US3284628A - Mass filter having an ion source structure with preselected relative potentials applied thereto - Google Patents

Mass filter having an ion source structure with preselected relative potentials applied thereto Download PDF

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Publication number
US3284628A
US3284628A US256169A US25616963A US3284628A US 3284628 A US3284628 A US 3284628A US 256169 A US256169 A US 256169A US 25616963 A US25616963 A US 25616963A US 3284628 A US3284628 A US 3284628A
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Prior art keywords
voltage
electrode
vessel
ion source
potential
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Expired - Lifetime
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US256169A
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English (en)
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Gunther Karl-Georg
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Siemens Schuckertwerke AG
Siemens Corp
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Siemens Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/26—Mass spectrometers or separator tubes
    • H01J49/34—Dynamic spectrometers
    • H01J49/42—Stability-of-path spectrometers, e.g. monopole, quadrupole, multipole, farvitrons
    • H01J49/4205—Device types
    • H01J49/421—Mass filters, i.e. deviating unwanted ions without trapping

Definitions

  • the Paul et al. method utilizes an electric field which is periodical in time and wherein the potential of the electric field is a quadratic function of the coordinates x, y, z.
  • the most general such potential is defined by the equation:
  • the specific charge, or charge to mass ratio e/ m, of a particular ion will determine whether it travels along a stable or unstable path. If e/m of the ions lies in a stable range, then all its possible paths are stable and, conversely, if e/m of the ion lies in an unstable range, then all its possible paths are unstable.
  • the positions and widths of the stable ranges of the specific charge can be varied within very wide limits solely by varying the amplitude, frequency and/or shape of the field creating voltages which determine the function f(t).
  • the volume of the filter cell (i.e. the analyzer tube) holding the electrodes of a Paul device depends in part on the electrode length. This length afiects the electrical conditions controlling the maximum resolving power and sensitivity of the device. It would seem generally that increased resolving power and sensitivity are incompatible with reduced cell or analyzer volume.
  • Another object is to provide an improved method and analyzing apparatus for ion separation, particularly one having increased sensitivity, resolving power, or both.
  • FIG. 1 is a block diagram of a mass filter system for separating ions according to the invention
  • FIG. 2 is a schematic representation of the mass-filter cell or analyzer in FIG. 1, together with. an associated D.C. energizing circuit according to the invention;
  • FIG. 3 is a circuit diagram of a supply system for energizing the analyzer rods according to the present invention
  • FIGS. 4a and b are two voltage graphs showing the respective potentials occurring at the electrode within the device of FIG. 3 for two different sets of applied voltages.
  • FIG. 5 is a graph of results obtained with the method of the present invention.
  • the mass-filter cell 1 is provided with an envelope 5 which contains an ion source 2, a group of rod-shaped deflector electrodes 3 having in dividually a circular cross section. Located at the end of the ion-beam path is a cup-shaped collector electrode 4. The ion source 2 and the collector electrode 4 are coaxially spaced from each other and thus define a center axis 3 for the ion beam issuing from the source 2 toward the electrode 4. The electrode rods 3 are uniformly distributed about the ion-beam axis and extend parallel thereto. A total number of four such electrodes may be used.
  • the above-mentioned envelope 5 of the cell 1 is vacuum-tightly sealed and has a nipple or neck 6 connected with a tank '7 containing the gaseous mixture to be investigated.
  • the rod electrodes 3 are electrically connected in pairs to a high-frequency generator 3 which supplies electric energy of suitable voltage and frequency.
  • the current due to the ions impinging upon the collector 4 is amplified by an amplifier 9 and supplied to a recorder 10 or other indicating or measuring device.
  • Another measuring instrument 10 is provided for supervising the electron emission of the cathode in the ion source 2.
  • a beam of ions is continuously being extracted from the source 2 and is directed toward the collector 4.
  • ions of a given specific electric charge or within a given range of charges, can reach the collector 4.
  • Those ions which have different specific charges travel on instable, pendulous paths and thus impinge upon the deflector electrodes 3, thus being filtered out of the mixture. This is more fully explained in the above-mentioned copending applications.
  • FIG. 2 diagrammatically illustrates the mass-filter cell 1 including the analyzer rods 3, of which there are four as in the Paul patent, and the collector 4.
  • the ion source 2 comprises a heater filament H, anode vessel A and extraction apertures or entrance diaphragms E.
  • a DC. voltage source S energizes the components of the ion source by means of a voltage divider device D. Connected to the device D is the member H at -20 volts to 20 volts, the member A at 50 volts to volts, and the member E at 100 volts to 200 volts, as indicated.
  • the potential of the analyzer rods 3 is applied asymmetrically with respect to ground.
  • High-frequency voltage for the analyzer rods is supplied to the pairs of rods 3 from a high-frequency voltage source 12 through a transformer 13 and blocking capacitors 14.
  • a variable capacitor 17 tunes secondary of transformer 13.
  • Two direct-voltage sources 15 and protective resistors 16 furnish direct voltage to analyzer rods 3.
  • a direct-voltage source 19 is connected between the center point 8 of the secondary of the high-frequency transformer 13 and ground.
  • FIGS. 4a and b show graphically the potentials prevailing at and bet-ween the components A, H, E, 3 and 4 in FIG. 2 for two values of U The curves have their respective potentials aligned below the components of FIG. 2.
  • ionizing electrons are emitted by the heated filament H and are axially shot through an aperture and into the anode vessel A, which receives a positive acceleration potential U Filament H preferably is kept at a potential constituting an optimum value for ionization purposes.
  • the ionizing electrodes serve to ionize particles in the ion source.
  • the positive ions are then drawn from the ion source by a negative extraction voltage, V volts less than the anode voltage U and pass through the rods 3.
  • the axis potential of the rods is maintained at zero or at a negative value, which is more positive by the value U than the extraction voltage.
  • the extraction potential U i.e. the potential dilference between the anode A and apertured extraction electrode E, is sufficiently high to achieve maximum extraction from the ion source 2.
  • the unsymmetrical field effects a higher resolving power than would occur where there is applied a symmetrical collector extraction voltage U E": U U U
  • the full-line curve which is measured in units on the left ordinate, illustrates the intensity curve of the filtered ion current as a function of the counter-voltage U for a constant U
  • the broken-line curve which is measured in units on the right-hand ordinate, shows the resolving power increasing up to a maximum value and, consequently, shows the efiiciency of the method of the present invention for the same constant U
  • the experiments were carried out with a device such as illustrated in FIG. 1a.
  • the present invention thus affords increasing the sensitivity, the resolving power, or both, in practical fourpole mass filters. Conversely, the invention permits reducing dimensions of the analyzer system, for systems where the requirements of sensitivity and resolving power are the same.
  • a system for separating ions having different chargeto-mass ratios comprising an evacuated vessel, electrode means, means for holding said electrode means in spaced relation in said vessel, ion source means for creating charged particles in said vessel and including in said vessel an anode and an apertured extraction electrode, voltage means for applying to said anode a positive voltage and for applying to said apertured extraction elec trode a negative voltage, and source means for generating a voltage having an arbitrary periodical function f(t) and applying it to said electrode means thereby creating a time-periodical field the potential of which is the general quadratic function of the rectangular coordinates x, y, z of the electrode arrangement, a, ⁇ 3, and 7 being constants satisfying the equation obi-[3:7, said source means including potential means for superimposing upon the axis of said electrode means a potential having a magnitude in the range from zero to the negative voltage of said apertured extraction electrode.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Electron Tubes For Measurement (AREA)
US256169A 1962-02-03 1963-02-04 Mass filter having an ion source structure with preselected relative potentials applied thereto Expired - Lifetime US3284628A (en)

