Liquid scintillation counting, measurement

The concentration was further corrected for radiochemical purity according to the manufacturer s specifications because liquid scintillation counting measures the total sample activity and does not account for the presence of radiolabeled impurities. Stock solutions were stored at -15°C or -20° C in order to minimize sample loss due to hydrolysis. Injected sample solutions were prepared in 0.25 mL plastic vials by diluting stock solutions with buffer or deionized water and were also stored at -15° C or -20° C. 

Liquid scintillation counting is by far the most common method of detection and quantitation of -emission (12). This technique involves the conversion of the emitted P-radiation into light by a solution of a mixture of fluorescent materials or fluors, called the Hquid scintillation cocktail. The sensitive detection of this light is affected by a pair of matched photomultiplier tubes (see Photodetectors) in the dark chamber. This signal is amplified, measured, and recorded by the Hquid scintillation counter. Efficiencies of detection are typically 25—60% for tritium >90% for and P and... 

Liquid scintillation counting has been used frequently for the measurement of environmental technetium. The specimens to be analyzed are treated by chemical procedures to obtain a technetium-bearing sample solution, which is mixed with a cocktail for scintillation counting. A low background scintillation counter with an anticoincidence system can be used for high precision measurements at a detection limit of 1-25 mBq. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

Hiraide et al. [68] used continuous flow coprecipitation-floatation for the radiochemical separation of cobalt from seawater. The 60cobalt activity was measured by liquid scintillation counting with greater than 90% yield and a detection limit of 5 fCi/1 seawater. 

A drin and Dieldrin Metabolism.— The in vivo metabolism of the chlorinated alicyclic insecticides, aldrin and dieldrin, has been measured. Fish were exposed to l c-labelled aldrin or dieldrin for 6 hours. The metabolism of each compound was monitored by thin layer chromatography of hexane and chloroform-methanol extracts of liver homogenates, followed by liquid scintillation counting of the spots (5,15,16). 

Traditionally, HAT activity is measured with a discontinuous radioactive filterbinding assay, which uses pH]acetyl-CoA as a histone acetyltransferase substrate [46]. The transfer of [ H]acetyl-groups to the histone substrate by histone acetyltransferases is detected by liquid scintillation counting of pHjacetylated histones, which are retained on a phosphocellulose disk. Due to its discontinuous character, this assay is technically problematic and not ideal for kinetic analysis. Hence, other assays that work with radiolabeled acetyl-CoA have been described that are suitable for a higher throughput. These work with streptavidin-covered beads [47] or a variant of the SPA with microtiter plates that contain a scintillant (FlashPlates) [48]. But as all these protocols are based on radioactively labeled substrates, they apparently show the same disadvantages that were described for the radioactive HDAC assay protocols. Therefore, nonradioactive assays have been developed to study histone acetyltransferase activity. 

Because specific activity is always an intensive variable, one need not recover all of the sample to determine the ratio mol A /mol A. To evaluate SAa, one need only obtain an amount that provides an accurate measurement of A and total A. The former is easily achieved by liquid scintillation counting, and spectrophotometry or some other enzymatic assay usually allows accurate determination of mol A in a sample. 

The LPL catalytic assay measures the hydrolysis of a [14C[- or [3H]-triolein emulsion producing the 14C- or 3H -labeled free oleic acid [6]. The 14C- or 3H-labeled oleic acid is isolated by a selective extraction procedure and its radioactivity is determined by liquid scintillation counting [40]. Lipase activity is calculated as nanomoles of oleic acid released per minute per milliliter of postheparin plasma [41]. 

The activity of dihydropyrimidinase or /J-urcidopropionasc can only be measured in liver or kidney. The activity of dihydropyrimidinase is determined using a radiochemical assay with subsequent separation of radiolabeled dihydrouracil from radiolabeled N-carbamyl-/>-alanine with reverse-phase HPLC combined with detection of 14C02by liquid scintillation counting [11]. The activity of /1-ureidopropionase can be determined using radiolabeled N-carbamyl-/l-alanine followed by separation of radiolabeled N-carbamyl-/>-alanine from radiolabeled /1-alanine by reverse-phase HPLC [10,14]. 

To commence measurements, 1 ml of labeled solution was added to one arm (donor), and at the same time an equal volume of unlabeled solution was dispensed to the remaining arm (receptor). Aliquots of 0.1 ml were withdrawn from both arms at suitable time intervals over 4r-5 days. The activity of samples from the receptor side was determined by liquid scintillation counting, and Wt/Wm vs. y/t plots were constructed. The temperature range studied was 20-50°C. (Note salicylic acid was shown not to penetrate disks composed of polystyrene alone, and self-diffusion kinetics were reproducible between different disks of the same polystyrene/zeolite composition). 

Amano, H. and Yanase, N., Measurement of 90Sr in environmental samples by cation-exchange and liquid scintillation counting, Talanta, 31, 585-590,1990. 

In the stage of drag discovery, LC/MS-MS analytics is the method of choice to quantify the unbound drag concentration. The sensitivity can be increased by the use of radiolabeled substance. But, the radiochemical purity, isotope decay, if not 14C-label is used as well a sufficient specific activity must be taken into consideration (Wright et al. 1996). The concentrations of radioactivity in bound and unbound fraction are measured by liquid scintillation counting. The use of radiolabeled material allows easily examination of the potential of adsorption. However, the identity of the drag in unbound fraction should additionally be veri-... 

OF THE RADIOACTIVITY CONCENTRATION Radioactivity measurements are carried out by the liquid scintillation counting procedure in -spectrometers using an external standard device which permitted the counting efficiency to be determined by the channel ratio method (explained for instance by Dyer (1980)). 

Three aliquots from each (processed) sample were used for radioactivity determination. The aliquots from the urine samples were measured directly in the liquid scintillation counting procedure after addition of the scintillator Roth-rotiszint eco plus (Roth, Karlsruhe, Germany). The other matrix aliquots taken up on Combusto Cones (Canberra-Packard), weighed, dried at room temperature, were combusted in a Tricarb combuster (Canberra-Packard GmbH, Model 307) and the 14CC>2 formed was absorbed by Carbo-Sorb (Canberra-Packard). The subsequent radioactivity measurements were carried out by the liquid scintillation counting procedure in a ((-spectrometer (Canberra-Packard 2500 TR) after addition of the scintillator Permafluor E+ (Canberra-Packard). 

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