Enrichment of perfluorinated alkyl substances on polyethersulfone using 1-methylpyperidine as ion-pair reagent for the clean-up of carrot and amended soil extracts

The development of a simple, cheap and environment friendly analytical method for the simultaneous determination of different perfluoroalkyl substances (PFASs) including seven perfluoroalkyl carboxylic acids, three perfluoroalkane sulfonic acids and perfluorooctanesulfonamide in carrot and amended soil was carried out in the present work. The method was based on focused ultrasound solid–liquid extraction followed by extract clean-up through enrichment of the target compounds on a polymeric material using an ion-pair reagent and detection by liquid chromatography-tandem mass spectrometry. The following variables affecting the clean-up step were evaluated: the nature of the polymeric material (polyethersulfone, PES, versus silicone rod), the amount of the polymeric material (from 1 to 9mg), the ion-pair reagent (1-methylpyperidine, 1-MP, versus tetrabutylammonium salts), the concentration of the ion-pair reagent (from 5 to 50mM) and the extraction time (from 15min to 24h). Optimum clean-up conditions were obtained using preconcentration on 9mg of PES polymeric material combined with 5mM 1-MP as ion-pair reagent for 3h. The method was validated in terms of apparent recoveries in the range of 77–140% and 95–137% at the low concentration (50ngg−1) and in the range of 70–136% and 79–132% at the high concentration (290ngg−1) for amended soil and carrot, respectively, after correction with the corresponding labeled standards. Precision, as relative standard deviation, was within 2–23%, while method detection limits were 0.31–2.85ngg−1 for amended soil and 0.11–1.83ngg−1 for carrot. In the absence of a certified reference material for the target analytes in the matrices studied, inter-method comparison was carried out and the same samples were processed using two independent clean-up procedures, the one developed in the present work and a classical based on solid-phase extraction. Statistically comparable results were obtained according to the one-way analysis of variance for peel, core, leaves as well as amended soil (FCalc=2.59, 5.06, 5.82 and 2.34