The aim of this project was to develop an analytical procedure for the determination of 90Sr in calcium-rich materials such as teeth and milk. The aim was also to use extraction chromatography for separation of Strontium. An initial investigation showed that high concentrations of Calcium interferes with the separation of Sr, and based on that knowledge, three different methods designed to reduce this interference were tested. Two of these methods are based on an initial Ca-Sr separation by nitrate- or phosphate/oxalate precipitation, while the third method utilises an increased amount of the extraction chromatographic material. The best results were achieved with Method III, which provided chemical yields of approximately 67 % and a good precision in the determination of 90Sr. This method has been validated by analysis of milkpowder spiked with 90Sr and milkpowder from an intercomparison test arranged by Nordic nuclear safety research (NKS).