Halogen bonding for increasing efficiency in liquid-liquid microextraction: Application to the extraction of...

Halogen bonding (XB) was here proposed, for the first time, as a solubilization mechanism for increasing efficiency in the liquid-liquid microextraction of halogenated compounds. The approach was illustrated by the extraction of hexabromocyclododecane (HBCD) enantiomers in natural waters with a supramolecular solvent (SUPRAS) made up of inverted hexagonal aggregates of decanoic acid. The XB and dispersion interactions offered by the SUPRAS were able to extract the six HBCD enantiomers (i.e. (+)-α-, (-)-α- (+)-β-, (-)-β-, (+)-γ- and (-)-γ-) quantitatively (e.g. recoveries in the range 89-106%) and reach concentration factors as high as 720 without the need for solvent evaporation. HBCD enantiomers in the SUPRAS extract were directly analysed by chiral liquid chromatography coupled to tandem mass spectrometry (LCMS/MS). Quantitation limits of the method (0.09-0.9 ng L^-1) were below the quality standard stablished by the European Union for HBCDs in inland surface water samples (1.6 ng L^-1), and the precision, expressed as relative standard deviation (n = 6), was below 9% for all the HBCD enantiomers at concentrations within the range 50-500 ng L^-1. The method was successfully applied to the enantioselective determination of HBCDs in the dissolved and the particle-bound fractions of river waters containing different concentration of suspended particles (10-57.8 mg L^-1) that were spiked at two concentration levels (10 and 100 ng L^-1). The results here obtained prove that XB is a valuable mechanism for the solubilisation of halogenated compounds that can effectively increase their recovery from liquid and solid samples.