GB2395786A

GB2395786A - Methods devices and calibration techniques for analysis by extraction

Info

Publication number: GB2395786A
Application number: GB0323643A
Authority: GB
Inventors: Ed Ramsey
Original assignee: CRITICAL SOLUTIONS TECHNOLOGY
Current assignee: CRITICAL SOLUTIONS TECHNOLOGY
Priority date: 2002-11-26
Filing date: 2003-10-08
Publication date: 2004-06-02
Also published as: GB0227643D0; GB0323643D0

Abstract

A method of calibrating an extraction apparatus by analysing a standard after diversion through a by-pass circuit which does not send the standard through the extraction chamber. Other inventions relate to a calibration technique including use of a plug of inert material comprising a known amount of analyte; and a method of cleaning an extraction vessel using a porous plug of inert material; A method of analysing a carbonaceous analyte by extraction in the presence of a diluent; An extraction technique wherein the extraction fluid enters the extraction vessel from above and below the sample; A sample receptacle for use in extraction wherein the receptacle includes a removable cover having a liner; An extraction chamber comprising a sample receptacle with a collar wherein the receptacle has a removable cover, and is connected to an IR analysis cell; A method of extraction wherein the rate of delivery of extraction fluid is reduced to permit analytes to migrate into the extraction fluid.

Description

-1 Analytical Apparatus The present invention relates to analytical

apparatus and 5 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 10 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 seas, rivers or 15 estuaries. Similarly in the manufacture of herbicides, there is a potential for the formation of carcinogenic nitrosamines, which manufacturing process therefore require careful monitoring.

20 There is a range of techniques that utilize analytical apparatus to monitor (qualitatively or quantitatively) a particular analyte, such as an organic compound, present in a sample of fluid. Examples of such techniques include gas chromatography and infrared spectroscopy. The analytical 25 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 30 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 35 types of analytical apparatus, such as gas chromatography,

-2- infrared spectrometers, or the like. Alternatively, after liquidliquid extraction an aliquot of the solvent used to extract the fluid sample can be directly submitted for analysis using various analytical apparatus, such as gas s chromatography, 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. However, the use of organic solvents 10 industrially has been restricted by legislation, such that users may be required to justify the purchase of some solvents (such as carbon tetrachloride or freon 113) which can only be supplied if their use falls within the essential use category. In accordance with Decision X/19, 15 the Parties to the Montreal Protocol decided at their 11th Meeting, in Beijing China 1999, to eliminate the global exemption for controlled substances for certain analytical measurements including the testing of oil, grease and total petroleum hydrocarbons in water (United Nations Environment 20 Programme, Report of the Technology and Economic Assessment Panel, April 2000, page 21) from the year 2002.

Supercritical fluids have previously been used as an alternative to organic solvents in extraction of analyses 25 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 30 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 35 dioxide, toluene, ammonia, fluorinated hydrocarbons, nitric

oxide, sulfur fluoride, helium and xenon. Supercritical fluid extraction is also a multistage technique requiring firstly extraction of the analyte from the fluid and secondly separation of the analyte from the supercritical 5 fluid. The analyte is finally collected and analysed by, for example, infrared spectroscopy. Alternatively, supercritical fluid, dense gas or near critical fluid extraction can be directly linked to a range of detection systems; see "Analytical Supercritical fluid Extraction 10 Techniques, editor E. D. Ramsey, Kluwer Academic, Dordrecht NL, 1998."

In addition to the use of supercritical fluids in analytical extraction, dense gases and also near critical 15 fluids (or subcritical fluids) may be used. A phase diagram that identifies, supercritical fluids, dense gases and near critical fluids is given in Figure l below.

A pure supercritical fluid is a substance at or above its 20 critical temperature and pressure (in the case of carbon dioxide, the critical temperature is 31.1 C and the critical pressure is 1070psi). Above its critical temperature and pressure, a supercritical fluid cannot be compressed to form a liquid. A supercritical fluid has properties 25 changing continuously from gas-like to liquid-like as the pressure increases.

Dense gases exist at pressures below critical pressure and temperatures ranging from below to higher than critical 30 temperature. For those dense gases which exist at temperatures at or above critical temperature they can be compressed to form a supercritical fluid. For those dense gases which exist at temperatures below critical temperature, they can be compressed to form a near critical 35 fluid.

-4 Near critical fluids (or subaritical fluids) exist at temperatures below critical temperature and pressures ranging from below to higher than critical pressure. For 5 those near critical fluids which exist at or above critical pressure they can be heated to form a supercritical fluid.

For those near critical fluids which exist below critical pressure, they can be heated to form a dense gas.

10 A review of the various physical conditions under which substances form supercritical fluids, and dense gases and their associated properties is given in "Introduction to

Supercritical fluid Extraction in Analytical Science", A. A. Clifford, in, "Analytical Supercritical fluid Extraction 15 Techniquesn, editor E. D. Ramsey, Kluwer Academic, Dordrecht NL, 1998, Chapter 1 - PP 1-42. Further information relating to dense gases can be found in "Dense Gases For Extraction and Refining" E. Stahl et al, Berlin 1988. A method and apparatus which provides monitoring of compounds, such as hydrocarbons present in a fluid, is disclosed in PCT application GB97/00047. However, the method and apparatus disclosed suffers from a number of 25 deficiencies which may result in reduced performance.

It is therefore an aim of the present invention to provide an improved apparatus and method for monitoring one or more analyses present in a fluid.

Therefore, according to a first aspect of the present invention, there is provided a sample receptacle for use in fluid extraction of an analyte present in a sample, wherein the sample receptacle includes a removable cover device 35 having a removable liner.

The removable liner is typically arranged to substantially prevent sample fluid in the sample receptacle from contracting the removable cover device.

s The fluid extraction is typically supercritical fluid extraction, dense gas extraction and/or subcritical (or near critical) fluid extraction. The supercritical fluid, dense gas and subcritical fluid are substantially as 10 described herein before.

