WO2004034038A1 - Sample cell - Google Patents

Sample cell Download PDF

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Publication number
WO2004034038A1
WO2004034038A1 PCT/GB2003/003148 GB0303148W WO2004034038A1 WO 2004034038 A1 WO2004034038 A1 WO 2004034038A1 GB 0303148 W GB0303148 W GB 0303148W WO 2004034038 A1 WO2004034038 A1 WO 2004034038A1
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WO
WIPO (PCT)
Prior art keywords
sample
cell
windows
window
separation
Prior art date
Application number
PCT/GB2003/003148
Other languages
French (fr)
Inventor
Gareth Jones
David Clarke
Original Assignee
Council For The Central Laboratory Of The Research
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Council For The Central Laboratory Of The Research filed Critical Council For The Central Laboratory Of The Research
Priority to AU2003300492A priority Critical patent/AU2003300492A1/en
Publication of WO2004034038A1 publication Critical patent/WO2004034038A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/05—Flow-through cuvettes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/0303—Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N2021/0346—Capillary cells; Microcells
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N2021/036—Cuvette constructions transformable, modifiable
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G01N2021/216—Polarisation-affecting properties using circular polarised light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/11—Filling or emptying of cuvettes

Definitions

  • the present invention relates to a cell for holding a fluid sample whilst performing an optical measurement on the sample.
  • a sample cell comprises a chamber for receiving a volume of a fluid sample provided with windows for the transmission of light through the chamber/sample.
  • Such cells may comprise windows provided in an otherwise opaque cell body, or the entire cell may be constructed from a suitable transparent material such as quartz etc.
  • quartz a suitable transparent material
  • the signal to noise ratio arising from the radiation path length through the sample (ie width of the cell) and absorbance of the sample itself is critical to the measurement accuracy.
  • CD circular dichroism
  • the polarisation dependant absorption is only of the order of one part in 10 5 of the total absorbance of the sample.
  • the sample absorbance is itself dependent on the molar absorbance of the sample substance and of the optical path length through the sample cell.
  • the absorption is calculated as a function of the change in intensity of the light transmitted through the cell as measured by a detector positioned behind the cell.
  • the functional relationship is logarithmic and thus relatively small changes in absorbance can have a large effect on the intensity of light reaching the detector and thus on the accuracy of measurement.
  • the cell pathlength is therefore a very important factor to be considered in optimising measurements.
  • conventional cells there can be a significant variation in pathlength between two cells of supposedly the same dimension. The effect that this can have on the final measurement is exacerbated when the cells have a very short pathlength.
  • pathlength of the order of 10 ⁇ m
  • the actual pathlength of any given "10 ⁇ m" cell could be anywhere between about 6 and 15 ⁇ m which can have a significant detrimental impact on the measurement.
  • apparatus for use in performing an optical measurement on a fluid sample by detecting radiation transmitted through the sample, the apparatus comprising; a sample cell for receiving said fluid sample, the sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, the windows being relatively moveable to increase and decrease their separation; and feedback control means operable in use to control the separation of the first and second windows dependent upon the detected radiation to thereby adjust the optical pathlength to optimise the particular optical measurement being performed.
  • the apparatus according to the invention enables the optical path length to be dynamically and accurately adjusted to an optimum path length during the course of a measurement. For instance, this allows the pathlength to be optimised for different wavelengths of illuminating radiation or different sample compositions with differing absorbance properties. Moreover, by providing continuous feedback adjustment, the pathlength may be changed over the course of a measurement as for instance the illuminating wavelength is scanned over a range of wavelengths, or the sample composition changes, for instance as a result of a reaction occurring within the sample or the continuous flow of a changing sample stream through the cell.
  • a sample cell for receiving a fluid sample for use in an optical measurement to be performed on the sample, the cell comprising: a cell housing; first and second opposing windows supported within the cell housing and defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, wherein the second window is slidably mounted within the cell housing and drive means are provided for sliding the second window towards and away from the first window to increase or decrease said separation thereby varying the optical pathlength of the cell.
  • this instruction provides for accurate positioning of the window at very small path lengths of the order of several ⁇ m.
  • This is not for instance possible with certain prior art adjustable volume cells which comprise a moveable window screwed into a cylindrical housing. With such arrangements tolerances in the screw thread give rise to variations in the precise orientation of the window as it moves back and forth. Whilst such variations must be small and thus of little significance at relatively large path lengths, at smaller path lengths of the order of several ⁇ m the positional errors can be significant.
