Radiochemical purity radioiodine

The labelling condition using a molar peptide to radionuclide ratio of 2.73 (7.4 MBq/pg of peptide) resulted in one radiochemical species (R = 22.7 min), probably the monoiodinated species (Fig. 3.1(a)). Under this labelling condition, high radiochemical purity (95.53 0.88%) was observed. After the SepPak purification procedure, the radiochemical purity of the ethanol fraction was found to be 99.32 0.09%. When a molar peptide to radionuclide ratio of 0.54 was used, a second radiochemical species R = 24.3 min) was also observed (Fig. 3.1(b)), which could be related to the diiodinated species in the radioiodination of [Tyr Joctreotide, as described by Bakker et al. [3.11]. With... 

When [ IJDOTATATE labelled using 30 mCi of radioiodine was purified using the SepPak procedure and stored in ethanol (96%) under refrigerated conditions, the radiochemical purity remained almost constant for 48 h, ranging from 98.32 0.54% immediately after purification to 94.80 0.78% after 48 h. 

The in vitro stabilities of the radioiodinated compound were evaluated by incubating the radiolabelled protein in PBS and in human serum. The radiochemical purities were evaluated at 12, 24, 48 and 72 h post-labelling. The stability of the labelled compound with low specific activity was compared with that of the labelled compound with high specific activity. The results showed complete retention of the radiochemical purity of the low specific activity preparation for up to 48 h in both media. However, in the case of the high specific activity preparation, rapid degradation of the radiolabelled protein was observed (Fig. 4.1), with a loss of 54% of the radioiodine in PBS and even higher losses in human serum. These results show a dependence of the stability on the specific activity and/or the radioactive concentration resulting from... 

Radiolabelling with 1 or 1 was carried out by the chloramine T method, and radioiodinated analogues were easily isolated with high chemical and radiochemical purity by HPLC, as shown for the labelling reaction mixture of I-Sugar-TATE in the representative chromatogram in Fig. 6.4. 

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