Method and apparatus for focussing and declustering trace ions

Details Method and apparatus for focussing and declustering trace ions Method and apparatus for focussing and declustering trace ions

1977-04-25

1978-10-17

Dixon, Harold A.

Radiant energy

Ionic separation or analysis

Static field-type ion path-bending selecting means

250281, B01D 5944

Patent

active

041210999

ABSTRACT:
A method and apparatus for focussing and declustering trace ions travelling from a gas through an orifice into a vacuum chamber and to a mass analyzer in the vacuum chamber. Advantage is taken of the free jet expansion of the gas into the vacuum chamber by applying an electric focussing field in a specific region of the free jet. The region is selected sufficiently close to the orifice that the gas density limits the kinetic energy spread which the ions can acquire under the applied field, typically to 2 ev or less, while the early focussing increases the available ion signal. Declustering can be collision induced in the region by providing a field in the region sufficient to impart an internal energy of between 0.1 and 1.5 ev to ions in the region. The kinetic energy which the ions can acquire under the applied field is still limited by the density of the gas in the free jet, so that the kinetic energy spread which the ions can acquire is still limited. Preferably the focussing and declustering fields are produced by a single conical tapered lens element located at distance X.sub.l from the orifice, where ##EQU1## and D is the orifice diameter, for atmospheric pressure and room temperature source conditions. The electric field between the lens element and the mass spectrometer is then controlled to limit the energy spread imparted to the ions in their travel from the lens elements to the mass spectrometer.

REFERENCES:
patent: 2287749 (1942-06-01), Slayter
patent: 2631255 (1953-03-01), Stavro
patent: 3920987 (1975-11-01), Anbar et al.
patent: 4031397 (1977-06-01), Cardillo

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