Caution to HPLC analysis of tricarbonyl technetium radiopharmaceuticals: An example of changing constitution of complexes in column

Radio-HPLC is a powerful tool for analyzing radioactive species in radiopharmaceutical chemistry. In this paper, we found an example that the commonly used eluting solvent, acetonitrile, could coordinate with the popular radiopharmaceutical nuclides, technetium-99m, during chromatography. [99mTc(CO)3(H2O)3]+ and [Re(CO)3(H2O)3]+ showed quite different retention time when they were eluted using acetonitrile/water as mobile phase. However, they almost demonstrated the same retention time when they were eluted using methanol/water as mobile phase. Further analysis showed that both [99mTc(CO)3(H2O)3]+ and [Re(CO)3(H2O)3]+ could be changed into [99mTc(CO)3(CH3CN)3]+ and [Re(CO)3(CH3CN)x(H2O)3−x]+ during the separation, respectively. Some former works mistook the [99mTc(CO)3(CH3CN)3]+ for [99mTc(CO)3(H2O)3]+ when using acetonitrile and water in analysis. Quality control of the radiopharmaceuticals containing metal complex should be careful since HPLC solvent could replace some liable ligand molecules.