The conventional volumetric micro-determination of phosphate depends upon the precipitation of phosphomolybdate, filtration and washing of the precipitate, and titration with standard base. The method is slow and tedious, subject to many interferences, and is not applicable to samples containing less than 1-2 mg of phosphate. Other weak acid anions, such as carbonate or acetate, interfere in the method. Strong acid anions, such as nitrate, sulfate, and chloride do not interfere.