Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition
Reexamination Certificate
1998-12-30
2001-08-28
Soderquist, Arlen (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
C422S105000, C436S164000, C356S244000
Reexamination Certificate
active
06280690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved method and apparatus for obtaining the transmission spectra of liquid, paste and solid samples, and in particular to sample holders. It is applicable over a wide spectral range, but especially in the mid infrared region where absorption coefficients are often very high and corresponding sample thicknesses need to be very small, typically of the order of 10 microns for pure substances or simple mixtures.
2. Discussion of the Prior Art
There are a number of methods known for supporting samples for infrared spectroscopy. For powdered solids the sample is normally held within pressed discs of infrared transmitting material, typically KBr. The disadvantage of this method is that this has only a limited spectral range due to the absorption of KBr.
Spaced sample cells of infrared transmitting material are also used to support liquid samples. However, these typically have a limited spectral range. Other disadvantages are difficulty of construction and use, cost, lack of chemical inertness and limited spectral range.
Another known method for supporting liquid samples involves the use of thin films of porous material. Such discs can be obtained from 3M, and consist of Teflon or polythene. Teflon and polythene have absorption bands, but in different regions of the spectrum. Therefore it is possible to cover a wide spectral range by the selective use of the two materials. However, it is inconvenient to use different materials for different spectral regions and the absorption bands again reduce the quality of the recorded spectra.
Another method for supporting liquid samples is the use of coarse gauzes which take up liquid by capillary action. Janos Technology Inc produce screens formed by such a gauze (ECRAN (RTM) Screen Cells), which are described in U.S. Pat. No. 5,453,252. The gauze is formed from polymer coated glass fibres, onto which a liquid or powdered solid is placed. The gauze is approximately 300 microns thick where the fibres cross each other, and the holes between the fibres are approximately 1 mm across. Solid samples can also by supported by such screens.
The disadvantage of the above screens is their thickness and hole size. For many samples a thickness of 10-20 microns is preferable, especially in the mid infrared region, and the thickness of 300 microns provided by the Ecran Screen Cells prevents samples being thin enough. There is also the problem that with hole sizes in the region of 1 mm, the surface tension of many liquids is not sufficient to hold the liquid in place across the holes. Solid samples may be introduced by covering the mesh with a solution of the sample in a suitable solvent and allowing the solvent to evaporate. The large hole size of the Ecran screen cell makes it extremely difficult to achieve a continuous film by this means.
SUMMARY OF THE INVENTION
The present invention seeks to overcome or at least mitigate these problems, and from a first aspect provides a spectroscopy sample holder for receiving a sample comprising a wire mesh which has been pressed to reduce its thickness.
From a second aspect the invention provides a method of forming a sample holder for spectroscopy, comprising: providing a mesh, and pressing said mesh between hardened dies so as to reduce its thickness.
By pressing a mesh, a thickness closer to that needed for optimum operation can be achieved, leading to improved results. The mesh can be pressed to a thickness considerably below mesh thicknesses available on the market. Such a mesh can support liquid, paste or solid samples.
The wires of the mesh are preferably formed from stainless steel. It is believed that the invention will improve the performance of existing meshes which, after pressing, will have a smaller thickness. Preferably, however, a mesh whose strands have a small diameter initially is used. The finest stainless steel mesh with high transmission, which it is practical to manufacture, uses wires with a diameter in the region of 25 microns. This means that a mesh formed from this wire will have a thickness of approximately 50 microns, which is well above the desired thickness of 10-20 microns. This mesh is advantageously reduced in thickness by pressing between hardened dies to reduce the overall thickness to the region of 10 to 20 microns.
When the mesh is pressed as described above, the transmission is reduced as the wires are deformed. Therefore the nominal transmission of a mesh as described is preferably in the region of 80% before pressing to reduce thickness and in the region of 60% after pressing, which is adequate for use in transmission spectroscopy.
The pressed mesh of the present invention can support liquid samples by capillary action. Solids can be sampled by wetting the mesh with a solution of the sample and allowing the solvent to evaporate, leaving a film of solid on the mesh. In both of these cases the mesh may with advantage be chemically or thermally treated to improve the wettability. It has been found that washing the mesh in hydrochloric acid followed by distilled water before use for supporting a liquid sample significantly increases its wettability.
If the transmission of a powdered sample is to be measured, the sample and the mesh can be pressed at the same time. This has the advantage that the thickness of the sample is reduced at the same time as that of the mesh.
Thus, according to a second aspect, the present invention provides a method of preparing a powdered sample for spectroscopic analysis, comprising the steps of placing the sample on a mesh, and pressing the sample into the mesh with sufficient force that the thickness of the mesh is reduced.
The mesh may be conveniently supported in a suitable frame of cardboard or other material with an open aperture, preferably circular, the size of the frame and aperture being appropriate to the spectrometer being used but typically a 15 mm diameter aperture in a suitable frame. The observed effective transmission is reduced slightly by diffraction effects and decreases slightly, in a smooth, continuous manner, from short to long wavelengths over the range of a typical infrared spectrometer. Compensation of this effect is readily achieved by recording a reference spectrum, or background, with a clean mesh in the radiation beam.
Since the mesh is electrically conducting it may conveniently be heated by passing an electric current through it in order to aid the formation of thin capillary films of viscous liquid or low melting point solid samples.
The mesh may be disposable.
REFERENCES:
patent: 966599 (1910-08-01), Reynolds
patent: 2694852 (1954-11-01), Rogers
patent: 3049796 (1962-08-01), Pall
patent: 5453252 (1995-09-01), Truett
patent: 5519218 (1996-05-01), Chang
patent: 5764355 (1998-06-01), Gagnon et al.
patent: 5786226 (1998-07-01), Böcker et al.
R. M. Ressler et al. Applied Optics 1967, 6, 893-896, May 1967.
Diederiks, Jr. Everett G.
Soderquist Arlen
LandOfFree
Methods and apparatus for obtaining transmission spectra of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods and apparatus for obtaining transmission spectra of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and apparatus for obtaining transmission spectra of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2525395