The thermodynamics and energetics of the ion exchange of four
amino acids at a synthetic ion
exchange resin have been studied. Experimental work included
determination of ion exchange
isotherms and the use of high-sensitivity titration microcalorimetry.
A rigorous thermodynamic
analysis of the data is developed allowing calculation of the standard
free energy, the standard
enthalpy, and standard entropy of exchange, and also the differential
free energy, incremental
enthalpy, and incremental entropy of exchange. The results show
that the relative contributions
of the enthalpy and entropy to the overall free energy differ markedly
for the chosen amino
acids. From a knowledge of these fundamental thermodynamic
properties, the solution conditions
giving enhanced separation are predicted. These predictions are
experimentally confirmed. The
paper establishes experimental protocols and data analysis methods that
allow progression from
a single isotherm and a single set of calorimetric data to a selection
of process conditions for
enhanced selectivity. The experimental techniques and analysis
procedures developed are
generally applicable to ion exchange separations of
biomolecules.