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In this work 55Fe is determined from spent ion exchange resins used in purification of nuclear power plant (Fortum, Loviisa) process waters. Radionuclides are eluted from the resin with strong acid (8 M HNO3) and iron carrier is added. A sample is taken from the acid solution and iron is precipitated as ferric hydroxide Fe(OH)3: alkali and alkaline earth metals remains in the solution. Iron is extracted rather specifically with isopropyl ether from 8 M HCl as FeCl3, however, Sb and Ru species follow. Iron is back-extracted into water at neutral pH. Cation exchange separates iron from the anionic Sb and Ru species. Iron is eluted from the column with 0.5% oxalic acid. Chemical yield is determined with AAS/ICP-MS/ICP-OES by the added iron carrier. Since the ion exchange resin also contains iron and this is eluted by nitric acid elution the iron concentration have to be determined after the addition of iron carrier. Radioactivity is measured by liquid scintillation counting. Before counting iron must be converted into colourless Fe(III) complex with e.g. strong HF.