The removable liner may be manufactured from a metal foil (such as aluminium foil) or a polymer, (such as PTFE).

15 Advantageously, the sample receptacle is particularly useful when using the apparatus for monitoring one or more analyses present in a fluid sample disclosed in GB97/00047.

The sample receptacle is typically for use in an apparatus 20 comprising: (a) an extraction chamber for extracting at least one analyte from the fluid sample by fluid extraction; the extraction chamber being arranged to receive the sample receptacle for the fluid extraction therein, 25 the extraction chamber having a removable cover member arranged to permit introduction of the receptacle into

the extraction chamber.

(b) an analysis cell in communication with the extraction 30 chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window which is substantially transparent to infrared radiation, and which window enables infrared radiation from an infrared source to pass through the extracted 35 analyte to means for analysing the infrared radiation.

-6 Therefore, according to a further aspect of the present invention, there is provided an apparatus for use in the 5 analysis of an analyte, the apparatus comprising: (a) an extraction chamber for extracting at least one analyte from a fluid sample by fluid extraction, the extraction chamber being arranged to receive a sample receptacle for fluid extraction therein, the extraction lo chamber having a removable cover member arranged to permit introduction of the receptacle into the extraction

chamber. (b) a removable sample receptacle arranged to be positioned in the extraction chamber, the sample 15 receptacle including a removable cover device having a removable liner; (c) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window which is 20 substantially transparent to infrared radiation, and which window enables infrared radiation from an infrared source to pass through the extracted analyte to means for analysing the infrared radiation.

25 Advantageously, prior to extraction of the analyte, the liner is removed from the removable cover device and placed inside the sample receptacle together with the fluid sample to be analysed. The removable liner and the sample receptacle are substantially as described hereinbefore.

Therefore, any sample adhering to the liner (which may be as a result of transportation of the sample receptacle from a collection site to the extraction apparatus) is also extracted and accounted for in the fluid analysis (which 35 may, for example, be by infrared analysis).

A further disadvantage of the apparatus disclosed in GB97/00047 is that the pump time (that is, the time required for the extraction fluid to reach the desired 5 pressure and/or temperature) may, in some circumstances be considered too long by the apparatus operator. In addition, a considerable amount of extraction fluid is required during this time, which may be wasteful and possibly expensive if the extraction fluid itself is 10 expensive. The use of greater volumes of extraction fluid than is actually required, results in the extracted analyte being diluted in the extraction fluid. A more concentrated extraction fluid is preferred.

15 Therefore, according to a further aspect of the present invention, there is provided apparatus for monitoring one or more analyses present in a liquid sample, which apparatus includes: (a) an extraction chamber for extracting at least one 20 analyte from the liquid sample by fluid extraction, the extraction chamber having a removable cover member and being arranged to receive a removable sample receptacle; (b) a collar member arranged to sleeve at least a portion of a sample receptacle when a sample receptacle is 25 positioned in the extraction chamber; (c) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window which is substantially transparent to infrared radiation, and 30 which window enables infrared radiation from an infrared source to pass through the extracted analyte.

The sample receptacle typically includes a neck portion having a smaller diameter than the remainder of the sample 35 receptacle. The sample receptacle may be in the form of a

-8 bottle, which may have a substantially circular (which is preferred), rectangular or square cross-section.

Advantageously, the collar substantially reduces the void 5 space between internal surfaces of the extraction chamber and the outer surface of the sample receptacle. Therefore, when the apparatus is in use, the apparatus can be pumped up more rapidly to the desired extraction pressure.

10 Furthermore, the collar provides the advantage that a reduced volume of extraction fluid may be used when achieving the desired extraction pressure. As a result, the sample is dissolved in a smaller volume of extraction fluid providing a more concentrated sample/extraction fluid 15 mixture to be analysed. This serves to provide lower analysis detection limits (and therefore improved sensitivity) when an aliquot of the extraction fluid containing the extracted analyte is analysed.

20 The extraction fluid is substantially as described hereinbefore. It is further envisaged that the removable sample receptacle may include a removable cover device which includes a removable liner substantially as described hereinbefore. The sample receptacle is substantially as 25 described hereinbefore.

According to a first embodiment of this aspect of the present invention, the removable cover member includes the collar member. Accordingly, the collar member and the 30 removable cover member are substantially a single unit.

They may be manufactured as a single piece; alternatively they can be manufactured separately and subsequently joined prior to use.

35 According to a second embodiment of this aspect of the

- 9 - present invention, the collar member is a distinct member.

In this embodiment, it is particularly preferred that the collar is positioned over the sample receptacle prior to, or immediately after, the sample receptacle is positioned 5 in the extraction vessel.

The collar may be machined from, for example, a thermally conductive material such as aluminium. Aluminium is particularly advantageous as the thermal conductivity 10 ensures that substantially no cold spots are formed within the same chamber. Alternatively, the collar may be of PTFE. It is envisaged that the collar and the removable cover 15 member may be of the same or a different material.

The collar member is typically shaped and dimensioned to substantially cover a neck portion of the sample receptacle. According to yet a further aspect of the present invention, there is provided apparatus for monitoring one or more analyses present in a fluid sample, which apparatus comprises: 25 (a) an extraction chamber for extracting at least one analyte from the fluid sample by fluid extraction; (b) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window 30 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; and 35 (c) a vortex mixer for creating a vortex of supercritical

-10 fluid and the liquid sample in the extraction chamber, the vortex mixer having an inert sleeve.

According to a first embodiment of this aspect of the 5 present invention, the inert sleeve is typically arranged to be positioned about a shaft member of the vortex mixer.

