The principle of thermal desorption

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Analysis of components in gas phase

Thermal desorption(TD) analysis is analysis of gaseous components in air. Although it is traditionally done on smaller molecules, the technology works well even for larger molecules as phthalates, PCB’s and PAH’s. Previously, gases for analysis were collected on activated charcoal, and the components were typically released with CS2. This however leads to a necessary dilution of the sample in at least 250µL of solvent, thereby limiting the sensitivity of the analysis. The sample preparation also involved some manual labour.

Ultra pure polymers collect the sample

With the development of polymers which could be produced to a sufficient purity for GC analysis, which had the ability to withstand temperatures in the 300°C range AND which could ad- and desorb smaller molecules; gas analysis became a much more sensitive and less manual labour demanding method. The gas samples can be collected on TD tubes, and these can be loaded on an autosampler for analysis. Because of the sample transfer without solvent, the sensitivity of the analysis is increased with at least a factor of 100. Manual work is minimized and the technique is essentially solvent free.

The principle in thermal desorption is described below:

TD_working_principle

 

The principle of thermal desorption(TD) analysis:

The TD tube used for collection of sample components is placed in the thermal desorber(1), which is essentially a heater cartridge designed to cover the entire area of the adsorbing material. When ready, the heater is activated and the trapped components(analytes) are transferred using a carrier gas, to a focusing trap (2) which is held cool during the transfer. After trapping of the analytes, the focusing trap is rapidly heated (“fired”) and the trapped components are transferred to the column. Because of the rapid heating, the analytes are well focused on the column. In both transfers there are a possibility to split the transfer, and the analysis may therefore be performed from splitless to a 1:100,000 split.