Methanetriyl-pi hydrogen bonding in nonpolar domains of supramolecular nanostructures: An efficient mechanism for extraction of carcinogenic polycyclic aromatic hydrocarbons from soils.

ABSTRACT

Methanetriyl-pi hydrogen bonding (CH-π HB) in nonpolar domains of supramolecular nanostructures is proposed here as a new mechanism to increase the extraction efficiency of aromatic compounds. The approach is illustrated by the extraction of priority carcinogenic polycyclic aromatic hydrocarbons (CPAHs) in soils using supramolecular nanostructures of carboxylic acids with nonpolar domains consisting of hydrocarbon chains (C6-C10) dispersed in tetrahydrofuran (THF). The high concentration of CH-groups available in the supramolecular nanostructures (38.7-47.3 M) enabled the efficient extraction of CPAHs (recoveries between 89 and 106%), using a supramolecular solvent (SUPRAS) volume/soil amount ratio of 1.5 µL mg-1 and a simple and quick procedure (stirring for 15 min and centrifugation for 10 min). SUPRAS extracts were directly analysed by liquid chromatography-fluorimetry (LC-FL). No sample clean-up or solvent evaporation was required. Optimization of the composition of the nonpolar domains of the SUPRASs was carried out varying the length and concentration of the hydrocarbon chain of the carboxylic acid and the concentration of THF. Method detection limits were in the interval 0.07-0.4 µg kg-1. The relative standard deviations (n = 18, CPAH concentration = 300 µg kg-1), obtained under repeatability and reproducibility conditions, varied within the ranges 2.8-5.4% and 4.3-8.8%, respectively. The accuracy of the method was proved by analysing a certified reference material (CRM) from an industrial soil, contaminated with priority CPAHs at concentrations at the mg kg-1 level (BAM-U013c). The concentration of CPAHs found in soils taken in Southern Spain varied in the range 0.51-49 µg kg-1. The results here obtained demonstrate that CH-π HB is a valuable mechanism for increasing the extraction of aromatic compounds from soils.