Reduced Mobility (K0)
Definition
The normalised ion drift velocity in an IMS instrument, correcting for temperature and pressure. A compound's K0 value at a given field strength is characteristic and forms the basis of IMS library matching.
- Corrects for
- Temperature and pressure of the drift gas
- Instrument
- Ion mobility spectrometer (IMS)
- Use
- Library matching against known explosive and narcotic K0 values
- Property type
- Compound-characteristic, analogous to retention time in chromatography
Common questions
Why not just use raw drift time instead of K0?+
Raw drift time shifts with ambient temperature and pressure changes between and even during runs, so a raw-time library match would drift out of tolerance. K0 normalises for those variables, letting a single library value apply across different operating conditions and instruments.
Can two different compounds share the same K0 value?+
Yes, this is a known limitation. Isobaric or structurally similar compounds can produce overlapping K0 values, which is why IMS alarms are treated as presumptive and confirmed with a second technique such as mass spectrometry before being reported as identification.
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