Complexation equilibria of some sulfoazoxines. Part IX. Influence of experimental strategy on reliability of protonation constants of 7-(4-sulfo-1-naphthylazo)-8-hydroxyquinoline-5-sulfonic acid oligomers

Abstract

Protonation constants of variously protonated oligomers of the sulfoazoxine SNAZOXS [7-(4-sulfo-1-naphthylazo)-8-hydroxyquinoline-5-sulfonic acid] were determined potentiometrically. Instead of proton activity the hydrogen ion concentration is used. The group parameters (E°, Nernstian slope, concentration of titrand and titrant, etc.) were refined by the computer programs ESAB and MAGEC and the common parameters (log β_qr for species L_qH_r) by MINIQUAD. The proposed strategy of efficient experimentation was validated by determining the effect of group parameters on common parameters. The reliability of protonation constants was examined by the propagation of errors. The accuracy of the protonation constants β_qr depends on accuracy of the group parameters. The precision of the protonation constants β_qr expressed by an estimate of the standard deviation s(log β_qr) is more pessimistic when a calculation of propagation of errors is applied when calculated by non-linear regression with the program MINIQUAD.