Quantitative evaluation by attenuated total reflectance infrared (ATR-FTIR) spectroscopy of the chemical composition of decayed wood preserved in waterlogged conditions Benedetto Pizzo a,n , Elisa Pecoraro a , Ana Alves b,c , Nicola Macchioni a , José Carlos Rodrigues b,c a CNR-IVALSA, Istituto per la Valorizzazione del Legno e delle Specie Arboree, via Madonna del Piano 10, Sesto Fiorentino (FI), Italy b Tropical Research Institute of Portugal (IICT), Forest and Forest Products Centre, 1349-017 Lisboa, Portugal c Centro de Estudos Florestais, Instituto Superior de Agronomia, 1349-017 Lisboa, Portugal article info Article history: Received 18 March 2014 Received in revised form 16 July 2014 Accepted 21 July 2014 Available online 1 August 2014 Keywords: Partial least square (PLS) regression Multivariate analysis Wet wood chemistry Infrared spectroscopy Archaeological wood Lignin Holocellulose abstract This paper reports on the assessment of lignin and holocellulose by means of ATR-FTIR analysis and multivariate PLS regression. The analysis was conducted on 59 samples coming from different excavations where wood had been preserved in waterlogged conditions. A range of results from different wood species (Alnus sp.p., Cupressus sempervirens, Larix decidua, Picea abies, Pinus sp.p., Quercus sp.p., Ulmus sp.p.), states of preservation, waterlogged environments, and burial times are presented. A calibration model was selected after comparing different reference data (samples extracted and not-extracted, and ash-rich and ash-free bases of calculation for the calibration values), and two different post-acquisition spectroscopic manipulations (both in terms of normalisation procedures and of spectral ranges used for the calibration). Results showed that the best models were different depending on which considered component (lignin or holocellulose) was measured and to which data set (softwood or hardwood) the samples belonged. It is shown that the predictive ability of the models is affected by high ash content (too contaminated samples had to be excluded in order to attain good results, because of excessive overlapping of bands related to the inorganic fraction) but not by the preliminary extraction of sample. Furthermore, the stability of best models is also demonstrated and a procedure of external validation carried out on an external set of samples confirmed the general validity of the identified models. & 2014 Elsevier B.V. All rights reserved. 1. Introduction The structural modifications which wood undergoes during burial in waterlogged conditions [1–3] require that an effective treatment to be carried out on artefacts after their discovery, to ensure their safe conservation. However, after consolidation, some changes may still occur in artefacts both in short and long term, even when they are kept in well-controlled conditions such as those found in a museum. For instance, this occurrence could be related to some kind of interaction between the selected con- solidant product and the maintenance environment [4–6]. In this perspective, a diagnostic evaluation of a piece should be carried prior to the application of any kind of conservation treatment, because it would provide the opportunity to check for the presence of potential interactions between the applied treatment and the remaining wood components. Moreover, the evaluation of the extent of decay prior to conservation allows the grading of the same decay, and potentially, therefore, the tailoring of a treatment to the specific state of preservation of the find. Within this framework, a quantitative, reliable and quick measure- ment of the residual structural chemical components constituting cell walls of the archaeological wood material represents an important step towards the broad applicability of a systematic approach intended to evaluate the state of preservation of archaeological wooden objects at the time of their discover. Conventional wet chemical analyses are accurate but they have major limitations especially with regard to the amount of material required for the test and the fact that they are not very quick. A previous work [7] has already shown how ATR-FTIR analysis can be reliably used as a very good alternative for the quantitative estimation of the structural biopolymers constituting archaeological wood (namely, lignin and holocellulose). That approach made use of a preliminary calibration procedure able to establish a correlation between the spectra obtained on some archaeological samples and the values obtained by the conventional wet chemical Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta http://dx.doi.org/10.1016/j.talanta.2014.07.062 0039-9140/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: pizzo@ivalsa.cnr.it (B. Pizzo). Talanta 131 (2015) 14–20