Application of Pyrolysis-GC/MS to Trace Lignin Phenols in Tree Leaves

Abstract

Pyrolysis combined with gas chromatography and mass spectrometry (Py-GC/MS) is a relatively rapid method (1-3 h) for investigating polymers. Tree leaves of five conifer species and six deciduous tree species were collected from Mt. Gwanak and Mt. Baekwoon and were analyzed to check if lignin-derived phenols can be used as biomarkers to trace organic carbon sources using Py-GC/MS. Lignin is a phenylpropanoid polymer which is complex and derives essentially from the oxidation process of three p-hydroxycinnamyl alcohol monomers. These monolignols are guaiacyl (G), syringyl (S) and p-hydroxyphenyl (H) types of alcohols. Py-GC/MS detected 21 kinds of lignin-derived compounds in deciduous tree leaves whereas 17 kinds in coniferous leaves. Conifer leaves contained more G-type compounds than deciduous leaves, which were 73.7% and 65.0% of the total detected compounds, respectively. In contrast, deciduous leaves contained more S-type compounds than conifer leaves, 20.6% and 11.3%, respectively. A unique S-type lignin-derived compound, 4-methylsringol, existed in all six deciduous tree leaves, suggesting that 4-methylsringol might be used as a biomarker to trace carbon sources using Py-GC/MS. However, the leaf samples have relatively higher organic carbon concentration than soils or sediments. If the organic carbon concentration is low, samples may need to be extracted and concentrated before Py-GC/MS analysis.