TT24-7: Near real-time monitoring 24 hours per day, 7 days per week


The TT24-7 continuous air / gas monitoring system incorporates two electrically-cooled traps which operate in tandem to ensure 100% data capture.


Continuous monitoring


The acute toxicity of many organic vapours means that near real-time (NRT) data is sometimes required to minimise risk to human health. Chemical processing plants and government / military installations are key examples of sites which may require one or more NRT systems for round-the-clock operation.


Continuous monitoring may also be required for general kinetic studies - i.e. monitoring changes in vapour / odour composition over time. Applications in this case range from atmospheric chemistry and biological research (e.g. monitoring the vapour profile of growing plants, moulds or insect colonies) to food, flavour and fragrance profiling.


Both of these application areas demand continuous monitoring and minimal cycle times. Typical requirements may include:

  • Data every 10 minutes or less
  • High sampling rate (>500 ml/min) for optimum sensitivity
  • 100% data capture - i.e. truly continuous sampling
  • Reliability

On-plant installations for monitoring toxic chemicals may also require unattended operation with remote access to analyser set points and data. Transportability can also be a key factor - such that systems can be safely deployed in the event of a chemical incident.

Introducing the TT24-7

Markes have developed an innovative continuous monitoring system to meet these needs. The model TT24-7 is a robust, transportable unit convenient for installation on-site or in mobile response vehicles as well as conventional laboratories. It interfaces to GC(-MS) or process MS technology and incorporates two electrically-cooled traps which operate in tandem to ensure 100% sampling efficiency (- no dead times).

TT24-7 Operation

Air / gas is first sampled onto the channel A focusing trap at electronically controlled flow rates up to 1 L/min. At the end of the sampling time, channel B is switched in-line while channel A is pre-purged, desorbed and analysed. Trap heating rates approaching 100°C/sec combined with a reverse flow of carrier gas ensure efficient backflush desorption of analytes over a wide boiling range - giving narrow peak widths and optimum sensitivity. When sampling switches back to channel A, channel B is desorbed and analysed.


Patented inert valves inside the TT24-7 isolate the sampling process from the analytical system allowing the analysis to overlap with collection of a subsequent sample. Sampling can proceed on the desorption system while GC or MS analysis of the previous sample continues.

System flexibility

The TT24-7 can operate standalone (i.e. connected directly to the analyser) or in combination with a UNITY desorber. Standalone versions work well for semi-volatiles which are refocused on-column. TT24-7-UNITY systems offer the ultimate concentration efficiency (analytical sensitivity) for volatiles - especially if isothermal chromatographic analysis is required.

Continuous monitoring with multi-stream selection

Trace heated and ambient temperature options are available for multi-stream selection. Systems can be custom configured to suit your network monitoring requirements.

Tube desorption for calibration and verification

The TT24-7 Tube Desorption Accessory allows standards to be introduced to either of the focusing traps from a sorbent tube. This facilitates routine calibration and allows certified reference standard tubes to be introduced for auditing analytical quality assurance.


Parallel sampling onto a sorbent tube at the inlet of a TT24-7 on-line sampling line also allows comparison of on- and off-line monitoring data for system verification. The sampled sorbent tubes are analysed on the TT24-7 system via the Tube Desorption Accessory. Since the quantitative recovery of GC-compatible organics from sorbent tubes is well documented, satisfactory correlation of the tube results with those for the same sample analysed on-line verifies analyte recovery through the on-line sample interface.


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