Radioactivity detector continuous flow

Figure 29. Diagram of an HPLC fitted with a continuous-flow radioactivity detector.

Two other filtration modules, which both formed part of automated radioimmunoassay systems, have been developed. - One of these, was based on conventional continuous flow techniques. At the filtration stage, a continuously moving strip of glass fiber filter paper was strengthened and wetted, the reaction mixture was filtered, and the precipitate was washed by two streams of buffer. The strip was dried and overlaid with cellulose adhesive tape before being counted as it passed between two end-window radioactivity detectors and wound onto a take-up spool. In the second system, glass fiber filter disks are mounted at intervals over perforated segments of a flexible plastic carrier tape. The contents of five... 

Another advantage of radioactive tracers is their ease of detection and determination. The radiating properties of the tracers are not affected at all by the physical and chemical condition of the sample, i.e., temperature, pressure, presence and concentration of chemicals, and so on. This exempts one from laborious preparation and treatment of the sample before measurement. In the measurement of a nuclide emitting a y ray, all one has to do is to put the sample near a detector and press a button to operate the electronic system. Radioactive tracers are also suitable for continuous-flow detection and some of them further for imaging. 

The minimum amount of radioactivity that can be detected by a flow-through radiochemical detector is a subject of continuing debate. It is generally accepted that a fairly sharp peak that contains counts that are at least twice background can be detected. One formula for calculating the minimum detectable activity (MDA) is given by... 

In this assay (Demel et al., 1977 Demel et al., 1982), a monolayer, containing 14C-labeled phospholipid, is formed at an air—water interface. Vesicles and exchange protein are injected into the subphase. The loss of radioactivity from the surface is monitored continuously with a gas flow detector. Alternatively, the rate of transfer of radiolabeled lipids is measured by recovering the subphase or monolayer and quantitating the radiolabeled lipids. The difficulty in preparing the monolayers and the... 

An inexpensive commercially available radioactivity flow detector (with improved flow cell) has been demonstrated to be practical and reliable over several months of continuous application and is still in operation. 

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