A new method is presented to remove sodium interferences from neutron-activated materials. The method is based on passage of the samples, dissolved in a concentrated acid solution on a column of hydrated antimony pentoxide (HAP). The retention is quantitative with a maximum capacity of 31 mg Na/g HAP. Only tantalum, in addition to sodium, was retained by HAP out of the 60 elements tested. The method should find applications in neutron activation analysis, particularly of biological materials. Applications are also foreseen in other analytical techniques, such as emission spectroscopy and flame spectrophotometry, where high sodium concentrations in the sample can be a source of interference.