  • the present invention also provides a method of performing an optical measurement on a fluid sample, the method comprising: a method of performing an optical measurement on a fluid sample, the method comprising; containing said sample within a sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell; illuminating the sample through said first window; detecting radiation transmitted through said sample and through said second window; controlling the separation of the first and second windows dependent upon the detector response to thereby adjust the optical pathlength to optimise the detector response for the particular measurement being performed.
  • the method is particularly advantageous when applied to the measurement of CD where measurement accuracy has a high dependence on optical pathlength through the cell.
  • Figure 1 is a schematic overview of a sample cell assembly in accordance with the present invention
  • Figure 2 is a schematic cross-section of one embodiment of a sample cell in accordance with the present invention.
  • a sample cell comprises front and back window elements 1 and 2 defining a sample volume therebetween.
  • Incident light (or other radiation) for performance of an optical measurement enters the cell through the front window 1 and leaves through the back window 2 (as indicated by arrows L).
  • the intensity of transmitted light is detected at detector 3.
  • the optical pathlength of the cell is the separation of the internal surfaces of the front and back windows 1 and 2.
  • the back window element 2 is moveable towards and away from the front window element 1 to vary the cell pathlength. Movement of the back window 2 is effected by a motor 4 under the control of a processing unit 5 in response to the intensity of radiation detected at the detector 3. Specifically, feedback from the detector 3 is used to adjust the pathlength of the cell to provide optimum measurement accuracy given any particular sample type or wavelength of light used to illuminate the sample.
  • variable pathlength cell will be of significant advantage wherever the accuracy of the measurement performed is highly dependent on the cell pathlength. For instance the cell will be particularly useful in CD measurements.
  • measurements are taken across a range of wavelengths (typically 240 nm to 190 nm) as CD is wavelength dependent.
  • wavelengths typically 240 nm to 190 nm
  • the pathlength can be continuously adjusted through feedback from the detector to enable measurement across the whole range of desired wavelengths without the need to actually change the cell.
  • the cell according to the present invention could be configured as a flow cell through which different samples are continuously passed.
  • rapid and continuous feedback from the detector enables optimisation of the pathlength as different samples flow through the cell to provide high-throughput measurement capabilities.
  • the present invention also overcomes problems associated with the loading of conventional cells. For instance, with short pathlength conventional cells it is not possible to inject a sample liquid into the cell volume and the usual loading technique is to introduce a droplet of the sample to the cell space and rely on capillary force to take up the sample which may not always be uniform. However, with the present invention the space between the window elements can be opened up as far as is necessary to allow injection of the sample fluid.
  • the pathlength could be increased to in excess of 1cm to enable the fluid to be injected without distorting the windows.
  • difficulties with loading the cell impose a practical minimum pathlength limitation of the order of 10 ⁇ m with conventional cells.
  • the cell can be filled and the pathlength reduced to the order of 1 ⁇ m or less. This broadens the range of measurement that may be made using the cell. For instance when conducting circular CD measurements it extends the available wavelength range down to of the order of 130 nm.
  • the change in pathlength could also be achieved by moving the front window element, or indeed both window elements. It will also be appreciated that data collection will be inhibited as the window element (or elements) is being moved during which time the pathlength is changing.
  • any suitable means could be used to determine the position of the moveable window element (or elements), and measure changes in the pathlength.
  • encoded stepper motors which are accurate to the order of 1 ⁇ m are commercially available.
  • the pathlength could be calibrated from a laser induced interference pattern given from an empty side panel of the cell.
  • Other appropriate instruments/techniques will be apparent to the skilled person.
  • the illustrated cell comprises a cylindrical cell body 6 with a fixed front window 7 and a moveable back window 8.
  • the back window 8 is slidably mounted between sides of the body 6 on a pusher ring 9.
  • the pusher ring 9 is itself slidably sealed with respect to the body 6, for instance by providing the surface of the pusher ring with a PTFE coating. Movement and positioning of the window 8 is controlled by an encoded stepper motor 10 which acts on the pusher ring 9 via a rotatable collar 11 which is in screw threaded engagement with the cell body 6.
  • encoded stepper motor 10 which acts on the pusher ring 9 via a rotatable collar 11 which is in screw threaded engagement with the cell body 6.
  • encoders which can be used in this application.
  • Sample fluid is introduced into the cell from a reservoir 12 positioned to one side of the cell. This allows fluid to flow freely into and out of the cell as the volume of the cell changes with adjustment of the pathlength.
  • the reservoir is positioned to one side of the cell rather than above the cell to avoid exerting a pressure head which might tend to distort the windows 7 and 8.
  • the present invention provides four major advantages over conventional sample cells. Firstly it enables accurate control of the pathlength; secondly it enables the pathlength to be optimised to suit different samples or optical wavelengths; thirdly it overcomes problems associated with loading short pathlength conventional cells; and fourthly it enables provision of cells with a much smaller pathlength than has previously been readily achievable.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Optical Measuring Cells (AREA)

