Electron capture detector for use with an effluent stream from a gas chromatograph includes a non-radioactive electron source means and an adjacent ionization chamber in which electron capture take place. The detector comprises two partial chambers, of which one contains the electron source, and the other contains connections for input and output of analysis gas as well as a collector electrode for detecting ions. The collector electrode and the electron source are each of cylindrical configurations, and are coaxially aligned but are spaced apart with respect to each other. The electron current to the collector electrode provides an indication of the presence of electronegative constituents in the gas passing into the second partial chamber.