Can cyclodextrins really improve the selectivity of extraction of BTEX compounds?

Solubility of BTEX compounds was determined in aqueous solutions of natural CDs (alpha-, beta-, gamma CD) as well as of some industrial beta CD derivatives (RAMEB, HPBCD, Ac beta CD) measured by UV photometry. From the phase solubility diagrams the complex association constants were determined. The beta CD derivatives increased the solubility of individual monoaromatic compounds, depending on the structure of the guest molecule. We have found that RAMEB (randomly methylated beta CD) and Ac beta CD (partially acetylated beta CD) are the most effective solubilizers while the effect of natural CDs is not significant because the complexes precipitate from the solutions. Extraction experiments were performed to see how the complexation of components influences the extraction using a mixture modeling the composition of these pollutants in soil. We have found that although the soluble CD derivatives are not as selective as expected based on complex association constants, they increased the efficacy of extraction by 4-6 times. The reason of the low selectivity is that the concentration ratio of certain BTEX compounds in CD solutions is smaller than in water. CD derivatives seem to have an equalizing effect: the solubility of the least soluble p-xylene is improved in the highest extent, but that of benzene the least. This result, however, is an advantage in the application of these CD derivatives in soil remediation (the availability of each BTEX compounds will be enhanced).