Talanta 53 (2001) 771–782
Supercritical fluid extraction in herbal and natural product
studies — a practical review
Qingyong Lang, Chien M. Wai *
Department of Chemistry, Uni?ersity of Idaho, Moscow, ID 83844-2343, USA
Received 26 June 2000; accepted 10 August 2000
Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide
acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compounds
in many analytical and industrial processes. In the past decade, SFE has been applied successfully to the extraction
of a variety of organic compounds from herbs and other plants. This review article presents the practical aspects of
SFE applications in sample preparation, selection of modifiers, collection methods, on-line coupling techniques,
means for avoiding mechanical problems, and approaches to optimization of SFE conditions. SFE can also be used
to clean up pesticides from herb medicines. SFE processes can be modeled to acquire useful information for better
understanding of the extraction, mechanisms and optimization of the extraction procedures. With increasing public
interest in natural products, SFE may become a standard extraction technique for studying herbal, food and
agricultural samples. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: SFE; Review; Herbal; Natural product; Modifier; Pesticide; On-line coupling
With the fast development of modern chro-
matographic and spectroscopic techniques, the
chemistry of natural products has made great
progress during the past decades . With better
understanding of natural products, an increasing
number of people has become interested in study-
ing the active natural products as medicines , as
food additives  or as natural pesticides . The
pharmaceutical studies of natural products are
one of the most interesting and active research
areas. Clinical tests have indicated that certain
herbal plants do contain pharmacologically active
ingredients that are effective for treating some
difficult diseases. For example, taxol, a diter-
penoid isolated from the bark of the Pacific yew
tree, showed promising results for the treatment
of ovarian, breast, lung and skin cancers [5–7].
Since pharmacologically active compounds in
herbal plants usually are in low concentrations, a
great deal of research has been done to develop
more effective and selective extraction methods
for recovery of these compounds from the raw
materials. For conventional extraction methods
* Corresponding author. Fax: +1-208-8856173.
E-mail address: firstname.lastname@example.org (C.M. Wai).
0039-9140/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
Q. Lang, C.M. Wai / Talanta 53 (2001) 771–782772
such as hydrodistillation (steam distillation) and
parameters to control the selectivity of the extrac-
tion processes. Therefore, developing alternative
extraction techniques with better selectivity and
efficiency are highly desirable. Consequently, su-
percritical fluid extraction (SFE) as an environ-
technique for solid materials was introduced and
extensively studied for separation of active com-
pounds from herbs and other plants .
The high solvation power of supercritical fluids
(SF) was first reported over a century ago .
Demonstration of SFE technology for industrial
applications was reported by Zosel at the Max
Planck Institute for Kohlemforschung in 1969
. In recent years, SFE has received a great deal
of attention as the full potential of this technology
in analytical applications has begun to emerge
[11–13]. Today, SFE has become an acceptable
extraction technique used in many areas. SFE of
active natural products from herbal, or more gen-
erally, from plant materials has become one of the
most important application areas [14,15]. With
the increasing public interest in herbal medicines
and natural products, numerous SFE-related re-
search papers in herbal or natural product studies
have been published in recent years. In this arti-
cle, a practical review of the recent development
in this area will be presented and some of the
interesting research results published within the
last decade will be discussed.
2. Major advantages of SFE technique
Because SFE has several distinct properties, it is
regarded as a promising alternative technique to
conventional solvent extraction methods. Some of
its major advantages are summarized as follows.
(1) SFs have relatively lower viscosity and higher
diffusivity (the diffusivity for SFs is ?10−4cm2
s−1and for liquid solvents is ?10−5cm2s−1).
Therefore, it can penetrate into porous solid ma-
terials more effectively than liquid solvents and,
consequently, it may render much faster mass
transfer resulting in faster extractions. For in-
stance, with comparable or better recoveries, the
extraction time could be reduced from hours or
days in a liquid–solid extraction (L–S) to a few
tens of minutes in SFE [16–19]. (2) In SFE, a
fresh fluid is continuously forced to flow through
the samples; therefore, it can provide quantitative
or complete extraction . (3) In SFE, the solva-
tion power of the fluid can be manipulated by
changing pressure (P) and/or temperature (T);
therefore, it may achieve a remarkably high selec-
tivity. This tunable solvation power of SFs is
particularly useful for the extraction of complex
samples such as plant materials . One good
example is the selective extraction of a vindoline
component from among more than 100 alkaloid
compounds from the leaves of Catharanthus
roseus . (4) Solutes dissolved in supercritical
CO2can be easily separated by depressurization.
