# Analytical Pyrolysis and Mass Spectrometry to Characterise Lignin in Archaeological Wood
## 3 Results and Discussion
### Evolved Gas Analysis Mass Spectrometry (EGA-MS)  
In EGA-MS, pyrolysis is also directly coupled to mass spectrometry. However, a temperature program is used instead of a single pyrolysis shot at fixed temperature, thus the products generated during heating are transferred to the mass spectrometer as a function of time (and pyrolysis temperature) at which they are produced. The result is the so-called total ion thermogram (TIT). The mass spectra obtained at different temperatures are overall mass spectra, as in the case of DE-MS, but the slow heating enables more detailed information to be obtained on the thermal degradation features of the sample components. In addition, single ions can be isolated, and their evolution profile extracted (extracted ion thermogram--EIT), thus providing a more selective chemical information. The results obtained by applying EGA-MS to the archaeological wood samples from La Marmotta are discussed in [PERSON] et al. (2018). Figure 3 shows the total ion thermograms (TITs) of a series of archaeological wood samples collected at increasing depths from the surface of pile 2212, where A corresponds to the surface and G to the core of the pile (T  
lignin pyrolysis products [87; 88]. Lignin dimers (\(m/z\) 272, 302 and 332) are also produced at high temperature [33; 52]. Ar Archaeological wood samples underwent thermal degradation approximately in the same temperature range observed for the reference sample, but they showed very different profiles. A progressive shift of the maximum degradation temperature towards a lower temperature was observed when proceeding from the core to the surface of the pile, indicating that less thermal energy was necessary to thermally degrade the lignocellulosic material. The reduced thermal stability can be explained by a more degraded wood structure. The detailed shoulders present in the profile of sound wood were no longer observed in the TITs of the archaeological wood samples, as a result of cellulose loss [33]. The mass spectra finally revealed that lignin was the main component present in the outermost part of the pile [33]. Lignin dimers were only detected in the innermost samples 2212-D, E, F, and G (Figure 4). Extracted ion thermograms (EITs) enabled the evolution of specific ions to be followed, therefore the thermal range of formation of specific pyrolysis products was determined. In addition, the area of the EITs can be integrated, thus enabling semi-quantitative calculations to be performed. This represents another powerful way to highlighting differences among samples. Figure 5 shows the EITs (\(m/z\) 107, 123, 167, 181 and 272, Table 2) for sample 2212-B (close to the surface of the pile) and for sample 2212-F (close to the core). Figure 3: Total ion thermograms (TITs) of sound oak wood (reference) and archaeological wood samples from pile 2212 from “La Marmotta” collected at increasing depths from the surface (A—surface, G—core) and mass spectra extracted from the three thermal degradation regions of sound oak wood. (**a**) Below 300 \({}^{\circ}\)C, (**b**) between 300 \({}^{\circ}\)C and 400 \({}^{\circ}\)C, and (**c**) above 450 \({}^{\circ}\)C.  
The lignin alteration in the archaeological woods was also evaluated considering the peaks at \(m/z\) 151 and 181, characteristic of the lignin oxidation, at \(m/z\) 272, 302, and 332,  
Figure 4: Overall mass spectra obtained by EGA-MS analysis of sound oak wood and archaeological wood samples collected at different depths from the surface, in the surface (A—rings 11–15), in the middle (D—rings 26–30), and in the core (G—rings 46–48) of pile 2212 from La Marmotta. Adopted from [33]. Figure 5: Extracted ion thermograms (EFTs) of specific \(m/z\) values for sample B (rings 16–20) from the surface (**top**) and sample F (rings 41–45) from the core (**bottom**) of pile 2212 from La Marmotta. related to the level of lignin depolymerisation, and at \(m/z\) 137 and 167, indicative of guaiacol and syringol species \(p\)-substituted with a free benzylic position (Table 2).