AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Drift Tube Ion Mobility Spectrometry of Sub-10 nm Nanoparticles
DEREK OBERREIT, Peter McMurry, Christopher Hogan Jr., University of Minnesota
Abstract Number: 685 Working Group: Instrumentation and Methods
Abstract A new drift tube type Ion Mobility Spectrometer (DT-IMS) designed specifically for aerosol particle measurements from ambient environments is presented. DT-IMS devices allow for determination of the electrical mobility of a charged particle through measurement of the time necessary for a particle to travel a fixed distance through a tube in the presence of an electrostatic gradient. These instruments have traditionally been limited to measurements of ionized molecules and small (~1 nm) charged clusters. Previously developed devices are not able to sample charged aerosol particles from the ambient because of the high electric fields present at the beginning of the drift region. An additional limitation of existing DT-IMS devices is the low sensitivity of the Faraday Cup Electrometers at concentrations found in typical aerosols. Conversely, DT-IMS devices have the advantages of mobility invariant high resolving power (>R~20), low drift gas flow rates compared to DMA sheath gas flowrates and shorter measurement times as compared to most scanning differential mobility analyses.
The modifications to traditional DT-IMS devices required for application ambient aerosol measurement include a novel gateless sample introduction scheme, and the ability to couple to an aspirating Condensation Particle Counter (CPC), which is able to detect single particles. The gateless sample introduction uses a combination of a controlled flow path and stepped voltage at the start of a measurement to effectively select a ‘packet’ of aerosol. Additional aerosol is not able to enter the sample region after the start of a measurement due to the presence of an electrostatic field. The coupling to a CPC requires a controlled flow that splits to provide the drift gas and the gas aspirated by the CPC. A prototype device was built and tested. The device has a linear relationship between drift time and mobility and a resolving power greater than ~10. Measurements of proteins show good peak separation and compare well to DMA measurements.