Samenvatting

Per-fluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent organic pollutants and do not degrade in the environment. They contain a carbon-fluorine bond, and these are called organic fluorides. A group of PFASs, which can be extracted from soil samples and be analysed, are called extractable organic fluorides (EOFs) and more attention has been brought to this parameter. SGS is interested in developing a method to determine EOF by combustion ion chromatography (C-IC). However, there is no existing (inter)national frame of reference for this yet. This research is about the development and optimization of EOFs by C-IC and the pre-treatment with methanol. A long-chained PFAS, PFOS, and short-chained PFAS, TFA, were used in this research. Eliminating inorganic fluoride before analysis is important since the technique is not able to differentiate between inorganic and organic fluorides. Optimization had been performed on the method to determine EOF in ground samples where inorganic fluorides are eliminated from the total organic fluoride content. A calibration curve has been made for concentrations ranging from 25 to 1,500 µg L-1 fluoride in methanol and resulted in a correlation of 0.9992. This was performed on another IC instrument since organic fluorides need to be combusted in order to be measured and therefore cannot be determined via this technique. Ten random ground samples measured concentrations between 24 and 1,878 µg kg-1, confirming that there is inorganic fluoride present after extraction. Evaporation after extraction is required to increase the concentration of EOF in the extract.
Evaporation of PFOS under a N2 stream while heating the sample between 40 – 60 °C resulted in the best recovery of 84.9 – 85.6 %. Solid-Phase Extraction (SPE) is used as clean-up method to optimize the elimination of inorganic fluoride where the sorbent is combusted in the C-IC. No inorganic fluoride was recovered after washing the sorbent with a NH4OH/MQ solution while organic fluoride had a recovery of 66.0 %. Not washing the sorbent gave a recovery of 13.6 % of inorganic fluoride and 61.0 % for PFOS. TFA was not recovered after SPE. Results of the C-IC could be unreliable since soot was formed after combusting the sorbent. Further optimization is required to develop a method for SGS to determine EOF in ground samples by C-IC.