Evaluation of a Correction for Photometric Errors in FT-IR Spectrometry Introduced by a Nonlinear Detector Response

For strongly absorbing bands measured with a Fourier transform infrared (FT-IR) spectrometer, the effects of a nonlinear detector response must be eliminated before Beer's law linearity can be achieved. An empirical method for greatly reducing the effect of detector nonlinearity on FT-IR Beer's law spectra measured by using an FT-IR spectrometer equipped with a mercury-cadmium-telluride (MCT) detector is investigated. This first-order analytical function has been applied to correct nonlinear vapor-phase spectra and statistically evaluated for validity for spectral regions above the detector cutoff. In addition, a series of second-order functions has been evaluated to investigate the possibility that the transmittance scale is slightly nonlinear even after the first-order correction has been applied. Any improvement caused by the second-order functions was not statistically significant.