GB2341925A

GB2341925A - Spectroscopic cell

Info

Publication number: GB2341925A
Application number: GB9922706A
Authority: GB
Inventors: Michael Alan Ford; Jay Tadion
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-25
Filing date: 1999-09-24
Publication date: 2000-03-29
Anticipated expiration: 2019-09-24
Also published as: GB9820776D0; GB9922706D0; GB2341925B

Abstract

A cell for use in Spectroscopic analysis comprises a pair of windows 10, 11 shaped and configured to define a space 15 for receiving a sample of material to be analysed and a reservoir 16 into which excess sample material can flow or move when the windows are placed in juxtaposed relationship. Utility may be in infra red analysis of liquids. Cell construction avoids need to use conventional spacers.

Description

2341925 Improvements in or relating to Cells for use in Spectroscopic

Analysis This invention relates to cells which are used in spectroscopic analysis and in particular, but not exclusively analysis using infrared radiation.

Typically such cells will form part of an accessory used in conjunction with a spectrometer such as an FT-IR spectrometer.

Known cells for use in infrared spectroscopy comprise two, optically flat, polished windows formed from infrared transmitting material such as sodium chloride or potassium bromide crystals. The two Windows are located in closely spaced relationship and spaced apart by a spacer or spacers which is formed from a lead amalgam or a plastics material such as PTFE. A sample to be anlaysed, usually a liquid, is placed between the windows so that it is sandwiched therebetween and its thickness is determined by the thickness of the spacer against which the Windows are mounted. The cell containing the liquid for analysis is then placed in a cell holder and located in a spectrometer.

The spacers need to be extremely thin in order that a spectroscopic analysis of the sample can be carried out, and typically will have a thickness of the order of 15 to 50 microns, although in some cases the thickness can be up to 200 microns or more. The thickness may need to be even less when strongly absorbing samples are being analysed. As can be appreciated, it is very 2 difficult to fabricate spacers having such small dimensions. Also conventional cells have been difficult and inconvenient to fill With a sample.

An object of the present invention is to provide a cell which at least alleviates these problems.

According to the present invention there is provided a cell for use in spectroscopic analysis, said cell comprising first and second members which are so shaped and configured that when placed in juxtaposed relationship they define therebetween a region of defined thickness which can receive a sample of a material to be analysed, and a reservoir portion which is in communication with said region. The members at least in areas corresponding to said region may comprise windows through which analysing radiation can be transmitted.

The said region may be circular. The reservoir may be annular.

The surface of the first member may have a recess which is arranged to receive a projecting part on a surface of tile second member such that there is a small axial spacing between the base of the recess on the surface of the projecting part which defines said region, and said projecting part may have a smaller lateral extent than said recess to thereby define a space around said region which constitutes said reservoir. The recess and projecting part may be frusto conical. Alternatively the recess and projecting part may be cylindrical.

The first member may have a planar surface and the second member may have a recess and a groove extending ci rcumferenti ally around the recess, 3 the space between the base of the recess and the first member defining said region and the circumferential groove defining said reservoir.

The first member may have a recess and the second member may have a groove, the space between the base of the recess and the second member defining said region and said groove defining said reservoir. The recess may be circular and the groove may be annular.

The members may be formed from sinterable infrared transmitting materials such as a powdered alkali halide. The axial extent of the region which receives the sample may be in the range 5 microns to 200 microns. The area of the region may be of the order of I cm'.

A significant feature of a cell in accordance with the present invention is that it is the configuration of the two windows which defines the space into which a sample is placed for analysis and therefore the construction of the cell avoids the need to provide spacers. This makes the cell easier to manufacture and to assemble.

The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings:

Figure I Is a side sectional view of a cell in accordance with the present invention, Figure 2 is a side sectional view showing the cell mounted in a holder; Figure 3 is a side sectional and plan view of an alternative form of cell, 4 and Figures 4 and 5 show further alternative cell constructions.

Referring to Figure 1, a cell for use in spectroscopic analysis, e.g, FT IR analysis, comprises -first and -second circular windows (101 11) mounted one on top of another. The window (11) has in its upper surface a recess (12) of frusto-conical form. This recess (12) can receive a projecting part (14), also of frusto conical form, which is formed on the window (10). The dimensions of the recess (12) and the frusto conical part (14) are such that when the window (10) is mounted on the window (11) a small space (15) of uniform thickness is provided between the base of the recess (12) and the lower surface of the frusto conical part (14). Also the radial extent of the frusto conical part (14) is less than the radial extent of the frusto conical recess (12) whereby an annular space (16) is provided around the circumferential surface of the frusto conical part (14).

Each window (10, 11) is made from infrared transmitting material such as a powdered alkaline halide or other sinterable infrared transmitting material.

The windows can be formed using suitably shaped dies.