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CH (1) CH409461A (de)
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GB (1) GB1035494A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3617736A (en) * 1968-06-19 1971-11-02 Hewlett Packard Co Quadrupole mass filter with electrode structure for fringing-field compensation
US4214160A (en) * 1976-03-04 1980-07-22 Finnigan Corporation Mass spectrometer system and method for control of ion energy for different masses
US20050269517A1 (en) * 2004-03-25 2005-12-08 Bruker Daltonik Gmbh DC voltage supply to RF electrode systems

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2636990A (en) * 1949-12-14 1953-04-28 Atomic Energy Commission Ion source unit
US2939952A (en) * 1953-12-24 1960-06-07 Paul Apparatus for separating charged particles of different specific charges
US2950389A (en) * 1957-12-27 1960-08-23 Siemens Ag Method of separating ions of different specific charges

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2636990A (en) * 1949-12-14 1953-04-28 Atomic Energy Commission Ion source unit
US2939952A (en) * 1953-12-24 1960-06-07 Paul Apparatus for separating charged particles of different specific charges
US2950389A (en) * 1957-12-27 1960-08-23 Siemens Ag Method of separating ions of different specific charges

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3617736A (en) * 1968-06-19 1971-11-02 Hewlett Packard Co Quadrupole mass filter with electrode structure for fringing-field compensation
US4214160A (en) * 1976-03-04 1980-07-22 Finnigan Corporation Mass spectrometer system and method for control of ion energy for different masses
US20050269517A1 (en) * 2004-03-25 2005-12-08 Bruker Daltonik Gmbh DC voltage supply to RF electrode systems

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Publication number Publication date
DE1498970A1 (de) 1969-04-03
CH409461A (de) 1966-03-15
GB1035494A (en) 1966-07-06

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