The shaft member typically permits delivery of the extraction fluid to the extraction vessel. Advantageously, the use of the inert sleeve serves to minimise the void 10 volume. Preferably in this embodiment, the sleeve and the removable cover member are distinct items.

According to a second embodiment of this aspect of the present invention, the removable cover member may include 15 the inert sleeve.

The inert sleeve may be of aluminium such as machinable aluminium or PTFE (which is preferred).

20 This aspect of the present invention substantially reduces the void volume in the extraction vessel. Therefore, as described previously less time is required to achieved the desired pressure and also a reduced amount of extraction fluid is required.

According to yet a further aspect of the present invention, there is provided a method of analysing one or more analyses in a fluid sample, which method includes: (a) permitting an extraction fluid to enter an extraction 30 vessel of an apparatus according to the present invention at a rate such that a desired pressure is attained in less than about 15 minutes; (b) substantially reducing the rate of delivery of extraction fluid so as to permit one or more analyses 35 present in the sample to migrate to a sample fluid

-11- extraction fluid interface so as to be extracted from the sample fluid into the extraction fluid thereby obtaining an extracted analyte; (c) permitting the extracted analyte to flow to an infra 5 red inspection cell; (d) maintaining the flow of extraction fluid such that the pressure of the extraction fluid is maintained substantially at the desired pressure attained in step (a); and 10 (e) analysing the extraction fluid in the infrared inspection cell (typically by infrared analysis) for the presence of the one or more extracted analyte.

The extraction fluid is substantially as described herein 15 before. The apparatus may be substantially as described hereinbefore with reference to an earlier aspect of the present invention.

Preferably, the extraction fluid is permitted to enter the 20 extraction vessel of an apparatus according to the present invention at a rate such that a desired pressure is attained in less than about 12 minutes (such as about lo minutes). 25 It is particularly preferred that the extraction fluid follows the pump program profile represented in figure 4.

A further problem associated with extraction vessels known in the art is that samples that contain certain oil, grease 30 and total petroleum hydrocarbon levels (for example oil levels > 80 ppm) extracted in vessels designed to accommodate about 500 ml of fluid sample, may result in the deposition of a very thin film of oil on the inner extraction vessel surfaces following vessel venting. This 35 is attributed to oil dropping out of the extraction fluid

-12 solution whilst the vessel is depressurised during the vent cycle. This provides the problem of cross-contamination.

It is therefore a further aim of the present invention to 5 alleviate at least some of the problems identified above.

It is still yet a further aim of the present invention to provide a method and apparatus for extracting an analyte from a fluid sample which method substantially reduces the 10 risk of cross-contamination of analyses.

Therefore according to a further aspect of the present invention, there is provided a method of monitoring one or more analyses present in a fluid sample, which method l5 comprises: (a) providing a sample receptacle containing the fluid sample, the sample receptacle having a removable shroud; (b) positioning the sample receptacle and the shroud in an 20 analytical apparatus having an extraction chamber, such that the shroud substantially provides a barrier between an inner surface of the extraction chamber and an outer surface of the sample receptacle; (c) permitting an extraction fluid to enter the extraction 25 chamber such that the extraction fluid is substantially prohibited from contacting the inner surface of the extraction chamber.

(d) permitting the extracted analyte to flow to an analysis cell; and 30 (e) carrying out infrared analysis of the extracted analyte. The extraction fluid is substantially as described hereinbefore. The analytical apparatus may be of the type 35 disclosed in POT application GB97/00047; alternatively, it

-13 may be of the type substantially described hereinbefore.

The shroud may be of an inert material, such as aluminium or PTFE.

Advantageously, subsequent to the analysis in step (e), the apparatus can be vented and the shroud and sample receptacle removed from the extraction chamber. The shroud and/or the sample receptacle may subsequently be cleaned 10 for reuse. Alternatively, the shroud may be disposable.

Accordingly, there is further provided a method of cleaning an analytical apparatus according to the present invention, which method includes: 15 (a) positioning a plug of inert material in an analytical apparatus extraction chamber; (b) permitting extraction fluid to enter the extraction chamber and attain a desired pressure and/or temperature such that contaminates present in the 20 extraction chamber are dissolved in the extraction fluid; and (c) venting the extraction chamber one or more times.

It is particularly preferred that the plug is shaped and 25 dimensioned to substantially fill the extraction chamber, so as to minimise void volume.

Advantageously, the plug may be of aluminium, such as machinable aluminium, however, it is envisaged that any 30 inert material may be used.

The analytical apparatus and/or the extraction fluid are substantially as described hereinbefore. Alternatively, the apparatus may be of the type disclosed in GB97/00047.

-14 This aspect of the present invention provides the advantage that the void volume within the extraction chamber is substantially reduced. Therefore the apparatus can be rapidly extracted and vented several times with the desired 5 extraction fluid, thereby providing a means of in si to vessel cleaning.

A further disadvantage of analytical apparatus known in the art is that the use of spiked water samples with known 10 quantities of analyte(s) is time consuming. A faster more efficient method is desired.

Accordingly, there is provided a method of calibrating an analytical apparatus for a desired analyte(s), which method 15 includes: (a) positioning a plug of inert material having a known amount of the analyte(s) thereon in an analytical apparatus extraction chamber; (b) permitting extraction fluid to enter the extraction 20 chamber and attain a desired pressure and/or temperature such that the analyte(s) is dissolved in the extraction fluid; (c) permitting the extracted analyte(s) in the extraction fluid to flow to an analysis cell; and 25 (d) carrying out analysis (by, for example, infrared analysis) of the extracted analyte(s).

The method is typically repeated one or more times so as to obtain a series of calibration results which can be used to 30 calibrate the apparatus.

The analyte may be directly applied onto the plug (in the case of a solid sample). Alternatively, if the sample is in fluid form, such as an oil, a known volume of the sample 35 may be injected onto an inert porous support matrix (such

-15 as filter paper or the like) which is subsequently placed on an upper surface of the plug.

