Varying frequency during a quadrupole scan for improved resolution and mass range

Patent metadata

Field	Value
Publication number	US-9490115-B2
Application number	US-201414575406-A
Country	US
Kind code	B2
Filing date	Dec 18, 2014
Priority date	Dec 18, 2014
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

Techniques are provided for scanning frequency and voltages of a multipole mass filter while maintaining substantially the same number of AC cycles per mass during a scan across a range of masses. For example, a mass spectrum can be obtained by controlling a DC axial voltage that accelerates ions into a mass filter, a DC resolving voltage applied to the mass filter, an AC voltage amplitude applied to the mass filter, and an AC frequency of the AC voltage. The settings can be controlled such that ions of different mass-to-charge ratios are within the mass filter for substantially a same number of AC cycles. To achieve the same number of AC cycles, the AC frequency is changed during the scan. For low masses, a higher AC frequency can be used. For high masses, a lower AC frequency can be used.

First claim

What is claimed is:

1. A method of operating a mass spectrometer, the method comprising:
providing ions having a plurality of mass-to-charge ratios;
accelerating the ions using a DC axial voltage such that the ions pass through a multipole mass filter;
filtering the ions using the multipole mass filter, the multipole mass filter coupled to:
a DC power supply providing a DC resolving voltage, and
an AC power supply providing an AC voltage, the AC voltage having an AC voltage amplitude and an AC frequency:

controlling the DC axial voltage, the DC resolving voltage, the AC voltage amplitude, and the AC frequency such that ions of different mass-to-charge ratios are within the multipole mass filter for substantially a same number of AC cycles when a first range of mass-to-charge ratios is scanned, wherein the controlling includes:
decreasing the AC frequency from lower mass-to-charge ratio to higher mass-to-charge ratio while:
keeping the DC axial voltage constant over the first range of mass-to-charge ratios, and
decreasing the DC resolving voltage and the AC voltage amplitude from lower mass-to-charge ratio to higher mass-to-charge ratio;

detecting the ions with a detector;
increasing the DC axial voltage over a second range of mass-to-charge ratios;
keeping the AC frequency constant over the second range of mass-to-charge ratios; and
increasing the DC resolving voltage and the AC voltage amplitude over the second range of mass-to-charge ratios.

2. A method of operating a mass spectrometer, the method comprising:
providing ions having a plurality of mass-to-charge ratios;
accelerating the ions using a DC axial voltage such that the ions pass through a multipole mass filter;
filtering the ions using the multipole mass filter, the multipole mass filter coupled to:
a DC power supply providing a DC resolving voltage, and
an AC power supply providing an AC voltage, the AC voltage having an AC voltage amplitude and an AC frequency;

controlling the DC axial voltage, the DC resolving voltage, the AC voltage amplitude, and the AC frequency such that ions of different mass-to-charge ratios are within the multipole mass filter for substantially a same number of AC cycles when a range of mass-to-charge ratios is scanned, wherein the controlling includes:
decreasing the AC frequency as the square root of mass-to-charge ratio while:
increasing the DC axial voltage as the square root of mass-to-charge ratio, and
keeping the DC resolving voltage and the AC voltage amplitude constant; and

detecting the ions with a detector.

3. A method of operating a mass spectrometer, the method comprising:
providing ions having a plurality of mass-to-charge ratios;
accelerating the ions using a DC axial voltage such that the ions pass through a multipole mass filter;
filtering the ions using the multipole mass filter, the multipole mass filter coupled to:
a DC power supply providing a DC resolving voltage, and
an AC power supply providing an AC voltage, the AC voltage having an AC voltage amplitude and an AC frequency;

controlling the DC axial voltage, the DC resolving voltage, the AC voltage amplitude, and the AC frequency such that ions of different mass-to-charge ratios are within the multipole mass filter for substantially a same number of AC cycles when a range of mass-to-charge ratios is scanned in an increasing manner, wherein the controlling includes:
decreasing the AC frequency with increasing mass-to-charge ratio while:
increasing the DC axial voltage as the square root of mass-to-charge ratio, and
keeping the DC resolving voltage and the AC voltage amplitude constant with increasing mass-to-charge ratio over the range of mass-to-charge ratios; and

detecting the ions with a detector.

