Supramolecular solvents for the extraction of perfluoroalkyl substances in water

Abstract: The aim of this project was to compare two methods for the extraction of perfluoroalkyl substances (PFASs) in water samples. The methods compared were solid phase extraction (SPE) and supramolecular solvents (SUPRAS). Solid phase extraction is a sample preparation process where the desired compound passes through a solid phase and the method uses the affinity for the compound of interest to retain it in the solid phase while the undesired compounds pass through. Supramolecular solvents are an alternative approach for extraction of contaminants, for example PFASs. Supramolecular solvents are liquids that generates from compounds known as amphiphiles. The desired compound is extracted by binding with ionic bond, hydrogen bond, dipole-dipole bond, or other depending on the desired compound. A comparison of methods was evaluated based on method detection limits (MDL), recovery, matrix effects and repeatability. The recoveries for SPE (n=11) were best for short-chain PFASs with recoveries between 81-128%. The recoveries decreased with increasing carbon chain length, probably due to the sorption of analytes to the wall of the container or the reservoir that were not washed thoroughly. The matrix (e.g. surface water) for the solid phase extracted samples were concluded to slightly suppress the signal of most PFASs. The repeatability for the SPE samples had values between 8-59%, with an average of 18%. The recoveries of PFASs (n=4) when using SUPRAS for the extraction of PFASs from water samples were generally lower than those of the SPE method. Especially the short-chain PFASs have poor recoveries in SUPRAS extraction. For longer carbon chain PFASs the recovery for the samples extracted with SUPRAS showed better values (58-135%) but with decreasing chain length the recoveries also decreased. For SUPRAS method to be a feasible option, extraction efficiency of 50-120% would be needed. The matrix effects indicated that the matrix of the SUPRAS extracted samples enhanced the signal of most PFASs. The repeatability could not be calculated for the environmental (SUPRAS Method 1) SUPRAS samples since no replicate blanks were extracted. Spiking experiments on Milli-Q water was performed and had RSD values between 22-85% with a mean value of 39 %. This preliminary test of using SUPRAS as extraction method of PFASs in water need to be further developed. At present SUPRAS is not as efficient for the extraction of PFASs from water as using solid phase extraction. Screening of solvents and possibly salting out need to be tested to increase the efficiency of the extracted compounds.