A method of separating charged particles or ions in a differential mobility analyzer, wherein a stream of charged particles or ions is introduced into an upstream portion of an analyzing region through an inlet slit or orifice and wherein a combination of a laminar flow field and an electrical field leads to ions of different mobilities separating in space, said method comprising the steps of: (a) introducing a stream of charged particles or ions of various electrical mobilities into said analyzing region; (b) laminarizing a flow of an ion-free sheath gas, and introducing said sheath gas into said differential mobility analyzer immediately upstream of said analyzing region; (c) maintaining the flow of said sheath gas within said analyzing region as laminar flow; (d) providing an electrical field in said analyzing region by a combination of electrodes and grids (14, 42) charged to various voltages and charging devices to maintain said electrodes and grids at said various voltages; (e) sampling or collecting said separated particles or ions within a narrow range of electrical mobilities through at least one sampling or collector device, the last of which defines the exit of said analyzing region, wherein the differential mobility analyzer includes: a laminarizing trumpet and laminarizing screens (45, 46) to provide a laminar flow of ion-free sheath gas into an upstream end of the analyzing region; ion supply means (4, 12, 15, 16) for introducing said ions and charged particles into said analyzing region; at least two electrodes or grids (14, 42), comprising an outer electrode and an inner electrode, charged to suitable potentials to create an electric field within said analyzing region; whereby said ions are separated in space by combined action of the electric field and the flow of sheath gas; at least one sampling or collecting device, wherein ions of a desired mobility are sampled or collected; and power supply means to charge said at least two electrodes or grids (14, 42) to said potentials, the differential mobility analyzer being further characterized in that it comprises: (i) a diverging diffuser (33, 38) and a throat positioned downstream from the analyzing region; (ii) a perforated piece for supporting the inner electrode upstream of the analyzing region, wherein the perforated piece also supports the laminarizing trumpet and laminarizing screens (45, 46). (a) introducing a stream of charged particles or ions of various electrical mobilities into said analyzing region; (b) laminarizing a flow of an ion-free sheath gas, and introducing said sheath gas into said differential mobility analyzer immediately upstream of said analyzing region; (c) maintaining the flow of said sheath gas within said analyzing region as laminar flow; (d) providing an electrical field in said analyzing region by a combination of electrodes and grids (14, 42) charged to various voltages and charging devices to maintain said electrodes and grids at said various voltages; (e) sampling or collecting said separated particles or ions within a narrow range of electrical mobilities through at least one sampling or collector device, the last of which defines the exit of said analyzing region, a laminarizing trumpet and laminarizing screens (45, 46) to provide a laminar flow of ion-free sheath gas into an upstream end of the analyzing region; ion supply means (4, 12, 15, 16) for introducing said ions and charged particles into said analyzing region; at least two electrodes or grids (14, 42), comprising an outer electrode and an inner electrode, charged to suitable potentials to create an electric field within said analyzing region; whereby said ions are separated in space by combined action of the electric field and the flow of sheath gas; at least one sampling or collecting device, wherein ions of a desired mobility are sampled or collected; and power supply means to charge said at least two electrodes or grids (14, 42) to said potentials, (i) a diverging diffuser (33, 38) and a throat positioned downstream from the analyzing region; (ii) a perforated piece for supporting the inner electrode upstream of the analyzing region, wherein the perforated piece also supports the laminarizing trumpet and laminarizing screens (45, 46).