Automated Detection of Acetone,Methyl Ethyl Ketone,and Sulfur Hexafluoride by Direct Analysis of Fourier Transform Infrared Interferograms

The lack of a valid background reference spectrum for many Fourier transform infrared (FT-IR) spectrometric open-air monitoring applications limits the ability to perform quantitative measurements. Direct interferogram analysis suppresses the broad-band detector envelope and maintains the spectral signature of interest to circumvent this limitation. The background suppression approach uses a combination of interferogram segment selection, digital filtering, and pattern discrimination techniques. The spectral band location, width, and contour of the vapor determine the parameters necessary for background suppression. Interferogram segment selection relies principally on the spectral bandwidth. Digital filter design employs inputs of both spectral band location and width. Pattern discrimination methods consider the variation in the spectral band contour with band intensity. FT-IR spectrometer measurements from both laboratory and open-air trials demonstrate the utility of the background suppression approach with analytes of acetone, methyl ethyl ketone (MEK), and sulfur hexafluoride (SF₆).