , wherein the second gate is a segmented ion gate.
13. A ion mobility spectrometer, comprising:
(a) a first ion gate to allow a packet of mixed ions into an ion mobility analyzer to separate ions,
(b) a second gate, and
(c) a controller controlling the gates such that, for each opening of the first gate, the second gate is opened multiple times at a series of time windows to allow ions with certain ion mobilities to pass through the second gate and/or to block the ions with other ion mobilities.
14. The apparatus of claim 13 , further comprising a Faraday detector.
15. The apparatus of claim 14 , wherein the Faraday detector is a pass-through Faraday detector which allows a portion of the ions to be detected and the remaining portion to pass into a mass spectrometer.
16. The apparatus of claim 15 , wherein the Faraday detector is before the second gate.
17. The apparatus of claim 15 , wherein the Faraday detector is after the second gate.
18. The apparatus of claim 15 , further comprising a mass spectrometer that is behind the second gate and/or the pass-through Faraday detector.
19. The apparatus of claim 18 , wherein the second ion gate is the mass spectrometer inlet.
20. The apparatus of claim 13 , further comprising a mass spectrometer that is behind the second gate.
21. The apparatus of claim 13 , wherein the second gate is a segmented ion gate.