In1962 the chromatographic technique called SFC came into existence. From thereonwards this technique has improvised and is widely used over a wide spectrumin analytical purposes due to its exceptional performance. In the 1960s gas chromatography (GC) was consideredthe premier mode of chromatography due to the high efficiency of the techniqueespecially when coupled with the power of flame ionization detection (FID).
Analyte volatility as well as thermal stability where two of the limitations ofGC that led researchers to pursue other alternatives for separations. ErnstKlesper’s article entitled “High Pressure Gas Chromatography Above CriticalPressure” published in 1962 was the first account of what is known today as SFCand combated the analyte stability limitation of GC (Klesper et al.,1962).This work setthe stage for the evolution of SFC.Jentoftand Gouw at Chevron continued the advancement of SFC thorough incorporation ofa pressure programmer into an LC set-up, utilizing high-pressure nitrogen asthe pressure source, enabling the execution of an SFC pressure gradient. Several of the individual peaks were captured post UV detectionand chromatographed a second time to ensure they were not artifacts, verysimilar to Klesper’s confirmational analysis after the inaugural SFC separation(Klesper et al.
, 1962). The ability to deliverpressure ramps to control elution provided a “new” mechanism to increase peakcapacity, while operating at linear velocities up to an order of magnitudegreater than those in LC and at the time SFC was suddenly being compared andcompeting with not only GC, but also LC. Capillary SFC originated through thework of Milos Novotny and Milton Lee who believed the pressure drop experiencedin packed column SFC had “disastrous consequences as far as the column efficiency goes”(Novotny et al.,1981).These groups sought to design an SFC system that wouldmaintain constant pressure across the entire column length and detector as wellas use a stationary phase of minimal thickness to reduce resistance to masstransfer.
The utilization of SFC for chiral analysis and purification wasconsidered by many to be the most dominant application of SFC, at least in thepharmaceutical industry, during its commercialization. Mourier postulated thatsupercritical carbon dioxide, possessing the relative polarity of hexane, couldbe substituted for hexane (or other nonpolar solvents) in a typical chiralchromatographic system (Mourier et al., 1985).
The transition from capillarySFC to packed column SFC experienced in the 1990s reflects the expandingmolecular diversity encountered at the time as well as the changing mindset onthe general working range of SFC. Capillary SFC was widely successful for theanalysis of relatively nonpolar compounds that exceeded the volatility range oftraditional GC and consequently was treated more as an extension of GC (Taylor,2013).Alternatively packed column SFC was found to provide superior performance forpolar compounds and was thus treated as a viable alternative to normal phaseHPLC (Berger,1993).