Abstract

Apparatus and method for performing an optical measurement on a fluid sample by detecting radiation transmitted through the sample. The apparatus includes a sample cell(1,2) with a moveable window(2) allowing for adjustment of the optical path length through the cell. Feedback control means(5) is included to control the separation of the windows, to optimise the instantaneous path length for the particular optical measurement being performed.

Description

SAMPLE CELL
The present invention relates to a cell for holding a fluid sample whilst performing an optical measurement on the sample.
In essence a sample cell comprises a chamber for receiving a volume of a fluid sample provided with windows for the transmission of light through the chamber/sample. Such cells may comprise windows provided in an otherwise opaque cell body, or the entire cell may be constructed from a suitable transparent material such as quartz etc. There are a great many different cell geometries and sizes available for use in different applications. Some cells are batch filled and others receive a continuous stream of sample material (known as flow cells).
For some optical measurements the signal to noise ratio arising from the radiation path length through the sample (ie width of the cell) and absorbance of the sample itself is critical to the measurement accuracy. For instance, when measuring circular dichroism (CD) the polarisation dependant absorption is only of the order of one part in 105 of the total absorbance of the sample. The sample absorbance is itself dependent on the molar absorbance of the sample substance and of the optical path length through the sample cell. The absorption is calculated as a function of the change in intensity of the light transmitted through the cell as measured by a detector positioned behind the cell. The functional relationship is logarithmic and thus relatively small changes in absorbance can have a large effect on the intensity of light reaching the detector and thus on the accuracy of measurement.
The cell pathlength is therefore a very important factor to be considered in optimising measurements. However with conventional cells there can be a significant variation in pathlength between two cells of supposedly the same dimension. The effect that this can have on the final measurement is exacerbated when the cells have a very short pathlength. For instance, when measuring CD flow cells of a pathlength of the order of 10 μm are conventionally used and in practice the actual pathlength of any given "10 μm" cell could be anywhere between about 6 and 15 μm which can have a significant detrimental impact on the measurement.
It is an object of the present invention to obviate or mitigate the above disadvantage. According to a first aspect of the present invention there is provided apparatus for use in performing an optical measurement on a fluid sample by detecting radiation transmitted through the sample, the apparatus comprising; a sample cell for receiving said fluid sample, the sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, the windows being relatively moveable to increase and decrease their separation; and feedback control means operable in use to control the separation of the first and second windows dependent upon the detected radiation to thereby adjust the optical pathlength to optimise the particular optical measurement being performed.
The apparatus according to the invention enables the optical path length to be dynamically and accurately adjusted to an optimum path length during the course of a measurement. For instance, this allows the pathlength to be optimised for different wavelengths of illuminating radiation or different sample compositions with differing absorbance properties. Moreover, by providing continuous feedback adjustment, the pathlength may be changed over the course of a measurement as for instance the illuminating wavelength is scanned over a range of wavelengths, or the sample composition changes, for instance as a result of a reaction occurring within the sample or the continuous flow of a changing sample stream through the cell.
According to a second aspect of the present invention there is provided a sample cell for receiving a fluid sample for use in an optical measurement to be performed on the sample, the cell comprising: a cell housing; first and second opposing windows supported within the cell housing and defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, wherein the second window is slidably mounted within the cell housing and drive means are provided for sliding the second window towards and away from the first window to increase or decrease said separation thereby varying the optical pathlength of the cell. By slidably mounting the second window within the cell housing it is possible to make very small yet accurate changes to the path length. Moreover, this instruction provides for accurate positioning of the window at very small path lengths of the order of several μm. This is not for instance possible with certain prior art adjustable volume cells which comprise a moveable window screwed into a cylindrical housing. With such arrangements tolerances in the screw thread give rise to variations in the precise orientation of the window as it moves back and forth. Whilst such variations must be small and thus of little significance at relatively large path lengths, at smaller path lengths of the order of several μm the positional errors can be significant.
The present invention also provides a method of performing an optical measurement on a fluid sample, the method comprising: a method of performing an optical measurement on a fluid sample, the method comprising; containing said sample within a sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell; illuminating the sample through said first window; detecting radiation transmitted through said sample and through said second window; controlling the separation of the first and second windows dependent upon the detector response to thereby adjust the optical pathlength to optimise the detector response for the particular measurement being performed.
The method is particularly advantageous when applied to the measurement of CD where measurement accuracy has a high dependence on optical pathlength through the cell.
Other features and advantages of the various aspects of the present invention will become apparent from the following description.
