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

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). 


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. 


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

Tube desorption for calibration and verification
The TT24-7 can be pre-configured with a tube desorption accessory to allow desorption of tube-based calibration standards and samples.  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. 

For part numbers and pricing please contact your local Markes distributor or visit our on-line shop

Relevant technical support publications from Markes International can be automatically downloaded from this web site (registration required). Examples include:

• Brochure - TT24-7: Near Real-Time Monitoring 24 hours per day, 7 days per week
• Brochure - Monitoring Chemical Agents
• TDTS 63 - Using the TT24-7 with twin electrically-cooled focusing traps for continuous monitoring of trace level toxic chemicals (e.g. chemical warfare agents) in air

Other thermal desorption instrumentation available from Markes International includes: 

UNITY platform thermal desorber
ULTRA multi-tube autosampler for UNITY TD 
ULTRA 50:50 automated TD with single autosampler re-collection
AutoSecure - Maximum throughput, fully automated system
Mass Flow Control Accessory
Air Server and ASIS 8 Systems for on-line automation


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