A Medium Flow, High-Resolution Vienna DMA Running in Recirculating Mode

In this work we present the latest design of the Vienna type Differential Mobility Analyzer (DMA). The so-called UDMA is specially designed for high-resolution mobility measurements for the particle size range between 1 and 5 nm and has been optimized to be combined with a mass spectrometer to provide a well-defined mobility fraction of molecular clusters. As the UDMA is designed for this narrow size range it features high-resolution mobility measurements already at flow rates of approximately 700 L/min, marked as medium flow conditions. This readily allows operating the UDMA in a recirculating sheath air flow system with gas cleaning filters, as the control over the purity of the sheath air is crucial for operating the UDMA inline with a mass spectrometer or other carrier gas sensible devices. The performance of the newly developed UDMA was tested by the analysis of well-defined molecular clusters produced by an electrospray source and compared with one of the state-of-the-art high resolution DMAs also known as Attoui DMA. For the UDMA, a relative FWHH of the transfer function of 2.5% in mobility-size was found for the monomer clusters of Tetraheptylammoniumbromide (THAB) at 1.44 nm mobility equivalent diameter.