Pyrolysis-gas chromatography-mass spectrometry with electron-ionization and resonance-enhanced-multi-photon-ionization for the characterization of terrestrial dissolved organic matter in the Baltic Sea

Abstract

With the effects of global warming the input of terrigenous material into the oceans is increasing, with unknown consequences for the ecosystem. The Baltic Sea is an ideal research object and observed effects can be transferred to the oceans. This paper combines the influence of biotic and abiotic factors especially for terrigenous dissolved organic matter (tDOM). The study is focused on specific lignin target molecules and reflects the influence of salinity and microbial activity. Samples were taken along the salt gradient. In addition, an incubation experiment, mixing of tDOM-rich river water with Baltic Sea water from three different stations, was carried out. A newly developed pyrolysis gas chromatography mass spectrometry (Py-GC/MS) method using two different mass selective analyzers in one measurement cycle was established for the analysis of tDOM species. It enables the characterization of natural samples by a universal (electron ionization quadrupole MS) as well as an aromatic fingerprint (resonance-enhanced-multi-photon-ionization time-of-flight MS). By thermal desorption (TD) and subsequent pyrolysis the free volatile and high molecular weight structures are accessible. A huge part of the chemical species exists as high molecular structures. The salt content has a high influence on the composition of DOM. Generally, under TD conditions greater changes were observed, especially for the incubation experiment. Under pyrolysis and the chosen experimental conditions, the lignin apparently is hardly degraded by microorganisms.