oil extraction and analysis phần 3 docx

Chapter 3

Accelerated Solvent Extraction

Devanand Luthriaa,*, Dutt Vinjamoorib, Kirk Noelc, and John Ezzelld

aUSDA/ARS/FCL, Beltsville, MD 20705; bMonsanto, St. Louis, MO 63167; cMonsanto, Ankeny,

IA 50021; dDionex Corporation, Salt Lake City Technical Center, Salt Lake City, UT 84119

Abstract

Extraction of solid and semisolid samples using liquid solvents is a common practice

in nearly every analytical laboratory. Years of empirical testing have resulted in

rugged and reproducible methodologies for a wide range of analyte classes. However,

recent concerns regarding the volumes of organic solvents used (with the associated

human exposure), along with increased purchase and disposal costs, have emphasized

the need for more efficient sample extraction methods. In response to these concerns,

accelerated solvent extraction (ASE®, Dionex Corporation, Salt Lake City, UT) was

introduced. Since its introduction in 1995, ASE has grown rapidly as an accepted

alternative to traditional extraction methods. Accelerated solvent extraction takes

advantage of the enhanced solubilities that occur as the temperature of a liquid solvent

is increased. Increasing the temperature of solvent results in a decrease in viscosity,

allowing better penetration of the sample matrix. In addition, analyte diffusion from

the sample matrix into the solvent and overall solvent capacity are increased. In tradi￾tional Soxhlet extraction, the solvent that comes into contact with the sample has

passed through a cooling condenser, and is therefore close to room temperature at the

point of contact. The time required to complete Soxhlet extractions ranges from 6 to

48 h. Semi-automated Soxhlet systems that immerse the sample into boiling solvent

are available. This increase in the temperature of the contacting solvent shortens the

required extraction time to ~2 h. Using these systems, a further increase in tempera￾ture beyond the boiling point of the solvent is not possible due to solvent loss because

these systems operate at atmospheric pressure. However, a continued increase in the

temperature should continue to enhance the extraction process. This can be accom￾plished by applying pressure, which maintains the solvent in its liquid state beyond its

atmospheric boiling point. This is the theoretical basis for ASE technology and repre￾sents the next step in liquid solvent extraction of environmental samples. There are, of

course, limits to which raising the temperature is feasible, due to thermal degradation

concerns. However, as evidenced by data published to date, there is room to continue

raising the temperature, thereby improving the extraction efficiency, without risking

analyte degradation in environmental samples. As the extraction efficiency is

*The research work was done at Monsanto.

Copyright © 2004 AOCS Press