Evaluation of the Deterioration State of Archaeological Wooden Artifacts: A Non-destructive Protocol based on Direct Analysis in Real Time - Mass Spectrometry (DART-MS) coupled to Chemometrics.

Evaluating the deterioration state of archaeological wood is obligatory before the preservation of archaeological wooden artifacts. Herein, a non-destructive, accurate and rapid methodology is firstly developed via Direct Analysis in Real Time-Mass spectrome-try (DART-MS) with chemometrics to classify archaeological wood and recent wood into 3 groups according to their deterioration states. As water in wooden artifacts probably affected the ion fragmentation process during DART-MS, ions responsible for eval-uating the deterioration state were separately screened towards waterlogged archaeological wood and dried archaeological wood by partial least squares discriminant analysis (PLS-DA). The well-defined separation of severely-decayed archaeological wood, moderately-decayed archaeological wood and recent wood was revealed in PLS-DA models. 20 and 27 wood fragment ions were further screened as key variables to evaluate the deterioration state of waterlogged archaeological wood and dried archaeological wood, respectively. They were tentatively identified as ions of lignin monomeric compositions, lignin dimers, lignin trimers and oligosaccharides. Results strongly suggested that differences in the structure and relative abundances of wood cell wall compo-nents accounts for the evaluation of deterioration state by DART-MS coupled to chemometrics. PLS-DA models provided R2Y=0.84, Q2=0.82 and R2Y=0.754, Q2=0.682 were then established separately using mass spectral fingerprints of respective po-tential predictive wood fragment ions. Furthermore, archaeological woods, consisting of Castanopsis, Quercus, Idesia, Populus and Cunninghamia species and with an average MWC range of 103%-465%, were used as an external validation set and evaluated with the methodology developed herein and the MWC criteria. Results showed that DART-MS coupled to chemometrics could accurately predict the inhomogeneous deterioration states of archaeological wooden artifacts and avoid the interference of inor-ganic deposits, in comparison with the MWC criteria.