Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na(+), NH4(+), Ca(2+), and Mg(2+)) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions.  The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). 
THERM