Determination of Impurities in Ethylenediamine-N, N’-Diacetic Acid – a Coligand in Some Radiopharmaceutical Complexes of 99mTc With Small Peptides

In EDDA (ethylenediamino-N,N'-diacetic acid), two main impurities, 2-oxopiperazine-1-ylacetic acid (OPPAA) and N-(2-aminoethylglycine) (AEG), were identified by LC-MS analysis. OPPAA is not commercially available. It was therefore synthesised and its structure was confirmed by elemental, 1H NMR, FT-IR and MS analysis, and an HPLC method with UV detection was developed to test its purity. It turned out that UV detection was inadequate for the analysis of EDDA purity - the results were not consistent with those obtained by titration and 1H NMR. Therefore, a method based on refractometric detection (RID) was developed. Validation of the method was performed, assessing system suitability (SST), limits of detection (LOD) and quantitation (LOQ), linearity, accuracy, precision and robustness. For both contaminants (AEG and OPPAA), a detection limit of 0.02% was achieved. A linear relationship between the signal of both contaminants was observed in the range of LOQ to 0.5 % vs EDDA. The method has satisfactory linearity and accuracy for both impurities and acceptable precision. The results obtained by three analysts were compared using statistical tests. Using refractometric detection, the results of OPPAA determination based on HPLC purity (as a percentage of the OPPAA peak area relative to the area of all signals) and relative to the standard are very similar.