Stationary phases for packed-column supercritical fluid chromatography

Analysis of fatty acids in foods by supercritical fluid chromatography

The effects of the pressure drop across the column on retention and efficiency in SFC have been studied. Numerical methods are described which enable the prediction of hold-up time and pressure drop in both packed and open tubular columns. Predictions of both hold-up time and pressure drop are in good agreement with experimental data.



The density gradient along the column can be calculated using the numerical methods and a procedure is described which enables the calculation of the overall capacity factors of the solutes from the density profile in the column. Significant variations of the capacity factor are observed along the column.



The effect of the density gradient along the column on local diffusivity and dispersion is studied. The column efficiency in systems with significant pressure drops is affected by changes in: the linear velocity of the mobile phase; the diffusion coefficients; and the capacity factors of the solutes along the column. The overall efficiency of the chromatographic system can be calculated if, as is the case for open tubular columns, adequate plate height equations are available.

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The effects of the column pressure drop on retention and efficiency in packed and open tubular supercritical fluid chromatography

Supercritical fluid chromatography (SFC) using formic acid modified carbon dioxide and polymer encapsulated silica based stationary phases is suitable for the analysis with flame ionization detection of organotin compounds of general structure RnSnX4−n where n=4, 3 or 2. For ionic organotin compounds the retention time is independent of the identity of the anion, probably due to the formation of formate salts at the time of injection. A solventless injector is shown to be useful for injecting solvent volumes in the range of 0.5–50 μl, with solvent elimination prior to transferring the sample in the mobile phase to the column and as a simple in-line collection interface for SFC with supercritical fluid extraction (SFE). Various organotin compounds in a marine paint and spiked into a potato or almond matrix were determined on line, by SFE/SFC with flame ionization detection, with a limit of determination of about 1 ppm. The detection limit for typical organotin compounds using the flame ionization detector is about 0.5 ng in the chromatographic system described. SFC using formic acid modified carbon dioxide and flame ionization detection represents a considerable advance in the chromatographic analysis of ionic organotin compounds which are often time consuming and problematic to analyze by other methods.

On-line supercritical fluid extraction and chromatography of organotins with packed microbore columns and formic acid modified carbon dioxide*

Packed-microbe supercritical fluid chromatography with flame ionization detection of abused vegetable oils

A newly developed polysiloxane-type packing material shows promise for use in SFC. Relatively polar compounds were eluted from a microbore column with good peakshape using a mobile phase consisting of CO2 modified with formic acid and water. The latter combination is an effective modifier suitable for use with pressure programming and FID detection.

H. H. Lauer

Papers

Comparison of packed and capillary columns for practical SFC separations

Packed vs. capillary columns for supercritical fluid chromatography: theoretical considerations