TGA-IR-GC-MS: A powerful evolved gas analysis technique

Some examples of projects we have carried out for our customers are:

• Polyurethane characterization: Identifying the building blocks of polyurethanes, which can be valuable for material development.
• Ink formulation analysis: Determining the composition of unknown cured ink formulations.
• Polymer analysis: Identifying plasticizers and additives in polymers, which is essential for understanding polymer properties.
• Thermal degradation studies: Investigating the thermal degradation of various polymers, which gives information about their use in various applications.

 

How does it work?

The TGA-IR-GC-MS analysis is an analytical method that integrates three powerful techniques: thermogravimetric analysis (TGA), infrared spectroscopy (IR), and gas chromatography-mass spectrometry (GC-MS). Each of these techniques offer unique insights into a material’s composition, molecular structure, and thermal behavior. However, when combined, they form an analytical synergy that provides comprehensive information on a material’s chemical properties.

TGA-IR-GC-MS setup with the TGA (right), the infrared gas cell (middle) and the GC-MS (left), coupled by the transfer line.

Within PTG/e’s infrastructure, TGA, IR, and GC-MS equipment can be combined with a heated transfer line. The TGA technique quantifies a sample’s weight change as a function of temperature or time. It subjects the sample to a precisely controlled temperature program while continuously monitoring its weight. This enables the determination of critical information related to a material’s thermal stability and decomposition behavior.

Thermogram of a polymer material, showing the weight percentage as a function of temperature. 

The gas that evolves from the sample by evaporation or thermal decomposition during the TGA measurement, is transferred via the heated transfer line through the IR gas-cell to be measured with IR spectroscopy. IR spectroscopy uses the interaction between infrared light with the molecular bonds within the evolved gas, which is unique for each type of material. The spectrum that results from this technique reveals valuable details about the functional groups within the evolving gases, aiding in the identification of chemical bonds, molecular structure, and functional groups of the original sample.

The overall absorbance during the online IR measurement (left), with the infrared spectrum at the peak of the thermal decomposition (right).

The gases that evolve from the sample at a specific temperature during the TGA measurement, can be collected to inject into the GC-MS. In GC the gasses (which are likely to be mixtures of various components) pass through a separation column, separating the individual components based on their volatility and column affinity. Then, MS analyzes these separated components, providing information regarding their molecular mass and fragmentation patterns. This helps identify the components released during thermal degradation of the material, providing further insight into the original composition of the material.

Gas chromatogram of the injected gas. The peaks indicate the response of the MS detector, showing the mass spectrum of the eluted component.

The flexibility of the whole evolved gas system offers several combinations of techniques including: TGA-IR, TGA-MS, TGA-GC-MS and TGA-IR-GC-MS analyses. This makes it possible to select the best combination of techniques to answer the material questions.

In conclusion, the combination of the TGA, IR, and GC-MS techniques presents a potent analytical tool capable of resolving complex and unknown material challenges.

For further information on how this analysis can benefit your specific material analysis needs, please don’t hesitate to contact us!