A new approach has been developed for precise and accurate quantitative determinations of phosphate with analysis times in the millisecond range. The method utilizes a completely automated stopped-flow system with direct digital readout of initial reaction rates to measure the initial rate of formation of 12molybdophosphoric acid from phosphate and Mo(VI) in acid medium. This rapid reaction yields digital rate data proportional to the phosphate concentration about 100 milliseconds after the reagents are automatically mixed. The phosphate concentration from 0.1 ppm and up can be read out directly on the digital meter or a printer. With the automatic sampling

Kinetics of the formation of 12-molybdophosphoric acid (12-MPA) has been investigated using rapid stoppedflow spectrophotometric reaction-rate techniques. A mechanism is proposed from the kinetic data which involves an initial reaction between phosphate ions and Mo(VI) followed by polymerization to form 12-molybdophosphoric acid. The rate law has been derived and is in agreement with the experimentally observed rates, and rate constants have been evaluated for the