Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Reexamination Certificate
1999-09-03
2002-04-30
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
C356S417000
Reexamination Certificate
active
06381014
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for analyzing gaseous samples comprising a device for generating a plasma, a feeding device for the sample to be analyzed and at least one detector unit, which in particular comprises at least one interference filter, a lens arrangement and a photodetector for detecting radiation, especially atomic emission or molecular emission, emitted by the sample to be analyzed.
A device for analyzing gaseous samples of this kind has for example been disclosed in U.S. Pat. No. 5,009,099, wherein a plasma generator, to which the sample can be introduced, is followed by a detector unit consisting of a multitude of photodetectors wherein the object of this known device is in particular to provide background correction in a plasma gas chromatography detector.
A detector unit for use in a device, as mentioned above, to record the radiation emitted from a sample to be analyzed has in its own been disclosed for example in DE-OS 39 42 375, wherein it is the object of this known device to simultaneously record several wavelength ranges of a polychromatic radiation, with one detector for each of the wavelength ranges considered. In this known embodiment the detector or each detector unit is formed of an interference filter, a lens arrangement and a following photodetector with an according readout electronics.
A modified sensor for a portable analysis instrument can be found for example in DE-A 38 40 106, wherein a plurality of folding mirrors is employed.
For the production of a plasma for various applications it is furthermore referred to for example U.S. Pat. No. 4,654,504, U.S. Pat. No. 5,394,090, U.S. Pat. No. 5,394,091, U.S. Pat. No. 5,394,092 or U.S. Pat. No. 5,153,519, wherein in these known embodiments various designs of microwave and RF plasma generators are proposed to provide a plasma for various applications or analytical procedures. Problematic with these known devices is the coupling of electromagnetic energy into the plasma gas, wherein the employed power is usually around several hundred watts. Therefore the power to be coupled is very high, so that adequate heat dissipation has to be provided in immediate vicinity of the produced plasma, to avoid damage to parts of the apparatus. For this purpose not only parts of the apparatus must be made of an electrically non-conducting, high-temperature resistant material to separate the gas or plasma from the remaining parts of the apparatus, but furthermore by providing such enclosing elements for the plasma, there results mostly an enormous requirement of space for the corresponding cooling devices, which renders the production of a plasma of low spatial spread more difficult or even impossible.
In the context of producing the plasma and in particular the use of additive gases and the correspondingly used plasma gases it can furthermore be referred to U.S. Pat. No. 4,776,690, U.S. Pat. No. 5,151,371, U.S. Pat. No. 3,887,280 or U.S. Pat. No. 4,517,824, where the use of various plasma gases and their additive gases is described in the context of specific applications in the analysis of gaseous samples.
Regarding the selection of plasma gases the use of a noble gas, and in particular helium or argon, has been for example disclosed in DE-A 41 10 343 or U.S. Pat. No. 5,394,092.
SUMMARY OF THE INVENTION
Starting from a device of the kind mentioned above and taking into account the disadvantages of known devices and designs, it is the object of the present invention to provide a device for the analysis of gaseous samples by which it is possible, with a simple and compact design and low plasma power and a small detector volume, which favors use of the device according to the invention in mobile or portable instruments, to achieve a correspondingly high accuracy and reliability of results on the samples to be analyzed.
To solve this problem, the device of the subject invention is essentially characterized in that the device for generating the plasma is made up of two in particular ring- or disk-shaped parallel, interspaced electrodes, each having one essentially centrical, in particular circular through-opening, and an isolator having a particularly circular through-opening for confining the plasma and that between said device for generating the plasma and the detector unit an optical unit, in particular a collimator lens for generating a parallel ray beam is provided. By forming, according to the invention, the device for generating a plasma from at least one isolator, which is positioned between parallel interspaced, in particular ring- or disk-shaped electrodes, wherein the electrodes and the interposed isolator forming the plasma producing unit are each provided with an essentially centrical opening, the establishment a plasma of low spatial spread and defined position is successfully achieved, wherein the dimensions of the plasma can be selected according to the various requirements. Furthermore it is possible to achieve through said isolator, in the particularly circular through-opening of which said plasma is produced and maintained, in a simple way and without the provision of (additional) confining elements, such as tubes, or additional means for heat dissipation, a safe confinement of said plasma and simultaneously securing heat dissipation from the immediate vicinity of said plasma. Through said in particular ring- or disk-shaped electrodes, which are positioned at both sides of said isolator and the through-openings of which are aligned with respect to each other, the supply of the energy necessary for the ignition and maintenance of said plasma is successfully achieved in a very small volume, such that overall a simple method for the production of such a low-power plasma, in particular noble gas plasma, can be provided at low power uptake and low gas consumption. Apart from the device for generating a plasma being formed from simple elements and overall small dimensions, it is possible to provide, by combination with the further provided optical unit, in particular a collimator lens for the formation of a parallel ray beam, and at least one detector unit an altogether compact, easy to use and simple to maintain overall design of the design according to the invention.
According to a preferred embodiment of the device for analyzing gaseous samples according to the invention, the design is such that, viewed with respect to the direction of plasma gas flow, another isolator with a through-opening, which is essentially equivalent to said through-opening of said isolator positioned between said electrodes, is positioned upstream of said first electrode. By an isolator positioned upstream, with respect to the direction of supply of plasma gas, a shielding action towards the direction of supply of plasma gas and sample is achieved, such that an impairment of the plasma gas to be introduced, and the sample to be introduced and subsequently analyzed, can be prevented. At this in particular the provision of a suitably small through-opening in said upstream isolator, which is essentially equivalent to the through-opening of the isolator positioned between the electrodes, in which the plasma is formed and confined, it is possible to achieve protection of the sample against decomposition or polymerization, caused by UV radiation or extended glow discharges, before reaching the plasma.
The isolator positioned upstream of said plasma could, if this side is at ground potential, be made of metal, for example Pt/Ir. To reduce the number of components it is proposed in another preferred embodiment that the first electrode, viewed with respect to the direction of gas flow, and the isolator positioned upstream of it are combined into one single component, and that the through-opening corresponding to the through-opening confining the plasma is followed by a preferably conically expanding section.
To protect operative equipment which is positioned downstream of the system of said electrodes and said interposed isolator it is proposed to position an additional isolator downstream of the, v
Knapp Günter
Platzer Bernhard
Evans F. L.
Jacobson & Holman PLLC
Platzer Bernhard
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