Fourier transform mass spectrometer

Patent metadata

Field	Value
Publication number	US-10446384-B2
Application number	US-201615567474-A
Country	US
Kind code	B2
Filing date	Apr 19, 2016
Priority date	Apr 25, 2015
Publication date	Oct 15, 2019
Grant date	Oct 15, 2019

Abstract

A quadrupole is filled with ions and the ions are cooled by applying a pressure and gas flow within the quadrupole. Ions are trapped in the quadrupole by applying a DC voltage and an RF voltage to quadrupole rods of the quadrupole, one or more DC voltages to a plurality of auxiliary electrodes of the quadrupole, and a DC voltage and an RF voltage to an exit lens at the end of the quadrupole. The ions are coherently oscillated after the filling and cooling by applying a coherent excitation between at least two rods of the quadrupole rods. The coherently oscillating ions are axially ejected through the exit lens and to a destructive detector for detection by changing one or more voltages of the one or more DC voltages of the plurality of auxiliary electrodes and changing the DC voltage of the exit lens.

First claim

What is claimed is:

1. A system for exciting and ejecting ions for destructive Fourier transform mass spectrometry (FTMS) mass analysis using a linear ion trap (LIT) quadrupole, comprising:
a quadrupole that includes quadrupole rods that have an entrance end for receiving ions and an exit end for ejecting ions and a plurality of auxiliary electrodes;
an exit lens located coaxially with the quadrupole rods near the exit end of the quadrupole rods;
a destructive detector located coaxially with the exit lens and located on the other side of the exit lens; and
a processor in communication with the quadrupole, the exit lens, and the destructive detector that
in order to fill the quadrupole with ions and cool the ions once filled, applies a pressure and gas flow within the quadrupole by controlling gas inlets and outlets of the quadrupole;
in order to trap the ions in the quadrupole during the filling and cooling, applies a direct current (DC) voltage and a radio frequency (RF) voltage to the quadrupole rods, one or more DC voltages to the plurality of auxiliary electrodes, and a DC voltage and an RF voltage to the exit lens,
in order to oscillate the ions after the filling and cooling, applies an excitation between at least two rods of the quadrupole rods, and
in order to axially eject the oscillating ions through the exit lens and to the destructive detector for detection after the excitation is applied, changes one or more voltages of the one or more DC voltages of the plurality of auxiliary electrodes and changes the DC voltage of the exit lens.

2. The system of claim 1 , wherein the processor changes the one or more voltages of the one or more DC voltages of the auxiliary electrodes and changes the DC voltage of the exit lens so that the oscillating ions are ejected fast enough to prevent the loss of coherence, but slow enough to provide the oscillating ions to the destructive detector over a period time long enough to calculate a spectrum from the oscillating ions.

3. The system of claim 1 , wherein the processor controls the gas inlets and outlets of the quadrupole to apply the pressure within the quadrupole at a value between 0.5×10 −5 and 5×10 −5 torr.

4. The system of claim 1 ,
wherein the plurality of auxiliary electrodes comprise a collar electrode surrounding the central portion of the quadrupole rods, and a plurality of linear accelerator (Linac) electrodes located near the exit end,
wherein in order to trap the ions in the quadrupole during the filling and cooling, the processor applies one or more DC voltages to the plurality of auxiliary electrodes by applying a DC voltage to the collar electrode, a DC voltage to the plurality of Linac electrodes, and
wherein in order to axially eject the oscillating ions, the processor changes one or more voltages of the one or more DC voltages of the plurality of auxiliary electrodes by changing the DC voltage of the collar electrode.

5. The system of claim 1 , wherein the excitation comprises a dipolar DC excitation pulse voltage.

6. The system of claim 5 , wherein the processor applies the dipolar DC excitation pulse voltage to the at least two rods of the quadrupole rods by controlling a frequency generator and a toroidal transformer placed between the at least two rods of the quadrupole rods.

