Ion detecting apparatus and methods

Ion injection in a drift tube apparatus for mobility spectrometry was accomplished without conventional ion shutters such as the Bradbury-Nielson or similar designs common to such drift tubes. Instead ions were passed between the ion source and drift region by using time-dependent electric field gradients that act as ion barriers between ordinary drift rings. Benefits of this design are simplicity and mechanical robustness. This ion injection technique dynamically accumulates the ions created between shutter grid pulses, as does the Bradbury-Nielson method. The invention provides not only structural improvements to the well known apparatus, but also provides inventive methods for operating a drift tube apparatus in achieve maximum analyte injection efficiency and improving ion detection sensitivity. Improving ion detection sensitivity of drift tubes has practical experimental application. Incorporation of the inventive apparatus into a smoke detector is a further practical application of the invention.