Column packing methods supercritical fluid

Supercritical fluid chromatography is the name for all chromatographic methods in which the mobile phase is supercritical under the conditions of analysis and the solvating properties of the fluid have a measurable effect on the separation. SFC has some advantages over GC and HPLC it extends the molecular weight range of GC, thermally labile compounds can be separated at lower temperatures, compounds without chromophores can be sensitively detected, and the use of open-tubular and packed columns is feasible. SFC can be employed in both the analysis of natural pigments and synthetic dyes, however it has not been frequently applied in up-to-date analytical practice. 

The most popular method used is a dynamic method, the saturation method. In this technique, the non-volatile, heavy solid solute is loaded into a saturator, or a battery of two or more saturators connected in series, and remains there as a stationary phase during the experiment. In most cases the saturator is in the form of a packed column. At constant pressure, a steady stream of supercritical fluid (solvent) passes through a preheater, where it reaches the desired system temperature. Then this fluid is continuously fed to the bottom of the saturator, and the solute is stripped from the stationary heavy phase in the column. The supercritical fluid saturated with the solute leaves the saturator at the top. 

Janicot et al. presented the separation of opium alkaloids using sub-critical and supercritical fluid chromatography [20]. Carbon dioxide-meth-anol-triethylamine-water mixtures were used as the mobile phase with packed aminopropyl or bare silica columns. The influence of aminated polar modifiers such as methylamine, ethylamine, and triethylamine was studied. Figure 7.15 shows the separation of six opium alkaloids narcotine, papaverine, thebaine, codeine, cryptopine, and morphine on a Lichrosorb Si-60 column. The method gave comparable results with HPLC. 

Supercritical fluid chromatography offers high selectivity and efficiency. Method development is faster and easier than HPLC. The future of SFC lies in the use of both capillary and packed columns. Although capillary... 

Fig. 4.31. Separation of a test mixture on capillary columns packed by different methods (A) pressure packing, (B) by centripetal forces, using supercritical fluid, and by electrokinetic packing. Columns were 50 pm I.D., 20 cm packed (30 cm total length) mobile phase 80 20 acetonitrile-4 mmol/1 aqueous borate. Separation voltage of 20 kV. Solutes 1, thiourea 2, benzyl alcohol 3, biphenyl 4, dimethylnaphthalene 5, ethylnaphthalene 6, amylbenzene.

TA Berger, WH Wilson. High-speed screening of combinatorial libraries by gradient packed-column supercritical fluid chromatography. J Biochem Biophys Methods 43 127-134, 2000. 

Berger, T.A. Wilson, W.H. High-speed Screening of Combinatorial Libraries by Gradient Packed-column Supercritical Fluid Chromatography, J. Biochem. Biophys. Methods 43,77-85 (2000). 

Supercritical Fluid Chromatography. The origin of SFC with packed columns goes back over two decades (17-26). The recent interest in SFC has been due in large part to the limitations in both chromatographic efficiency and detection methods with HPLC. The introduction of fused silica capillary columns with nonextractable stationary phases for SFC (O and the potential compatibility with gas phase detection methods (13) has served to further increase the attention given these methods. 

High Speed Capillary SFC. Until recently the practice of SFC was restricted to packed columns (17,20-26.43). Capillary colusins are clearly superior for most applications in gas chrootatography, while packed columns in liquid chromatography have tremendous advantages compared to open tubular capillary columns due to the small column diameter (< 10 ym) required to produce equivalent separations (44). Since supercritical fluids have properties intermediate between those of a gas and those of a liquid, one might expect that both packed and capillary SFC methods would be competitive and the method of choice depend on the particular separation desired. 

Supercritical Fluid Chromatography 1 Chromatographic Integration Methods 2 Packed Column SFC... 

---