A simple effective method for estimating the [18O] enrichment of water mixtures

Isotopically enriched water, [18O] H2O, recovered from the synthesis of [18F] fluorine-labelled PET radiopharmaceuticals, is frequently diluted with natural water, [16O] H2O. The extent of isotope dilution limits the usefulness of the recovered water. A simple method for determining the [18O] enrichment of water mixtures could aid PET cyclotron facilities to calculate the [18F] yields to be expected when the recovered [18O] H2O is reused. A gravimetric method (repeatability for high enrichment ±0.3% [18O], detection limit ∼2% [18O] enrichment) is described