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Issue 19, June 2006
Innovative Technology
for Monitoring Trace Level Compounds in Soil and Air
Sorbent tube sampling technology together with thermal desorption
- gas chromatography (TD-GC) or TD-GC-mass spectrometry (TD-GC-MS)
analytical technology has been optimised and validated over many years
for monitoring vapour-phase volatile organic chemicals (VOCs) in air.
Both diffusive1,2,3 and pumped4,5,6 sampling
mechanisms have proved their worth for a wide range of common volatile
organic pollutants at concentrations ranging from hundreds of parts per
million in polluted industrial air to low / sub-part per billion levels
in the ambient environment.
The cost and performance of sorbent tube monitoring methods have also
been enhanced by the now widespread acceptance of TD-GC(-MS) analytical
technology. Thermal desorption offers a significant improvement in
sensitivity and numerous practical advantages over conventional solvent
extraction methods7. It eliminates manual sample
preparation and allows sorbent tubes to be reused up to
100 times without regeneration or repacking. These factors combine
to make sorbent tubes among the most affordable of air sampling
techniques.
ULTRA-UNITY™ (see picture) is an automated thermal desorption
platform from Markes International with capacity for up to 100 tubes
and incorporating an electrically-cooled focusing trap for optimum
concentration enhancement. It is compliant with a suite of international
air monitoring standards (including US EPA Method TO-17, ISO 16017 parts
1 & 2, ASTM D-6196-97) for monitoring vapor-phase organic compounds in
ambient air. The thermal desorber incorporates a stringent, no-flow
ambient temperature leak test of each sample tube prior to analysis
which helps ensure data quality and preserves the integrity of failed
tubes.
The key features of a standard ULTRA-UNITY™ system are:
• simultaneous analysis of VOC compounds (C3 – C40)
• quantitative re-collection of split flow for data and method
validation in accordance with ASTM 6196-03 and
• quantitative recovery of compounds, including labile sulfur compounds
(Mercaptans) and high boiling compounds such as di-decyl phthalate up to
n-C408.
Continuous on-line monitoring can be achieved by using a twin
trap thermal desorber (TT24/7), or by using a UNITY- Air Server. The
Air server, suitable for analytes with boiling points in the range of
n-C2 to n-C16, also facilitates the analysis of air samples collected in
vessels such as canisters and Tedlar bags9.
The advantages conferred by TD-GC-MS analytical
technology, including superior sensitivity, ease of use,
fast throughput and automation, have contributed to
its ubiquity within the field of air / gas (and solid) sample analysis.
Thermal desorption technology has been exploited by a multitude
of different analytical applications including;
• ozone precursor monitoring in ambient air10
• monitoring toxic, odorous and labile land fill gas,11, 12
• soil analysis of contaminated land using the Markes
International Ltd VOC-Mole™ soil probe13
• biological monitoring using a Bio-VOC breath sampler14
and;
• continuous on-line monitoring of trace level toxic chemicals in air
such as chemical warfare agents 15,16.
Markes International Ltd., represented in Australia by Agilent
Technologies, is one of the worlds leading suppliers of thermal
desorption equipment and sampling accessories. This article was
submitted by
Peter Hughes from Markes International Ltd.
References for this article
Other related articles
Indoor Environment Quality and Facility Ecology
Testing
the Air
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