Purity, Stability and Storage of Labelled Compounds

Abstract

Most scientists are familiar with the concept of ‘purity’ as it is applied to conventional chemical substances. Normally expressed in percentage terms, the chemical purity of a material may be defined as the percentage of the mass of material present which is in the specified chemical form. Thus a sample of toluene may be described as 98% CH₃-C₆H₅. Unfortunately when dealing with radiolabelled compounds the situation is not so straightforward. For example, impurities may or may not be radioactive, or may even be labelled with ‘the wrong radioisotope’. Furthermore, the amount of impurity present in a given sample may vary with time or, particularly in the case of materials labelled with short-lived radionuclides, may become relatively more important as the principal radiolabel decays.