Modulation of an ion beam is crucial to several applications in time‐of‐flight (TOF) mass spectrometry, especially for tandem TOF instruments which require selection of a particular precursorm/z(mass to charge) value prior to fragmentation. Here we present a detailed description of an ‘‘interleaved comb’’ ion deflection gate device with suitable electronics which offers a performance advantage over the more commonly used deflection plate devices. We demonstrate unit mass resolution for selection tom/z167 in the tandem TOF instrument constructed in our laboratory. Calculations suggest that the real time of unit resolution for our experimental arrangement is greater than 300. ©1996 American Institute of Physics.