The method is typically repeated at least twice, preferably 5 three or four times. A calibration graph is subsequently constructed which equates detector response arising from analyte(s) extracted from the cleaning block to detector response for quantities of analyte extracted from water samples. According to still yet a further aspect of the present invention, there is provided a method of monitoring one or more analyses present in a carbonaceous sample (such as soil) which method includes: IS (a) providing a sample receptacle containing the carbonaceous sample; (b) adding a predetermined volume of a dilution fluid to the sample receptacle; (c) permitting an extraction fluid to contact the diluted 20 sample from step (b) such that the sample is extracted and dissolved in the extraction fluid.

(d) permitting direct communication of the extracted analyte(s) from the extraction chamber to an analysis cell; 25 (e) performing analysis (typically infra red analysis) of extracted analyte(s) in the analysis cell.

The dilution fluid typically includes substantially pure water. The water is typically substantially free of 30 organic species, however, it is envisaged that improved extraction efficiencies may be obtained by using certain additives, such as acids/bases and salts. The additives preferably make the water a more polar medium thereby further promoting the higher recovery of hydrophobic 35 organic species.

-16 This aspect of the present invention is particularly advantageous when analysing soil or the like for pollutants or contaminants such as petrochemicals.

s The analytical apparatus substantially as described hereinbefore, is particularly suitable for this method.

Typically, the sample receptacle has an internal volume of 10 about 500 ml. Preferably, the dilution fluid is added to the sample receptacle such that the sample receptacle includes substantially no void volume.

A further disadvantage of known methods and apparatus for 15 analysis of an analyte in a fluid sample is that when extraction fluid enters the sample receptacle in the extraction chamber, there is a risk of the liquid sample being displaced by bubbles of gas. This typically results in splashing above the level of liquid sample in the 20 extraction vessel. In the case of a liquid sample held in a sample receptacle, splashing would require the vessel chamber to be dried between consecutive analyses to ensure sample integrity. A further disadvantage associated with splashing can occur as a result of a liquid sample being 25 displaced into the transfer lines/analytical inspection cell used for analysis; water droplets deposited onto the high pressure inspection cell can give rise to unstable detector performance.

30 It is therefore a further object of the present invention to provide a method of analysis of a sample which alleviates at least some of the disadvantages identified above. 35 Therefore according to yet a further aspect of the present

-17 invention, there is provided a method of analysing a fluid sample, which method includes: (a) providing a fluid sample to be analysed in an extraction vessel; 5 (b) permitting extraction fluid to enter the extraction vessel at a position substantially above the level of the fluid sample in the extraction vessel, for a predetermined period of time or until a predetermined pressure substantially below a final target pressure 10 has been attained in the extraction vessel; (c) permitting extraction fluid to enter the extraction vessel substantially below the level of fluid sample; so as to extract analyses in the sample; (d) analysing (typically by infra-red analysis), extracted 15 analyses dissolved in the extraction fluid.

Typically, the flow of extraction fluid in step (b) is substantially stopped prior to commencement of the flow of extraction fluid in step (c).

The extraction fluid is substantially as described herein before with reference to an earlier aspect of the present invention. 25 The fluid sample may be arranged directly in the extraction chamber, however, it is preferred that the fluid sample is arranged in a sample receptacle in the extraction chamber.

Initially, once the liquid sample is sealed within the 30 extraction chamber, the pressure above the liquid sample is at atmosphere until the extraction fluid is introduced in step (b).

During step (b), the extraction fluid initially expands 35 very rapidly to its volume at atmospheric pressure. During

-18 this initial period, if the extraction fluid (which is typically delivered as a liquid at this stage) is permitted to discharge and expand through the bulk of the liquid sample there would be a risk of the liquid sample being 5 displaced by bubbles of gas resulting in splashing above the level of liquid sample in the extraction vessel at atmosphere. Advantageously, by initially admitting the extraction medium above the level of the liquid sample contained within the extraction chamber it is possible to 10 prevent splashing of the liquid sample once the extraction fluid has passed through the sample fluid. This is a result of the pressure above the fluid sample being substantially greater than atmosphere and therefore the extraction fluid dispensed in step (b) no longer rapidly 15 expands when it enters the pressurised extraction chamber.

A further advantage of the method according to this aspect of the present invention is that water immiscible analyte species less dense than water form a layer on the surface 20 of the water sample (for example oils and grease in water).

By minimising the disruption of the water surface it is possible to bringthe analyte species into direct contact with the extraction fluid used for their extraction at the interface boundary between the water and extraction fluid 25 at an early stage thereby improving extraction efficiencies. If the extraction fluid was initially used to pressurize the vessel by initially being passed through the fluid 30 sample and subsequently passing the extraction fluid through the bulk of the fluid sample, the liquid surface would have been disturbed with a tendency for less dense water immiscible species to be mixed into the interior bulk of the liquid sample. Once mixed into the interior bulk of 35 the fluid sample, water immiscible analyses are less

-19 amenable for extraction once initial fluid extraction conditions have been achieved.

Advantageously, switching the flow of extraction fluid in s step (c) permits extraction of analyses which are contained within the interior bulk of the fluid sample (including less dense, water immiscible analyte species which have become associated with particulate matter denser than the liquid). Additionally, this aspect of the present invention permits mixing the composition of the extraction fluid above the level of the fluid sample as a result of displacement as the less dense extraction fluid exits the fluid sample. In 15 addition, the method disclosed promotes the extraction fluid becoming homogenous which enables the withdrawal of a representative aliquot of extraction fluid for analysis.

