Atmospheric Compensation in Fourier Transform Infrared (FT-IR) Spectra of Clinical Samples

A new method is proposed for the elimination of the spectral contribution of two atmospheric gases (CO₂ and H₂O) in Fourier transform infrared (FT-IR) spectra of clinical samples. The algorithm is based on the measurement of reference spectra of H₂O followed by an automatic calculation of the spectral contribution of the above-mentioned gases to the sample spectra. Then this contribution is compensated by spectral subtraction. Attenuated total reflectance FT-IR spectra of serum and urine samples in the presence of atmospheric gases were corrected and compared with spectra obtained with an N₂ purge. Visual inspection of the spectra as well as calculated noise levels confirmed that the method compensated for the contribution of CO₂ and H₂O to serum and urine spectra to a great extent. As compared with the correction performed by a commercial software package, the proposed method clearly improved the correction of CO₂ and provided similar results for H₂O compensation. Correlation values between corrected spectra and those obtained under N₂-purged conditions in the fingerprint region were higher than 0.995, and noise values in regions where samples did not absorb confirmed the suitability of the correction. The proposed method is fast, easy, and extensible to other gaseous interferences, devices, and acquisition conditions.