Transfer Functions and Resolutions of Seven Differential Mobility Analyzers for Sub-2 nm Particle Classification

Differential mobility analyzers (DMAs) that classifying particles according to their electrical mobility have been used extensively as a particle size analyzer and classifier. Most DMAs are operated in the size range from approximately 3 to 1000 nm. The classification of nanoparticles down to molecular dimensions has become of special interest in many disciplines, such as atmospheric nucleation research, nanomaterial synthesis, and nanoscale analytical chemistry. The transfer functions of most commercially available DMAs for sub-2 nm particle classification have not been systematically evaluated before. It is mainly due to the lack of sub-2 nm particle standard. The tandem DMA method was often used to evaluate DMA transfer function. In the 1-2 nm size range, diffusion broadening can significantly degrade the DMA resolution such that it is difficult to generate pseudo-monodisperse particlesusing a conventional DMA as the first DMA. Recent developments in high flow DMAs greatly improved the resolution in nanometer size range and allowed molecular monodisperse mobility standards to be demonstrated (Rosser and Fernández de la Mora
2005; Ude and Fernández de la Mora 2004).