Chemistry

Chromatography


Pyrolysis gas chromatography

For the direct introduction of the samples into the gas chromatograph, slight volatility and indestructibility of the sample components must be assumed. If a sample contains solid components, salts or non-volatile components, the chromatographic system will be heavily contaminated and the subsequent separations will be falsified. The analytes must be separated from the interfering matrix beforehand.

But if you want to get information about the non-volatile components of a sample, e.g. the composition of polymers, a representative mixture of volatile decomposition products can be used by means of pyrolysis (thermal decomposition). It is always important to maintain the pyrolysis conditions exactly (temperature, oxygen content).

The pyrolysis can be carried out separately from the gas chromatograph. Online pairing is also widespread. The transfer of the large amount of heat must take place quickly and reproducibly.

Hot wire pyrolysis: A continuously adjustable heating wire takes over the heat transfer to the sample. First, the solvent is evaporated at a low temperature. The decomposition temperature is then set at a high heating rate. However, the temperature setting is still too slow for some applications.

Curie point pyrolysis: An induction coil contains an electrical conductor made of alloys of iron, cobalt and nickel. The temperature in the conductor is suddenly increased by a high-frequency field until the Curie point temperature is reached. At the substance-specific Curie point, the alloy changes from ferromagnetism to paramagnetism with energy absorption. As a result, the temperature at the Curie point remains constant. With this technique, very short heating rates are achieved (20-30ms) always with the same temperature profile.

Examples of the application of pyrolysis gas chromatography

▪ Synthetic Polymers ▪ Rubber ▪ Polysaccharides ▪ Organic Salts ▪ Cellulose