SOME OBSERVATIONS ON THE INSTABILITY OF TC-99M-COMPLEXES OF PROPYLENEAMINE OXIME (PNAO)

When eluates from expired Mo-99m/Tc-99m generators were used to form t he neutral lipophilic complexes of PnAO and its derivatives, degradati on of these chelates occurred on standing to form secondary Tc-99m-spe cies. It was determined that the conversion of the primary complexes t o secondary complexes was due to the impurities present in the (TcO4-) -Tc-99m eluate. The stability was found to be improved by extraction o f the complexes into CHCl3 and reconstituting in buffer after evaporat ion of CHCl3, indicating that the impurities are non extractable into CHCl3. Purification of the (TcO4-)-Tc-99m eluate from the generator by MEK extraction and its use for the preparation of the PnAO complex pr oduced products which showed practically no degradation for a 6 h peri od of storage. All the secondary Tc-99m complexes of PnAO are converte d back to primary complex, when the solution was heated in a boiling w ater bath for 10-20 min.