Quantitative analysis of bandpass-filtered Fourier transform infrared interferograms

The feasibility of performing quantitative analysis with short segments of bandpass-filtered Fourier transform infrared (FT-IR) interferograms is demonstrated. The protocol developed in this work addresses four limitations that hinder the use of FT-IR spectroscopy in nonlaboratory applications: (1) the need for a rugged, low-cost, and reliable spectrometer, (2) the lack of representative background spectra for use in acquiring absorbance spectra of the target analyte, (3) the presence of overlapping spectral bands that interfere with the analyte determination, and (4) the difficulty in obtaining useful information from data collected near the limit of detection. In this work, spectral information pertaining to a specific analyte band of interest is isolated directly from a short interferogram segment by the application of narrow-bandpass digital filters. When processed in this way, the filtered interferogram segments contain compound-specific information that can be utilized for quantitative analysis. Successful use of a univariate calibration procedure with filtered interferogram data of benzene and nitrobenzene of varying concentrations is demonstrated. Calibrations based on filtered interferogram segment magnitudes vs concentration yield models with values of R2 in excess of 99%. These results are obtained without the use of a separate background or reference interferogram. This interferogram-based analysis is shown to perform analogously to a conventional spectral-based analysis, with the interferogram method being more efficient in terms of data collection and computational requirements.