Archive for October 2011
Liquid Scintillation and Radiation Safety
Working with radioactive isotopes requires diligent attention to safety measures, in order to avoid hazardous exposure(s). Because radioactivity cannot be detected without instrumentation, spills can easily be spread through and even out of the lab before they are noticed. Safety in radioisotope work requires sufficient attention to both containment and surveillance. Containment measures are designed…
Read MoreHPLC Flow Counting
Radiolabeled materials are often analyzed by chromatography. The original application of liquid scintillation counting to chromatographic techniques was to collect and count discrete fractions. This manner of counting is extremely laborious, and resolution is limited by the size of the fractions collected. Flow detectors were introduced to allow continuous LSC monitoring of column effluents. This…
Read MorePreparing Samples in PAGE Gels for LSC
Complex radioactive samples are often fractionated on polyacrylamide gels. Analysis of radiolabeled samples in electrophoretic gels follow the same pattern as that on TLC plates. The gel is analyzed as a whole for radioactive bands, which are then excised and counted to obtain quantitative results. National Diagnostics’ Autofluor can be used to enhance the autoradiography…
Read MorePreparing Tissue Samples for Scintillation Counting
Samples of animal or plant tissue are rarely thin or small enough to allow for full counting efficiency. Homogenization of such samples will allow them to be dispersed into a cocktail, but processing large numbers of radioactive samples by homogenization is not practical. To allow for efficient and consistent counting of tissue samples, tissue solubilizers…
Read MoreCounting Samples on Cellulose-Ester Filters
A common radiotracer technique is to precipitate macromolecules (protein & DNA) with TCA or some other strong denaturant, collect the precipitate on a filter and count it. Often such procedures give variable results, depending upon the degree to which the sample disperses from the filter into the cocktail. A typical artifact is counts which rise…
Read MoreCounting Samples from TLC Plates by LSC
In a typical TLC experiment, the radioactivity is detected at two points: after TLC it is analyzed by autoradiography, to locate radioactive spots. These spots are then scraped off of the plate and counted to provide quantitative information. Each of these steps can be enhanced using the following protocols. Autoradiography and LSC with TLC Plates…
Read MoreWaste Disposal Issues in Scintillation Counting
An aspect of LSC which must be considered in experimental design, is waste disposal. Unlike solid scintillation, LSC adds components to the sample increasing the volume of radioactive material by up to 1000 fold. The components of the LSC cocktail may represent a hazard or a disposal problem in addition to the radioactivity. For many…
Read MoreChemiluminescence and Static Electricity
Another commonly encountered artifact is chemiluminescence. This is caused by any chemical reaction which generates an excited product molecule, which decays to emit light. These reactions generate only a single photon, which may be quenched, or may reach the counter to register as a low energy emission event. Such reactions can generate 105-106 cpm, skewing…
Read MoreThe Complete Scintillation Cocktail
Living creatures contain both hydrophobic and hydrophilic compounds, any of which may be labeled during the course of a radioactive experiment. As discussed in earlier sections, the best solvents for scintillation counting are the aromatic organics, such as toluene and xylene. Hydrophobic compounds can be counted directly in such solvents, but hydrophilic materials, which include…
Read MoreCounting Efficiency and Quenching
While the effectiveness of a scintillation cocktail may be expressed a number of ways, it is most often given as the percentage of emission events that produce a detectable pulse of photons, referred to as the counting efficiency. In other words, one way to express the counting efficiency is to take the ratio of the…
Read More