a detector for gas chromatography using two ionization sources within a single body to separately provide ionization energy to a column gas eluent to provide electrical discharge to two or more collecting electrodes provides improved selectivity and may be so used . use is made of combined bias / collecting electrodes . the use of two ionization sources permits generation of two detector outputs from within a common body and of a common constituent flow . the ionization sources and any applicable discharge gas and dopant may be selected based on desired selectivity .