The Spectrophotometric Determination of Phosphorus with o-Hydroxyhydroquinonephthalein and Iron(III)

Abstract

Abstract On this basis of the coloration formed with o-hydroxyhydroquinonephthalein, an anionic dye, and iron(III) in aqueous media, trace amounts of phosphorus(as orthophosphate ion) was determined. A sample solution containing posphorus and the reagent blank in an amber-colored test tube with a stopper were heated at 40 °C for 20 min in the presence of poly(oxyethylene)sorbitan monolaurate, a nonionic surfactant, as a dispersion agent. Beer’s law was obeyed over the range of ≈1 μg/10 cm3 of phosphorus, and the apparent molar absorptivity of the complex was 2.5×105 dm3 mol−1 cm−1 at 610 nm. The present method was applied to the determination of total phosphorus in water — a sample solution containing small amounts of metal ions —, and the recovery percentage was satisfactory, about 95%. Other compounds containing phosphorus such as 5′-adenosine triphosphate could also be determined without a preliminary treatment.