Optical probe with sensor made of optical polymer

Details Optical probe with sensor made of optical polymer Optical probe with sensor made of optical polymer

1998-03-13

1999-07-20

Evans, F. L.

Optics: measuring and testing

By dispersed light spectroscopy

356326, 25033911, G01N 2101

Patent

active

059262699

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an ATR spectrometer, containing an optical probe, and to a method of analyzing liquid media which may or may not contain a solid.
Methods, spectrometers and probes of the abovementioned type are known, for example, from EP 0 221 011 A 2, from N. J. Harrick: Internal Reflection Spectroscopy, J. Wiley & Sons, New York 1976 and from the review article by P. A. Wilks in International Laboratory July/August 1989, p. 47-55. The publications by Harrick and Wilks describe "Attenuated Total Reflection" (ATR) spectroscopy. In brief, ATR spectroscopy operates as follows: A probe having a transparent sensor made of high-index material is brought into contact with a liquid medium having lower refractive index. In the sensor, a light beam is guided by total reflection at the interface between the sensor and the medium. At each reflection from the interface, the light enters the medium as a so-called transversely damped wave and interacts with the molecules in the medium, some of the light being absorbed and the rest being scattered back into the sensor. The light beam guided in the probe then has a deficit in the excitation energy range of particular molecules, and can therefore be analyzed with a spectrometer and used to identify these molecules. In contrast to conventional transmission spectroscopy, in which light is passed through glass cuvettes which are a few mm thick, the measurements in ATR spectroscopy relate only to a very thin layer around the probe. The thickness of this layer depends on the wavelength, the refractive indices, the angle of incidence and the polarization, and is of the order of magnitude of one wavelength of the absorbed light. The fact that the measuring layer is very thin makes it possible to take measurements in highly concentrated solutions, while these measurements can only be taken using transmission spectroscopy after the solutions have been diluted several times. EP 221 011 describes a method which, using ATR spectroscopy, makes it possible to measure highly concentrated dyestuff solutions and dispersions. In addition to high-index glasses, for example heavy flint glass, aluminum oxide (sapphire), diamond, strontium titanate, titanium oxide, zirconium oxide and quartz glass are also mentioned as materials for the relevant sensors. Particular emphasis is placed on the good measurement results obtained using sapphire prisms.
Probes having sensors made of these materials have the disadvantages that they are comparatively expensive and rigid and, depending on the material and design, can break easily.
The invention provides an improvement to this situation.
According to the invention, this is achieved in that the sensor contains an optical polymer or a mixture of different optical polymers.
The invention therefore relates to an ATR spectrometer, containing an optical probe having a sensor made of transparent material and a feed line and an exit line for light, wherein the sensor contains an optical polymer or a mixture of different optical polymers.
The spectrometer according to the invention is outstandingly suitable for methods of analyzing liquid media which may or may not contain a solid, in particular dyestuff solutions. The spectrometer is also particularly suitable for the analysis of blood, since the sensor is employed sterilized and, after use, can be disposed of without entailing great expense. The optical (transparent) polymer may be present as an essentially pure material, but may also be a mixture of different optical polymers.
Suitable polymers include transparent polymers such as polymethyl methacrylate, polycarbonates, polystyrenes, polyolefins, polyesters, polysulfones, polyether sulfones, polyether imides, polyarylates, polyamides, polyester carbonates, copolymers such as, for example, methyl methacrylate and n-pentafluoropropyl methacrylate, and polymer blends of polymethyl methacrylate/polyvinylidene fluoride. Polymethyl methacrylate is preferably used.
In one particular embodiment, the sensor is in the form of a fiber which can simultaneously b

REFERENCES:
patent: 5170056 (1992-12-01), Berard et al.
patent: 5396325 (1995-03-01), Carome et al.
Wilks, P. A., Jr., InternationalLaboratory: Jul./Aug. pp. 47-54 (1980).
"Proceedings of the Annual International Conference of the IEEE Eng. in Med. and Biol. Soc.", vol. 14, pp. 171-172, Pub. date: Oct. 29, 1992, Ed'd by J.P.Morucci et al.

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