Quantification of Nitromethane with Complementary Super Clip Apodization and an Iterative Spectral Comparison Routine

One of the main challenges in remote Fourier transform infrared (FT-IR) spectroscopy is the collection of a reliable background spectrum. Although suggested as a method to address the problem in prior literature, super clip apodization (SCA) has had little reported success for wide spectral features. SCA is a technique that involves the manipulation of different parts of the interferogram to calculate an absorbance spectrum from a single interferogram. A new method called complementary super clip apodization (CSCA) is developed here and is successfully used in conjunction with SCA in an iterative optimization algorithm. The umbrella term of super clip mathematics is also defined to encompass spectral calculation using SCA, CSCA or both in combination. The validity of super clip mathematics is demonstrated in an experimental study of gas-phase nitromethane. In an effort to mimic errors present in standoff detection, uniformly distributed noise and/or wavenumber shifting is added to the interferometric sample data to test the robustness of the algorithm. It will be shown that the implementation of SCA and CSCA in combination is more successful for concentration assessment than using SCA or CSCA alone.