Human exposure to volatile organic compounds and other gases is an on-going health concern. Hand-portable, sensitive (capable of detecting parts-per-million to parts-per-billion concentrations), and power-efficient instruments are desired for the field detection, identification, and quantitation of organic vapors. We report here initial experiments involving a student-designed and built, laboratory-based ion mobility spectrometer (IMS). (Future efforts will be directed towards the miniaturization of the device for eventual field use.) The instrument features an atmospheric pressure chemical ionization (�corona discharge� or high voltage) source, capable of creating either positively or negatively charged ions. Ions are gently accelerated through a region of constant axial electric field (approximately 3000 V over 10-20 cm) before impinging upon a Faraday Plate detector. Ion current is read by an electrometer/picoammeter or oscilloscope. Experiments are currently conducted at atmospheric pressure throughout the IMS device. Preliminary experiments demonstrate ion transmission through the IMS. Calculations using SIMION (version 8.1, Scientific Instrument Services) have been conducted with reasonable qualitative agreement. Calculations involve solving the Laplace equation for the electrode geometry and running ion trajectories on the resulting electric potential distribution. Using SIMION's programming capability, a �viscous-drag� model, based on Stoke's Law, is employed to model the effect of ion transport through the atmospheric pressure background gas. Input parameters for the calculations include electrode geometry, electrode potentials, gas pressure and temperature.

Ion mobility spectrometry for vapor and gas detection

247th National Meeting (2014)

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