Space charge effects on resolution in a miniature ion mobility spectrometer

Miniaturization of ion mobility spectrometry (IMS) is expected to have many advantages, as well as difficulties, in the separation of chemical species at atmospheric pressure. We report the results of studies of a miniature i on mobility spectrometer that has a drift channel 1.7 mm in diameter, the s mallest cross section reported to date. The miniature cell contains a homog eneous drift field and is operated at atmospheric pressure. The miniature I MS has been characterized by measuring both negative and positive ion spect ra using a frequency-quadrupled Nd: YAG laser on samples of NO, O-2, and me thyl iodide; a useful resolution (>10) was achieved with an operating volta ge of 500 V. Peak broadening due to Coulomb repulsion was determined to hav e a major effect on the resolution of the miniature device.