Neue Methoden zur spektrophotometrischen pK-W ertbestimmung, II / New Methods for Spectrophotometric Determination of pK-Values, II

Abstract

The number of linear independent dissociation equilibria of spectrophotometric titration may be determined experimentally by means of absorbance diagrams and absorbance-difference-quotient diagrams. The different types of spectrophotometric titration curves in two-step titrations are classified. By simulation of systematic error functions the limits of pK determination using turning points of two-step titration curves are demonstrated. By means of certain absorbance diagrams it is possible to determine the absorbance of pure ampholyte and to construct the absorbance triangle of all three pure components. From this triangle all concentration- vs pH-curves and the pK-values of a bivalent protolyte may be established. To avoid electrometric pH-measurements new methods are devised to calculate the difference of pK-values of bivalent protolytes. These new methods are demonstrated using as examples o-phthalic acid, 3-hydroxy-4-nitrobenzoic acid and sozoiodolic acid.