Neue Methoden zur spektrophotom etrischen pK-Wertbestimmung, I / New Methods for Spectrophotometric Determination of pK-Values, I

Abstract

By means of a spectrophotometric titration at many wavelengths it is possible to determine the uniformity („Einheitlichkeit“) of the system, respectively, the number and kind of dissociable groups. Isosbestic points, absorbance-, absorbance-difference diagrams and other graphs are used for the analysis of spectrophotometric titration data. Different methods for determination of absolute pK-values of one-step titration systems are compared critically. To avoid the problems of electrometric pH-measurements some new methods are proposed to evaluate relative pK-values ( Δ pK -values) by means of a simultaneous titration of a protolyte together with a standard substance. The efficiency of these relative methods is demonstrated using two compounds with a very small pK-difference (o- and p-nitrophenol, Δ pK = 0.1). The results are controlled by simulation with a digital computer.