Micro extraction technique

Details Micro extraction technique Micro extraction technique

2000-08-11

2004-11-30

Ludlow, Jan M. (Department: 1743)

Chemistry: analytical and immunological testing

Including sample preparation

Liberation or purification of sample or separation of...

C436S161000, C436S177000, C422S069000, C422S070000, C422S105000

Reexamination Certificate

active

06825046

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the method for solid phase micro extraction and analysis and in particular to the micro extraction and analysis using various types of solid supports which can be coated with various materials.
2. Description of the Prior Art
The analysis of environmental, food, biomedical and pharmaceutical samples involves the separation of components or analytes of interest from the sample matrix such as soil, water, food, tissue or other material. Liquid/liquid extraction is a traditional method of sample extraction and separation—an example is the extraction of a water sample with an immiscible organic solvent such as hexane. Solid samples can be mixed with anhydrous sodium sulfate, ground to a free flowing powder, packed into a chromatography column and then extracted with an organic solvent. Solvent-based extraction methods are frequently time consuming and expensive since high purity solvents must be purchased and properly disposed. Also, many solvents are relatively toxic and should be handled only under proper laboratory conditions. Solvent extraction is not very selective so further analyte isolation is usually accomplished by other chromatographic techniques before the analytes can be quantitated. This increases the cost and complexity of the analysis.
Solid phase extraction is an alternative to liquid/liquid extraction. This involves the selective adsorption of the analytes of interest onto a solid substrate/sorbent (typically a chemically modified silica surface) while other co-extractives are unretained. Pre-made solid phase extraction cartridges are available but there is significant variation between manufacturers products. The analytes of interest are then eluted from the sorbent by the use of selective solvent or solvent mixtures. The analyte(s) can then be analyzed. Many different types of sorbents are available so that a wide range of selectivities are possible. Although solvent use is reduced relative to liquid/liquid extraction, purchase and disposal costs remain and the procedure is still time consuming.
U.S. Pat. No. 5,691,206 describes a prior solid phase micro extraction apparatus and method. The method consists of two process steps—partitioning of analytes between the coating (sorbent) and sample, and desorption of the collected analytes into an analytical instrument. This is accomplished by exposing the coated substrate, typically in the form of a fibre, to the sample, allowing the target analytes to be extracted e.g. adsorbed into the coating from either the head space above the sample or from the sample directly. Various coatings are available to adjust selectivity of the extraction and no solvent is used for the extraction. After exposure, the fibre (now containing concentrated analytes) is then typically moved to a thermal desorption instrument, where the analyte is thermally desorbed, followed by separation and quantitation of the analytes. The method is simple, inexpensive and eliminates some of the disadvantages of solid phase extraction including: solvent consumption, extract preconcentration and high blank values. However, it has a significant limitation of low sample throughput which has been only partially overcome by expensive automation options.
SUMMARY OF THE INVENTION
According to the invention, an apparatus and method for carrying out solid phase micro extraction of analytes contained within a fluid or a solid sample, is provided.
In one embodiment of the invention, an apparatus for carrying out solid phase microextraction of analytes included in a fluid or a solid sample is provided, comprising gas tight enclosure means, means for introducing a sample including target analytes into the enclosure means, and means located within the enclosure means for extracting the target analytes from the sample, wherein the extraction means either samples a head space near the sample or samples the sample directly.
In another embodiment of the invention, an apparatus is provided comprising, an assembly for carrying out solid phase microextraction of analytes contained within a fluid or a solid sample, and a gas tight sampling enclosure. The assembly is arranged such that it either samples the head space above the sample or samples the sample matrix directly, within the gas tight enclosure. The assembly includes a solid support, which may be in the form of a fibre which may be coated or uncoated. The fibre and/or the coating material is selected, based upon selectivity of the fibre and/or coating for at least one of the analytes present in the sample.
In a further embodiment of the invention, a method for solid phase micro extraction of analytes included in a fluid or a solid sample is provided, comprising
(a) exposing a fluid or a solid sample including target analytes, to a solid support which may be coated or uncoated, the support and/or the coating being selected based upon selectivity of the support and/or coating for at least one of the analytes in the sample, for a sufficient time to permit chemical extraction of the analytes by the support to occur, and
(b) ending said contact and then placing said solid support into a micro volume of solvent where chemical desorption of the analytes from the support occurs.
In yet another embodiment of the invention, a method is provided for solid phase micro extraction of analytes contained within a fluid or a solid sample, comprising exposing a solid support, which may be in the form of a fibre, which may be coated or uncoated, the fibre and/or the coating material being selected based upon selectivity of the fibre and/or coating for at least one of the analytes in the sample, for a sufficient time to permit chemical extraction of the analytes to occur, ending said contact and then placing said solid support into a suitable micro volume of solvent where desorption of the analytes from the support occurs. Quantitation of the analytes in the extracting solvent can then proceed by conventional means.


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Fisher Scientific Catalog, 1988, pp. 142-143 and 1159-1163.

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