FIELD OF THE INVENTION
The present invention relates to an advancement in the art of Supercritical Fluid Chromatography (SFC) and, more particularly, to an SFC system having improved resolution capabilities and minimized test durations.
BACKGROUND OF THE INVENTION
In analytical chemistry, liquid and gas chromatography techniques have become important tools in the identification of chemical sample components. The basic principle underlying all chromatographic techniques is the separation of a sample chemical mixture into individual components by transporting the mixture in a moving fluid through a porous retentive media. The moving fluid is referred to as the mobile phase and the retentive media has been referred to as the stationary phase. One of the differences between liquid and gas chromatography is that the mobile phase is either a liquid or a gas, respectively.
Consider, for example, a gas chromatograph. Typically, a supply of inert carrier gas (mobile phase) is continually passed as a stream through a heated column containing porous sorptive media (stationary phase). A sample of the subject mixture is injected into the mobile phase stream and passed through the column. A detector, positioned at the outlet end of the column, detects each of the separated components as they exit the column. Separation is due primarily to differences in the volatility characteristics of each sample component at the temperature in the column.
The analytical choice between liquid and gas chromatography techniques is largely dependent on the molecular weight of the compound being analyzed. Liquid chromatographs are capable of analyzing much heavier compounds than gas chromatographs. However, since gas chromatography detection techniques are more sensitive, they are preferred.
The advent of Supercritical Fluid Chromatography (SFC) provided a potential bridge between gas and liquid chromatography advantages, i.e., high sensitivity and heavier molecular weight samples. In SFC, a fluid heated above the critical point, is used as the mobile phase. Such fluid is passed under pressure through a media which differentially retains sample components. As the pressure of the mobile phase is increased, for example, from about 40 ATM to approximately 400 ATM, the sample being analyzed separates into its various components dependent upon the relative differential solubility of each component with the mobile phase. Since the mobile phase is a gas, gas chromatography detectors can be utilized, significantly enhancing detection sensitivity and selectivity. SFC can be simplistically viewed as an extension of gas chromatography to higher molecular weight components. SFC has been found to be primarily useful in the analysis of moderate molecular weight homologous series (M.W. 100 to 10,000) and some thermally labile molecules such as pesticides and pharmaceuticals.
Due to problems with analysis times and resolution, SFC as an analytical tool has not achieved its full potential. The term "resolution" as used herein refers to the distinctiveness with which component peaks appear in an SAFC chromatogram. Chromatograms are those graphs of detector output signal vs. time which are produced by the connection of an X-Y plotter or other chart recorder to a chromatograph detector, wherein a peak indicates the detection of a component.