Chemistry: analytical and immunological testing – Including sample preparation – Liberation or purification of sample or separation of...
Reexamination Certificate
1998-04-16
2001-02-20
Ludlow, Jan (Department: 1743)
Chemistry: analytical and immunological testing
Including sample preparation
Liberation or purification of sample or separation of...
C210S662000, C210S691000, C436S125000, C436S139000
Reexamination Certificate
active
06190922
ABSTRACT:
BACKGROUND
1. The Field of the Invention
This invention relates generally to a method for the extraction of organic liquid contaminates from an aqueous sample. This invention is directed to the surprising ability of hydrophobic sheet or ribbon tape made of a hydrophobic polymer to facilitate the extraction of liquid organic contaminates from an aqueous sample. This invention further provides a method which facilitates the analysis of hazardous or toxic waste sites in the field, i.e. outside a laboratory environment.
2. The Background Art
In general, historical methods for the extraction of organic contaminates from an aqueous sample involved the addition of a suitable amount of a non-polar organic solvent such as methylene chloride or octane to the aqueous sample from which contaminates were to be extracted. Because the added organic solvent is non-polar and water is polar the two liquids are immiscible. This opposition in polarity and inherent immiscibility causes the two liquid systems to separate into two layers, much like the separation of oil and water into two layers. A typical separation would place both liquid phases in a separatory funnel which allows for the separation of the two phases by selectively removing one layer. The two phases are shaken or vigorously stirred together to provide sufficient contact between the two phases. The contact between the two phases allows the components of the mixture to migrate into the phase which resembles the contaminate's polarity. Because most contaminates of interest are non-polar, the non-polar organic phase tends to extract the contaminates from the polar aqueous phase into the organic phase. The organic phase including the contaminates can then be separated from the water phase. Once the organic phase is separated from the aqueous phase and had all water removed therefrom it is analyzed for contaminate content. Frequently this analysis has as its goal the determination of the presence or absence of a specific organic contaminate, such as the presence of polyaromatic hydrocarbons or polychloro phenols. Moreover, these organic contaminates may be present in only minor amounts when compared to the volume of the sample to be tested. Because the organic contaminate is present in only minor amounts, it is frequently desirable to concentrate the sample many hundred-fold to facilitate the observation of the contaminate. Indeed where the contaminate is present in parts per million (ppm) or parts per billion(ppb) it would likely remain undetected unless the contaminate concentration were increased.
The process of concentration often involves an evaporative process. This process involves heating of the sample whereby the majority of the solvents are driven off, leaving the contaminates in the evaporative reservoir. However, this process relies on the contaminate having both a higher boiling point and a lower vapor pressure than the organic solvent used to effectuate the contaminate's extraction. If the contaminate has a higher boiling point than the solvent, the evaporative process results in the evaporation of the solvent, resulting in a concentrated mixture containing the contaminates. But where the contaminate has a lower boiling point than the solvent, the contaminate will evaporate with the solvent and be discarded, thus destroying the reliability of the extraction. Additional concerns exist where the extraction solvent forms a binary or tertiary vapor state complex with one or more of the contaminates. When such a vapor phase interaction occurs, the involved contaminates co-distill with the solvent, even where the compounds involved have different vapor pressures and boiling points. The co-distillation would result in one or more contaminates being distilled with and disposed with the solvent. Such an interaction would likewise defeat the goal of the extraction and concentration procedure because unknown contaminates would be lost or disposed of prior to detection providing a false negative regarding the presence of the contaminate in the sample.
Accordingly, the process of concentration through evaporation is fraught with difficulties and concerns. These concerns are more prominent in the area of waste analysis where the goal is the elucidation of contaminates within an aqueous sample. Often in such samples, the contaminates and corresponding concentrations within the sample are unknown. Therefore, any method of analysis which increases the potential for loss of a contaminate renders the result of the analysis questionable. In order to circumvent these concerns, methods of extraction and analysis have been developed which are able to extract very small quantities of contaminates from within a sample.
One method of extraction which has been investigated involves the injection of a sample containing an unknown into a liquid chromatography column (LC). The LC facilitates the extraction of the organic unknowns from the aqueous sample. The LC further allows for the separation of the organic unknowns into individual compounds for individual analysis. The LC requires, however, substantial amounts of organic solvents, increasing the quantity of organic waste. The LC also causes an increase in the dilution of the organic contaminates after extraction and requires bulky instrumentation. Moreover, LC extraction is a time intensive process not suited for the rapid extraction of organic contaminates from an aqueous sample. Neither can the LC method be used outside of a laboratory setting at a field site for the extraction of contaminates from waste at a site.
It has been proposed that an efficient extraction technique would maximize the extraction of contaminates from an aqueous sample and minimize the organic solvent waste produced by the extraction. One intensely investigated field, solvent extraction-flow injection, involves the careful formation of a wetting film on the interior surface of a capillary tube with an hydrophobic organic solvent. Solvent extraction-flow injection (SE-FI) has become an essential analytical tool for a direct method of analysis or as a separation and pre-concentration step for further analysis of unknown samples. The SE-FI method is a form of liquid-liquid extraction where the contaminates within the aqueous phase are washed out or extracted from the aqueous phase through the interaction of an organic solvent. However, the SE-FI system allows for LC type extraction but with the use of less solvent.
Classical SE-FI involves the following operations: (1) segmentation with an immiscible organic solvent, (2) equilibration in an extraction coil, and (3) separation of the organic phase from the aqueous phase for determination. The most critical aspects of the conventional SE-FI system are the segmentation and phase separation, with respect to their influences on the reproducibility, reliability, stability and overall dispersion of the sample zone. These processes have been extensively studied and many refinements of segmentation and phase separation of solvent extraction in flow systems have been made. The SE-FI method relies on the formation of discrete segments of liquid corresponding to the aqueous and organic portions of the sample within a small diameter tube. The extraction mechanism of the SE-FI systems to date is basically the same as that of batch LC separation procedures. Two immiscible phases are brought together and mixed with each other causing the extraction of the contaminate from the aqueous system into the organic phase and an analysis of the contaminates is then made with or without phase separation. However, the SE-FI method relies on the same LC type liquid-liquid extraction to separate the contaminates from the aqueous sample. The tubing serves only as a support for the segments where the extraction which occurs between the segments is determined by the two liquids used to facilitate the extraction, not the chemical make-up of the tubing.
Contrasted to the SE-FI method, in a segmented flow system the reproducibility and reliability of the results depend on the repeatability of flow rat
Chen Dong
Shattuck M. David
Kilpatrick & Stockton LLP
Ludlow Jan
Strategic Diagnostics Inc.
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