JESS at thirty: Strengths, weaknesses and future needs in the modelling of chemical speciation

Abstract

The current status of the software package JESS (Joint Expert Speciation System), which has been developed over the last 30years, is described. Chemical speciation models of seawater and of metal-ion complexation in human blood plasma are used as large equilibrium systems to explore the present capabilities of the code and database. Strengths of JESS are considered to be (a) the power and flexibility of its command-driven programs, (b) the size, generality and openness of its reaction database, (c) its automatic facility to achieve thermodynamic consistency, and (d) its ability to partition chemical reactions to model kinetic constraints. A special feature of JESS is its ability automatically to generate a complete, stand-alone FORTRAN program for any particular chemical equilibrium model that has been developed. Weaknesses of JESS include the lack of a graphical user interface, the resulting effort required in familiarisation, and certain limitations regarding pressure and temperature corrections in concentrated solutions. However, the most troublesome issues – common to all ‘ion-association’ frameworks – are due to inadequacies in the thermodynamic data available from the literature and to persistent deficiencies in the fundamental theory of concentrated electrolyte solutions. Accordingly, work on JESS has commenced to construct a global parameterisation facility using both reaction data and the physicochemical properties of strong electrolytes in aqueous solution (including solubilities) intended to improve model function testing and to provide even better mechanisms for data harmonisation.