Artefacts in XAD-8 NOM fractionation

The XAD-8 resin has been widely used during the last decades to characterize and isolate natural organic matter (NOM) in water. The present work focuses on the performance and limitations of the XAD-8 method. A number of different NOM samples (mostly RO-isolates) have been XAD-8 fractionated with the purpose to study (1) the impact of DOC concentration of the samples on the quality of the resulting fractions and (2) the stability of NOM in the different fractions during the XAD-8 fractionation procedure and storage. Focus is placed on the method's independence of NOM concentration, the stability (quantity and quality) of the hydrophilic fraction during the fractionation, the relationship between hydrophilic and hydrophobic fractions, and the stability of the obtained fractions after the fractionation is completed. The main conclusions are that the division into hydrophobic and hydrophilic fractions are not independent of the NOM concentration and not constant during the procedure, furthermore that the XAD-8 fractions may undergo irreversible alteration of structure due to the procedure or storage that will influence on the interpretation of the data. The possible consequences for the interpretation of results and further analysis or use of the XAD-8 based fractions are discussed.