Speeding up the extraction of hexabromocyclododecane enantiomers in soils and sediments based on halogen bonding.

Halogen bonding (XB), a highly energetic and directional interaction, is here proposed as a new mechanism to increase solute solubilisation in solvent extractions. The approach is illustrated by the extraction of hexabromocyclododecane (HBCD) enantiomers in soils and sediments using supramolecular solvents (SUPRAS) containing XB donors in their structure. SUPRAS consisting of inverted hexagonal aggregates of decanoic acid, synthesized by water-induced coacervation of the amphiphile in tetrahydrofuran (THF), were explored for this purpose. Sample treatment involved the extraction of 400 mg of soil or sediment with 250 μL of SUPRAS for 5 min and then centrifugation for 10 min. SUPRAS extracts were directly analyzed by chiral liquid chromatography tandem mass spectrometry (LC-MS/MS) and quantification was carried out using isotopically labelled internal standards. Quantitative recoveries (93-102%) were obtained for the six HBCD enantiomers in both fresh and aged spiked samples. The mild experimental conditions required for extraction (room temperature and atmospheric pressure), the low SUPRAS volume/sample amount ratio needed (0.6 mL g), the short time required for sample treatment (15 min), and the simplicity of the procedure (use of conventional equipment and the possibility of treating several samples simultaneously), makes this method clearly superior to those previously reported. Method quantitation limits were in the intervals 0.58-2.23 ng g, and the relative standard deviations (n = 18, HBCD stereoisomer concentration = 50 ng g) obtained under repeatability and reproducibility conditions varied within the ranges 1.0-4% and 2.5-5%, respectively. The approach here described could be easily extended to the extraction of brominated flame retardants in different types of matrices.