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Biogeochemistry of organic matter and associated elements along the river-estuary-ocean continuum
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Elucidating molecular level information of dissolved organic matter in aquatic environments using two novel advanced analytical instruments
Tuesday 8th @ 1530-1550, Conference Hall
Zhanfei Liu* , The University of Texas at Austin
Presenter Email: zhanfei.liu@utexas.edu |
| Deciphering molecular structures of dissolved organic matter (DOM) components is key to understanding the formation and transformation of this globally important carbon pool in aquatic environments. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been the key tool to providing molecular level information of DOM since 2000s owing to its ultrahigh resolving power that can offer accurate molecular formula. However, we still know little about the structural detail of DOM molecules. Such a task may have to depend on the integrated use of complimentary analytical techniques. We recently developed two novel techniques for DOM analysis: ion mobility quadrupole time of flight liquid chromatography mass spectrometry (IM Q-TOF LC/MS) and thermal slicing ramped pyrolysis gas chromatography mass spectrometry (TS-RP GC/MS). In this talk, I will use both published and preliminary data to show the power of these two techniques in DOM analysis. For example,
the IM Q-TOF LC/MS provides multidimensional structural information of DOM molecules including the geometric conformation and isomers of DOM. Our results show that natural DOM molecules from several south Texas rivers and adjacent coastal waters have smaller geometric conformation compared with standard biomolecules, suggesting that environmental degradation may make DOM molecules become more compacted. Furthermore, of all DOM molecules resolved within the detection limit of IM-MS, about 10% had at least one but no more than four isomers. Using TS-RP GC/MS on ultrafiltered DOM from a wide range of rivers, our results clearly show that pyrolysis produced fragments, or pyrolyzates, tend to be more diverse in fresher DOM than those from relatively more refractory DOM as determined by amino acid degradation index, suggesting that molecule composition becomes more homogeneous as degradation proceeds. These two novel techniques show great promise in further deciphering molecular level information of DOM in rivers, coastal and open oceans.
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