According to still yet a further aspect of the present 20 invention, there is provided a method of calibrating an analysis apparatus, which method includes: (a) providing analytical extraction apparatus for analysing a fluid sample by fluid extraction, (b) injecting one or more predetermined samples typically 2s as a fluid of the analyte species to be analysed into an extraction fluid, such that the flow of extraction fluid by-passes an extraction chamber present in the analytical extraction apparatus; (c) analysing the extraction fluid for the presence of the 30 analyte; and (d) determining the efficiency of the extraction apparatus so as to obtain a calibration value.

The method id typically repeated one or more time so as to 3s obtain a calibration curve.

-20 The efficiency of the extraction apparatus may be determined by allowing for dilution and extraction efficiency factors between analyses extracted from water 5 samples and direct injection into the extraction fluid which is arranged to by-pass the extraction vessel.

The injection in step (b) may typically be by means of an injection loop or the like.

Advantageously, this method substantially reduces the necessity to construct a calibration graph without having to analyse fluid samples spiked with known quantities of analyses (which is a particularly time consuming, slow 15 method).

The method according to this aspect of the present invention preferably includes obtaining the same detector responses for known quantities of analyte(s) injected using 20 the high pressure valve loop injection valve to those obtained for known quantities of analyte(s) spiked in water samples which are extracted. In this embodiment a calibration graph can be constructed which equates detector response arising from high pressure valve loop analyte(s) 25 injection to quantities of analyte(s) extracted from water samples. Advantageously, the method may be used to inject one or more aliquot of a volatile organic solvent (such as 30 dichloromethane, ethyl acetate, hexane, or the like) such that an analysis cell (such as a high pressure infra-red cell) can be more rapidly cleaned when the valve is switched to introduce the solvent into the analysis cell when it is transported to the cell in the stream of 35 extraction fluid such as carbon dioxide.

-21 Analytical standards for valve loop injection can be analysed by partial loop filling or preparing standards for full loop injection. When full loop injection is used in 5 conjunction with infrared detection, infrared transparent solvents in the region used for analyte(s) analysis must be used to make analytical standards. For example, tetrachloroethene is suitable for preparing oils and greases analytical standard solutions.

One aspect of the present invention will now be understood by way of example only, with reference to the following example:

A 50g soil sample having a density of lg/ml was placed in a 15 sample receptacle, 490 ml of substantially pure water was added to the sample receptacle. The sample receptacle was then introduced into the extraction\ chamber via the removable cover member.

20 Carbon dioxide was introduced into the extraction chamber whilst the pressure and the temperature levels were raised such that the carbon dioxide enters a supercritical state.

The extraction and analysis were subsequently performed using methods known to a person skilled in the art (such as 25 the method disclosed in GB97/00047).

The present invention will now be described by way of example only, wherein: Figure 1 is a schematic representation of the phase diagram 30 of a single substance; Figure 2 represents a portion of analytical apparatus including a collar means according to a first embodiment of the present invention; 3s

-22 Figure 3 represents a portion of analytical apparatus including a collar means according to a second embodiment of the present invention.

5 Figure 4 represents a liquid carbon dioxide pump program profile for supercritical fluid extraction.

Figures 5, 6 and 7 represent a flow chart of an apparatus suitable for use in the method according to the present 10 invention.

Referring to Figure 1, S represents sets of pressure and temperature values at which a solid phase exists in isolation; L represents sets of pressure and temperature 15 values at which a liquid phase exists in isolation; G represents sets of pressure and temperature values at which a gas phase exists in isolation; F represents sets of pressure and temperature values at which a supercritical fluid phase exists in isolation; T represents the triple 20 point (a unique pressure and temperature value at which the solid, liquid and gas phase co-exist in equilibrium with one another); DO represents sets of pressure and temperature values at which a substance exists as a dense gas; NC represents sets of pressure and temperature values 25 at which a substance exists as a near critical fluid (sometimes referred to as a subcritical fluid).

The line between points T and C is the phase boundary line, defining sets of pressures and temperatures at which the 30 liquid and gas phase coexist in equilibrium with one another. C is the critical point, a unique pressure (critical pressure, Pc) and temperature value (critical temperature, Tc) at which the gas and liquid phases become indistinguishable to form a supercritical fluid.

-23 Referring to Figure 2, there is provided a SFE vessel main body 1 having an extraction chamber 2. Chamber 2, when in use, contains sample receptacle 3. Removable cover member 4 includes collar member 5 which is shaped and dimensioned 5 to sleeve an upper portion of sample receptacle 3. During use of the apparatus, the collar member substantially reduces the void volume in the extraction chamber 2. Fluid delivery tube 6 permits entry of the extraction fluid into the extraction chamber.

Referring to Figure 3, where like numerals have been used to identify like parts given in Figure 2, there is provided a SFE vessel main body 1 having an extraction chamber 2.

Chamber 2, when in use, contains sample receptacle 3.

15 Collar member 15 is positioned on the neck of sample receptacle 3 between the removable cover member 14 and the sample receptacle 3. Fluid delivery sleeve 16 is positioned about fluid delivery tube 6 to further reduce the void volume.

Referring to Figure 4, an extraction fluid pump programme is shown. During period (a), rapid pump speeds are used to attain the selected supercritical fluid extraction pressure. During this period, highly extractable species 2s may become completely dissolved within the supercritical fluid medium.

During period (b), the pump delivers either zero or drastically reduced delivery of the supercritical fluid 30 medium. This is necessary because some less supercritical fluid extractable components within in the sample are not completely extracted during stage (a). This is because such components are swept from the surface of the water sample down into the vortex produced during stage (a) from 35 where they are distributed into the internal bulk of the

-24 liquid sample. During step (b), time is given to allow hydrocarbon species within the water sample bulk to float back up to the water surface. At the water surface they are extracted from the watersupercritical fluid interface 5 into a supercritical fluid which has now attained the correct solvating strength for this purpose (supercritical fluid solvating power is related to supercritical fluid density which is itself normally regulated through delivery pump pressure control).

