Numerical analysis of the Gran methods A comparative study

The paper concerns mainly the modified Gran methods, considered as extrapolative standard addition methods. Particularly, the approximation:ln(1+x1)−ln(1−x2)≅11/x1+1/ξ+11/x2−1/ξwhere ξ≅2ξ≅2, is applied for the needs of the modified Gran I methods, in accurate and simplified versions, denoted as MG(I)A and MG(I)S methods. These methods are compared with Gran II methods, in original (G(II)) and modified accurate (MG(II)A) versions. All the methods were tested with use of results obtained from simulated potentiometric titrations. The effects involved with a pre-assumed slope ϑ*-value for a redox indicator electrode and in errors in potential (E) and volume (V) readouts on the error in equivalence volume (Veq) value thus determined is considered. It is recognized that MG(I)A and MG(II)A appear to be the best methods applicable for Veq determination among ones considered hitherto. Moreover, the MG(I)S method is the best choice for determination of the true slope ϑ-value for the redox indicator electrode.