Characterization of Aqueous Organics by Specific Ultraviolet Absorbance and Octanol Water Partition Coefficient

Specific ultraviolet absorbance (SUVA) is the ratio of ultraviolet absorbance (UVA) to dissolved organic carbon (DOC) or UVA per unit of DOC. The octanol water partition coefficient ($K_{OW}$) is the ratio of the concentration of the organic compound in octanol to that in water. Both of these parameters depend on the nature of the organic substance or the functional groups present in the organic compound. Two very different compounds may have the same $K_{OW}$ or SUVA, the ratio of $K_{OW}$ to SUVA of these will be different. Therefore, these two parameters for a particular category or nature of compounds are likely to be correlated. The present project aims at preliminary investigations to establish the correlation between $K_{OW}$ and SUVA for four categories of organic compounds. Keeping this objective in view, 41 synthetic samples containing a single organic compound of known concentration were prepared and analyzed for SUVA and $K_{OW}$. UVA was measured at 254 nm and at maximum absorption (${\lambda }_{\max }$). The $K_{OW}$, ${\mathrm{SUVA}}_{254}$, and ${\mathrm{SUVA}}_{\lambda \max }$ of a particular group of organics other than the aromatic compounds are found to be linearly correlated. The slope of the line is characteristic of the nature of the organic or functional groups in the organic compounds. The slopes (ratios) between $K_{OW}$ and ${\mathrm{SUVA}}_{\lambda \max }$ for carbohydrates, alcohols, and acids are 0.2, 17.4, and 11.2, respectively. The correlation is more sensitive at ${\lambda }_{\max }$ than at 254 nm. Regarding aromatic organic compounds, $\log K_{OW}$ is linearly correlated to SUVA and logSUVA.