Application of Pyrolysis–Gas Chromatography–Mass Spectrometry for the Identification of Polymeric Materials


The analytical pyrolysis technique hyphenated to gas chromatography–mass spectrometry (GC–MS) has extended the range of possible tools for the characterization of synthetic polymers and copolymers. Pyrolysis involves thermal fragmentation of the analytical sample at temperatures of 500–1400 °C. In the presence of an inert gas, reproducible decomposition products characteristic for the original polymer or copolymer sample are formed. The pyrolysis products are chromatographically separated using a fused-silica capillary column and are subsequently identified by interpretation of the obtained mass spectra or by using mass spectra libraries. The analytical technique eliminates the need for pretreatment by performing analyses directly on the solid or liquid polymer sample. In this article, application examples of analytical pyrolysis hyphenated to GC–MS for the identification of different polymeric materials in the plastic and automotive industry, dentistry, and occupational safety are demonstrated. For the first time, results of identification of commercial light-curing dental filling material and a car wrapping foil by pyrolysis–GC–MS are presented.

Structural analysis and the study of degradation properties are important to understand and improve performance characteristics of synthetic polymers and copolymers in many industrial applications. Traditional analytical techniques used for characterization of polymers and copolymers such as thermal analysis and Fourier transform infrared (FT–IR) spectroscopy have limitations or are not sufficiently sensitive (1). Pyrolysis techniques hyphenated to gas chromatography–mass spectrometry (GC–MS) have extended the range of possible tools for the characterization of synthetic polymers and copolymers. Under controlled conditions, at elevated temperatures (500–1400 °C) in the presence of an inert gas, reproducible decomposition products characteristic for the original polymer or copolymer sample are formed. The pyrolysis products are chromatographically separated using a fused-silica capillary column and subsequently identified by interpretation of the obtained mass spectra or by using mass spectra libraries (such as the National Institute of Standards and Technology [NIST] or Wiley). Pyrolysis methods eliminate the need for pretreatment by performing analyses directly on the solid polymer or copolymer sample (1). (Please note that this article was presented at the XVII European Conference on Analytical Chemistry, which was held in Warsaw, Poland, on August 25–29, 2013).


Figure 1: Schematic view of the furnace pyrolyzer used in this study.
Most of the thermal degradation results from free radical reactions initiated by bond breaking and depends on the relative strengths of the bonds that hold the molecules together. A large molecule will break apart and rearrange in a characteristic way (2–4). If the energy transfer to the sample is controlled by temperature, heating rate, and time, the fragmentation pattern is reproducible and characteristic for the original polymer or copolymer. Another sample of the same composition, heated at the same rate to the same temperature for the same period of time, will produce the same decomposition products. Therefore, the essential requirements of the apparatus in analytical pyrolysis are reproducibility of the final pyrolysis temperature, rapid temperature rise, and accurate temperature control. Depending on the heating mechanism, pyrolysis systems have been classified into two groups: the continuous-mode pyrolyzer (furnace pyrolyzer) and pulse-mode pyrolyzer (flash pyrolyzer, such as the heated filament, Curie-point, and laser pyrolyzer). The pyrolysis unit is directly connected to the injector port of a gas chromatograph. A flow of an inert carrier gas, such as helium, flushes the pyrolyzates into the fused-silica capillary column. Figure 1 shows the schematic view of the furnace pyrolyzer used in our investigation. The detection technique of the separated compounds is typically MS, but other GC detectors have also been used depending on the intentions of the analysis (1,4).

The applications of analytical pyrolysis–GC–MS range from research and development of new materials, quality control, characterization and competitor product evaluation, medicine, biology and biotechnology, geology, airspace, and environmental analysis to forensic purposes or conservation and restoration of cultural heritage. These applications cover analysis and identification of polymers, copolymers, and additives in components of automobiles, tires, packaging materials, textile fibers, coatings, half-finished products for electronics, paints or varnishes, lacquers, leather, paper or wood products, food, pharmaceuticals, surfactants, and fragrances.

Our earlier publications (1,5–12) presented the analysis and identification of degradation products of commercially available synthetic polymers and copolymers by using analytical pyrolysis hyphenated to gas chromatography with flame ionization detection (GC–FID) and GC–MS. In this work, new examples of applications of this analytical technique for the identification of different polymeric materials are demonstrated.