Theory for inverse pulsing of the shutter grid in ion mobility spectrometry.

The fundamental transport theory for ion mobility spectrometry is modified to include effects of space charge. The new theory is then applied to describing the performance of "inverse ion mobility spectrometry" recently reported in Tabrizchi, M.; Jazan, E. Anal. Chem. 2010, 82, 746-750 using a discharge ionization source. The improved separation capabilities arise from space charge repulsion of the greater number of ions that are introduced into the drift tube by the technique. A larger effective diffusion coefficient and additional displacement velocities for the leading and trailing edges of the ion mobility peak account for the results. Performance is compared to conventional linear ion mobility spectrometry, with and without a radioactive source for ionization.