Evaluation of errors associated with δ13C analysis of lignin-derived TMAH thermochemolysis products by gas chromatography–combustion–isotope ratio mass spectrometry

This study reports the compound specific stable carbon isotope compositions (δ13C) of lignin tetramethylammonium hydroxide (TMAH) chemolysates obtained with gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS). The possible sources of the errors associated are considered. Off-line (TMAH) thermochemolysis was performed on wood samples and the δ13C values of the chemolysates were compared with the bulk δ13C of the native woods and their Klason lignins. For the four woods investigated, the δ13C values, corrected for derivative carbons added, were spread over a wide range of values, ranging from −40 to −25‰ and were, on average, depleted in 13C by ca. 9‰ relative to the native woods and by ca. 7‰ relative to the Klason lignins. This large variability can be partially attributed to overlapping chromatographic peaks and to the low intensity of some of the peaks. However, isotopic fractionation cannot be ruled out, especially in compounds resulting from CC bond cleavage in the propyl side chain. The uncertainties associated with the correction for carbons added by derivatisation were found to be high, especially for compounds having high contribution of derivative carbons.