|Luthria, Devanand - Dave|
Submitted to: American Oil Chemists' Society Meeting
Publication Type: Book / Chapter
Publication Acceptance Date: 2/10/2004
Publication Date: 5/1/2004
Citation: Luthria, D.L., Vinjamoori, D., Noel, K., Ezzell, J. 2004. Accelerated solvent extraction. Oil Extraction and Analysis: In: Luthria, D.L. editor. Oil Extraction and Analysis: Critical Issues and Compartative Studies. Champaign, IL: Critical Issues and Comparative Studeis. Champaign, IL: AOCS Press. p. 25-38.
Technical Abstract: Extraction of solid and semi-solid 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 (ASE7) has been introduced. Since its introduction in 1995, ASE has grown rapidly as an accepted alternative to traditional extraction methods. Accelerated solvent extraction takes advantage of enhanced solubilities which 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 traditional Soxhlet extraction, the solvent which 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 hours. Semi-automated Soxhlet systems which immerse the sample into boiling solvent are available. This increase in the temperature of the contacting solvent shortens the required extraction time to approximately 2 hours. Using these systems, a further increase in temperature beyond the boiling point of the solvent is not possible due to solvent loss, since these systems operate at atmospheric pressure. However, a continued increase in the temperature should continue to enhance the extraction process. This can be accomplished by applying pressure, which maintains the solvent in its liquid state beyond its atmospheric boiling point. This is the theoretical basis for accelerated solvent extraction technology and represents 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 increased, the time required to perform extractions and the amount of solvent needed is reduced. When performing ASE, a 10 gram sample can be extracted in approximately 12 minutes using 12-15 mL of solvent. As the sample size is increased (33 mL volume max.) the amount of solvent used increases proportionally (45-50 mL max.) but the total extraction time remains unchanged. The short extraction times and small solvent usage make this technique amenable to automation. Samples loaded into stainless steel extraction vessels (11, 22 or 33 mL internal volume) are extracted sequentially into standard 40 or 60 mL glass collection vials. Following extraction, the spent sample remains in the cell, while the extract is immediately ready for processing. The system is designed to extract up to 24 samples unattended. Since existing solvent based extraction methods can be readily transferred to ASE technology, methods development is greatly simplified. Existing sample preparation and post extraction processing steps remain in place, as the extracts generated by ASE will be very nearly the same composition as the existing solvent based extraction technique. The large range of polarities and solvent strengths available when using liquid solvents, including solvent mixtures, allows a high degree of flexibility and selectivity when developing methods for new sample matrices.