Control of magnetic sector mass spectrometer magnet

Patent metadata

Field	Value
Publication number	US-2019157063-A1
Application number	US-201916240663-A
Country	US
Kind code	A1
Filing date	Jan 4, 2019
Priority date	Dec 12, 2014
Publication date	May 23, 2019
Grant date	—

Abstract

A control system for controlling a magnet of a magnetic sector mass spectrometer comprises a magnetic field sensor for sensing the magnetic field of the magnet and generating an output representative thereof; a set point generator configured to generate an output representative of, or related to, a desired magnetic field of the magnet; and a digital controller configured to receive a variable digital input signal from the output of the magnetic field sensor and a set point digital input signal from the output of the set point generator, and to generate a digital output from which is derived a control signal for controlling a current to the magnet so as to control the magnetic field thereof. The control system is arranged to apply to the digital controller a selected one of a plurality of different controller settings, in accordance with the desired magnetic field of the magnet.

First claim

1 . A control system for controlling a magnet ( 70 ) of a magnetic sector mass spectrometer ( 10 ), comprising:
a magnetic field sensor for sensing the magnetic field of the magnet ( 70 ) and generating an output representative thereof; a set point generator ( 210 ) configured to generate an output representative of, or related to, a desired magnetic field of the magnet ( 70 ); and a controller ( 130 ) configured to receive a variable input signal from the output of the magnetic field sensor and a set point input signal from the output of the set point generator ( 210 ), and to generate an output from which is derived a control signal for controlling a current to the magnet ( 70 ) so as to control, in turn, the magnetic field thereof; and a processor; wherein the magnetic field sensor for sensing the magnetic field is an ion detector ( 120 ) for detecting ions passing through the magnetic sector mass spectrometer ( 10 ), the ion detector ( 120 ) being configured to generate a detector output signal representative of the quantity of ions incident upon the detector ( 120 ); and wherein the processor is arranged to receive the detector output signal, and configured to calculate a controller setting based upon the detection of ions at the detector ( 120 ), and wherein the control system is arranged to apply to the controller ( 130 ) a selected one of a plurality of different controller settings calculated by the processor based upon the detection of ions at the detector ( 120 ), in accordance with the desired magnetic field of the magnet ( 70 ).

2 . The control system of claim 1 , wherein the control system is configured to control the parameters of the mass spectrometer ( 10 ), so as to align an edge of a mass spectral peak of an ion species with the ion detector ( 120 ), and to determine, by perturbing the mass spectrometer parameters when the peak edge is aligned with the ion detector ( 120 ), controller settings suitable for the particular magnetic flux density of the magnet ( 70 ) generated in accordance with the corresponding magnet current control signal.

3 . A magnetic sector mass spectrometer ( 10 ) comprising:
an ion source ( 20 ) arranged to generate a beam of ions having a mass to charge ratio m/z; an ion accelerator arranged to accelerate ions to a potential U o ; a control system according to claim 1 ; a magnet ( 70 ) under the control of the control system, arranged to divert the accelerated ions along a circular path in accordance with m/z, U o and the magnetic flux density within the magnet ( 70 ).

4 . The magnetic sector mass spectrometer ( 10 ) of claim 3 , further comprising a second ion detector ( 500 , 510 ) also positioned downstream of the magnet but spatially separated in a transverse direction perpendicular to the direction of travel of the ion beam; wherein the ion beam comprises ions of first and second mass-to-charge ratios, the processor being configured to control the parameters of the mass spectrometer so as to align an edge of a mass spectral peak of ions of the first mass-to-charge ratio with the ion detector ( 520 ) which is sensing the magnetic field, whilst ions of the second mass to charge ratio are directed toward the second ion detector ( 500 , 510 ).

