10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Experimental Results of a Novel Inverted Drift Tube with Diffusion Auto-Correction for the Characterization of sub 100nm Nanoparticles
XI CHEN, Md Minal Nahin, Carlos Larriba-Andaluz, IUPUI
Abstract Number: 1658 Working Group: Instrumentation
Abstract A new mobility particle analyzer, termed Inverted Drift Tube(IDT), has been previously modeled analytically as well as numerically and proven to be a very capable instrument. The idea of the instrument was supported on the notion of existing shortcomings in previous instruments, i.e. diffusional broadening for high mobilities and inadequately low and fixed resolution (and hence not mobility dependent). The IDT, on the contrary uses two varying controllable opposite forces, a gas flow with velocity driving the particles, and a linearly increasing electric field that opposes movement. The effect of the linearly increasing field allows the IDT to overcome the diffusional broadening in the axial direction, constraining the charged nanoparticles and increasing the resolution several folds. Simultaneously, the use of two varying controllable forces allows controlled particle separation focusing on a given mobility. Hence, the separation ratio , is employed to determine the best possible separation for a given set of nanoparticles yielding a mobility dependent resolution which increases with particle size. Due to the system’s need to operate at room pressure- in order to make it portable- two methods of capturing the ions have been developed; Intermittent Push Flow for a large range of mobilities, and Nearly-Stopping Potential Separation with very high separation but limited to a very narrow mobility range. The system has been extensively proven analytically and numerically showing a resolution increase of several fold over conventional DMAs attesting to the capability of the system.
To prove its validity, here we will show the construction, testing and results of an experimental prototype. The system consists of a set of concentric ring/electrodes arranged similarly to a drift type instrument with an electrostatic gate and an electrometer detector. An existing gas flow pushing the ions through the tube is carefully controlled through several flow meters, laminarizers and mechanical pumps while a linearly increasing electric field is controlled through a home-made software. Nanoparticles entering the system are subject to mobility separation and reach the detector at different times. The arrival time distribution does not provide a direct relation between signal and mobility (or diameter) so a dedicated software captures the signal as a function of the duty cycle, averages it over several cycles, and converts it into signal versus diameter. Preliminary data shows that enhanced separation is a function of your choice of separation ratio, maximum voltage applied and target mobility (or diameter) of choice. This focusing technology that allows the user to enhance separation for a given mobility precludes the use of instrument resolution as a reliable parameter and uses instead the chromatographic existing concept of resolving power to establish the degree of separation between two adjacent peaks. For example, two peaks with particles mobility of 2 and 2.3nm, respectively can now be separated several seconds.