Pyrolysis–gas chromatography–mass spectrometry

Pyrolysis–gas chromatography–mass spectrometry

Acronym	PyGCMS
Classification	Mass spectrometry
Analytes	polymers biomolecules paint
Other techniques
Related	gas chromatography

Pyrolysis–gas chromatography–mass spectrometry is a method of chemical analysis in which the sample is heated to decomposition to produce smaller molecules that are separated by gas chromatography and detected using mass spectrometry.^[1]

How it works

Pyrolysis is the thermal decomposition of materials in an inert atmosphere or a vacuum. The sample is put into direct contact with a platinum wire, or placed in a quartz sample tube, and rapidly heated to 600–1000 °C. Depending on the application even higher temperatures are used. Three different heating techniques are used in actual pyrolyzers: Isothermal furnace, inductive heating (Curie Point filament), and resistive heating using platinum filaments. Large molecules cleave at their weakest points and produce smaller, more volatile fragments. These fragments can be separated by gas chromatography. Pyrolysis GC chromatograms are typically complex because a wide range of different decomposition products is formed. The data can either be used as fingerprint to prove material identity or the GC/MS data is used to identify individual fragments to obtain structural information.
To increase the volatility of polar fragments, various methylating reagents can be added to a sample before pyrolysis.

Besides the usage of dedicated pyrolyzers, pyrolysis GC of solid and liquid samples can be performed directly inside Programmable Temperature Vaporizer (PTV) injectors that provide quick heating (up to 60 °C/s) and high maximum temperatures of 600-650 °C. This is sufficient for many pyrolysis applications. The main advantage is that no dedicated instrument has to be purchased and pyrolysis can be performed as part of routine GC analysis. In this case quartz GC inlet liners can be used. Quantitative data can be acquired, and good results of derivatization inside the PTV injector are published as well.^[2][3]

Applications

Pyrolysis gas chromatography is useful for the identification of synthetic polymeric media, such as acrylics or alkyds, and synthetic varnishes.^[4] It can also be used for environmental samples.,^[5] including fossils.^[6] Trace evidence scientists in forensic laboratories use Pyroylsis GC to compare and identify paint or finish found at crime scenes or victims.

References

1. Halket JM, Zaikin VG (2006). "Derivatization in mass spectrometry --7. On-line derivatisation/degradation". European Journal of Mass Spectrometry 12 (1): 1–13. doi:10.1255/ejms.785. PMID 16531644.
2. Erwin R. Kaal, Mitsuhiro Kurano, Margit Geißler, Hans-Gerd Janssen (2008). "Hyphenation of aqueous liquid chromatography to pyrolysis-gas chromatography and mass spectrometry for the comprehensive characterization of water-soluble polymers". Journal of Chromatography A 1186 (1-2): 222–227. doi:10.1016/j.chroma.2007.10.035.
3. Eckerle, P., Pursch, M., Cortes, H. J., Sun, K., Winniford, B. and Luong, J. (2008). "Determination of short-chain branching content in polyethylene by pyrolysis comprehensive multidimensional gas chromatography using low thermal mass column technology". Journal of Separation Science (1): 3416–3422. doi:10.1002/jssc.200800218.
4. "National Gallery of Art Conservation: Scientific Research". Retrieved 2007-08-21.
5. Janos P (2003). "Separation methods in the chemistry of humic substances". Journal of Chromatography A 983 (1-2): 1–18. doi:10.1016/S0021-9673(02)01687-4. PMID 12568366.
6. Poinar HN (2002). "The genetic secrets some fossils hold". Acc. Chem. Res. 35 (8): 676–84. doi:10.1021/ar000207x. PMID 12186573.