Highlights of SFC 2019

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A review of the 13th International Symposium on Packed Column SFC and SFE Techniques (SFC 2019), which was held in Philadelphia, Pennsylvania, USA, on 29 September–1 October 2019.

The 13th International Symposium on Packed Column SFC and Techniques (SFC 2019), which alternates between the United States, Europe, and Asia, was held in Philadelphia, Pennsylvania, USA, on 29 September–1 October 2019. The symposium is dedicated to bringing scientists together to discuss the latest advances in supercritical fluid chromatography (SFC), supercritical fluid extraction (SFE), and related technologies. It is organized annually by the Green Chemistry Group (GCG) (see https://www.greenchemistrygroup.org/ for more information) and more than 120 people were in attendance. In addition, 14 vendors participated in the exhibition. The three‑day programme began with a short course on the first day regarding the theory of SFC and SFE, instrumentation and method development in analytical and preparative SFC, as well as applications thereof. This was followed by two days that included 23 oral presentations, 30 poster presentations, and three vendor workshops.

Day two began with a lifetime achievement award presentation to Larry T. Taylor (Professor Emeritus, Virginia Tech University, USA) by Ray McClain (GCG board president; Merck, USA) for his sustained and outstanding contributions to the GCG as well as his many contributions advancing the science of SFC, SFE, and SF processing during a career that spanned more than 40 years. J. David Pinkston (GCG board; Archer Daniels Midland Co., USA) then gave a lecture entitled “Footsteps of a Giant-Intellectual Travels with Larry T. Taylor”, which highlighted many of Larry’s accomplishments over his esteemed career. These include 40 years as a professor, >400 publications including three books, book chapters, patents, and reports, and organization of 20 major supercritical fluids conferences. His research career has spanned various chemistry fields such as electrochemistry, material science, polymer science, and separation science with the latter including extraction, gas chromatography (GC), high performance liquid chromatography (HPLC), and SFC. David then provided
more detailed highlights of Larry’s contributions in these areas as well as describing how Larry impacted the lives of many of his students and colleagues along with other people outside of his work in chemistry.

Erik Regalado (Merck, USA) kicked off the first oral presentation session with a talk entitled “SFC-PDA-ESIMS as a Framework for Impurity Fate Mapping in the Development and Manufacture of Drug Substances”. He gave an overview of various SFC approaches provided by Merck and then described the use of SFC to resolve a complex mixture using a chiral column and EtOH–CO2 mobile phase where reversed-phase LC failed to do so. Combining SFC with photodiode array (PDA) and electrospray ionization‑mass spectrometry (ESI-MS) allowed this approach to be used for downstream production monitoring (1).

Bill Farrell (Pfizer, USA) gave a talk entitled “Active Flow Technology Improves Peak Efficiency in SFC”. He introduced the topic active flow technology (AFT)-SFC and research performed with AFT in HPLC and now SFC. By modifying the internal column geometry as well as components, such as the end frits, and then studying the various performance attributes, he and his collaborators were able to demonstrate improved SFC column efficiency, peak shape, and resolution.

Kevin Thurbide (University of Calgary, Alberta Canada) presented “New Approaches to SFC Separations Using Water as a Stationary Phase”. This involves using a GC capillary column internally coated with water to take advantage of the immiscibility of carbon dioxide with water to act as the mobile phase. The separation of various analytes can be tuned via temperature and pressure. Variables such as carbon dioxide flow as well as gradient control via dehydration and rehydration of the column can be used for additional control of selectivity. The pH of the water stationary phase can be modified and chiral selectors can also be introduced for chiral resolution of isomers.

Blair Berger (University of Texas at Arlington, USA) discussed the application of on-line SFE–SFC–MS to the analysis of drugs of abuse from human hair. The samples were put directly into various extraction vessels and extracted under static and dynamic conditions. Extracted components were introduced to the analytical SFC column followed by elution and detection thereof. The optimized extraction, separation, and detection of 17 known drugs could be accomplished in 30 min with the optimized SFE step utilizing about 80% of that time. A. Paige Wicker (also from the University of Texas at Arlington) described a similar SFE–SFC–MS approach to the extraction and analysis of polyaromatic hydrocarbons (PAHs) from various types of soils. A 32-min assay that resolved 16 different compounds was presented. Gioacchino Luca Losacco (University of Geneva, Switzerland) then described the application of SFC–MS/MS to anti-doping analysis of prohibited drugs in urine as an alternative to LC–MS/MS.

Raffeal Bennett (Merck, USA) gave a presentation discussing the application of SFC to biomolecules analysis and purification. An enhanced fluidity liquid chromatography (EFLC) approach was used to extend the modifier range (including the addition of water to the methanol) beyond the more typical SFC approach (for example, 5–50% methanol in CO2). This was then applied to the separation of various oligosaccharides and monitored via mass spectrometry. A mixture of nucleotides was also resolved with this approach while ammonium hydroxide was included in the modifier mixture. Proteins were also evaluated and conformational changes were observed for most structures tested.

