An indirect sequential determination of phosphorus and silicon by atomic-absorption spectrophotometry

Abstract

Phosphorus and silicon are determined sequentially as phosphate and silicate in a single aliquot of solution by an amplification procedure. Phosphomolybdic acid, H₃PO₄(MoO₃)₁₂, is formed and selectively extracted away from silicate and excess of molybdate reagent into isobutyl acetate. After adjustment of the acidity of the remaining silicate solution, silicomolybdic acid, H₄SiO₄(MoO₃)₁₂, is extracted into butanol. The twelve molybdate ions associated with each phosphate and silicate ion are determined by direct atomic-absorption spectroscopy in the isobutyl acetate and butanol phases in a nitrous oxide-acetylene flame at 3132 Å. With this procedure 0·08 to 1 p.p.m. of phosphorus, and 0·08 to 1·2 p.p.m. of silicon can be determined in the same solution. The most suitable conditions for the determination have been established, and a study of the effect of other cations and anions is presented.