Encoding FT-IR spectra in a hopfield network and its application to compound identification in open-path FT IR measurements

Vapor-phase Fourier transform infrared (FT-IR) reference spectra of five al cohols (methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol) from 1277 to 891 cm(-1) were encoded as prototype vectors for a Hopfield network, al ong with four baseline spectra in the same spectral region, For each input spectrum, the Hopfield network is designed to identify one component of a m ixture at a time (usually the major component), Inclusion of the baseline s pectra in the Hopfield network allowed the network to classify spectra as u nknowns, when they were not stored as prototype vectors in the network, A m ethod that can minimize the number of spurious points and maximize the doma in of attraction of the designed equilibrium points was used to design the Hopfield network, Over 100 spectra of different compounds were input to thi s network, and only three of them were incorrectly classified, The network could usually identify each of the five alcohols correctly even in the pres ence of noise and interfering compounds. When random noise was added to eac h spectrum up to a level of 20% of the maximum absorbance of the analyte, t he network could still identify each alcohol with 100% accuracy. The networ k could also correctly identify one component of representative mixture spe ctra, The Hopfield network was successfully used to identify ethanol and 1- butanol from their open-path FTIR (OP/FT-IR) spectra despite the large degr ee of similarity of these spectra, the weakness of the hands, and the fact that the measured spectra were dominated by lines due to the absorption of atmospheric water vapor.