Computer-aided similarity and identify search with a FTIR library of surfactants and surfactant mixtures

Abstract

A digitized library of about 1100 standardized FTIR spectra of surfactants and related materials was evaluated with Lowry-Huppler algorithms and a combination algorithm specially developed for the detection of the components in mixtures. “Spectacle” by LabControl was used as the data management system. The LH algorithms 1 and 2 (sum of the absorbance differences and sum of the squared differences) were, in similarity searches, superior to 3 and 4 (derivatives). Both spectral identity of an analytical sample with components of the library and that belonging to a certain surfactant family can be established by a hit index.

An algorithm combining similarity and peak search was tested with intramolecular and intermolecular binary and multicomponent systems. In most cases the resulting list of the first 20 hits presented, in the highest ranks, the most similar spectra of mixtures represented in the library. Spectra of the components of the analytical mixture followed in lower ranks, usually down to rank 10. Tentative theoretical explanations for the results are given.