At point (c) a valve in direct communication with the infrared inspection cell opens (the cell's internal pressure is at atmosphere until this point to ensure the transfer of pressurized supercritical fluid extract for 15 analysis, hence an initial albeit small pressure drop within the SEE vessel occurs). Simultaneously, the pump delivers carbon dioxide at a much reduced flow rate to restore (at point (d)) the final supercritical fluid extraction pressure. During this stage the supercritical 20 fluid solution is gently mixed, as it flows into the infrared inspection cell. This ensures a homogenous supercritical fluid solution of the extracted oil, grease and total petroleum hydrocarbons, is admitted into the infrared inspection cell for accurate and representative 25 analysis. Therefore, since the infrared inspection cell is initially at atmospheric pressure (whereas the extraction vessel is now pressurized) once the valve opens an aliquot of the supercritical fluid/dense gas is transferred such that the infrared inspection cell attains the final 30 pressure was used to complete the extraction process.

Advantageously, at point (d), the value shuts such that the infrared inspection cell is no longer in communication with the SEE vessel which may then be vented to receive another 35 sample bottle whilst "stop-flow" infrared analysis is

-25 taking place.

Referring to figures 5 to 7 where like numerals have been used to identify like parts.

5 A - High pressure pumping system used for delivering extraction medium (generally the pump dispenses the medium in the liquid phase).

B - High pressure flow switching valve (one inlet, two outlet configuration shown).

10 C - High pressure flow switching valve (one inlet, two outlet configuration shown).

D - High pressure vessel used for supercritical fluid/dense gas/near critical extraction. Liquid sample preferably held in sample receptacle placed into vessel chamber.

IS E - High pressure "T" valve or "T" piece F - Open/Close valve.

G - High pressure "T" valve or "T" piece H - High pressure liquid sample injection valve, equipped with variable volume loop(P) (the valve and variable volume 20 loop is optional).

I - High pressure injection valve, equipped with solid phase sorbent holder (J) (the valve and solid phase sorbent holder is optional).

J - High pressure solid phase sorbent holder.

25 K - Demisting chamber/expansion chamber.

L - High pressure inspection cell equipped with infrared/ultraviolet/visible transparent cell windows.

M - Expansion chamber.

N - Open/Close valve.

30 O - Open/Close valve.

P - Variable volume loop.

In use, fluid sample is placed into the extraction vessel (D) and the vessel is then sealed. Valve configurations 35 are set as shown in Figure 5. Valves F. N & O are closed.

-26 No part of system on the outlet side of the extraction vessel, in particular analysis cell, (L), are pressurized.

Pump A starts to deliver extraction medium to extraction 5 vessel D. Medium flows through valve B then through valve C then through "T"-piece E into extraction vessel, (D) above the level of the liquid sample. Once pressure/time reached to prevent splashing, valve C preferably electronically actuated under microprocessor control switches (see Figure 10 6). Extraction medium now flows through the bulk of the liquid sample until a final target selected pressure for final supercritical fluid/dense gas/near critical extraction is reached.

15 After final extraction pressure has been reached valve F. preferably electronically actuated under microprocessor control, opens to allow an aliquot of the supercritical fluid/dense gas/near critical extract to expand into high pressure analytical inspection cell for analysis. Enroute 20 to the inspection cell (L) there is the option to allow the aliquot of supercritical fluid/dense gas/near critical extract to pass through a solid phase sorbent by incorporating a high pressure injection valve (such as a Rheodyne 7125) connected to a high pressure solid phase 25 sorbent holder(J). An example of using a sorbent would involve removing co-extracted vegetable oils and polar species from an extraction fluid when mineral oils and greases are to be analysed, in which case the solid phase sorbent would for example be composed of dry particulate 30 silica gel.

After an aliquot of extraction fluid having the analyte(s) dissolved therein has been transmitted to the high pressure inspection cell(L) (typically using the pump programme 35 identified in figure 4), valve F closes (see figure 6).

-27 Therefore, the analytical side is effectively isolated from the high pressure extraction vessel(D). The high pressure vessel(D) may be vented at this point since pump(A) has now ceased to deliver extraction medium to the extraction 5 vessel. High pressure vessel(D) venting is performed by opening valve O. Once analysis has been completed the aliquot of supercritical fluid/dense gas/near critical extract is vented from the inspection cell(L) by opening valve N. Using the valve configuration shown in Figure 7 the inspection cell may be cleaned, Valves F & N closed, the pump(A) delivers extraction medium to achieve the extraction fluid conditions used for the analysis. By 15 opening and closing valve N. the inspection cell can be repeatedly flushed with supercritical fluid/dense gas/near critical fluid until the last traces of previously extracted sample species are no longer detected.

20 As previously described, Figure 7 represents the inclusion of an optional valve(H) equipped with a fixed loop injector which can be used to rapidly construct a calibration graph once dilution factors are established.

25 Referring to figure 7, the apparatus represented by the schematic shown is particularly suitable for use in the method of calibrating an analysis apparatus according to the present invention. In use, once extraction and analysis have been performed, the high pressure analytical 30 inspection call (infra-red/ultra violet/visible transparent depending upon the mode of detection) can be rapidly cleaned in situ using the valve configuration shown whereby valve (F) is shut. A high pressure liquid sample injection valve (such as a Rheodyne 7125 valve) with a fixed loop (P) 35 can be used to inject a series of liquid samples/solutions

-28 of the analyte(s) species to be analysed into the extraction medium.

Dilution and extraction efficiency factors between analyses 5 extracted from water samples and direct injection into the extraction fluid flow which by-passes the extraction vessel (D) shows a means by which a liquid sample injection valve (H) equipped with an injection loop (P) can be used to rapidly construct a calibration graph without having to 10 slowly analyse water samples spiked with known quantities of analyses.

