Abstract: A high performance liquid chromatography method of an imaging agent, a precursor of the imaging agent, or an intermediate of the imaging agent is revealed. Instead of using the same eluent, a first eluent with a lower proportion of methanol is used to elute target compounds. Then a second eluent having a higher ratio of methanol ranging from 95-99% is used to elute for at least 15 minutes. Next use the first eluent again to elute for at least 60 minutes. Thus the target compounds are retained stably in the column and retention time of respective reproductive characteristic peak is obtained.