Experimental Study on “One-strip” Thin-layer Chromatography for Determining the Radiochemical Purity of ⁹⁹Tc^m Radiopharmaceuticals

The clinical skeletal imaging performed by injection of ⁹⁹Tc^m-MDP, has to wait for 2～3 h so as to reduce the background radiation, the low radiochemical purity of ⁹⁹Tc^m-MDP may be the major cause so that its radiochemical purity was assessed by socalled “onestrip method” in 2002, i.e. ascending thinlayer chromatography with one silica gel strip as the stationary phase and V(10% ammonium)∶V(acetate-methanol)=1∶1 as the mobile phase. After developing and drying this strip was tested by autoradiography. In 2008 ⁹⁹Tc^m-MDP and the other five ⁹⁹Tc^m radiopharmaceuticals as ⁹⁹Tc^mO₄^-, ⁹⁹Tc^m-EC, ⁹⁹Tc^m-DTPA, ⁹⁹Tc^m-MIBI and ⁹⁹Tc^m-MAA were assessed by these methods as mentioned above, but the only difference was the self-developing film instead of traditional X-ray film. The autoradiogram of ⁹⁹Tc^m-MDP was observed by naked eye and the results showed that the radiochemical purity of ⁹⁹Tc^m-MDP was higher than that in 2002, and the R_f values of 0.7 was assessed. Using these methods assessed ⁹⁹Tc^m-DTPA, ⁹⁹Tc^m-MIBI and ⁹⁹Tc^m-MDP in 2009 respectively, the autoradiogram of former two drugs was as same as that in 2008, and the R_f average value was 0.78±0.02 and 0.39±0.03 separately. The R_f values of two ⁹⁹Tc^m-MDP samples were all closed to zero, which were rather different from those in 2008. It might be that ⁹⁹Tc^m-MDP was a composite compound of characteristics of ⁹⁹Tc^m-Sn colloid, in the storing effective time for 52 weeks, since the decrease of contents of stannous chloride in the box caused the significant change of R_f value, which could not be measured by two-strip method (one strip for free pertechtate, one strip for ⁹⁹Tc^m-Sn colloid). It is suggested that the drug manufacturers should continue to study to find out the optimum TLC for testing the radiochemical purity of ⁹⁹Tc^m radiopharmaceuticals, after the components are separated completely, calculate the radiochemical purity or ⁹⁹Tc^m labeling efficiency by using these peak areas of the radioactive curve. The normalization of ⁹⁹Tc^mradiopharmaceuticals measuring method might be helpful for the further developing radiopharmacy.