Tc NMR determination of the oxygen isotope content in O-enriched water.

Tc NMR has been suggested as an original method of evaluating the content of oxygen isotopes in oxygen-18-enriched water, a precursor for the production of radioisotope fluorine-18 used in positron emission tomography. To this end, solutions of NH TcO or NaTcO (up to 0.28 mol/L) with natural abundance of oxygen isotopes in virgin or recycled O-enriched water have been studied by Tc NMR. The method is based on O/ O/ O intrinsic isotope effects in the Tc NMR chemical shifts, and the statistical distribution of oxygen isotopes in the coordination sphere of TcO and makes it possible to quantify the composition of enriched water by measuring the relative intensities of the Tc NMR signals of the Tc O O isotopologues. Because the oxygen exchange between TcO and enriched water in neutral and alkaline solutions is characterized by slow kinetics, gaseous HCl was bubbled through a solution for a few seconds to achieve the equilibrium distribution of oxygen isotopes in the Tc coordination sphere without distortion of the oxygen composition of the water. Pertechnetate ion was selected as a probe due to its high stability in solutions and the significant Tc NMR shift induced by a single O→ O substitution (-0.43 ± 0.01 ppm) in TcO and spin coupling constant J( Tc- O) (131.46 Hz) favourable for the observation of individual signals of Tc O O isotopologues.