Martin Enmark (Karlstad University, Sweden) described a strategy for improving SFC method transfer and scaleup. An isocratic plot approach that shows how the molar concentration of co‑solvent varies with the mass fraction and density of the fluid was described and shown to help predict analyte retention change. Another strategy to match retention was also introduced where retention time shifts due to pressure drop changes can be compensated for by adjusting the fluid composition. A rule of thumb was devised that simply requires measuring the relative retention factor shift and then changing the co-solvent mass fraction appropriately.

Abhijit Tarafder (Amgen USA) described a model-based estimation approach for preparative SFC injection volumes versus the more traditional experimental increasing volume approach that can be time-consuming. An Excel-based spreadsheet was used to make the calculations. Pierre Billemont (UCB Pharma, Belgium) gave a presentation showing the preparative chromatography capabilities of their centralized purification group. Milligram- to kilogram-scale separations with both LC and SFC modes were discussed, with SFC being used for most of this work now.

Robert Campbell (Dow Chemical, USA) presented the application of SFC to the analysis of synthetic sebum oil. Terry Berger (SFC Solutions Inc., USA) described ongoing issues with the overall efficiency of newer ultrahigh-pressure (UHP)SFC instrumentation and columns and his studies with modified designs to lower the dispersion effects thereof. Tony Yan (Pfizer, USA) showed the use of SFC–high resolution (HR)MS for stability testing and clinical release for very low concentration (ng/mL) samples in plasma. The application of this approach to chiral inversion case studies was described.

Day three began with a keynote presentation from Jerry King (CFS, USA) entitled “Critical Fluid Extraction and Chromatography-Application to Cannabis/Hemp Processing”. He gave an overview of the present state of processes and the optimization as applied in this industry. Extraction techniques (including SFE) and chromatographic approaches (including SFC) are relied upon heavily to generate the end products. He described the use of solubility parameter theory (SPT) and activity coefficients to determine processing conditions and product formulation. He also mentioned the importance of physiochemical data for modelling and scaleup of these processes.

Susan Olesik (The Ohio State University, USA) described the use of EFLC for disease diagnostics in her laboratory. Significant improvements in both chromatographic resolution and MS detection were observed by using an EFLC approach combined with hydrophobic interaction chromatography (HIC) assay conditions for the separation of a protein mixture (2). Gilles Goetz (Pfizer, USA) and Romulo Romero (AstraZeneca, USA) described the use of SFC to ascertain exposed polar surface area (EPSA) for enabling drug design at their respective pharmaceutical companies. This measurement is used to help predict the membrane permeability of molecules in a rapid fashion.

Matthew Przybyceil (ES Industries, USA) discussed the development of new SFC stationary phases for the separation of natural products and, in particular, cannabinoids. Quentin Gros (University of Orleans, France) showed the application of linear solvation energy relationships (LSER) towards the characterization of some newer column chemistries. Daniel Hengst (Eurofins, USA) gave a great talk that demonstrated the power of SFE–SFC–MS as applied to fat-soluble vitamin testing, reducing sample turnaround times from several hours each to less than 20 min cycle time each. Lucie Novakova (Charles University, Czech Republic) outlined the application of SFC–MS/MS to the analysis of cannabinoids along with SFE for their extraction from various cannabis products. Takeshi Bamba (Kyushi University, Japan) followed with a presentation showing the use of SFC–MS for the profiling of assorted polar metabolites.

The final talk of the conference was given by Victor Abrahamsson (Cal. Tech., USA) describing the potential use of SFE and SFC for the analysis of aqueous and solid materials for astrobiological studies and ongoing efforts to build a prototype SFE–SFC–MS system for use in space. The possible use of SF–CO2 technologies seem boundless given the breadth of applications described during the three‑day event. We are looking forward to the next SFC conference instalment, which is being planned for Prague, Czech Republic, from 19–22 October 2020 (see https://greenchemistrygroup.org/ for details)!

References

1. E.L. Regalado et al., Journal of Chromatography B1080, 42–49 (2018).
2. Y. Wang and S.V. Olesik, Anal. Chem.91, 935–942 (2019).

Eric Seest is a member of the Green Chemistry Group board of directors, which is a volunteer group of dedicated academics, industrial scientists, and leaders from sponsor organizations. The GCG mission is to advance the use of SFC and SFE and build maximum interaction within this growing community by hosting annual international conferences. He is also a senior research scientist and analytical chemist in Discovery Chemistry at Eli Lilly involved with analytical and preparative chromatography support and research.

E-mail:register@greenchemistrygroup.orgWebsite:https://greenchemistrygroup.org/