Triplet-specific probe compounds are powerful tools for the investigation of photochemically produced triplet states of dissolved organic matter (3DOM). Unlike laser-flash photolysis or phosphorescence quenching, chemical probes allow the determination of overall 3DOM quantum yield, steady state concentration, and formation rate in organic matter solutions under environmentally relevant conditions. Trans, trans-hexadienoic acid (t,t-HDA) and 2,4,6-trimethylphenol (TMP) quench 3DOM by energy-transfer and electron-transfer mechanisms, respectively. Used in tandem, these probes allow explorations of 3DOM reactivity. However, there is significant variation in the experimental parameters under which these probes are used and the sensitivity of measurements to disparities in these parameters is unknown. This work investigates the significance of experimental parameters in determining calculated photochemical 3DOM production. Two natural surface waters and an organic matter isolate (Suwannee River fulvic acid) were irradiated under UV-A light to demonstrate the influence of irradiation duration, [probe]:[organic carbon] ratio, probe reaction mechanism, and solution pH on the apparent 3DOM quantum yield, steady state concentration, and formation and quenching rates. Additionally, observed loss rates of t,t-HDA and TMP are compared under diverse conditions to determine if identical populations of 3DOM are measured. This work demonstrates that observed 3DOM measurements are more dependent on experimental conditions than organic matter source. For example, varying [probe] and experimental duration using the same DOM sample can generate [3DOM]ss values that vary by an order of magnitude. Furthermore, the side-by-side comparison of t,t-HDA and TMP suggests that the probes quench different 3DOM populations. By identifying the experimental parameters that are the most sensitive to variation, our results can be used to assess the comparability of measurements produced by different investigators and to determine the experimental conditions that would produce the most widely reproducible results.

Effect of experimental parameters on the apparent photochemical properties of dissolved organic matter

251st National Meeting (2016)

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