Simultaneous kinetic determination of phosphate and silicate based on heteropoly blue formation

Small amounts of phosphate (0.08–1.16 μg ml^-1) and larger amounts of silicate (12–60 μg ml^-1) can be determined simultaneously by a kinetic method based on the difference in the rates of the heteropoly blue formation with molybdenum (V)—molybdenum (VI) mixtures in 0.28 M perchloric acid. The interference of large amounts of iron(III) on the determination of phosphate can be eliminated by masking with sodium hydrogen sulfite; this method is applicable to reagent-grade iron(III) chloride.