Direct Inlet Py-GC-MS analysis of cultural heritage materials

Abstract

Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) is an invaluable tool in the analysis of cultural heritage materials, particularly those containing complex polymerised components, whether natural or synthetic in origin. As the field embraces non-destructive and micro-sampling analysis, it is not always possible to perform traditional flash Py-GC-MS due to the sample size requirements of the technique, which are typically in the range of 50–100 µg. The development of a pyrolysis method using a Thermal Separation Probe (Agilent Technologies Inc.) has allowed for splitless Py-GC-MS analysis to be carried out on much smaller samples. This technique makes use of a multi-mode inlet that is capable of rapidly heating to 450 °C. Because pyrolysis takes place within the inlet, the methodology has been designated Direct Inlet Pyrolysis (DIP). Examples of synthetic reference materials, as well as case studies of archaeological residues and a varnish from the 1960 s were employed to demonstrate this adapted analytical technique. The results obtained using DIP-GC-MS were compared to published thermal degradation data and higher-temperature flash Py-GC-MS chromatograms. The results indicate that DIP-GC-MS can characterise the organic fraction of complex polymeric samples. Differences in pyrolysate formation and relative abundance occur for some polymers which are caused by lower and prolonged pyrolysis conditions. The technique can be performed in splitless mode with just a few micrograms of precious sample from cultural heritage objects, or by employing a low split if desired for more abundant reference materials. Like other Py-GC-MS methods, the on-line use of a reagent such as tetramethylammonium hydroxide (TMAH) allows for the derivatisation of polar functional groups.