CHEMICAL CHARACTERIZATION OF LIGNIN PREPARATIONS OF FRESH AND DECOMPOSING SPARTINA-ANGLICA BY PYROLYSIS MASS-SPECTROMETRY

In order to determine terrestrial contributions to the organic matter pool in the marine environment, a reliable chemical tracer is required . Lignin, an abundant component of vascular plant tissue is often used as such. In this study the lignin moiety of both fresh and degraded t issue of the model halophyte Spartina anglica was purified and chemica lly characterized to investigate its suitability as tracer. The study can be split into three parts. In the first part several enzymatic lig nin purifications of fresh S. anglica tissue were compared with each o ther. In the second part pyrolysis gas chromatography mass spectrometr y was applied to analyse untreated and on-line methylated milled wood lignin preparations. The previous characterizations of the lignin moie ty of S. anglica were used in the third part to monitor modifications in the chemical composition induced by natural aerobic decomposition i n the field. The temperature at which lipids were extracted from the o riginal tissue was not critical, although low temperatures improved th e purification to some extent. For enzymatic purification of lignin th e use of a polysaccharidase turned out to be the most important prereq uisite. The use of a protease did not have much influence on the ligni n residue. After 2 yr of aerobic decomposition, the lignin character o f untreated S. anglica tissue was no longer identifiable with direct t emperature-resolved mass spectrometry, but it still could be retrieved in the residue obtained after enzyme treatment. With continuing decom position the chemical structure of the lignin moieties became partly m odified. The very complicated spectra obtained after longer decomposit ion periods suggest the formation of a heterogeneous organic fraction, probably representing ''humic substances''. The gradual loss of ligni n characteristics in the litter makes its suitability as tracer for te rrestrial material in a complex mixture of substances doubtful, at lea st with the analytical technique applied in this study. (C) 1998 Elsev ier Science Ltd. All rights reserved.