THM-GC-MS is one standard technique for the analysis of wood that uses tetramethylammonium hydroxide as a regent and sub-pyrolysis temperatures (300-500°C) for the selective cleavage of ester and ether bonds , although pyrolysis HMDS-GC-MC is the technique most commonly used for waterlogged archaeological timbers . During thermally assisted hydrolysis and methylation, lignin is fragmented into syringyl and guaiacyl products. The ratio of acids to aldehydes (Ac/AlS, Ac/AlG) and the ratio of overall syringyl to guaiacyl (S/G) are used as proxies for the chemical degradation of the lignin. An increase in the Ac/Al ratio indicates oxidative cleavage on the alkyl side chain which has been associated with WRF and some SRF . The oxidation and cleavage of the β-O-4 bond, the most common linkage in lignin, is the primary cause of increases in Ac/Al. In waterlogged wood, an increase in the Ac/Al ratio has rarely been seen, indicating that depolymerization of the lignin is not a major process in this environment . One proposed major limiting factor is the availability of oxygen .