Evaluating the triplet state photoreactivity of dissolved organic matter isolated by chromatography and ultrafiltration using an alkylphenol probe molecule

Kaelin M. Cawley, J. Alexandra Hakala, Yu-Ping Chin

Limnol. Oceanogr. Methods 7:391-398 (2009) | DOI: 10.4319/lom.2009.7.391

ABSTRACT: The triplet state photochemistry of dissolved organic matter (DOM) isolated by XAD and C-18 chromatography and tangential flow ultrafiltration (TFUF) was investigated using 2,4,6 trimethylphenol (TMP) as a molecular probe. Water samples were taken from an Arctic seep adjacent the Oksrukuyik River (OKS) on the north slope of Alaska, USA, where DOM is derived primarily from allochthonous material and from a eutrophic midlatitude wetland, Old Woman Creek (OWC), in northern Ohio, USA, where the DOM is formed from both allochthonous and autochthonous precursors. DOM-mediated TMP photolysis occurred for all samples, but was significantly faster in the OWC isolates. The method used to isolate DOM also influenced TMP photoreactivity, whereby the C-18 and XAD isolated material were typically more reactive than ultrafiltered DOM. Analysis of the isolates by spectroscopy revealed that the materials isolated by chromatography were relatively enriched in aromatic constituents, while the TFUF fraction had the lowest aromaticity based on molar absorptivity at 280 nm. The fluorescence index values revealed differences between OKS and OWC, but no discernable trends were observed among isolates. This study shows that both the manner in which DOM is isolated and the composition of its precursors will influence its triplet state photoreactivity.