Thermal Desorption
SKC sorbent technology research has produced superior materials for the collection of organic compounds for thermal desorption. Thermal desorption techniques offer the advantage of greatly improved analytical sensitivity. Because a solvent is not used, the collected sample is not diluted and, in most cases, analytical recovery is so close to 100% that desorption efficiency corrections are not required.
Sorbents
To be suitable for thermal desorption, sorbents must meet exacting specifications that include:
- Low contaminant background
- High thermal stability
- Sufficient adsorptive strength to retain components of interest and to release them quickly when heat is applied
Recent developments in sorbent technology have provided some superior materials for the collection of organic compounds for thermal desorption.
Anasorb® 747 (20/40 mesh size and 980 m2/gm surface area)
This beaded active carbon has the capacity for organic vapors similar to petroleum-based and coconut-shell charcoals. It also can be used to sample nonpolar organic compounds.
Anasorb GCB1 (20/40 mesh size and 100 m2/gm surface area)
Anasorb Graphitized Carbon Black 1 (GCB1) has a moderate surface area and is equivalent to Carbopack B (60/80). This sorbent has proven to be valuable for sampling compounds of intermediate to high volatility.
Anasorb GCB2 (20/40 mesh size and 10 m2/gm surface area)
This sorbent has a low surface area and is equivalent to Carbopack C (60/80).Anasorb GCB2 is useful in collectingsemi-volatile organic compounds (SVOCs).
Carbosieve S-III (60/80 mesh size and 975 m2/gm surface area)
This carbon-based molecular sieve has properties similar to the obsolete Anasorb CMS and replaces it in SKC thermal desorption tubes. Carbosieve S-III has a high capacity/breakthrough volume for small molecules and is moderately hydrophilic. It can be used for the lower boiling compounds such as halogenated hydrocarbons and alcohols.
Chromosorb® 106 (60/80 mesh size and 700 to 800 m2/gm surface area)
A porous polymer sorbent, Chromosorb 106 is used to trap low-boiling hydrocarbons, benzene, labile compounds, and volatile oxygenated compounds. This hydrophobic sorbent is the least polar polymer in the Chromosorb family and is functionally similar to Anasorb 727.
Tenax® TA (20/35 or 35/60 mesh size and 30 to 35 m2/gm surface area)
Tenax TA is a traditional sorbent (porous polymer) for trapping medium to high boiling compounds; it is especially useful for low concentrations because of its low background. Tenax TA is hydrophobic and is suitable for use in EPA Method TO-17 or IP-1B and other thermal desorption applications.
Tenax GR (20/35 mesh size and 35 m2/gm surface area)
This Tenax/graphite composite extends the range of Tenax to lower boiling compounds. It retains the ability of Tenax to be cleaned easily to a very low background and is widely used in thermal desorption applications.
Carbopack X (40/60 mesh size and 240 m2/gm surface area)
This is a strong graphitized carbon sorbent for collecting C3 to C9 hydrocarbons. It is hydrophobic.
Thermal Desorption Tube Selection for Perkin Elmer or Markes International Thermal Desorber Tubes
SKC offers single and multiple-bed thermal desorption tubes that meet the requirements of EPA TO-17 for the determination of VOCs in ambient air. All SKC thermal desorption tubes are sealed with PTFE end caps and marked with a permanent serial number. SKC thermal desorption tubes are available purged or unpurged (UP). Purchase unpurged tubes for thermal purging by your laboratory as needed. These tubes measure 0.25-inch OD x 3.5-inch length (6.35-mm OD x 88.9-mm length) and are available in glass or stainless steel. Glass transport tubes and Swagelok® fittings are available as accessory items.
