RAPID PHOSPHATE DETERMINATION BY FLUORIMETRY

If a metal ion reacts with an organic ligand to form a fluorescent complex, and the metal also forms a complex with a particular anionic species, it is possible to measure the concentration of the anion by a fluorescence technique. The anion, in complexing the metal, prevents the metal from reacting with the organic ligand, and the resulting diminished fluorescence intensity is proportional to the concentration of the anion. Such an interaction for phosphate has been qualitatively observed in the aluminum-morin system,1 and in the tin-flavonol system.2 These interactions have been investigated, and quantitative fluorometric methods for the phosphate ion developed. The only other such report is that of Land and Edmonds 3 in which the concentration ranges studied were quite narrow. Of the common anions, only fluoride interferes seriously, and its effect may be sharply decreased by boiling the slightly acidified water sample for a few minutes. Cationic interferences are