Abstract: A method for preparing a contrast agent precursor is revealed. The method includes several steps. First dissolve di-tert-butyl 2,2?-(1,4,7-triazacyclononane-1,4-diyl)diacetate, benzyl-2-bromoacetate and an alkaline compound in a first solvent to perform a bimolecular nucleophilic substitution reaction and get a product. Then dissolve the product in a second solvent to get a solution and adjust the pH value of the solution. Next add an organic solvent when the solution becomes acid and then remove a first organic layer that contains the organic solvent. Adjust the solution to become an alkaline solution and add the organic solvent again to get a second organic layer containing the organic solvent. The second organic layer contains the final product, di-tert-butyl 2,2?-{7-[2-(benzyloxy)-2-oxyethyl-(1,4,7-triazacyclononane-1,4-diyl}-diacetate.

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.