Among the different extraction techniques used at analytical and preparative scale, supercritical fluid extraction (SFE) is one of the most used. This review covers the most recent developments of SFE in different fields, such as food science, natural products, by-product recovery, pharmaceutical and environmental sciences, during the period 2007-2009. The revision is focused on the most recent advances and applications in the different areas; among them, it is remarkable the strong impact of SFE to extract high value compounds from food and natural products but also its increasing importance in areas such as heavy metals recovery, enantiomeric resolution or drug delivery systems.

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ABSTRACT.The improvement of sample preparation and extraction techniques for natural bioactive compounds determinations is of great importance nowadays. New concepts are being introduced in this field, not only related to enhancement of extraction efficiencies but also related to environmental impact. This evolution towards Green Chemistry is pushing to new extraction and sample preparation processes that should be faster, more reproducible and more environmentally friendly. In this context, compressed fluidsbased sample preparation techniques (such as supercritical fluid extraction and pressurized liquid extraction) are demonstrating good capabilities. In this review, an updated knowledge on the techniques will be presented together with the main technical developments and the most notable recent applications for the extraction of bioactive compounds.Keywords: bioactive compounds, natural samples, plants, agricultural by-products, pressurized liquid extraction, supercritical fluid extraction, subcritical water extraction Abbreviations: ASE, accelerated solvent extraction; DHA, docosahexaenoic acid; EAE, enzyme-assisted extraction; EPA, eicosapentaenoic acid; IL, ionic liquids; MIP, molecular imprinted polymers; PFE, pressurized fluid extraction; PHSE, pressurized hot solvent extraction; PHWE, pressurized hot water extraction; PLE, pressurized liquid extraction; PLPW, pressurized low polarity water extraction; n-3 PUFA, n-3 polyunsaturated fatty acid; RAM, restricted access media; scCO2, supercritical CO2; SFE, supercritical fluid extraction; SHWE, superheated water extraction; SPE, solid Published in TrAC. Trends in analytical chemistry [0165-99362012 vol:43 pg:67 -83 http://dx.doi.org/10.1016/j.trac.2012.12.008 3 phase extraction; SWE, subcritical water extraction; TG, triglycerides; UAE, ultrasound assisted extraction; WEPO, water extraction and particle formation on-line.

This review attempts to provide an updated overview (including works published till June 2006) on the latest applications of compressed fluids as sample preparation techniques for food analysis. After a general review of the principles of supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE; also called accelerated solvent extraction, ASE or subcritical water extraction, SWE, when water is employed as extraction solvent), the principal applications of such techniques in the mentioned fields of food and natural products are described, discussing their main advantages and drawbacks.