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 and spectrophotometric methods. The complex of Tc-d,1-HMPAO is stable in basic solution. In an acid solution, however, it is attacked by hydrogen ions forming hydrophilic complexes. As final products, pertechnetate and reduced hydrolysed technetium (TcO2) were recognized. The rate equation is simply expressed as R = k1 [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 decomposition rate constants were determined. A strong correlation between [H+] and k values (rate constant) was found, supporting the hypothesis that the concentration of the hydrogen ion is the predominant factor for the conversion of the lipophilic complex to its hydrophilic derivatives.