Methodology of the spectrophotometric analysis of mixtures of organic substances: Nonadditivity of light absorption

The typology of the problems being solved in the analysis of multicomponent mixtures of organic substances (pharmaceutical preparations, petroleum products, and others) is proposed. The difficulties associated with the problems of each type are discussed, and the potential of spectrophotometry without the separation of components in overcoming the difficulties is considered. The nonadditivity of light absorption due to the interaction of components is the most complicated problem. The methods for revealing deviations from additivity, the correlation of these deviations with the composition of the mixture, the effect of nonadditivity on the results of determination, and the approaches to reducing the corresponding systematic errors based on chemometric algorithms are discussed.