What do results of common sequential fractionation and single-step extractions tell us about P binding with Fe and Al compounds in non-calcareous sediments?

► Selectivities of fractionation, oxalate and ascorbate extractions were compared. ► Fe and Al minerals with adsorbed P and non-calcareous sediment were used. ► Sequential fractionation can distinguish Fe and Al (hydr)oxides but not their crystallinity. ► Ascorbate and oxalate extractions are not specific for Fe/P and/or Al/P complexes. ► Oxalate extraction is selective for determination of amorphous Al (hydr)oxides.