US 5,205,154 AGranted

Apparatus and method for simultaneous supercritical fluid extraction and gas chromatography

AssigneeBrigham Young University

InventorsMilton L. Lee, Paul B. Farnsworth, Zaiyou Liu

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Abstract

A system and method for carrying out supercritical fluid extraction and gas chromatography simultaneously. Sample substances contained in solid (or liquid) matrices are extracted by means of supercritical fluid extraction and carried directly onto a thermal desorption modulator which functions as an interface between the extraction and chromatography systems. Analytes carried by the supercritical fluid are retained in the modulator while the fluid passes through during the cool cycle of the modulator. A thermal pulse raises the temperature of the modulator and releases retained substances, serving as a sharp injection of such substances into a fast separating column to provide high-speed separations. A complete chromatogram with reasonable resolution is generated within a few seconds time period. Thermal modulation signals at a fixed time interval are so chosen that the consequent chromatograms do not interfere with one another. A series of high-speed chromatograms are generated during one extraction, and the extraction and the chromatography are carried out simultaneously. Assemble signal averaging provides a higher signal to noise ratio. Segmented signal averaging of a number of consecutive chromatograms generated from one extraction is similar to off-line fraction collection, but the speed of analysis is substantially enhanced without sacrificing analytical accuracy.

A method for conducting simultaneous on-line supercritical fluid extraction and chromatographic analysis of one or more organic species of interest from a sample matrix comprising;

(a) providing in sequence, a supercritical fluid extraction cell, a thermal desorption modulator and a heated gas chromatography column;
said system also containing a supercritical fluid source, pump means for directing the flow of supercritical fluid through said system, heating means for applying heat to said thermal desorption modulator at regulated time intervals, detection means for detecting bands eluted from said gas chromatography column at regulated time intervals, means for transducing said detected bands into electrical signals, and processing means for receiving, processing and displaying said signals as analytical results;
(b) directing supercritical fluid from said fluid source to said extraction cell containing said matrix sample at a constant pressure via said pump means thereby forming an extractant in said cell consisting of said organic species dissolved into said supercritical fluid;
(c) passing said extractant into said thermal desorption modulator, maintained at a minimum standing temperature by said heating means, under reduced pressure where the organic species are retained as a deposit onto a stationary phase in said modulator and said supercritical fluid as a gas passes through said modulator to said analytical column;
(d) applying additional heat at regulated time intervals to said modulator whereby the retained organic species are suddenly released from said stationary phase of said modulator as a shortband concentration pulse,
(e) injecting said short-band concentration pulse containing said organic species into said heated gas chromatography column by means of said supercritical fluid gas where said organic species are separated into detectable bands;
(f) detecting said bands by said detection means at regulated time intervals as chromatograms and transducing said chromatograms to electrical signals;
and
(g) digitizing and recording said electrical signals, as a function of time, by said processing means into displayable analytical results.

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Abstract

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