A UV-visible spectral library has been generated after the spectra have been preprocessed with a Fourier analysis. Both the library and unknown spectra are Fourier transformed and are represented by a window of coefficients from the transforms. In order that the optimum window for the coefficients could be determined, synthetic spectra were generated and used to test the effects of band shifts, high-frequency noise, and background fluctuations. Spectra of 24 compounds, many of which were very similar, were measured and processed from 200 to 712 nm. Eight of the samples were treated as unknowns and their spectra remeasured. The arc-cosine of the dot product was used as the similarity metric. All eight of the unknowns were correctly identified with the use of as few as 16 coefficients to represent the spectra. Since many of the spectra were very similar, the success of the algorithm is due to the fact that it incorporates wavelengths and band shapes, widths, and heights into the comparison process.
Chris W. Brown and Steven M. Donahue, "Searching a UV-Visible Spectral Library," Appl. Spectrosc. 42, 347-352 (1988)