THERMIONIC IONIZATION DETECTOR (TID)

The Thermion Ionization Detector (TID) is similar in design to the FID and NPD detectors.  The TID is extremely selective, having little or no response to most aromatic and aliphatic hydrocarbons.  At slightly less sensitivity, the TID also responds to chlorinated phenols such as pentachlorophenol (PCP).

An electrically heated thermionic bead (TID bead) is positioned so that the column effluent contacts the hot bead surface.  Upon contact, analyte molecules containing nitro-functional groups such as TNT undergo a catalytic surface chemistry reaction.  The ions created in this reaction are attracted to the collector electrode, amplified and output to the data system.

The TID can operate in a nitrogen-only environment with similar but not identical response characteristics.  No detector gases other than air or nitrogen are required.  A make-up gas is provided so nitrogen can be used as a carrier while air or another gas can be added at the end of the column.

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