Concept and properties of an infrared hybrid single-beam spectrum and its application to eliminate solvent bands and other background interferences

For infrared (IR) spectral measurements, if a quality single-beam background spectrum with desired intensity could be obtained, the contributions from solvent and other background components could be completely suppressed and their bands would not appear in a final transmittance/absorbance spectrum. In order to achieve this ideal but difficult goal, the concept of hybrid single-beam spectrum is introduced in this paper. The hybrid single-beam spectrum (phi(h)) is defined as a mixture of two single-beam spectra (phi(b1) and phi(b2)) of the same sample but with different pathlengths (b(1) and b(2)), namely, phi(h)=alpha phi(b1)+(1 - alpha) phi(b2), where alpha(0 <= alpha <= 1) is the component factor. The properties of the hybrid spectrum have been investigated. Under conditions of b(2) > b(1) >= 0.7b(2) and A(max) <= 0.60 (A(max) is the maximum absorbance of b(2) sample in the spectral range of interest), all the synthesized hybrid spectra are free from significant distortion regardless of the component factor. Therefore, the hybrid single-beam spectrum with desired intensity can be easily obtained simply by choosing an appropriate component factor. The proposed methodology has been demonstrated experimentally by the complete removal of the interference from the atmospheric water vapor and solvent. (C) 2013 Elsevier B.V. All rights reserved.