A possibility for modulation of molecular flow through a capillary by its periodic heating and cooling has been investigated. The Knudsen gas flow (when the length of the molecule free path is greater than the diameter of the capillary) at variable temperatures of the capillary and the linear isotherm of adsorption have been analyzed in terms of diffusion approximation. The analytical expression for the outlet flow has been obtained for any given time dependence of the capillary temperature and inlet flow. It has been demonstrated that such modulation can increase both sensitivity and selectivity of mass spectrometric measurements and could be used for on-line analysis of gas streams.
V. A. Kvitsinsky, S. I. Krivosheev, and V. N. Makarchuk, "Adsorption Gas Flow Modulator for Sensitivity Increase of Mass-Spectrometric Measurements," Appl. Spectrosc. 52, 919-927 (1998)