AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Innovative Analytical Solution for Inverted Drift Tube Characterization and Validation by Experimental Methods
MD MINAL NAHIN, Carlos Larriba-Andaluz, IUPUI
Abstract Number: 374 Working Group: Instrumentation and Methods
Abstract A new mobility particle analyzer, which has been termed Inverted Drift Tube(IDT), has been modeled analytically as well as numerically and proven to be a very capable instrument. The basis for the new design have been the shortcomings of the previous ion mobility spectrometers: a) diffusional broadening for high mobilities and b) inadequate low and fixed resolution (not mobility dependent). To overcome the diffusional broadening and have a mobility based resolution, the IDT uses two varying controllable opposite forces, a gas flow with velocity vgas, and a linearly increasing electric field that opposes movement. The separation ratio Λ=vdrift/vgas, is employed to determine the best possible separation for a given set of nanoparticles. Due to the system’s need to operate at room pressure, 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 only to a very narrow mobility range. The following conclusions have been obtained:
1) Analytical description of the 1D IDT problem for an initial distribution of nanoparticles has been shown to yield very high resolutions without any optimization. Resolution is close to being proportional to the square root of the length, but has a dampening effect on the standard deviation that increases the resolution several folds when compared to a drift tube. It is shown that the resolution is an ill-conditioned parameter to express whether or not separation occurs inside the drift cell. The IDT has autocorrecting capabilities and fixes the diffusional broadening existing in other commercial instruments.
2) 3D numerical simulations for single particle trajectories using stochastic diffusion in SIMION for the IDT are used to obtain separation ratios. Instrument is shown to be able to separate particles of 55.89 and 55.93nm with ease. This would require effective resolutions of several thousands.
3) A chromatography existing concept of resolving power is used to differentiate between peak resolution in the IDT and acceptable separation between similar mobility sizes (resolving power).
4) A prototype of the instrument has been built and experimental results are shown in comparison to those achieved theoretically.