High-resolution ion trap mass spectrometer

Patent metadata

Field	Value
Publication number	US-9847218-B2
Application number	US-201514933961-A
Country	US
Kind code	B2
Filing date	Nov 5, 2015
Priority date	Nov 5, 2015
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

Techniques can increase the resolution and accuracy of mass spectra obtained using ion traps through the use of the actual shape of the ion trap peaks, which is a series of smaller ion ejection events. The peak shapes are identified as changing over a common period of the trapping signal and the excitation signal, at which point the peak shapes repeat. Peak shapes can be characterized over the common period to create N basis functions, each for a different fractional mass for a given scan rate. The N basis functions over the common period can be duplicated (e.g., shifted by the common period) to obtain a set of mass functions that characterize fractional masses over the full scan range. The mass spectrum can be obtained by fitting the set of mass functions to the measured data to obtain a best fit contribution of each mass function to the measured data.

First claim

What is claimed is:

1. A method for mass analyzing ions in an ion trap, comprising:
(a) confining ions of different mass-to-charge ratios (m/z's) in a trap volume by applying a trapping signal to the ion trap;
(b) mass sequentially ejecting the confined ions to a detector by applying a resonant excitation signal to the ion trap and progressively scanning the trapping signal amplitude over time, wherein at least one of: (i) a scan starting time, (ii) a frequency of the resonant excitation signal or the trapping signal, or (iii) a phase of the resonant excitation signal or the trapping signal, is or are controlled to cause ions of a particular m/z to be ejected in a reproducible pattern of plural micropackets;
(c) generating at the detector a plurality of measurement points extending over a time range, each measurement point representing an intensity of ejected ions detected at a discrete timepoint, at a data acquisition frequency sufficiently high to resolve adjacent micropackets;
(d) determining a linear combination of stored micropacket patterns that approximates the plurality of measurement points, wherein each stored micropacket pattern corresponds to an ion of a particular m/z and wherein the stored micropacket patterns define a repeating sequence over an m/z interval, the stored micropacket patterns including patterns of micropackets at different initial phases which define the phase shift between the trapping signal and the resonant excitation signal; and
(e) constructing a mass spectrum based on the determined linear combination of stored micropacket patterns.

2. The method of claim 1 , wherein step (c) is performed at a data acquisition frequency of between 2Ω and 4Ω, where Ω is the frequency of the trapping signal.

3. The method of claim 1 , wherein the ratio of the frequency ω of the resonant excitation signal to the frequency Ω of the trapping signal is ⅓.

4. The method of claim 1 , wherein step (b) comprises scanning the trapping signal amplitude over a time period greater than a common cycle period corresponding to the frequencies of the trapping signal and the resonant excitation signal.

5. A mass spectrometer, comprising:
an ion trap having a plurality of electrodes interiorly defining a trap volume;
a trapping signal supply for applying a trapping signal to one or more electrodes of the ion trap;
a resonant excitation signal supply for applying a resonant excitation signal to one or more electrodes of the electrode trap;
a controller, coupled to the trapping signal supply and the resonant ejection signal supply, configured to progressively scan the trapping signal amplitude over time to cause ions confined in the trap volume to be mass sequentially ejected from the ion trap, the controller controlling at least one of i) a scan starting time, (ii) a frequency of the resonant excitation signal or the trapping signal, or (iii) a phase of the resonant excitation signal or the trapping signal to cause ions of a particular m/z to be ejected in a reproducible pattern of plural micropackets;
a detector positioned to receive ions ejected from the ion trap and to responsively generate a plurality of measurement points extending over a time range, each measurement point representing an intensity of ejected ions detected at a discrete timepoint, the detector being operated at a data acquisition frequency sufficiently high to resolve adjacent micropackets;
a data system programmed with instructions for determining a linear combination of stored micropacket patterns that approximates the plurality of measurement points, wherein each stored micropacket pattern corresponds to an ion of a particular m/z and wherein the stored micropacket patterns define a repeating sequence over an m/z interval, and for constructing a mass spectrum based on the determined linear combination of stored micropacket patterns, the stored micropacket patterns including patterns of micropackets at different initial phases which define the phase shift between the trapping signal and the resonant excitation signal.

Assignees

• Thermo Finnigan Llc

Inventors

• Remes Philip M
• Schwartz Jae C

Classifications

• H01J49/429 Primary

  Scanning an electric parameter, e.g. voltage amplitude or frequency · CPC title

• H01J49/0031

  Step by step routines describing the use of the apparatus (H01J49/0081 takes precedence) · CPC title

• H01J49/0036

  Step by step routines describing the handling of the data generated during a measurement · CPC title