Elsevier

Talanta

Volume 53, Issue 4, 5 January 2001, Pages 771-782
Talanta

Supercritical fluid extraction in herbal and natural product studies — a practical review

https://doi.org/10.1016/S0039-9140(00)00557-9Get rights and content

Abstract

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.

Introduction

With the fast development of modern chromatographic and spectroscopic techniques, the chemistry of natural products has made great progress during the past decades [1]. With better understanding of natural products, an increasing number of people has become interested in studying the active natural products as medicines [2], as food additives [3] or as natural pesticides [4]. 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 diterpenoid isolated from the bark of the Pacific yew tree, showed promising results for the treatment of ovarian, breast, lung and skin cancers [5], [6], [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 such as hydrodistillation (steam distillation) and solvent extraction, there are few adjustable parameters to control the selectivity of the extraction processes. Therefore, developing alternative extraction techniques with better selectivity and efficiency are highly desirable. Consequently, supercritical fluid extraction (SFE) as an environmentally responsible and efficient extraction technique for solid materials was introduced and extensively studied for separation of active compounds from herbs and other plants [8].

The high solvation power of supercritical fluids (SF) was first reported over a century ago [9]. Demonstration of SFE technology for industrial applications was reported by Zosel at the Max Planck Institute for Kohlemforschung in 1969 [10]. 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], [12], [13]. Today, SFE has become an acceptable extraction technique used in many areas. SFE of active natural products from herbal, or more generally, 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 research papers in herbal or natural product studies have been published in recent years. In this article, 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.

Section snippets

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 ∼10−4 cm2 s−1 and for liquid solvents is ∼10−5 cm2 s−1). Therefore, it can penetrate into porous solid materials more effectively than liquid solvents and, consequently, it may render much faster mass transfer

Fluid materials and modifiers

Of all the gases and liquids studied, CO2 remains the most commonly used fluid for SFE applications because of its low critical constants (Tc=31.1°C; Pc=72.8 atm), its non-toxic and non-flammable properties, and its availability in high purity with low cost. Supercritical CO2 has good solvent properties for extraction of non-polar compounds such as hydrocarbons, while its large quadrupole moment also enables it to dissolve some moderately polar compounds such as alcohols, esters, aldehydes and

Sample preparation

In SFE of natural products, fresh plant materials are frequently used if the desired compounds are volatile or labile. When a fresh sample is extracted, its high moisture content can cause mechanical difficulties such as restrictor clogging due to ice formation. One simple yet effective way to avoid such problems is to mix the sample with anhydrous Na2SO4. Anhydrous Na2SO4 can improve SFE results because (1) it can provide better contact between SFs and samples; (2) it can reduce the dead

Extraction conditions

For successful SFE, several factors must be taken into consideration prior to the experiments. These factors include the type of sample, method of sample preparation, type of fluid, choice of modifiers, method of fluid feeding, and extraction conditions including pressure, temperature, flow rate and extraction time. In order to optimize the SFE conditions, a statistical experimental design based on a ‘second order central composite design’ was used and reported by Adasoglu et al. [65].

In most

Collection methods

In SFE of natural products, a commonly used collection method is to trap the extract in a liquid solvent such as CH2Cl2 [28] or ethyl acetate [59]. Keeping the collection vial in water at room temperature was found helpful in increasing the recovery of kava lactones [44]. Under cooling conditions during expansion of a fluid, different collection solvents may show different collection efficiencies. For instance, as the collection vial was cooled to −8°C, CH2Cl2 and acetone would still give

Clean-up of pesticides from herbal plants and other samples

In addition to extracting desired compounds from plants, another very interesting application of the SFE technique is the extraction or clean up of pesticides from natural products including herbal medicines [48], [59], [72], [73], [74], [75]. Because the natural resource of medicinal plants is limited, manufacturers usually get their raw materials through cultivation of the plants. For instance, millions of ginkgo trees have been cultivated in Europe, North America and China [76]. The

On-line fractionation and coupling with chromatographic methods

On-line fractionation is another distinctive advantage of SFE. By manipulating the SFE conditions, it is feasible to separate the extracted compounds into two to more groups. For example, in SFE of Thymus mastichina L., Blanch et al. [77] used two on-line separation vessels to obtain the less and the medium volatile fractions (temperature and pressure were set at 50°C, 150 bar and 25°C, 50 bar, respectively) and a glass liner of PTV with a 22.5-mg plug of Tenax TA as adsorbent to collect the