Therefore, SFE can eliminate the sample concen-
tration process, which usually is time-consuming
and often results in loss of volatile components
. (5) SFE usually is performed at low tempera-
tures, so it may be an ideal technique to study
thermally labile compounds [23–25] and may lead
to the discovery of new natural compounds .
For example, when SFE was used to extract gin-
ger, many undesirable reactions such as hydroly-
sis, oxidation, degradation and rearrangement
could be effectively prevented. Therefore, the
common difficulties for quality assessment in clas-
sical hydrodistillation could be avoided in SFE
. (6) Compared with the 20–100 g of samples
typically required in L–S methods, as little as
0.5–1.5 g of samples are needed in SFE methods
[18,28,29]. It has been reported that from only 1.5
g of fresh plant samples, more than 100 volatile
and semi-volatile compounds could be extracted
and detected by gas chromatography (GC)–mass
spectroscopy (MS), of which more than 80 com-
pounds were in sufficient quantity for accurate
quantifications . (7) SFE uses no or signifi-
cantly less environmentally hostile organic sol-
vents. A SFE method may need no or only a few
milliliters of an organic solvent while a typical
L–S extraction method would require tens to
hundreds of milliliters [16,30]. (8) SFE may allow
direct coupling with a chromatographic method,
which can be a useful means to extract and di-
rectly quantify highly volatile compounds [31–
Q. Lang, C.M. Wai / Talanta 53 (2001) 771–782781
 K.B.G. Torssel, Natural Product Chemistry, Swedish
Pharm. Society, Sweden, 1997.
 J. Greenwald, Time 152 (1998) 60.
 E. Anklam, H. Berg, L. Mathiasson, M. Sharman, F.
Ulberth, Food Addit. Contam. 15 (1998) 729.
 P. Ambrosino, R. Fresa, V. Fogliano, S.M. Monti, A.
Ritieni, J. Agric, Food Chem. 47 (1999) 5252.
 D.M. Heaton, K.D. Bartle, C.M. Rayner, A.A. Clifford,
J. HRC 16 (1993) 666.
 V. Vandana, A.S. Teja, L.H. Zalkow, Fluid Phase Equilb.
116 (1996) 162.
 M. Chun, H. Shin, H. Lee, Supercrit. Fluids 9 (1996) 192.
 W.K. Modey, D.A. Mulholland, M.W. Raynor, Phy-
tochem. Anal. 7 (1996) 1.
 J.B. Hannay, J. Hogarth, Proc. R. Soc. London A 29
 K. Zosel, Ger. Pat. 1 493 (1969) 190.
 B.A. Charpentier, in: M.R. Sevenants (Ed.), Supercritical
Fluid Extraction and Chromatography, (ACS Symposium
Series, No. 366), ACS, Washington, DC, 1987.
 R.M. Smith (Ed.), Supercritical Fluid Chromatography,
The Royal Society of Chemistry, London, 1988.
 J. Rein, C.M. Cork, K.G. Furton, J. Chromatogr. 545
 M.A. McHugh, V.J. Krukonis, Supercritical Fluid Ex-
traction, second ed., Butterworth-Heinemann, Boston,
 M.D. Luque de Castro, M. Valcarel, M.T. Tena, Analyt-
ical Supercritical Fluid Extraction, Springer, Berlin, 1994.
 J.R. Wheeler, M.E. McNally, J. Chromatogr. Sci. 27
 R. Marsili, D. Callahan, J. Chromatogr. Sci. 31 (1993)
 J.A. Henning, R.J. Core, J.L. Gardea-Torresdey, Crop
Sci. 34 (1994) 1120.
