A method is disclosed to prepare a microsphere-forming composition. The method provides a carbon-containing first solvent, where that first solvent is water soluble but does not comprise water The method further provides a second solvent comprising water, and (N) phosphorus-containing compounds, where (N) is greater or equal to than 1. The method forms a first mixture by mixing each of the (N) phosphorus-containing compound with the first solvent, and forms a second mixture comprising the second solvent and sodium chloride. The method then combines the first mixture and the second mixture to form the microsphere-forming composition.