Investigation on the locus of solubilization of polycyclic aromatic hydrocarbons in non-ionic surfactant micelles with H NMR spectroscopy

This research investigates the locus of solubilization of two significant compounds, the polycyclic aromatic hydrocarbons (PAHs) naphthalene and phenanthrene from a synthesized organic liquid phase comprised of the two PAHs and hexadecane in micelles of five polyoxyethylene non-ionic surfactants. The locus was inferred by the examination of the nuclear magnetic resonance (NMR) spectra. In this method, the ring current shifts on the ¹H resonance of the surfactant chain protons are monitored. ¹H NMR spectra were recorded for the five surfactant solutions in absence and presence of PAHs. The presence of the PAH induced the ¹H to shift along the surfactant chain. The proton shift changes were obtained by comparing the NMR spectra for the pure surfactant solutions with those for surfactant solution contacted with various non-aqueous phase liquids. It was demonstrated that the distribution of PAHs between the shell and the core of the micelles changed with the concentration of PAHs in the micelles and in the NAPL phase. The ¹H NMR analysis identified the presence of both PAHs in the shell region of the non-ionic micelles. This is an important observation because it is commonly assumed that in multi-component systems the solutes with relatively greater hydrophobicity are partitioned only in core of the non-ionic micelles. The results demonstrated the potential of the ¹H NMR analysis for the identification of the locus of solubilization of PAHs in micelles of non-ionic surfactant.