Organic radioactive, direct analysis

At the surface of the solution the cationic soap constitutes a positive layer of organic cations neutralized by Cl" and PoCl62" ions 210Po emits a-rays. The surface density as well as the kinetics of the adsorption of PoCl62" are determined by measuring the radioactivity above the surface of the solution. An analogous technique is used to determine the density of the soap adsorbed at the air-solution interface, when the soap is labelled with 14C. Therefore, these measurements allow a direct analysis of the composition of the adsorbed soap films at equilibrium and during their formation. 

IAEA currently specializes in the production of certified RM for radioactive isotope content, but also offers CRM for inorganic trace analysis, organic analysis, and determination of stable isotopes. Information can be foimd via the IAEA homepage, www.iaea.org, or directly from nucleus.iaea.org/rpst/Reference Products/ReferenceMaterials/index.htm... 

Levels of radioactivity were highest in the liver and kidneys of male and female rats at two hours post final dose and averaged 3.A63 ug equivalents/g and 4.073 ug equivalents/g in male and female rat liver, respectively, and 2.383 and 2.132 yg equivalents/g in male and female rat kidney. Urine samples were analyzed by direct injection onto the HPLC column, whereas feces and liver samples were homogenized and extracted with methanol and subjected to solid phase extraction (if necessary) prior to HPLC analysis of the organic extract. The major radiolabeled component in male and female rat urine co-chromatographed with flunixin. Lesser amounts of the two hydroxylated metabolites, 5-hydroxyflunixin and 2 -methyIhydroxyflunixin, were also detected. Two major radiolabeled residues, identified by retention characteristics as flunixin and 5-hydroxyflunixin, were observed in rat feces. The major radiolabeled component in male and female rat liver co-chromatographed with authentic flunixin standard. The monohydroxymetabolite, 5-hydroxyflunixin was also detected in male rat liver. 

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. 

Preparation of samples for use in RRAs varies. If the substance of interest is in biological fluids (e.g., urine, spinal fluid, plasma) it may be possible to add fluid directly to the RRA. In many instances, however, components (salts, proteins) interfere with assay integrity. In this case, it is necessary to devise a preparation scheme suitable for use with the RRA and which does not alter the quantities of the substance of interest, or to incorporate an appropriate internal standard in the method (e.g., radioactive tracer amounts of the compound of interest preferably labeled with an isotope different from that incorporated in the ligand). In the case of natural product analysis, standard aqueous or organic extraction procedures are followed and the sample is freeze-dried or dried to provide the final preparation. Aqueous fractions can be redissolved in assay buffers whereas dimethylsulfoxide (DMSO) is a useful solvent for organic extracts since many RRAs tolerate < 1 % DMSO in the final assay. 

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