Semiautomated solid-phase extraction followed by derivatisation and gas chromatography–mass spectrometry for determination of perfluoroalkyl acids in water

Abstract

This paper describes a sensitive approach for the determination of 6 perfluoroalkyl carboxylic acids and perfluorooctane sulfonic acid in water. Samples were preconcentrated using an automatic solid-phase extraction module and then manually derivatised and determined by gas chromatography–mass spectrometry. The analytes were derivatised with a isobutyl chloroformate/isobutanol mixture, using 3% N,N-dicyclohexylcarbodiimide in pyridine as the catalyst. From a systematic comparison of several reversed-phase and anion-exchange sorbent materials for the retention of perfluoroalkyl acids, the highest retention efficiencies (∼100%) were achieved with LiChrolut EN and Discovery DSC-SAX columns. LiChrolut EN was the sorbent selected due to several advantages (sample pH ∼1; sample flow rate, 5.5mL/min; breakthrough volume, 300mL) over Discovery DSC-SAX (sample pH ∼6; sample flow rate, 3.0mL/min; breakthrough volume, 45mL), for the retention of the studied compounds. Detection and quantification limits within the range of 0.1–0.5ng/L and 0.4–1.7ng/L, respectively, were obtained for a sorbent column of 70mg of LiChrolut EN and 250mL of sample, the relative standard deviation being lower than 7%. The method was applied both to the analysis of water collected at the intake (raw) and at the exit (treated) of two drinking water treatment plants, as well as to various types of water. Few samples were positive for perfluoroalkyl acids and only one acid (perfluoroheptanoic or perfluorooctanoic) was found in each treatment plant. The highest number and concentration of analytes (perfluoroheptanoic, perfluorooctanoic and perfluorodecanoic acid) were found in one wastewater.