Determination of dissociation constants of 7-(carboxyphenylazo)-8-hydroxyquinoline-5-sulphonic acids by nonlinear regression of spectrophotometric data

Abstract

Dissociation constants of three metallochromic indicators 7-(o-, m-, p-carboxyphenylazo)-8-hydroxyquinoline-5-sulphonic acids and values of molar absorption coefficients of the forms L3-, HL2-, H2L-, H3L have been determined in 0.1M-NaClO4 medium by non-linear regression of pH-absorbance curves by the program DCLET and by regression matrix analysis of the spectra by the program FA608 + EY608, respectively. All the three derivatives have been synthesized, purified, and their purity checked by chromatography.