Radioactive scintillation counting

A further consideration is whether the solvent is likely to interfere with the analysis. Toluene is a poor first choice for a method that is to quantify the drug by ultraviolet detection. It is difficult to remove all traces of the solvent, and even a small residual amount can affect the detection limit seriously. Similarly, chlorinated solvents are best avoided if radioactive scintillation counting or electron-capture detection is to be used. Some solvents may not be suitable because they would react with the analyte, for example a ketone such as ethyl methyl ketone would react with primary amines. Solvent impurities and additives may be unknown to the analyst. Antioxidants such as hydroquinone and pyrogallol are added to diethyl ether to limit peroxide formation. These highly electroactive molecules can affect electrochemical detection methods adversely, particularly if they have been concentrated by solvent evaporation. Freshly distilled diethyl ether may be used, but it should not be stored as this is not only potentially dangerous, the peroxides that form may decompose the analyte. Methyl /-butyl ether (boiling point 55°C) is supplied without antioxidants and is a useful alternative to diethyl ether. Chloroform and dichloro-methane may be stabilized with ethanol although pentene is used by at least one manufacturer and may... 

In the carbon-14 expts, HMX/RDX product was isolated qualitatively, separated Into its components, and each component assayed for carbon-14 beta radioactivity using a liquid scintillation counting technique (Ref 11). DPT-l4C was isolated as an intermediate product from the reaction mixt and similarly radioassayed. For the nitrogen-15 tagged AN expts, HMX and RDX were assayed mass spectrometrically for i5N/i4N ratios from which atom %1SN contents were calcd. In die course of these expts, each tagged species was added initially and also at subsequent stages of the reaction process. The important observations and results are summarized as ... 

Radioactivity Analysis. Samples of urine, feces, and tissues were combusted to COo and analyzed for radioactivity (5). By using this method the recovery of radioactivity from samples spiked with C was 95 dt 5%. To determine the radioactivity expired as CO2, 5-ml aliquots of the solution used to trap the CO2 were added to 15 ml of a scintillation counting solution containing 4 grams 2,5-diphenyloxazole (PPO) and 0.1 grams l,4-bis-2(5-phenyloxazolyl)-benzene (POPOP) per liter of 1 1 toluene 2-methoxyethanol. Samples were counted for radioactivity in a Nuclear Chicago Mark II liquid scintillation counter. Counting eflSciency was corrected by the internal standard technique. 

Since cigarette tobacco already contains several micrograms of the TSNA, we determined the transfer rate of NNN into the smoke by spiking the tobacco column with NNN-2 - C. The smoke from such radiolabeled cigarettes is then analyzed by HPLC and the amount of unchanged NNN-2 - C is determined by liquid scintillation counting. Independent of the smoke pH, about 11% of the radioactive NNN is found in the mainstream smoke thus 41-46% of mainstream smoke NNN stems from the tobacco NNN and 54-59% are pyrosynthesized (11). 

Instead of scraping and manual collection of the adsorbent, the band can be sucked off the plate with a Vacuum-cleaner -type apparatus. Dekker [50] described an apparatus for the isolation of compounds from layers by elution and direct Millipore filtration, and Platt [51] designed a zone collector that used vacuum to transfer separated zones from layers direcdy to vials for hquid scintillation counting of radioactivity. 

To determine the efficiency of aminoacylation of [14C]Phe-tRNA, 5 fil aliquots of the aminoacylation mixture are withdrawn before and after the reaction the samples taken from the reaction mixture at the end of the incubation are spotted onto 3-MM paper discs (Schleicher Schuell) and processed by the cold TCA precipitation method, while the sample taken before the reaction is spotted on a paper disc pretreated empty by the same cold TCA procedure. Determination of the radioactivity present on these filters by liquid scintillation counting allows one to calculate the aminoacylation efficiency of the reaction (which, for phenylalanine, should be >2% of total tRNA). The specific activity of the [14C] Phe-tRNA can be determined after one-step purification of Phe-tRNA by BD cellulose chromatography (Gillam et al., 1968), followed by determination of the radioactivity and of the A260. 

At the end of the aminoacylation reaction, a 5-fA aliquot of the reaction mixture is spotted onto a 3MM paper disc (Schleicher Schuell) that is immediately placed in 10% ice-cold TCA for 30 min. After three washes in 5% TCA at room temperature for 5 to 10 min, the filter is placed in an ethyl ether ethanol (1 1) mixture for 10 min and then in ethyl ether for 10 min before being dried under an infrared lamp. The amount of radioactivity precipitated on each filter is finally determined by liquid scintillation counting. 

For the quantitation of in vivo absorption of 5Ca2+, 200 jd 1 of radioactive solutions were administered by gastric gavage to male mice kept on a deionized water diet during the previous 18 hours. After 4 hours blood was obtained by axillary incision and Ca2+ was extracted with TCA and determined by liquid scintillation counting (26). 

Arukwe et al. [15] dosed Atlantic salmon with radioactive labeled NP. Fish were frozen immediately until gall bladder, skin, kidney, gill, liver, muscle, fat, remaining carcass and viscera were sampled and analysed. Tissue radioactivity was analysed by liquid scintillation counting after combustion of aliquots in an oxidiser apparatus. Metabolites (biliary and urinary) were separated by radio-HPLC. 

The washed-precipitate, containing antibody-bound morphine, is dissolved in NCS-solubilizer, and the radioactivity is counted with the help of a Packard-Iri-card Liquid Scintillation Spectrometer,... 

DDT Metabolism.-- The metabolism of DDT has been studied in R and S fish, following similar protocols to chlorinated cyclodiene metabolism organic extraction (acetonitrile), thin layer chromatography of organic extracts, and liquid scintillation counting of the resultant spots (4). When S and R fish were exposed to 60 yg/l of 14C-labelled , -DDT for 4 hr, radioactivity was found in the spots which co-chromatographed with... 

Separated metabolites (and parent compound) are quantitated by first scanning developed thin-layer chromatographic plates to locate radioactive spots by means of a radiochromatogram scanner and then accurately measuring radioactivity by scintillation counting. Unknowns are identified by the usual chemical and spectrometric methods. 

Drug levels within the stratum corneum can be assessed by sampling single corneocyte layers with adhesive film. The drug is then extracted from the tape-strips and quantified by a suitable analytical method. Usually, scintillation counting (for radioactive compounds) or high performance liquid... 

For Ptdins 4 kinase and Ptdins (4) P5 kinase activities, the assay can be modified with assay buffer (50 mM Tris-HCl, pH 7.2 10mM MgCh 1 mM DTT 0.4% Triton X-100), 0.5 mM of substrate Ptdins or PtdIns4P, and 1 (xCi [y- P]-ATP. Terminate the reaction with 0.6 mL chloroformimethanol (1 1, v/v). After addition of 0.5mL 12N HCl, phosphoinosi-tides are extracted into the lower chloroform phase, which are washed with 1 mL methanoLlM HCl (1 1, v/v) followed by 1 mL methanoLO.l mol/L HCl (1 1, v/v). The radioactive reaction product can be isolated by TLC and quantified by liquid scintillation counting. 

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