IMS Positive-Ion Mode
Definition
An operating mode for ion mobility spectrometry instruments in which analyte ions are formed with positive charge through proton attachment or ammonium adduct formation. Required for TATP detection, as TATP has no electron-withdrawing groups for negative-ion detection.
- Ion formation
- Proton attachment or ammonium adduct
- Required for
- TATP detection
- Reason
- TATP lacks electron-withdrawing groups
- Contrast
- Negative-ion mode for nitro-based explosives
Common questions
Why can't TATP be detected in the negative-ion mode used for many explosives?+
Negative-ion detection relies on electron-withdrawing groups such as nitro groups to stabilise a negative charge, and TATP, a peroxide with no such groups, cannot form stable negative ions, so it must be ionised as a positive adduct instead.
Does an instrument need reconfiguring to switch ion modes?+
Most modern IMS instruments can switch between positive and negative ion modes electronically or run dual-mode scans, so a single unit can screen for both nitro-based and peroxide-based explosives without hardware changes.
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