Indirect method of radio-labeling using tri-carbonyl as
conjugating agent
In the indirect method, at optimal reaction conductions, around 97% of
radio-labeling yield was obtained (Fig.3A and 3B). The labeling was also
validated with HPLC method 14, peak at 3.370 minutes
is anticipated to be the labeled rifampicin peak (Fig.4).
Optimization of radiolabeling parameters of rifampicin with99mTc tricarbonyls
Maximum radio-labeling yield was achieved by increasing the amount of
rifampicin to 500 µg, pH at 6.5-7, incubated at 80oC
for 30 minutes in reaction 1 and 100oC for 40 minutes
in reaction 2. When the preparation was stored at room temperature,
there was no significant product degradation up to 12 h. Radionuclide
(99mTc) used for labeling was passed through a low
gamma energy filter made of lead, cadmium, and copper to reduce the
radiation from 99mTc and high energy photons from
common impurities, such as Ru-103, I-131, and Mo-99. Single peak at
70th channel was found, which corresponds to 140 KeV
energy of 99mTc. Therefore, radionuclide
(99mTc) used for labeling was found without any
impurity.