ANALYTICAL APPARATUS

Abstract: Analytical apparatus which may be used for monitoring compounds present in a fluid, and a method of analysis. Compounds are extracted from the fluid sample in an extraction chamber by means of a supercritical fluid and analysed in an analysis cell, which is in direct communication with the extraction cell.

Description: Analytical Apparatus 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, which manufacturing processes therefore require careful monitoring. There is a range of techniques which utilise 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 analysed accurately. Once the analyte is eluted from the separation medium it may be analysed 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 an alternative 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 utilises 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 fluid and secondly separation of the analyte from the supercritical fluid. The analyte is finally collected and analysed by, for example, infra-red spectroscopy. We have now devised analytical apparatus which obviates chromatographic separation and which provides accurate monitoring of compounds such as hydrocarbons, present in a fluid. The fluid sample which is to be analysed may be in a contaminated solution, present in a solid matrix such as soil, or on the surface of a solid, such as steel. Therefore, according to a first aspect of the present invention, there is provided apparatus for monitoring one or more analytes present in a fluid sample, which apparatus comprises: (a) an extraction chamber for extracting at least one analyte from the fluid sample by means of a supercritical fluid; (b) an analysis cell in communication with the extraction chamber for receiving the supercritical fluid and extracted analyte, the analysis cell having a window which is substantially transparent to infra-red radiation, and which window enables infra-red radiation from an infra-red source to pass through the extracted analyte to means for analysing the infra-red radiation. Preferably the analysing means includes an infra-red spectrometer arranged to analyse 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. 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. Preferably, the extraction chamber includes a removable cover member arranged to allow a sample receptacle to be introduced into the extraction chamber. Further preferably, the sample receptacle has a volume in the range 100 to 3000 ml. Such a sample receptacle permits substantially all the analyte to be extracted from the fluid sample and transferred to the extraction chamber. This embodiment avoids significant amounts of analyte being left behind, if the contents of the sample receptacle were first transferred to the extraction chamber prior to analysis, and are therefore also accounted for in the final 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 C0 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 fibre optic links adjacent one of said windows of said analysis cell. Further preferably, the fibre 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 kept at the temperature necessary to maintain the supercritical fluid (such as carbon dioxide) in its supercritical state. A pressure transducer may also be connected to the apparatus so as to provide an indication of pressure in the housing. It is also preferred that the apparatus includes heating means for said window of said analysis cell thus substantially alleviating accumulation of water droplets or mist or the like on the window. Preferably the apparatus contains two windows for the analysis cell, the windows being arranged to allow the infra-red radiation from the radiation source to pass into and through the analysis cell. According to a second aspect of the present invention there is also provided a method for monitoring one or more analytes present in a fluid sample, which method comprises: (a) extracting in an extraction chamber at least one analyte from a fluid sample by means of a supercritical fluid; and (b) permitting direct communication of extracted analyte from the extraction chamber to an analysis cell; and (c) infra-red analysis of extracted analyte in said analysis cell. Desirably, the infra-red analysis is by an infra-red spectrometer. Preferably, the supercritical fluid comprises supercritical carbon dioxide. Advantageously, supercritical carbon dioxide is transparent over a wide portion of the mid infra-red spectrum. Therefore, although supercritical carbon dioxide may be present in the analysis cell, accurate monitoring of the extracted compounds is substantially unaffected. For some types of analytes, the supercritical fluid may contain up to 30% of a modifying fluid. Preferably, the modifying fluid comprises an aliphatic alcohol. Preferably, the fluid sample contains at least one hydrocarbon. In some embodiments, the analyte may be thermally labile. Desirably, the analyte comprises substantially non- polar hydrocarbons from which polar organic compounds have been removed prior to the extraction. It is preferred that water present is substantially removed from the extracted analyte and supercritical fluid before the extracted analyte and supercritical fluid enter the analysis cell. It is also preferred that separation means comprise a baffle arrangement, which comprises one or more chicane-type baffles of stainless steel. Preferably, the sample of fluid is mixed initially with liquid carbon dioxide in the extraction chamber, the temperature inside the chamber being subsequently adjusted to convert the carbon dioxide to its supercritical state. The invention may be more clearly understood from the following description given, by way of example only. Apparatus for monitoring compounds present in a fluid, comprises an extraction chamber for extracting compounds, such as hydrocarbons, from the fluid sample. The fluid sample is contained in a sample bottle, which is inserted into the extraction chamber, via a removable cover member. A vortex mixer is arranged to introduce carbon dioxide into the sample bottle. The apparatus also comprises a FTIR analysis cell. The analysis cell has two mutually opposed windows on opposite sides of the analysis cell, which windows are transparent to infra-red radiation emitted from an infra-red source. The analysis cell further comprises a heater to prevent accumulation of water droplets or the like on the surface of the windows. The extraction chamber further comprises stainless steel baffles to prevent further potential accumulation of water droplets or mist on the windows of the analysis cell. A demisting chamber is sited between the extraction chamber and the analysis cell. A solid phase sorbent trap is also sited between the demisting chamber and the analysis cell. This is in order that extracted polar organics may be removed prior to the analysis of non-polar hydrocarbons. The analysis cell is fitted with an expansion chamber. The expansion chamber is fitted with an inlet valve and a vent valve to facilitate operation. A HPLC high pressure valve is sited between the extraction vessel and the analysis cell, to enable either valve loop injections or pumping of water-miscible organic solvent, such as acetone, to wash the analysis cell windows and/or to displace trapped polar organic compounds from a solid phase sorbent trap. In use, the sample fluid to be analysed is collected in sample bottle, which is then introduced into the extraction chamber via the removable cover member. The vortex mixer is then used to introduce carbon dioxide into the sample container which is placed inside the extraction chamber. The use of the vortex mixer reduces the quantity of water aerosol droplets reaching the analysis cell windows. The stainless steel baffles complements the vortex mixer. When the temperature and pressure levels are raised sufficiently inside the extraction chamber, the carbon dioxide enters the supercritical state. The compounds in the fluid sample are dissolved in the supercritical fluid and circumvent the baffle arrangement to enter the analysis cell. Both the supercritical carbon dioxide and the extracted compound enter the analysis cell, but the infra-red spectrum of the supercritical fluid is transparent over a wide portion of the mid infra-red spectrum so that the infra-red spectrum of the extracted compound(s) is substantially unaffected by the presence of the supercritical carbon dioxide. The infra-red source emits a beam of radiation which passes initially through one of the windows and through the extracted compoun (s) . The infra-red beam exits the collection chamber through a second window where the infra¬ red spectrum of the extracted compound(s) can be analysed by a infra-red spectrometer. The infra-red spectrometer is connected to a microprocessor which enables the spectrum to be observed on a cathode ray tube or displayed on a computer screen or the like.

