LARRY MILLER
Amgen, 360 Binney Street, Cambridge, MA 02142 USA

Abstract

Small molecule purification is a critical component of pharmaceutical R&D. Supercritical Fluid Chromatography (SFC) is a chromatographic technique used for small molecule analysis and purification which utilizes a carbon dioxide based mobile phase. The low viscosity and high diffusivity of carbon dioxide allows higher flowrates than HPLC. In addition the use of carbon dioxide based mobile phases reduces solvent requirements and waste generation often resulting in a greener separation process compared to HPLC. This article provides an overview of SFC technology and discusses how the technique is revolutionizing small molecule purification in pharmaceutical R&D. Examples of both chiral and achiral SFC purifications from a pharmaceutical discovery laboratory are presented to show the advantages of SFC over HPLC.

INTRODUCTION

For over forty years HPLC has been the most frequently used technique for purification in support of pharmaceutical R&D. Recently, supercritical fluid chromatography (SFC) has become a viable alternative for the purification of small molecules during drug discovery (1-5). With SFC a majority of the solvent in the mobile phase, usually greater than 60%, is liquid CO₂. Carbon dioxide has a critical temperature of 31 C and a critical pressure of 73 atm. Above this point it exists as a supercritical fluid and has properties intermediate between a liquid and a gas. The low viscosity and high diffusivity of a carbon dioxide based mobile phase allows higher flow rates relative to liquid chromatography, resulting in shorter run times and increased efficiencies. This is illustrated in the Van Deemter curve for HPLC and SFC shown in Figure 1. A Van Deemter curve shows the effect of increasing flow rate (linear velocity, u) on column efficiency (plate height, H). Using the same particle size column HPLC and SFC will generate equivalent efficiencies (~ 10 um in this example). With HPLC using a five micron particle size column, maximum eff ...