Chapter 6
Pressurized Water Extraction: Resources and Techniques for Optimizing Analytical Applications
Downloaded by NORTH CAROLINA STATE UNIV on December 4, 2012 | http://pubs.acs.org Publication Date: January 6, 2006 | doi: 10.1021/bk-2006-0926.ch006
Jerry W . King Department of Chemical Engineering, University of Arkansas, 3202 Bell Engineering Center, Fayetteville, AR 72701
Pressurized hot water extraction above and below the boiling point of water has been demonstrated to be an effective analytical technique. However optimization of this type of extraction often is empirical in approach and fails to take advantage of experimental findings in associated fields or theoretical correlations. In this presentation it will be shown that contributions from four areas can be utilized in the design and optimization of hot water extraction processes: (1) scaled— up processing applications, (2) sub-critical water chromatography, (3) solute (analyte) solubility predictive schemes, and (4) increase of analyte flux rates from sample matrices via mass transport design. The selectivity of pressurized hot water extraction can be maximized not only by regulating the dielectric constant of water, but employing principles noted in the four above areas. Fractionation of solutes then becomes feasible using hot water alone, or with the aid of an associated technique, such as supercritical fluid extraction with SC-CO . Examples will be cited of pesticide, essential oil, herbal mixtures, anthocyanins, and hydrocarbon separation using hot water media. The effect of hot water on common food matrices containing lipids/oils, carbohydrates, and proteins will be cited utilizing examples from the 2
© 2006 American Chemical Society
In Modern Extraction Techniques; Turner, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.
79
80
Downloaded by NORTH CAROLINA STATE UNIV on December 4, 2012 | http://pubs.acs.org Publication Date: January 6, 2006 | doi: 10.1021/bk-2006-0926.ch006
literature, and how this effect can be both advantageous or a disadvantage in analyzing food or agricultural samples. Finally, several examples will be presented which illustrate the application of hot water extraction to food and agricultural analyses.
Introduction The use of environmental compatible solvent media that is benign toward laboratory workers has received extensive study over the past decade. Such "green" solvents frequently consist of carbon dioxide in either its supercritical or sub-critical states, the use of environmental-benign solvents such as ethanol, and more recently compressed water above its boiling point under pressure (/). This latter medium, also referred to as subcritical water (sub-H 0), complements the C 0 - based technologies in providing the analyst with both a non-polar and polar solvent medium whose solvent power can be regulated by the manipulation of temperature and pressure (2,5) . Subcritical water is readily available, non toxic, and inexpensive; and is generally defined as water under 250°C and pressures less than 40 atm (4MPa). However, within this temperature and pressure range its solvent power and polarity can be varied considerably, permitting control of its dielectric constant (4) and reduction in its cohesional energy density (5). The utility of sub-H 0 extends into several areas of application, including the following: 2
2
2
•
Selective extraction solvent (SWE - subcritical water extraction)
•
Fractionating agent (SWF - subcritical water fractionation)
•
Reaction medium (SWR - subcritical water reaction)
•
Analytical or chromatographic agent
•
Degradation agent
•
Sterilization agent
•
Modifying agent for materials
Many of these areas of application relate to using sub-H 0 in various processing schemes, as reported by Clifford and others (tf-
