Nafion membrane-supported ionic liquid–solid phase microextraction for analyzing ultra trace PAHs in water samples

A Nafion membrane-supported ionic liquid (IL)–solid phase microextraction (SPME) coupled to gas chromatography (GC)–mass spectrometry (MS) technique for the simultaneous sampling and determination of ultra trace polycyclic aromatic hydrocarbons (PAHs) in aqueous samples has been developed. The hybrid IL–SPME fiber was precoated with Nafion membrane prior to IL film to enhance the amount and stability of IL film absorbed on the fiber. The analytes were extracted by the head space mode, and then directly desorbed in the injection port of GC–MS. The hybrid IL–SPME fiber was newly coated for each extraction, and the coating and washing out processes accomplished in a few minutes. The extraction efficiency between the IL–SPME fibers coated with and without Nafion-supported membrane for the five tested PAHs was compared. The results show that fibers coated with Nafion could extract two to three times more amount of analytes (based on peak area) than those without it. The extraction efficiency of three ILs (1-methyl-3-octylimidazolium trifluoromethanesulfonate: [C8mim][TfO], 1-benzyl-3-methylimidazolium trifluoromethanesulfonate: [Bemim][TfO] and 1-methyl-3-phenylpropylimidazolium trifluoromethanesulfonate: [Phpromim][TfO]) was evaluated; [C8mim][TfO] has the greatest extraction efficiency. The SPME experimental conditions, the extraction temperature, time and the salt effect were studied and optimized. Two natural water samples were used to evaluate this proposed method. Naphthalene, fluorene and anthracene were detected in sample 1 (29.7–70.0 pg mL−1), whereas fluoranthene and pyrene were below the detection limit (5 pg mL−1). For sample 2, all of the five PAHs were below the detection limit (4–5 pg mL−1). However, good spiking recoveries (80–110%) and repeatability (R.S.D. < 12%) were achieved. The results suggest that Nafion-supported IL–SPME has the potential for determining the ultra trace PAHs in aqueous samples.