Strontium (Sr) isotopes have been used for over 40 years to examine geological processes, e.g. age of rocks or provenance. More recently they have been applied to biological samples to examine animal migration and nutrition. These latter applications assume that Sr isotopes are not fractionated in these biological systems. It is this hypothesis that will be tested by this project. Should there be significant mass dependent fractionation of Sr, much of the current Sr isotope measurements in non-geological systems would have to be revisited to check for accuracy. This will have a substantial impact on the use of Sr isotopes across many avenues of the biological sciences and open up new fields of research in earth sciences working with the mass dependence of Sr isotopic fractionation. For the further use of the Sr isotope system as a robust tracer it is vital that the mass dependence fraction of Sr is completely understood. This project will examine in detail how prolific this effect is.