Enhancing Air Monitoring Methods with Thermal Desorption
Liz Woolfenden, Director, Markes International, UK.
- Accurately monitor down to ppb/ppt levels.
- Use thermal desorption tubes for either passive or active sampling, without modification.
- Compliant with air sampling methods.
Introduction
Use of active sampling onto glass tubes packed with charcoal, followed by carbon disulfide (CS2) extraction and gas chromatography (GC) analysis, was developed as an air monitoring method for vapor-phase organic compounds (VOCs) in the 1970s. The approach is still used today for some personal exposure assessment (occupational hygiene) applications and stack emission testing, but is fundamentally limited with respect to detection limits. Thermal desorption (TD) is a complementary gas extraction technique whereby sorbent tubes (Figure 1) are heated in a flow of carrier gas. Trapped vapours desorb from the sample tubes into the gas stream and are transferred, via a refocusing device, into the GC/MS analyzer.
