Chemistry: analytical and immunological testing – Including sample preparation – Liberation or purification of sample or separation of...
Utility Patent
1998-07-07
2001-01-02
Ludlow, Jan (Department: 1743)
Chemistry: analytical and immunological testing
Including sample preparation
Liberation or purification of sample or separation of...
C210S634000, C422S082050, C422S105000, C436S139000, C436S164000
Utility Patent
active
06168955
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to analytical apparatus and in particular to apparatus for monitoring compounds present in a fluid, and a method of analysis.
Typically in, for example, the petrochemical or steel manufacturing industries, it is necessary to monitor effluents and other manufacturing by-products, which are often disposed of by discharging into rivers or the like. For example, in the petrochemical industry, the hydrocarbon content of waste waters must be closely monitored so as to avoid discharging toxic effluent into rivers or estuaries. Similarly in the manufacture of herbicides, there is a potential for the formation of carcinogenic nitrosamines. Such manufacturing processes therefore require careful monitoring.
There is a range of techniques which utilize analytical apparatus to monitor (qualitatively or quantitatively) a particular analyte, such as an organic compound, present in a sample of a fluid. Examples of such techniques include gas chromatography and infra-red spectrometry. The analytical methods currently available employ multi-stage procedures in order to provide an accurate analysis of the sample to be tested. Firstly it is necessary to mix the sample in a solvent and subsequently extract the analyte from the mixture. The next stage is to collect the analyte using a separation medium such as, for example, trapping the analyte onto a solid surface such as in packed column chromatography, so that the analyte is substantially pure and can be analyzed accurately. Once the analyte is eluted from the separation medium it may be analyzed using various types of analytical apparatus, such as gas spectrometers, infra-red spectrometers, or the like.
A further disadvantage of using such traditional extraction techniques is that they generally require the use of organic solvents. The use of organic solvents industrially is now being restricted by legislation, such that users may be required to justify the purchase of some solvent i.e. some solvent such as carbontetrachloride or Freon 113 can only be supplied if their use falls within the essential use category.
Supercritical fluids have previously been used as alternatives to organic solvents in extraction of analytes from a fluid. In particular, the technique of supercritical fluid extraction provides an effective method for extracting materials, such as complex high molecular weight mixtures which are difficult to separate. Supercritical fluid extraction generally utilizes a mobile phase of highly compressed gas at or above its critical temperature and pressure. When such compounds are subjected to extremes of pressure and temperature, they enter a supercritical state being neither fluid nor gas. Examples of such supercritical fluids include carbon dioxide, toluene, ammonia, fluorinated hydrocarbons, nitric oxide, sulfur fluoride, helium and xenon. A complete review of supercritical fluid extraction and its applications is disclosed in Anal. Chem 1994, 66 106R-130R. Supercritical fluid extraction is also a multi-stage technique requiring firstly extraction of the analyte from the sample and secondly separation of the analyte from the supercritical fluid. The analyte is finally collected and analyzed by, for example, infra-red spectroscopy.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide analytical apparatus which obviates chromatographic separation.
It is a further object of the invention to provide apparatus which can enable accurate monitoring of compounds such as hydrocarbons, present in a fluid sample which is to be analyzed.
SUMMARY OF THE INVENTION
The invention comprises apparatus for monitoring one or more analytes present in a fluid sample, which comprises:
(a) an extraction chamber shaped and dimensioned to receive a sample receptacle for a fluid sample such that at least one analyte can be extracted from the fluid sample by supercritical fluid extraction;
(b) a removable cover member shaped and dimensioned to permit introduction of the receptacle into the extraction chamber;
(c) an analysis cell having a window which is substantially transparent to infra-red radiation and permits infra-red radiation from an external infra-red source to pass through extracted analyte to means for analyzing the infra-red radiation; and
(d) means for permitting communication between the extraction chamber and the analysis cell.
The sample to be analyzed may be in a contaminated solution, present in a solid matrix such as soil, or on the surface of a solid, such as steel.
Preferably the analyzing means includes an infra-red spectrometer arranged to analyze infra-red radiation passed through the extracted analyte. Thus advantageously the apparatus may be used not only to provide a quantitative indication of compounds present, but also a qualitative indication of the types of compound present in the fluid sample.
Preferably, the apparatus includes a vortex mixer for creating a vortex of the supercritical fluid and the analyte in the chamber.
Preferably, the vortex mixer is arranged to introduce into the extraction chamber a non-supercritical fluid which is to be converted into the supercritical fluid. Advantageously, the vortex mixer promotes efficient extraction and prevents water droplets from reaching the analysis cell.
The extraction chamber includes a removable cover member arranged to allow the sample receptacle to be introduced into the extraction chamber. Such a sample receptacle preferably has a volume in the range 100 to 3000 ml, and preferably permits substantially all the analyte to be extracted from the fluid sample and transferred to the extraction chamber. The invention provides the advantage that significant amounts of analyte are not left behind, as would happen if the contents of the sample receptacle were first transferred to the extraction chamber prior to analysis. Such erroneously transferred material would be accounted for in the infra-red analysis.
Desirably, the apparatus includes a solid phase sorbent trap arranged between said extraction chamber and said analysis cell. The solid phase sorbent trap may contain a material such as the material commercially available as “Florisil”.
Desirably, the apparatus includes a demisting chamber arranged between said extraction chamber and said analysis cell.
The apparatus advantageously obviates the need for chromatographic separation phase making analysis of a fluid sample quicker and easier. When the sample of fluid is mixed with the supercritical fluid, under the extremes of temperature and pressure the compounds are dissolved in the supercritical fluid which may then be collected in the collection chamber for subsequent analysis by, for example, the infra-red spectrometer.
Preferably, the apparatus includes means to provide the pressure required to reach and maintain said supercritical fluid in its supercritical state. In the present invention the temperature of the fluid is maintained at or near its critical point. “Near” in this context generally means up to 100° C. above the critical point of the fluid. For example, for CO
2
the critical point temperature is 31.3° C., so the preferred range is from 31.3° C. to 131.3° C.
Preferably the apparatus includes a baffle arrangement arranged to allow the extracted analyte and the supercritical fluid to pass from the extraction chamber to the analysis cell while substantially preventing transfer of water from the extraction chamber to the analysis cell. Further preferably the baffle arrangement comprises one or more chicane-type baffles of stainless steel. The baffles substantially alleviate water splashback or aerosol droplets accumulating on the windows of the analysis cell.
Preferably, the infra-red source comprises interfacing fiber optic links adjacent one of said windows of said analysis cell. Further preferably, the fiber optic links are contained within a temperature regulated housing.
It is preferred that the apparatus includes heating means arranged to surround the extraction chamber and the analysis cell, thus ensuring the complete housing is k
Ludlow Jan
University of Glamorgam Commercial Services Limited
Vinson & Elkins L.L.P.
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