Method and apparatus for identifying substances using ion mobility based ion separation techniques

An ion mobility spectrometer comprising:

• a reaction region,
• a drift region, comprising a voltage profile along which ions travel in a drift direction from the reaction region to a collector;
• an ion gate comprising a first electrode and a second electrode;
• and
• a gate voltage controller configured to:
• apply a voltage difference between the first electrode of the ion gate and the second electrode of the ion gate to prevent ions from leaving the reaction region;
• open the ion gate to allow the ions to travel from the reaction region into a modification region between the first electrode of the ion gate and the second electrode of the ion gate;
• apply a radio frequency voltage between first electrode of the ion gate and the second electrode of the ion gate to fragment ions in the modification region to provide daughter ions;
• to allow the daughter ions to pass from the modification region and into the drift region;
• and
• to close the ion gate by applying the voltage difference between the first electrode of the ion gate and the second electrode of the ion gate;
• wherein the ion mobility spectrometer is configured to determine the time of flight of the daughter ions from the ion gate through the drift region to the collector.