The cell shown in Figure I is arranged for mounting in a mounting plate (20) as shown in Figure 2. The mounting plate has a central aperture (21) into which is received an annular mounting member (22). The cell comprising windows (10, 11) is mounted upon the annular mounting (22) and secured in place by a ring (25) which threadably engages an external thread on the annular member (22) as shown at (26). The ring (25) includes an annular groove (27) into which is located an O-ring (28) which resiliently presses down upon the top surface of the cell as the ring (25) is screwed onto the ring (22).

In order to use the cell the lower window (11) is located on the ring (22) in the mounting plate (20). One or more drops of a sample for analysis are then placed on the base of the recess (12) and the upper windows (10) is then placed on the lower window (11) to close the cell and the screw ring is then attached to the ring (22) as shown in Figure 3. The sample to be analysed is spread over the region (15) between the two windows and therefore has a uniform and clearly defined thickness. The cell in its mounting plate (20) can then be located in an infrared spectrometer by sliding the mounting plate into a standard guide in the spectrometer. Analysis is carried out in a way which will be apparent to those skilled in the art.

The region (16) around frusto conical part (14) acts as a reservoir into which excess sample and air bubbles can migrate when the two windows are placed one on the other to close the cell. The sample to be analysed is retained in the space (15) by capillary action. It will be seen that a feature of the present construction is that it is the configuration of the windows (10, 11) which defines the dimension of the sample space (15) and no additional elements such as spacers are required. The sample thickness (T) shown in 6 Figure I can be made reproducibly to vary from 0 to 500 microns or even more. An optimum range is 10 to 50 microns. The cell is very cheap to fabricate and can be used in a spectrometer for relatively long periods without the formation of bubbles which would interfere with analysis.

The cell can be used with a wide range of materials ranging from liquids to low melting point solids. It is particularly suitable for use with viscous materials. When low melting point solids are used it will usually be necessary to heat the whole cell before the analysis in order to at least partially liquify the sample to allow It to spread within the space (15).

Figure 3 shows an alternative form of cell in which the recess (12) is cylindrical and the projecting part (14) is cylindrical. In all other material respects the cell is the same as that described with reference to Figure 1.

Figure 4 shows an alternative construction in which the lower window (31) has a recess (32) surrounded by an annular groove (33). The upper window (30) is a circular disc shape. The space between the upper window (30) and the upper surface of the recess (32) is the region into which a sample for analysis is to be located. The annular groove (33) acts as a reservoir.

A further alternative is shown in Figure 5 in which the lower window (41) has a recess (42) and the upper window (40) has an annular groove (43) which acts as the reservoir.

A feature of the present cell is that the windows are sufficiently 7 inexpensive that they can be treated as disposable when cleaning is a problem.

Cleaning can be a problem at very short path lengths in conventional cells and incomplete cleaning can result in a spectral measurement being corrupted by components from a previous sample. This problem is eliminated with disposable windows.

The embodiments described above all have circular windows. It will be appreciated that windows can have other shapes e.g. rectangular or square.

8

Claims

Claims:

I. A cell for use in spectroscopic analysis, said cell comprising first and second members which are so shaped and configured that when placed in juxtaposed relationship they define therebetween a region of defined thickness which can receive a sample of a material to be analysed, and a reservoir porfion which is in communication with said region.
2. A cell according to claim 1, wherein said members at least in areas corresponding to said region comprise windows through which infrared radiation can be transmitted.
3. A cell according to claim I or claim 2, wherein said region is circular.
4. A cell according to claim 3, wherein the reservoir is annular.
5. A cell according to any preceding claim, wherein the surface of said first member has a recess which is arranged to receive a projecting part on a surface of the second member, such that there is a small axial spacing between the base of the recess on the surface of the projecting which defines said region, and said projecting part has a smaller lateral extent than said recess to 9 thereby define a space around said region which defines said reservoir.
6. A cell according to claim 5, wherein said recess and said projecting part are frusto conical.
7. A cell according to claim 5, wherein said recess and said projecting part are cylindrical.
8. A cell according to any one of claims 1 to 4, wherein said first member has a planar surface and said second member has a recess and a groove extending circumferentially around the recess, the space between the base of the recess and said first member defining said region and said circumferential groove defining said reservoir.
9. A cell according to any one of claims 1 to 4, wherein said first member has a recess and said second member has a groove, the space between the base of the recess and the second member defining said region and said groove defining said reservoir.
10. A cell according to claim 8 or claim 9, wherein said recess is circular and said groove is annular.

I ()
11. A cell according to any preceding claim, wherein the members are formed from sinterable infrared transmitting material.
12. A cell according to claim 11, wherein said material is a powdered alkali halide.
13. A cell according to any preceding claim, wherein the axial extent of said region is in the range 5 microns to 200 microns.
14. A cell according to any preceding claim in which the area of said region is of the order of I cm'.