Environmental Monitoring

Trace organics in air, soil and water using thermal desorption

Air Monitoring

Vapour-phase organic chemicals (volatile and semi-volatile compounds - VOC & SVOC) are present, at varying concentrations, in all atmospheres. Many of them are toxic (known to pose a risk to human health) and have strictly regulated limit levels.  Other species, like organic sulphides, may not present a direct health risk but may still cause discomfort because of their low odour threshold.  

Given that the toxicity and odour thresholds of different organic chemicals range over several orders of magnitude, it is not generally possible to assess the impact of VOC & SVOC pollution in any given atmosphere by measuring the total or overall concentration of organic vapours.  Individual measurements are needed for each chemical present.  This invariably requires GC(MS) in combination with analytical thermal desorption (TD) to provide the concentration enhancement required.

Workplace and ambient air

TD is used as a high sensitivity alternative to solvent extraction for personal exposure assessment and workplace air monitoring (occupational hygiene). It has become the method of choice for environmental monitoring – indoor air, ambient air, odour, atmospheric research, etc. – and is also preferred for many ancillary applications such as measuring toxic/odorous industrial emissions, materials emissions testing and monitoring tracer gases in ventilation tests.

Higher sensitivity than solvent extraction

TD is compatible with a range of air sampling methods – diffusive/pumped sorbent tubes, canisters/bags and online (near real-time) monitoring. It also offers significant advantages versus conventional solvent extraction. Key benefits include: up to 1000-fold enhancement in sensitivity, reusable tubes, >95% desorption efficiency and no toxic solvent. 

Use of thermal desorption for environmental and workplace air monitoring is supported by a large number of national and international standard methods, including US EPA Methods TO-15/17, EN ISO 16017, EN ISO 16000, NIOSH 2549 and ASTM D6196.

Water and Soil Monitoring

In addition to air monitoring, thermal desorption is used extensively for measuring volatile organics in water and soil. Key applications include:

• TD in combination with headspace (HS) for routine measurement of geosmin, MIB and other odorants in drinking water at ppt levels
  
• In situ monitoring/mapping of contaminated land using soil probes in combination with diffusive or pumped sorbent tubes
  
• ‘Purgeables’ in water using purge and trap (incorporates TD) or HS-TD
  
• Solid phase extraction (SPE) of semi-volatiles followed by TD-GC/MS analysis

Thermal Desorption Products

Markes uniquely powerful thermal desorption (TD) systems and related air sampling equipment address all environmental health and safety applications. Key products include:

1. UNITY 2 – Platform thermal desorber for single tagged or untagged tubes (3.5-inch or 4.5-inch). UNITY 2 is a cryogen-free two-stage desorber for single sorbent tubes (pumped or diffusive) and features SecureTD-Q (quantitative re-collection for repeat analysis). 
   

2. TD-100 – High throughput, automated analytical thermal desorption unit for up to 100 RFID-tagged or untagged sorbent tubes. The TD-100 has built-in tag read/write capability. 
   

3. ULTRA 2 – Adds to Markes UNITY 2 TD platform to provide automatic desorption of up to 100 industry standard (3.5-inch) or DAAMS (4.5-inch) tubes with or without RFID tags. ULTRA 2 units also have a tag read/write facility.
   
   
4. Air Server/CIA 8 – Used for semi-continuous online monitoring of up to 8 whole air/gas streams, canisters or Tedlar bags.
   
   
5. HS-TD – Robust routine analysis of VOCs and odorants in water down to ppt levels.
   
   
6. MTS-32 – Sequential pumped sampling onto a series of up to 32 sorbent tubes. 
   
   
7. TC-20 – Simultaneous offline conditioning/dry-purging for up to 20 tubes. Temperature range: ambient to 400°C
   
   
8. Diffusive sampling – Low cost sampling for personal exposure monitoring or ambient air. 
   
   
9. Bio-VOC Breath sampler – Non-invasive biological exposure monitoring via breath.
   
   
10. VOC-Mole – In situ screening of VOCs in soil.
    
    
11. TubeTAG – RFID tube tracking for sorbent tube informatics.
    

Markes TD systems can be connected to any make of GC(MS) including systems from Agilent Technologies, Perkin Elmer, Shimadzu, Thermo Fisher and Varian.

Available free of charge to all TD users:
Thermal Desorption: A Practical Applications Guide. I Environmental Air Monitoring and Occupational Health and Safety.