In of a pressure programmer into an LC set-up,

In
1962 the chromatographic technique called SFC came into existence. From there
onwards this technique has improvised and is widely used over a wide spectrum
in analytical purposes due to its exceptional performance. In the 1960s gas chromatography (GC) was considered
the premier mode of chromatography due to the high efficiency of the technique
especially when coupled with the power of flame ionization detection (FID).
Analyte volatility as well as thermal stability where two of the limitations of
GC that led researchers to pursue other alternatives for separations. Ernst
Klesper’s article entitled “High Pressure Gas Chromatography Above Critical
Pressure” published in 1962 was the first account of what is known today as SFC
and combated the analyte stability limitation of GC (Klesper et al.,1962).This  work set
the stage for the evolution of SFC.

Jentoft
and Gouw at Chevron continued the advancement of SFC thorough incorporation of
a pressure programmer into an LC set-up, utilizing high-pressure nitrogen as
the pressure source, enabling the execution of an SFC pressure gradient. Several of the individual peaks were captured post UV detection
and chromatographed a second time to ensure they were not artifacts, very
similar to Klesper’s confirmational analysis after the inaugural SFC separation
(Klesper et al., 1962). The ability to deliver
pressure ramps to control elution provided a “new” mechanism to increase peak
capacity, while operating at linear velocities up to an order of magnitude
greater than those in LC and at the time SFC was suddenly being compared and
competing with not only GC, but also LC. Capillary SFC originated through the
work of Milos Novotny and Milton Lee who believed the pressure drop experienced
in 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 would
maintain constant pressure across the entire column length and detector as well
as use a stationary phase of minimal thickness to reduce resistance to mass
transfer. The utilization of SFC for chiral analysis and purification was
considered by many to be the most dominant application of SFC, at least in the
pharmaceutical industry, during its commercialization. Mourier postulated that
supercritical carbon dioxide, possessing the relative polarity of hexane, could
be substituted for hexane (or other nonpolar solvents) in a typical chiral
chromatographic system (Mourier et al., 1985). The transition from capillary
SFC to packed column SFC experienced in the 1990s reflects the expanding
molecular diversity encountered at the time as well as the changing mindset on
the general working range of SFC. Capillary SFC was widely successful for the
analysis of relatively nonpolar compounds that exceeded the volatility range of
traditional GC and consequently was treated more as an extension of GC (Taylor,2013).
Alternatively packed column SFC was found to provide superior performance for
polar compounds and was thus treated as a viable alternative to normal phase
HPLC (Berger,1993).

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