GB2096347A

GB2096347A - Cell assembly for spectrophotometers

Info

Publication number: GB2096347A
Application number: GB8203083A
Authority: GB
Original assignee: Bodenseewerk Perkin Elmer and Co GmbH
Current assignee: PE Manufacturing GmbH
Priority date: 1981-03-28
Filing date: 1982-02-03
Publication date: 1982-10-13
Also published as: GB2096347B; JPS57175246A; DE3112308A1

Abstract

Sample and reference light beams 12, 14 from a light source and monochromator unit 10 are differently modulated and are imaged at 16 and 18 respectively at the entrances to flexible light pipes 30, 32 which pass the beams to sample and reference cells 20, 22 in a cell holder 24 located in a removable unit 28 which also includes a detector 26. In this way the cells and detector are situated outside the housing of the spectrophotometer, with advantages in handling samples. <IMAGE>

Description

SPECIFICATION Ceil assembly for spectrophotometers This invention relates generally to spectrophotometers and more particularly to the arrangement of cells, i.e. sample cell and reference cell in conjunction with a spectrophotometer of the type comprising a light source and a monochromator unit producing sample and reference light beams directed onto a common detector in a differently modulated manner through a sample and a reference cell respectively, mounted in a cell holder.

In conventional spectrophotometers the entrance slit of a monochromator is illuminated by a light source and a light beam having a wavelength which is variable by the monochromator emerges from the exit slit. This light beam is split into a sample light beam and a reference light beam, for example by means of a chopper and mirror assembly. A cell holder is disposed within a sample space within the housing of the spectrophotometer, into which sample and reference cells are fitted. The sample and reference light beams are focused onto the sample and the reference cell respectively and the light passing through the cells is alternatingly (or otherwise differently modulated) directed onto a common detector.

With conventional cell assemblies for spectrophotometers the cells are fixed within the sample space formed within the housing of the spectrophotometer. The necessity of installing cells in this sample space is inconvenient with certain applications.

According to the invention, a cell assembly for a spectrophotometer of the type referred to has both the cell holder and the detector disposed in a removable unit and the sample and refernece light beams are directed from the light source and monochromator unit onto sample and reference cells in the cell holder by means of light pipes. As a consequence, the cells may be used together with the detector outside the sample space provided in the housing of the spectrophotometer proper. This offers distinct advantages when examining radioactive samples, for example, which have to be moved in the sample space in a very inconvenient manner by means of radiation shielding gloves.

Examples of cell assembly in accordance with the invention are illustrated in the accompanying drawings, in which: Figure 1 is a schematic plan view of one form of cell assembly; Figure 2 is a plan view of a form of assembly for use with long path cells; Figure 3 is a plan view of a form of assembly for fluorescence measurements; Figure 4 is a plan view of a form of assembly having an integrating sphere; Figure 5 is a schematic representation of the physical arrangement of part of the assembly shown in Figure 4; and Figure 6 is a plan view of a modification of the assembly of Figure 1.

In each Figure of the drawings, a spectrophotometer includes a light source and monochromator unit 10. A light beam emerging from the light source is directed in the usual manner onto the entrance slit of the monochromator unit and the monochromatic light beam appearing at the exit slit of the monochromator is split into a sample and a reference light beam 12 and 14, respectively, by means of a chopper assembly, which light beams are differently modulated, being alternatingly interrupted, for example, in this manner. Optical imaging systems are provided through which sample and reference light beams 12 and 14 respectively are each focused on a respective region 1 6 and 1 8 which is fixed with respect to the light source and monochromator unit 1 0.

During normal operation of the spectrophotometer sample and reference cells are disposed at the regions 1 6 and 1 8.

In the arrangement illustrated in Figure 1, sample and reference cells 20 and 22 respectively are mounted on a cell holder 24 and the sample and reference light beams are passed through the respective cells and directed onto a common detector 26. Cell holder 24 is disposed in a removable unit 28 which also includes the detector 26 and a base plate 34 upon which the different components of the unit are mounted.

