Preparative SFC

The main use of SFC for the past 15 years has been the preparative resolution of enantiomers. Although SFC is expanding into other areas, the preparative arena is expected to remain prominent because of the advantages of SFC over HPLC such as speed, lower costs, and reduced solvent usage. Arvind Rajendran of Nanyang Technological University presented work on the two injection approaches in preparative SFC (mixed stream and modifier stream injection). Mixed-stream injection introduces the sample in the carbon dioxide or modifier stream, whereas modifier stream injection introduces the sample in the modifier stream before mixing with carbon dioxide. It has been shown that large-volume injections in the mixed-stream injection mode can result in peak distortion. Further experiments were performed in Rajendran's laboratory to explore this effect. Large-volume injection studies under mixed-stream injection and a low modifier percentage yielded an increase in retention with increased injection volume. He proposed that this impact was caused by the large viscosity difference between the injection plug and the SFC mobile phase, which resulted in increased pressure and reduced linear velocities. Further experiments are planned to confirm this theory.

Alexander Bozic reported on the role of SFC for pharmaceutical purification at Sanofi-Aventis. He discussed limitations of the commercially available equipment in their laboratories that ultimately resulted in the design and construction of an in-house preparative SFC system. The main advantage of this system was a gas–liquid separator that allowed open-bed fraction collection at higher flow rates (up to 350 mL/min) without the need for a make-up pump, while affording higher product recoveries than currently available gas–liquid separators. Manny Ventura of Amgen presented an investigation on the coupling of achiral and chiral columns during SFC method development. Often, samples submitted for chiral separation have achiral impurities. If those impurities are coeluted with either enantiomer, an achiral separation must be done before or after the chiral purification. Ventura evaluated the coupling of achiral and chiral columns to resolve all sample components in one step, thus increasing the process efficiency.

Larry Taylor of Virginia Tech reported on the analysis of hydrophilic analytes using water-rich modifiers. He showed that adding 5–10% more water to the modifier allows the elution of polar molecules, even those with high water solubility. For all this work he used bare silica stationary phases. Taylor calls this approach hydrophilic interaction liquid chromatography (HILIC) SFC. This approach was demonstrated through multiple examples, including polar pharmaceutical compounds and unprotected dodecaptide isomers.

SFC Column Selection

Pat Sandra of the Research Institute for Chromatography presented a review of column selection for SFC. In his opinion, silica is the first choice for achiral SFC method development. Sandra also presented work on using small internal diameter columns in SFC. He showed that 2-mm i.d. columns could not achieve the same efficiency under SFC operation that is seen under HPLC conditions.

Green SFC

Caroline West of the Universite d'Orleans gave a thought-provoking talk on the "greenness" of SFC. SFC is referred to as a green technology; West reduced the "12 principles of green chemistry" to six principles of green chromatography and evaluated SFC for each of these principles. Her conclusion was that although SFC is green, it could be made even greener. The main areas to consider are the amount of organic modifier required for separation, which results in increased waste, and the energy required for the production and recycling of carbon dioxide. She suggested the use of appropriate stationary phases that would allow elution at lower modifier percentages. One example of a seven-component mixture showed that solvent usage could be reduced from 10.5 mL to 0.5 mL per sample with only a stationary phase change. Currently, carbon dioxide recycling is used only for high-flow-rate preparative SFC systems. To increase energy efficiency for carbon dioxide production, she recommended its use for smaller SFC systems.

Poster Sessions and Best Poster Awards

As with previous SFC meetings, many attendees chose to present their work in poster format. Topics covered all areas related to SFC, including analytical and preparative SFC and stationary phase development and evaluation. Best poster awards consisting of cash prizes were given to the top two posters as judged by the scientific committee.

This year's winning poster was "Effects of Modifier Nature and Percentage on Retention and Selectivity in SFC" by Caroline West and coauthors from the Universite d'Orleans. This work investigated the changes in retention and selectivity that occur when the modifier (methanol, ethanol, isopropanol, or acetonitrile) is varied. Seven stationary phases with different column chemistries were studied using chemometric methods. This study showed that selectivity was only marginally affected by the modifier, with acetonitrile showing the most significant differences. In addition, these results support the theory of a "HILIC-like" retention mechanism in SFC in which the adsorbed mobile-phase molecules have an active role in the retention process as they interact with the analytes.

The second place winner was "Development of a High-Throughput Lipid Profiling Method by Using a Quadrupole Orbitrap Mass Spectrometer and an Automated Lipid Identification Software" by Takeshi Bambi and coauthors from Osaka University. This poster reported on the use of SFC–MS for high-throughput lipid analysis and the use of lipid search software for identification of the separated lipids. With this approach, more than 200 lipid molecular species were detected and automatically identified from mouse plasma.

SFC 2013

The 7th annual Symposium on Packed Column SFC (SFC 2013) will be held in Boston, Massachusetts, from July 10 to 12, 2013. Location and timing were chosen to precede Prep 2013, allowing scientists to attend both meetings. Additional information on SFC 2013 can be found on the Green Chemistry Group web site: http://www.greenchemistrygroup.org/.

Larry Miller is with Amgen in Cambridge, Massachusetts.

Larry Taylor is with the Department of Chemistry at Virginia Tech in Blacksburg, Virginia.

Direct correspondence to: millerl@amgen.com
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