A data compression technique using factor analysis and the Karhunen-Loeve transformation has been applied to a library of vapor phase infrared spectra. Application of the compression algorithm results in a fivefold reduction in storage requirements for the spectral library and a corresponding reduction in search time. A search system based on the compression data has been evaluated and found to compare favorably with a search using the entire spectrum.
Dramatlc Improvements in the sensltlvity of Fourier transform infrared detectors for supercritical fluid chromatography are explained In terms of optical and chromatographic parameters. By use of methyl palmitate as a model compound, minimum ldentlkation HmHs of 10 ng of component delivered to the column using carbon dioxide mobile phase are reported. Detectlon limits such as these are achieved by balancing optical throughput of a 600 q internal diameter flow ceU against the effect of moMle phase absorption with a 5inm path length. Results from a study of the detector cell temperature indicate an improvement In sensJtivity can also be attributed to concentration of the chromatographic peak when using cooler detector cell temperatures.Supercritical fluid chromatography (SFC) is attracting a great deal of interest as a powerful new technique in the field of chromatographic analysis. One of the primary areas of current research in SFC is the development of full range spectral detectors such as Fourier transform infrared (FT-IR) spectroscopy. This is an important development because FT-IR detectors with SFC can provide full infrared spectral information for identification of chromatographic peaks.Recently, there has been a dramatic improvement in the performance of FT-IR flow cell detectors with SFC. While this improvement has generated considerable interest, there has been little explanation of how these improved detection limits were obtained or the factors affecting detection limits. This paper addresses these concerns and reports results from experiments that study the optical and chromatographic parameters involved in the SFC/FT-IR experiment. By use of model compounds, the identification capability and chromatographic performance of the flow cell type of SFC/FT-IR interface are defined.
Supercritical fluid extraction using 100% carbon dioxide is able to remove antioxidant additives from flaked polyethylene. SFE appears to be more selective for the lower-range low-MW polymer than Soxhlet-type extraction. This yields a chromatogram with less interference from low-MW polymer peaks in the region where the additive components elute. Infrared detection is able to locate peaks corresponding to distinct types of additives by generating chromatograms from chemically specific regions of the SFC/IR data. Infrared spectra are sufficient for identification of additives and determination of the oxidation state of phosphorus-containing antioxidants.
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