The sample and reference light beams 12 and 14 respectively are directed from the light source and monochromator unit 10 to the respective cells 20 and 22 in the sample holder 24 of the removable unit 28 by means of flexible light pipes 30 and 32 respectively of which the entrance ends are mounted at the regions 16 and 18 respectively and the exit ends are adjacent the sample and reference cells 20 and 22 respectively. The detector 26 is preferably a photo-multiplier disposed immediately behind the sample and reference cells 20 and 22 respectively within removable unit 28.

An infra-red sensitive detector 36 is also provided for measurements in the near infra-red.

A focusing optical system 38 is located in front of infra-red sensitive detector 36, which systems focuses the light passing through sample and reference cells 20 and 22, respectively, onto the infra-red sensitive detector 36. Photo-multiplier 26 and infra-red sensitive detector 36 with focusing optical system 38 are arranged on a carriage which is movable relative to base plate 34 and cell holder 24 transversely to the path of rays such that either the photo-multiplier 26 or the infra-red sensitive detector 36 may be located in the path of rays behind the sample and reference cells 20 and 22 respectively.As an alternative, cell holder 24 with the exit ends 40 and 42 respectively of the light pipes 30 and 32 may be disposed on a carriage 44 which is movable transversely with respect to the path of rays relative to photo-multiplier 26 and infra-red sensitive detector 36 because of the flexibility of light pipes 30 and 32. Imaging optical elements 46 and 48 are provided in the respective light pipes 30 and 32 at a distance from the exit ends 40 and 42 through which optical elements 46 and 48 the light beams 12 and 14 respectively are focused to form a spot of approximately 3 mm edge length on the centre of cell holder 24. The exit ends 40 and 42 of the light pipes 30 and 32 are also longitudinally adjustable so that it is possible to compensate for cells having different thickness.

In the modification of Figure 2 which is particularly suitable for long path cells, corresponding components are designated by the same reference numerals as in Figure 1. In this example, the exit ends 40 and 42 of light pipes 30 and 32 are co-axial, spaced apart and facing each other. Sample and reference cells 50 and 52 respectively are also co-axial and spaced from the exit ends 40 and 42 of light pipes 30 and 32. An optical deflecting element 54 is disposed between the sample and reference cells 50 and 52 which deflects the sample and reference light beams to detector 26 or 36. Cells 50 and 52 are long path cells, i.e. cells in which the light beam is passed repeatedly through the sample along a zigzag path. The exit ends 40 and 42 of light pipes 30 and 32 may also be longitudinally adjusted in this arrangement.

Figure 3 shows a device for use in making fluorescence measurements. Again the same reference numerals as in Figure 1 are used for corresponding components. For fluorescence measurement light pipe 30 directing the sample light beam 12 is led to a lateral surface 55 of sample cell 20 extending parallel to the observation direction of detector 26. A filter 56 which is substantially opaque to the exciting radiation of the sample light beam 12 is disposed between sample cell 20 and detector 26.

Reference light beam 14 serves for the stabilisation of energy.

In this arrangement, the sample light beam is directed through lateral surface 55 into the sample cell as an exciting radiation.

Photomultiplier 26 detects the fluorescence radiation from a position perpendicular to the direction of this exciting light beam. The radiation of the exciting light beam emerging towards the photomultiplier by reflection or scattering is eliminated by filter 56.

In the embodiment of Figure 4, sample and reference cells 20 and 22 are disposed in sample holders 57 and 58 in front of apertures 60 and 62 of a light integrating sphere 64. Detector 66 can close an aperture 68 of light integrating sphere 64. Sample and reference cells 20 and 22 are preferably disposed laterally adjacent the integrating sphere 64 and angularly spaced by 900, whereas detector 66 is located on the upper or lower side of integrating sphere 64. A detector, a photomultiplier for UV and visible light, for example, may also be disposed on one side of integrating sphere 64, whereas another detector for infra-red radiation, for example, is provided on the opposite side of the integrating sphere. Thus movement of the detectors relative to the sample and reference cell is no longer necessary.

