Reaction-rate method for the determination of phosphorus in agricultural products

A new automated reaction-rate method for the quantitative determination of phosphorus in grains and feeds is presented. The chemical methodology has been investigated, resulting in a high analytical throughput with precise, accurate results. The phosphomolybdenum blue reaction is used for the reaction-rate determination. After digestion of the samples by the official AOAC block digestion procedure, automated instrumentation is used for precise and rapid combination of the reactants and transfer of the mixed solution to an automated spectrophotometer. The rate of formation of the product during 5 sec is automatically determined and compared with rates obtained for phosphorus standards to determine the phosphorus content of the sample. Relative standard deviations of about 0.3% are obtained and results for determinations of phosphorus in grains and feeds are accurate as indicated by comparison with the average obtained by all laboratories participating in the AAFCO check sample programme.