Specific activity radiochemical

A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

Muelder and Shadoff (3) prepared C-2,3,7,8-Cl4-DBpD (0.9 mCi/ mmole) by chlorination of C-2,7-dichlorodibenzo-p-dioxin made from potassium C-2,4-dichlorophenate. The preparation of tritium-labeled 2,3,7,8-Cl4-DBpD is justified because the radiolabeled intermediates are less expensive and more accessible and because a higher specific activity is potentially attainable. Here, we consider the optimal conditions for the reaction sequence designed to obtain products of high chemical and radiochemical purity shown at the top of p. 8. 

Photoactivation analysis has also been used to determine fluoride in seawater [73]. In this method a sample and simulated seawater standards containing known amounts of fluoride are freeze-dried, and then irradiated simultaneously and identically, for 20 min, with high-energy photons. The half-life of 18F (110 min) allows sufficient time for radiochemical separation from the seawater matrix before counting. The specific activities of sample and standards being the same, the amount of fluoride in the unknown may be calculated. The limit of detection is 7 ng fluoride, and the precision is sufficient to permit detection of variations in the fluoride content of oceans. The method can be adapted for the simultaneous determination of fluorine, bromine, and iodine. 

At room temperature the chemical and radiochemical yields of 155 were different. The chemical yields were in the 30-40% range, while the radiochemical, not very reproducible yields were in the 6-15% range. Cattel and coworkers122 assigned these differences to tritium isotope effect in the Wittig reaction. No correlation between the specific activity of 155 and the degree of chemical conversion of 157 into 155 has been presented. The temperature dependence of the observed secondary tritium isotope effect has also not been... 

R1 = 14 (XXII I2CI, R2 = Me, specific activity 55 mCimmol, radiochemical yield 26.1%... 

I] 214) 52% radiochemical yield after HPLC, specific activity 27 Ci mmol ( 100% radiochemical purity... 

The chemical and radiochemical purity of the labeled compound must be ascertained prior to use. In practice a value of 95% or greater is usually acceptable. The desired specific activity of the administered radioactive compound depends on the dose to be used as well as the species studied. Doses of 14C on the order of 5 pCi/kg for the dog and 20 pCi/kg for the rat have been found adequate in most studies, while doses of 3H are usually two to three times higher owing to lower counting efficiency of this isotope. 

Carrier-free radiochemical is a radionuclide that is not contaminated with a stable or radioactive nuclide of the same element. The no carrier added (NCA) designation applies to most of the elements to which the term carrier free is indicated. The specific activity of a carrier-free radioisotope can be calculated by the following formula ... 

Radioligand, [reference] R Radiochemical yield (%) Synthesis time (min) Specific activity (GBq/pmol)... 

Combination of sample weights and radiochemical results for the KH fractions allowed several types of specific activity (s) to be calculated. Table IV shows these results. In terms of s95, the number of... 

Isotope dilution analysis permits one to determine the purity of a radiochemical. Compound X, molecular weight of 150 (specific activity 1.0 mCi/mmol), was checked for purity by carefully weighing 1.5 mg of the radiochemical and mixing with 1000 mg of unlabeled compound X and recrystallizing until a... 

I]GR 190028a was purified by HPLC from a non-radioactive impurity which was formed during the reaction, and isolated in a radiochemical purity of greater than 99% and a specific activity of 18 Ci/mmol in a yield of 72 % [21]. 

F]VUF 5000 was obtained in 23-34% radiochemical yield (decay corrected) within 3.5 hours and purified with HPLC. It was isolated with a radiochemical purity of > 99% and a specific activity of more then 2500 Ci/pmol [25], Biodistribution however showed a very low brain uptake after iv injection in the rat and so [1SF]VUF 5000 proved to be inappropriate for brain imaging with PET. 

---