One step carbon nanotubes-based solid-phase extraction for the gas chromatographic–mass spectrometric multiclass pesticide control in virgin olive oils

This article presents a novel application of carbon nanotubes for the determination of pesticides (chlortoluron, diuron, atrazine, simazine, terbuthylazin-desethyl, dimetoathe, malathion and parathion) in virgin olive oil samples. For this purpose, two carbon nanotubes, multi-walled and carboxylated single-walled, were evaluated, the later being the most appropriate for the aim of the work. The sorbent (30 mg) was packed in 3-mL commercial cartridge and the virgin olive oil samples diluted (20%, v/v) in hexane were passed through it. After a washing step with 3 mL of hexane to remove the sample matrix, the pesticides were eluted with 500 μL of ethyl acetate. In order to achieve lower detection limits, the eluent was evaporated under a nitrogen stream and the residue reconstituted in 50 μL of the same solvent. Aliquots of 2 μL of the extract were directly injected into the GC–MS system for analysis. The low limits of detection achieved, between 1.5 and 3.0 μg L−1, permit the application of the method to control the presence of these pollutants in very restrictive samples such as the ecological virgin olive oil. In addition to the sensitivity enhancement, the solid-phase extraction procedure is rather simple as it involves a single preconcentration–elution step, which allows sample processing in less than 8 min. Moreover, the cartridge can be reused at least 100 times without losing performance. The method was applied to the determination of the pesticides in two monovarietal and one ecologic commercial extra virgin olive oil samples. Two pesticides were detected in each of the monovarietal virgin olive oils while the ecological sample resulted to be a pesticide-free one.