Job plot

The method is named after Paul Job and is also used in instrumental analysis and advanced chemical equilibrium texts and research articles.

An observable that is proportional to complex formation (such as absorption signal or enzymatic activity) is plotted against the mole fractions of these two components.

χA is the mole fraction of compound A and P is the physical property being measured to understand complex formation.

A greater curvature leads to a more evenly distributed equilibrium, while a more triangle-shaped plot signifies a large Keq.

In addition, the total concentration of the two binding partners, the pH and ionic strength of the solution must all be maintained at fixed values throughout the experiment.

A simple Job Plot showing how a physical property (P) changes upon changing the mole fraction of compound A (Χ A ).