sorption

It is sometimes difficult or impossible to discriminate experimentally between adsorption and absorption : in such cases it is convenient to use the noncommittal term sorption. In ion exchange, sorption is the uptake of electrolytes or nonelectrolytes by ion exchangers through mechanisms other than pure ion exchange.
With respect to surface phenomena, this term is also used when the retention mechanism at a
surface is unknown. Adsorption, surface precipitation, and polymerization are all examples of sorption.