Determination of purity of some tritiated steroids

When radiolabeled steroids at high specific activities are required for biological studies, the particular requirements of purity must be determined. The analyses to which the compound is subjected is based on these requirements. Analytical methods are complicated because of the radiochemical instability and the lack of aufficient sample. Methods have been developed which will allow IR and UV spectra to be determined with subsequent recovery of the sample. A prime requisite for this is specially purified solvents. The acceptability of certain solvents for this use can be determined by concentrating an aliquot of the solvent and then examining the residue by TLC. Spraying the developed chromatogram with a 5% solution of phosphomolybdic acid in ethanol, followed by heating will reveal the presence of impurities in the solvents. These impurities appear as spots and can readily be misinterpreted as contaminants in the sample if unpurified solvents are used to manipulate a pure steroid. Problems associated with the determination of radiochemical purity via GLC and TLC will be discussed. The synthesis of tritiated ethynyl estraniol its cyclopentul ether and the cyclopentyl ether of norethinarone acetate will illustrate the above problems.