Qualitative Analyses of Open-Path Fourier Transform Spectra

Open-path Fourier transform infrared (OP/FT-IR) spectra were arranged into data matrices and then analyzed with target factor analysis (TFA) and band-target entropy minimization (BTEM), respectively, aiming to reconstruct the spectra of interested molecules. Five sessions of continuous OP/FT-IR monitoring were carried out around farms. For each session, the spectra were arranged row-wisely in the order of measuring time, which yielded five matrices for data analysis. The analyses results showed that both TFA and BTEM could reconstruct spectral features of target molecules from the spectra data matrix, but performance of the two methods differed slightly. TFA can retrieve spectral features of target molecules in the presence of interferences, and the reconstructed spectrum is similar to corresponding reference. BTEM can implement such spectral retrieval without the reference spectrum. This paper presents not only the application of BTEM method to qualitative analyses of OP/FT-IR spectra, but also a thorough comparison between TFA and BTEM, which is helpful to qualitative analysis of complex multi-component systems.

As effective chemometric methods, TFA and BTEM were applied to reconstruct the spectra of NH3, C2H5OH, and O3 from OP/FT-IR spectroscopic data despite of absorption of water vapor and noise. The interferences are so severe that it is difficult, if not possible to identify the spectral information of those molecules.Figure optionsDownload as PowerPoint slide