Dedicated to Edmund R. Malinowski. Secondary, model-based examination of model-free analysis results: Making the most of soft-modelling outcomes

Edmund R. Malinowski is well known for his factor analysis-based work; he is clearly less well known for his chemical model-based analyses of chemical data. In this contribution, we discuss the, at the time innovative, idea of subjecting the primary model-free analysis results to a secondary quantitative model-based evaluation. Two examples from his research serve as illustrations: the complexation of Cu²⁺ with cyclodextrin and the dimerisation and trimerisation of methylene blue. In both examples, the spectrophotometric titration data are first analysed by window factor analysis, WFA, resulting in the concentration profiles. These primary, model-free results allowed Malinowski to gain qualitative insight in the chemical processes. Additional quantitative analyses of the concentration profiles, based on the previously obtained reaction model, resulted in the numerical values of the underlying equilibrium constants. This contribution relates and compares this methodology with alternative ways of analysing the same data.