Surfactant-coated carbon nanotubes for the liquid-liquid extraction of phthalates and other migrants in virgin olive oils.

This article presents a novel application of the surfactant-coated carbon nanotubes for the joint extraction of phthalates, xylene isomers and styrene from virgin olive oils. For this purpose, two carbon nanotubes, multi-walled and single-walled carbon nanotubes, were evaluated, the former providing the better results. The target migrants were liquid-liquid extracted from the virgin olive oil samples by means of the carbon nanotube pseudophase, and the aqueous extracts were analysed by headspace-gas chromatography-mass spectrometry. Sodium chloride was added to favour the release of the analytes to the gaseous phase of the vial. The comparison of the chromatograms obtained with the direct analysis reveals a sensitivity enhancement with the use of the surfactant-coated carbon nanotubes, especially for the phthalates, which can be ascribed to the pi-pi interaction between the aromatic ring and the nanotube surface. Limits of detection were between 6 and 30 microg L(-1) for 1 mL of sample. The precision of the method was better than 7.6% and the recoveries higher than 92%. Finally, the influence of the package material and the storage conditions on the concentration of the analytes was accomplished, and it was found that the concentration of phthalates increases with time in all the packages studied, while the more volatile compounds were found to decrease under the same conditions.