Method for separation and enrichment of isotopes in gaseous phase

The present invention provides an apparatus for selectively transmitting ions and trapping the ions within a defined 3-dimensional space at atmospheric pressure. The invention is based on the ion focussing principles of high field asymmetric waveform ion mobility spectrometry in which an analyzer region is defined by a space between first and second spaced apart electrodes, the analyzer region having a gas inlet and a gas outlet for providing a flow of gas through the analyzer region. Ions which are introduced into the analyzer region are carried by a gas flow towards a gas outlet. At least one of the electrodes has a curved surface terminus located near the gas outlet and the gas flow is adjusted so that ions are trapped in a defined 3-dimensional space located near the tip of the terminus. Trapping of ions in a defined 3-dimensional space allows a more concentrated flow of desired ions.