Analytical Methods for Measuring Kdom

The solubility enhancement method is the most straightforward static technique in which the apparent solubility (S w) of a HOC is measured in the presence of increasing amounts of DOM (Chiou et al., 1986, 1987 Chin et al., 1997 Uhle et al., 1999). Briefly, the analyte is added in excess (10-100 times the reported aqueous solubility) to glass reactors by plating the solute out from a stock solution. Buffered DOM solutions at various concentrations are added to each tube along with a control reactor containing 

The dialysis method is another technique that measures the distribution of a HOC in static equilibrium with the DOM substrate (Carter and Suffet, 1982 Chin and Weber, 1989 Arnold et al., 1999 O Toughlin et al., 2000). 

Fluorescence quenching is a popular technique for measuring Kiom values for polycyclic aromatic hydrocarbons (PAHs) (Gauthier et al., 1986, 1987  

Work conducted by Tiller and Jones (1997) demonstrated that the fluorescence of PAHs decayed over time under both under anoxic and oxic conditions. Typically, however, the presence of dissolved oxygen had a more pronounced influence on baseline fluorescence decay for all the PAHs studied. Moreover, certain PAHs (pyrene and anthracene) were more susceptible to this phenomenon than others. To date a mechanism to explain this phenomenon has not been identified, but it is probably a combination of complex pathways including the reaction of the analyte with reactive oxygen species formed from the excited triplet state DOM and the direct photolysis of the analyte by the excitation light source. Thus, the application of fluorescence quenching for measuring Kdom is probably limited to systems, which can be analyzed under anoxic conditions. 

Conversely, Kdom values modeled using fluorescence quenching binding constants significantly underestimated the breakthrough curves. 

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