Real-Time Measurement Of Nanoparticle Size Distributions Using Electrical Mobility Technique

The benefits of sizing aerosolized submicrometer particles using an electrical mobility sizing technique have been well documented. The technique is highly accurate and has been shown to size 60 nm and 100 nm Standard Reference Material (SRM) with an uncertainty of only 1%. The National Institute of Standards and Technology (NIST) have been using electrical mobility to measure its 0.1μm Standard Reference Material (SRM) Particles for well over a decade.

With the commercialization of nanotechnology, occupational health risks associated with manufacturing and handling of nanoparticles is a growing concern. Workers may be exposed to nanoparticles through means of inhalation, at levels that greatly exceed ambient concentrations; and no workplace standards currently exist to limit exposure to nanoparticles. Nanoparticle size governs their deposition pattern in various parts of the lung and their ultimate fate within the human body. Thus, ambient measurements of nanoparticle size distributions provided by the electrical mobility technique is a powerful tool in understanding adverse health effects associated with nanoparticle related exposure.

This application note provides a brief overview of the electrical mobility technology as integrated in TSI scanning Mobility Particle SizerTM (SMPS) spectrometer followed by a discussion on applications in nanoparticle synthesis and exposure research.

The Scanning Mobility Particle SizerTM (SMPS) spectrometer consists of a sample preconditioner, a bipolar charger, a nanoparticle size classifier and a nanoparticle detector.

The pre-conditioner (typically an impactor or a cyclone) eliminates large micrometer sized particles. The bipolar charger (also referred to as neutralizer) establishes bipolar charge equilibrium on the particles. This defined charge condition is necessary for the size classification using electrical mobility. Particles are size classified in a Differential Mobility Analyzer (DMA). Only particles within a narrow range of electrical mobility have the correct trajectory to pass through an open slit near the DMA exit. The electrical mobility of these selected particles is a function of flow rates, geometric parameters and the voltage of the center electrode.