Claims: Claims: 1. Apparatus for monitoring one or more analytes present in a fluid sample, which apparatus comprises: (a) an extraction chamber for extracting at least one analyte from said fluid sample by means of a supercritical fluid; and (b) an analysis cell in communication with said extraction chamber for receiving said supercritical fluid and extracted analyte, said analysis cell having a window which is substantially transparent to infra-red radiation, and which window enables infra-red radiation from an infra-red source to pass through said extracted analyte to means for analysing said infra-red radiation. 2. Apparatus according to claim 1, which includes an infra-red spectrometer arranged to analyse infra-red radiation passed through said extracted analyte in said analysis cell. 3. Apparatus according to claim 1 or 2, which includes a vortex mixer for creating a vortex of said supercritical fluid and said analyte in said chamber. 4. Apparatus according to claim 3, wherein said vortex mixer is arranged to introduce into said extraction chamber a non-supercritical fluid which is to be converted into said supercritical fluid. 5. Apparatus according to any of claims 1 to 4, wherein said extraction chamber includes a removable cover member arranged to allow a sample receptacle to be introduced into said extraction chamber. 6. Apparatus according to claim 5, wherein said sample receptacle has a volume in the range 100 to 3000 ml. 7. Apparatus according to any of claims 1 to 6, which includes a solid phase sorbent trap arranged between said extraction chamber and said analysis cell. 8. Apparatus according to any of claims 1 to 7, which includes a demisting chamber arranged between said extraction chamber and said analysis cell. 9. Apparatus according to any of claims 1 to 8, which includes means to provide the pressure required to reach and maintain said supercritical fluid in its supercritical state. 10. Apparatus according to any of claims 1 to 9, which includes a baffle arrangement arranged to allow said extracted analyte and said supercritical fluid to pass from said extraction chamber to said analysis cell while substantially preventing transfer of water from said extraction chamber to said analysis cell. 11. Apparatus according to claim 10, wherein said baffle arrangement comprises one or more chicane-type baffles of stainless steel. 12. Apparatus according to any of claims 1 to 11, wherein said infra-red source comprises interfacing fibre optic links adjacent one of said windows of said analysis cell. 13. Apparatus according to claim 12, wherein said fibre optic links are within a temperature regulated housing. 14. Apparatus according to any of claims 1 to 13, which includes heating means arranged to surround said extraction chamber and said analysis cell. 15. Apparatus according to any of claims l to 14, which includes heating means for said window of said analysis cell. 16. Apparatus according to any of claims l to 15, which contains two said windows for said analysis cell, said windows being arranged to allow said infra-red radiation from said radiation source to pass into and through said analysis cell. 17. Apparatus according to any of claims 1 to 16, wherein said analysis cell is provided with an expansion chamber. 18. A method for monitoring one or more analytes present in a fluid sample, which method comprises: (a) extracting in an extraction chamber at least one analyte from a fluid sample by means of a supercritical fluid; and (b) permitting direct communication of extracted analyte from said extraction chamber to an analysis cell; and (c) infra-red analysis of extracted analyte in said analysis cell. 19. A method according to claim 18, wherein said infra-red analysis is by an infra-red spectrometer. 20. A method according to claim 18 or 19, wherein said supercritical fluid comprises supercritical carbon dioxide. 21. A method according to any of claims 18 to 20, wherein said supercritical fluid contains up to 30% of a modifying fluid. 22. A method according to claim 21, wherein said modifying fluid comprises an aliphatic alcohol. 23. A method according to any of claims 18 to 22, wherein said fluid sample contains at least one hydrocarbon and/or at least one thermally labile compound. 24. A method according to any of claims 18 to 23, wherein said analyte comprises substantially non-polar hydrocarbons from which polar organic compounds have been removed prior to said extraction. 25. A method according to any of claims 18 to 24, wherein water is substantially removed from said extracted analyte and supercritical fluid before said extracted analyte and supercritical fluid enter said analysis cell. 26. A method according to any of claims 18 to 25, wherein said fluid sample is mixed with liquid carbon dioxide in the extraction chamber, the temperature inside the extraction chamber being subsequently adjusted to convert the carbon dioxide to its supercritical state.

Inventors: RAMSEY EDWARD, RAMSEY, EDWARD
Applicants: RAMSEY EDWARD, UGCS LIMITED, RAMSEY, EDWARD
Application year: 1997
Main classification: G01N21
IPC codes: B01D11, G01N1, G01N21, G01N30