Handbook of Radiopharmaceutical Controls

Abstract

Radiochemical purity is defined by Charlton as the fraction of a given radionuclide in a defined chemical form. An example will enlighten this definition: for a source of sodium pyrophosphate (32P) containing 98,5 % P as pyrophosphate and 1,5 % 32P as orthophosphate, radiochemical purity will be 9.8,5%. Radiochemical purity is influenced by a series of factors. First of all, preparation as well as purification methods of radiopharmaceuticals do not allow to reach 100% purity. On the other hand, stability depends on medium, radioactive concentration, storage time and conditions. Decomposition of the original labelled compound causes the apparition of radiochemical impurities. Hence the importance of knowing all the factors that contribute to the stability of a compound as well as the methods for determinating radiochemical purity. We will try to point out briefly same ideas about storage and stability of radiopharmaceuticals and will describe methods and techniques used for purity determination. Further on, details will be given about the analytical procedures to be used in each case.