Experimental tests of a nano-DMA with no voltage change between aerosol inlet and outlet slits

A novel isopotential differential mobility analyzer (DMA) concept described by Labowsky and Fernández de la Mora [(2006). Novel ion mobility analyzers and filters. Journal of Aerosol Science, 37, 340–362.] is tested experimentally. Its aerosol inlet and outlet lines are grounded, while the electric field is created with a metallic grid electrode that also acts as a laminarization screen. A minimum gas suction qo is required at the outlet for aerosol to be sampled, so that qo at optimal operation conditions tends to exceed the aerosol inlet flow rate qi. A resolving power of 50 (full peak width at half height FWHH=2%) is demonstrated for ions with mobility diameter of 1.44 nm when operating at sheath flow Qs up to 2300 l/min, with qi/Qs=0.6% and qo/Qs=2%. Remarkably, this high resolution is achieved with a very modest area ratio of 1.27 between the laminarization section and the aerosol inlet section. The lack of voltage jumps anywhere in the aerosol path is an effective means to eliminate electrophoretic losses of nanoparticles, particularly when several DMAs are operated in tandem.