4. A mass spectrometer comprising:
a mass filter having a plurality of rods;
a DC resolving voltage power supply coupled to the plurality of rods and configured to provide a DC resolving voltage to the plurality of rods;
an AC voltage power supply coupled to the plurality of rods and configured to provide an AC voltage to the plurality of rods, the AC voltage having an AC voltage amplitude and an AC frequency;
ion optics for receiving ions and accelerating the ions toward the mass filter;
a DC axial voltage supply coupled to the ion optics and configured to provide a DC axial voltage to the ion optics, the DC axial voltage for accelerating the ion optics; and
a controller coupled to the DC resolving voltage power supply, the AC voltage power supply, and the DC axial voltage supply, wherein the controller is configured to control the DC axial voltage, the DC resolving voltage, the AC voltage amplitude, and the AC frequency such that ions of different mass-to-charge ratios are within the multipole mass filter for substantially a same number of AC cycles when a first range of mass-to-charge ratios is scanned,
wherein the controlling includes changing the AC frequency while changing at least one of:
the DC axial voltage, and
the DC resolving voltage and the AC voltage amplitude;

wherein the controller is further configured to:
keep the DC axial voltage constant over the first range of mass-to-charge ratios,
decrease the AC frequency from lower mass-to-charge ratio to higher mass-to-charge ratio, and
decrease the DC resolving voltage and the AC voltage amplitude from lower mass-to-charge ratio to higher mass-to-charge ratio; and

wherein the controller is further configured to:
increase the DC axial voltage over a second range of mass-to-charge ratios,
keep the AC frequency constant over the second range of mass-to-charge ratios, and
increase the DC resolving voltage and the AC voltage amplitude over the second range of mass-to-charge ratios.

5. A mass spectrometer comprising:
a mass filter having a plurality of rods;
a DC resolving voltage power supply coupled to the plurality of rods and configured to provide a DC resolving voltage to the plurality of rods;
an AC voltage power supply coupled to the plurality of rods and configured to provide an AC voltage to the plurality of rods, the AC voltage having an AC voltage amplitude and an AC frequency;
ion optics for receiving ions and accelerating the ions toward the mass filter;
a DC axial voltage supply coupled to the ion optics and configured to provide a DC axial voltage to the ion optics, the DC axial voltage for accelerating the ion optics; and
a controller coupled to the DC resolving voltage power supply, the AC voltage power supply, and the DC axial voltage supply, wherein the controller is configured to control the DC axial voltage, the DC resolving voltage, the AC voltage amplitude, and the AC frequency such that ions of different mass-to-charge ratios are within the multipole mass filter for substantially a same number of AC cycles when a range of mass-to-charge ratios is scanned,
wherein the controlling includes changing the AC frequency while changing at least one of:
the DC axial voltage, and
the DC resolving voltage and the AC voltage amplitude; and

wherein the controller is further configured to:
keep the DC resolving voltage and the AC voltage amplitude constant over the range of mass-to-charge ratios,
decrease the AC frequency as the square root of mass-to-charge ratio, and
increase the DC axial voltage as the square root of mass-to-charge ratio.

6. A computer product comprising a non-transitory computer readable medium storing a plurality of instructions that when executed control a computer system to operate a mass spectrometer, the mass spectrometer comprising settings of: a DC resolving voltage applied to the plurality of rods; an AC voltage applied to the plurality of rods, the AC voltage having an AC voltage amplitude and an AC frequency; and a DC axial voltage for accelera

Assignees

• Thermo Finnigan Llc

Inventors

• Smith Johnathan W

Classifications

• H01J49/426

  Methods for controlling ions · CPC title

• H01J49/0031

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

• H01J49/429

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

• H01J49/4215 Primary

  Quadrupole mass filters (H01J49/4225 takes precedence) · CPC title