Highlights of SFC 2012

Jan 01, 2013

The 6th International Symposium on Packed Column SFC (SFC 2012) this past October included plenary lectures, scientific talks, poster sessions, and award presentations. Key areas addressed include supercritical fluid chromatography (SFC) for food analysis, medicinal chemistry purifications, hydrophilic interaction liquid chromatography SFC, SFC column selection, green SFC, and analytical and preparative SFC.

The 6th International Symposium on Packed Column SFC (SFC 2012) was dedicated to bringing scientists together to discuss the latest advances in supercritical fluid chromatography (SFC). The symposium is organized by the Green Chemistry Group and alternates between the United States and Europe. The 2012 conference was held in Brussels, Belgium, from October 3 to 5. SFC 2012 attracted more than 150 scientists from 18 countries. In addition, eight exhibitors displayed equipment and stationary phases for SFC use. The three-day conference included 19 oral presentations, 41 poster presentations, and two vendor workshops. A short course dedicated to SFC theory and achiral, chiral, and preparative SFC was held before the conference. The program and many of the oral and poster presentations from SFC 2012 and previous SFC conferences can be found at http://www.greenchemistrygroup.org/index.html.

Plenary Lectures

On Thursday and Friday mornings, the conference started with a plenary lecture from a recognized expert in SFC. Here is a brief description of those two lectures.

SFC for Food Analysis

Terry Berger (Aurora SFC) led off the first day of the conference with a discussion of separation problems that are not currently addressed by SFC. Over the past 20 years SFC has become a technique dominated by pharmaceutical applications. In the late 1980s, SFC had a much wider base of applications including polymers, fuels, food, and environmental contaminants, as well as pharmaceutical applications. Berger's talk focused on the potential of SFC for food and nutritional analysis. SFC separations have been developed for a number of food-related analyses including sulfa residues in milk, preservatives, natural food colorings, antioxidants, and vitamins. In those examples, SFC afforded shorter analysis times and used less solvent. Berger also reported on the first baseline separation of eight sulfonamides by SFC. The SFC method was four times faster than the reported high performance liquid chromatography (HPLC) separation. Recent advances in analytical SFC equipment and sensitivity have allowed sulfamethazine to be quantitated to 9 ng/mL (below the legal limit).

SFC in Medicinal Chemistry Purifications

The second plenary lecture of the conference was given by Eric Francotte (Novartis Institutes for Biomedical Research), who reported on the expanding role SFC is playing in medicinal chemistry purifications. Novartis has implemented a worldwide initiative to promote the use of SFC purifications to increase medicinal chemistry productivity. The company is promoting the use of SFC over reversed-phase HPLC whenever possible. This approach shortens the time necessary to purify final compounds and frees up medicinal chemists' time by routing the time-intensive purification process to a specialty group. There is currently no generic achiral SFC stationary phase, thus an efficient screening process must be developed to minimize analysis time while maximizing purification success. Francotte reported on the use of eight column chemistries and a parallel SFC–mass spectrometry (MS) system to efficiently develop analytical SFC methods suitable for purification. In the two years since this initiative began, the purification approach has moved from 90% reversed-phase HPLC in 2010 to 80% SFC in 2012.

Analytical SFC

Although purification is still the main application for SFC, the use of analytical SFC has been increasing. This was evident by the higher number of talks discussing analytical SFC compared to past conferences. Didier Thiébaut (ESPCI Paris Tech) presented his recent work on exploring two-dimensional SFC to separate complex mixtures. He presented work concerning the impact of various instrument parameters on the number of peaks observed and reported on the 2D SFC separation of a vacuum distillate from coal tar, showing comparable results to 2D gas chromatography (GC). Two-dimensional SFC allows for the use of long columns and can be used for heavier (higher molecular weight and more polar) samples; it is not restricted to oil samples.

Claudio Brunelli presented work from Pfizer's Sandwich, UK, facility where they are working to move SFC from a generic approach to a critical tool for analytical method development. He reported on the use of SFC–time-of-flight (TOF) MS for the identification of minor enantiomers in chiral SFC methods without requiring enantiomer standards. The use of SFC for analytical method development for Dacomitib (a development candidate for non-small cell lung cancer) was also presented. Dacamotib and its intermediates presented numerous analytical challenges, including low solubility and stability in aqueous and acidic mobile phases. SFC methods were quickly developed for step 1 and 2 products that eliminated the stability issues observed with reversed-phase HPLC. The largest separation problem for this project was the separation and quantitation of up to 47 genotoxic impurities that required limits of quantitation <1 ppm. SFC was explored for this separation and has shown impressive initial results.

Sub-2-μm particles are routinely used in HPLC but, because of equipment design, they have not been routinely used in SFC. The latest analytical SFC designs have reduced extracolumn and dwell volumes such that the advantages of sub-2-μm particles can be realized with SFC. Alexandre Grand-Guillaurne-Perrenoud of the University of Geneva presented a critical analysis of sub-2-μm columns for SFC and their application for the analysis of pharmaceutical compounds. His study showed the extracolumn volume for the new generation of SFC equipment (60 μL) is higher than that for ultrahigh-pressure liquid chromatography (UHPLC) (13 μL), and the smallest column internal diameter that should be used on the new generation of SFC equipment is 3 mm. A higher value for height equivalent to the theoretical plate (HETP) was seen for SFC compared to HPLC (2.8 vs. 2.2), possibly because of packing issues or decompression cooling. In SFC, as pressure increases, mobile-phase density changes and temperature gradients are generated that can affect selectivity, making system pressure drop a critical parameter for method transfer. Grand-Guillaurne-Perrenoud also reported on SFC analysis of basic pharmaceutical compounds. Using 2-ethylpyridine columns, poor peak shape was observed, especially for compounds with pK a > 8. The use of a hybrid silica column with a volatile additive (ammonium hydroxide) gave good peak shapes for all compounds.