The present invention relates to an improved [18F]labelled synthon composition, wherein the non-radioactive impurities in said composition have been found to be more straightforward to remove than with known compositions comprising said [18F]labelled synthon. The resultant purified [18F]label led synthon therefore can be used in the production of a positron emission tomography (PET) tracer having improved properties for in vivo imaging. The invention also includes methods of imaging and/or diagnosis using the radiopharmaceutical compositions described.
