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Supercritical Fluid Chromatography for the Determination of Chiral Pharmaceuticals
by Dr. Amanda Jenkins and William Hedgepeth, Jasco Inc.
A large percentage of commercial and investigational pharmaceutical compounds are enantiomers, many of them showing significant enantioselective differences in their pharmacokinetics and pharmacodynamics. The use of supercritical fluid chromatography in separation and detection of these materials not only reduces the cost of producing chirally pure materials, but also is an environmentally friendly alternative to the conventional solvents used in HPLC. This application note describes the application of SFC for chiral pharmaceuticals.
Introduction
Many molecules made up of the same number and type of atoms, come in two forms commonly referred to as enantiomers. The biological activity of enantiomers often depends upon their stereochemistry. HPLC has been the method of choice for many chiral separations, however Supercritical Fluid Chromatography (SFC) is faster and has higher resolving power than LC. For Preparative Chromatography, SFC offers the added advantage that fractions are collected in a small volume of a volatile solvent such as methanol that significantly reduces both solvent costs and sample recovery time.
Figure 1. Jasco SFC system.
Compression of a gas results in change of state to liquid. However when a gas is heated beyond a particular temperature, it cannot be liquefied regardless of any further increase in the pressure. The "fluid" exhibits many of the properties of both gas and liquid, with the state of the fluid being called the supercritical state. The closeness to the gaseous state helps in faster diffusion by almost two orders of magnitude higher than that of other liquids, while the proximity to the liquid state helps in better solubility of the components to be separated. The dissolving power of supercritical CO2 increases with increased pressure.
Experimental
Chiral separations were performed using a Chiralpak AD column and a mixture of carbon dioxide and methanol.
Detection of the chiral compounds was performed with Jasco's circular dichroism chiral detector that provides simultaneous outputs of both UV and chiral signals, allowing easy differentiation of enantiomers.
Results and Discussion
Figures 2 and 3 show chiral separations of various chiral compounds. The upper chromatogram reflects the chiral signal from the detector, and the UV signal is observed in the lower chromatogram. Figure 2 shows the chiral detector's response to Nexium. Only one peak is observed since Nexium contains only the S-enantiomer. Figure 3 displays the chiral separation of Warfarin, and the chiral signal confirms that this compound is racemic.
Figure 2. SFC separation of Nexium.
Figure 3. SFC separation of Warfarin.
Conclusions
Supercritical fluid chromatography in separations not only reduces the cost of separating materials, but is an environmentally friendly alternative to the conventional solvents used in HPLC. SFC is faster and has higher resolving power than conventional HPLC.
JASCO Inc.
8649 Commerce Drive
Easton, MD 21601
JASCO Incorporated
8649 Commerce Drive
Easton, MD, 21601
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