On-line anion exchange purification of [13N]NH3 produced by 10 MeV proton irradiation of dilute aqueous ethanol

[13N]NH3 prepared by irradiating dilute aqueous ethanol with 10 MeV protons is contaminated with small amounts of [18F]fluoride and [13N]NO2−/NO3−. The content of 18F is negligible at end of bombardment but increases as a function of time due to the longer half-life of 18F. We developed a simple on-line purification method in which the irradiated water directly passes through a small anion exchange column. Both the radionuclidic impurity [18F]fluoride and the radiochemical impurities [13N]NO3−/NO2− are efficiently removed by this procedure which results in highly pure (>99.9%) [13N]NH3 preparations.