Gerstel

Advanced Analytical Pyrolysis: Enhancing Polymer and Material Analysis with GC-MS

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What is Analytical Pyrolysis?

Analytical Pyrolysis is the process of heating a material to a high temperature to thermally degrade it into smaller molecules. When combined with GC-MS, characterization of a wide variety of pyrolysates and thermal decomposition products is possible.

Applications for Pyrolysis

Pyrolysis is used in several fields, including:

The GERSTEL PYRO: Advanced Pyrolysis Technology

The GERSTEL PYRO performs highly flexible and efficient pyrolysis of solids and liquids up to 1000 °C. It uses a four-conductor dual platinum filament that provides uniform heating throughout the sample zone. It uses a short valveless sample path with a liner-in-liner design for improved recovery of high-boiling or active compounds with low sample-to-sample carryover. The GERSTEL PYRO option can be used with a variety of pyrolysis methods.

Pyrolysis Modes Available with the GERSTEL PYRO

The GERSTEL PYRO module offers multiple pyrolysis modes, including:

Pulsed Pyrolysis: The Classic Approach

This classic process involves applying a rapid heating pulse at an optimized temperature to the sample.

The pyrogram shows the analysis of an acrylonitrile-styrene-acrylate copolymer. The pyrogram was generated using pulsed mode at 600 °C for 20 seconds. The monomers, acrylonitrile, styrene and butylacrylate are seen early in the chromatogram. The rest of the pyrogram shows the fragmentation of the polymer into dimers and trimers of the three monomers.

Smart-Ramped Pyrolysis: The Ideal Mode for Unknown Samples

A GERSTEL-exclusive technology, Smart-Ramped Pyrolysis applies a controlled temperature ramp, enabling continuous sample pyrolysis. It produces a pyrogram in a single sample run that is equivalent to or provides more data compared to pulsed pyrolysis mode. This mode is ideal for unknown samples and greatly reduces method development time.

The pyrograms show the analysis of a car finish using pulsed mode (top) and Smart Ramped Pyrolysis mode (SRP) (bottom). SRP mode shows an equivalent pyrogram for this sample. SRP mode uses a temperature ramp (100 °C to 800 °C at 5°C/s) to produce pyrograms equivalent to pulsed pyrolysis at temperatures within this range with minimal formation of secondary pyrolysis products.

This is the preferred mode of operation for unknown samples as an optimum chromatogram is produced without the need for method development, saving the user both time and sample.

Solvent Venting and Pulsed Pyrolysis: Improved Sample Purity

The sample is purged and thermally extracted prior to pyrolysis, providing a clean pyrogram without interfering contaminants. This mode is suitable for humid samples.

The pyrogram above shows the analysis of a water-soluble polymer, dextran sulfate (MW = 8000) dissolved in water using solvent venting and pulsed pyrolysis. Two microliters of the solution were applied to quartz wool in a quartz pyrolysis discharge tube. The sample was dried for 4 minutes at 200 °C in the PYRO unit. The PYRO body split vent is open during this time to allow the water to vent. After drying, the split vent is closed, and the sample is pyrolyzed. This example used pulsed pyrolysis at 650 °C for 20 seconds. Dextran sulfate is commonly used in cosmetics as a binding agent that improves dispersion. It is also used as a thickening agent to control viscosity.

Fractionated Pyrolysis: Enhanced Compound Differentiation

In this mode, multiple thermal extraction and pyrolysis temperatures are applied to the same sample with separate GC-MS runs at each temperature. This clearly differentiates between adsorbed volatiles (additives) and pyrolysates.

Case Study: Commercial Facial Wash Product

In this case study, a sample of a commercial facial wash product was first analyzed using Smart-Ramped Pyrolysis, generating a complex chromatogram.
The chromatogram above shows the GC-MS results of the pyrolysis of a commercial facial wash product. A small amount of the product was placed in an open-ended quartz pyrolysis tube and analyzed using SRP mode. The chromatogram is complex, and important peaks may be obscured.

To simplify the analysis, fractionated pyrolysis was performed on the sample. In this mode, an aliquot of the sample is analyzed three times at increasing temperatures.

For this analysis, temperatures of 120 °C, 300 °C, and 600°C were chosen. The lower figure shows a stacked view of the three chromatograms obtained at these temperatures. The fractionated approach greatly simplifies the analysis.

  • 120 °C: A large glycerol peak is present in the top chromatogram, resulting from heating the sample to 120 °C. The compound is added to the product to increase skin smoothness and aid in moisture retention. 1,3-butanediol is a skin conditioner and stabilizer, 2-phenoxyethanol is added as a preservative, and the long-chain acids are added as moisturizers and anti-microbial agents.
  • 300 °C: The middle chromatogram, run after heating the sample to 300 °C, shows more long-chain acids and long-chain amides used as emulsifiers, siloxanes, and sulfur dioxide. Sulfur dioxide can be a thermal degradation product of dextran sulfate, which is commonly added to cosmetics as a binder/skin conditioning agent.
  • 600 °C: The bottom chromatogram shows a pattern for polyethylene, most likely from beads added as an exfoliant.

Conclusion

These examples show that pyrolysis GC-MS can be used to identify polymers and additives in a wide variety of sample types. Smart-Ramped Pyrolysis applies a controlled temperature ramp, enabling continuous sample pyrolysis. It produces a pyrogram in a single sample run that is equivalent to or provides more data compared to pulsed pyrolysis mode. This mode is ideal for unknown samples and greatly reduces method development time. This results in an optimized pyrogram for a sample without having to determine the optimal pulsed pyrolysis temperature, which is especially important for unknown samples or when the sample amount is limited. 

Fractionated pyrolysis, on the other hand, enhances compound differentiation by applying multiple thermal extraction and pyrolysis steps, effectively simplifying complex chromatograms. For improved sample purity, solvent venting can be used to remove volatile interferences before pyrolysis, while pulsed pyrolysis offers a classic, rapid heating approach that is well-suited for targeted analysis of known materials.

The GERSTEL PYRO system enables highly flexible and efficient automated pyrolysis of solids and liquids up to 1000 °C combined with GC-MS determination of the thermal decomposition products. Its versatile pyrolysis modes—pulsed, smart-ramped, solvent venting, and fractionated—allow analysts to tailor their approach based on sample characteristics and analytical objectives. It provides an excellent tool for analyzing polymers, polymer mixtures, and polymer additives.

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