On the restrictiveness of equality constraints in multivariate curve resolution.

Multivariate curve resolution methods suffer from the non-uniqueness of the solutions of the nonnegative matrix factorization problem. The solution ambiguity can be considerably reduced by equality constraints in the form of known spectra or concentration profiles. Two measures are suggested that indicate the impact of the equality constraints. The representation of these measures in the area of feasible solutions show strong variations in the restrictiveness of equality constraints. The measures are tested for a three-component model problem and experimental data sets from the hydroformylation process and a catalyst cluster formation. • The strongly varying restrictiveness of the equality constraint in MCR computations is analyzed by two estimators. • The estimator values are visualized in the area of feasible solutions (AFS) by means of an additional color coordinate. • The additional AFS color coordinate improves the information content and can be generalized to other indicator variables. [ABSTRACT FROM AUTHOR]