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...http://www.google.com/patents/US4121099?utm_source=gb-gplus-sharePatent US4121099 - Method and apparatus for focussing and declustering trace ions
