Scintillation counting tissue samples

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. 

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. 

After solubilisation, the sample is added to a sdntillation cocktail suitable for aqueous solutions. Solubilisation of tissues often produces chemiluminescent materials which can distort measurements of radioactivity. To reduce or remove this problem, it is recommended that samples should be kept in the dark before counting. An expensive alternative to scintillation counting for tissue samples, and one which is only justified when handling highly repetitive samples, is combustion of the sample in an appropriate furnace the 14C and 3H labelled material is converted respectively into C02 and H20 which are collected in suitable wash bottles. 32P label is converted into phosphate which remains in the ash following combustion. 

In most tissue samples, three metabolite peaks are apparent, whereas only a single metabolite is produced in peripheral blood cells (see Note 9). For systems using the Berthold LB506C detector (see Note 10), the software allows quantitation of the counts contained in each peak. Alternatively, fraction collection and scintillation counting can be applied. From the counts per peak for metabolites (see Note 11), the activity of an individual sample can be calculated using the equation ... 

Each animal was sacrificed by captive bolt after the appropriate withdrawal interval (4, 6, 14 and 28 days after the 2nd dose) and processed as in an abattoir. The entire liver, kidneys and udder were excised and 1-2 kg samples of muscle from both the flank and the udder diaphragm and 1-2 kg samples of fat from the abdominal area were collected. Each organ and tissue was minced and processed three times through a commercial meat grinder to prepare respective homogenate samples. Sub-samples (200-300 mg) were prepared in triplicate for total residue analysis. Total radioactivity concentrations, expressed as pirlimycin free base equivalents, were determined by direct liquid scintillation counting (liquids) or combustion analysis (solids) following standard techniques. 

Assay Procedures. Tissues, feces, urine samples, and sample fractions were assayed for radioactivity (RA) by liquid scintillation counting essentially as described by Magnussen et al. (9). Tissues were assayed for parent tilmicosin by methanol extraction, purification by liquid-liquid partitioning, and measurement by high performance liquid chromatography (HPLC) on a reversed phase phenyl column with detection by UV absorption at 280 nm. Elution was with a nonlinear gradient of mobile phase consisting of water, acetonitrile, and dibutyl ammonium phosphate at pH 2.5. 

Sensitive methods for analysis of plutonium in urine are particularly important for estimating occupational plutonium body burdens. Routinely available instrumentation, such as the alpha spectrometer, can readily detect these low concentrations. More sensitive methods are commonly required for urine samples in order to assess chronic exposures to plutonium. These low detection limits were first achieved in the past by nuclear emulsion track counting (see Table 6-1). In this method, the electrodeposited sample is exposed to nuclear track film, subsequent to the isolation of plutonium. The alpha-particle emitting isotopes of plutonium will leave tracks on the film which are counted to quantify the amount of plutonium. Nuclear emulsion track counting has been used in the past to measure plutonium concentrations in the urine of workers at a nuclear reactor plant (Nielsen and Beasley 1980). A type of scintillation counting has been used to measure plutonium-239 and americium-241 in animal tissues (NCRP 1985). 

More recently we have measured the turnover rate of lAA in tomato shoots after different incubation times, as part of a study of lAA biosynthesis in that tissue. lAA was supplied to the surface of the youngest leaf, 1 cm or longer, of excised shoots from twenty, 4-week-old tomato plants, as a 10 /xl drop (2 1 1, ethanol propan-2-ol H2O) containing 3711 Bq pH]IAA (1.11 GBq//xmol). Uptake was allowed for 2 h, surface radioactivity was then removed by several washes with 50% aqueous propan-2-ol followed with water, and the plants equilibrated for 1 h. After 0,4,10 or 20 h incubation in continuous light, lAA was extracted, purified, derivatised to form the pentafluorobenzyl ester [10] and the specific activity measured by liquid scintillation counting and GC-ecd. The purity and identity of selected samples was confirmed by combined GC-MS. 

Two batches of 2 mm zucchini hypocotyl segments (3 g fw/90 ml 1.5%(w/v) sucrose at 25 C) were loaded for 50 min to equivalent levels of [ C] using 0.3 /xM [ 1 - CjlAA in the absence of quercetin and 0.18 /xM [1- C]IAA in the presence of 10 /xM quercetin. The segments were collected, rinsed briefly with 50 ml ice-cold sucrose (1.5%), and then resuspended in 150 ml 1.5% sucrose (25 C conical flask) and placed in an orbital shaker (120 rpm) at 25 C. Samples of medium (1 ml) were withdrawn over a 60 min time course and transferred to a scintillation fluid designed to count aqueous samples [5]. Conventional compartmental analysis by curve peeling [3, 29, 37] allowed estimation of first-order rate constants for efflux from the tissue considered to be comprised of a series of three compartments. 

The total taxane (TTAX) concentration, a sum of the concentrations for CT-2103, TXL, and TXL-metabohtes was determined from scintillation counting of the plasma or tissue sample homogenates. Extractable taxanes, including TXL and organically extractable TXL metabolites, were determined by scintillation counting of ethyl acetate extractions of the plasma, tumour, liver, and spleen samples. Plasma and tissue TXL concentrations were also determined by HPLC/radiometric analysis of the extracts. Metabolites were identified by HPLC followed by mass spectrometry on a Quattro It (Micromass, Manchester, UK) triple quadrupole mass spectrometer fitted with an electrospray orthogonal Z spray ion interface operating in the positive ion mode. ... 

The interesting study on the uptake of carrier-free Cs by Ramalina reticulata (Handley and Overstreet, 1968) supports the uptake model outlined above. Cesium-137 was employed at a concentration of l.OyuCi/liter and the living tissue samples were washed in running water for 5 minutes just before immersion in the solutions. The uptake was determined by counting the material with a well-type scintillation detector. It was shown that the uptake of Cs was not directly linked to metabolism. The authors also observed both the rapid establishment of the equilibrium and the low temperature dependence of the uptake. The process was 70% complete within half an hour. This time for the establishment of the equilibrium, in contrast to Tuominen s few minutes, is obviously due to the use of a radioisotope with a higher accuracy of detection compared with the inactive Sr. 

Third, difficult samples of materials containing 3H or 14C (e.g., tissue slices, etc.) can be converted to 3H20 or 14C02 in commercially available sample oxidizers. These units burn samples under controlled conditions and then separate the 3H20 and the 14C02 for counting in an acceptable scintillation cocktail. Sample oxidation also eliminates color-quenching problems. 

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