5 . A method of controlling a magnetic field generated by a magnet ( 70 ) in a magnetic sector mass spectrometer ( 10 ), comprising:
sensing the magnetic field of the magnet ( 70 ) and generating a sensor output representative thereof; generating a set point signal representative of, or related to, a desired magnetic field of the magnet; applying one of a plurality of different controller settings to a system controller, the controller setting which is applied being selected in accordance with system parameters of the magnetic sector mass spectrometer ( 10 ); at the system controller ( 130 ), receiving, as a first input, a variable input signal derived from the sensor output, and, as a second input, the set point signal, and generating a control signal output which is determined by the first and second inputs and the particular controller setting applied to the system controller ( 130 ); and controlling the current supplied to the magnet ( 70 ) by a magnet power supply ( 80 ), based upon the control signal output, so as, in turn, to control the magnet field generated by the magnet ( 70 ), further comprising: generating ions of a first mass to charge ratio (m/z) 1 ; accelerating the ions of mass to charge ratio (m/z) 1 to an energy z 1 U o , where U o is an electrical potential applied to the ions; generating a magnetic field, having a magnetic flux density B m , in the magnet; directing ions of mass (m/z) 1 into the magnet ( 70 ), where they follow a curved path; and detecting, with an ion detector ( 120 ), those ions that have followed a curved path within the magnet of radius r m defined by
r m =B m −1 (2. U o .( m/z ) 1 ) 1/2 ; and
adjusting the parameters of the magnetic sector mass spectrometer ( 10 ) so as to cause an edge of a mass peak corresponding with the ions of mass (m/z) 1 to align with the ion detector ( 120 ) for detecting a change in an ion intensity at the ion detector ( 120 ) corresponding to a change in the magnetic field for sensing the magnetic field of the magnet ( 70 ).

6 . The method of claim 5 , wherein the adjusting step comprises adjusting the accelerating potential U o so as to align the peak edge with the ion detector ( 120 ).

7 . The method of claim 5 , further comprising:
perturbing the parameters of the magnetic sector mass spectrometer ( 10 ) once the edge of the mass peak has been aligned with the ion detector ( 120 ), deriving, from the applied perturbation, a first static field controller setting for the system controller ( 130 ) for application to the system controller ( 130 ) for the magnetic flux density B m ; and applying that derived first static field controller setting to the system controller ( 130 ) for subsequent detection of ions at that magnetic field B m .

8 . The method of claim 5 , further comprising:
accelerating the ions of mass to charge ratio (m/z) 1 to an energy z 1 U 1 where U 1 ≠U o ; generating a magnetic field, having a magnetic flux density B n , in the magnet ( 70 ), where B m ≠B n ; directing ions of mass (m/z) 1 into the magnet ( 70 ) where they follow a curved path; and detecting, with the ion detector ( 120 ), those ions that have followed a curved path within the magnet of radius r n defined by r n =B n −1 (2.U 1 .(m/z) 1 ) 1/2 ; wherein adjusting the accelerating potential U 1 so as to align the peak edge with the ion detector ( 120 ) and wherein the controller settings for B n are different to the first static field controller settings for B m .

9 . The method of claim 8 , further comprising:
perturbing the parameters of the magnetic sector mass spectrometer ( 10 ) once the edge of the mass peak has been aligned with the detector ( 120 ); deriving, from the applied perturbation, a second static field controller setting for the system controller ( 130 ) for application to the system controller ( 130 ) for the magnetic flux density B n ; and applying that derived second static field controller setting to the system controller for subsequent detection of ions at that magnetic field B n .

10 . The method of claim 8 , further comprising determining a transitioning field controller setting for a transition from B m to B n ; and
applying that transitioning field controller setting to the system controller ( 130 ) for subsequent detection of ions when transitioning from B m to B n .

11 . The method of claim 5 , further comprising:
generating ions of a second mass to ch

Assignees

• Thermo Fisher Scient Bremen Gmbh

Inventors

• Jaeschke Jürgen
• Deerberg Michael
• Schlüter Hans-Jürgen

Classifications

• G01R33/091

  Constructional adaptation of the sensor to specific applications · CPC title

• H01J49/30 Primary

  using magnetic analysers {, e.g. Dempster spectrometer} · CPC title

• H01J49/022

  Circuit arrangements, e.g. for generating deviation currents or voltages (regulating electric or magnetic variables in general, e.g. current, magnetic field G05F); Components associated with high voltage supply (high voltage supply per se H02M) · CPC title

• H01J49/0009 Primary

  Calibration of the apparatus · CPC title

• H01J49/0031

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