Evaluation of errors associated with d 13 C analysis of lignin-derived TMAH thermochemolysis products by gas chromatography–combustion–isotope ratio mass spectrometry L.E. Beramendi-Orosco a, * , C.H. Vane b , M. Cooper a , C.G. Sun a , D.J. Large a , C.E. Snape a a Nottingham Fuel and Energy Centre, School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK b British Geological Survey, Keyworth, Nottingham NG12 5GG, UK Received 17 July 2005; accepted 19 July 2005 Available online 14 November 2005 Abstract This study reports the compound specific stable carbon isotope compositions (d 13 C) 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 d 13 C values of the chemolysates were compared with the bulk d 13 C of the native woods and their Klason lignins. For the four woods investigated, the d 13 C 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 13 C 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 C–C 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. # 2005 Elsevier B.V. All rights reserved. Keywords: Tetramethylammonium hydroxide; Thermochemolysis; Lignin; Lignin derivatives; Stable carbon isotope; Gas chromatography–combustion– isotope ratio mass spectrometry 1. Introduction Lignin-derived products have the potential to be used as geochemical indicators because lignin is a specific component of vascular plants and is relatively refractory [1,2]. In particular, stable carbon isotope composition (d 13 C) of lignin and its derivatives can be used to complement palaeoenvir- onmental studies based on structural data obtained from its pyrolysates and phenols generated by CuO oxidation [3–7]. The combination of detailed molecular information with stable carbon isotope analysis in palaeoenvironmental studies allows the assessment of whether variations in d 13 C values are due to the presence of polysaccharides, or due to alterations suffered by the lignin polymer [8,9]. A key issue in obtaining reliable d 13 C data of lignin derivatives by gas chromato- graphy–combustion–isotope ratio mass spectrometry (GC– C–IRMS) is to determine if these compounds reflect the isotopic composition of the parent macromolecule. Analytical pyrolysis and CuO oxidation, both widely used methods for lignin structural studies, have been combined with GC–C–IRMS to study past vegetation changes [5], sources and distribution of organic matter in marine sediments [6,10] and genesis of humic substances www.elsevier.com/locate/jaap J. Anal. Appl. Pyrolysis 76 (2006) 88–95 * Corresponding author. Present address: Instituto de Geofisica, Univer- sidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico DF 04510, Mexico. E-mail address: laura@geofisica.unam.mx (L.E. Beramendi-Orosco). 0165-2370/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2004.07.010