Potential of pyrolysis-GC–MS molecular fingerprint as a proxy of Modern Age Iberian shipwreck wood preservation

Abstract

Even though pyrolysis in combination with gas chromatography and mass spectrometry (Py-GC–MS) is widely used for molecular characterization of wood, its abilities to determine the taxonomy (species), provenance and the nature and intensity of degradation of archaeological woods are hardly explored. We performed principal component analysis (PCA) on Py-GC–MS data of sound woods and shipwreck woods of Pinus sp. and Quercus sp., to identify the impact of diagenesis on pyrolysis fingerprints. It was found that the proportion of most polysaccharide products decreased significantly upon diagenesis with the exception of 3-hydroxy-2-methyl-2-cyclopenten-1-one, which remains relatively well preserved. Furthermore, the guaiacyl lignin products were generally well preserved with the exception of 4-propylguaiacol, the relative contribution of which decreased considerably. New indices are proposed to establish the preservation state of shipwreck wood (shipwreck wood preservation index; SWPI) on the basis of polysaccharides (SWPIPS) and guaiacyl lignin (SWPILG) and syringyl lignin (SWPILS) fingerprints. Stepwise multiple linear regressions analyses applied on FTIR data of the same samples are indicative of the consistency of both techniques and the potential to identify changes in wood chemistry as a result of degradation. Other factors that influence wood composition, such as the differences between soft- and hardwood lignin and sap- and heartwood were also recognized