Auxiliary techniques in gas chromatography

1 Head-space analysis. As previously mentioned, polymers often contain substances of medium volatility such as monomers and polymerisation solvents. In addition, when heated polymers release volatiles as a result of the thermal degradation of the polymer itself or of the formulation additives used. Characterisation of such volatiles is now becoming increasingly important for regulatory requirements. Head-space gas chromatography as a technique offers considerable potential in this area. Head-space analysis can be carried out in either the static or the dynamic mode and can be readily automated. In static head-space analysis, the substance to be analysed is placed in a sealed vessel, where the material under examination comes into equilibrium with its vapours at a predetermined temperature. When equilibrium has been reached, an 

33 Inverse gas chromatography. The term inverse refers to the fact that the method is used to examine the stationary phase. Here, the injected vapour sample is referred to as the probe. 

The column is the most important part of the system, as its function is to encourage repetitive partitioning of each solute molecule between the gas and the liquid or solid phase. Packed columns are commonly used with the polymer or blend to be analysed coated on to a non-reactive substrate (Chromasorb W) which is then packed into the stainless-steel GC column. More recently capillary columns have been employed. Here the polymer is dynamically or statically coated as a uniform film on to the walls of the fused silica capillary. Inverse gas chromatography is a very flexible analytical technique however, full commercialisation of the technique has yet to be realised. 

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