A portable DMA for high-resolution classification of 1 nm particles
The Half-Mini DMA is the most recent and lightest (3.2 kg) member of a class of Yale-developed supercritical DMAs, later improved by SEADM, able to isolate with high resolution aerosol particles as small as 1 nm (including molecular ions). Its broad range of particle sizes (1-30 nm) is achieved with a single DMA configuration (2 cm long working section), greatly simplifying operation.
New Half Mini (p) model
The new (p) model Half mini DMA [Fernandez de la Mora, J Aer Sci Tec, 2016] introduces substantial flow improvements over the prior (m) model. It operates under near ideal flow conditions over a much wider range of aerosol and sheath gas flow rates, enabling classification of 30 nm particles with a resolving power close to the theoretically predicted value. This improvement relies on a new scheme for injecting the aerosol sample flow into the sheath gas flow with greatly improved axisymmetry. The new (p) model will become commercially available in April 2017.
Acquisition of fast size spectra: A key advantage of the Half Mini DMA over other existing DMAs is its ability to complete mobility spectra exceptionally fast without distorsion of the size distribution. This advantage is due in part to the minimal particle residence time in the classification region (0.2 -2 ms), as well as to the high resolving power of the instrument (which yields almost the same residence time to all particles over the whole size range). Undistorted size spectra from 1 nm to 30 nm can therefore be obtained every 2 s [Fernandez de la Mora, Aer. Sci. Tec., accepted, Jan-2017].
Features and advantages
- Unmatched size range for a high resolution instrument, recently extended beyond 30 nm by the (p) model (Fernandez de la Mora 2017)
- Highest resolutions available in the market (see results of independent studies below)
- Excellent transmission for enhanced sensitivity, see right (internal semiconducting tube bringing the classified particles to the grounded outlet)
- Exceptionally fast delivery of mobility spectra without distorsion of the size distribution
- Safe operation (internally protected high voltage)
- Optimized flow dynamics technology to ensure laminarity even at high (Re > 20,000) flow
- Diffusion broadening minimized
- Robust architecture, mirror polishing, total thermal control
- Stand alone operation (control and monitorization units built-in) directly connected to PC-USB
Size distributions of T.H. Ammonium Bromide (THAB) ions obtained with Half Mini and Nano-DMA in an indepedent study (Wang et Al, see Ref. 2014). Note the higher resolution of Half Mini enabling to identify all ions present in the sample.
Mobility spectra of the THA+ monomer measured with the Half Mini and with Nano DMA. The resolution, defined as the ratio Full Range/FWMH is almost three times bigger for the Half mini .
Applications and sectors
The instrument has been widely used for studies of Condensation Particle Counters (CPCs) sensitive to particles smaller than 3 nm, and other investigations involving pure nanometer size standards.
For users having a charge-reduction component (not provided by SEADM), the increased size range of this DMA (relative to earlier supercritical DMAs) permits high resolution analysis of charge-reduced biomolecules and small viruses produced by electrospray.
Range of applications include:
- Environmental/pollution research
- Atmospheric/climate research (Ref. Kangasluoma, 2014)
- Indoor air quality control
- Combustion (including particles produced by road vehicles)
- Synthesis of nano-particles via gas or wet techniques (Ref. Wang, 2014 and 2015).
- Nano-materials development
- Biomolecules and viruses
- Nano-particles applications: medical imaging, drug delivery, catalysis, etc.
- Generation of particle standards (Ref. Attoui, 2013)