Optics: measuring and testing – Photometers – Integrating spheres
Patent
1993-03-22
1995-04-18
Limanek, Robert P.
Optics: measuring and testing
Photometers
Integrating spheres
250228, G01J 104
Patent
active
054083125
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for the qualitative and/or quantative determination of the composition of a sample which is to be analyzed.
STATE OF THE ART
Known are so-called photometer balls which are capable of reflecting on the inside: photometer balls have the job of integrating diffusely reflected radiation of a sample that is to be analyzed and/or of a standard (sample with a known composition). Such photometer balls, also called Ulbricht balls, require primary radiation, which is either beamed into the ball or whose source of radiation is located within the cavity of the ball, respectively inside the wall of the ball, in order to generate diffuse reflection. The reflected part of the radiation regularly reflected by the sample that is to be analyzed has a disturbing effect because it adulterates the measuring signal significantly. Therefore, usually an attempt is made to screen out the regularly reflected radiation (incidence angle= reflection angle) by means of a so-called radiation trap.
In addition to this a reflection method is known which utilizes the physical phenomena accompanying radiation reflection at the interface of two optically differently thick media. This process is known by the names ATR (Attenuated Total Reflection) spectroscopy or FMIR method. The device required to conduct this process contains the so-called ATR element, which, for example, consists of a prism of trapezoidal design. Deposited on the top side and underside of the element is the probe that is to be examined. Due to the trapezoidal cross-section of the ATR element, the parallel beam pencil which hitting the slanted side of the element is totally reflected (usually) several times back and forth inside the element.
Nonetheless, however, some of the electromagnetic energy penetrates the optically thinner medium. As soon as the thinner medium absorbs the radiation that has penetrated, reflection is no longer total. The depth of penetration, for instance, of an infrared radiation depends, i.a., on the selected wavelength and the incidence angle. Following passage of the radiation through the element, the radiation, weakened by the absorbed part thereof, is measured. This process, which works with the "weakened total reflection", has, however, the drawback that it practically permits only, according to the present state of the art, semi-quantative analyses.
DESCRIPTION OF THE INVENTION
The object of the present invention is therefore to provide a device for the determination of the composition of a sample to be analyzed with which both the qualitative and quantitative determination can be conducted with great accuracy. Compared to the state of the art devices, considerably improved are to be primarily analysis and measuring precision as well as detection ability, which is an essential criterium for the assessment of the quality of the analytical method.
The present invention is based on the striking revelation that this goal can be realized by means of a combination of the, as such known, photometer ball and an, as such known, ATR element. Herein the present invention proceeds from the idea to conduct primary radiation to the sample outside the photometer ball as well as from the sample outside the photometer. In this manner only the diffuse radiation coming from the sample reaches the cavity of the photometer ball so that the normally occurring disturbance due to primary radiation is obviated.
In the present invention, therefore, the ATR element or elements are initially utilized, contrary to the present state of the art, only to conduct radiation to the sample that is to be examined.
An element of the invention is, therefore, that in order to be able to integrate diffuse radiation, a device is created which is provided with at least one hollow body capable of reflecting from its interior and having at least one aperture which is covered by an ATR element. The sample to be analyzed is disposed on the underside of the ATR element or elements (FIGS. 1 and 2), respectively on the side turn
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Pries Ralph H.
Yoon Dae-Jin
Yoon-Ok Kim
Limanek Robert P.
Tran Minhloan
Yoon-Ok Kim
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