This poster deals with the use of the oxygen isotopic composition (δ18Op) of dissolved inorganic phosphate (DIP) as a tracer for phosphate sources. Recent studies have shown that δ18Op values can be used as a tracer to identify the sources and cycling of P in different environments including marine and freshwater systems (Paytan and McLaughlin., 2006). Several studies were made for the purification and the analysis of phosphates oxygen isotopic composition since the pioneering works of Tudge 1960. Thus, many methods have been developed for the purification of phosphate from apatite. However, they are not easily applied to DIP purification. In 2004, Karen McLaughlin et al. propose a new method for purifying phosphate by precipitation as cerium phosphate. Currently, this method was never repeated. Here we present the first results of reproducibility and repeatability tests of this method with the goal in mind to apply this one to trace phosphate sources in Lake Geneva.