Quantitative analysis scintillation counting

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

The use of LC-ARC or 96-well microtiter plates containing solid scintillant, in contrast, represents low-cost methodologies to improve the sensitivity of the semi-quantitative analysis of metabolites. The LC-ARC and 96-well microtiter plate approaches have similar LOD for 14C and 3H and both can be used in combination with MS to generate quantitative and structural data. Both approaches are particularly useful in cases where the sample is limited. The throughput of LC-ARC is higher than for the plate approach due to the need to dry and count the plates offline. However, the 96-well plate approach is nondestructive, such that drug-related components can be subsequently eluted from the plates for further analysis, if necessary. 

Residue Analysis Methods. Among the methods routinely used for residue analysis are determination of weight loss, extraction of the residue and quantitation of the extract by either gas chromatography or liquid scintillation counting, and measurement of the increase in void space within a fiber with time, or meniscus regression method. 

Quantitate the radioactivity, as a measure of RT activity in 1 pL of the culture supernatant, either by liquid scintillation counting (cut out the spots and place them directly into scintillation fluid), by phosphorimage analysis and quantitation of relative pixel units, or by autoradiography and laser densitometry. 

Liquid chromatography is routinely used for the quantitative analysis of a drug and its metabolites in radiolabeled in vitro metabolism experiments and in humans and animal ADME studies. Online radio-flow detection (RFD) and offline microplate scintillation counting (MSC) are the most commonly used radiochromatographic techniques in radiolabeled metabolite profiling and quantification (Boernsen et al., 2000 Nassar et ah, 2003 Bruin et al., 2006). LC/RFD is compatible with ESI mass spectrometry and provides high analytical speed and excellent separation resolution (Athersuch et al., 2008). 

The sensitivity and accuracy of measurement of radioactivity with liquid scintillators is far superior to that of all other counting methods in quantitative analysis. 

The reliability and accuracy of liquid scintillation counting in suspension is superior to that of all other radiometric methods for quantitative analysis of whole spots or of narrow zones. This is for the following reasons ... 

Radionuclidic purity is only of concern in the context of dual-isotope labeling, or if crosscontamination from a laboratory mishap is suspected. Radionuclidic purity is best measured by liquid scintillation counting modem LSC instruments have detectors and analysis software designed to discriminate quantitatively between the different isotopes used in the life sciences, except at very low counting levels. Radionuclidic purity is entirely distinct from isotopic purity, or content, of compounds labeled with stable isotopes, such as deuterium or carbon-13. Such information may be very important to the utility of stable-labeled compounds such as internal standards for mass spectrometric quantitation assays. ... 

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