7. The system of claim 6 , wherein the processor applies the dipolar DC excitation pulse voltage with a pulse width between 0.5 to 5 μs.

8. The system of claim 4 , wherein the processor changes the DC voltage of the collar electrode and changes the DC voltage of the exit lens so that the oscillating ions are ejected through the exit lens and to the destructive detector over a time period of between 15 and 30 ms.

9. The system of claim 4 , wherein in order to trap positive ions in the quadrupole during the filling and cooling, the processor applies a first DC Linac voltage to the plurality of Linac electrodes, a first DC collar voltage to the collar electrode that is more negative than the first DC Linac voltage, and a first DC exit lens voltage to the exit lens that is more positive than the first DC Linac voltage.

10. The system of claim 9 , wherein in order to axially eject the oscillating positive ions through the exit lens and to the destructive detector for detection after the excitation is applied, the processor changes the DC voltage of the collar electrode from the first DC collar voltage to a second DC collar voltage and changes the DC voltage of the exit lens from the first DC exit lens voltage to a second exit lens voltage, wherein the second DC collar voltage is less negative than the first DC collar voltage, but still more negative than the first Linac voltage, and the second exit lens voltage is the same as the first Linac voltage.

11. The system of claim 4 , wherein in order to trap negative ions in the quadrupole during the filling and cooling, the processor applies a first DC Linac voltage to the plurality of Linac electrodes, a first DC collar voltage to the collar electrode that is more positive than the first DC Linac voltage, and a first DC exit lens voltage to the exit lens that is more negative than the first DC Linac voltage.

12. The system of claim 11 , wherein in order to axially eject the oscillating negative ions through the exit lens and to the destructive detector for detection after the excitation is applied, the processor changes the DC voltage of the collar electrode from the first DC collar voltage to a second DC collar voltage and changes the DC voltage of the exit lens from the first DC exit lens voltage to a second exit lens voltage, wherein the second DC collar voltage is less positive than the first DC collar voltage, but still more positive than the first Linac voltage, and the second exit lens voltage is the same as the first Linac voltage.

13. The system of claim 4 , wherein a vertical height of a vertical portion of each Linac electrode of the plurality of Linac electrodes is tapered along a direction of an axis of the quadrupole so that the Linac electrodes are further from an axis of the quadrupole as the Linac electrodes get closer to the exit lens, so that a component of the electric field produced by the DC voltage applied to the plurality of Linac electrodes axially accelerates the oscillating ions towards the exit end of the quadrupole rods.

14. The system of claim 1 , wherein the processor further records in a memory over a period of time intensities produced by the destructive detector as the oscillating ions hit the destructive detector, converts the intensities recorded over the period of time to a frequency spectrum using a Fourier transform, and calculates a mass spectrum of the oscillating ions from the frequency spectrum.

15. A method for exciting and ejecting ions for destructive Fourier transform mass spectrometry (FTMS) mass analysis using a linear ion trap (LIT) quadrupole, comprising:
filling a quadrupole with ions and cooling the ions by applying a pressure and gas flow within the quadrupole by controlling gas inlets and outlets of the quadrupole using a processor,
wherein the quadrupole includes quadrupole rods that have an entrance end for receiving ions and an exit end for ejecting ions and a plurality of auxiliary electrodes,
wherein an exit lens is located coaxially with the quadrupole rods near the exit end of the quadrupole rods, and
wherein a destructive detector is located coaxially with the exit lens and located on the other side of the exit lens;

trapping the ions in the quadrupole during the filling and cooling by applying a direct current (DC) voltage and a radio frequency (RF) voltage to the quad

Assignees

• Dh Technologies Dev Pte Ltd

Inventors

• Hager James Walter

Classifications

• H01J49/38 Primary

  Omegatrons {; using ion cyclotron resonance} · CPC title

• H01J49/4205

  Device types · CPC title

• H01J49/08

  Electron sources, e.g. for generating photo-electrons, secondary electrons or Auger electrons · CPC title