Automated colorimetric determination of phosphorus in silicate rocks in the presence of silicon

Abstract

An automated colorimetric method has been developed for the determination of phosphorus as the blue molybdophosphate complex in the presence of silicon following fusion of rock samples with sodium hydroxide or a lithium tetraborate-lithium carbonate mixture. Operating conditions and reagent concentrations have been chosen so as to achieve complete reaction and high sensitivity. Values obtained for some French reference standards, using the proposed method, compare well with recommended values and those using the molybdovanadate method. Coefficients of variation of less than 2.5% and 1% were obtained for phosphorus concentration levels [expressed as phosphorus(V) oxide] of 0.15 and 0.5%, respectively.