 L. Bru ¨hl, B. Mattha ¨us, Fresenius J. Anal. Chem. 364
 E.E. Stashenko, M.A. Puertas, M.Y. Combariza, J. Chro-
matogr. A 752 (1996) 223.
 E. Reverchon, G. Donsi, L.S. Osseo, Ind. Eng. Chem.
Res. 32 (1993) 2721.
 K.M. Song, S.W. Park, W.H. Hong, H. Lee, S.S. Kwak,
J.R. Liu, Biotechnol. Prog. 8 (1992) 583.
 S. Polesello, F. Lovati, A. Rizzolo, C. Rovida, J. HRC 16
 W.H.T. Pan, C.C. Chang, T.T. Su, F. Lee, M.R.S. Fuh,
Talanta 42 (1995) 1745.
 A. Dron, D.E. Guyer, C.T. Lira, J. Food Process. Eng. 20
 M.R.S. Fuh, W.H. Pan, C.M. Chuo, Am. Lab. 27 (1995)
 J.P. Bartley, P. Foley, J. Sci. Food Agric. 66 (1994) 365.
 S.B. Hawthorne, M. Riekkola, K. Serenius, Y. Holm, R.
Hiltunen, K. Hartonen, J. Chromatogr. 634 (1993) 297.
 J.H.Y. Vilegas, F.M. Lanc ¸as, W. Vilegas, G.L. Pozetti,
Phytochem. Anal. 4 (1993) 230.
 A. Otterbach, B.W. Wenclawiak, Fresenius J. Anal.
Chem. 365 (1999) 472.
 C.K. Huston, H. Ji, J. Agric. Food Chem. 39 (1991) 1229.
 T.J. Nielsen, I.M. Jagerstad, R.E. Oste, B.T.G. Sivik, J.
Agric. Food Chem. 39 (1991) 1234.
 R.M. Smith, M.D. Burford, J. Chromatogr. 600 (1992)
 W.K. Modey, D.A. Mulholland, H. Mahomed, M.W.
Raynor, J. Microcolumn Sep. 8 (1996) 67.
 Q.Y. Lang, C.M. Wai, Yankuang Ceshi 17 (1998) 216.
 S.F.Y. Li, C.O. Ong, M.L. Lee, H.K. Lee, J. Chro-
matogr. 515 (1990) 515.
 G. Klink, A. Buchs, F.O. Gulacar, Org. Geochem. 21
 D. Bro ¨ll, C. Kaul, A. Kra ¨mer, P. Krammer, T. Richter,
M. Jung, H. Vogel, P. Zehner, Angrew. Chem. Int. Ed. 38
 A. Basile, M.M. Jime ´nez-Carmona, A.A. Clifford, J.
Agric. Food Chem. 46 (1998) 5205.
 A. Ammann, D.C. Hinz, R.S. Addleman, C.M. Wai,
B.W. Wenclawiak, Fresenius J. Anal. Chem. 364 (1999)
 A.A. Clifford, A. Basile, S.H.R. Al-Saidi, Fresenius J.
Anal. Chem. 364 (1999) 635.
 C. Bicchi, P. Rubiolo, C. Frattini, P. Sandra, F. David, J.
Nat. Prod. 54 (1991) 941.
 M.K. Chun, H.W. Shin, H. Lee, Biotech. Technol. 8
 V. Lopez-Avila, J. Benedicto, J. HRC 20 (1997) 555.
 M. Ashraf-Khorassani, S. Gidanian, Y. Yamini, J. Chro-
matogr. Sci. 33 (1995) 658.
 S.R. Sargenti, F.M. Lanc ¸as, Chromatographia 5/6 (1997)
 M. Palma, L.T. Talor, R.M. Varela, S.J. Cutler, H.G.
Cutler, J. Agric. Food Chem. 47 (1999) 5044.
 Y.-C. Ling, H.-C. Teng, C. Cartwright, J. Chromatogr. A
835 (1999) 145.
 H. Miyachi, A. Manabe, T. Tokumori, Y. Sumida, T.
Yoshida, S. Nishibe, T. Agata, T. Nomura, T. Okuda,
Yakugaku. Zasshi 107 (1987) 435.
