A new high-current trochoidal electron monochromator1 has been designed and interfaced to a JEOL AX505 magnetic-sector mass spectrometer. The electron monochromator provides a means for controlling the ionizing electron energy over the 0 eV to 30 eV range with an electron energy resolution of +/- 0.3 eV and output currents in excess of 200 μA. This permits the direct formation of negative ions without using an energy-moderating buffer gas, and it provides a means for measuring electron capture resonances and forming ions in specific energy states. The electron monochromator has demonstrated a detection limit of 10 fg of hexachlorobenzene (splitless injection) with a signal-to-noise ration of 31:1. A linear response has been measured for octafluoronapthalene with concentrations ranging over seven orders of magnitude. Linked-scan MS/MS and selected reaction monitoring have been used to examine energy-dependent fragmentation.