Optics: measuring and testing – Sample – specimen – or standard holder or support – Fluid containers
Reexamination Certificate
2000-08-23
2002-12-10
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Sample, specimen, or standard holder or support
Fluid containers
C356S244000
Reexamination Certificate
active
06493080
ABSTRACT:
This application claims Paris Convention priority of DE 199 49 953.5 filed Oct. 16, 1999 the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns a total reflection measuring cell for the spectroscopic examination of an, in particular, fluid sample in an infrared (=IR) spectrometer comprising an ATR (=attenuated total reflectance) crystal having a plane surface and a diaphragm clamped on several sides in a clamping frame, wherein the clamping frame is disposed such that the diaphragm extends at a small separation from the plane surface of the ATR crystal.
ATR measuring cells of this type are known from U.S. Pat. No. 5,362,445 A1 or DE 196 12 877 C1.
To study the interactions between biomolecules by means of FTIR-ATR spectroscopy, it is important to introduce ligands in the evanescent field without causing mechanical disturbances of the sensitive layer on the ATR crystal or changing the concentrations of the dissolved substances which interact with the immobilized molecules. This is realized by a diaphragm, generally a dialysis diaphragm which is disposed above the sensitive crystal surface and separates a sample chamber below the diaphragm from a dialysis chamber above the diaphragm. Compounds having a low molecular weight can be dialyzed into and out of the sample chamber according to the MW Cut-Off of the diaphragm without lessening macromolecules in the evanescent field or destroying the immobilized thin layers on the crystal surfaces. Introduction of the ligands into the evanescent field can be accelerated beyond the thermal diffusion rate. Through the use of electrophoretical currents, charged ligands can be specifically transported into and out of the sample chamber through the diffusion barrier and the mechanical obstacle formed by the dialysis diaphragm.
The construction and use of such total reflection measuring cells through the initially mentioned features is described in detail in the above cited DE 196 12 877 C1, the complete disclosure of which is hereby incorporated by reference. The use of a diaphragm in an ATR cell includes, however, the problem of keeping an exact distance from the plane surface of the ATR crystal. Unfortunately, the diaphragms clamped in a clamping frame have generally the tendency to form waves or sag through. The filling or emptying of the hollow space above the diaphragm can cause pressure transfer to the hollow space below the diaphragm such that the sensitive sample layer on the crystal is damaged and the IR measurement becomes impossible. In the extreme case, the diaphragm will sag that much that during filling/removing processes it comes even in direct contact to the crystal surface thus removing the immobilized sample from the crystal.
It is therefore the object of the present invention to present a total reflection measuring cell of the initially mentioned type which does not have the above-mentioned disadvantages, guarantees a considerably increased measuring accuracy and thus reliably ensures the quality of the measuring results.
SUMMARY OF THE INVENTION
In accordance with the invention, this is achieved by additionally providing a tensioning device for displacing the diaphragm on an inner partial area of its surface clamped between the legs of the clamping frame in the direction of the plane surface of the ATR crystal such that the displaced inner partial area of the diaphragm surface has a higher tension than before the diaphragm surface merely clamped in the clamping frame, and providing a stop to which the tensioning device is forced and fixed in this position such that the inner partial area of the diaphragm surface has an identical defined distance from the plane surface of the ATR crystal.
The tensioning device reliably prevents sagging of the diaphragm in the tensioned inner partial area such that the natural waviness of the diaphragm material does not present any problems any more. The mechanical stop achieves an extremely exact positioning of the tensioned diaphragm surface in the inner partial area relative to the plane surface of the ATR crystal, in particular an exact parallelism with simple means and without great production effort.
Particularly preferred is an embodiment of the inventive ATR measuring cell wherein the tensioning device comprises a continuous wedge whose continuous closed edge line tensions the inner partial area of the diaphragm and forces same towards the ATR crystal. A continuous wedge of this type can be produced in a mechanically simple manner and with high accuracy.
In an advantageous further development of this embodiment, the angle of the wedge sides of the continuous wedge towards the plane surface of the ATR crystal in the fixed position of the tensioning device is between 30° and 60°, preferably approximately 45°. In general, one will choose a symmetrical wedge shape, i.e. both wedge sides having the same angle. Variants are also feasible wherein the two wedge sides have different angles.
Due to the longitudinal shape of the common ATR crystals, a further development is preferred wherein the continuous enclosed edge line of the continuous wedge forms a longitudinal oval comprising two parallel longitudinal sides forming a semi-circle at each of their ends.
One embodiment is particularly preferred, wherein the stop towards which the tensioning device can be forced and fixed in this position comprises a continuous inclined surface of an inclination corresponding to the wedge angle. This guarantees positioning of the diaphragm tensioned in the inner partial area plane-parallel to the sensitive surface of the ATR crystal with high precision whereby the production effort is very small.
A further advantageous embodiment of the inventive ATR measuring cell is characterized in that between the inner partial area of the tensioned diaphragm surface within the continuous enclosed edge line of the continuous wedge and a cover part of the tensioning device facing away from the diaphragm in the unfolded state, a hollow volume is formed which can be filled or emptied via an inlet and an outlet in the cover part. The sample fluid can flow through this hollow space when fluid samples are measured.
A further development is advantageous, wherein the cover part is produced from transparent material, preferably plexiglass. This allows in particular observation of the flow behaviour of the sample fluid but also discovery of possible contamination in the hollow space and removal thereof through rinsing.
Also preferred is one embodiment wherein a hollow volume is formed between the plane surface of the ATR crystal and the tensioned inner partial area of the diaphragm surface which can be filled or emptied via an inlet and an outlet. In this manner, the molecules diffused through the diaphragm can contact the sensitive surface of the ATR crystal. Moreover, the inlet and outlet allow rinsing of the sensitive area of the ATR crystal for cleaning which may serve i.a. to prepare subsequent measurements.
One embodiment of the inventive ATR cell is particularly preferred wherein the tensioning device can be detachably and rigidly connected, preferably screwed to a base plate onto which the ATR crystal is fixed. This considerably facilitates the relative positioning and fixing of the achieved optimum position between diaphragm and ATR crystal.
One further development of this embodiment is particularly preferred for geometrical reasons, wherein the inlet and outlet lead, through the base plate, to the hollow space between the plane surface of the ATR crystal and the tensioned inner partial area of the diaphragm surface.
In a further development, the optimum relative position can be achieved and fixed in that the clamping frame comprising the clamped diaphragm is disposed between the base plate and the tensioning device and comprises through-bores for receiving and guiding the screws for screwing the tensioning device to the base plate.
In a particularly simple further development of these embodiments, the stop for the tensioning device is integ
Bruker Optik GmbH
Stafira Michael P.
Vincent Paul
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