A method of separating ions includes providing a FAIMS analyzer region for
separating ions, the FAIMS analyzer region in fluid communication with an
ionization source and with an ion detecting device. The method further
includes affecting a gas composition within a first portion of the FAIMS
analyzer region to be different from a gas composition within a second
portion of the FAIMS analyzer region. The establishment of a gas
composition gradient within the FAIMS analyzer region enhances ion
focusing and ion transport efficiency.