XAD-fractionation of “new” dissolved organic matter: is the hydrophobic fraction seriously underestimated?

Freshly produced radiolabelled dissolved organic carbon (PDOC) from a marine diatom culture was fractionated on XAD-2 by NaOH/methanol elution. A large portion (32%) of the hydrophobic fraction could not be eluted by standard procedures. Only after severe hydrolysis and further extraction was it possible to recover most of this material. These findings indicate that usual XAD-2 fractionation methods may result in large underestimates of the hydrophobic fraction of PDOC.