Thomas L. Chester

Pressure-regulating fluid interface and phase behavior considerations in the coupling of packed-column supercritical fluid chromatography with low-pressure detectors

Abstract Packed-column supercritical fluid chromatography is usually performed with flow control on the upstream side of the column and pressure control on the downstream side. This arrangement is compatible with detectors that can be operated at column-outlet pressure and placed between the column outlet and a pressure-regulating device. However, mass transfer problems may arise when low-pressure detectors like a mass spectrometer or evaporative-light-scattering detector are used with downstream pressure regulators or programmable nozzles. These problems can be avoided by replacing the regulator or nozzle with a tee delivering a pressure-regulating make-up fluid from a pressure-controlled pump. Parameters are chosen to avoid the liquid–vapor two-phase regions of the phase diagram for the resulting mixture. We demonstrate this approach and show how to use phase diagrams and their pressure–temperature projections for setting operating conditions.

Separation of malto-oligosaccharide derivatives by capillary supercritical fluid chromatography and supercritical fluid chromatography-mass spectrometry

Pressure-programmed, capillary supercritical fluid chromatography (SFC) can be used to separate silylated malto-oligosaccharides of degree of polymerization (d.p.) 1 to beyond 20 in a single analysis

Investigation of derivatizing agents for polar solutes in supercritical fluid chromatography

Supercritical fluid chromatography (SFC) is a chromatographic technique with certain advantages over both liquid and gas chromatography (GC); however, the analysis of polar solutes by SFC can be difficult due to long retention times and peak tailing. Although chemical derivatization has been extensively used in GC, it has received little attention as a method for lowering the polarity of solutes in SFC. A systematic study of common derivatizing agents has been conducted to examine their utility in derivatizing polar solutes and for improving peak shapes in SFC. Unique derivatizing agents, particularly those with large blocking groups, have also been investigated as a means of reducing the polarity of certain functional groups more efficiently. A summary of derivatizing agents in terms of their ability to derivatize polar functional groups is provided.

Further considerations of exact equations for peak capacity in isocratic liquid chromatography.

Further consideration is made of the exact equation for peak capacity by Potts, L. W.; Carr, P. W. Anal. Chem. 2011, 83, 7614-7615 for liquid chromatographs with significant extra-column broadening. Equivalent exact equations are easily derived that provide comprehension and insight of how extra-column broadening degrades chromatographic performance as measured by peak capacity.

Investigation of carbon dioxide modified supercritical and near supercritical carrier streams for flow injection systems.

Since flow injection (FI) is a dilution technique, efforts have been undertaken to minimize online dilution or dispersion. Solutes in supercritical fluids exhibit increased diffusion coefficients which have been shown to decrease dispersion of the sample zone. This work investigates the use of supercritical fluids (or CO(2) modified fluids) as carrier streams for FI. Both a non-reacting tracer and an online chemical reaction were employed to investigate the behavior of solutes in supercritical and near critical systems. Further, these results are compared to those obtained in the system studied with a conventional carrier stream. Plots of peak response vs% CO(2) modifier increase with a sharp break at moderate modifier composition (20-30%). Plots of peak variance vs% CO(2) modifier show decreased variance with increasing % modifier. The system was also optimized with regards to temperature and pressure. The optimized system displayed improved limits of detection and decreased variance relative to 0% CO(2) modifier carrier streams.

Books and Software: SFC for all stages.

A review of Supercritical Fluid Chromatography with Packed Columns-Techniques and Applications.