[en] The electrostatic energy filter designed especially for ion energy separation prior to their entry in a mass spectrometer filter consists of two coaxial cylindrical electrodes. The inner electrode is provided with two pairs of separation slots, one after the other on the opposite sides of the electrode. Metal baffles are provided inside the inner cylindrical electrode. The advantages of the filter include improved signal-to-noise ratio, the elimination of foreign lines in the spectrum, improved energy resolution of the mass filter, reduced losses and improved permeability for ions in the selected energy range. (J.B.)