An assessment of thermodynamic consistency tests for vapor-liquid equilibrium data

Consistency tests are techniques that allow, in principle, the assessment of experimental vapor-liquid equilibrium data on the basis of the Gibbs-Duhem equation. Much empiricism and arbitrariness is frequently observed in the analysis and application of consistency tests, a situation that may question their usefulness. Perfect data satisfy exactly the Gibbs-Duhem relation, but acceptable data obey it within a tolerable limits (consistency criteria) which does not give a unique answer, regarding the quality of the data, when different consistency procedures are used. As with any approximation, application of consistency tests requires rigour, reasonable assumptions and models, and an examination of the data and results of the test. In this work, a set of guidelines that allow a critical interpretation of consistency analysis is proposed and special attention is given to the point-to-point test which is extensively used today in data evaluation.