Flow driven transmission of charged particles against an axial field in antistatic tubes at the sample outlet of a Differential Mobility Analyzer

Electrophoretic losses at the outlet of Differential Mobility Analyzers result from the need to transport the aerosol from the high voltage V-Bias, typically applied to the inner electrode, to the ground potential at which a particle detector is usually connected. Here we examine the sample transmission efficiency eta for mobility-selected ions brought to ground through a commercial Static Dissipative Polyurethane tube. eta(V-Bias) is defined as the ratio of the ion current transmitted through the tube with bias voltage V-Bias over that transmitted when V-Bias = O. We find eta values close to unity under common DMA operational conditions. eta is measured also under adverse fields strong enough for all charged particles to be lost, with a sample transmission efficiency comparable to that expected for a uniform velocity profile within the tube. Outlet tube Reynolds numbers are examined in the range 446 < Re < 4460, with an increased transmission associated to decreasing Re. The sample transmission efficiency is close to ideal, but geometrical non-idealities are apparent from small decreases in transmission under favorable bias voltages. (C) 2016 Elsevier Ltd. All rights reserved.