Ionization for tandem ion mobility spectrometry

An ion-mobility spectrometer system, comprising:

• a housing with an upstream end, a downstream end, and a drift zone defined along a longitudinal axis through the housing between the upstream and downstream ends;
• a tandem ion source at the upstream end of the housing, wherein the tandem ion source includes:
• a first ionizer operatively connected to the housing to supply ions at the upstream end;
• and
• a second ionizer operatively connected to the housing to supply ions at the upstream end, wherein the first and second ionizers are both situated upstream of the drift zone relative to an ion flow path through the drift zone;
• an electric field generator operatively connected to the housing to drive ions through the drift zone in a direction from the upstream end toward the downstream end;
• and
• a detector mounted at the downstream end of the housing for detecting ions from the drift zone reaching the detector, wherein the second ionizer is a radioactive ionizer mounted to the housing at the upstream end and positioned to direct irradiated ions into the housing, wherein the first ionizer source is a photoionizer/photofragmenter mounted to the housing on an upstream side of the drift zone, positioned to direct photons axially into the housing along the longitudinal axis, wherein the second ionizer is a 63Ni ionizer, wherein the 63Ni ionizer is mounted in a side passage of the housing that includes a gas inlet upstream of the 63Ni ionizer, wherein the side passage meets the ion flow path in a radial direction;
• and
• a wire grid traversing the side passage downstream of the 63Ni ionizer, wherein the wire grid is connected to a power circuit as an electrode, and wherein the power circuit includes a switch for selectively activating and deactivating ion flow from the 63Ni ionizer.