A tutorial on potentiometric data processing. Analysis of software for optimization of protonation constants

Defining the distribution of the chemical species in a multicomponent system is a task of great importance with applications in many fields. To clarify the identity and the abundance of the species that can be formed by the interaction of the components of a solution, it is fundamental to know the formation constants of those species. The determination of equilibrium constants is mainly performed through the analysis of experimental data obtained by different instrumental techniques. Among them, potentiometry is the elective technique for this purpose. As such, a survey was run within the NECTAR COST Action - Network for Equilibria and Chemical Thermodynamics Advanced Research, to identify the most used software for the analysis of potentiometric data and to highlight their strengths and weaknesses. The features and the calculation processes of each software were analyzed and rationalized, and a simulated titration dataset of a hypothetic hexaprotic acid was processed by each software to compare and discuss the optimized protonation constants. Moreover, further data analysis was also carried out on the original dataset including some systematic errors from different sources, as some calibration parameters, the total analytical concentration of reagents and ionic strength variations during titrations, to evaluate their impact on the refined parameters. Results showed that differences on the protonation constants estimated by the tested software are not significant, while some of the considered systematic errors affect results. Overall, it emerged that software commonly used suffer from many limitations, highlighting the urgency of new dedicated and modern tools. In this context, some guidelines for data generation and treatment are also given.