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ARS Home » Research » Publications at this Location » Publication #106494
Title: THEORETICAL OPTIMIZATION OF ANALYTE COLLECTION IN ANALYTICAL SUPERCRITICAL FLUID EXTRACTION (SFE)

Author
item King, Jerry
item ZHANG, ZHOUYAO - MONSANTO, MT. PROSPECT,IL

Submitted to: Chromatographia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The isolation of chemical compounds for analysis usually requires their removal (extraction) from a sample of food, soil, etc. A technique know as analytical supercritical fluid extraction (SFE) provides an environmentally safe method of affecting the removal of these compounds using harmless pressurized carbon dioxide as an extraction solvent. Collection of the extract is critical as the extraction gas (carbon dioxide) is depressurize and few guidelines exist to optimizing this process. The research reported in this document provides some theoretical guidelines and calculations which permit the scientist to optimize the collection of the extract and its chemical compounds without resorting to tedious and time-consuming experiments. Guidelines are provided for collecting the above extracts in an open vessel, in a specific liquid, or on a solid with an affinity for the extracted chemical compounds. Results from this study will save the taxpayer by eliminating the need for experimental measurements every time analytical SFE is performed, as well as speed up the development of methods for analysis of pesticides, food contaminants, and veterinary drugs required by regulatory agencies such as FSIS, FDA, and EPA.

Technical Abstract: Optimizing the extracted analyte collection step in analytical supercritical fluid extraction (SFE) is of key importance in achieving high analyte recoveries and extraction efficiencies. Whereas the extraction step in SFE has been well characterized both theoretically and experimentally, the analyte collection step after SFE has few theoretical guidelines, aside from a few empirical studies which have appeared in the literature. In this study, we have applied several theoretical approaches using experimental data to optimize analyte trapping efficiency in SFE. A vapor liquid equilibrium model has been formulated to predict the trapping efficiency for extracted solute collection in an open collection vessel. Secondly, a simple solution thermodynamic model for predicting solute (analyte) activity coefficients in various trapping solvents has been shown to have utility in predicting collection efficiencies. Finally, effective trapping efficiency after SFE using sorbent media is related to the extent of analyte breakthrough on the sorbent filled trap after depressurization of supercritical fluid. Using experimental data determined via physicochemical gas chromatographic measurements (i.e., specific retention volumes), we have shown the relationship between analyte breakthrough volume off of the trapping sorbent and volume of depressurized fluid through the collection trap. The above theoretical guidelines should prove of value to analysts in designing and optimizing the best conditions for trapping analytes after extraction via analytical SFE.