SFE modeling

Another distinguished advantage of SFE methods is that through modeling, one can obtain more useful information than it can be obtainable from conventional extraction methods. Modeling SFE processes can help to better understand the extraction mechanisms and quickly optimize the extraction conditions. A large amount of research has been done in this area [5], [21], [62], [63], [79]. Discussed below is one simple but practically useful model — the hot-ball model, which was developed by Bartle et

Conclusion

Several years ago, Modey et al. summarized the applications of SFE in different classes of natural products such as carotenoids, lipid materials, flavor and fragrance compounds, triterpenes and sterols, alkaloids, mycotoxins and others [8]. In another review paper, Reverchon mainly focused on the SFE of essential oil and related compounds [82]. This review article presents the practical aspects of SFE such as modifiers, sample preparation, special considerations for collection, modeling, and as

References (82)

  • V. Vandana et al.

    Fluid Phase Equilb.

    (1996)
  • M. Chun et al.

    Supercrit. Fluids

    (1996)
  • J. Rein et al.

    J. Chromatogr.

    (1991)
  • E.E. Stashenko et al.

    J. Chromatogr. A

    (1996)
  • W.H.T. Pan et al.

    Talanta

    (1995)
  • S.B. Hawthorne et al.

    J. Chromatogr.

    (1993)
  • R.M. Smith et al.

    J. Chromatogr.

    (1992)
  • S.F.Y. Li et al.

    J. Chromatogr.

    (1990)
  • G. Klink et al.

    Org. Geochem.

    (1994)
  • Y.-C. Ling et al.

    J. Chromatogr. A

    (1999)
  • M.C. Lin et al.

    J. Chromatogr. A

    (1999)
  • M. Ashraf-Khorassani et al.

    Anal. Chim. Acta

    (1997)
  • G.V.R. Rao et al.

    J. Supercrit. Fluids

    (1992)
  • S.J. Lehotay

    J. Chromatogr. A

    (1997)
  • N. Adasoglu et al.

    J. Supercrit. Fluids

    (1994)
  • A. Birtigh et al.

    J. Supercrit. Fluids

    (1995)
  • B.W. Wenclawiak et al.

    J. Chromatogr. A

    (1997)
  • C.M. Lino et al.

    J. Chromatogr. A

    (1997)
  • R. Stefani et al.

    J. Chromatogr. A

    (1997)
  • S.J. Lehotay et al.

    J. Chromatogr. A

    (1997)
  • K.D. Bartle et al.

    J. Supercrit. Fluids

    (1990)
  • E. Reverchon

    J. Supercrit. Fluids

    (1997)
  • K.B.G. Torssel

    Natural Product Chemistry

    (1997)
  • J. Greenwald

    Time

    (1998)
  • E. Anklam et al.

    Food Addit. Contam.

    (1998)
  • P. Ambrosino et al.

    Food Chem.

    (1999)
  • D.M. Heaton et al.

    J. HRC

    (1993)
  • W.K. Modey et al.

    Phytochem. Anal.

    (1996)
  • J.B. Hannay et al.

    Proc. R. Soc. London A

    (1879)
  • K. Zosel, Ger. Pat. 1 493 (1969)...
  • B.A. Charpentier
  • M.A. McHugh et al.

    Supercritical Fluid Extraction

    (1994)
  • M.D. Luque de Castro et al.

    Analytical Supercritical Fluid Extraction

    (1994)
  • J.R. Wheeler et al.

    J. Chromatogr. Sci.

    (1989)
  • R. Marsili et al.

    J. Chromatogr. Sci.

    (1993)
  • J.A. Henning et al.

    Crop Sci.

    (1994)
  • L. Brühl et al.

    Fresenius J. Anal. Chem.

    (1999)
  • E. Reverchon et al.

    Ind. Eng. Chem. Res.

    (1993)
  • K.M. Song et al.

    Biotechnol. Prog.

    (1992)
  • S. Polesello et al.

    J. HRC

    (1993)
  • Cited by (0)

    View full text