Coulometric Determination of Perfluoroalkyl Substances (PFAS) with the Thin-layer Electrolysis Flow Cell for the Ion Transfer

Coulometric determination of perfluorooctane sulfonate (PFOS−) and perfluorohexanesulfonate (PFHxS−), which are ionic perfluoroalkyl substances (PFAS ion), was demonstrated with a thin-layer electrolysis flow cell for the ion transfer (flow-TLECIT). Flow-TLECIT has a simple structure consisting of a Ag/AgCl plate electrode, a spacer with a flow path for aqueous sample solution, an organic liquid membrane hold in the porous membrane, and the conducting polymer paste-coated carbon electrode. The conductive polymer paste was made of poly(3,4-ethylenedioxythiophene) modified with lauryl-terminated bispoly(ethyleneglycol) (PEDOT-PEG) for screen-printing the conducting polymer on the carbon electrode. Flow-TLECIT achieved the complete mass transfer of PFAS ion from the aqueous sample solution to the organic membrane under applying a constant potential between the Ag/AgCl plate electrode and the conducting polymer paste-coated carbon electrode and detects the transfer of PFAS ion as current. The integrated current (electrical charge) can be converted to the mole amount of PFAS ion. For PFHxS−, the evaluated amount was 97 %–103 % of the theoretical mole amount in the concentration range of 5–200 µM and the repeatability in the same cell were ±1 %–±5 % (n = 8). For PFOS−, the evaluated amount was 102 % of the theoretical mole amount in the concentration of 18.3 µM and the repeatability in the same cell is ±4 % (n = 3). Flow-TLECIT has advantages such as (1) the flow system suitable for continuous measurement, (2) a simple and inexpensive device, and (3) calibration-free.