Diffusion Distortions in a Differential Mobility Analyzer with Inclined Electric Field

An approach based on the calculation of the probabilities of the random displacements of particles around their regular trajectories enables us to derive analytical expressions for the normalized apparent mobility spectrum. A particular derivation is carried out for the case of a DMA with one collecting electrode, with inclined electric field, and variable electric field strength. Calculations show that an inclined electric field actually results in a sharper apparent spectrum, i.e., in a higher resolution than a transverse electric field does. A way to improve resolution by calculations is outlined.