US 5,572,025 A · Method and apparatus for scanning an ion trap mass spectrometer in the resonance ejection mode

Abstract

A method of operation of an ion trap mass spectrometer having a ring electrode and pair of end-cap electrodes in a resonance ejection mode is disclosed. The method includes producing ions from a plurality of biomolecules, applying a trapping RF voltage to the ring electrode, applying an excitation voltage to the end-cap electrodes, scanning the trapping RF voltage in order to sequentially eject the ions, controlling a ration of the amplitude of the trapping RF voltage to the amplitude of the excitation voltage in order that the ratio is generally constant, and determining a ratio of mass to charge of the ejected ions. In one embodiment, a feedback voltage which is proportional to the trapping RF voltage is sensed, and the amplitude of the excitation voltage is controlled as a function of the amplitude of the feedback voltage. In another embodiment, a first value related to the amplitude of the trapping RF voltage and a second value, which is proportional to the first value and related to the amplitude of the excitation voltage, are determined. The amplitude of the trapping RF voltage is modulated employing the first value and the amplitude of the excitation voltage is modulated employing the second value. Preferably, the determined mass-to-charge ratio (m/z) of the ejected ions is equal to a constant (.alpha.) times the trapping RF voltage (V). Associated apparatus and method of calibration are also disclosed.

Claims52

Dependent claims

A method of operation of an ion trap mass spectrometer having a ring electrode and a pair of end-cap electrodes in a resonance ejection mode comprising

producing ions from a plurality of atoms or molecules, trapping the ions in an ion trap;
applying a trapping voltage to said ring electrode,
applying an excitation voltage to said pair of end-cap electrodes,
scanning the trapping voltage in order to sequentially eject the ions from the ion trap,
controlling a ratio of the amplitude of the trapping voltage to the amplitude of the excitation voltage in order that the ratio is generally constant, and
determining a ratio of mass to charge of the ejected ions.

3 more elements

A method of calibrating an ion trap mass spectrometer for operation in a resonance ejection mode, said mass spectrometer having an excitation voltage associated therewith which excites ions of a plurality of atoms or molecules and a trapping voltage associated therewith for sequentially ejecting the ions, with the ions having a mass and a charge, said mass spectrometer determining a mass-to-charge ratio of the ejected ions, said method comprising

performing mass spectrum measurements on a plurality of ions having a known mass in order to provide a single datum point associated therewith, with the single datum point being representative of a ratio of a trapping voltage associated with said ions having the known mass and a mass-to-charge ratio of said ions having the known mass, and
defining a calibration line which converges near a reference point where the mass-to-charge ratio and the trapping voltage of said mass spectrometer are both equal to about zero, and
calibrating said mass spectrometer employing the single datum point in order that a ratio of the amplitude of the trapping voltage to the amplitude of the excitation voltage of said mass spectrometer is generally constant.

Ion trap mass spectrometer apparatus for operation in a resonance ejection mode comprising

ionizing means for producing ions from a plurality of atoms or molecules,
trapping means for trapping the produced ions,
separating means for separating the trapped ions according to a ratio of mass to charge thereof, said separating means including a ring electrode and a pair of end-cap electrodes,
applying means for applying a trapping voltage to the ring electrode and for applying an excitation voltage to the end-cap electrodes, with a ratio of the amplitude of the trapping voltage to the amplitude of the excitation voltage being generally constant, and
determining means for determining the mass-to-charge ratio of at least some of the separated ions.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for scanning an ion trap mass spectrometer in the resonance ejection mode

Life of this patent

Method and apparatus for scanning an ion trap mass spectrometer in the resonance ejection mode

Life of this patent

Abstract

Claims52