Gram-Schmidt reconstructed chromatogram

Figure 2. a) FID chromatogram from capillary SFC separation of pesticide mixture, b) Gram-Schmidt reconstructed chromatogram of the same separation. 

Figure 6 is a Gram-Schmidt reconstructed chromatogram of a citrus oil components test mixture. The major peak in the chromatogram is due to limonene which is essentially a solvent. Note that the analysis time is extremely short, less than 5 minutes/ and is accomplished under mild temperature conditions, 50 C. The resolution is not superb on all the compounds present. However, infrared detection can be used to resolve overlapping chromatographic bands. For example, the peak prior to limonene in the chromatogram (denoted with an ) appears to be pure with no shoulders evident. Close examination of the infrared spectra of the peak shows that the peak actually consists of two compounds. 

Figure 6. Gram-Schmidt reconstructed chromatogram of citrus oil test mixture.

A sensitive technique used for real time reconstruction of chromatograms from the interferogram is the Gram Schmidt vector orthogonalization method. The Gram Schmidt method relies on the fact that the interferogram contains information on absorbing samples at all optical retardations less than the reciprocal of the width of each band in the spectrum. 

Figure 4a is the spectrum of supercritical CO2 (same as Figure 1) plotted to visually compare the two spectra. It is important to realize that the Gram-Schmidt Plus algorithm removes the CO2 interference from the reconstructed chromatograms only. It does not affect the actual FT-IR spectra in any way. 

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