Radionuclidic purity of 68Ga eluted from 68Ge/68Ga generators by Thin Layer Chromatography

Abstract

Background: 68Ga is a PET emitter radionuclide with an important role in nuclear medicine diagnosis procedures. The physical half-life of 68 min is compatible with the pharmacokinetics of many biomolecules and low molecular weight substrates. Another important feature is its availability from a generator system, where the parent radionuclide, 68Ge (t1/2=270.95 days) is adsorbed on a column and daughter, 68Ga, is eluted in ionic form 68Ga3+. The objective of this work was to develop a new method for the determination of the radionuclidic purity [1] of 68Ga, allowing a fast determination of the 68Ge breakthrough in 68Ga eluates. Materials and methods: The method to evaluate the 68Ge impurity in 68Ga samples recommended by the European Pharmacopeia is to measure the activity of 68Ga eluted from the generator, allow 24 h decay and measure the same sample. All 68Ga activity will come from the decay of 68Ge, so the level of 68Ge is calculated. The proposed methodology was based on the different behaviour of Ge and Ga in thin layer/paper chromatography [2]. Several solvents and strips were tested, as well as different solutions added to the spot point to interact with the species. The detection and quantification limits were calculated for the best system to evaluate the possibility of reaching the maximum level of 68Ge given in the monograph. Results: The best system was achieved using TLC-SG-IB-F strips, acetone as solvent and a solution of 3 mol L−1 HCl added to the spot point of the strip. The retention factors were 0.1 for 68Ge and 0.5-0.6 for 68Ga, allowing to cut the strips into 2 pieces for measuring in the detector. The detection and quantification limits showed that the strip sample could be measured 2 h after the beginning of the quality control procedure, then correcting to the full growth of 68Ge. Samples were measured using the traditional and the proposed method and the values were similar. Conclusions: The proposed method is simple, fast and allow the evaluation of the 68Ge impurity in samples of 68Ga freshly eluted from the generators.