Multiparametric curve fitting--VIII: The reliability of dissociation constants estimated by analysis of absorbance-pH curves

The program SPOPT estimates stability constants beta(pqr) and molar absorptivities epsilon(pqr) of all light-absorbing species M(p)L(q)H(r) by analysis of the absorbance-concentration (or absorbance-pH) curve. The program DCMINUIT estimates dissociation constants and molar absorptivities of protonated species. Both programs have been tested and compared with DCLET and LETAGROP-SPEFO for analysis of the overlapping equilibria of a triprotic acid. Computer plots of the residual-square-sum function are used to test the conditioning of parameters. Two approaches are made to formulation of the mathematical model, and several optimization algorithms are tested to find a reliable minimization procedure. The accuracy of ill-conditioned parameters is shown to be dependent on the precision of the absorbance measurements. General rules for investigation of A -pH curves are recommended.