Method and apparatus to increase the resolution and widen the range of differential mobility analyzers (DMAs)

A differential mobility analyzer for separating ions and charged particles suspended in a mixture comprising:

• means to provide a laminar flow of ion-free sheath gas into an upstream end of an analyzing region;
• ion supply means for introducing said ions and charged particles into said analyzing region;
• at least two electrodes or grids 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;
• power supply means to charge said at least two electrodes or grids to said potentials;
• means for maintaining said laminar flow within said analyzing region;
• and
• means for minimizing flow resistance of the ion-free sheath gas by placing a diffuser downstream from the analyzing region.

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) providing an electrical field in said analyzing region by a combination of electrodes and grids charged to various voltages and charging devices to maintain said electrodes and grids at said various voltages;
• (d) 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;
• and
• (e) minimizing tendency towards turbulent transition through the differential mobility analyzer by introducing a gradual reduction of the flow cross-section as the sheath gas moves downstream through the analyzing region.

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, wherein said laminar flow has a Reynolds number in excess of 2000;
• (c) providing an electrical field in said analyzing region by a combination of electrodes and grids charged to various voltages and charging devices to maintain said electrodes and grids at said various voltages;
• (d) 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;
• and
• (e) minimizing upstream propagation of flow disturbances and flow asymmetry of the ion-free sheath gas originating in an exhaust system of the differential mobility analyzer, and minimizing flow resistance of the ion-free sheath gas through the differential mobility analyzer by supporting one or more of said electrodes or grids upstream of the analyzing region.

A differential mobility analyzer for separating ions and charged particles suspended in a mixture comprising:

• means to provide a laminar flow of ion-free sheath gas into an upstream end of an analyzing region;
• ion supply means for introducing said ions and charged particles into said analyzing region;
• at least two electrodes 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;
• power supply means to charge said at least two electrodes to said potentials;
• means for maintaining said laminar flow within said analyzing region;
• and
• means for minimizing tendency towards turbulent transition comprising introducing a gradual reduction of the flow cross-section as the flow moves downstream through the analyzing region.

A differential mobility analyzer for separating ions, and charged particles suspended in a mixture comprising:

• means to provide a laminar flow of ion-free sheath gas into an upstream end of an analyzing region at a Reynolds number in excess of 2000;
• ion supply means for introducing said ions and charged particles into said analyzing region;
• at least two electrodes or grids 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;
• power supply means to charge said at least two electrodes or grids to said potentials;
• means for maintaining said laminar flow within said analyzing region;
• and
• means for minimizing upstream propagation of flow disturbances, flow asymmetry, and flow resistance through the differential mobility analyzer, wherein said means comprise supporting one or more of said electrodes or grids upstream of the analyzing region.