Specific examples of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a schematic overview of a sample cell assembly in accordance with the present invention; and Figure 2 is a schematic cross-section of one embodiment of a sample cell in accordance with the present invention.
Referring to Figure 1, a sample cell comprises front and back window elements 1 and 2 defining a sample volume therebetween. Incident light (or other radiation) for performance of an optical measurement (such as a CD measurement) enters the cell through the front window 1 and leaves through the back window 2 (as indicated by arrows L). The intensity of transmitted light is detected at detector 3. The optical pathlength of the cell is the separation of the internal surfaces of the front and back windows 1 and 2.
In accordance with the present invention the back window element 2 is moveable towards and away from the front window element 1 to vary the cell pathlength. Movement of the back window 2 is effected by a motor 4 under the control of a processing unit 5 in response to the intensity of radiation detected at the detector 3. Specifically, feedback from the detector 3 is used to adjust the pathlength of the cell to provide optimum measurement accuracy given any particular sample type or wavelength of light used to illuminate the sample.
The variable pathlength cell according to the present invention will be of significant advantage wherever the accuracy of the measurement performed is highly dependent on the cell pathlength. For instance the cell will be particularly useful in CD measurements. In addition, with a conventional CD measurement, measurements are taken across a range of wavelengths (typically 240 nm to 190 nm) as CD is wavelength dependent. With conventional sample cells it is necessary to use different cells of differing pathlengths for measurements over different sub-ranges of the overall wavelength range because of the absorbance dependence on pathlength. However, with the present invention the pathlength can be continuously adjusted through feedback from the detector to enable measurement across the whole range of desired wavelengths without the need to actually change the cell.
Similarly, the cell according to the present invention could be configured as a flow cell through which different samples are continuously passed. In this case, rapid and continuous feedback from the detector enables optimisation of the pathlength as different samples flow through the cell to provide high-throughput measurement capabilities. The present invention also overcomes problems associated with the loading of conventional cells. For instance, with short pathlength conventional cells it is not possible to inject a sample liquid into the cell volume and the usual loading technique is to introduce a droplet of the sample to the cell space and rely on capillary force to take up the sample which may not always be uniform. However, with the present invention the space between the window elements can be opened up as far as is necessary to allow injection of the sample fluid. For instance, the pathlength could be increased to in excess of 1cm to enable the fluid to be injected without distorting the windows. Furthermore, difficulties with loading the cell impose a practical minimum pathlength limitation of the order of 10 μm with conventional cells. However with the present invention the cell can be filled and the pathlength reduced to the order of 1 μm or less. This broadens the range of measurement that may be made using the cell. For instance when conducting circular CD measurements it extends the available wavelength range down to of the order of 130 nm.
It will be appreciated that whereas with the above example of the invention the rear window element is moved, the change in pathlength could also be achieved by moving the front window element, or indeed both window elements. It will also be appreciated that data collection will be inhibited as the window element (or elements) is being moved during which time the pathlength is changing.
Any suitable means could be used to determine the position of the moveable window element (or elements), and measure changes in the pathlength. For instance, encoded stepper motors which are accurate to the order of 1 μm are commercially available. Alternatively, the pathlength could be calibrated from a laser induced interference pattern given from an empty side panel of the cell. Other appropriate instruments/techniques will be apparent to the skilled person.
Referring now to Figure 2, this schematically illustrates one particular embodiment of the present invention. The illustrated cell comprises a cylindrical cell body 6 with a fixed front window 7 and a moveable back window 8. The back window 8 is slidably mounted between sides of the body 6 on a pusher ring 9. The pusher ring 9 is itself slidably sealed with respect to the body 6, for instance by providing the surface of the pusher ring with a PTFE coating. Movement and positioning of the window 8 is controlled by an encoded stepper motor 10 which acts on the pusher ring 9 via a rotatable collar 11 which is in screw threaded engagement with the cell body 6. There are commercially available encoders which can be used in this application.
Sample fluid is introduced into the cell from a reservoir 12 positioned to one side of the cell. This allows fluid to flow freely into and out of the cell as the volume of the cell changes with adjustment of the pathlength. The reservoir is positioned to one side of the cell rather than above the cell to avoid exerting a pressure head which might tend to distort the windows 7 and 8.
In summary, the present invention provides four major advantages over conventional sample cells. Firstly it enables accurate control of the pathlength; secondly it enables the pathlength to be optimised to suit different samples or optical wavelengths; thirdly it overcomes problems associated with loading short pathlength conventional cells; and fourthly it enables provision of cells with a much smaller pathlength than has previously been readily achievable.
It will be appreciated that various modifications could be made to the basic structures outlined above to suit different applications, and that the invention is not limited to application in the measurement of CD. The various alternative possibilities will be readily apparent to the appropriately skilled person.

