Radiochemical purity (RCP) may be defined as "the proportion of the total radioactivity in the sample which is present as the desired radiolabelled species".
Measurement of RCP requires the use of a method to separate the different labelled chemical species which may be present in the radiopharmaceutical preparation.
The most commonly used method is chromatography which separates the different species on the basis of their differing affinities for a variety of liquid or solid phases.
The simplest and widely performed procedure uses thin-layer chromatography (TLC) in which the various compounds may be separated because they are differentially distributed between a liquid (mobile) phase and a solid (stationary) support mostly consisting of silica gel, normally bound to glass-fibre sheets. (Instant thin-layer chromatography or ITLC).
Liquid Chromatography (LC) is an
increasingly popular alternative to TLC in which the components are separated
down a column by elution with a suitable mobile phase.
LC can be performed using High Pressure Liquid Chromatography (HPLC) a very efficient separation mode which requires expensive specialised equipment but the same principles apply to Solid-Phase Extraction (SPE) a low-tech version of liquid chromatography which requires very little in the way of equipment.
- Source: https://humanhealth.iaea.org/HHW/Radiopharmacy/VirRad/Quality_Control_Procedures/Quality_Control_Module/Radiochemical_Purity/index.html
- You tube video, Thin-Layer Chromatography (TLC):