Generation of Synthetic Background Spectra by Filtering the Sample Interferogram in FT-IR

Abstract

The calculation of an absorbance spectrum depends on the measurement of a blank, or background spectrum. In many cases, such as the determination of atmospheric constituents with the use of open-path Fourier transform infrared spectroscopy (FT-IR) or the determination of water vapor in a gaseous sample, it is very difficult to obtain a good background spectrum. The difficulty is due to the fact that it is nearly impossible in these situations to measure a spectrum with no analyte features present. We present a method of generating a background spectrum based on filtering the analyte features from the sample spectrum. When the filtering method is used, the accuracy of the results obtained is found to be dependent upon the analyte peak width, peak height, and type of filter employed. Guidelines for the use of this background generation technique for quantitative determinations are presented.

Multivariate Analysis of Infrared Spectra for Monitoring and Understanding the Kinetics and Mechanisms of Adsorption Processes

“…The transmission cell was connected to a manifold used to prepare and introduce a nitrogen flow containing known amounts of water vapor to the transmission cell. 12 The manifold was constructed using electropolished 316-L stainless-steel tubing, VCR and Swagelok connections, and Nupro valves. The system contained a moisture generator (Panametrics model MG101), mass flow controllers (MKS model 1160B), and a diaphragm/turbomolecular pumping station.…”

Phase Correction of Fourier Transform Spectrometer Interferograms by Optimization of the Local Oscillator Phase Angle Term

“…However, truncation of the interferogram in this fashion induces a large phase shift that poorly affects the spectral result; this observation has already been established in the literature [1]. The induced phase shift is too large for compensation with an extra iteration of FIR phase correction [3], and therefore requires phase optimization in the time-domain cosine multiplier.…”

“…If the spectral features of interest are narrow, a background and sample spectrum can be extracted from a single interferogram. This process is done by isolating the center burst of the wave form and subtracting its frequency spectrum from that of the original interferogram; this subtraction results in suitable background and sample spectra [1,2].…”

Improved strategies for quantitative evaluation of atmospheric FTIR spectra obtained in open-path monitoring

“…Other strategies reach out toward a synthetic background spectrum by applying different filters. 29,30 The theory behind CLS is described in detail elsewhere. 31 For reliable multivariate evaluation a first qualitative analysis of the atmospheric components from the measured spectrum is necessary for the selection of reference spectra when setting up the calibration matrix.…”