Technical note: Characterization of a Half-Mini DMA with 38 nm viral particles

Abstract

The Half-Mini Differential Mobility Analyzer (HM-DMA) developed at our laboratory for the study of particles smaller than 10 nm can theoretically classify at moderately high resolution particles as large as 30 nm. However, this prediction was not tested in earlier characterizations due to lack of monodisperse particles in that size range. Here we report tests of this DMA carried with 38 nm particles from the Chronic Bee Paralysis Virus (CBPV), recently shown to have a narrow mobility distribution with relative FWHM<2%. An earlier characterization of the CBPV showed a main peak at about 38 nm, accompanied by a considerably weaker secondary peak at a slightly smaller diameter and comparable width. After this sample had been stored for several months at 4–6 °C, both peaks still differ by about 4.5% in mean mobility, but have become comparably tall. When operating at a sheath gas flow rate of about 9 L/min and an aerosol flow below 0.1 L/min, the DMA is able to resolve these two relatively close singly charged particles. The FWHM values obtained in repeated tests for both peaks are below 5%. This provides a direct confirmation of the ability of the HM-DMA to classify 40 nm particles with a resolving power in excess of 20. This DMA covers also particles with mobility diameters as small as 1 nm with considerably better resolution.