 M.C. Lin, M.J. Tsai, K.C. Wen, J. Chromatogr. A 830
 J.L. Janicot, M. Caude, R. Rosset, J.L. Veuthey, J.
Chromatogr. 505 (1990) 242.
 M.M. Sanagi, W.P. Hung, S.M. Yasir, J. Chromatogr. A
785 (1997) 361.
 S.H. Page, S.R. Sumpter, M.L. Lee, J. Microcolumn Sep.
4 (1992) 91.
 M. Ashraf-Khorassani, L.T. Taylor, Anal. Chim. Acta
347 (1997) 305.
 G.V.R. Rao, P. Srinivas, S.V.G.K. Sastry, M. Mukho-
padhyay, J. Supercrit. Fluids 5 (1992) 19.
 M. Verschuere, P. Sandra, F. David, J. Chromatogr. Sci.
30 (1992) 388.
Q. Lang, C.M. Wai / Talanta 53 (2001) 771–782782
 M. Ashraf-Khorassani, L.T. Taylor, M. Martin, Chro-
matographia 5/6 (1999) 287.
 L.A.F. Coelho, J.V. Oliveira, F.M. Lancas, J. HRC 20
 K.G. Miller, C.F. Poole, T.M.P. Chichila, J. HRC 18
 S.J. Lehotay, J. Chromatogr. A 785 (1997) 289.
 R.M. Weathers, D.A. Beckholt, A.L. Lavella, N.D.
Danielson, J. Liq. Chromatogr. Rel. Technol. 22 (1999)
 E. Iba ´n ˜ez, S. Lo ´pez-Sebastia ´n, E. Ramos, J. Tabera, G.
Reglero, J. Agric. Food Chem. 45 (1997) 3940.
 W.K. Modey, D.A. Mulholland, M.W. Raynor, J. Chro-
matogr. Sci. 34 (1996) 320.
 D.F.G. Walker, K.D. Bartle, D.G.P.A. Breen, A.A. Clif-
ford, S. Costiou, Analyst 119 (1994) 2789.
 N. Adasoglu, S. Dincer, E. Bolat, J. Supercrit. Fluids 7
 E. Stahl, A. Glatz, Fette Seifen Anstruich. 9 (1984) 346.
 Y.H. Choi, J. Kim, S.H. Jeon, K.P. Yoo, H.K. Lee,
Chromatographia 9/10 (1998) 695.
 J. Gawdzik, M. Mardarowicz, T. Wolski, J. HRC 19
 A. Birtigh, M. Johannsen, G. Brunner, J. Supercrit. Flu-
ids 8 (1995) 46.
 E. Iba ´n ˜ez, A. Oca, G. de Murga, S. Lo ´pez-Sebastia ´n, J.
Tabera, G. Reglero, J. Agric. Food Chem. 47 (1999)
 B.W. Wenclawiak, M. Krappe, A. Otterbach, J. Chro-
matogr. A 785 (1997) 263.
 C.M. Lino, M.I.N. da Silveira, J. Chromatogr. A 769
 F.M. Lanc ¸as, S.R. Rissato, M.S. Galhiane, J. HRC 21
 R. Stefani, M. Buzzi, R. Grazzi, J. Chromatogr. A 782
 S.J. Lehotay, A. Valverde-Garcia, J. Chromatogr. A 765
 W. Schmid, Nature 386 (1997) 755.
 G.P. Blanch, M.M. Caja, M.L.R. del Castillo, G. Santa-
Marı ´a, M. Herraiz, J. Chromatogr. Sci. 37 (1999) 407.
 E.D Ramsey, B. Minty, A.T. Rees, Anal. Commun. 9
 M. Poletto, E. Reverchon, Ind. Eng. Chem. Res. 35
 K.D. Bartle, A.A. Clifford, S.B. Hawthorne, J.J. Langen-
feld, D.J. Miller, R. Robinson, J. Supercrit. Fluids 3
 J.R. Dean, B. Liu, Phytochem. Anal. 11 (2000) 1.
 E. Reverchon, J. Supercrit. Fluids 10 (1997) 1.