Claims

-29 CLAIMS

l. A method of calibrating an analysis apparatus, which method includes: 5 (a) providing analytical extraction apparatus for analysing a fluid sample by fluid extraction; (b) injecting one or more predetermined samples typically as a fluid of the analyte species to be analysed into an extraction fluid, such that the 10 flow of extraction fluid by-passes an extraction chamber present in the analytical extraction apparatus; (c) analysing the extraction fluid for the presence of the analyte; and 15 (d) determining the efficiency of the extraction apparatus so as to obtain a calibration value.
2. A method according to claim l, wherein the injection in step (b) may typically be by means of an injection 20 loop or the like.
3. A method according to claim l or 2, which includes obtaining the same detector responses for known quantities of analyte(s) injected using the high 25 pressure valve loop injection valve to those obtained for known quantities of analyte(s) spiked in water samples which are extracted.
4. A method according to any of claims l to 3, wherein 30 the method further includes injecting one or more aliquot of a volatile organic solvent (such as dichloromethane, ethyl acetate, hexane, or the like) such that an analysis cell is substantially cleaned when solvent is introduced into the analysis cell when 35 it is transported to the analysis cell in the

-30 extraction fluid.
5. A method of monitoring one or more analyses present in a carbonaceous sample (such as soil) which method 5 includes: (a) providing a sample receptacle containing the carbonaceous sample; (b) adding a predetermined volume of a dilution fluid to the sample receptacle; lo (c) permitting an extraction fluid to contact the diluted sample from step (b) such that the sample is extracted and dissolved in the extraction fluid; (d) permitting direct communication of the extracted 15 analyte(s) from the extraction chamber to an analysis cell; and (e) performing analysis (typically infra-red analysis) of extracted analyte(s) in the analysis \ cell.
6. A method according to claim 5, wherein the dilution fluid includes substantially pure water.
7. A method according to claim 5 or 6, wherein the 25 dilution fluid includes an additive, such as acids/bases and salts.
8. A method of analysing a fluid sample, which method includes: 30 (a) providing a fluid sample to be analysed in an extraction vessel; (b) permitting extraction fluid to enter the extraction vessel at a position substantially above the level of the fluid sample in the 35 extraction vessel, for a predetermined period of

-31 time or until a predetermined pressure substantially below a final target pressure has been attained in the extraction vessel; (c) permitting extraction fluid to enter the 5 extraction vessel substantially below the level of fluid sample, so as to extract analyses in the sample; and (d) analysing (typically by infra-red analysis), extracted analyses dissolved in the extraction 10 fluid.
9. A method according to claim 8, wherein the flow of extraction fluid in step (b) is substantially stopped prior to commencement of the flow of extraction fluid 15 in step (c).
10. A method according to claim 8 or 9, wherein the fluid sample is arranged directly in the extraction chamber, however, it is preferred that the fluid sample is 20 arranged in a sample receptacle in the extraction chamber.
11. A method according to any of claims 8 to 10, wherein the liquid sample is sealed within the extraction 25 chamber, the pressure above the liquid sample is at atmosphere until the extraction fluid is introduced in step (b).
12. Apparatus for monitoring one or more analyses present 30 in a liquid sample, which apparatus includes: (a) an extraction chamber for extracting at least one analyte from the liquid sample by fluid extraction, the extraction chamber having a removable cover member and being arranged to 35 receive a removable sample receptacle;

-32 (b) a collar member arranged to sleeve at least a portion of a sample receptacle when a sample receptacle is positioned in the extraction chamber; and 5 (c) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window which is substantially transparent to infrared radiation, and which lo window enables infrared radiation from an infrared source to pass through the extracted analyte.
13. Apparatus according to claim 12, wherein the sample 15 receptacle includes a neck portion having a smaller diameter than the remainder of the sample receptacle.
14. Apparatus according to claim 12 or 13, wherein the sample receptacle is in the form of a bottle, which 20 may have a substantially circular (which is preferred), rectangular or square cross-section.
15. Apparatus according to any of claims 12 to 14, wherein the sample receptacle includes a removable cover 25 device which includes a removable liner substantially as described hereinbefore.
16. Apparatus according to claim 15, wherein the removable cover member includes the collar member.
17. Apparatus according to claim 16, wherein the collar member and the removable cover member are substantially a single unit.

3s

-33
18. Apparatus according to claim 17, wherein the collar member and the removable cover member are manufactured as a single unit, or manufactured separately and subsequently joined prior to use.
19. Apparatus according to claim 15, wherein the collar member is a distinct member.
20. Apparatus according to any of claims 12 to 19, wherein lo the collar is machined from a thermally conductive material such as aluminium.
21. Apparatus according to any of claims 12 to 20, wherein the collar and the removable cover member may be of 15 the same or a different material.
22. Apparatus according to any of claims 12 to 21, wherein the collar member is shaped and dimensioned to substantially cover a neck portion of the sample 20 receptacle.
23. A sample receptacle for use in fluid extraction of an analyte present in a sample, wherein the sample receptacle includes a removable cover device having a 25 removable liner.
24. A receptacle according to claim 23, wherein the removable liner is arranged to substantially prevent sample fluid in the sample receptacle from contracting 30 the removable cover device.
25. A receptacle according to claim 23 or 24, wherein the fluid extraction is supercritical fluid extraction, dense gas extraction and/or subcritical (or near 35 critical) fluid extraction.

