Simple correction for variable post column split ratios using pure carbon dioxide in packed column supercritical fluid chromatography with independent pressure and flow control

Bioanalytical applications using supercritical fluid techniques

The bioanalytical applications of supercritical fluid techniques, such as supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC), are of increasing interest. The main role of these techniques is in the sample preparation and separation of biologically active compounds, particularly drugs and their metabolites, as well as endogenous compounds. An insight is given into the different types of extracting fluids and modifiers, detectors, stationary phases, mobile phases and collection strategies. A critical discussion is presented on the existing state of the art concerning the applications of SFC and SFE with a specific focus on its advantages and limitations in the bioanalytical field. New developments and the possibilities for routine work in the near future are also covered.

Advantages and drawbacks of popular supercritical fluid chromatography/mass interfacing approaches--a user's perspective

Mobile phases in supercritical fluid chromatography (SFC) have low viscosities and high diffusion coefficients with respect to those of traditional high performance liquid chromatography (HPLC). These properties allow higher mobile phase flow rates and/or longer columns in SFC, resulting in rapid analyses and high efficiency separations. In addition, chiral SFC is becoming especially popular. Mass spectrometry (MS) is arguably the most popular "informative" detector for chromatographic separations. Most SFC/MS is performed with atmospheric pressure ionization (API) sources. Unlike LC/MS, the interface between the SFC column and the API source must allow control of the downstream (post-column) pressure while also providing good chromatographic fidelity. Here we compare and contrast the popular interfacing approaches. Some are simple, such as direct effluent introduction with no active back-pressure-regulator (BPR) in high speed bioanalytical applications. The pressure-regulating-fluid interface is more versatile and provides excellent chromatographic fidelity, but is less user friendly. The pre-BPR- split interface and an interface which provides total-flow-introduction with a mechanical BPR are good compromises between user friendliness and performance, and have become the most popular among practitioners. Applications of SFC/MS using these various interfaces are also discussed.