Model based design of experimental procedures for efficient investigation of some chemical equilibria

The chemical model which governing a chemical process can be the basis for selecting or designing an appropriate laboratory method. In an equilibrium system, the model defines a mathematical function which in expresses the relationship between equilibrium concentrations and thermodynamic parameters. The mass balance equations, which are the main basis for the expression of an equilibrium chemical model in a system, can be used for designing laboratory methods for the study of equilibrium processes [1]. A common method for studying equilibrium systems is to change the concentration of components through titrations. But some of the equilibrium systems which is studied by this way do not provide enough information about some species. Therefore, the data would not well-fitted to the model [2]. There may also be some linear dependency between some species in the system. Thus, the system will be faced rank deficiency problem [3]. In this case, although the parameters of the model could be achieved by data fitting, but the signals could not resolve properly. Augmentation of different data sets with various initial conditions is one of the offered solutions for these problems in the literature. The goal of this research is to proper designing of the chemical equilibrium reactions based on the chemical models. So that, the gained information which collected by several data sets in a classic method could be achieved only by a data set. For example, as the metal ion Ni+2 forms 1:1,1:2 and 1:3 complexes with tryptophan amino acid, the pH metric titration of 1:1 ratio of Ni+2 and tryptophan with NaOH lead to least information about 1:3 complex. Same results are achieved for 1:1 complex in titration of 1:3 ratio of metal-amino acid with NaOH. For achieving enough information about all complexes in one data set, it can be possible to start with 1:1 ratio and adding tryptophan as the second titrant during the procedure. The fitting results of formation constants of all complexes in this condition are comparable with augmented data sets of different conditions. Also for the case of rank deficiency system,acid-base titrations of a mixture of three nucleic bases (adenine, cytosine,and uracil), were investigated. The acidic and basic forms of nucleic bases are spectroscopically active. Due to the linear dependency between concentration profiles, the rank of mixed solution is 4 instead of 6. For this case, during the titration of this mixture with NaOH, a nucleic acid is added as the second titrant. So, the linear dependency is disappeared.