US 5,352,893 AGranted

Isotopic-ratio plasma source mass spectrometer

AssigneeFisons Limited

InventorPhilip A. Freedman

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Abstract

An isotopic-ratio mass spectrometer comprises an r.f. or microwave induced plasma ion source (1, 2, 3), an electrostatic ion-energy analyzer (75), a magnetic sector ion-momentum analyzer (82) wherein ions are dispersed at a first potential according to their mass-to-charge ratios, and two or more ion collectors (77) for receiving ions of different mass-to-charge ratios, wherein an apertured electrically conductive sampling member (19) is provided adjacent to the plasma (3) and communicates between the plasma and a first vacuum enclosure (23) evacuated by first pumping means (25); an apertured skimmer member (28) separates the first vacuum enclosure from a second vacuum enclosure (4) evacuated by second pumping means (5); an apertured differential pumping member (6) separates the second vacuum enclosure from a third vacuum enclosure (7) evacuated by third pumping means (43); an apertured analyzer entrance member (46) separates the third vacuum enclosure from a vacuum envelope (75, 76, 77) in which the electrostatic ion-energy analyzer ion-momentum analyzer, and ion detectors are disposed, the vacuum envelope being evacuated by fourth pumping means (131); and means (40) are provided for maintaining the sampling member at a second potential whereby ions generated in the plasma pass through each of the apertures and are accelerated to have a kinetic energy suitable for their mass analysis in the ion-momentum analyzer at said first potential.

Claims27

Dependent claims

An isotopic-ratio mass spectrometer comprising ion source means, an electrostatic ion-energy analyzer, a magnetic sector ion-momentum analyzer wherein ions are dispersed at a first potential according to their mass-to-charge ratios, and ion detecting means comprising two or more ion collectors for receiving ions of different mass-to-charge ratios, wherein:

a) said ion source means comprises means for establishing a plasma discharge in an inert gas by the action of an electromagnetic field created by a radio-frequency or microwave generator;
b) means are provided for introducing into said plasma a sample whose isotopic composition is to be determined;
c) an electrically conductive sampling member is provided adjacent to said plasma, said sampling member having an aperture communicating between said plasma and a first vacuum enclosure evacuated by first pumping means;
d) a skimmer member is provided downstream of said sampling member, said skimmer member separating said first vacuum enclosure from a second vacuum enclosure evacuated by second pumping means, and comprising an aperture communicating between said first and said second vacuum enclosures;
e) a differential pumping member is provided downstream of said skimmer member, said differential pumping member separating said second vacuum enclosure from a third vacuum enclosure evacuated by third pumping means, and comprising an aperture communicating between said second and said third vacuum enclosures;
f) an analyzer entrance member is provided downstream of said differential pumping member, said entrance member separating said third vacuum enclosure from a vacuum envelope in which said electrostatic ion-energy analyzer, said ion-momentum analyzer, and said ion detecting means are disposed, said vacuum envelope being evacuated by fourth pumping means and said entrance member comprising an aperture communicating between said third vacuum enclosure and said vacuum envelope;
and
g) means are provided for maintaining said sampling member at a second potential whereby ions generated in said plasma pass through each of said apertures and are accelerated to have a kinetic energy as they enter said ion-momentum analyzer, which energy is suitable for their mass analysis in said ion-momentum analyzer at said first potential.

5 more elements

A method of high-precision isotopic analysis of a sample comprising the steps of generating ions characteristic of a said sample, selecting said ions according to their energy and dispersing them according to their mass-to-change ratios, collecting at spatially, separated positions at least some ions of at least two different mass-to-charge ratios, and determining the isotopic composition of a said sample by measurement of the ratio of the currents due to ions collected at said spatially separated positions, said method also comprising the steps of:

a) generating said ions in a plasma established in an inert gas by an electromagnetic field generated by a radio-frequency or microwave generator;
b) passing at least some of the ions so generated in sequence through;
i) an aperture in an electrically conductive sampling member adjacent said plasma into a first vacuum enclosure evacuated by first pumping means;
ii) an aperture in a skimmer member from said first vacuum enclosure into a second vacuum enclosure evacuated by second pumping means;
iii) an aperture in a differential pumping member from said second vacuum enclosure into a third vacuum enclosure evacuated by third pumping means;
iv) an aperture in a vacuum envelope evacuated by fourth pumping means, in which envelope said ions are selected according to their energy and dispersed according to their mass-to-charge ratios;
and
c) maintaining said sampling member at a potential whereby ions are generated in said plasma at a first potential energy and are subsequently accelerated as they pass through said apertures to a first kinetic energy at which they are dispersed according to their mass-to-charge ratios.

5 more elements

Dependencies are inferred from the claim text.