Dissolved organic matter: Precautions for the study of hydrophilic substances using XAD resins

This study concerns the possible changes in the repartition and the molecular characteristics of hydrophilic substances (HyS) isolated by XAD resins from the same source of organic matter as a function of the distribution coefficient k′ and the DOM concentration. We tested that on two different sources of organic matter (a surface water and a landfill leachate). Breakthrough curves column experiments highlighted a modification of the repartition between hydrophilic and humic substances according to the k′ value applied. But, we find that the composition of HyS is significantly modified between k′ = 50 and 100. Our observations tend to suggest a higher contribution of humic-like matter (high-molecular weight aromatic compounds) with an increase of the k′ value. This results in a shift of fluorescence bands to longer wavelengths and changing patterns of the SEC profiles and molecular fingerprints performed by flash pyrolysis. Our results show that DOM concentration also influences the composition of HyS while little effect is observed on their quantification at k′ = 50 or 100.