Description of sorption data with isotherm equations

Analysis of sorption data is important for characterizing retention of chem icals by soil. In this paper I review the most common isotherm equations us ed in soil science. The mathematical descriptions of these equations are cl assified into rational, power, and transcendental functions which are relat ed to the isotherm classification. I use most well-known isotherm equation as special cases of a general equation. The meaning of the parameters of th is equation is discussed in terms of the Giles classification. Guidelines a re presented for choosing the correct type of isotherm equations to describ e a set of sorption data. Tn particular, I show that plotting the distribut ion coefficient vs, the amount of solute sorbed to the solid phase on a log -log scale is the best way to identify the class and subgroup of isotherms based on the Giles classification. Examples of how to apply the guidelines to determine and modify isotherm equations are presented. (C) 2001 Elsevier Science B.V. All rights reserved.