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

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.

Triplet Photochemistry of Effluent and Natural Organic Matter in Whole Water and Isolates from Effluent-Receiving Rivers

“…Although many past studies of DOM photoreactivity have been conducted using isolates, it is not clear whether the photoreactivity of solutions prepared with isolates is truly representative of whole water samples, 43,44 particularly those with effluent contributions.…”

“…In this work, we also compared the formation of 3 OM* and 1 O 2 between whole water samples and solutions prepared with organic matter isolates obtained from aliquots of the same water. Quantum yields are commonly measured using isolated DOM due to its stability and the overall convenience of this approach 44. Solutions prepared from paired OM isolates collected upstream and downstream of each WWTP showed little differences in f TMP and Φ 1O2 values (Figure 2), as was the case for whole water samples.…”

Direct and indirect photolysis of triclocarban in the presence of dissolved organic matter

“…As such allochthonous DOM precursors contain significant amounts of lignins and are characterized by high levels of aromaticity. In our previous studies we demonstrated that allochthonous DOM is effective at generating ROS such as the hydroxyl radical (OH•), while autochthonous organic matter is effective at forming 3 DOM (Guerard et al, 2009;Cawley et al, 2009). Subsequent research by Wenk et al (2011Wenk et al ( , 2012 demonstrated that the presence of unknown anti-oxidant moieties (presumably phenolic compounds) present in allochthonous DOM (and much less prevalent in autochthonous DOM) maybe responsible for this dichotomy in DOM photo-reactivity.…”

Characterizing the Molecular Structure and Reactivity of Natural Organic Matter in The Everglades

“…Reactive species (RS) measured in the present study include: hydroxyl radicals (•OH), singlet oxygen (¹O₂) and excited triplet states of dissolved organic matter (³DOM*) using the following probe: benzene (Balakrishnan et al, 1970;Warneck et al, 1988), Furfuryl alcohol (FFA) (Haag et al,1984a;1984b) and 2,4,6-trimethylphenol (TMP) (Cawley et al, 2009;Rosado-Lausell et al, 2013), respectively.…”

“…The methyl groups on TMP act as electron donors to the conjugated ring, which stabilizes the TMP cation after oxidation by ³DOM (Cawley et al, 2009). …”