By S. M. Hitchen, J. R. Dean (auth.), John R. Dean (eds.)
The persisted look for swift, effective and low-cost technique of analytical dimension has brought supercritical fluids into the sector of analytical chemistry. parts are universal: supercritical fluid chroma tography and supercritical fluid extraction. either search to use the original houses of a gasoline at temperatures and pressures above the severe aspect. the most typical supercritical fluid is carbon dioxide, hired as a result of its low serious temperature (31 °C), inertness, purity, non-toxicity and cheapness. replacement supercritical fluids also are used and sometimes together with modifiers. The mixed gas-like mass move and liquid-like solvating features were used for more suitable chroma tographic separation and speedier pattern practise. Supercritical fluid chromatography (SFC) is complementary to gasoline chro matography ( GC) and excessive functionality liquid chromatography (HPLC), offering better potency than HPLC, including the power to examine thermally labile and excessive molecular weight analytes. either packed and open tubular columns might be hired, offering the potential to examine quite a lot of pattern kinds. moreover, flame ionization detection can be utilized, hence supplying 'universal' detection.
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D. , 1988). 5). The major part of the solvent is vented through a restrictor at a rapid (10-15 em s- 1) but controlled flow rate. With a 2m precolumn the venting time is only 15-20 s. Too long venting times discriminate the early-eluting peaks and too high starting pressure degrades the peak shape (Berg and Greibrokk, 1989). The peak focusing at the column inlet is based on phase ratios, by using a thicker film on the column than on the precolumn, or by partition coefficients, by using a more retaining stationary phase on the column, or both.
57, 2239-2242. , Lafosse, M. , (1992), Comparison of ethoxylated alcohols and polyethylene glycols by high performance liquid chromatography or supercritical fluid chromatography using evaporative light-scattering detection. J. , 591, 149-157. K. , (1990), The performance of electron-capture detection after capillary SFC. J. Chrornatogr. , 28, 29-33. P. , (1989), Ultra-sensitive UV detection in micro separation. J. High Resolut. , 12, 278-281. , (1984), Capillary SFC with FID: reduction of detection artifacts and extension of detectable molecular weight range.
Part of the sample elutes with the solvent plug until complete mixing is obtained on the column, while the rest of the sample is slightly retained by partitioning at the first part of the column. The splitting was found to be reduced by raising the column temperature, apparently due to increased diffusion and mixing at higher temperature. The initial pressure may also have an effect on the peak shape. At lower pressure the increased diffusion rate and the increased mixing time result in better mixing and the peak splitting disappears.