Claims

1. Apparatus for use in performing an optical measurement on a fluid sample by detecting radiation transmitted through the sample, the apparatus comprising; a sample cell for receiving said fluid sample, the sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, the windows being relatively moveable to increase and decrease their separation; and feedback control means operable in use to control the separation of the first and second windows dependent upon the detected radiation to thereby adjust the optical pathlength to optimise the particular optical measurement being performed.
2. Apparatus according to claim 1, wherein the feedback control means includes means for adjusting the position of the first and/or second window.
3. Apparatus according to claim 1 or claim 2, wherein said feedback control means comprises drive means for moving one or both of said first and second windows, and position control means for controlling operation of said drive means in response to the detected radiation.
4. Apparatus according to any preceding claim, further comprising a radiation source for illuminating the sample through said first window and a radiation detector positioned for detecting radiation transmitted through said sample and through said second window.
5. Apparatus according to claim 4, wherein said feedback control of the separation of the first and second windows is dependent upon the response of said detector and is adjusted to optimise the detector response for the particular optical measurement being performed.
6. Apparatus according to claim 5 when dependent from claim 3, wherein the position control means receives a signal from said detector.
7. Apparatus according to anyone of claims 4 to 6, wherein the wavelength of the illuminating radiation is scanned across a wavelength range and wherein said optical pathlength is adjusted to optimise the detector response for each wavelength within the wavelength range.
8. Apparatus according to any preceding claim, wherein the cell is a flow cell adapted to receive a continuous stream of sample fluid, and wherein said optical pathlength is adjusted to optimise the optical measurement as the composition of the sample fluid changes.
9. Apparatus according to any preceding claim, wherein the optical pathlength can be varied over a range of values between predetermined minimum and maximum measurement values.
10. Apparatus according to claim 9, wherein the optical path length can be varied over said range in increments which are relatively small compared to the difference between said minimum and maximum measurement values.
11. Apparatus according to any preceding claim, wherein only one of said first and second windows is moveable to adjust the separation.
12. Apparatus according to claim 11, wherein said moveable window is slidably mounted in a sample cell housing which together with said first and second windows defines the sample cell receiving volume.
13. Apparatus according to any preceding claim, wherein the first and second windows are planar and supported in parallel planes.
14. Apparatus according to any preceding claim, wherein the cell is a flow cell adapted to receive a continuous stream of sample fluid.
15. Apparatus according to claim 3 and any claim dependent thereon, wherein said drive means comprises a motor.
16. Apparatus according to claim 15, wherein said motor is a stepper motor or encoder.
17. Apparatus according to any preceding claim, wherein said feedback control means includes an interferometer for measuring the separation of the first and second windows.
18. A sample cell for receiving a fluid sample for use in an optical measurement to be performed on the sample, the cell comprising: a cell housing; first and second opposing windows supported within the cell housing and defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell, wherein the second window is slidably mounted within the cell housing and drive means are provided for sliding the second window towards and away from the first window to increase or decrease said separation thereby varying the optical pathlength of the cell.
