Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1998-09-30
2001-05-08
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S370100, C250S370110
Reexamination Certificate
active
06229146
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for the position sensitive detection and analysis of radioactivity in a fluid stream, and more particularly to such detection and analysis in gas and liquid chromatography.
Chromatography has been an important research tool for many years in a wide variety of applications. The principles of chromatography are well known to those of ordinary skill in the art. Essentially, a sample containing a mixture of constituent components, referred to herein as analytes, is introduced into a fluid stream. In a simple type of chromatographic apparatus, the fluid stream is brought into contact with a resin bed. The resin has been chemically or physically treated so as to selectively retard the passage of the analytes. The result is that the sample mixture is collimated, that is, separated into its discrete analytes. The fluid stream with the collimated sample then flows out, as an effluent stream, from the collimating means. The collimated effluent fluid stream is typically passed through a detector or analyzer which determines the presence, amount, and or type of analyte. The presence of a particular analyte can be depicted graphically as a peak on a chart. The timing and size of each peak provides significant information regarding the analyte.
While chromatographic techniques and technology have enjoyed great advances generally, one aspect of chromatography has not. This area is the detection and analysis of radioactive and radiolabelled analytes. Indeed, the current state of the art in this area has not changed greatly since the early 1970's except for the fairly peripheral advancements in the use of computers and integrated circuits.
The current method of radioactivity detection in gas chromatography is referred to as gas proportional counting (GPC). Typical of the state of the art in this regard is the original design of the Packard Model 894 counter used for GPC. In this instrument the effluent stream from the chromatograph contains or has added to it a quenched gas. The stream is then passed into a counting tube. In the counting tube is mounted a high voltage wire. Radioactive decay events, such as the emission of a beta particle or a gamma ray, create ions in the gas stream, which in turn is electrically detected via the wire. The events can be detected and counted to determine the presence and approximate amount of the radioactive analyte in the tube.
This technology has significant limitations. The wire in the counting tube is sensitive to background noise such as ambient radiation and radiation from internally deposited debris. The apparatus can be “tuned,” that is, adjusted so as to increase efficiency, but is then sensitive to voltage and gas fluxes that may produce false readings. Typically, then, the instruments are not tuned in order to increase operational ease at the expense of analytical efficiency.
The resolution capability of this type of instrument also lags significantly behind the resolution capability of modern gas chromatography. Modern gas chromatography can separate and resolve many analyte peaks per minute. The state of the art GPC, however, can only recognize a single peak for all decay events occurring within the entire volume and length of the counting tube. Peak detection for radioactivity is thus limited to less than one per minute, making it impossible to correlate the radioactivity peak with the analyte peaks. Moreover, due to low counting efficiencies, quenching, detuning, and high background, detecting smaller radioactive peaks (for example, less than 250 disintegrations per minute (dpm)) is difficult. Thus a small but analytically important radiolabelled analyte may be completely missed or ignored by even modern GPC detectors.
Problems exist with radioactive assays performed with liquid chromatography also. In order to detect radioactive analytes, the liquid effluent stream from a liquid chromatograph must include or be mixed with liquid scintillation fluid. Decay events excite the liquid scintillation fluid to produce light, which can then be detected and measured. This process is expensive and inefficient. Relatively large amounts of scintillation fluid must be used and then safely disposed. Sample sizes typically must be larger, increasing the trouble and expense of obtaining the sample analyte.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method and apparatus for position sensitive detection of radioactivity in a fluid stream.
It is a further object of this invention to provide a highly efficient and relatively inexpensive method and apparatus for detecting the position of a radioactive decay event in a fluid stream.
It is a further object of this invention to provide a method and apparatus that can be used in conjunction with standard liquid or gas chromatography techniques to obtain position sensitive data regarding radiolabelled analytes in the chromatographic effluent stream.
This invention is a method and apparatus that provides for the highly efficient, yet relatively inexpensive, detection and analysis of radioactive or radiolabelled material in a fluid stream. More particularly, it can be used in chromatographic analysis to detect and measure radioactive or radiolabelled analytes in the effluent fluid stream from the chromatograph, providing higher and faster peak resolution while requiring a smaller sample size of the analytes in question. The invention is useful with both types of fluid (liquid or gas) chromatography. The method and apparatus have even broader application in any system having a fluid stream where position sensitive detection of radioactivity is desired.
In one embodiment of the invention, the apparatus comprises a channel through which the effluent fluid carrying the collimated analytes passes. A scintillant material, reactive to radioactive decay events such as the emission of a beta particle, is placed along the channel, at or near it, so as to be exposed to radioactive decay events occurring in the fluid. The channel and the scintillant can take any desired shape or geometry as is known to those of ordinary skill in the art. Detectors, for example in the case of a light-emitting scintillant, photomultiplier tubes, are placed so as to detect the effect on the scintillant of a decay event. Each detector will produce an output voltage, or output signal, upon detecting light emitted from the scintillant indicative of a radioactive decay event. The output signals of the detectors can then be analyzed by conventional means to generate data indicative of the number, position, and other characteristics of the decay event. The data can then be displayed in any conventional manner, such as in the form of graphs, histograms, and the like. The data can also be processed in conjunction with other data from the chromatograph, such as is obtained by the conventional chromatograph detector.
While there are many known ways to place detectors with respect to a scintillant, in one embodiment of this invention a detector is placed at either end of the scintillant. The output signals from the paired detectors can be transmitted to an analytically means. The analytical means can compare the output signals of the pair of detectors by a comparator of conventional design to determine the time differential between the respective output signals produced by a single event. The time differential provides an indication of the position of the event along the scintillant, and hence an indication of the position of the radioactive analyte within the channel and the fluid stream. An accumulator, or counter, can utilize the output of either the photomultiplier tubes or the comparator to generate data indicative of the total number of events detected. The accumulator can determine the number of events as a matter of time or volume as desired. The output from the comparator and/or the accumulator can also be input to a processor also receiving data from the chromatograph's conventional detector and/or a flow meter, whereby the radioactive peak
Cochran Joseph L.
McCarthy John F.
Palumbo Anthony V.
Phelps Tommy J.
Gagliardi Albert
Hannaher Constantine
Hardaway/Mann IP Group
Nexsen Pruet Jacobs & Pollard LLC
Towler, III Oscar A.
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