Radiochromatographic methods

Radiochemical Purity Determination of the percentage of fixed iodine on the molecule is usually done by the radiochromatographic method. It can also be done by a precipitation test for proteins. Proteins are precipitated with trichloroacetic acid, and the different phases are counted in a gamma counter. 

This radiochromatographic method, joining the resolution and reproducibility of HPLC with the sensitivity of scintillation counting, allows the detection of FAAH at the femtomolar level in specimens available not only in large amounts, but also in small quantities, such as brain areas or primary cells in culture. The method involves the procedure for both extraction of the proteins from samples and enzyme assay, performed by measuring the release of pHjarachi-donic acid from pHjanandamide. 

Plates DC-Plastik-folien, Kieselgel 60 Radiochromatographic method... 

Radioisotope-labeled nitrosamines have proven valuable in development of analytical methods and for demonstrating efficiency of recovery of nitrosamines from tobacco products and smoke (37-39). The very high specific activity required for low part-per-billion determinations has discouraged most analysts from using this approach. Unless a radiochromatographic detector with adequate sensitivity is available, samples must be counted independently of the final chromatographic determination, and one of the advantages of internal standardization, correction for variation in volume injected, is lost. 

High sensitivity. Detecdon limits are in the range of 0.05-5 pmol/mol of unmodified parent base. This compares well to the sensidvides of commonly used methods, such as high pressure liquid chromatography with fluorescence detection (6,7), radiochromatographic analysis (8), radioimmunoassays, and enzyme-linked immunosorbent assays (9,10). 

Iccular structures are. however, only analyzable on weighable compounds that arc obtained by synthesis of a model radiopharmaceutical with the long-lived nuclide Its structure will be determined with standard methods used in complex chemistry. After adapting the synthesis procedure for the Tc compound in a modified form to the analogous "Tc compound, the same structure of the radiopharmaceutical can be confirmed by radiochromatographic techniques (HPI.C, TLC) and electrophoresis. However, the structure of several " Tc radiopharmaceuticals, which have been successfully applied for some decades, have still not been characterized [1). A number of reviews and books dealing with " Tc radiopharmaceuticals has appeared in the last ten years [1.4-14). 

West et al. [188] have used TLC to determine the thyroxine level in human serum. For 43 persons with normal thyroid function they found an average of 5.4 jxg thyroxine per 100 ml serum with a normal range from 3.2 to 7.9 jxg per 100 ml. Altogether 339 patients were examined. ScHOBN and Winkler [148] have reported the radiochromatographic determination of labelled tri- and tetraiodothyronine in the serum of a patient who had been dosed with carrier-free Na I for therapy of hyperthyroidism (Fig. 172). This separation is important because triiodothyronine is about four times as active as tetraiodothyronine. Determination of total hormone iodine in serum with the usual methods does not reveal any pathologically modified ratio of tri- to tetraiodothyronine. 

---