Spectrophotometric study of complexation equilibria and of a method for the determination of Fe(III) ions with 4-(2-pyridylazo)resorcinol and 4-(2-thiazolylazo)resorcinol

The composition, molar absorption, coefficients, equilibrium constants and stability constants for the MLH, ML, M(LH)2 and ML2 complexes have been determined graphically using slope-intercept transformations and numerically from the absorbance-pH curves and from the absorbance dependence on the component concentration, using the PRCEK III and SPEKTFOT programs, or from the continuous variation plots using the JOBCON program. The optimum conditions were found for a spectrophotometric determination of ferric ions with TAR and PAR reagents in pure solutions. The basic parameters of the analytical curves were evaluated using the STAT program.