As shown in Figure 5, cell holder 58 comprises a light-tight housing 68 which may be closed by a light-tight cover 70. The end of light pipe 32 extends into the housing 68 which light pipe is mounted on light integrating sphere 64 independently of housing 68 by means of a holder 72. Cell 22 is preferably disposed immediately in front of aperture 62 of light integrating sphere 64.

As shown in Figure 5 by dashed lines, it may also be located immediately in front of the end of light pipe 32.

The embodiment of Figure 6 corresponds to a large extent to the embodiment of Figure 1. Unit 28 however including cell holder 24 and detectors 26 and 36 respectively, is disposed in an additional separate sample space 74.

The device of Figures 4 and 5 may, as illustrated in Figure 4 by dashed lines, also be used for the remission (reflectance) measurement in the known manner as disclosed in German AS 26 06 675. To this end, further apertures of integrating sphere 64 may be provided opposite apertures 60 and 62, behind which are disposed carriers 76 and 78 for a sample and a standard, respectively, the remission of which is to be measured. Instead of a sample mounted on a carrier 76 some other surface may be measured to which the integrating sphere 64 is moved.

Claims

1. A cell assembly for a spectrophotometer of the type referred to in which both the cell holder and the detector are disposed in a removable unit and the sample and reference light beams are directed from the light source and monochromator unit onto sample and reference cells in the cell holder by means of light pipes.

2. A cell assembly as claimed in claim 1 wherein the light pipes are flexible.

3. A cell assembly as claimed in claim 1 or claim 2 having optical imaging systems through which the sample and reference light beams are each focused onto a respective region which is fixed with respect to the light source and monochromator unit and in which the entrance ends of the light pipes are mounted at the fixed regions.

4. A cell assembly as claimed in any one of claims 1 to 3 wherein the detector is a photomultiplier disposed in the removable unit immediately behind the sample and reference cells.

5. A cell assembly as claimed in claim 4 wherein the photo-multiplier is disposed side by side with another detector sensitive to a different range of wavelengths and the cell holder and/or the detectors are mounted on respective carriers arranged for transverse movement in the removable unit so that either the photo-multiplier or the other detector may be located in the path of rays behind the sample and reference cells.

6. A cell assembly as claimed in any one of the preceding claims wherein the exit ends of the light pipes are co-axially spaced and facing each other, the sample and reference cells are co-axial with each other and with the exit ends of the light pipes and are spaced from each other between the exit ends of the light pipes and optical deflection elements are disposed between the sample and reference cells to deflect the sample and reference light beams onto the detector.

7. A cell assembly as claimed in any one of the preceding claims wherein the exit ends of the light pipes are longitudinally adjustable.

8. A cell assembly as claimed in claim 7 wherein the cells are long path cells.

9. A cell assembly as claimed in any one of claims 1 to 5 wherein for fluorescence measurements the light pipe guiding the sample light beam is led to a lateral surface of the sample cell extending parallel to the observation direction of the detector.

10. A cell assembly as claimed in claim 9 wherein a filter substantially opaque to the exciting radiation of the sample light beam is disposed between the sample cell and the detector.

11. A cell assembly as claimed in any one of claims 1 to 3 wherein the sample and reference cells are disposed in front of apertures of a light integrating sphere and the detector closes a further aperture of the light integrating sphere.

12. A cell assembly as claimed in claim 11 wherein imaging optical elements are provided in each of the light pipes at a distance in front of the exit end.

1 3. A cell assembly for a spectrophotometer of the type referred to and having its components disposed substantially as described and as illustrated with reference to any one of the Figures of the accompanying drawings.