-34
26. A receptacle according to any of claims 23 to 25, wherein the removable liner is manufactured from a metal foil (such as aluminium foil) or a polymer, 5 (such as PTFE).
27. A receptacle according to any of claims 23 to 26 for use in an apparatus comprising: (a) an extraction chamber for extracting at least one 10 analyte from the fluid sample by fluid extraction; the extraction chamber being arranged to receive the sample receptacle for the fluid extraction therein, the extraction chamber having a removable cover member arranged to permit IS introduction of the receptacle into the

extraction chamber; and (b) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell 20 having a window which is substantially transparent to infrared radiation, and which window enables infrared radiation from an infrared source to pass through the extracted analyte to means for analysing the infrared 25 radiation.
28. Apparatus for use in the analysis of an analyte, the apparatus comprising: (a) an extraction chamber for extracting at least one 30 analyte from a fluid sample by fluid extraction, the extraction chamber being arranged to receive a sample receptacle for fluid extraction therein, the extraction chamber having a removable cover member arranged to permit introduction of the

3s receptacle into the extraction chamber;

-35 (b) a removable sample receptacle arranged to be positioned in the extraction chamber, the sample receptacle including a removable cover device having a removable liner; and 5 (c) an analysis cell in communication with the extraction chamber for receiving the extraction fluid and extracted analyte, the analysis cell having a window which is substantially transparent to infrared radiation, and which lo window enables infrared radiation from an infrared source to pass through the extracted analyte to means for analysing the infrared radiation. 15
29. A method of cleaning an analytical apparatus, which method includes: (a) positioning a plug of inert material in an analytical apparatus extraction chamber; (b) permitting extraction fluid to enter the 20 extraction chamber and attain a desired pressure and/or temperature such that contaminates present in the extraction chamber are dissolved in the extraction fluid; and (c) venting the extraction chamber one or more times.

30. A method according to claim 29, wherein the plug is shaped and dimensioned to substantially fill the extraction chamber, so as to minimise void volume.
30
31. A method according to claim 29 or 30, wherein the plug is of an inert material.
32. A method of calibrating an analytical apparatus for a desired analyte(s), which method includes: 35 (a) positioning a plug of inert material having a

-36 known amount of the analyte(s) thereon in an analytical apparatus extraction chamber; (b) permitting extraction fluid to enter the extraction chamber and attain a desired pressure 5 and/or temperature such that the analyte(s) is dissolved in the extraction fluid; (c) permitting the extracted analyte(s) in the extraction fluid to flow to an analysis cell; and (d) carrying out analysis (by, for example, infra-red lo analysis) of the extracted analyte(s).
33. A method according to claim 32, which is repeated one or more times so as to obtain a series of calibration results which can be used to calibrate the apparatus.
34. A method according to claim 32 or 33, wherein the analyte is directly applied onto the plug.
35. A method according to claim 32 or 33, wherein the 20 sample is injected onto an inert porous support matrix (such as filter paper or the like) which is subsequently placed on an upper surface of the plug.
36. Apparatus for monitoring one or more analyses present 25 in a fluid sample, which apparatus comprises: (a) an extraction chamber for extracting at least one analyte from the fluid sample by fluid extraction; (b) an analysis cell in communication with the 30 extraction chamber for receiving the extraction 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 35 red source to pass through the extracted analyte

-37 to means for analysing the infra-red radiation; and (c) a vortex mixer for creating a vortex of supercritical fluid and the liquid sample in the 5 extraction chamber, the vortex mixer having an inert sleeve.
37. Apparatus according to claim 36, wherein the inert sleeve is typically arranged to be positioned about a 10 shaft member of the vortex mixer.
38. Apparatus according to claim 37, wherein the sleeve and the removable cover member are distinct items.

15
39. Apparatus according to claim 36, wherein the removable cover member may include the inert sleeve.
40. Apparatus according to any of claims 36 to 39, wherein the inert sleeve is of aluminium such as machinable 20 aluminium or PTFE.
41. A method of analysing one or more analyses in a fluid sample, which method includes: (a) permitting an extraction fluid to enter an 25 extraction vessel of an analytical extraction apparatus at a rate such that a desired pressure is attained in less than about 15 minutes; (b) substantially reducing the rate of delivery of extraction fluid so as to permit one or more 30 analyses present in the sample to migrate to a sample fluid-extraction fluid interface so as to be extracted from the sample fluid into the extraction fluid thereby obtaining an extracted analyte; 35 (c) permitting the extracted analyte to flow to an

-38 infra-red inspection cell; (d) maintaining the flow of extraction fluid such that the pressure of the extraction fluid is maintained substantially at the desired pressure 5 attained in step (a); and (e) analysing the extraction fluid in the infra-red inspection cell (typically by infrared analysis) for the presence of the one or more extracted analyte.
42. A method according to claim 41, wherein the extraction fluid is permitted to enter the extraction vessel of an apparatus according to the present invention at a rate such that a desired pressure is attained in less IS than about 12 minutes.
43. A method according to claim 41 or 42, wherein the extraction fluid follows the pump program profile identified in Figure 4.
44. A method of monitoring one or more analyses present in a fluid sample, which method comprises: (a) providing a sample receptacle containing the fluid sample, the sample receptacle having a 25 removable shroud; (b) positioning the sample receptacle and the shroud in an analytical apparatus having an extraction chamber, such that the shroud substantially provides a barrier between an inner surface of 30 the extraction chamber and an outer surface of the sample receptacle; (c) permitting an extraction fluid to enter the extraction chamber such that the extraction fluid is substantially prohibited from contacting the 35 inner surface of the extraction chamber;

-39 (d) permitting the extracted analyte to flow to an analysis cell; and (e) carrying out infra-red analysis of the extracted analyte.
45. A method according to claim 44, wherein the shroud is of an inert material, such as aluminium or PTFE.
46. A method according to claim 44 or 45, wherein lo subsequent to the analysis in step (e), the apparatus can be vented and the shroud and sample receptacle removed from the extraction chamber.
47. A method according to any of claims 44 to 46, wherein 15 the shroud and/or sample receptacle are subsequently cleaned for reuse.
48. A method according to any of claims 44 to 47, wherein the shroud is disposable.