Characterizing dissolved organic matter by thermal slicing ramped pyrolysis gas chromatography mass spectrometry

Dissolved organic matter (DOM) is one of the largest pools of reduced carbon on the planet. A molecular level characterization is key to understanding the formation mechanisms and refractory nature of the DOM in aquatic systems. Among the advanced instrumentation including high resolution mass spectrometry for the DOM analysis, thermal slicing ramped pyrolysis gas chromatography–mass spectrometry (TSRP-GC/MS) is promising in that it can differentiate molecules, or pyrolysates, from the DOM matrix according to the binding energy, from intact molecules to those generated from cracking. In a unique way, a single sample can be consecutively pyrolzed in multiple thermal slices that are preselected, thus two dimensional information can be obtained, one with GC elution time and the other with thermal slices. In this work, we analyzed DOM samples, obtained by either ultrafiltration or solid phase extraction (SPE), from different aquatic environments. Using a set of riverine samples, our data show that the pyrolyzates from labile DOM tend to be more in amount and more diverse in molecular type than those from refractory DOM. This result hints that degradation may lead to homogenization of DOM structures. Data analysis on samples from estuaries and coastal waters is still on going and will be presented, including comparison of ultrafiltered- and SPE-isolated DOM from the TSRP-GC/MS.