Abstract A method for the determination of trace uranium levels in brines and waters with a high content of iron(III) based on the separation of uranium from a mixture of masking agents by sorption on an activated silica gel column was developed in connection with the Scintrex UA-3 uranium analyser. The detection limit of uranyl ions was 1.4 ng. This value can be achieved even with solutions containing 56 mg of iron, 480 mg of magnesium and/or 1000 mg of chloride. The relative standard deviation of the method is 5%. An analysis requires less than 20 min.