Supercritical fluid extraction/chromatography and Fourier transform infrared spectrometry : methods optimization and applications
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This work examines the use of supercritical fluid extraction (SFE)as a sample introduction technique for supercritical fluid chromatography (SFC) and Fourier transform infrared spectrometry (FT-IR). In order to study the effects of a supercritical mobile phase on the resulting IR spectra, carbon dioxide was compared to xenon as a supercritical fluid mobile phase for flow cell SFC/FT-IR. A packed capillary column (30 cm x 320 Î¼m, DeltabondÂ® Cyano, 5 Î¼m particle) was employed for the chromatographic portion of the study. Various samples were tested, such as an ethoxylated alcohol mixture and a unique polarity mix. The roles of temperature and density on the IR spectra were also examined as each was independently varied for the analysis of five different probe compounds. Comparisons of spectra produced in supercritical CO2 and xenon each matched well with the Nicolet vapor phase library. CO2 spectra matched the vapor phase spectra equally as well as did the xenon spectra, despite the fact that CO2 spectra have blanked regions where the mobile phase absorbs in the IR.
Following this study, SFE was coupled directly to FT-IR to produce the novel method of on-line SFE/FT-IR. This technique was optimized for the analysis of ntetracosane, yielding a detection limit of 74 ng. The method was later applied to the quantitative and qualitative analysis of fiber finishes from textile matrices with equivalent success. Finish was extracted directly from the fiber or textile surface and passed through the IR flow cell as an analyte "plug". In this way, the entire finish was quickly quantified, and if desired, qualitatively analyzed as well, without need of prior chromatographic separation. The method required no organic solvent and was proven to be fairly reproducible for four fiber finish types tested.
Lastly, supercritica1 fluid extraction (SFE) was examined and optimized as a sample introduction technique for on-line SFE/SFC. Trapping and recovery of analytes in SFE/SFC were studied under varying conditions using a currently marketed system. The system was replumbed using a 12 cm x 100 Î¼m fused silica capillary (100% methyl, df = 0.25 Î¼m) for trapping and increased solute focusing. These changes nearly doubled the total analyte recovery (as based on FID peak areas) and lowered the overall system recovery RSDs from 30 % to 4 %.
- Doctoral Dissertations