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Focusing traps

Focusing traps (also known as cold traps) are at the heart of all Markes’ thermal desorption instruments and perform a preconcentration function by focusing analytes to achieve maximum sensitivity. They are constructed of quartz for optimum inertness and packed with a sorbent bed up to 60 mm long and a series of sorbents of increasing strength.


The thermal desorption instrument transfers compounds from a sorbent tube, canister or via on-line sampling to the focusing trap, which is subsequently heated to rapidly transfer compounds to the GC column in a narrow band of carrier gas. Markes instrument's focusing trap module offers super-fast desorption in a reverse (‘backflush’) flow of carrier gas. This optimises transfer/injection of the widest range of analytes, enabling simultaneous analysis of VOCs and SVOCs with market-leading sensitivity.

Focusing traps for the UNITY and TD-100 series are narrower at the GC end to optimise linear gas velocity and minimise band broadening.

Benefits of focusing traps

  • Traps can contain multiple sorbents for analysis of an extended range of analytes.
  • Traps can be custom-packed for specific applications.
  • Electrical cooling eliminates cryofocusing, which saves money, improves safety and performance, and uses laboratory space more efficiently.