Computer estimation of dissociation constants. Part IV. Precision and accuracy of potentiometric determinations

The protonation constants logK_Hj of the acidH_J are determined by regression analysis of potentiometric titration data whencommon parameters (logK_Hj,j = 1,...,J) andgroup parameters (E⁰,L₀,H_T) are refined. Two kinds of systematic error have been investigated: the error from an uncertainty of group parameters and the error from a computational strategy of the minimization algorithm used. An analysis of variance of logK_Hj matrix was made for 6 reproduced titrations and 7 computational strategies of 6 various regression programs. It was concluded that the influence of the program used is negligible. From two ways of calibration of the glass electrode cell,the internal calibration (performed during titration) was slightly more accurate thanthe external calibration (done separately). Of programs tested, the ESAB and ACBA are most powerful because they permit refinement of group parameters and internal calibration. D-tartaric acid was chosen as model substance.Previous Part III.: Iraqi J. Sci.1981,22, 67.