The past and future development of analytical supercritical fluid extraction (SFE) is traced in terms of experimental strategies,
applications, vendor support, and timely acceptance of the existing technology. The current state of the art is compared with
research activity in the 1980s. New vendor activity, in terms of automation and hyphenation with chromatographic separations,
For someone who has between 1980 and 2000 (i) published hundreds of peer-reviewed manuscripts on analytical supercritical
fluid extraction (SFE) for chromatographic analysis and isolation of additives, neutraceuticals, pollutants, and so on; (ii)
co-taught short courses on SFE in Europe, South America, North America, and Asia; and (iii) guest lectured numerous times
on an ACS short course entitled "Sample Preparation for Chromatography" organized by Harold McNair, the current state of SFE
does sometimes sound as if we are going back to the future.
A sample preparation survey in 2002 suggested that SFE was being used by less than 2% of respondents. A similar survey repeated
in 2012 showed that the use of SFE had only doubled, despite the obvious overall advantages of supercritical carbon dioxide-based
The situation now is different from the 1980s because instrumentation is more robust and engineering applications in food,
pharmaceuticals, bioanalytical, and materials are more plentiful. On the other hand, analytical SFE has not changed very much
because there is a lack of support from major vendors and newcomers to the technology are forced to re-learn SFE history and
protocols that have been around for years.
To put it in perspective, consider a report of the 9th Annual Waste Testing and Quality Assurance Symposium held in Crystal
City, Virginia (USA) dated 23 July 1993 by Robert Stevenson, entitled "SFE in Purgatory". He writes: "SFE generates high interest
in surveys, but low sales. All the necessary groundwork seems to be there, but where are the orders? Where are the users?"
Parenthetically, at about this same time, it was reported by experts in the field that "SFE is over the hump and that it is
rapidly developing into the extraction method of choice for the 21st century with more and more laboratories around the U.S.
and the world embracing it for sample cleanup and sample preparation" (2). No doubt this assessment was partly based upon
the fact that between 1987 and 1989 more than 100 papers were published concerning the use of supercritical fluids for extraction
Possible explanations for the perceived current lack of enthusiastic growth among analytical SFE practitioners are the limited
number of suppliers that market the technology today and the exodus of vital vendors such as Hewlett Packard, Suprex, Dionex,
ISCO, and Lee Scientific from the field around the turn of the century. A somewhat similar vendor exodus occurred slightly
earlier in time in the field of SFC but, thanks to the efforts of Terry Berger and associates, the drought was not as long-lived,
and SFC has survived to "live" again. Hopefully many of the developments that benefited the SFC community will now foster
further development of analytical SFE. Currently, there appears to be a small core of established vendors, as well as relatively
new vendors, that are committed to making analytical SFE a viable method for sample preparation prior to chromatographic analysis.
Today these vendors are Jasco, Inc., Supercritical Fluid Technologies, Inc., Waters Corp., Applied Separations, and Taiwan
The problem of long-term analytical SFE exploitation may also be in part an education issue as evidenced by the failure of
academicians to both learn, explore, and apply the technology in junior-senior chemistry laboratory courses at the university
level even when new instrumentation is made available. Furthermore, the perceived remarkable speed and versatility of SFE
often tempts beginners to look for shortcuts rather than to examine the application systematically (4). A hasty approach to
method development often leads to unexpected problems and analytical SFE is a sophisticated technology that is best mastered
by adhering to the rigour required when developing any analytical method. It should be remembered that while there has been
and continues to be a plethora of applications in engineering, SFE was only developed as an analytical technique in the mid-1980s.
To gain some appreciation for past developments (5–10), the reader is encouraged to read the numerous reviews that have appeared
recently as well as in the older literature. Look for details concerning the pros and cons of: (a) On-line or off-line coupling
with a variety of separation techniques; (b) dynamic versus static extraction protocols; (c) solid-phase or liquid-phase extract
trapping; (d) modifier addition to the matrix versus modifier addition to the fluid; (e) adsorbent in the extraction thimble
to retain unwanted compounds such as water; (f) experimental strategies for extracting analytes from solids, gels, creams,
sludges, liquids, and so on; and (g) polar-modified, high density CO2.
The use of SFE in modern process engineering applications was initiated in Germany during the late 1960s. These early studies
showed that SFE was a viable alternative to distillation and solvent extraction processes. Furthermore, it allowed the processing
of substances whose extraction could be adversely affected by high temperatures and the presence of solvent residuals. SFE
using CO2 is now an established industrial process for the production of high-value natural products such as hops, decaffeinated tea
and coffee, herbs and spices, medicinal herbs, seeds, and marine oils. Further examples include extraction processes where
an undesirable component is removed from the matrix, such as pesticides from medicinal herbs. In ancillary fashion, SFE processing
continues to find applications as shown by the variety of lipophilic extracts available as commercial products such as polyunsaturated
fatty acid esters derived from fish oils, neat and roasted sesame seed oil, cranberry seed-based oils, oils high in n-3 and
n-6 fatty acid content, and pumpkin seed extracts coupled with more traditional SFE-derived products such as decaffeinated
The scope of this report is therefore limited to advances concerning analytical SFE. The goals of this article are to both
describe the current state of the art in relation to new instrumentation and to address unique extraction strategies, theories,
and applications. In addition, interesting hyphenations of analytical SFE with chromatography and spectroscopy that have been
reported during the past three years, as well as new aids for achieving successful extraction with CO2 will be considered.