In this article, a modified formulation of the well known Lagergren pseudo first order rate equation is suggested. The equation is obtained simply by substituting the mass balance equation of a single stage batch-type system into integrated first order rate equation. The suggested new formulation relies on maximum sorption (or removal) rather than equilibrium sorption, as given by Lagergren equation. The exact value of equilibrium sorption is not easy to define in many cases, and it is shown that the modified formulation provides better correlation with sorption data when the process is far from completion. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.