Tc-99(m)-MAG3: Problems with radiochemical purity testing

The radiochemical purity (RCP) of Tc-99(m)-MAG3 was determined using solid- phase extraction (SPE), highperformance liquid chromatography (HPLC) and th in-layer chromatography (TLC). The difference between the HPLC and SPE meth ods was highly significant (P < 0.001), yielding values for RCP of 86.0 +/- 5.196 and 94.4+/- 1.4% respectively (mean +/- s). Further qualitative anal ysis of the SPE fractions obtained, was carried out using HPLC and TLC. The unexpected presence of Tc-99(m)-MAG3 in one of the fractions was observed together with the appearance of hydrophilic impurities in the hydrophobic e xtract. This lack of specificity may be the reason for the discrepancy betw een the SPE and HPLC methods. Use of the SPE method leads to an underestima tion of the RCP of Tc-99(m)-MAG3 and, indeed, had we been relied solely on this method of analysis, we would have had to reject most kits we prepared. in a separate study, we compared a TLC method with HPLC. Differences were found to be highly significant (P < 0.001), yielding values of 98.3 +/- 0.6 % and 95.8 +/- 0.9% respectively. Comparison of the data points showed that TLC gave consistently higher RCP yield than HPLC. This elevated value was found to be due to the inability of the TLC method to separate Tc-99(m)-lip ophilic impurity, seen on HPLC, from the Tc-99(m)-MAG3. Therefore, use of t his TLC method leads to an overestimation of the RCP of Tc-99(m)-MAG3. ((C) 2000 Lippincott Williams & Wilkins).