Solvent-Jump Method

Abstract

Chemical equilibria can be disturbed by changing intensive or extensive thermodynamic variables of the system. For experimental reasons, usually intensive variables are changed (1).From an operational point of view, one can distinguish perturbations by external and internal intensives variables. The external parameters usually altered are the temperature T, the pressure P, or the electric field strength E and the internal ones are the chemiocal potensials μ_i of the species present, i.e. the concentration of solutes and/or the composition of the solvent. A perturbation of the total solute concentration can be achieved by sudden dillution (concentration-jump) of the equilibrium system using rapid mixing devices (2). Similarly, the composition of the solvent can be abruptly changed by fast mixing of two equilibrium solutions of different solvents, or one equilibrium solution with another solvent. Since the total concentration of the solute is not necessarily changed in the experiment, the name of solvent-jump is more generally descriptive of the method than concentration-jump. This type of relaxation experiment was first suggested by Ljunggren and Lamm (3) and has been applied to slow (4) as well as to fast reactions (5,6) using transient and also non-transient (7) observation in stopped- and continuous flow systems, respectively.