Ribbon-shaped supramolecular solvents: Synthesis, characterization and potential for making greener the microextraction of water organic pollutants.

Liquid-liquid microextraction (LLME) techniques have experienced a tremendous growth over the last years but still face major challenges related to the use of more efficient and environmentally friendly solvents. Supramolecular solvents (SUPRASs) have proved outstanding efficiency in LLME, but many of the experimental conditions required for SUPRAS formation and/or application cannot be considered green or experimentally convenient. This paper was intended to make greener both SUPRAS formation and their application to the LLME of low-concentration organic pollutants in environmental waters. For this purpose, a variety of SUPRASs were produced at room temperature by simply mixing alkyl phosphonates (A6-12PO3H- and A6-12PO3-2) and tetrahexylammonium (He4N+) ions in aqueous media. Among them, the SUPRASs produced from decyl hydrogen phosphonate (DePO3H-) and He4N+ allowed, for the first time, the development of SUPRAS-based LLMEs where the SUPRAS previously synthesized was added to the liquid sample, instead of being formed in situ as usual, which was proved particularly advantageous for analyses involving large sample/SUPRAS volume ratios. At near equimolar amounts of DePO3H- and He4N+, the amphiphile arranged in the SUPRAS as planar ribbons consisting of water (21 ± 3%, w/v) and DePO3H- and He4N+ in the concentration range 1.0-1.4 M. The application of these SUPRASs to LLMEs was proved by extracting carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from drinking (tap and bottled) and natural (river, reservoir and underground) water (recoveries between 84 and 117% with standard deviations varying between 1 and 14%). The developed method was simple (it only required the addition of 500 µL of SUPRAS to 75 mL of sample, stirring and centrifugation), sensitive (method quantitation limits were below the maximum allowed limits set by the EU; were 0.6-7.1 ng L-1) and selective (SUPRAS extracts were directly analyzed by liquid chromatography-fluorimetry). This research proves that SUPRASs can be operationally used in LLMEs similarly to conventional solvents, which should favor their routine application in high-sample throughput laboratories.

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

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.