STUDY OF DECOMPOSITION KINETICS OF TC-99-D,1-HMPAO COMPLEX IN AQUEOUS-SOLUTION

The kinetic behaviour of Tc-d,1-hexamethylpropyleneamine oxime (Tc-d,1 -HMPAO) complex being an efficacious cerebral perfusion imaging agent in aqueous solution was investigated by means of solvent extraction an d spectrophotometric methods. The complex of Tc-d,l-HMPAO is stable in basic solution. In an acid solution, however, it is attacked by hydro gen ions forming hydrophilic complexes. As final products, pertechneta te and reduced hydrolysed technetium (TcO2) were recognized. The rate equation is simply expressed as R = k(1) [H+] [Tc-d,1-HMPAO] in a high concentration of hydrogen ion, whereas it becomes complicated when a decrease in the concentration of hydrogen ion occurs. The respective d ecomposition rate constants were determined. A strong correlation betw een [H+] and k values (rate constant) was found, supporting the hypoth esis that the concentration of the hydrogen ion is the predominant fac tor for the conversion of the lipophilic complex to its hydrophilic de rivates. (C) 1997 Elsevier Science Ltd.