Abstract: A soft chemical ionization source can be small, require low power, reliably produce different ions depending on the operating conditions and configuration, and produce ions that ionize many sample chemicals in different phases in air, or solutions, or on surfaces. In one embodiment, an ionization source is comprised of a housing having a center post extending therefrom, a plurality of needles extending from the housing, and a counterelectrode extending around the housing. The plurality of needles and the counterelectrode are each coupled to an electrical supply. The center post and the plurality of needles extend through the counterelectrode. A voltage applied to the plurality of needles and the counterelectrode forms a gas discharge. By changing the dimensional or electrical characteristics of the ionization source elements, singularly, or relative to other sources in an array, the types, ratios among, and quantities of reagent ions can be changed and controlled.