Quantifying hydrophobicity of natural organic matter using partition coefficients in aqueous two-phase systems

The hydrophobicity of natural organic matter (NOM) is of great significance for its interfacial processes in natural and engineered systems. However, there is no well-accepted method for the routine determination of NOM hydrophobicity. In this study, the hydrophobicity of NOM spanning a wide range of origins and properties was quantified based on their partition coefficients (KATPS) in poly (ethylene glycol)/potassium citrate aqueous two-phase systems (ATPS). The LnKATPS of NOM correlated well with the elemental, structural, and thermodynamic indices commonly used to characterize NOM hydrophobicity, including (O + N)/C, O/C, aromatic and aliphatic carbon, and the free energy of interactions between molecules (ΔGiwi). A simple linear model was developed to predict NOM hydrophobicity using KATPS. The model was validated using 20 natural water samples collected from rivers and lakes, which suggested good prediction power. ATPS scale system is simple, fast, low-cost, environmentally friendly, and requires little pretreatment and small sample volume. Overall, KATPS can be used as quantitative measure of NOM hydrophobicity that facilitates routinely characterizing the interfacial properties of NOM.