By S. M. Hitchen, J. R. Dean (auth.), John R. Dean (eds.)
The endured look for fast, effective and low-priced technique of analytical size 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 homes of a gasoline at temperatures and pressures above the severe aspect. the commonest supercritical fluid is carbon dioxide, hired as a result of its low serious temperature (31 °C), inertness, purity, non-toxicity and cheapness. substitute 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 swifter pattern instruction. Supercritical fluid chromatography (SFC) is complementary to fuel chro matography ( GC) and excessive functionality liquid chromatography (HPLC), supplying greater potency than HPLC, including the power to examine thermally labile and excessive molecular weight analytes. either packed and open tubular columns should be hired, supplying the potential to examine a variety of pattern kinds. additionally, flame ionization detection can be utilized, hence supplying 'universal' detection.
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1, 230-233. P. , (1985), Separation of sucrose esters by capillary SFC/FID with robot-pulled capillary restrictors. Anal. , 57, 2243-2247. E. , (1987), Porous ceramic bed supports for fused silica packed capillary columns used in LC. J. High Resolut. , IO, 446-448. A. , (1991), Formic acid modified carbon dioxide as a mobile phase in capillary SFC. J. Microbial. , 3, 47-57. A. , (1989), Analysis of steroids by capillary SFC with phosphorusselective detection. J. , 46I, 111-120. D. , (1989), Multidimensional open-tubular column SFC using a flow-switching interface.
After 25 INSTRUMENTATION: SFC -l Detector Injector Pump C02 ~ \0 He I Precolumn II J. 5 Instrumentation for two injection modes: solvent venting at supercritical conditions or solvent elimination by purging with an inert gas (He). the solvent is evaporated and the solutes are coated on the walls of the precolumn, the purging valve is switched back to the carbon dioxide line, and liquid or supercritical C02 is introduced. , 1991). The temperature gradient on the precolumn can be obtained by passing an electric current through a conductive paint coated on the outer surface.
As in gas chromatography, there is no linear relationship between peak area and split ratio, and the split ratio changes with sample viscosity and mobile-phase density. If injections are made at different densities, good quantitation is difficult to obtain. e. with a high proportion of the sample going to waste. A high linear velocity of the fluid passing at the outside of the column is expected to improve the homogeneity of the sample. A high linear flow in the restrictor will also reduce the probability of accumulation of precipitated solutes in the restrictor, which leads to changes in the split ratio.