19. A sample cell according to claim 18, wherein the optical pathlength can be varied over a range of values between pre-determined minimum and maximum measurement values.
20. A sample cell according to claim 19, wherein the optical pathlength can be varied over said range in increments which are relatively small compared to the difference between said minimum and maximum measurement values.
21. A sample cell according to claim 2 or claim 3, wherein said minimum measurement value of the optical pathlength is of the order of 1 μm.
22. A sample cell according to any one of claims 19-21, wherein said maximum measurement value of said optical pathlength is of the order of 20 μm.
23. A sample cell according to any one of claims 19-22, wherein said separation can be increased beyond said maximum measurement value to a loading separation suitable for loading a liquid sample into the cell.
24. A sample cell according to claim 23, wherein said loading separation is greater than 1 cm.
25. A sample cell according to anyone of claims 18 to 24, wherein said drive means comprises a motor.
26. Appratus according to claim 25, wherein said first window is secured to a slidable mounting member supported within the housing and said motor is operable to control the position of said mounting member and window.
27. A sample cell according to claim 26, wherein said drive means further comprises a drive member in screw threaded engagement with the housing and said motor is operable to rotate said drive member thereby causing it to move within the housing to adjust the position of the first window.
28. A method of performing an optical measurement on a fluid sample, the method comprising; containing said sample within a sample cell comprising first and second opposing windows defining a sample receiving space therebetween, the separation of mutually facing surfaces of the first and second windows defining an optical pathlength of the cell; illuminating the sample through said first window; detecting radiation transmitted through said sample and through said second window; controlling the separation of the first and second windows dependent upon the detector response to thereby adjust the optical pathlength to optimise the detector response for the particular measurement being performed.
29. A method according to claim 29, wherein the radiation wavelength is scanned over a range of wavelengths and the optical pathlength of the cell is varied to optimise the detector response at each wavelength.
30. A method according to claim 28 or claim 19, wherein the cell is configured as a flow cell which receives a continuous stream of sample fluid, and the optical pathlength is adjusted as the sample composition changes to optimise the detector response for different sample compositions.
31. A method according to any one of claims 28-30, wherein said optical measurement is a circular dichroism measurement.
PCT/GB2003/003148 2002-10-10 2003-07-24 Sample cell WO2004034038A1 (en)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008011393A2 (en) * 2006-07-20 2008-01-24 Sas Photonics, Llc System and method for optical analysis
EP1956358A1 (en) * 2007-02-07 2008-08-13 FOSS Analytical AB Sample holder
WO2009039920A1 (en) * 2007-09-20 2009-04-02 Technische Universität München Arrangement, method, and sensor for detecting fluid parameters
GB2486435A (en) * 2010-12-14 2012-06-20 Morteza Bahrami Liquid sample receiving apparatus
WO2017060159A1 (en) * 2015-10-07 2017-04-13 Pyreos Ltd. Absorption spectrometer
CN106645231A (en) * 2016-12-27 2017-05-10 中国科学院山西煤炭化学研究所 Light path continuously adjustable catalyst dynamic structure in-suit representation device, and applications thereof
CN114199795A (en) * 2021-10-26 2022-03-18 中国科学院深圳先进技术研究院 Underwater absorptiometer and water quality detection method

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